Senjuti De

Effect of the size of discrete anions on the nuclearity of a complex cation

Reactions of 2,3-diphenylquinoxaline (L) with AgClO4·xH2O, AgCF3SO3, AgBF4, AgCF3CO2 and AgNO3 in equimolar proportions at room temperature yield, respectively, AgL·ClO4·2CH3OH (1), AgL2·CF3SO3 (2), AgL·BF4·H2O·½C2H5OH (3), AgL2·CF3CO2 (4) and Ag·½L·NO3 (5). From X-ray crystallography, complexes 1, 3 and 5 are found to be 1-D hybrid polymers while 2 and 4 are mononuclear. In these five structures, only the nitrate anion is found to be coordinating; other anions are more or less non-coordinating. For the non-coordinating anions, it is concluded that small anions lead to a polymeric cationic complex and larger ones exert a non-proliferating effect in the countercation. In 1 and 3 the polymerization in the complex cation is brought about by bidentate L. But in 5, the anion also becomes a part of the polymeric assembly. The nature of the solvent seems to have little effect on these general observations.

Molecular and supramolecular structures of benzil dihydrazone, an organic helical molecule. Comparison with diacetyl dihydrazone

The synthesis and X-ray crystal structure of benzil dihydrazone are reported. It is found to be a twisted molecule with a NC–CN torsion angle of ∼70°. The H-bonding pattern in the crystal gives rise to columnar single helical supramolecular structure. In contrast, diacetyl dihydrazone, a planar molecule, has a H-bonded 3-D network with pores in the solid state.

A monoaqua zinc complex. Unique acid dissociation behaviour

Using the 1 : 2 condensate of benzil dihydrazone and 2-acetylpyridine as the ligand L, two complexes of zinc, [ZnL(CH3COO)]PF6 (1) and [ZnL(H2O)ClO4]ClO4·H2O (2), are synthesised from Zn(CH3COO)2·2H2O and Zn(ClO4)2·6H2O, respectively. From X-ray crystallography, both the complexes are found to be single helical with the metal in distorted octahedral N4O2 environment. In 1, the two oxygen atoms come from the bidentate acetate while 2 is a monoaqua complex with a perchlorate anion bound to the metal in monodentate fashion. The perchlorate in 2 is not at all weakly bound [Zn–O(perchlorate) 2.256(4) A]. Still in acetonitrile solution, the coordinated perchlorate ion dissociates upon deprotonation [reaction (i)]. This is supported by gas phase AM1 calculations. From solution conductivity, the pKa value of reaction (i) is determined as 5.71 (±0.19). It is estimated that had 2 been soluble in water, it would have a pKa value of ∼2 in water. The cation [ZnL(OH)]+ generated in reaction (i) could not be isolated in the solid state. From AM1 calculations, it is found to have a distorted tetrahedral ZnN3O core. Complex 2 is ineffective in bringing about hydration of CO2.

Linking number analysis of a self-assembled lemniscular Möbius-metallamacrocycle

A 26 membered, 24π-electron metallamacrocycle containing two Ag(I) centers is shown to be a double-twist Mobius cycle by a linking number analysis.