Theoretical and Spectroscopic Studies of Tetrahedral Clusters of the Type [L3M(μ-H)x{AuL′}3]2+ (M = Rh, Ir, x = 2; M = Ru, x = 3)

Alberto Albinati, Jürgen Eckert, Peter Hofmann, Heinz Rüegger, Luigi M. Venanzi

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The structural and bonding aspects of the hydride ligands in the cationic clusters [(triphos) MH2{Au(PPh3)}3]2+(triphos = CH3C(CH2PPh2)3; M = Rh and Ir) and [(triphos)RuH3{Au(PPh3)}3]2+ were investigated by a variety of techniques. The 31P-CP-MAS spectra (162 MHz) of the clusters [(triphos)MH2{Au(PPh3)}3] (CF3SO3)2 (M = Rh and Ir), [(triphos)RuH3{Au(PPh3)}3] [PF6]2, and [(triphos)RuH2{Au(PPh3)}3] [PF6] show that in the dihydrido complexes the phosphorus atoms of the triphos ligands, as well as those of the PPh3 molecules, are inequivalent while the corresponding donors in the trihydrido complex are equivalent. The 197Au Mössbauer spectra of the rhodium and iridium complexes show that two of the gold atoms in the dihydrido clusters are different from the third. Furthermore, the values of the isomer shifts and quadrupole splittings indicate that the bridging hydride ligands are best described as being intermediate between ·2 and ·3 (quasi-·3). Incoherent inelastic neutron spectroscopic (IINS) and IR studies of the rhodium and ruthenium clusters were carried out to unambiguously assign the M-H vibrational modes. These spectra show bands at ca. 1600 cm−1 (assigned to Vas(M-H-Au) that exclude a pure ·3 bridging mode for the hydride ligands but are consistent with a quasi-·3 model. Finally MO model calculations of the extended Hückel type for[(PH3)3Rh(AuPH3)3](H)33+,[(PH3)3Rh(AuPH3)3](H)22+, and[(PH3)3Rh(AuPH3)3]-(H)+, which served as simplified models of real hydrido cluster cations, have been performed. A general bonding scheme is presented, analyzing electronic and molecular structures for this class of compounds, including the question of possible hydride locations, on the basis of a transparent fragment orbital (FMO) description and by means of various geometry optimization calculations. The theoretical results are in accord with spectroscopic data and allow their consistent interpretation. Thus, all these studies are in agreement with a quasi-·3 structure for the hydride ligands in these clusters.

Original languageEnglish
Pages (from-to)2377-2390
Number of pages14
JournalInorganic Chemistry
Issue number11
StatePublished - 1993


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