Nitro-Nitrito Photoisomerization of Cationic Platinum(II) Complexes in the Solid State: Reactivity in Polymorphic Crystals and Glassy State

Nitro-nitrito isomerization is a well-known photoreaction exhibited by metal complexes in the solid state. We previously reported that the isomerization ratio in the salts of a cationic platinum(II) nitrito complex [Pt(L)(NO2)](+) (L = N-1-(2-(dimethylamino)ethyl)-N-2,N-2-dimethyl-N-1-pentyl-1,2-ethanediamine) is correlated to the reaction cavity surrounding the nitrito ligand. In this study, to further elucidate the effect of the packing structure on the reaction, we investigated the photoisomerization of the same cation in different packing environments. The salt of the cationic complex with the PF6 anion gave three polymorphs (alpha-, beta-, and gamma-forms) and a pseudopolymorph (delta-form, acetonitrile solvate), of which the gamma-form is formed from the delta-form upon desorption of acetonitrile. These polymorphs exhibited 36-100% conversions at 180 K depending on the reaction cavity. In addition, the beta-form exhibited a space group change upon photoirradiation. The salt with the (CF3SO2)(2)N- anion was an ionic liquid, taking both the crystalline and glassy states at low temperature. The crystalline state exhibited approximately 30% conversion at 100 K, whereas photoisomerization was not observed in its glassy state as investigated by IR spectroscopy. In these salts, less densely packed crystals deteriorated upon photoirradiation.

Automated summary

Nitro-nitrito isomerization, a well-known photoreaction in metal complexes, was studied in different packing environments using a cationic platinum(II) nitrito complex. The polymorphs of the salt exhibited various conversion rates at different temperatures, with the beta-form showing a space group change upon photoirradiation. A salt with the (CF3SO2)(2)N- anion displayed both crystalline and glassy states at low temperatures, with the crystalline state showing around 30% conversion at 100 K. Less densely packed crystals in these salts deteriorated upon photoirradiation.