Bhaskar Nath

Metallacycles of cadmium, mercury dicarboxylates

A series of linear coordination polymers, metallacycles of cadmium(II) and mercury(II) of flexible carboxylic acid ligands, RCH{3-CH(3)-,5-CH(3)-,6-(-OCH(2)CO(2)H)C(6)H(2)}(2), (when R = C(6)H(5), (H(2)L(1)); 2-NO(2)C(6)H(4)- (H(2)L(2)) and 3-NO(2)C(6)H(4)- (H(2)L(3))) are synthesized and characterized. [CdL(1) (py)(3)](n)·3nH(2)O (py = pyridine) is a linear coordination polymer, whereas [CdL(2)(py)(CH(3)OH)](2)·CH(3)OH is a dinuclear complex of cadmium with a Cd(2)O(2) type of core. The latter is obtained from reaction of cadmium(II) acetate with H(2)L(2) in methanol followed by reaction with pyridine. A similar reaction of cadmium(II) acetate with H(2)L(2) in dimethylformamide results in the formation of a cadmium metallacycle, namely [CdL(2) (py)(2)(H(2)O)](2)·H(2)O. The H(2)L(3) reacted with cadmium(II) acetate in the presence of pyridine to form a metallacycle [CdL(3)(py)(2)(H(2)O)](2)·3H(2)O. The ligand H(2)L(2) form mercury(II) metallacycle [HgL(2)(4-mepy)(2)](2) in the presence of 4-methylpyridine (4-mepy) and the ligand H(2)L(3) forms metallacycle [HgL(3)(3-mepy)(2)](2)·DMF in the presence of 3-methylpyridine (3-mepy). The potassium salts of H(2)L(1) and H(2)L(2) were found to be coordination polymers and these potassium coordination polymers were structurally characterized.

Five-coordinate dicarboxylate complexes of copper (+2) and zinc (+2)

A new dicarboxylic acid, LH2 , derived from 2-[(2-hydroxy-3,5-dimethylphenyl) (phenyl)methyl]-4,6-dimethylphenol (1) was prepared by reacting it with methyl bromoacetate followed by alkaline hydrolysis. Two five-coordinate mononuclear complexes of L with zinc (+2) and copper (+2), [Zn(L)(py)2(H2O)] · H2O · py (IV), and [Cu(L)(py)2(H2O)] (V), were prepared (py = pyridine) and characterized. The packing patterns of these two complexes are different and the H-bond interactions in their lattices are controlled by the presence or absence of water molecules. This difference arises from subtle change in the orientation of carbonyl groups of the carboxylates.

Polymorphism and porosity in 4-[(4-hydroxy-3,5-dimethylphenyl)(5-methyl-1H-imidazol-4-yl)methyl]-2,6-dimethylphenol

The structural aspects of the solvates and polymorphs of 4-[(4-hydroxy-3,5-dimethylphenyl)(5-methyl-1H-imidazol-4-yl)methyl]-2,6-dimethylphenol (Imbp) are discussed. Two polymorphs of Imbp, namely a non-porous (polymorph I) and porous (polymorph II) polymorph, are reported. The packing pattern of the acetone solvate is guided by strong O–H⋯N as well as weak η5-type N–H⋯π interactions. The packing pattern of the acetone solvate (III) is closely related to polymorph II, which has η4-type N–H⋯π interactions. Polymorph II reversibly absorbs acetone. On the other hand, a DMSO solvate (IV) of Imbp comprises water assisted assemblies of the host molecules encapsulating DMSO molecules. The color of the solutions of Imbp in acetone and DMSO are visually distinguishable.

Structural Variations in Coordination Polymers of Sodium and Cesium Dicarboxylates

The coordination polymer {[Na2L(μ-H2O)(H2O)3]·H2O}n (1) derived from 2,2′-(phenylmethylidene-bis(3,5-methyl-2-phenyleneoxy)] diacetic acid (H2L) has repeat units comprising of hexa-coordinate diaqua-bridged dinuclear sodium complex ions. These units are connected through intervening mononuclear complex parts having penta-coordinated sodium ions. The sodium ions adopt repeated hexameric chair-like arrangement in the polymer. The cesium salt of H2L namely [Cs(HL)(μ-H2O)(H2O)]n (2) is a coordination polymer. In this case one acid group of the ligand is deprotonated and 2 form self-assembly by intermolecular hydrogen bonds between the free carboxylic acid groups. The fluoro-substituted ligand 2,2′-(2-fluorophenylmethyledene-bis(3,5-methyl-2-phenyleneoxy)] diacetic acid (H2Lf) forms disodium salt with a composition [{Na2Lf(μ-H2O)(H2O)3}·H2O]n (3); which is a two dimensional coordination polymer. On the other hand the corresponding cesium salt of H2Lf has a composition [{(H2O)Cs(μ-H2O)(μ-Lf)Cs(H2O)2}] (4); which is also a 2-D coordination polymer. The cesium ions are six or nine coordinate in the polymer and the coordination polymer possesses unusual Cs···F–C coordination bond.

Cocrystals of Quinoline Derivatives with 5-Aminoisophthalic Acid

The structures of cocrystals of 5-aminoisophthalic acid (AIA) with various quinoline derivatives are investigated. The cocrystals of AIA with isoquinoline are comprised of dimers of carboxylic acids end capped by isoquinoline molecules. The repeat units have length 30.05 Å each. The hydrated cocrystals of AIA with quinoline and 8-hydroxyquinoline are structurally characterized and they have four and six coordination environment around water molecules respectively. The cocrystal of 4-hydroxyquinazoline with AIA has sheet like structure with repeated dimeric carboxylic acids possessing R2 2(14) type of H-bond patterns. In thermogrvimetry, the cocrystals of 5-aminophthalic acid with quinoline or 8-hydroxyquinoline loses the quinoline counterparts followed by decarboxylation of the parent acid, the decarboxylation takes place at 275°C–450°C.