HALIDE DERIVATIVES OF PALLADIUM-GOLD CLUSTER COMPOUNDS - X-RAY CRYSTAL AND MOLECULAR-STRUCTURE OF (I)PD(AUPPH3)7(AUI)2

The reaction chemistry of [Pd(AuPPh3)8](NO3)2 with the halide ions Cl- , Br- and 1- and with the pseudohalide CN- has been studied. Acetone s olutions of [Pd(AuPPh3)8](NO3)2 reacted with these ions to give the ne w Pd-Au clusters (I)Pd(AuPPh3)7(AuI)2, [Pd(AuPPh3)7(AuBr)3]+, Pd(AuPPh 3)8(AuCl)3 and Pd(AUPPh3)8(AuCN)3, respectively. In the presence of ad ded acid the reaction with Cl- yielded the cationic cluster [Pd(AuPPh3 )7(AuCl)3]+. The structure of (I)Pd(AuPPh3)7(AuI)2 has been determined by X-ray diffraction (unit cell: P2(1)/n, a = 37.29, b = 22.69, c = 1 6.639 angstrom, beta = 114.61-degrees, Z = 4, V = 12 800 angstrom; ref inement: R = 0.069). The geometry of this cluster is that of a Pd-cent ered icosahedral fragment in accord with its eighteen-electron configu ration. The coordinated iodine anion of this cluster can be displaced by reaction with CO to give [(CO)Pd(AuPPh3)7(AuI)2]+, while the sixtee n-electron clusters [Pd(AuPPh3)7(AuBr)3]+ and [Pd(AuPPh3)7(AuCl)3]+ re acted cleanly with CO to give simple adducts. The eighteen-electron cl usters Pd(AuPPh3)8(AuCl)3 and Pd(AuPPh3)8(AuCN)3 showed no reaction wi th CO. The mechanism of these interesting cluster fragmentation and gr owth reactions is discussed.