Vibrational and solid-state phosphorus-31 nuclear magnetic resonance spectroscopic studies of 1:1 complexes of PPh(3) with gold(I) halides; Crystal structure of [AuBr(PMe(3))]

The crystal structure of [AuBr(PMe(3))], 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) Angstrom] 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(PMe(3))] (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 v(Au-2) bands. The X=Cl or I compounds show a strong Raman band which can be assigned to the delta(PAuX) deformation, but no v(Au-2) 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 v(Au-2) and delta(PAuX) modes, are discussed. The solid-state cross polarization magic angle spinning P-31 NMR spectra of the chloride and iodide complexes consist of doublets due to the presence of (1)J(Au-197-(31)p) coupling. This is a rare observation of spin-spin coupling between the spin I=1/2(31)P nucleus and the strongly quadrupole coupled Au-197 nucleus, and permits estimation of the (1)J((197)AU-(31)p) coupling constants for these complexes.