A structural study of copper(II) carboxylates: Crystal structure and physical characterisation of [Cu2(2-bromopropanoato)4(caffeine)2]

Based on the bond-valence sum model the continual transition between the bidentate and monodentate bonding mode of carboxylato group and minimum of Cu–O bond lengths were estimated. The dependence of Cu⋯Cu separation on Cu–N bond length in binuclear Cu(II) carboxylates with caffeine were derived and fitted to the observed data. The crystal structure of [Cu2(2-bromopropanoato)4(caffeine)2] has been determined by X-ray crystallography. The structure consists of centrosymmetric binuclear units where the two Cu atoms are coordinated by four disordered bridging 2-bromopropionates and two caffeine ligands at the apices of a bicapped square prism. Both 2-bromopropionates show disorder of their –Br and –CH3 substituents. Stacking π·π interactions between the adjacent caffeine molecules link the complex units in 1-D networks. The binuclear structure of the studied compound is consistent with magnetic data and EPR spectrum.