The synthesis, structure, magnetic and Mössbauer spectral properties of an Fe–Zr carboxylate–alkoxide derivative containing an {Fe2Zr2(μ3-O)2} core

Reaction of [Fe-3(mu (3)-O)(O2CPh)(6)(H2O)(3)](O2CPh) with pyridine yields a product (2) which on recrystallisation rearranges to [Fe-6(mu -O)(2)(mu -OH)(2)(O2CPh)(12)(py)(2)] (3). Magnetic and Mossbauer spectral analyses suggest that compound (2) contains an Fe-4(O)(2) cluster. The unrecrystallised material (2) reacts with Zr(OBut)(4) to form [Fe2Zr2(mu (3)-O)(2)(mu -O2CPh)(6)(OBut)(4)(py)(2)] (4). The mixed metal cluster has a "butterfly" configuration with Fe-III atoms coordinated by pyridine forming the "body" position. It displays weak antiferromagnetic behaviour, closely modelled as an Fe2O2 dimer with g = 2.01 and J = -1.42 cm(-1). Its Mossbauer spectrum has the high-spin Fe(III) parameters delta = 0.51 mm s(-1) and DeltaE(Q) = 0.65 mm s(-1) at 5 K. The molecular species [Zr-3(mu (3)-O)(mu -O2CPh)(2)(mu -OBut)(2)(OBut)(6)] (5) is also detected in the reaction when excess Zr(OBut)(4) is present.