STRUCTURAL STUDIES OF PHOTOINDUCED INTRAMOLECULAR ELECTRON-TRANSFER IN CYCLOPENTADIENYLNITROSYLNICKEL

A structural study based on EXAFS, FTIR, and optical absorption spectr oscopies has been conducted on; a photogenerated, metastable state of cyclopentadienylnitrosylnickel (CpNiNO) produced by a reversible photo chemical reaction. The photogenerated, metastable state with distincti vely different EXAFS, FTIR, and optical absorption spectra from those of the ground state was created by irradiating the sample at 20 K with the 365-nm line of a mercury lamp. At the same temperature, the rever se reaction was induced by irradiation with the 313-nm line from a mer cury lamp. On the basis of the analysis of the EXAFS data, the photoge nerated, metastable state of CpNiNO has undergone considerable nuclear rearrangements cmopared to its ground state. The nuclear movement is characterized by a 0.12-Angstrom elongation of the Ni-N bond and by a bending of the Ni-N-O. A shift of the N-O stretching frequency from 18 24 to 1387 cm(-1) was observed in the photoinduced reaction with 365-n m Light, consistent with previous studies. This implies that a NO- lik e species results from intramolecular electron transfer from Ni to NO. The absorption spectrum of the long-lived, metastable, charge-transfe r state exhibited reduced absorption of the 385-nm band and an additio nal broad band in the near-IR region, which is likely a consequence of the intramolecular electron transfer and the Ni-N-O bending. On the b asis of the structures obtained from EXAFS, ZINDO calculations for the ground state of CpNiNO reproduced the general features of the observe d absorption spectrum and were qualitatively consistent with the compl icated dependence of the charge-transfer photoreaction on wavelength.