Photogeneration of Nitrosyl Linkage Isomers in Octahedrally Coordinated Platinum Complexes in the Red Spectral Range SchanielDominik WoikeTheo BehrndNorwid-R. HauserJürg KrämerKarl W. TodorovaTeodora DelleyBernard 2009 Octahedrally coordinated platinum nitrosyl complexes [Pt(NH<sub>3</sub>)<sub>4</sub>(NO<sub>3</sub>)(NO)](NO<sub>3</sub>)<sub>2</sub> (<b>1</b>) and [Pt(NH<sub>3</sub>)<sub>4</sub>(SO<sub>4</sub>)(NO)](HSO<sub>4</sub>)(CH<sub>3</sub>CN) (<b>2</b>) 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 ν(NO) stretching vibration from 1744 to 1815 cm<sup>−1</sup> in <b>1</b> and from 1714 to 1814 cm<sup>−1</sup> in <b>2</b> allowed the unambiguous identification of the respective nitrosyl isomers. Up to 26% of the complexes of <b>1</b> and 20% of <b>2</b> 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}<sup>8</sup> complexes exhibits a bent arrangement with a Pt−N−O angle in the range of 117−120°. As a consequence and in contrast to the known {MNO}<sup>6</sup> 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) → π<sup>★</sup>(NO) is responsible for the formation of the metastable state.