V. R. Pedireddi

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.

Creation of crystalline supramolecular assemblies using a C–H⋯O/O–H⋯N pair-wise hydrogen bond coupling

The systematic construction of various supramolecular motifs using a cyclic coupling involving both a strong and a weak hydrogen bond is described.

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.

pKa‐Directed Host–Guest Assemblies: Rational Analysis of Molecular Adducts of 2,4‐Diamino‐6‐methyl‐1,3,5‐triazine with Various Aliphatic Dicarboxylic Acids

Molecular adducts of 2,4-diamino-6-methyl-1,3,5-triazine (1) have been prepared with various aliphatic dicarboxylic acids. The molecular complexes (1 a-1 i) thus formed by co-crystallizing 1 with oxalic, malonic, succinic, fumaric, acetylene dicarboxylic, glutaric, thiodiglycolic, diglycolic, and adipic acids have been found to give two types of host-guest assemblies that have voids or channels in a three-dimensional arrangement. The different types of host-guest arrangement appear to result from differences in the acidity of the dicarboxylic acids, that is, acids with pK(a)<3.0 give host networks that consist of 1 and the corresponding acid with water or solvent molecules of crystallization present as guests, whereas acids with pK(a)>3.0 exist as guests in voids in a host network formed by 1. The former arrangement is observed in adducts 1 a, 1 b, 1 e, and 1 h and the latter arrangement is found in adducts 1 c, 1 d, 1 f, 1 g, and 1 i.

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.

The nature of halogen···halogen interactions and the crystal structure of 1,3,5,7-tetraiodoadamantane

An analysis of halogen ⋯ halogen (X ⋯ X) intermolecular interactions in crystals, using the Cambridge Structural Database (CSD). is presented. A total of 794 crystal structures yielded 1051 contacts corresponding to symmetrical and unsymmetrical X ⋯ X interactions of the type Cl ⋯ Cl, Br ⋯ Br, I ⋯ I, Cl ⋯ F, Br ⋯ F, I ⋯ F, Br ⋯ Cl, I ⋯ Cl and I ⋯ Br. These 1051 contacts are divided mainly into two categories, type I and type II depending upon the values of the two C–X ⋯ X angles θ1and θ2around the X atoms in a fragment of the type C–X ⋯ X–C. Type I contacts are defined as those in which θ1=θ2 while type II are defined as those in which θ1≅ 90° and θ2≅ 180°. Our results indicate that as the polarisability of the X atom increases, type II contacts become more significant than type I contacts and the X ⋯ X interaction may be more nearly considered to arise from specific attractive forces between the X atoms. A number of these concepts are succinctly illustrated in the crystal structure of 1,3,5,7-tetraiodoadamantane, 1. This structure has been reported to a very limited accuracy previously and the present work reveals an unusual twinned structure for this compound wherein the geometry of the stabilising I ⋯ I interactions is retained across the twin boundary. Compound 1 is tetragonal, space group I41/a, a= b = 7.1984(7) and c= 28.582(4)A, and Z = 4. The packing of the molecules in the crystal is controlled by I ⋯ I interactions. The supramolecular network of I ⋯ I connected molecules in crystalline 1 is closely related to that in adamantane-1,3,5,7-tetracarboxylic acid. Indeed, the stabilising nature of the I ⋯ I interactions is crucial for the crystallisation of 1 in this particular structure because otherwise, it should also have formed plastic crystals as do the analogous tetrachloro and tetrabromo derivatives.

Creation of crystalline supramolecular arrays: a comparison of co-crystal formation from solution and by solid-state grinding

The importance of appropriate chemical substitution in generating co-crystals of some dinitrobenzoic acids and anthracene from solution and by solid-state grinding is discussed.

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 ).