A three-dimensional copper(II) 12-metallacrown-4 complex with malonomonohydroxamic acid (H3mmh) as a ligand

Abstract

Slow diffusion of an ethanolic solution of copper(ii) into an aqueous solution of partially deprotonated malonodihydroxamic acid (H4mdh) affords the pentanuclear complex of formula {[K(H2O) 2]2[Cu5(mmh)4]}n (1) (H3mmh = malonomonohydroxamic acid) which is formed by 12-MC-4 metallacrown units with the fifth copper(ii) ion being placed at the center of the square metallacrown unit. The dianionic pentacopper(ii) planar entity interacts with diaquapotassium(i) counterions through the carboxylate-oxygen atoms resulting in a neutral three-dimensional structure. Magnetic susceptibility measurements in the temperature range 1.9-300 K for 1 show the occurrence of relatively strong antiferromagnetic interactions within the pentanuclear copper(ii) core leading to two degenerated low-lying spin doublets at T < 50 K. X-band EPR spectra at low temperatures give additional support to the ground spin doublet nature. The topology of the pentanuclear copper(ii) unit of 1 together with good ability to mediate magnetic interactions between the copper(ii) ions of the diatomic N-O(oximato) and monoatomic O(oximato) bridges which connect the metal centers within the pentanuclear core account for this magnetic behaviour. © 2011 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.