Infrared spectra and density functional theory calculations of group 10 transition metal sulfide molecules and complexes.

Laser-ablated Ni, Pd, and Pt atoms were reacted with sulfur molecules emerging from a microwave discharge in argon during condensation at 7 K. Reaction products were identified from matrix infrared spectra, sulfur isotopic shifts, spectra of sulfur isotopic mixtures, and frequencies from density functional calculations. The strongest absorptions are observed at 597.9, 596.1, and 583.6 cm(-1), respectively, for the group 10 metals. These absorptions show large sulfur-34 shifts and 32/34 isotopic frequency ratios (1.0282, 1.0285, 1.0298) that are appropriate for S-S stretching modes. Of most importance, mixed 32/34 isotopic 1/4/4/2/4/1 sextets identify this product with two equivalent S(2) molecules containing equivalent atomic positions as the bisdisulfur pi complexes M(S(2))(2). Our DFT calculations find stable D(2h) structures with B(1u) ground states and intense b(1u) infrared active modes a few wavenumbers higher than the observed values. A minor Ni product at 505.8, 502.7 cm(-1) shows the proper sulfur-34 shift for assignment to (58)NiS, (60)NiS. Another major product with Pt at 512.2 cm(-1) reveals an asymmetric triplet absorption with mixed sulfur 32/34, which is appropriate for assignment to the SPtS disulfide molecule. A weak 491.7 cm(-1) peak exhibits the sulfur-34 shift expected for PtS, and this assignment follows.