X-ray analysis of excited-state structures of the diplatinum complex anions in five crystals with different cations

The photo-excited structures of [Pt-2(pop)(4)](4-) and [Pt-2(pop)(2)(popH)(2)](2-), (pop = diphosphite) in five kinds of complexes were analyzed by X-rays. For the complex with tetrabutylammonium (Bu), tetrapentylammonium (Pn), benzyltriethylammonium (Bzte), or benzyltributylammonium (Bztbu) as a counter cation, the Pt complex anion is attached by two protons and is represented as [Pt-2(pop)(2)(popH)(2)](2-), whereas the anion is [Pt-2(pop)(4)](4-) for the complex with benzyldimethylphenylammonium (Bzdmp) as a cation. Since the Bu, Pn, and Bzte complexes have two crystal forms, the structures of eight crystals, Bu1, Bu2, Pn1, Pn2, Bzte1, Bzte2, Bztbu, and Bzdmp, were determined by X-ray analysis before irradiation. The five crystals of Bu1, Pn1, Bzte1, Bztbu, and Bzdmp were irradiated with a xenon lamp. The intensity data were collected at the light-on and light-off stages at 173 K for Bu1, Pn1, and Bzdmp crystals and at 103 K for Bzte1 and Bztbu crystals. Each crystal showed the contraction of the unit-cell volume significantly at light-on stage and returns to the original one at light-off stage. The analyzed structures at light-on and light-off stages clearly indicated that the Pt-Pt and Pt-P bond distances became significantly shorter at light-on stage than the corresponding distances at light-off stage. The decreased values for the Pt-Pt and Pt-P distances at the light-on stage are 0.0038(3) and 0.0069(10) Angstrom for Bu1, 0.0081(3) and 0.0053(11) Angstrom for Pn1, 0.0127(5) and 0.0085(14) Angstrom for Bzte1 0.0031(3) and 0.0019(12) Angstrom for Bztbu, and 0.0019(2) and 0.0033(8) Angstrom for Bzdmp, respectively. The other bond distances in anions and cations are not significantly changed. These structural changes indicate that the excited- and ground-state molecules reach the equilibrium state at the light-on stage; the values are in good agreement with the results observed by spectroscopic methods and theoretical calculation.