ON THE ELECTRONIC-STRUCTURE OF METASTABLE NITROPRUSSIDE ION IN NA2[FE(CN)5NO].2H2O - A COMPARATIVE SINGLE-CRYSTAL ESR STUDY

Laser irradiation of Na2[Fe(CN)5NO].2H2O at low temperature produces two long-living nitroprusside metastable states which, upon heating, decay at two different temperatures. In addition, laser illumination of previously X-ray irradiated crystals generates traces of the closely related [Fe(CN)5NO]3- species with linear (axial) NCFeNO geometry where the unpaired electron is localized on a dz2 orbital as detected by ESR spectroscopy [g|=2.0055(6), g∥=2.0348(4); A|=16.9(1)G, A|=14.8(1)G]. There also exists another stable form of [Fe(CN)5NO]3- with bent FeNO group and the odd electron located in a π*NO orbital. The comparison of metastable [Fe(CN)5NO]2- and the [Fe(CN)5NO]3- (dz2) species suggest that the electronic structure of the high-temperature metastable state should be described as 1B2: 6e(dxz,dyz)4 2b2(dxy)1 5a1(dz2)1. This assignment is consistent with reported optical absorption, Mössbauer, Raman, and IR data. © 1990.