Synthesis, crystal structure, vibrational spectra, and normal coordinate analysis of (n-Bu4N)2[PtX4(ox)], X = Cl, Br

By oxidation of (n-Bu4N)(2)[PtX2(ox)], X = Cl, Br, with Cl-2 or Br-2 in dichloromethane (n-Bu4N)(2)[PtCl4(ox)] (1) and (nBu(4)N)(2)[PtBr4(ox)] (2) are formed. The crystal structure of [(C5H5N)(2)CH2][PtCl4(ox)] (monoclinic, space group C2/m, a = 15.562(1), b = 13.779(1), c = 10. 168(1) Angstrom, beta = 128.099(9)degrees, Z = 4) reveals complex anions with nearly C-2nu point symmetry. The bond lengths in the Cl'-Pt-O-. axes are Pt-Cl' = 2.287 and Pt-O-. = 2.048 and in the Cl-Pt-Cl axis Pt-Cl = 2.314 Angstrom. The oxalato ligand is nearly plane with an O-C-C-O torsion angle of 0.5degrees. In the vibrational spectra the PtX stretching vibrations are observed at 328 and 353 (1) and 201 and 212 cm(-1) (2). The PtX' modes appear at 360 and 343 (1) and 227 and 238 cm(-1) (2). The PtO. stretching vibrations are coupled with internal modes of the oxalato ligands and appear in the range of 400-800 cm(-1). Based on the molecular parameters of the X-ray determination (1) and estimated data (2) the IR and Raman spectra are assigned by normal coordinate analysis. The valence force constants are f(d)(PtCl) = 2.08, f(d)(PtCl') = 2.29, f(d)(PtBr) = 1.56, f(d)(PtBr') = 2.02 and f(d)(PtO.) = 2.46 (1) and 2.35 mdyn/Angstrom (2). Taking into account increments of the trans influence a good agreement between observed and calculated frequencies is achieved. The NMR shifts are delta(Pt-195) = 5623.0 (1) and 4536.1 (2).