Dipankar Datta

Occurrence of ribbons of cyclic water pentamers in a metallo-organic framework formed by spontaneous fixation of CO2

In the reaction of equimolar amounts of copper(II) acetate with 2,2′-dipyridylamine (DPA) in aqueous tetrahydrofuran, in presence of KOH, aerial CO2 is spontaneously fixed to the carbonate anion yielding [Cu(DPA)(CO3)]·3H2O (1). X-ray crystallography shows the presence of zigzag ribbons of cyclic water pentamers in the channels of a chain-like metallo-organic framework. The water ribbons are stabilised by hydrogen bonds to the metallo-organic backbone. Each (H2O)5 pentamer is approximately planar.

Estimation of the van der Waals radii of the d-block elements using the concept of bond valence

It is assumed that the valence v of the bond between a metal M and a non-metal X is negligibly small but not equal to zero when the distance between them is equal to the sum of their R values; the R value derived here for a d-block element with the Pauling RX values does not seem to depend on the oxidation state of M.

Aromatic–aromatic interaction between metallacycle and phenyl ring

Abstract The X-ray crystal structure of [CuL2]ClO4 where L is the 1:1 condensate of benzil-monohydrazone and 2-pyridinecarboxaldehyde, reveals unprecedented π–π interaction between the metallacycles and phenyl rings. The interaction is intramolecular.

A novel copper(I) complex that is a monomeric single helix in solid state but a dimeric double helix in solution

Single helical [CuIL]ClO4·½CH2Cl2 (L = 1∶2 condensate of benzil dihydrazone and 2-acetylpyridine) unfolds and coils up in CH2Cl2 solution to generate double helical [CuI2L2]2+.

The electrooxidation of the tetraphenylborate ion revisited

The electrochemistry of the tetraphenylborate ion, BPh4−, has been studied by cyclic voltammetry and coulometry in water, methanol, ethanol, acetonitrile, acetone, dimethylformamide and dichloromethane under an N2 atmosphere. While a one-electron and somewhat irreversible oxidation (with an E1/2 of 0.87 V vs. SCE at a glassy carbon electrode) is observed in dichloromethane, eqn. (i), the oxidation is somewhat complicated in all other solvents by the occurrence of several consecutive reactions. Epa, the anodic peak potential in cyclic voltammetry, changes from 0.41 V vs. SCE in water to 0.94 V vs. SCE in dimethylformamide at a glassy carbon electrode. The variation in Epa with solvent (S) is explained by invoking reaction (ii). The coulometric results in solvents other than dichloromethane indicate a disproportionation of S–BPh3, eqn. (iii).

New bond-valence sum model

A new expression is devised empirically to accommodate zero and some negative oxidation states in the bond-valence sum approach. The method is worked out in detail for a number of homoleptic copper and nickel complexes of various coordinating atoms in several oxidation states of the metals. An implication of the expression is a linear variation between 1/req and 1/rax in octahedral MX6 moieties, where req and rax are, respectively, the average equatorial and axial bond lengths. This is verified in Cu2+X6 chromophores for X = F, O, N and S. The usefulness of the new expression in assessing the compatibility of a coordination sphere with an oxidation state of a metal ion is demonstrated by exemplary applications to some inorganic complexes, azurin and urease.

Metal-assisted electrocyclic reaction in a CN–NC–CN system

In a reaction with cis-Ru(phen)2Cl2, the 1:2 condensate of benzil dihydrazone and 2-formylpyridine or 2-acetylpyridine is found to undergo an electrocyclic rearrangement to yield the cation [Ru(phen)2{5,6-diphenyl-3-(pyridin-2-yl)-1,2,4-triazine}]2+, which has been isolated as its hexafluorophosphate salt and characterised by X-ray crystallography.

Chemistry of the copper( I )–water bond. Some new observations

One-dimensional polymeric copper(I) complexes of the type {[CuL(H2O)]BF4·H2O}n, where L = 2,3-diphenylquinoxaline, and {[CuL′(H2O)]X}n, where L′ = 2,3-dimethylquinoxaline and X− = ClO4− or BF4−, containing a rare copper(I)–water bond were synthesised. From the X-ray crystal structures of two of them, the copper(I) centres in these complexes are found to have a planar T-shaped N2O coordination sphere. It is concluded from the observed Cu(I)–O(water) bond lengths [2.167(7)–2.307(14) A] that the copper(I)–water bonds in these complexes are rather weak. With L, a monomeric complex of the type CuL2ClO4 has also been synthesised. But it has not been possible to obtain such a monomeric copper(I) complex with the BF4− anion or the ligand L′. In CuL2ClO4 the metal is also found to have, from the X-ray crystal structure, a planar T-shaped N2O coordination sphere with the perchlorate anion very weakly bound to the metal through an oxygen atom [Cu(I)–O(perchlorate) = 2.442(8) A]. While in the solid state electronic spectra, CuL2ClO4 displays a band at 346 nm, the aqua complexes show additional band(s) in the 400–480 nm range. CuL2ClO4 reacts with water in dichloromethane to yield an aqua copper(I) complex: CuL2ClO4 + H2O  → [CuL2(H2O)]ClO4 → 1/n{[CuL(H2O)]ClO4}n + L. In cyclic voltammetry at a glassy carbon electrode in anhydrous dichloromethane under N2 atmosphere, CuL2ClO4 shows a quasi-reversible CuII/I couple with a very high redox potential of 0.91 V vs. SCE, which is lowered to 0.79 V vs. SCE upon addition of water. This indicates that binding of water destabilises copper(I), a result expected on the basis of Pearsons HSAB Principle.

A case of four-coordinate silver(I) adopting a high energy planar geometry. Experiment and theory

The ligands PhL and MeL are obtained by condensing 2-formylpyridine with benzil dihydrazone and diacetyl dihydrazone, respectively, in 2∶1 molar proportion. With silver(I), PhL yields a double-stranded dinuclear cationic helicate 1 in which the metal is tetrahedral but MeL gives a cationic one-dimensional polymeric complex 2 where silver(I) is distorted square planar and the ligand backbone is nearly planar. In both complexes, metal:ligand ratio is 1∶1. Ab initio calculations on the ligands at the HF/6-31+G* level reveal that while PhL strongly prefers a helical conformation, MeL has a natural inclination to remain in a planar conformation. Density functional theory calculations on model silver(I) complexes show that formation of the linear polymer in the case of MeL is also an important factor in imposing the planar geometry of Ag(I) in 2.

A novel double-stranded dinuclear copper(I) helicate having a photoluminescent CuI2N8 chromophore

Bis-(pyridinal)-ethylenediimine (L) affords [(Cu2L2)-L-I]X-2 (X = ClO4- and PF6-). The X-ray crystal structure of the ClO4- salt shows that the cation [Cu-2(I):L-2](2+) is a double-stranded helicate. The PF6- salt exhibits a single emission band (maxima, 540 nm) in solution at room temperature (quantum yield: 2 x 10(-5) in methanol, 1 x 10(-5) in CH2Cl2)