Heterometallic M 2 Cr 4 (M II = Sr, Pb) Clusters Assembled by Tris(μ‐aqua) Bridges

Three heterometallic compounds formulated as [CaCr 2 (μ‐OH)(μ‐OAc)(nta) 2 · 6H 2 O]2H 2 O ( I ) [M 2 Cr 4 (μ‐OH) 2 (μ‐OAc) 2 (nta) 4 7H 2 O]14H 2 O, [M = Sr 2+ ( II ) Pb 2+ ( III ), H 3 nta = 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 , Ca 2+ 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 Sr 2+ or Pb 2+ counterions, which results in hexanuclear M 2 Cr 4 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)