MOLECULAR-STRUCTURE AND MAGNETIC-PROPERTIES OF COPPER(II), MANGANESE(II) AND IRON(II) CROCONATE TRI-HYDRATE

The compounds M(II)CO5 . 3H2O 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) angstrom for I, a = 12.063(3), b = 8.213(2), c = 15.652(3) angstrom for 11, a = 11.999(2), b = 8.158(I), c = 15.536(4) angstrom 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 less-than-or-equal-to 0.54 cm-1 for I, II and III, respectively) appear to be responsible of most of the observed magnetic behavior.