Molecular structure and magnetic properties of copper(II), manganese(II) and iron(II) croconate tri-hydrate

Abstract

The compounds M IIC 5O 5·3H 2O with M=Cu ( I), Mn ( II), Fe ( III), were prepared and characterized by means of structural and magnetic measurements. The crystals are orthorhombic, space group Pbca, with a=11.770(2), b=8.085(2), c=15.571(2) Å for I, a=12.063(3), b=8.213(2), c=15.652(3) Å. for II, a=11.999(2), b=8.158(1), c=15.536(4) Å for III; Z=8. The previously reported structures of I and II, refined in this work, and the novel structure of III were solved by direct methods and least-squares refinement of structural parameters led to conventional R factors of 0.029, 0.025 and 0.025 for I, II and III, respectively. The overall structure is similar for the three compounds and consists of infinite one-dimensional chains of metal ions bridged by croconate ligands acting in a monodentate and bidentate fashion. The magnetic properties of I, II and III are reported and discussed on the basis of intrachain and interchain exchange couplings and, for III, of single-ion axial zero-field splitting contributions. Weak antiferromagnetic intrachain interactions via the croconate dianion ( J=0.99(3), 0.22(1) and ⩽0.54 cm −1 for I, II and III, respectively) appear to be responsible of most of the observed magnetic behavior.