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(PEt(3))(2)(NO(2))(2)] 1, [Pd(PPh(3))(2)(NO(2))(2)] 2, [Pd(AsPh(3))(2)(NO(2))(2)] 3 and [Pt(PPh(3))(2)(NO(2))(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 η(1)-NO(2) nitro form to the η(1)-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.

The impact of hydrogen bonding on 100% photo-switching in solid-state nitro–nitrito linkage isomers

“…There is precedent for slower reaction kinetics in photoactive linkage isomer crystals with heavier transition metals (TMs), 29 and this has generally been linked to the expectation of lower kinetic lability for ligands attached to heavier TMs. 30 Secondly, though high photo-activation is achieved in both 1 and 2 at 150 and 200 K respectively, despite structural similarities 100% conversion is only reached in the Pd-system 1.…”

Solid-state photochemistry of molecular photo-switchable species: the role of photocrystallographic techniques

“…Nitro-nitrito isomerism has also been reported in systems containing different transition-metal centres, including palladium (Bajwa et al, 2012) and platinum species (Warren et al, 2012). In the latter photocrystallographic study, the absorption properties of the sample are shown to be affected by the nature of the metal centre.…”

Chemical Crystallography at the Advanced Light Source

“…The conversion rate varied from 16% for endo-Ni(aep)(ONO) 2 after exposure to 470 nm light, to 46% for endo-Pd(PPh 3 ) 2 (ONO) 2 after exposure to 362 nm light (up from 30% using 400 nm light). In addition to displaying lower nitrite to nitrito conversion, the nitrito anions in Ni(aepy)(ONO) 2 Partial conversions could be obtained by illumination of Ni(aep)(NO2)2, Ni(aepy)(NO2)2 (aep = 1-(2-aminoethyl)piperidine, aepy = 1-(2-aminoethyl)pyrrolidine) [55], Pd(PPh3)2(NO2)2 and Pd(AsPh3)2(NO2)2 [56] (Figure 6). The conversion rate varied from 16% for endo-Ni(aep)(ONO)2 after exposure to 470 nm light, to 46% for endo-Pd(PPh3)2(ONO)2 after exposure to 362 nm light (up from 30% using 400 nm light).…”

“…Partial conversions could be obtained by illumination of Ni(aep)(NO 2 ) 2 , Ni(aepy)(NO 2 ) 2 (aep = 1-(2-aminoethyl)piperidine, aepy = 1-(2-aminoethyl)pyrrolidine) [55], Pd(PPh 3 ) 2 (NO 2 ) 2 and Pd(AsPh 3 ) 2 (NO 2 ) 2 [56] (Figure 6). The conversion rate varied from 16% for endo-Ni(aep)(ONO) 2 after exposure to 470 nm light, to 46% for endo-Pd(PPh 3 ) 2 (ONO) 2 after exposure to 362 nm light (up from 30% using 400 nm light).…”

“…2 . Generated from data contained in [55] and [56]. In all cases, residual nitro ligands are shown using blue bonds and hollow atoms; exo-nitrito ligands (if any) are shown with green bonds and striped atoms, while endo-nitrito ligands are shown using red bonds and hatched atoms or gold bonds with solid atoms.…”