Vibrational and solid-state phosphorus-31 nuclear magnetic resonance spectroscopic studies of 1 : 1 complexes of PPh3 with gold(I) halides; crystal structure of [AuBr(PMe3)

Abstract

The crystal structure of [AuBr(PMe3)], like that of the corresponding chloride, was found to consist of three crystallographically independent molecules linked through weak Au ⋯ Au contacts to form helical chains. The Au ⋯ Au distances [3.648(1), 3.980(2), 3.548(2)Å] are, however, significantly longer than in the chloro- and iodo-complexes, implying that the Au ⋯ Au interaction is weakest in the bromide. The far-IR and Raman spectra of [AuX(PMe3)](X = Cl, Br or I) have been measured, and assignments made for the bands observed. The spectra were analysed to see whether they show any effects of the weak Au ⋯ Au bonding evident in the crystal structures. In particular, the low-wavenumber limit of previously reported Raman spectra for these species has been extended in order to search for ν(Au2) bands. The X = Cl or I compounds show a strong Raman band which can be assigned to the δ(PAuX) deformation, but no ν(Au2) bands were found in the region predicted on the basis of recent assignments for such modes in other complexes which display Au ⋯ Au contacts of similar length. Possible reasons, including an interaction between ν(Au2) and δ(PAuX) modes, are discussed. The solid-state cross polarization magic angle spinning 31P NMR spectra of the chloride and iodide complexes consist of doublets due to the presence of 1J(197Au–31P) coupling. This is a rare observation of spin–spin coupling between the spin I=½31P nucleus and the strongly quadrupole coupled 197Au nucleus, and permits estimation of the 1J(197Au–31P) coupling constants for these complexes.