Pentanuclear pivalate Ni(II) and Co(II) clusters: modulation of molecular structures and magnetic properties

Abstract Reaction of nickel cluster Ni9(HOOCCMe3)4(μ4-OH)3(μ3-OH)3(μn-OOCCMe3)12 (1) or cobalt pivalate polymer [Co(OH)n(OOCCMe3)2−n]x (7) with bis[3,5-(dimethylpyrazolyl)]-1,2,4,5-tetrazine (3) in MeCN solution was found as a result in the formation of isostructural pentanuclear clusters of composition M5(μ3-OH)2(μ-OOCCMe3)4(μ-N,N′,N″-3,5-Me2C3HN2C2(O)N4)4(MeCN)2 (M=Ni (4), Co (8)) with a planar spirane metal core. Reaction of cobalt complex 7 with 3 in benzene gives rise to a pentanuclear cluster Co5(μ3-OH)2(μ-OOCCMe3)4(μ-N,N′,N″-3,5-Me2C3HN2C2(O)N4)4(C5N2H8)2 (9), containing coordinated pyrazole molecules as terminating ligands instead of labile MeCN ligands in 8. The reaction of cluster 8 with 2,6-diaminopyridine (T=85 ° C ) in MeCN results in the substitution of MeCN ligands and formation of a new cluster Co5(μ3-OH)2(μ-OOCCMe3)4(μ-N,N′,N″-3,5-Me2C3HN2C2(O)N4)4(C5H7N3)2 (10) with two 2,6-diaminopyridine ligands instead of MeCN molecules. The reactions of 4 and 8 with NiCl2·6H2O in MeCN/EtOH solution (3:1) give rise to isostructural ferromagnetic pentanuclear chloro-bridged clusters M5(μ3-OH)2(μ-CI)2(μ-OOCCMe3)2(μ-N,N′,N″-3,5-Me2C3HN2C2(O)N4)2(μ-N,N′,N″,O-3,5-Me2C3HN2C2(O)N4)2(MeCN)2 (M=Co (11), Ni (12)).The reaction of 8 with solid CoCl2·6H2O in MeCN results in new seven-nuclear ferromagnetic cluster Co5(μ3-OH)2(μ-CI)2(μ-OOCCMe3)2(μ-N,N′,N″-3,5-Me2C3HN2C2(O)N4)2(μ-N,N′,N″,O-3,5-Me2C3HN2C2(O)N4)2(MeCN)2[Co(CH3CN)CI2]2 (13). The molecular structures of 4, 8, 9, 10, 12 and 13 established by X-ray diffraction studies and magnetic behavior of new nickel and cobalt pivalate clusters are discussed.