HIGH-TEMPERATURE MOLECULAR MAGNETS BASED ON CYANOVANADATE BUILDING-BLOCKS - SPONTANEOUS MAGNETIZATION AT 230-K

The molecular-based magnetic materials Cs2MnII[V-II(CN)6] (1) and (Et(4)N)(0.5)Mn-1.25-[V(CN)(5)] . 2H(2)O (2) (where Et is ethyl) were prepared by the addition of manganese(ll) triflate to aqueous solutions of the hexacyanovanadate(II) ion at 0 degrees C. Whereas 1 crystallizes in a face-centered cubic lattice, 2 crystallizes in a noncubic space group. The cesium salt (1) has features characteristic of a three-dimensional ferrimagnet with a Neel transition at 125 kelvin. The tetraethylammonium salt (2) also behaves as a three-dimensional ferrimagnet with a Neel temperature of 230 kelvin; only two other molecular magnets have higher magnetic ordering temperatures. Saturation magnetization measurements indicate that in both compounds the V-II and high-spin Mn-II centers are antiferromagnetically coupled. Both 1 and 2 exhibit hysteresis loops characteristic of soft magnets below their magnetic phase-transition temperatures. The high magnetic ordering temperatures of these cyano-bridged solids confirm that the incorporation of early transition elements into the lattice promotes stronger magnetic coupling by enhancing the backbonding into the cyanide pi* orbitals.