Anupama Ranganathan

A study of supramolecular hydrogen bonded complexes formed by aliphatic dicarboxylic acids with azaaromatic donors

Abstract Crystal structures of the hydrogen bonded, 1:1 molecular complexes of malonic, glutaric, adipic, thiodiglycolic and thiodipropionic acids with 4,4′-bipyridyl have been investigated in detail. All the dicarboxylic acids form molecular tape-like structures, but thiodiglycolic acid gives a cyclic structure, favoured by intermolecular π- π interaction between the heteroatom-rings. The cyclic structure is indeed unique, in the sense that it represents a noncovalent synthesis of a rectangle. Crystal structures of hydrogen bonded molecular complexes of malonic, succinic, glutaric, adipic and thiodipropionic acids with 2,4,6-triaminopyrimidine have been studied. By and large, only tape-like structures are formed, the crossed ribbon network being favoured in the complexes of malonic and glutaric acids with an odd number carbon atoms. In all the complexes of 2,4,6-triaminopyrimidine, proton transfer occurs from the carboxyl group to the heteroatom nitrogen, giving rise to a strong hydrogen bonded cyclic system.

Sensitive dependence of the hydrogen-bonded assemblies in cyanuric acid–4,4′-bipyridyl adducts on the solvent and the structure of the parent acid

Abstract Cyanuric acid (CA) forms a 2:1 hydrogen-bonded adduct with 4,4′-bipyridyl (BP) when co-crystallized from a methanol solution and a 1:1 adduct from an aqueous solution. The sheet structure of the 2:1 adduct involves cyclic hydrogen bonds between the amide units of adjacent CA molecules and N–H⋯N bonds between CA and BP. The 1:1 adduct crystallized from water has a chain structure with single N–H⋯O hydrogen bonds between the adjacent CA molecules. The structures of these hydrogen-bonded assemblies bear a close resemblance to the structures of CA crystallized from the corresponding solvents. N-methylcyanuric acid (MCA) forms a chain structure with single N–H⋯O bonds between the adjacent MCA molecules. The 1:1 hydrogen-bonded adduct of MCA with BP, crystallized from methanol or water solution, retains the chain structure. The structural sensitivity of the hydrogen-bonded assemblies to the solvent of crystallization and the relation between the supramolecular assembly of the adduct and the parent structure of CA are noteworthy.

Novel supramolecular organizations in melamine complexes with 4,4′-bipyridyl and silver nitrate

Abstract Complexes of melamine with 4,4′-bipyridyl and AgNO3 having compositions, C10H8N2:0.5(C3H6N6):H2O and [Ag(C3H6N6)]NO3, respectively, have been prepared for the first time. A crystallographic investigation has shown unique hydrogen bonding patterns in the two systems. The melamine–4,4′-bipyridyl complex shows a supramolecular organization wherein hydrogen bonding between melamine and water molecules results in tapes. The tapes are connected by hydrogen bonding to 4,4′-bipyridyl giving rise to a rectangular box. In the melamine–AgNO3 complex, the melamine molecules are bound to Ag+ ions forming N–Ag–N chains, giving rise to a helix. The helices are held together by interchain hydrogen bonds.

Self-assembled four-membered networks of trimesic acid forming organic channel structures

Abstract By the co-crystallization of trimesic acid, TMA, with molecules such as dimethylamine, N,N,N′,N′-tetramethylethylenediamine and methanol, it has been possible to generate hydrogen-bonded four-membered networks of TMA. The three-dimensional arrangement of the four-membered networks gives rise to channels occupied by the guest molecules. It has also been possible to generate a four-membered network by co-ordination of TMA with Co(II).

Layered structures formed by dinitrobenzoic acids

Abstract 3,5-dinitrobenzoic acid, 1 and 3,5-dinitro-4-methylbenzoic acid, 2 , form cocrystals with 4,4′-bipyridyl but only the latter forms a layered structure, which can incorporate anthracene molecules. Furthermore, 2 forms a pillared type structure with thionicotinamide.

A NOVEL 2:1 SUPRAMOLECULAR ASSEMBLY OF 3,5-DINITROBENZOIC ACID AND 1,4-DIIODOBENZENE

Abstract 3,5-Dinitrobenzoic acid, 1 , forms a 2:1 molecular complex with 1,4-diiodobenzene, 2 , through the formation of iodo-nitro interactions utilising one of its nitro groups, rather than forming a 1:1 molecular complex using both the nitro groups. The result suggests the importance of the hydrogen bond interactions present in the crystal of the parent molecule ( 1 ) in directing the interaction with other donor molecules ( 2 ).

Probing the hydrogen bond through experimental charge densities

Abstract Experimental charge density analysis has been carried out by using low-temperature X-ray diffraction data on molecular crystals exhibiting a variety of hydrogen bond interactions. The various types of hydrogen-bonded interactions examined include O–H⋯O, N–H⋯O, C–H⋯O, O–H⋯N, N–H⋯N, N–H⋯S and C–H⋯S bonds. Static deformation density maps reveal depletion of electron density in the hydrogen-acceptor (H⋯A) regions. While the total density and the Laplacian at the H⋯A critical points exhibit an exponential dependence on the H⋯A distance, the positive curvature of the density, λ 3 , closely follows the exponential relation with a considerably better correlation factor. The relation derived based on the data for 218 hydrogen bonds of various types is given by 0.47×10 3 exp (−2.5×d H ⋯ A ).

Replacing the hydrogen in the intermolecular hydrogen bond of the cyanuric acid-bipyridyl adduct by Ag(I)

A complex between cyanuric acid (CA), 4,4′-bipyridyl (BP) and Ag(I), with the composition, [Ag2(C3H2N3O3-κN)2 (C10H8N2-κN)] has been prepared. Crystal structure analysis shows that it has a chain structure in which the CA molecules are linked to the BP units through silver atoms by the formation of N-Ag-N bonds, wherein one of the hydrogens of CA is replaced by Ag(I), showing thereby the chains connected to one another by N-H...O hydrogen bonds formed between the CA molecules. This intermolecular chain structure resembles the chain structure of the CA.BP adduct where CA-BP-CA chains formed by N-H...N hydrogen bonds are linked to one another by N-H...O hydrogen bonds between the CA molecules.

Aromaticity in benzene-like rings — An experimental electron density investigation

An experimental charge density study has been carried out on perylene based on X-ray diffraction measurements at 130 K. The electron density and its associated properties have been evaluated at the bond and the ring critical points for the naphthalene residues as well as for the central ring. The variation of the Laplacian along the axis, above and below the ring plane, is found to be symmetric for the central ring while for the naphthalene rings, the Laplacian values are enhanced under the bow-shaped region. A plot of the Laplacian versus density evaluated at various points along the axis above the ring plane, shows a steep variation in the case of the central ring implying that theπ-density is smeared out compared to that over the naphthalene rings. Similar data extracted from a quinoid ring and a regular phenyl ring (both based on earlier reports from this laboratory) exhibit increasingly shallower trends and indicate, by contrast, that the central ring of perylene is much less aromatic.

A novel hybrid layer compound containing silver sheetsand an organic spacer

A novel compound of the formula Ag2·CA (CA = cyanuric acid) possessing Ag sheets and hydrogen-bonded CA chains, exhibits anisotropic conductivity and acts as an infinite parallel plate capacitor with a high dielectric constant.