Shubhamoy Chowdhury

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).

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.

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)

A new photoluminescent CuI2N6 chromophore

A novel CuI2N6 chromophore has been isolated with 2,2′-bis[(4R)-phenyl]-1,3-oxazoline (L) in the optically pure triple-stranded helicate [Cu2L3](ClO4)2, which displays photoluminescence in methanol at room temperature (emission maximum λem = 385 nm; quantum yield ϕ = 1.6 × 10−4; lifetime τ ≈ 2 ns) as well as at 77 K (λem = 430 nm; τ = 0.89 ± 0.13 s).

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.

Synthesis and DFT calculations of oxido and phenylimido-rhenium(V) complexes incorporating the N, O donor ligand 2-[(2-hydroxyethylimino)methyl]phenol

Abstract The reactions of equimolar amounts of trans-[ReOC13(PPh3)2] or trans-[Re(NPh)(PPh3)2Cl3] with a Schiff base formed by condensation of 2-hydroxy-4-methoxybenzaldehyde and ethanolamine (H2L) result in the formation of cis-[ReO(HL)PPh3Cl2] (1a) and trans-[Re(NPh)(HL)(PPh3)Cl2] (2b), respectively, in good yields. 1a and 2b have been characterized by a range of spectroscopic and analytical techniques. The X-ray crystal structures of 1a and 2b reveal that 1a is an octahedral cis-Cl,Cl oxorhenium(V) complex, while 2b is a trans-Cl,Cl phenylimidorhenium(V) complex. The complexes are weakly emissive at room temperature with quantum yields of 10−4. Density functional theory calculations of the electronic properties of the complexes were performed and are in agreement with the experimental results. The complexes display quasi-reversible Re(V)/Re(VI) redox couples in acetonitrile. There is reasonable agreement between the experimental and calculated redox potentials of 1a and 2b.

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.