Infrared Studies of the Isomerization of Cis -Pd(NH 3 ) 2 X 2

Palladium complexes of the type cis-PdL₂X₂ have been found to be unstable at room temperature and isomerize to the corresponding trans isomers. Neglecting lattice interactions, symmetry considerations would predict two Pd–N stretching vibrations. These vibrations have been observed at 495 and 476 cm⁻¹ for the cis-chloride isomer and at 480 and 460 cm⁻¹ for the cis-bromide isomer. The trans isomer, by the same considerations, should have but one Pd–N stretching vibration. This vibration was observed for the trans-chloride isomer at 496 cm⁻¹ and for the trans-bromide isomer at 490 cm⁻¹. It has been found that as isomerization proceeds, from the cis to the trans forms, the lower Pd–N stretching vibration decreases in intensity and eventually disappears. The intensity changes for these vibrations over a period of 72 h indicated that the reaction follows a first-order rate law. A reaction mechanism has been proposed.