Square Planar versus Tetrahedral NiS₄ Cores in the Coordination Spheres of (HMB)Ru(II) and Cp*Ru(III) and a Related CuS₄ Complex. Synthetic, Single-Crystal X-ray Diffraction, and Magnetic Studies {HMB = η⁶-C₆Me₆ and Cp* = η⁵-C₅Me₅}

The reaction of [LRu(κ³SSS‘-tpdt)] (L = η⁶-C₆Me₆ (HMB), (1); L = η⁵-C₅Me₅ (Cp*), (2); tpdt = S(CH₂CH₂S^-)₂) with Cl₂Ni(PPh₃)₂ gave diamagnetic trinuclear complexes, [{(HMB)Ru^II(μ-1κ³SSS‘:2κ²SS-tpdt)}₂Ni^II]²⁺ (3) and [{Cp*Ru^III(μ-1κ³SSS‘:2κ²SS-tpdt)}₂Ni^II]²⁺ (4), isolated as hexafluorophosphate salts in 96 and 61% yields, respectively. A similar reaction of 2 with CuSO₄ in excess gave a dinuclear species, [Cp*Ru^III(μ-1κ³SSS‘:2κ²SS-tpdt)Cu^II-(CH₃CN)₂]²⁺ (5) (73% yield, as PF₆^- salt), which further reacted with 1 molar equiv of 2 to give a paramagnetic complex, [{Cp*Ru^III(μ-1κ³SSS‘:2κ²SS-tpdt)}₂Cu^II]²⁺ (6) (81% yield, as PF₆^- salt), or 1 molar equiv of 1 to give the “mixed-ring” tpdt dithiolate-bridged diamagnetic complex [{Cp*Ru^III(μ-1κ³SSS‘:2κ²SS-tpdt)}Cu^II{(HMB)Ru^II(μ-1κ³SSS‘:2κ²SS-tpdt}]²⁺ (7) (89% yield, as PF₆^- salt). The molecular structures of complexes 3−7 were determined by single-crystal X-ray diffraction analysis. Notably it was observed that the trimetallic array Ru−M−Ru possesses a M−M bond between the central metal atom (Ni(II) or Cu(II)) and terminal Ru atoms in +3 oxidation state, i.e., Ru atoms bearing a Cp* ligand. Thus, while Ni is in a square planar environment in 3, in the other trinuclear complexes, viz., 4, 6, and 7, Ni/Cu is in a slightly distorted tetrahedral environment with respect to the four thiolate S donors, but is formally five- or six-coordinate, in the presence of one or two M−M bonds, respectively. Variable-temperature magnetic susceptibility studies on neat powders of representative compounds 2, 3, 4, and 6 show S = ¹/₂ Curie-like behavior for mononuclear Ru(III) complex 2, as expected, and also for the trinuclear {Ru(III)Cu(II)Ru(III)} complex 6, the behavior of the latter being ascribed either to a 19e electron count on Cu, involving Ru−Cu bonding, or to a strongly antiferromagnetically coupled {Ru(III)(S = ¹/₂)Cu(II)(S = ¹/₂)Ru(III)(S = ¹/₂)} sulfur-bridged moiety. Complexes 3 and 4, having oxidation states Ru(II)Ni(II)Ru(II) and Ru(III)Ni(II)Ru(III), respectively, are close to being diamagnetic but display very weak paramagnetism between 4.2 and 300 K.