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)](NO(3))(2) (1) and [Pt(NH(3))(4)(SO(4))(NO)](HSO(4))(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.