Photoactivated linkage isomerism in single crystals of nickel, palladium and platinum di-nitro complexes – a photocrystallographic investigation

Abstract

Low temperature, single crystal photocrystallographic studies have been carried out on four square planar Group 10 complexes [Ni(PEt₃)₂(NO₂)₂] 1, [Pd(PPh₃)₂(NO₂)₂] 2, [Pd(AsPh₃)₂(NO₂)₂] 3 and [Pt(PPh₃)₂(NO₂)₂] 4, in which the two nitro groups adopt the trans configuration. Irradiation with UV light, at 100 K, of single crystals of complexes 1–3 photoisomerise from the η¹-NO₂ nitro form to the η¹-ONO nitrito form occurred. Complex 1 underwent 25% conversion to the nitrito form before crystal decomposition occurred. 2 and 3 underwent 46% and 39% conversion, respectively, to the nitrito form when a photostationary state was reached. While under the same experimental conditions 4 showed no isomerisation. The photocrystallographic results can be correlated with the results of DFT calculations and with the observed trends in the solution UV/visible absorption spectroscopy obtained for these complexes. The results suggest that while steric factors in the isomerization processes are important there may also be a kinetic effect relating to the lability of the metal involved.