Cyanide-Bridged [Fe8M6] Clusters Displaying Single-Molecule Magnetism (M = Ni) and Electron-Transfer-Coupled Spin Transitions (M = Co)

Cyanide-bridged metal complexes of [Fe8M6(mu-CN)(14)(CN)(10)(tp)(8)(HL)(10)(CH3CN)(2)][PF6](4)center dot nCH(3)CN center dot mH(2)O (HL=3-(2-pyridyl)-5-[4-(diphenylamino)phenyl]-1H-pyrazole), tp(-) = hydrotris(pyrazolylborate), 1: M = Ni with n = 11 and m = 7, and 2: M = Co with n = 14 and m = 5) were prepared. Complexes 1 and 2 are isomorphous, and crystallized in the monoclinic space group P2(1)/n. They have tetradecanuclear cores composed of eight low-spin (LS) Fe-III and six high-spin (HS) M-II ions (M = Ni and Co), all of which are bridged by cyanide ions, to form a crown-like core structure. Magnetic susceptibility measurements revealed that intramolecular ferro-and antiferromagnetic interactions are operative in 1 and in a fresh sample of 2, respectively. Ac magnetic susceptibility measurements of 1 showed frequency-dependent in- and out-of-phase signals, characteristic of single-molecule magnetism (SMM), while desolvated samples of 2 showed thermal- and photoinduced intramolecular electron-transfer-coupled spin transition (ETCST) between the [(LS-Fe-II)(3)(LS-Fe-III)(5)(HS-Co-II)(3)(LS-Co-III)(3)] and the [(LS-Fe-III)(8)(HS-Co-II)(6)] states.