Synthesis, structure, and magnetism of heterometallic carboxylate complexes [MnIII2MII4O2(PhCOO)10(DMF)4], M = MnII, CoII, NiII

Three new homo- and heterometallic hexanuclear complexes [(Mn2M4O2)-O-II(PhCOO)(10)(DMF)(4)] (With M = Mn (1), Cc (2) or Ni (3) and DMF = dimethylformamide) have been synthesized by redox generation of benzoate ligands from benzaldehyde in a one-pot reaction. All of the compounds are isostructural and crystallize in the 1-42d space group of the tetragonal system, data for 1: a = 27.2249(8) angstrom, c = 25.5182(5) angstrom, R1 = 0.0681. The crystal structure contains isolated molecules. Each molecule consists of 2 x Mn-III surrounded by four M-II ions to form two edgesharing OMn2M2 tetrahedra giving rise to the [Mn2M4O2] core. The coordination sphere of each metal is completed by the bridging benzoate ligands and DMF molecules. The magnetic susceptibilities of 1-3 have been measured in the 1.8 K < T < 300 K temperature range. The magnetic susceptibilities for 1 and 2 pass through a broad maximum at low temperature which is characteristic of the diamagnetic ground state, while for 3 no maximum is detected down to 1.8 K. The magnetic data have been interpreted quantitatively for 1 and 3 on the basis of spin exchange interactions between the metallic centers (spin Hamiltonian for a pair being H-AB = -J(AB) S-A center dot S-B)- Singlecrystal measurements on [Mn6O2(PhCOO)(10)(CH3CN)(4)] (4) show that significant magnetic anisotropy develops at low temperature.