PYRAZINE-MEDIATED ANTIFERROMAGNETIC INTERMOLECULAR EXCHANGE IN MIXED-VALENT DIRUTHENIUM TETRACARBOXYLATES

Two mixed-valent diruthenium tetracarboxylates, [Ru-2-(AcO)(4)(H2O)(2) ]BPh(4) (1) and [Ru-2(AcO)(4)(pz)]BPh(4)(2) (AcO= acetate, BPh(4)=tetr aphenylborate, pz=pyrazine), were synthesized and characterized by ele mental analysis, IR and UV-Vis spectroscopies, and magnetic susceptibi lity measurements between 6 and 320 K. The magnetic behaviour of 1 can be understood in terms of non-interacting spin 3/2 dimers undergoing a large (c. 72 cm(-1)) zero-field splitting, whereas an intermolecular antiferromagnetic interaction (c. -2 cm(-1)), in addition to a large zero-field splitting (c. 63 cm(-1)), is required to account for the da ta for 2.