NI-IV CUBANES - SYNTHESIS AND CHARACTERIZATION OF THE [NI4SE4(SE3)5(SE4)]4- AND [NI4TE4(TE2)2(TE3)4]4- ANIONS

The compounds [NEt4]4[Ni4Se4(Se3)5(Se4)].xNEt4Cl (x = 0, 1) and [NEt4]4[Ni4Te4(Te2)2(Te3)4] have been prepared from the reaction in DMF of Ni(S2COEt)2 with Li2Se and Se or Li2Te and Te, respectively. These compounds result from spontaneous assembly reactions in which Ni(II) centers are oxidized to Ni(IV) with concomitant reduction of Se- or Te-containing species. The anion [Ni4Se4(Se3)5(Se4)]4- possesses a Ni4Se4 cubane core and has five Se-3(2-) chains and one Se-4(2-) chain bridging the Ni atoms on the cubane faces. The anion [Ni4Te4(Te2)2(Te3)4]4- has a Ni4Te4 cubane core and has two Te-2(2-) chains bridging Ni atoms on opposite faces of the cubane core and four Te-3(2-) chains bridging the Ni(IV) atoms on the remaining cubane faces. The presence of Ni(IV) is necessitated by charge balance. As expected for such d6 systems the compounds are diamagnetic. The [Ni4Se4(Se3)5(Se4)] 4- anion exhibits a sharp, albeit complex, Se-77 NMR spectrum with fifteen resonances at delta-103, 134, 289, 361, 387, 401, 411, 470, 660, 680, 726, 749, 773, 789 and 804 ppm. The [Ni4Te4(Te2)2(Te3)4]4- anion exhibits a simpler Te-125 NMR spectrum with five resonances at delta - 632, - 324, 65, 325 and 766 ppm. In the cubane anions each Ni atom is in a distorted octahedral environment, being coordinated by three Se or Te atoms in the cubane framework and by three Se or Te atoms in chains that bridge to the other three Ni atoms. While the bridging Se-3(2-) chains appear to produce little strain on the Ni4Se4 cubane core, the Se-4(2-) chain distorts it, as evidenced from the Ni-Ni distances, the Se(cub)-Se(cub) distances and the cubane bond angles. In contrast, the bridging Te-3(2-) chains distort the Ni4Te4 cubane core as evidenced from the Ni-Ni distances, the Te(cub)-Te(cub) distances and the cubane bond angles; the Te-2(2-) chains produce less strain. [NEt4]4[Ni4Se4(Se3)5(Se4)].NEt4Cl crystallizes in the monoclinic space group C-2h(5)-P2(1)/n with a = 21.817(4), b = 14.319(1), c = 26.421(5) angstrom, beta = 112.69(2)-degrees, V = 7615 angstrom3 and Z = 4 (- 120-degrees-C). [NEt4]4[Ni4Te4(Te2)2(Te3)4] crystallizes in the triclinic space group C(i)1-P1BAR with a = 14.399(2), b = 15.153(2), c = 18.069(3) angstrom, alpha = 70.97(1), beta = 79.05(1), gamma = 74.20(1)-degrees, V = 3564 angstrom3 and Z = 2 (-167-degrees-C).