STRUCTURAL INVESTIGATIONS OF TRANS-RH(PY3)(2)(CO)X (X=F, CL, NCO, Y=H, ME, PH) USING DENSITY-FUNCTIONAL THEORY AND X-RAY-ANALYSIS

A study of trans-Rh(PY3)(2)(CO)X (X = F, Cl; Y = H, Me) and trans-Rh(P H3)(2)(CO)NCO using density functional theory is presented together wi th the results of new high-resolution, low-temperature x-ray data anal ysis of trans-Rh(PPh(3))(2)(CO)X (X = F, NCO). In our calculations, we employed the Becke-exchange functional with the Lee, Yang, and Parr c orrelation functional (B-LYP) and the double-zeta plus polarization ba sis set (DZP). Our optimized complexes have a slightly distorted squar e-planar structure with moderate bending of the phosphine ligands towa rd the uninegative ligand X(-). The predicted structures compare favor ably with experimental data for trans-Rh(PPh(3))(2)(CO)X (X = F, Cl, N CO). New X-ray data for trans-Rh(PPh(3))(2)-(CO)X (X = F, NCO) clearly indicate a nonlinear configuration of P-Rh-P atoms, in agreement with our calculations. The apparent linear configuration of P-Rh-P atoms r ecently reported for the structure of the orthorhombic form of trans-R h(PPh(3))(2)(CO)Cl is most likely an artifact resulting from the disor der and symmetry imposed by the space group of the crystal structure. Computationally predicted vibrational frequencies v(C-O) and v(C-N) (f or X = NCO) compare well with solution-phase FTIR data.