Synthesis and molecular structure of diamagnetic heterometallic clusters (RC5H4)2Cr2(μ3-S)2(μ4-S)Co2(CO)4 with a Cr2Co2 "butterfly" frame

Abstract The interaction of (RC5H4)2Cr2(SCMe3)2(μ-S) (I, R = H; Ia, R = CH3) with Co2(CO)8 in a molar ratio of 1 1 gave the 62-electron, heteronuclear clusters (RC5H4)2Cr2(μ3-S)2(μ4-S)Co2(CO)4 (II and IIa respectively), which were characterized by X-ray crystallography. Crystals of Illa are monoclinic, space group C2/c, a 15.246(1), b 11.846(9), c 9.9434(6) A, β 100.965(6)°, V 1763 A3, Z = 4, R = 0.046, Rw = 0.057. Crystals of IIa are triclinic, space group P , a 9.9771(9), b 10.1120(10), c 11.0770(10) A, α 116.982(8), β 99.560(8), γ 82.054(8)° , V 979.5 A3, Z = 2, R = 0.064, Rw = 0.060. The two clusters have a Cr2Co2 “metal butterfly” framework. In II, the CrCr separation is 2.544(1) A and those of CrCo are 2.622(1) and 2.617(1) A, the dihedral angle between the Cr2Co wings of the butterfly is 124.2°. The μ3-sulphide bridge is situated below each wing whereas the μ4-sulphide bridge is located between the wings. The average distances are: Cr-(μ3-S), 2.258(2), Cr-(μ4-S), 2.326(2), CO-(μ3-S), 2.178(2), Co-(μ4-S) 2.205(2) A. The geometry of IIa differs from II in that it has the staggered ring conformation instead of the eclipsed, it has non-equivalent CoCr bonds (av. 2.634(2) and 2.614(2) A) and has slightly shortened Co-(μ4-S) bonds (av. to 2.193(3) A). The structures of II and IIa were compared with the geometries of previously studied clusters, viz. the 66-electron “metal chain” Cp2Cr2(μ3-S)2(μ4-S)Ni2Cp2 and 62-electron “metal butterfly” Cp2Mo2(μ3-S)2(μ4-S)Co2(CO)4.