Dominik Schaniel, Theo Woike, Bernard Delley, Daniel Biner, Karl W. Krämer and Hans-Ueli Güdel
Generation of one light-induced metastable nitrosyl linkage isomer in [Pt(NH₃)₄Cl(NO)]Cl₂ in the red spectral range
Phys. Chem. Chem. Phys. 9, 5149-5157 (2007)                       

Abstract: One metastable linkage nitrosyl isomer can be generated in [Pt(NH₃)₄Cl(NO)]Cl₂ by irradiation with light in the red spectral range. The potential energy barrier for the thermal relaxation of the metastable state to the ground state has an amount of E_A = (0.27 ± 0.03) eV. The decay follows the Arrhenius law and E_A is independent of temperature. At room temperature the metastable state has a lifetime of t = 3.8 × 10^–5 s after generation by pulsed laser illumination. Below T = 100 K about 30% linkage NO isomers can be generated in a powder sample by irradiation with l = 658 nm. DFT calculations demonstrate the rotation of the NO ligand from Pt–N–O to Pt–O–N as a unique linkage isomer. Consequently, only one new n(NO) stretching vibration is detected with a shift from 1673 cm^–1 to 1793 cm^–1 by 120 cm^–1, to higher frequencies in good agreement with the DFT calculations. In the metastable state new electronic absorption bands are observed in the blue-green and near infrared spectral range. The metastable state can be optically accessed via a (5d + p(NO)) p*(NO) transition. [Pt(NH₃)₄Cl(NO)]Cl₂ is diamagnetic with a Pt(5d⁸) configuration and thus represents the first {MNO}⁸ complex with experimental evidence for a light-induced nitrosyl linkage isomer.