Infrared Spectra of the Square Planar Rhodium(I) Complexescis-[Rh(CO)2(pyridine) (X)] (X = Cl, Br): Isotopic Labelling Studies and Normal Coordinate Analysis

Abstract The infrared spectra (4000 - 50 cm−1) of the square planar rhodium(I) complexes cis-[Rh(CO)2 (pyridine) (X)] (X = Cl, Br) and their isotopomers with pyridine-d 5 and 13CO have been determined. Assignments are based on earlier studies on pyridine and its complexes and on the shifts in infrared bands which are caused by the isotopic substitutions employed. Normal coordinate analysis following the procedure of Becher and Mattes has been used to confirm the empirical assignments. The two v(RhC) bands are observed near 490 and 450 cm−1. v(RhN) is found near 210 cm−1 and v(RhX) occurs at 310 (X = Cl) and 235 (X = Br) cm−1. At frequencies below 200 cm−1, the bands are assigned to bending modes in the following sequence: δ (RhN) > δ (CRhC) > δ (RhCl) > γ (RhCl) > γ (RhN).