Photogeneration of nitrosyl linkage isomers in octahedrally coordinated platinum complexes in the red spectral range.

Octahedrally coordinated platinum nitrosyl complexes Pt(NH(3))(4)(NO(3))(NO)(2) (1) and Pt(NH(3))(4)(SO(4))(NO)(CH(3)CN) (2) undergo linkage isomerization at temperatures below 130 K when excited with red light. Irradiation in the spectral range of 570-800 nm results in an inversion of the NO ligand from a Pt-NO to a Pt-ON configuration. The metastable state Pt-ON can be reverted back to the ground state (GS) Pt-NO by irradiation with blue-green or infrared light or by heating above 130 K. The characteristic shift of the nu(NO) stretching vibration from 1744 to 1815 cm(-1) in 1 and from 1714 to 1814 cm(-1) in 2 allowed the unambiguous identification of the respective nitrosyl isomers. Up to 26% of the complexes of 1 and 20% of 2 may be photochemically excited toward the metastable state (MS). Using X-ray crystallography and DFT calculations, it is shown that the Pt-NO in these {MNO}(8) complexes exhibits a bent arrangement with a Pt-N-O angle in the range of 117-120 degrees. As a consequence and in contrast to the known {MNO}(6) complexes only one metastable linkage isomer Pt-ON with a correspondingly bent Pt-O-N arrangement is formed, as evidenced by spectroscopy and DFT calculations. The calculated partial density of states shows that the charge transfer transition Pt(5d) --> pi(star)(NO) is responsible for the formation of the metastable state.