Synthesis and properties of charge-transfer solids with cluster units [Mo6X14]2- (X = Br, I)

The preparation of charge-transfer (CT) solids using [Mo6X14](2-) (X = Br, I) cluster units and several organic electron donor molecules (D) including a variety of tetrathiafulvalene (TTF) derivatives was studied. Galvanostatic electrochemical oxidation afforded single crystals of the cation radical salts of (tetrathionaphthacene)Mo6Br14(PhCN)(3) (1, PhCN: benzonitrile), (hexamethylene-TTF)(2)Mo6I14(PhCN)(4) (2), (bis(ethylenedioxy)-TTF)(2)Mo6Br14(PhCN)(4) (3), (tetrakis(methylthio)-TTF)(2)Mo6Br14 (4), (perylene)(6)Mo6Br14 (5), and powders from several TTF derivatives combined with other kinds of electron donors. In 1, the donor molecules were in the diamagnetic dicationic state and formed two-dimensional D(2+)A(2-) (A = Mo6Br14) layers. Moreover, in 2-4, the donor molecules were in the monocationic radical state. The structural analysis of 3 indicated the presence of isolated cation radical molecules, whereas in 2 and 4, the donor cation radicals formed segregated stacks with dimerized units. Donor dimers and [Mo6I14](2-) cluster units in 2 formed a CsCl-related structural pattern with solvent molecules occupying the free space in the crystal. The donor dimers and [Mo6Br14](2-) cluster units in 4 formed infinite alternating stacks parallel to each other. The static magnetic susceptibility of 2 exhibited singlet-triplet behavior with vertical bar J vertical bar/k(B) = 190 K, whereas the radical spins in 4 were strongly coupled antiferromagnetically. There were two kinds of perylene molecules in 5: one formed segregated columns with weakly dimerized units having a charge of approximately +0.5, while the other enclosed the columns with parallel molecular planes having nearly zero charge. 5 was similar to that of a dimer-type Mott insulator. The electrochemical reaction of N-(3-perylenylmethyl)-N, N-bis(2-pyridylmethyl)amine (perbpa), which is a perylene-pendant tridentate ligand, and CuCl2 in the presence of (Bu4N)(2)Mo6Br14 in PhCN afforded a dinuclear Cu(II) complex [Cu-2(mu-Cl)(2)(perbpa)(2)]Mo6Br14(PhCN)(4) (6). The perylene groups in 6 were in a neutral electronic state. The temperature-dependent magnetic susceptibility measurement of 6 showed a weak ferromagnetic exchange interaction between the Cl-bridged Cu(II) cores with the S = 1 ground state (g = 2.14, J = +0.56 K) based on H = -2JS(1.)S(2). The boundary between the neutral and ionic ground states of the CT solids of [Mo6Br14](2-) shifted to the negative side by 0.5 V and 0.3-0.6 V from those of the TTF.p-quinone and TTF.TCNQ system, respectively, with respect to the redox potential differences between the donor and acceptor species.