Synthesis and crystal structure of the pentanuclear metal cluster complex [PtRh4(µ-CO)4(η-C5Me5)4]

Abstract

The compound [Rh₂(µ-CO)₂(η-C₅Me₅)₂] reacts with [Pt(C₂H₄)₃] to give the pentanuclear cluster complex [PtRh₄(µ-CO)₄(η-C₅Me₅)₄], the structure of which has been established by X-ray diffraction. Crystals grown from light petroleum–dichloromethane belong to the monoclinic system but on cooling to 200 K and rewarming to room temperature undergo an irreversible phase change to the orthorhombic system. Data were collected for both phases: (I) orthorhombic, space group Pnma, with Z= 4 in a unit cell of dimensions a= 17.945(5), b= 17.978(6), and c= 13.764(4)Å; (II) monoclinic, space group A2a, with Z= 4, a= 17.826(4), b= 13.944(3), c= 18.112(5)Å, and β= 97.19(2)°. Intensities were measured to 2θ⩽ 45° for (I) and to 2θ⩽ 40° for (II), and were refined for (I) to R 0.048 (R′ 0.050) and for (II) to R 0.066 (R′ 0.070) for 1 606 and 1 718 independent reflections respectively. The two molecules have very similar structures, based on the platinum atom being ‘co-ordinated’ to two Rh₂(µ-CO)₂(η-C₅Me₅)₂ fragments. The four rhodium atoms are disposed around the platinum in an essentially tetrahedral arrangement, with the dihedral angles between the PtRh₂ planes being 90°for (I) and 100° for (II). In both molecules the PtRh₂ groups form essentially equilateral triangles [Rh–Rh(mean) and Pt–Rh(mean) 2.618(2)Å]. The four CO ligands, in addition to bridging the Rh–Rh vectors, weakly interact with the platinum atom, a feature which persists in solution, as deduced from ¹⁹⁵Pt–¹³C coupling observed in the ¹³C n.m.r. spectrum of [PtRh₄(µ-CO)₄(η-C₅Me₅)₄].