Antiferromagnetic complexes with a metal-metal bond. VIII. Synthesis and structure of the antiferromagnetic heteronuclear cluster, "butterfly" (or "metal-chain"), (Cp4Cr2Ni2)(μ³-S)2(μ⁴-S)

By heating the mixture of solutions of (CpCrSCMe 3 ) 2 S (I) in benzene and [CpNi(CO)] 2 in pentane followed by chromatography on alumina, dark cherry-red needles of the heteronuclear cluster (Cp 4 Cr 2 Ni 2 )(μ 3 -S) 2 (μ 4 -S) (II) were obtained, whose structure was established on the basis of a complete X-ray analysis. The crystals are rhombic, spatial group Pbca ; a = 12.07(1), b = 18.50(2), c = 17.36(1) A, Z = 8. The metallic skeleton of II has the “butterfly” or “metal-chain” structure with a direct CrCr bond (2.62(1) A) and inequivalent CrNi bonds, 2.86(1) and 2.64(1) A, while the Ni·Ni distance is nonbonding (4.34(1) A). The NiCr 2 triangle planes produce a dihedral angle of 127°. The two μ 3 -bridged sulfur atoms locate under these triangles whereas the third sulfur atom is μ 4 -bridging coordinating all four metal atoms in the cluster with mean NiS and CrS distances of 2.29(1) and 2.25(1) A, respectively. The Ni 2 S 3 group is planar and almost perpendicular to the CrCr axis. Complex II is anti-ferromagnetic and its exchange parameter — 2 J (418 cm -1 ) is close to that found for the initial binuclear complex I (— 2 J = 430 cm -1 with a CrCr bond length of 2.689(8) A). The role of the Ni coordination number in the generation of II is discussed.