An oximate-based hexanuclear mixed-valence MnIII4MnII2 edge-sharing bitetrahedral core with an St = 5 spin ground state

The synthesis, structures and magnetic properties of two hexanuclear Mn6 clusters are reported: Mn6(mu4-O)2(dapdo)2(dapdoH)4(mu2-OH)2](ClO4)(2).6MeCN (1.6MeCN) and [Mn6(mu4-O)2(dapdo)2(dapdoH)4(mu2-OCH3)2](ClO4)(2).2Et2O (2.2Et2O) [dapdo2- is the dianion of 2,6-diacetylpyridine dioxime and dapdoH- is the monoanion of the aforesaid dioxime ligand]. Both complexes are mixed-valent with two Mn(II) and four Mn(III) atoms disposed in an edge-sharing bitetrahedral core. Both complexes 1 and 2 display the same [Mn(III)4Mn(II)2(mu4-O)2(mu2-OR)2]10+ core in which R = H for 1 and R = Me for 2. The [Mn(III)4Mn(II)2] core is rather uncommon compared to the reported [Mn(III)2Mn(II)4] core in the literature. DC magnetic susceptibility measurements on 1 and 2 reveal the presence of competing exchange interactions resulting in an St = 5 ground spin state. The magnetic behavior of the compounds indicates antiferromagnetic coupling between the manganese(III) centers, whereas the coupling between the manganese(III) and manganese(II) is weakly antiferromagnetic or ferromagnetic depending on the bridging environments. Finally the interaction between the manganese(II) centers from the two fused tetrahedra is weakly ferromagnetic in nature stabilizing St = 5 ground spin state in compounds 1 and 2.