Synthesis, Crystal Structures and Magnetic Properties of a Linear Trinuclear Cu(II) Complex [Cu3(ClCH2COO)6(bpy)2] and a Dinuclear Complex [Cu2(bpy)2(μ-OH)(μ-OH2) (μ-ClCH2COO)](ClO4)2

Two new triply bridged Cu(II) compounds [Cu-3(bpy)(2)(mu-ClCH2COO)(6)] (1) and [Cu-2(bpy)(2)(mu-OH)(mu-OH2)(mu-ClCH2COO)](ClO4)(2) (2) (where, bpy=2,2'-bipyridine) have been synthesized and their magnetic properties have been measured and correlated with structure. Compound 1 is a novel centrosymmetric tricopper compound with only carboxylate bridges. The terminal Cu2+ ions have [5 + 1] coordination while the central ion has [4 + 2] coordination. The three centres are antiferromagnetically coupled, the exchange parameters for the neighbouring and distant pairs of Cu(II) atoms being 2 J=-28.6 cm(-1) and 2 J'=-1.0 cm(-1), respectively. In compound 2 three types bridging modes are observed, viz., hydroxo, aquo and carboxylato. The two Cu(II) centers are ferromagnetically coupled (2 J=73.8 cm(-1)) as previously observed for several di-copper complexes with the same bridges. DFT calculations are in reasonable agreement with the magnetic exchange parameters for both dinuclear and trinuclear compounds.