Apurba K. Patra

Magneto–structural studies of monohydroxo-bridged dicopper(II) complexes M[Cu2L2(OH)]·2H2O (M=Na+ (1) and K+ (2); H2L=2,6-bis[N-(phenyl)carbamoyl]pyridine). Effect of CuOHCu bridge angle on antiferromagnetic coupling

Abstract Using a tridentate bis-amide ligand 2,6-bis[N-(phenyl)carbamoyl]pyridine (H2L), in its deprotonated form, two new monohydroxo-bridged dicopper(II) complexes M[Cu2L2(OH)]·2H2O (M=Na+ (1) and K+ (2)) have been prepared and characterised by a number of methods, including X-ray crystallography. Each copper(II) ion is terminally coordinated by one pyridyl and two amide nitrogen donors. The two copper(II) centres are bridged by a hydroxo group, with each copper(II) centre assuming a distorted square planar geometry. The observation of short CuNpy and long CuNamide bonds is caused by the steric requirement of the ligand. Interestingly, each cation Na+/K+ is coordinated to four different [Cu2L2(OH)]− units through the amide O-donors, in an uncommon distorted tetrahedral coordination environment. Temperature-dependent magnetic susceptibility measurements revealed that the compounds have S=0 ground state with singlet–triplet energy separation, 2J=−334 and −296 cm−1 for 1 and 2, respectively. The larger CuOHCu bridge angle in 1 (131.1(6)°) causes better antiferromagnetic exchange coupling than that in 2 (125.7(6)°).

Synthesis and properties of a monomeric and a μ-oxo-bridged dimeric iron(III) complex with a tetradentate pyridine amide in-plane ligand. X-ray structure of [Fe(bpc)Cl(DMF)] [H2bpc=4,5-dichloro-1,2-bis(pyridine-2-carboxamido)benzene]

Abstract The controlled nucleophilic halide displacement reaction of [NEt4][Fe(bpc)Cl2] [H2bpc=4,5-dichloro-1,2-bis(pyridine-2-carboxamido) benzene] with AgClO4 in MeCN afforded a crystalline iron(III) complex Fe(bpc)Cl·H2O 1. The mixed chloro-dimethylformamide (DMF) axially ligated complex [Fe(bpc)Cl(DMF)] (obtained during recrystallization of 1 from DMF; however, it loses DMF quite readily to revert back to 1) has been structurally characterized. It belongs to only a handful of mononuclear high-spin iron(III) complexes having deprotonated picolinamide ligand. The iron(III) centre is co-ordinated in the equatorial plane by two pyridine nitrogens and two deprotonated amide nitrogens of the ligand, and two axial sites are co-ordinated by a chloride ion and a DMF molecule. The metal atom has a distorted octahedral geometry. Reaction of 1 with [nBu4N][OH] in MeOH afforded a μ-oxo-bridged diiron(III) complex, [Fe(bpc)]2O·DMF·2H2O, 2. The spin state and the co-ordination environment of the iron(III) centres in 1 and 2 have been determined by temperature-dependent (25–300 K) magnetic susceptibility measurements in the solid state (Faraday method) and Mossbauer spectral studies at 300 K. Complex 1 behaves as a perfect S=5/2 system, in the solid-state as well as in DMF solution. The two iron(III) centres in 2 are antiferromagnetically coupled (J=−117.8 cm−1) and the bridged dimeric structure is retained in DMF solution. Bridge-cleavage reactions of 2 have been demonstrated by its ready reaction with mineral acids such as HCl and MeCO2H to generate authentic S=5/2 complexes, [Fe(bpc)Cl2]− and [Fe(bpc)(O2CMe)2]−, respectively.