Synthesis, structures and spectroscopic properties of 1:1 complexes of gold(I) halides with trimesitylphosphine

Monomeric two-coordinate gold(I) complexes, [Au(P(mes)(3))X] (P(mes)(3) = tris(2,4,6-trimethylphenyl)phosphine, X = Cl, Br and I), have been prepared and characterized by single-crystal X-ray structure determinations, far-infrared spectroscopy and solution and solid-state CPMAS P-31 n.m.r. spectroscopy. X-Ray structure determinations show that crystals obtained from solutions of [NBu4] [AuX2] and P(mes)(3) in acetonitrile for X = Cl, Br and I and in dimethylformamide (dmf) for X = Br and I form an isomorphous series of complexes, crystallizing in space group P2(1)/c with a approximate to 8, b approximate to 22, c approximate to 13 Angstrom, beta approximate to 98 degrees (alpha form). Crystallization of the chloride from dimethylformamide yields the solvated complex [Au(P(mes)(3))X].1/2(dmf) in space group P2/a with a 15.224(2), b 10.070(1), c 18.210(4) Angstrom, beta 100.42(2)degrees. Electrochemical synthesis of the complexes for X = Cl and Br yield two new crystalline phases; the chloride in space group P2(1)/c with a 10.249(2), b 8.189(2), c 31.844(3) Angstrom, beta 91.68(1)degrees (beta form) and the bromide in space group Pbca with a 19.208(4), b 15.586(3), c 16.962(4) Angstrom (gamma form). The Au-P bond lengths increase in the order Cl < Br < I with distances c. 0.02-0.03 Angstrom longer than average values for other [Au(PR3)X] complexes, reflecting steric congestion by the P(mes)(3) ligand. For the unsolvated complexes, the Au-X distances are c. 0.02 Angstrom shorter than average values. For the Cl/dmf solvate, both Au-P and Au-X bond lengths increase. For the complexes, far-infrared spectra show nu((AuCl)-Cl-35,37) 336, 329 cm(-1), nu(AuBr) 234 cm(-1) and nu(AuI) 195 cm(-1) and solid-state P-31 CPMAS n.m.r. spectra yield broad peaks with delta -3.9 (Cl), -0.6 (Br) and +6.0 (I). For the Cl/dmf solvate, nu((AuCl)-Cl-35,37) are 334, 327 cm(-1) and delta is -4.4. Solution P-31 n.m.r. spectra in CDCl3 give sharp single peaks at delta -5.0 (Cl), -1.4 (Br) and +5.5 (I) with the similarity of the values with those for the solid-state spectra consistent with similar conformational structures for the [Au(P(mes)(3))X] molecules in the two states.