Synthesis and magnetization of new room-temperature molecule-based magnets: Effect of stoichiometry on local magnetic structure by X-ray magnetic circular dichroism

The synthesis and the magnetic properties of two new bimetallic chromium-vanadium ferrimagnets, compounds 1 and 2, are reported. They belong to a set of nonstoichiometric Prussian blue analogues C-y(I) V-[Cr-III(CN)(6)](z). nH(2)O (C, alkali cation) with T-C varying between 295 and 315 K (T-C = 310 K for 1 and 315 K for 2). They are obtained through mild chemistry from the molecular precursor [Cr-III(CN)(6)](3-) and from vanadium V-II salts. The synthetic conditions determine (i) the oxidation State of the vanadium(V-II, V-III, or V-IV), (ii) the stoichiometry, and (iii) hence the magnetic properties. The reported systems present a larger magnetization than the first reported V-Cr analogue (0.36N(A)beta for 1 and 0.40N(A)beta for 2). Furthermore, X-ray magnetic circular dichroism (XMCD) data demonstrate (i) the short-range antiferromagnetic coupling between the spins borne by the chromium(III) and vanadium ions and (ii) the reversal of the local magnetization on vanadium and chromium when changing the stoichiometry.