Mixed ruthenium-rhodium carbonyl clusters. Synthesis and crystal structure of the [PPh(4)](+) salts of the anions [Ru2Rh2(CO)(7)(mu-CO)(5)](2-), [Ru2Rh2(CO)(9)(mu-CO)(3)(mu-H)](-), and [Ru2Rh2(CO)(7)(mu-CO)(5)(mu(3)-AuPPh(3))](-)

The anion [RU(2)Rh(2)(CO)(12)](2-) (1) has been obtained by reaction of Ru-3(CO)(12) with [Rh(CO)(4)](-) as [N(PPh(3))(2)](+) or (PPh(4)())+ salts; this species reacts with acids or AuPPh(3)Cl to give respectively [RU(2)Rh(2)(CO)(12)H](-) (2) and [Ru2Rh2(CO)(12)(AuPPh(3))](-) (3). The phosphonium salts (PPh(4))(2)[Ru2Rh2(CO)(12)]. THF (I), (PPh(4))[Ru2Rh2(CO)(12)H] (II), and (PPh(4))[RU(2)Rh(2)(CO)(12)(AUPPh(3))] (III) were characterized by single-crystal X-ray diffraction: I, space group P2(1)/n, Z = 4, a = 11.256(2) Angstrom, b = 26.712(2) Angstrom, c = 20.048(5) Angstrom beta = 90.45(2)degrees, R1 = 0.048 for 4049 independent reflections with I > 3 sigma(I); II space group P2(1)/a, Z = 4, a = 12.453(2) Angstrom, b = 24.074(3) Angstrom, c = 13.174(2) Angstrom, beta = 90.67(1)degrees, R1 = 0.039 for 4034 independent reflections with I > 3 sigma(I); III, space group P2(1)/n, z = 4, a = 11.720(2) Angstrom, b = 13.133(3) Angstrom, c = 35.614(2) Angstrom, beta = 95.70(1)degrees, R1 = 0.054 for 4231 independent reflections with I > 3 sigma(I). Anions 1 and 2 have a tetrahedral Ru2Rh2 metal frame, while in 3 there is a trigonal-bipyramidal frame with one ruthenium atom and the gold atom in apical positions; in 2 the H atom bridges the Ru-Ru edge. H-1 and P-31 NMR spectra of, respectively, 2 and 3 are consistent with the crystal structures. C-13 NMR spectra of both 1 and 2 show evidence of fluxional behavior at 295 K which cannot be frozen at 178 K, where the signals collapse; compound 3 at room temperature shows a partially fluxional solution structure which becomes static at ca. 250 K.