Synthesis, structural characterization and magnetic properties of mixed-valent bis-bipyridine manganese carboxylate clusters

Procedures have been developed for the synthesis of complexes containing th e cations [Mn4O2(O2CR)(4)(L)(2)](2+) (R = Me, Et, Ph) (1) and [Mn4O2(MeO)(3 )(O2CPh)(2)(L)(2)(MeOH)](2+) (2). Treatment of the corresponding [Mn3O(O2CR )(6)(py)(3)](ClO4) complex with the ligand 1,2-bis(bipyridine-6'-yl)ethane (L) in MeCN or MeOH leads to the formation of 1 and 2, respectively. Both c omplexes contain [Mn4O2] cores. Complex 1 has overall antiferromagnetic cou pling resulting in a S = 1 spin ground state. The metal centers in the core of complex 2 are also antiferromagnetic ally coupled, but in this case the spin ground state is S = 7/2. Complex 2 also displays an out of phase sign al in the ac magnetic susceptibility study, indicating it to be a new examp le of single molecule magnet (SMM). (C) 2001 Elsevier Science Ltd. All righ ts reserved.