Ni IV cubanes: synthesis and characterization of the [Ni 4Se 4(Se 3) 5(Se 4)] 4− and [Ni 4Te 4(Te 2) 2(Te 3) 4] 4− anions

Abstract

The compounds [NEt 4] 4[Ni 4Se 4(Se 3) 5(Se 4)]· xNEt 4Cl ( x=0, 1) and [NEt 4] 4[Ni 4Te 4(Te 2) 2(Te 3) 4] have been prepared from the reaction in DMF of Ni(S 2COEt) 2 with Li 2Se and Se or Li 2Te 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 [Ni 4Se 4(Se 3) 5(Se 4)] 4− possesses a Ni 4Se 4 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 [Ni 4Te 4(Te 2) 2(Te 3) 4] 4− has a Ni 4Te 4 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 d 6 systems the compounds are diamagnetic. The [Ni 4Se 4(Se 3) 5(Se 4)] 4− anion exhibits a sharp, albeit complex, 77Se NMR spectrum with fifteen resonances at δ 103, 134, 289, 361, 387, 401, 411, 470, 660, 680, 726, 749, 773, 789 and 804 ppm. The [Ni 4Te 4(Te 2) 2(Te 3) 4] 4− anion exhibits a simpler 125Te NMR spectrum with five resonances at δ −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 Ni 4Se 4 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 Ni 4Te 4 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. [NEt 4] 4[Ni 4Se 4(Se 3) 5(Se 4)]·NEt 4Cl crystallizes in the monoclinic space group C 5 2 h - P2 1/ n with a=21.817(4), b=14.319(1), c=26.421(5) Å, β=112.69(2)°, V=7615 Å 3 and Z=4 (−120 °C). [NEt 4] 4[Ni 4Te 4(Te 2) 2(Te 3) 4] crystallizes in the triclinic space group C i 1- P 1 with a=14.399(2), b=15.153(2), c=18.069(3) Å, α=70.97(1), β=79.05(1), γ=74.20(1)°, V=3564 Å 3 and Z=2 (−167 °C).