Crystal structure, magnetism and spectroscopy of two strongly antiferromagnetically coupled dinuclear Cu(II) paddlewheel-like compounds with 4-azabenzimidazole as a ligand

Abstract

Two dinuclear compounds, [Cu 2(azab) 4Cl 2]Cl 2(CH 3OH) 3 ( 1) and [Cu 2(azab) 4Br 2]Br 2(H 2O) 1/2 ( 2) (in which azab = 4-azabenzimidazole), have been synthesized and characterized by infrared spectroscopy and EPR. Also the X-ray structures of both compounds and the magnetic susceptibility have been investigated, and the dinuclear structural details are presented. The geometries of both structures are similar. Each copper(II) ion has a square pyramidal geometry with the basal plane formed by four nitrogen atoms of four bischelating azab molecules in a paddlewheel-like fashion. The apical position is occupied by a chloride or bromide anion, respectively. The EPR spectra show a resolved triplet, S = 1, spectrum for both compounds (including the Δ M s = ±2 transition splitted into seven lines at 77 K) with a zero-field splitting ( D) of 0.124 cm −1. The magnetic susceptibility measurements (from 5 to 300 K) agree with a strong overall antiferromagnetic interaction with a large singlet–triplet splitting of J = −329 and −349 cm −1, for compounds 1 and 2, respectively.