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Crystal Structures of Organic Compounds

Written By

Nader Noroozi Pesyan

Submitted: December 3rd, 2011 Published: September 19th, 2012

DOI: 10.5772/48536

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1. Introduction

X-ray crystallography is an important method for determination of the arrangement of atoms within a crystal of compound in which a beam of X-rays strikes a crystal and causes the beam of light to spread into many specific directions. From electron density, in the molecule the mean positions of the atoms in the crystal can be determined, as well as their chemical bonds and various other information.

The hexamethylenetetramine as an organic compound was solved in 1923 “(Dickinson & Raymond, 1923)”. Several studies of long-chain fatty acids were followed which are an important component of biological membranes “(Bragg, 1925; de Broglie & Trillat, 1925; Caspari, 1928; Müller, 1923, 1928, 1929; Piper, 1929; Saville & Shearer, 1925; Trillat, 1926)”. In the 1930s, the structures of larger molecules with two-dimensional complexity began to be solved. An important advance was the structure of phthalocyanine “(Robertson, 1936)”, that is closely related to porphyrin molecules important in biology, such as heme, corrin, chlorophyll and etc.


2. Crystal structures of organic compounds

In this chapter, crystal structures of some organic compounds such as organic torsion helicoids, organic compounds consists of intra- and intermolecular hydrogen bond and their some metal complexes and crystal structures of some organic spiro compounds were described.

2.1. Crystal structure of organic torsion helicoids

In recent years, several different interesting organic compounds structures have been found by X-ray crystallography. Helicenes are an extremely attractive and interesting class of conjugated molecules currently investigated for optoelectronic applications “(Groen et al., 1971; Katz, 2000; Rajca et al., 2007; Schmuck, 2003; Urbano, 2003)”. They combine the electronic properties afforded by their conjugated system with the chiroptical properties “(Bossi et al., 2009; Collins & Vachon, 2006; Larsen et al., 1996)” afforded by their interesting and peculiar helix-like structure, resulting from the condensation of aromatic (and/or heteroaromatic) rings, all of them in ortho position. For example, the formula and crystal structures of tetrathia-[7]-helicene 1 are shown in Figures 1 and 2, respectively. The compound 1 has been synthesized in three step by starting material of benzo[1,2-b:4,3-b']dithiophene and is shown in Scheme 1 “(Maiorana et al., 2003)” and this compound showed second-order non-linear optical (NLO) properties and has been investigated (Clays et al., 2003). In particular, carbohelicenes only include benzene rings, and also in heterohelicenes one or more aromatic rings are heterocyclic (pyridine, thiophene, pyrrole and etc.) “(Miyasaka et al., 2005; Rajca et al., 2004)”. With increasing number of condensed rings (typically, n > 4), the steric interference of the terminal rings forces the molecule to be a helicoidal form. For n > 4 the energetic barrier is such that the two enantiomers can be separated and stored “(Martin, 1974; Newman, et al., 1955, 1967; Newman & Lednicer, 1956; Newman & Chen, 1972)”. Of course, the conjugation of π system decreases with decreasing of planarity; however, in longer helicenes π-stack interactions can also take place between overlapping rings “(Caronna et al., 2001; Liberko et al., 1993)”. All helicenes (generally, n > 4) are chiral molecules and exhibit huge specific optical rotations “(Nuckolls et al., 1996, 1998)” since the chromophore itself, in this case the entire aromatic molecule, is inherently dissymmetric (right-hand or left-hand helix), having a twofold symmetry axis, C2, perpendicular to its cylindrical helix (in carbohelicenes), or inherently asymmetric (in heterohelicenes) “(Wynberg, 1971)”.

Figure 1.

Formula structures of 1 and 2.

Figure 2.

The helicoid structures of unsubstituted tetrathia-[7]-helicene 1 and unsubstituted hexathia-[11]-helicene 3 “(Caronna et al., 2001)” with the labelling scheme adopted for structural discussion “(Bossi et al., 2009)”.

Scheme 1.

The synthesis of 1 from benzo[1,2-b:4,3-b']dithiophene as a starting material.

Scheme 2.

Reaction mechanism for formation of 5 “Garcia et al., 2009)”.

Tetrathia-[7]-helicene 1 have been used for the synthesis of organometallic complexes “(Garcia et al., 2009)”. A series of organometallic complexes possessing tetrathia-[7]-helicene nitrile derivative ligands 5 as chromophores, has been synthesized and fully characterized by Garcia et al. “(Garcia et al., 2009)”. This compound was analyzed by means of 1H NMR, FT-IR, UV–Vis and X-ray crystallography techniques. The spectroscopic data of this compound was shown with in order to evaluate the existence of electronic delocalization from the metal centre to the coordinated ligand to have some insight on the potentiality of this compound as non-linear optical molecular materials. Slow crystallization of compound 4 revealed an interesting isomerization of the helical ligand with formation of two carbon-carbon bonds between the two terminal thiophenes, leading to the total closure of the helix 5. The reaction mechanism for the formation of 5 is shown in Scheme 2. Crystal structure of 5 is shown in Figure 3. A selected bond length, angles and torsion angles for compound 5 is summarized in Table 1Garcia et al., 2009)”.

Another example about helicenes is the hexahelicene 2 and its derivatives that is a chiral molecule “(Noroozi Pesyan, 2006; Smith & March, 2001)”. A convenient route for the synthesis of [7]-helicene (6a) and [7]-bromohelicene (6b) is reported “(Liu et al., 1991)”. The crystal structure of 6b is shown in Fig. 4. The crystal structure of 6b and its unusual oxidation reaction product 7 (as a major product) has been reported “(Fuchter et al., 2012)” (Figure 4 and Scheme 3). Alternatively, compound 6 may be an option for a neutral helicene-derived metallocene complex, since the seven-membered benzenoid rings give rise to a scaffold that completes one full turn of the helix with the two terminal rings being co-facial. It has been theoretically predicted and reported that the 6 has potential to bind some metal cation such as Cr, Mo, W, and Pt in a sandwich model “(Johansson & Patzschke, 2009)”. Fuchter and co-workers “(Fuchter et al., 2012)” also reported the crystal structure of 7 that obtained via unusual oxidation rearrangement of 6. In this structure, The bonds within the pyrenyl unit range between 1.3726(19) and 1.4388(14) Å with the exception of one outlier at 1.3512(18) Å for the C(26)–C(27) bond. The C=C double bonds in rings D and E are 1.3603(15) and 1.3417(16) Å respectively, and the C=O bond is 1.2419(14) Å. The structure of 7 revealed the dominant canonical form to have a pyrenyl group consisting of rings A, B, C and H linked by single bonds to a C–C=C–C=C–C=O unit to form rings D and E (Scheme 3). The pyrenyl unit is flat, the sixteen carbon atoms being coplanar. Ring I has four single bonds and two aromatic bonds, and has a folded conformation with the methylene carbon lying ca. 0.87Å out of the plane of the other five carbons which are coplanar. Aryl ring G forming the five-membered ring J, links to ring I. The planes of the five coplanar atoms of ring I and the four coplanar atoms of ring J are inclined by ca. 108° to each other. The ring of E is slightly distorted in a boat-like fashion with the carbon shared just with ring D and that shared with rings I and J, out of the plane of the other four atoms which are coplanar to within ca. 0.01 Å.

The formula structure of Katz's helical ferrocene 8 is shown in Figure 5 “(Katz & Pesti, 1982; Sudhakar & Katz, 1986)”.

Figure 3.

Crystal structure of 5.

Bond distances (Å)
Ru(1)–N(1)2.030(5)P(2)–C(221) 1.850(7)
Ru(1)–Cpa1.8595(6)P(2)–C(231) 1.829(6)
Ru(1)–P(1)2.350(2)N(1)–C(1) 1.147(8)
Ru(1)–P(2)2.353(2)C(1)–C(2) 1.433(9)
P(1)–C(111)1.843(6)C(2)–C(3) 1.598(9)
P(1)–C(121)1.831(7)C(3)–C(4) 1.535(9)
P(1)–C(131)1.817(7)C(4)–C(23) 1.519(9)
P(2)–C(211)1.846(7)C(23)–C(2) 1.565(9)
Bond angles (°)
N(1)–Ru(1)–Cpa121.79(14)C(1)–C(2)–C(3) 115.3(6)
N(1)–Ru(1)–P(1)87.93(14)C(2)–C(3)–C(4) 88.8(5)
N(1)–Ru(1)–P(2)90.83(15)C(2)–C(23)–C(4) 90.6(5)
P(1)–Ru(1)–P(2)99.84(6)C(3)–C(4)–C(23) 91.2(5)
P(1)–Ru(1)–Cpa124.15(5)C(3)–C(2)–C(23) 87.2(5)
P(2)–Ru(1)–Cpa122.98(5)C(5)–C(4)–C(23) 106.9(6)
Ru(1)–N(1)-C(1)169.9(5)C(4)–C(23)–C(22) 107.7(5)
N(1)–C(1)–C(2)175.7(7)C(2)–C(3)-S(1) 119.3(5)
C(1)–C(2)–C(23)116.4(6)C(3)–C(2)–S(4) 116.5(5)
Torsion angles (°)
Ru(1)–N(1)–C(1)–C(2)29(11)N(1)-C(1)–C(2)–C(23) 62(9)
N(1)–C(1)–C(2)–C(3)-38(9)C(2)–C(3)–C(4)–C(23) -11.0(5)

Table 1.

Selected bond distances and bond and torsion angles for compound 5 “(Garcia et al., 2009)”.

Scheme 3.

The formula structures of 6a and 6b and its unusual reaction for synthesis of 7a (and also its structure).

Figure 4.

Crystal structures of 6b and 7a.

Figure 5.

The formula structure of Katz's helical ferrocene 8.

Scheme 4.

Two possible different torsion helicoids of 9.

Figure 6.

Two independent molecules of 9 in the crystal studied.

Diazepinone dervatives are of pharmaceutical compounds. Another interesting helical diazepinone compound that is discussed in this section, is 1,9-dimethyl-4,5-dihydro-6H-pyrido[3',2':4,5]thieno[2,3-f]pyrrolo[1,2-a][1,4]diazepin-6-one (9). This molecule show two crystallographically independent molecules that form the asymmetric unit of the structure are shown in Figure 6. The X-ray crystallographic analysis shows the molecular structure of the compound 9 and reveals an interesting fact that this structure features two stereochemically different molecules (9A and 9B) that can be understood as different torsion helicoids (Figure 6). The compound has two stereoisomers (R and S conformers). In each structure the seven-membered diazepinone ring exhibits a boat conformation. The fused pyrido[3',2':4,5]thieno ring moiety has planar geometry. The C3–H3 bond is slightly off the fused pyrido[3',2':4,5]thieno ring plane. The hindrance repulsion between the hydrogen atom at C3 on pyridine ring and methyl group on pyrrole ring makes the molecule of 9 essentially non-planar (repulsion of C3–H3A with C15 and C3'–H3'B with C15' of methyl groups) (Scheme 4). The torsion angles between the pyrrole and thiophene rings in 9A and 9B are 45.7(6)° and –49.3(6)°, respectively “(Noroozi Pesyan, 2010)”.

The –NH– group of each molecule (e.g. molecule 9A) makes an intermolecular hydrogen bond to the C=O functional group of the molecule of another kind (molecule 9B), and vice versa. For example, the intermolecular hydrogen bond N3–H3····O1' involves the N3 atom from molecule 9A and O1' atom from the carbonyl group of molecule 9B, and vice versa for N3'–H3'····O1 (Figure 7). The crystal packing diagram indicates zigzag hydrogen-bonded chains along the crystallographic axes with two distinct hydrogen bonds (Figure 7). The intermolecular hydrogen bonds play a principal and important role in the crystal packing diagram of 9 “(Noroozi Pesyan, 2010)”.

Figure 7.

Crystal packing diagram of 9 showing zigzag H-bonds (shown by dashed lines).

One of the most interesting helical primary structure is sown in Figure 8 has been reported by Fitjer et al. “(Fitjer et al., 2003)”. Helical primary structures of spiro annelated rings are unknown in nature but have been artificially produced, both in racemic and enantiomerically pure form. The formula structure of 1-cyclobutylidenespiro[3.3]heptane (10) as a starting material is shown in Scheme 5. The compound 10 yielded enantiomeric mixture of 11 and 12 in the presence of zinc and 2,2,2-trichloroacetyl chloride. Reductive dehalogenation of 11 and 12 then Wolff–Kishner reduction yielded the desired trispiro[]tridecane [rac-(15), (symmetry, C2)]. The crystal structure of the camphanic acid derivative of 15 ((1S,5'S,10'S)-16) is shown in Figure 8 “(Fitjer et al., 2003)”.

Scheme 5.

Synthesis of the compounds trispiro[]tridecane (15) and the formula structure of its derivative (1S,5'S,10'S)-16 “(Fitjer et al., 2003)”.

Figure 8.

Crystal structure of (1S,5'S,10'S)-16.

Helquats, the family of N-heteroaromatic cations “(Arai & Hida, 1992)”, recently were introduced helical dications that represent a missing structural link between helicenes and viologens“(Casado et al., 2008)”. Specifically, basic [7]-helquat (17) “(Severa et al., 2010)” is a structural hybrid between [7]-helicene and a well-known herbicide diquat (Scheme 6). Synthesis of [7]-helquat (17) starts with bisquaternization of bis-isoquinoline precursor (18) with an excess of 3-butynyltriflate followed by the key metal catalyzed [2‏+2+‏2] cycloisomerization of the resulting triyne, formed 17 (Scheme 7).

Scheme 6.

Structural relation of [7]-helquat (17) to [7]-helicene 6a and herbicide diquat.

Scheme 7.

Synthesis of 17 via one-pot bis-quaternization of 18.

Recently, Nakano et al. have been reported the helical structure, λ5-phospha [7]-helicenes 9-phenyl-9H-naphtho[1,2-e]phenanthro[3,4-b]phosphindole-9-oxide (21) and its thio analogue 9-phenyl-9H-naphtho[1,2-e]phenanthro[3,4-b]phosphindole-9-sulfide (22) “(Nakano et al., 2012)”. The formula structure of 21 and 22 and the crystal structure of 21 are shown in Fig. 10. Phospha [7]-helicenes 21 and 22 have more distorted structures than the other heterohelicenes. In the structure of 21, the sums of the five dihedral angles that are derived from the seven C–C bonds [C(17)-C(17a)-C(17b)-C(17c), C(17a)-C(17b)-C(17c)-C-(17d), C(17b)-C(17c)-C(17d)-C(17e), C(17c)-C(17d)-C(17e)-C(17f), and C(17d)-C(17e)-C(17f)-C(1)] are 95.28 for 21 and 99.68 for 22. These angles are larger than those of hetero[7]-helicenes 23–25 (79–88°). This case can be attributed to the large angles between the two double bonds of phosphole oxide (50°) and phosphole sulfide (50°) relative to furan (32°), pyrrole (35°), and thiophene (45°). Owing to the larger angle, a larger overlap of the two terminal benzene rings was occurred in the λ5-phospha[7]-helicenes, therefore, a stronger steric repulsion. These larger distortions in 21 and 22 explain the higher tolerance of 21 and 22 towards racemization.

Figure 9.

Formula and X-ray single crystal structure of compounds 19 and 20 (Triflate counterions are omitted for clarity) “(Severa et al., 2010)”.

Figure 10.

Formula structures of λ5-Phospha[7]-helicenes 21 and 22 and crystal structure of 21 as representative.

2.2. Inter- and intramolecular hydrogen bonds in the crystal structure of organic compounds

Hydrogen bond plays a key and major role in the biological and pharmaceutical systems and remains a topic of intense current interest. Few selected recent articles exemplify the general scope of the topic, ranging from the role of H-bonding such as in: weak interaction in gas phase “(Nishio, 2005; Wang et al., 2005)”, supramolecular assemblies “(McKinlay et al., 2005)”, helical structures “(Azumaya et al., 2004; Noroozi Pesyan, 2010)”. Important consequences of both inter- and intra-molecular H-bonding have long been recognized in the physicochemical behavior of DNA and RNA “(Jeffery & Saenger, 1991)”.

Several kinds of hydrogen bond have been reported. If the donor-acceptor distance to be in the range of; 2.50 ≤ d (O O) ≤ 2.65, this kind of hydrogen bond is strong and when shorter than 2.50 Å (d(O O)≤ 2.50), to be very strong hydrogen bond “(Gilli et al., 1994)”.

In very short O H O bonds (2.40-2.45 Å) the major distribution of the proton are as follows:

  1. The proton is closer to one of the O atoms (asymmetric hydrogen bond).

  2. The proton is located precisely at the centre (symmetric or centred hydrogen bond).

  3. There is statistically disorder of the proton between two positions on either side of the centre (the proton is closer to one or the other side in different domains of the crystal).

  4. There is a dynamical disorder between two positions as in (iii); the proton jumps between the two positions in the same hydrogen bond “(Gilli et al., 1994; P. Gilli & G. Gilli, 2000; Olovsson et al., 2001; Steiner, 2002)”.

For instance, the structure of the potassium hydrogen dichloromaleate (26) has been studied by neutron diffraction at 30 and 295 K, with the emphasis on the location of the protons. There are two crystallographically independent hydrogen atoms in two very short hydrogen bonds, 2.437(2) and 2.442(2) Å at 30 K. For the centrosymmetric space group P1, with the hydrogen atoms located at the centres of symmetry, the structure could be refined successfully. Olovsson et al. have then been applied several different types of refinements on this structure, including unconventional models; with all atoms except hydrogen constrained in P1, but with hydrogen allowed to refine without any constraints in P1, anisotropic refinement of all atoms resulted in clearly off-centred hydrogen positions. The shifts of the two hydrogen atoms from the centres of symmetry are 0.15(1) and 0.12(1) Å, respectively, at 30 K, and 0.15(1) Å for both hydrogen atoms at room temperature. At 30 K: R(F) = 0.036 for 1485 reflections; at 295 K: R(F) = 0.035 for 1349 reflections (Olovsson et al., 2001)” (Fig. 11).

One of the most interesting example about intermolecular hydrogen bond is the heptan-4-yl (2'-hydroxy-[1,1'-binaphthalen]-2-yl) phosphonate (27a) “(Dabbagh et al., 2007)”. The phosphonate 27a was existed in dimmer form via two strong intermolecular hydrogen bonds with centrocymmetric (Ci) 18-membered dimmer form consisting of two monomers strongly hydrogen-bonded between the oxygen of P=O units and hydroxyl hydrogen atoms (Fig. 12). The crystal structure of 27a was determined by X-ray crystallography and is shown in Fig. 12. The selected bond lengthes, angles and torsion angles of 27a are summarized in Tables 2-4, respectively. Crystal data indicated the torsion angles (φ) between two naphthalenic rings moieties in BINOL species are 95.28(16)° and are transoid forms (Fig. 13). The intermolecular hydrogen bond distance in the structure of 27a was obtained 2.70 Å (strong hydrogen bond) and comparised with other hydrogen bonds P-containing systems (Table 5).

Figure 11.

Crystal structure of potassium hydrogen dichloromaleate (26).

Figure 12.

Crystal structure of 27a.

Figure 13.

Representatively, two strong intermolecular hydrogen bonds with centrocymmetric 18-membered dimmer form in 27a and 27b.

EntryBond length (Å)
1P(1) – O(3)1.4578(11)
2P(1) – O(2)1.5544(12)
3P(1) – O(1)1.5865(11)
4P(1) – H(1)1.295(16)
5O(1) – C(1)1.4073(17)
6O(2) – C(21)1.5006(19)
7O(4) – C(12)1.3634(18)
8O(4) – H(4)0.89(2)
9O(3) – H(4)1.81(2)
10C(10) – C(11)1.4942(19)

Table 2.

Selected bond length (Å) of dimmer 27a.

EntryBondAngle (θ, °)
1O(3) – P(1) – O(2)118.32(7)
2O(3) – P(1) – O(1)113.50(7)
3O(2) – P(1) – O(1)102.16(6)
4O(3) – P(1) – H(1)112.7(7)
5O(2) – P(1) – H(1)103.9(7)
6O(1) – P(1) – H(1)104.7(8)
7C(1) – O(1) – P(1)122.24(9)
8C(21) – O(2) – P(1)122.27(10)
9C(12) – O(4) – H(4)114.4(14)
10C(10) – C(1) – C(2)123.47(14)
11C(10) – C(1) – O(1)117.78(13)
12C(2) – C(1) – O(1)118.66(13)
13C(9) – C(10) – C(11)120.98(12)
14O(4) – C(12) – C(11)124.08(14)
15O(4) – C(12) – C(13)114.68(13)
16O(2) – C(21) – C(22)107.92(12)
17O(2) – C(21) – C(25)111.86(18)
18C(22) – C(21) – C(25)108.84(18)
19O(2) – C(21) – H(21)109.4
20C(22) – C(21) – H(21)109.4
21C(25) – C(21) – H(21)109.4

Table 3.

Selected bond angle of dimmer 27a.

EntryBondTorsion angles (Φ, °)
1O(3) – P(1) – O(1) – C(1)51.11(13)
2O(2) – P(1) – O(1) – C(1)179.64(11)
3O(3) – P(1) – O(2) – C(21)58.93(13)
4O(1) – P(1) – O(2) – C(21)-66.49(12)
5P(1) – O(1) – C(1) – C(10)110.03(13)
6P(1) – O(1) – C(1) – C(2)-73.13(15)
7O(1) – C(1) – C(2) – C(3)-177.12(12)
8C(7) – C(8) – C(9) – C(10)178.21(14)
9C(2) – C(1) – C(10) – C(11)-178.59(12)
10O(1) – C(1) – C(10) – C(11)-2.11(19)
11C(1) – C(10) – C(11) – C(12)-97.30(17)
12C(9) – C(10) – C(11) – C(12)83.69(18)
13C(1) – C(10) – C(11) – C(20)83.73(17)
14C(9) – C(10) – C(11) – C(20)-95.28(16)
15C(20) – C(11) – C(12) – O(4)179.63(140
16C(10) – C(11) – C(12) – O(4)0.6(2)
17P(1) – O(2) – C(21) – C(22)-119.33(13)
18P(1) – O(2) – C(21) – C(25)120.97(19)
19O(2) – C(21) – C(22) – C(23)62.75(18)
20C(25) – C(21) – C(22) – C(23)-175.66(19)
21C(21) – C(22) – C(23) – C(24)166.78(15)
22O(2) – C(21) – C(25) – C(26)-68.8(3)
23C(22) – C(21) – C(25) – C(26)172.0(2)
24C(21) – C(25) – C(26) – C(27)-173.4(3)

Table 4.

Selected torsion angles of dimmer 27a.

LinkagesBond distance [Range, donor….H….acceptor] (Å)Strength
P–O–H....O–P2.39-2.50Very strong
Dimmer 272.70Strong

Table 5.

Classification of hydrogen bonds within P-containing systems.

Dimeric centrosymmetric ring structures are quite common within phosphorous chemistry: for example; the structures of 28 and 29 are of 12- and 8-membered structures, respectively “(Corbridge, 1990)”. According to spectroscopic evidence, esters of (trichloroacetyl) amidophosphoric acid (29) exist as 29I rather than 29II, which suggests that the hydrogen bond in N-H O=P is stable than that of in N-H O=C “(Corbridge, 1990)”.

The formula structures of (E)-2-benzamido-3-(pyridin-2-yl)acrylic acid (30a) and (E)-2-benzamido-3-(pyridin-4-yl)acrylic acid (30b) are shown in Figure 14. The isomer 30a possesses a strong seven-membered ring intramolecular hydrogen bonding and shows quite different physicochemical properties, such as solubility and pKa, comparing with its isomer 30b. The p-conjugation between pyridyl and acrylate moieties is extended by intramolecular hydrogen bonding leading to a strong absorption at about 340 nm. Intramolecular proton transfer facilitates in the excited state, resulting in dual emission at around 420 nm and 490 nm in acetonitrile “(Guo et al., 2011)”. Crystal structure of 30a show a strong seven-membered ring intramolecular hydrogen bonding (Figure 15). The intramolecular proton transfer is facilitated by intramolecular hydrogen bond of O–H N. Tautomeric forms of 30a is shown in Scheme 8.

Figure 14.

Formula structures of 30a and 30b.

Figure 15.

Crystal structure of 30a.

Scheme 8.

Possible tautomeric forms of 30a.

There is hydrogen bonding between the acrylate O(3) and the pyridine N(2) atoms; the distance between these two atoms is 2.483 Å, and the O(3)-H(12)-N(2) angle is 171.3°. The O(3)-H(12) distance is 1.345 Å (the theoretical distance is 0.920 Å for general carboxyl O-H bond), which is longer than the N(2)-H(12) distance of 1.145 Å (the general distance is 0.960 Å). The distance difference revealed that H(12) is closer to the pyridine N(2) than it is to the acrylate O(3). The O(2)-C(9) and O(3)-C(9) distances are 1.233 Å and 1.272 Å, respectively. These results show that H(12) is involved in a strong intramolecular hydrogen bonding. N(2)-H(12)····O(3), in which the H(12) interaction with the pyridine N(2) is stronger than that with O(3) atom. The carboxylic acid proton moves to the pyridine N atom, while an electron delocalizes across O(2), O(3), and C(9) to form two almost equivalent carbonyl groups. These results provide further evidence that compound 30a exists mainly as a tautomeric form 30a (NH) in the solid state (30a[II]) form “(Guo, et al. (2011)”.

Resorcarene derivatives are used as units in self-assembled capsules via hydrogen bonds. Like to calixarenes, resorcarenes are the core to which specific functional groups are attached. These groups are responsible for the hydrogen bonds while the resorcarenes offer the right spatial arrangement of them. McGillivray and Atwood found that 31 forms in the crystalline state a hexameric capsule with the internal volume of about 1375Å3. There are 60 hydrogen bonds in hexameric with the help of eight molecules of water (Fig. 16) “(McGillivray & Atwood, 1997)”.

Figure 16.

Formula structure of 31 unit and crystal structure of (31)6·8H2O.

Yoshida et al. have also been reported the formation of a three-dimensional hydrogen bonding network by self-assembly of the Cu(II) complex of a semi-bidentate Schiff base “(Yoshida et al., 1997)”. The crystal structure of the Cu(II) complex of Shiff base 32 is shown in Fig. 17. The infinite overall structure of 32 is found to be organized by a three-dimensional hydrogen-bonding network in which the –NH2 O2S– type intermolecular hydrogen bonds play an important role, as shown in Fig. 18. One complex molecule is surrounded by four adjacent complexed molecules through four –NH2 O2S– hydrogen bonds. These hydrogen bonds would be strong judging from the NH O distances in the range 2.032–2.941 Å. From the neutron diffraction study of sulfamic acid (NH3+SO3-), a comparably strong hydrogen bond has been observed (–N+H -O–S– distances in the range 1.95–2.56 Å) “(Jeffrey & Saenger, 1991)”. Similar hydrogen bonds between sulfone and hydroxyl groups [2.898(6) Å] have been found in a supramolecular carpet formed via self-assembly of bis(4,4’-dihydroxyphenyl) sulfone “(Davies et al., 1997)”. Furthermore, four weak Br H hydrogen bonds may participate in the hydrogen-bonding arrays “(Yoshida et al., 1997)”.

Yang et al. reported the crystal structure of Bis(barbiturato)triwater complex of copper(II). The neutral Cu(H2O)3(barb)2 molecules are held together to form an extensive three- dimensional network via –OH·····O– and –NH·····O– hydrogen-bonded contacts “(Yang et al., 2003)”. Hydrogen bonding motifs in fullerene chemistry have been reported by Martín et al. as a minireviewe. The combination of fullerenes and hydrogen bonding motifs is a new interdisciplinary field in which weak intermolecular forces allow modulation of one-, two-, and three-dimensional fullerene-based architectures and control of their function “(Martín et al., 2005)”.

Figure 17.

Crystal structure of 32 unit.

Figure 18.

Crystal packing diagram of 32.

Methyl 2,4-dimethoxy salicylate (33) as potential antitumor activity, was synthesized from the reaction of 1,3,5-trimethoxybenzene (the most electron-rich aromatic ring) with 2-methoxycarbonyl-5-(4-nitrophenoxy) tetrazole, under solvent-free conditions, a low yield product was obtained (< 2%), while in the presence of a Lewis acid (AlCl3), the yield was increased to 30% (a kind of trans esterification reaction) “(Dabbagh et al., 2003)”.

Crystal structure of 33 is shown in Fig. 19. The carbon-oxygen framework of the molecular structure of 33 is essentially planar; bond lengths and angles are summarized in Table 6, while a structural diagram is shown also in Fig. 20. Planarity is maintained by a strong intramolecular hydrogen bonding interaction between the carbonyl-oxygen and phenolic-H atom [H(1) O(1) = 1.68(4) Å; O(5) – H(1) = 1.00(4) Å], and a much weaker intramolecular hydrogen bond of distance 2.535 Å between Me hydrogen’s [H(8)] and the C=O group (in what we label a “bisected” conformation with Cs symmetry, Figs. 19 and 20). The orientations of the o-OMe and ester-OMe are such to minimize steric interactions. The structure of 33 was also calculated by semi-empirical ab-initio, PM3 and AM1 methods, and data for bond lengths, angles and torsion angles are in good agreement together with the experimental ones (Tables 6 and 7), while the corresponding calculated H(1) O(1) bond lengths were 1.57, 1.78 and 1.97 Å, and the calculated O(5) – H(1) values were 1.00, 0.980, 0.970 Å, respectively. The ab-initio value for the weaker hydrogen bonding interaction was 2.574 Å. The ab-initio calculation also revealed a 1.40 Kcal higher energy, eclipsed conformation with C1 symmetry (Fig. 21 c and d, Fig. 20, Table 7) with an H(8) – carbonyl bond length of 2.14 Å “(Dabbagh et al., 2004)”.

Figure 19.

Crystal structure of 33 with 50% probability ellipsoids.

Figure 20.

Diagrams showing the favored so-called “bisected” (left) and “eclipsed” (right) conformations of 33.

Figure 21.

Molecular structures for 33 from ab-initio analysis [side-view: a (bisected); c (eclipsed), and front-view: b (bisected0; d (eclipsed)].

AtomsBond lengths (Å)AtomsBond angles(º)
O(1) – C(7) 1.247(4)C(7) – O(2) – C(8) 116.1(3)
O(2) – C(7) 1.325(4)C(2) – O(3) – C(9) 117.1(3)
O(2) – C(8) 1.465(4)C(4) – O(4) – C(10) 115.8(2)
O(3) – C(2) 1.363(4)C(2) – C(1) – C(6) 116.9(3)
O(3) – C(9) 1.438(4)C(2) – C(1) – C(7) 124.7(3)
O(4) – C(4) 1.362(4)C(6) – C(1) – C(7) 118.3(3)
O(4) – C(10) 1.443(4)O(3) – C(2) – C(1) 117.1(3)
C(1) – C(2) 1.432(4)O(3) – C(2) – C(3) 121.9(3)
C(1) – C(6) 1.393(4)C(1) – C(2) – C(3) 121.03
C(1) – C(7) 1.465(4)C(2) – C(3) – C(4) 119.8(3)
C(2) – C(3) 1.378(4)O(4) – C(4) – C(3) 114.4(3)
C(3) – C(4) 1.406(4)O(4) – C(4) – C(5) 125.1(3)
C(4) – C(5) 1.364(4)C(3) – C(4) – C(5) 120.6(3)
C(5) – C(6) 1.402(5)C(4) – C(5) – C(6) 119.7(3)
O(5) – C(6) 1.349(4)O(5) – C(6) – C(1) 122.3(3)
--O(5) – C(6) – C(5) 115.7(3)
--C(1) – C(6) – C(5) 122.0(3)
--O(1) – C(7) – O(2) 120.7(3)
--O(1) – C(7) – C(1) 122.0(3)
--O(2) – C(7) – C(1) 117.3(3)

Table 6.

Bond lengths (Å) and angles (o) of 33.

BisectedEclipsedRelative Energy
(kcal/mol)ÅÅ(kcal/mol)ÅÅ(Eeclip -Ebist)
Ab-intio- 470792.802.5741.565-470791.402.1391.5571.40

Table 7.

Experimental and calculateda hydrogen bond lengths and energies (kcal/mol) for bisected and eclipsed structure of 33.

Figure 22.

Crystal packing diagram of 34 (a) and 35 (b). Intermolecular hydrogen bond assigned by red dashed line (Carbon: grey; hydrogen: white; oxygen: red and nitrogen: blue).

Tetrazole ring can exist to be an equilibrium mixture of two tautomeric forms (1H and 2H-tetrazoles) “(Dabbagh & Lwowski, 2000)”. 5-Aryloxy (1H) and/or (2H)-tetrazoles often show intermolecular hydrogen bond “(Noroozi Pesyan, 2011)”. For instance, the crystal packing diagram of 5-(2,6-dimetylphenoxy)-(1H)-tetrazole (34) and 5-(2,6-diisopropylphenoxy)-(1H)-tetrazole (35) show intermolecular hydrogen bond (Fig. 22). In the compound 34, the crystal structure indicated that the tetrazole and phenyl rings are nearly perpendicular to each other, forming a dihedral angle of 95.5° (versus 92.06° from calcd. B3LYP/6-31G(d) and 6-31+G(d)). Because of the conjugation of O1 with tetrazole ring, the bond distance C1–O1 [1.322 Å] is slightly shorter than O1–C7 [1.399 Å]. These bond distances for C1–O1 and O1–C2 were obtained 1.333 and 1.419 Å with calculation by B3LYP/6-31G(d) method, respectively and also 1.332 and 1.420 Å derived with calculation by B3LYP/6-31+G(d) basis set, respectively. These data are in good agreement with experimental results (Table 8). In the compound 35, the crystal structure indicated that the tetrazole and phenyl rings are nearly perpendicular to each other, forming a dihedral angle of 85.91° (versus 107.2° from calcd. B3LYP/6-31G(d)). Because of the conjugation of O1 with tetrazole ring, the bond distance C2–O1 [1.3266(14) Å] is slightly shorter than O1–C7 [1.4257(13) Å]. These bond distances for C2–O1 and O1–C7 were obtained 1.332 and 1.423 Å with calculation by B3LYP/6-31+G(d) method, respectively and are in good agreement with experimental results. These bond distances were also obtained 1.322 and 1.422 Å with calculation by B3LYP/6-31G(d) method, respectively. The torsion angles between phenyl ring and each of methyl units on two isopropyl groups are -110.70°, 124.18° and 116.15° and 154.12°, respectively (Table 9).The selected parameters of bond length, angles and torsion angles of 34 and 35 derived by experimental and calculated results are shown in Tables 8 and 9.

The crystal packing of 34 exhibits an intermolecular N1–H1 N4 hydrogen bonds and comparized with the calculated at DFT (B3LYP) at 6-31G(d) and 6-31+G(d) basis sets (Table 10). The crystal structure indicated that the bond distance value between donor – hydrogen (N1–H1) and hydrogen-acceptor (H1 N4) were found in results 0.861 and 1.959 Å, respectively. For instance, these bond distances were also found in results 1.033 for (N1–H1) and 1.814 for (H1 N4) by calculated at B3LYP/6-31G(d) and 1.031 for (N1–H1) and 1.809 for (H1 N4) B3LYP/6-31+G(d), respectively. The donor-acceptor distance value (N1 N4) was obtained 2.804 by experimental method. This parameter was found 2.842 and 2.838 Å by calculated methods B3LYP/6-31G(d) and 6-31+G(d), respectively. The angle of N1-H1 N4 was found 169.9, 172.9 and 172.1° by experimental, calculated B3LYP/6-31G(d) and B3LYP/6-31+G(d) basis sets, respectively. The results of calculated method (specially 6-31+G(d) basis set) are in good agreement with experimental results (Table 10).

Compd. 34

Table 8.

The selected bond lengths (Å), angles (°) and torsion angles (φ) for 34. Experimental and B3LYP/6-31+G(d) and B3LYP/6-31G(d).

The crystal packing of 35 also exhibits an intermolecular N3–H31 N6 hydrogen bonds and comparized with the calculated at DFT (B3LYP) at 6-31G(d) and 6-31+G(d) basis sets (Table 10). The crystal structure indicated that the bond distance value between donor – hydrogen (N3–H) and hydrogen-acceptor (H31 N6) were found in results 0.926 and 1.919 Å, respectively. For instance, these bond distances were also found in results 1.03 for (N3–H31) and 1.91 for (H31 N6) by calculated at B3LYP/6-31G(d) and 1.01 for (N3–H) and 1.93 for (H N6) B3LYP/6-31+G(d), respectively. The donor-acceptor distance value (N3 N6) was obtained 2.835 by experimental method. This parameter was found 2.941 and 2.912 Å by calculated methods B3LYP/6-31G(d) and 6-31+G(d), respectively. The angle of N3–H31 N6 was found 169.1, 177.0 and 173.0° by experimental, calculated B3LYP/6-31G(d) and B3LYP/6-31+G(d) basis sets, respectively. The results of calculated method (specially 6-31+G(d) basis set) are in good agreement with experimental results (Table 10). Compounds 34 (entry no. CCDC-838541) and 35 (entry no. CCDC-819010) were deposited to the Cambridge Crystallographic Data Center and are available free of charge upon request to CCDC, 12 Union Road, Cambridge, UK (Fax: +44-1223-336033, e-mail:

Compd. 35

Table 9.

The selected bond lengths (Å), angles (°) and torsion angles (φ) for 35. Experimental and B3LYP/6-31+G(d) and B3LYP/6-31G(d).

D-H····AD-HH····AD····AD-H····A (degree, °)
Exp.a (34)N1-H1····N4b0.8611.9592.804166.9
Calcd.c (34)1.0331.8142.842172.9
Calcd.d (34)1.0311.8092.838172.1
Exp.a (35)N3-H31····N6e0.9261.9192.835169.1
Calcd.c (35)1.031.912.941177
Calcd.d (35)1.011.932.912174

Table 10.

Experimental and calculated B3LYP/6-31+G(d) and B3LYP/6-31G(d) levels for hydrogen-bond geometry of 34 and 35 (Å, °)

Figure 23.

Formula and crystal structures of the compounds 36a and 36b.

Nickel(II) complexes containing specific phosphorus– oxygen chelating ligands are very efficient catalysts for the oligomerisation of ethylene to linear form “(Braunstein et al., 1994)”. For instance, Nickel(II) diphenylphosphinoenolate complexes have been prepared from (ortho-HX- substituted benzoylmethylene)triphenyl phosphoranes (X = NMe, NPh) and [Ni(1,5-cod)2] in the presence of a tertiary phosphine (PPh3 or P(p-C6H4F)3) and their crystal structures have been studied by Braunstein et al. (structures of 36a and 36b). Formula and crystal structures of the compounds 36a and 36b are shown in Fig. 23. Crystallographic study of the complexes 36a and 36b establishes the presence of strong intramolecular hydrogen bonding between the enolate oxygen and the N–H functional group “(Braunstein et al., 2005)”. The most notable feature in these structures is the strong intramolecular N–H O hydrogen bonding: the calculated distance between the NH hydrogen atom and the oxygen atom of the enolate ligand is short: 2.18(5) Å in 36a and 2.00(5) Å in 36b, respectively “(Taylor & Kennard, 1982)”.

Intramolecular hydrogen bond is also shown in alkoxyamines. These compounds and persistent nitroxide radicals are important regulators of nitroxide mediated radical polymerization (NMP). The formula and crystal structure of β-phosphorylated nitroxide radical (37) is shown in Fig. 24. Compound 37 show an eight-membered intramolecular hydrogen bond between P=O····H-O (versus N-O····H-O). The hydrogen bond distance for two enantiomers of 37 is different. The hydrogen bond distances of P=O····H-O in (R)- and (S)-37 are 1.570 and 2.040 Å, respectively and favored. Instead, the hydrogen bond distance for N-O····H-O in (R)- and (S)-37 are 3.070 and 3.000 Å, respectively and unfavored “(Acerbis et al., 2006)”.

Figure 24.

Formula and crystal structure of two enantiomers of compound 37 (O: red, N: blue and P: yellow).

1,8-diaminonaphthalene derivatives such as; N-(8-(dimethylamino)naphthalen-1-yl)-2-fluoro-N-methylbenzamide (38) is a proton sponge. An unusual strong intramolecular hydrogen bond was observed in the protonated 38. In compound 38 in which a protonated amine group (38-H+) can act as a donor suitably positioned to engage in a strong intramolecular hydrogen bond with the amide nitrogen atom rather than with the carbonyl oxygen atom (Scheme 9). Crystal structure of the triflate salt of 38-H+ is shown in Fig. 25. The unit cell consists of two molecules of 38-H+, two triflate counter ions, and one molecule of water. The dashed line indicates the proposed hydrogen bond between H1A and N2A. Selected bond lengths and angles are N2A–H1A = 2.17(4), N1A–N2A = 2.869(5), C14A–N2A = 1.369(5) (Å) and N2A–H1A–N1A = 136(3)° “(Cox et al., 1999)”.

Scheme 9.

Protonation of 38 in the presence of trifluoromethanesulfonic acid (TfOH).

Figure 25.

Crystal structure of the triflate salt of 38-H+ (50% ellipsoids and triflate counter ion is omitted).

2,4,6-Trisubstituted phenolic compounds such as 2,4,6-tri-tert-butyl phenol are as antioxidant “(Jeong et al., 2004)”. Owing to the nature of the catalytic centres of galactose oxidase (GAO) and glyoxal oxidase (GLO), the N,O-bidentate pro-ligand, 2'-(4',6'-di-tert-butylhydroxyphenyl)-4,5-diphenyl imidazole (LH) (39) has been synthesized “(Benisvy et al., 2001)”. The compound 39 possesses no readily oxidisable position (other than the phenol) and involves o- and p-substituents on the phenol ring that prevent radical coupling reactions. The compound 39 undergoes a reversible one-electron oxidation to generate the corresponding [LH]·+ radical cation that possesses phenoxyl radical character. The unusual reversibility of the [LH]/[LH]·+ redox couple is attributed to a stabilisation of [LH]·+ by intramolecular O–H N hydrogen bonding “(Benisvy et al., 2003)”. The formula and crystal structure of 39 are shown in Fig. 26. Crystal structure of 39 shows an intra- and intermolecular hydrogen bonds in 39. In respect of the chemical properties of 39, there is a strong intramolecular hydrogen bond between the phenolic O–H group and N(5) of imidazole ring. The strength of this hydrogen bond, as measured by the O(1) N(5) distance of 2.596(2) Å and the O(1)–H(1) N(5) angle of 150.7°. Also, the N–H group of imidazole ring in 39 is involved in an intermolecular N–H O hydrogen bond [N(2) O(1S) 2.852(2) Å and N(2)–H(2A) O(1S) 168.8°] to an adjacent trapped acetone molecule (39·Me2CO) “(Benisvy et al., 2003)”.

Figure 26.

Formula and crystal structure of 39·Me2CO.

The azamacrocyclic ligand 1,4,7-triazacyclononane or TACN, 40, has attracted considerable interest in recent years for its applications in oxidative catalysis. Another application of this compound was discussed by Pulacchini, et al. “(Pulacchini et al., 2003)”. The incorporation of the 1,2-diaminocyclohexane moiety into a 1,4,7-triazacyclononane macrocyclic ligand was done by this research group, as it is an inexpensive starting material and both enantiomers are readily available. Moreover, this chiral framework has been included in a number of ligands that have been successfully applied in a range of asymmetric catalytic processes by Jacobsen et al. in metallosalen complexes “(Jacobsen & Wu, 1999)”.

Crystal structure of 41 is shown in Fig. 27 and revealed the structure of the macrocyclic ligand in which the six-membered ring has chair conformation (Fig. 27). The asymmetric unit is completed by the two chloride ions and a water molecule in which all C–C, C–O and C–N bonds are unexceptional. Two short hydrogen bonding interactions of 2.724(4) Å between N(1)–H(01) O(1) and 2.884(5) between N(2)–H(05) O(1) within the macrocycle are then supplemented by an extensive hydrogen bonding network between the ammonium nitrogen atoms N(1) and N(2) the two chloride ions Cl(1) and Cl(2), as well as the water molecule of crystallisation, as shown in Fig. 28. The roles of the two chloride ions in the network are distinct with Cl(1) acting as a direct bridge between two macrocyclic moieties as well as linking to a third via a water molecule. In contrast, the second chloride ion, appears to essentially serve to template the macrocyclic ligand into the conformation observed via hydrogen bonding interactions with N(1)–H(01) and N(2)–H(05). The second chloride ion also links to other macrocyclic moieties via the water molecules.

The following hydrogen bond lengths (Å) were observed from the polymeric hydrogen bonding array in 41·2HCl·H2O.; N(1)–H(06) Cl(1) 3.099(4), N(1)–H(01) Cl(2) 3.185(4), N(1)–H(01) N(2) 3.043(5), N(1)–H(01) O(1) 2.724(4), N(2)–H(02) Cl(1)#1 3.103(4), N(2)–H(05) Cl(2) 3.108(3), N(2)–H(05) O(1) 2.884(5), O(2)– H(04) Cl(1) 3.271(4), O(2)–H(03) Cl(2)#2 3.217(4) “(Pulacchini, (2003)”.

Figure 27.

Formula structures of 40 and 41 and crystal structure of 41·2HCl·H2O.

Figure 28.

Polymeric hydrogen bonding network in 41·2HCl·H2O “(Pulacchini, (2003)”.

In all thiohelicene crystals (see also Figs. 1 and 2) specific interactions were found involving sulfur “(Nakagawa et al., 1985; Yamada et al., 1981)” and hydrogen atoms at distances slightly shorter than the sum of van der Waals radii (1.80 Å for S and 1.20 Å for H). They are quite probably attractive, and, in all structures except TH11 (hexathia-[11]-helicene 3) they involve only atoms of terminal rings. In the case of the 5-ring system each molecule has two equivalent S S interactions of 3.544 Å, while each TH7 (tetrathia-[7]-helicene 1) molecule is involved in four equivalent S H contacts measuring 2.89 Å. All these interactions occur between enantiomeric pairs. Crystal structyre of pentathia-[9]-helicene (TH9, 42) and crystal packing diagram of this compound including S H contacts are shown in Figs. 29 and 30, respectively. For 42, each molecule presents four equivalent S H contacts at 2.87 Å, all with homochiral molecules giving rise to a quasi-hexagonal packing of tilted helices in planes parallel to the ab lattice plane. The crystal structure of TH11 (3) is unusual because the asymmetric unit is formed by two complete molecules as opposed to half a molecule in all the lower racemic thiohelicenes. The packing environment of each of the two closely similar but crystallographically independent molecules, and of each of its halves, is unique: thus the C2 axes bisecting the central ring of each TH11 (3) molecule are noncrystallographic. This situation is likely to arise in order to optimize the complex network of specific interactions involving S and H atoms. It leads to larger than expected asymmetric units and lower crystal symmetry, common occurrences in hydrogen bonded molecular systems. In the triclinic TH11 (3) crystals four nonequivalent short S S and an equal number of S H interactions are found “(Caronna et al., 2001)”. The essential geometric features of all these contacts in the racemic thiohelicene series and evidencing a remarkable consistency of the S H interaction with expectations for weak hydrogen bonds have been reported “(Desiraju & Steiner, 2000)”.

Figure 29.

Crystal structure of TH9 (42).

Figure 30.

Crystal packing diagram of 42 in which each molecule consists of four equivalent S····H contacts.

The fused pyrimidines such as pyrimido[4,5-c]pyridazine-5,7(6H,8H)-diones, which are common sources for the development of new potential therapeutic agents, is well known “(Altomare et al., 1998; Brown, 1984; Hamilton, 1971)”. Some of this class of compounds play new heterocyclizations based on {SNH} methodology as N(2)-oxide and 3-alkylamino derivatives of 6,8-dimethylpyrimido[4,5-c]pyridazine-5,7(6H,8H)-dione “(Gulevskaya et al., 2003)”.

Recently, the synthesis of 3-arylpyrimido[4,5-c]pyridazine-5,7(6H,8H)-diones (43a–d) and their sulfur analogs 3-aryl-7-thioxo-7,8-dihydropyrimido[4,5-c]pyridazin-5(6H)-ones 44a–d have been reported “(Rimaz et al., 2010)”. One of the most interesting intermolecular hydrogen bond in 43a–d have been reported by our research group “(Rimaz et al., 2010)” (Figure 31). Owing to the less solubility of 43a–d and 44a–d, an attempt to achieve the single crystal of these compounds for investigation of the clustered water in their crystalline structure was failed. The 1H NMR spectra of 43a–d show two broad singlets in the range of δ = 7.00–8.00 ppm that correspond to the protons of clustered water molecule in the 43a-d. The chemical shift values of two variable protons of water in 43a–d in ambient temperature are shown in Table 11. There are some reasons for demonstration and interpretation of this criterion. (i) One of the evidence is the mass spectra. The mass spectra of the compounds 43a–d show not only the molecular ion fragment (M) but also the fragment of M+18. Therefore, the strength of hydrogen bond between the proton of H2O (Ha) and oxygen atom of carbonyl group (C5=O Ha–O) and also hydrogen bond between the N6–H of 43a–d and oxygen atom of H2O (N6–H O–Ha) is considered more than that of the hydrogen bonding in the dimer form of 43a–d (judging by the observation of the M+18 ion) (Fig. 32) “(Rimaz et al., 2010)”. It seems that at least one molecule of water clustered and joined to 43 and 44 by two strong intermolecular hydrogen bonds and dissociated neither by DMSO molecules as a polar aprotic solvent nor in mass ionization chamber. Presumably, this intermolecular hydrogen bond is of quasi-covalent hydrogen bond type. There are some reports on literatures about quasi-covalent hydrogen bonds “(Dabbagh et al., 2007; Gilli et al., 1994, 2000, 2004; G. Gilli & P. Gilli, 2000; Golič et al., 1971; Madsen et al., 1999; Nelson, 2002; Steiner, 2002; Vishweshwar et al., 2004; Wilson, 2000)”.

Figure 31.

Formula structures of 43a–d·(H2O) and 44a–d·(H2O).

Figure 32.

Representatively, strong intermolecular hydrogen bond and the chemical shifts of two hydrogen bonded protons of clustered water molecule with 43a “(Rimaz et al., 2010)”.

Compd.δ (ppm)

Table 11.

The chemical shift values of the two protons of a clustered water molecule in 43a–d and 44a–da at ambient temperature “(Rimaz et al., 2010)”.

The proton/deuterium exchange was examined on 43a–d by adding one drop of D2O. Interestingly, from hydrogen to fluorine substituent on phenyl ring in 43a–d the exchange rate was decreased, and no deuterium exchanging of Ha and Hb was observed in 43d while the amide protons were easily exchanged (Fig. 33). This phenomenon attributed to the fluorine atom that has made new intermolecular hydrogen bond with Ha and Hb of clustered water molecule in another molecule of 43d. The intermolecular hydrogen bond of fluorine with the proton of clustered water (–F····Ha– and –F····Hb–) in 43d inhibited the proton/deuterium exchanging of the clustered water protons. However, the electronegativity of fluorine atom caused deshielding of Ha and Hb on 43d and blocked the proton/deuterium exchange (Fig. 33 and Scheme 10). Two conformational forms of IA and IB in 43d are equivalent because of free rotation of phenyl ring about the C3–C9 and C12–F single bonds (Scheme 10) “(Rimaz et al., 2010)”.

2.3. Crystal structure of some organic spiro compounds

Spiro compounds are very important and useful compounds and versatile applications. Many of heterocyclic spirobarbituric acids “(Kotha et al., 2005)”, furo[2,3-d]pyrimidines “(Campaigne et al., 1969)” and fused uracils “(Katritzky & Rees, 1997; Naya et al., 2003)” are well known for their pharmaceutical and biological effects.

Recently, we have reported new spiro compound based on barbiturates; 5-alkyl and/or 5-aryl-1H, 1’H-spiro[furo[2,3-d]pyrimidine-6,5’-pyrimidine]2,2’,4,4’,6’(3H, 3’H, 5H)-pentaones which are dimeric forms of barbiturate (uracil and thiouracil derivatives) “(Jalilzadeh et al., 2011)”. Reaction of 1,3-dimethyl barbituric acid (DMBA) with cyanogen bromide (BrCN) and acetaldehyde in the presence of triethylamine afforded 1,1’,3,3’,5-pentamethyl-1H,1’H-spiro[furo[2,3-d]pyrimidine-6,5’-pyrimidine]-2,2’,4,4’,6’(3H,3’H,5H)-pentaone (46) in excellent yield “(Jalilzadeh et al., 2011)”. The formula structures of spiro compounds derived from barbituric acid (BA, 45), DMBA 46 and 1,3-thiobarbituric acid (TBA, 47) is shown in Fig. 34. Attempt for single crystallization of spiro compounds 45 and 47 were unsuccessful. The crystal structure and crystal packing diagram of 46 are shown in Figs. 35 and 36. This compound was crystalized in triclinic system. Selected crystallographic data for 46 is summarized at Table 12.

Figure 33.

Proton/deuterium exchangeability of the Ha and Hb of clustered H2O molecule in 1H NMR spectra of 43a (A), 43b (B), 43c (C) and 43d (D). The assigned spectra are shown before (a) and after added D2O (b). No exchange occurred in 43d of clustered H2O protons (D) “(Rimaz et al., 2010)”.

Scheme 10.

Possible various types of intermolecular hydrogen bond of fluorine with a proton of a clustered were (-F····Hb- and -F····Ha-) in 43d. This phenomenon presumably inhibited the proton/deuterium exchangeability of the clustered water protons.

Figure 34.

Formula structures of 45-47.

Figure 35.

Crystal structure of 46.

Figure 36.

Crystal packing diagram of 46.

Crystal data
Emprical formula C14H16N4O6
M 336.30
T 298 K
a (Å) 8.974 (5)
b (Å) 9.539 (5)
c (Å) 10.314 (5)
α ( ◦)64.782 (5)
β ( ◦) 69.349 (5)
γ ( ◦) 69.349 (5)
V (Å3) 725.8 (7)
Z 2
F(000) 352
Dx (mg m−3) 1.539
λ (Å) 0.71073
μ(mm−1) 0.12
Data collection
Rint 0.062
θmax 29.0 ◦
θmin 2.3 ◦
R[F2 "/> 2σ(F2)] 0.067
wR(F2) 0.203

Table 12.

Selected crystallographic data for 46.

Another spiro barbiturate compound derived from the reaction of DMBA with BrCN and acetone in the presence of triethylamine is 1,1’,3,3’,5,5’-Hexamethylspiro[furo-[2,3-d]pyrimidine-6(5H),5’-pyrimidine]-2,2’,4,4’,6’(1H,3H,1’H,3’H,5H)-pentaone (48) “(Noroozi Pesyan et al., 2009)”. Reaction of aldehydes with (thio)barbiturates is faster than ketones due to the reactivity and less hindrance in aldehydes. The formula and crystal structure of 48 is shown in Figs. 37 and 38, respectively. In Fig. 38, the fused 2,3-dihydrofurane ring has an envaloped conformation, and spiro pyrimidine ring has a half-chair conformation. Spiro pyrimidine ring is nearly perpendicular to 2,3-dihydro furan ring moiety as was observed earlier in the related compound. Torsion angles C2-C1-O4-C7 and C2-C1-C5-C6 are -99.39(3)° and 94.87(3) °, respectively. In the crystal, short intermolecular interaction O C contacts between the carbonyl groups prove an existing of electrostatic interactions, which link the molecules into corrugated sheets parallel to ab plane (Table 13).

C8····O2i2.835 (4)C3····O5ii2.868 (4)

Table 13.

Selected interatomic distances (Å) in 48.

Figure 37.

Formula structure of 48.

Figure 38.

Crystal structure of 48.

One of another interesting spiro barbiturate compound is the trimeric form of 1,3- DMBA; 5,6-dihydro - 1,3-dimethyl - 5,6 – bis - [l’,3’-dimethyl-2’,4’,6’-trioxo-pyrimid(5’,5’)yl]furo[2,3-d]uracil (49). This compound was first reported by electrochemical method “(Kato et al., 1974; Kato & Dryhurst, 1975; Poling & van der Helm, 1976)” and it has been reported the synthesis of 49 by chemical method for a first time two years ago “(Hosseini et al., 2011)”. The formula and crystal structures of 49 are shown in Figs. 39 and 40, respectively. Crystals of 49 were obtained by slow evaporation of a solution of 49 in acetone at room temperature. The data were acquired using a STOE IPDS II diffractometer, data collection and cell refinement were processed using STOE X-AREA “(Stoe & Cie, 2002)” and data reduction was processed using STOE X-RED “(Stoe & Cie, 2002)” program. Program(s) used to refine structure was SHELXL97 “(Sheldrick, 1997). Crystal data for 49: Orthorhombic; C18H18N6O9; M = 462.38; Unit cell parameters at 293(2) K: a = 13.2422(4), b = 15.9176(6), c = 19.5817(6) Å; α = β = γ = 90°; V = 4127.5(2) Å3; Z = 8; μ = 0.122 mm–1; Total reflection number 4275; 304 parameters; λ = 0.71073 Å; 2916 reflections with I > 2σ(I); Rint = 0.056; θmax = 26.49°; R[F2 > 2 σ(F2)] = 0.048; wR(F2) = 0.112; S = 1.02, F000 = 1920 “(Hosseini et al., 2011)”.

Figure 39.

Formula structure of 49.

Figure 40.

Crystal structure of 49.

Amino acids derived from sugar are of extensive family of peptidomimetics “(Baron et al., 2004; Chakraborty et al., 2004)”, an important sub-class of which incorporate an α-amino acid with a carbohydrate has anomeric effect. Such sugar amino acids may form spiro derivatives, some of which have been demonstrated to possess significant biological activity. For instance, the formula and crystal structure of (2'S,3aR,6S,6aR)-2,2,6-trimethyldihydro-3aH-spiro[furo[3,4-d][1,3]dioxole-4,2'-piperazine]-3',6'-dione (50) are shown in Figs. 41 and 42 “(Watkin et al., 2004)”. This molecule show hydrogen bonds between N-H….O=C groups and are shown in crystal packing diagram, viewed along the c axis as dashed lines (Fig. 43).

Figure 41.

Formula structure of compound 50.

Figure 42.

Crystal structure of compound 50 (Green: C, blue: N and red: O atom).

Figure 43.

Crystal packing diagram of 50.

Another interesting spiro linked barbituric acid to the cyclopentane ring moiety (spiro-nucleoside) possessing of hydroxyl and hydroxymethyl groups is (3S,2R)-3-hydroxy-2-hydroxymethyl-7,9-diazaspiro[4.5]decane-6,8,10-trione (51) (Figs. 44 and 45). Crystal structure of 51 shows trans stereochemical relationship of the two substituents hydroxyl and hydroxymethyl on cyclopentane ring moiety. The barbituric acid ring is almost planar, while the cyclopentane moiety adopts the C3'-endo-type conformation. Molecules of 51 interconnected by a two-dimensional network of hydrogen bonds build layers parallel to the ab plane. The hydrogen bond data for 51 is outlined at Table 14 “(Averbuch-Pouchot et al., 2002)”.

Figure 44.

Formula structure of 51.

Figure 45.

Crystal structure of 51.

O11—H12····O6v0.812.002.809 (2)173
N7—H8····O10iv0.861.992.840 (2)170
N9—H9····O2vii0.852.042.8620 (10)161

Table 14.

Hydrogen-bond geometry in 51 (Å, º).

Hydantoins are very useful compounds due to their pharmaceutical behaviour such as; antitumor “(Kumar et al., 2009)”, anticonvulsant “(Sadarangani et al., 2012)” and antidiabetic activity “(Hussain et al., 2009)”. In the molecules of 52 and 53 (Figs. 46 and 47), the atoms in the hydantoin ring are coplanar. The crystal structures of 52 and 53 are stabilized by intermolecular N—H····O=C hydrogen bonds. The hydrogen bond lengthes and angles for 52 and 53 are summarized at Table 15. Crystal packing diagram of these molecules show the molecules are centrosymmetric dimer forms. The dihedral angle subtended by the 4-chloro- and 4-bromophenyl groups with the plane passing through the hydantoin unit are 82.98(4)° and 83.29(5)°, respectively. The cyclohexyl ring in both molecules adopts an ideal chair conformation and methyl group in an equatorial position “(Kashif et al., 2009)”.

52N2—H2····O4i0.84 (2)2.04 (2)2.8763 (15)171.5 (19)
53N2—H2····O4i0.82 (3)2.06 (3)2.871 (2)171 (3)

Table 15.

Hydrogen-bond geometry in 52 (Å, º).

Figure 46.

Formula structures of 52 and 53.

Figure 47.

Crystal structures of 52 (top) and 53 (bottom).

Dihydropyridine are interesting and important systems because of their exceptional properties as calcium channel antagonists “(Si et al., 2006)” and as powerful arteriolar vasodilators “(Kiowski et al., 1990)”. 4',4'-Dimethyl-2-methylsulfanyl-3,4,5,6,7,8-hexahydropyrido-[2,3-d]pyrimidine-6-spiro-1'-cyclohexane-2',4,6'-trione, (54), has a markedly polarized molecular electronic structure, and the molecules are linked into a three-dimensional framework by a combination of N–H O, C–H O and C–H л hydrogen bonds (Table 16). Two independent N–H O hydrogen bonds generate a one-dimensional substructure in the form of a chain of rings; these chains are linked into sheets by the C–H O hydrogen bonds, and the sheets are linked by C–H л hydrogen bonds. Crystal packing diagram of 54 show four types of centrosymmetric ring. “(Low et al., 2004)” (Fig. 48). Compound 54 can exist in two zwitterionic forms of 54I and 54II (Scheme 11). For example, the bond lengths of N3–C4 and C4–O4 are both long for their types, the C4–C4A and C4A–C8A bonds are too similar in length to be characterized as single and double bonds, respectively. Also, the C8A–N8 bond, involving a three-coordinate N atom, is much shorter than the C8A–N1 bond, which involves a two-coordinate N atom. These observations, taken together, effectively preclude the polarized form (54I) as an effective contributor to the overall molecular electronic structure, instead pointing to the importance of the polarized vinylogous amide form (54II) “(Low et al., 2004)”.

Scheme 11.

Zwitterionic forms of 54.

Figure 48.

Crystal structure of 54.

N3–H3····O4i0.881.842.715 (2)176
N8–H8····O65ii0.882.102.965 (2)166
C5–H5B....O61iii0.992.463.389 (2)155
C64–H64A....Cg1iv0.992.873.854 (2)173

Table 16.

Hydrogen-bonding geometry (Å, °) for 54.


3. Conclusion

In summary, X-ray single crystal diffraction analysis of the some helicenes and other helix molecules were discussed. In continuation, the crystal structure of some organic and organometallic compounds consists of intra- and/or intermolecular hydrogen bond were described. Finally, crystal structures of some new spiro compounds were analyzed.



The author gratefully acknowledge financial support by Research Council of Urmia University


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Written By

Nader Noroozi Pesyan

Submitted: December 3rd, 2011 Published: September 19th, 2012