Heterometallic M₂Cr₄ (M^II = Sr, Pb) Clusters Assembled by Tris(μ‐aqua) Bridges

Abstract

Three heterometallic compounds formulated as [CaCr2(μ‐OH)(μ‐OAc)(nta)2·6H2O]2H2O (I) [M2Cr4(μ‐OH)2(μ‐OAc)2(nta)47H2O]14H2O, [M = Sr2+ (II) Pb2+ (III), H3nta = nitrilotriacetic acid] were prepared and structurally characterised. In all three compounds a common core [Cr(μ‐OH)(μ‐OAc)Cr] containing two different bridging ligands, hydroxido and acetato groups, is present. In I, Ca2+ counterions link the dinuclear chromium units together through outer carboxylate oxygen atoms and a hydrogen‐bonded network, whereas in II and III the nuclearity is extended by the presence of three bridging water molecules linking together two Sr2+ or Pb2+ counterions, which results in hexanuclear M2Cr4 clusters. The temperature dependence of the magnetic susceptibilities of I–III, which were fitted with an isotropic Hamiltonian, yielded antiferromagnetic interaction parameters (J) for I–III close to –14 cm–1. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)