Zn2Ln2 complexes with carbonate bridges formed by the fixation of carbon dioxide in the atmosphere: single-molecule magnet behaviour and magnetocaloric effect

Three novel isostructural Zn(2)Ln(2) cluster complexes with carbonate bridging ligands, {Zn(2)Ln(2)(mu(3)-CO3)(2)L-2(acacF(6))(2)}CH3OH [H2L = N,N '-dimethyl-N,N '-(2-hydroxy-3-methoxy-5-methyl-benzyl)ethylenediamine; HacacF(6) = hexafluoroacetylacetone; Ln = Dy, 1; Ln = Gd, 2; Ln = Eu, 3], have been prepared by fixing carbon dioxide in the atmosphere. Such carbonate bridging ligands may mediate ferromagnetic exchange between Ln(3+) ions. The Zn2Dy2 compound (1) displays the properties of a single molecule magnet (SMM), showing slow magnetic relaxation at a 1500 Oe dc field, with an obviously larger U-eff/k value (83 K) with respect to the other carbonate-bridged Zn2Dy2 SMMs (<= 34 K) and ZnDy dinuclear SMMs derived from the same ligand H2L used in this work (<= 36.5 K), while the Zn2Gd2 compound (2) shows a moderate magnetocaloric effect and can be looked upon as a potential molecular material for low temperature magnetic refrigeration.