Vibrational and structural mapping of [Os(bpY)(3)](3+/2+) and [Os(phen)(3)](3+/2+)

摘要

Structural changes between [(OsL3)-L-II](2+) and [(OsL3)-L-III](3+) (L 2,2'-bipyridine; 1,10-phenanthroline) and molecular and electronic structures of the Os-III complexes [Os-III(bpy)(3)](3+) and [Os-III(phen)(3)](3+) are discussed in this paper. Mid-infrared spectra in the v(bpy) and v(phen) ring stretching region for [Os-II(bpy)(3)](PF6)(2), [Os-III(bpy)(3)](PF6)(3), [Os-II(phen)(3)](PF6)(2), and [Os-III(phen)(3)](PF6)(3) are compared, as are X-ray crystal structures. Absorption spectra in the UV region for [Os-III(bpy)(3)](PF6)(3) and [Os-III(phen)(3)](PF6)(3) are dominated by very intense absorptions (epsilon = 40 000-50 000 M-1 cm(-1)) due to bpy and phen intra-ligand pi ->pi* transitions. In the visible region, relatively narrow bands with vibronic progressions of similar to 1500 cm(-1) appear, and have been assigned to bpy or phen-based, spin-orbit coupling enhanced, (1)pi -> 3 pi* electronic transitions. Also present in the visible region are ligand-to-metal charge transfer bands (LMCT) arising from pi(bpy) -> t(2g)(Os-III) or pi(phen) -> t(2g)(Os-III) transitions. In the near infrared, two broad absorption features appear for oxidized forms [Os-III(bpy)(3)](PF6)(3) and [Os-III(phen)(3)](PF6)(3) arising from d pi-d pi interconfigurational bands characteristic of d pi Os-5(III). They are observed at 4580 and 5090 cm(-1) for [Os-III(bpy)(3)](PF6)(3) and at 4400 and 4990 cm(-1) for [Os-III(phen)(3)](PF6)(3). The bpy and phen infrared vibrational bands shift to higher energy upon oxidation of Os(II) to Os(III). In the cation structure in [Os-III(bpy)(3)](PF6)(3), the Os-III atom resides at a distorted octahedral site, as judged by angle N-Os-N, which varies from 78.78(22)degrees to 96.61(22)degrees. Os-N bond lengths are also in general longer for [Os-III(bpy)(3)](PF6)(3) compared to [Os-II(bpy)(3)](PF6)(2) (0.010 angstrom), and for [Os-III(phen)(3)](PF6)(3) compared to [Os-II(phen)(3)](PF6)(2) (0.014 angstrom). Structural changes in the ligands between oxidation states are discussed as originating from a combination of d pi(Os-II) -> pi* (bpy or phen) backbonding and charge redistribution on the ligands as calculated by natural population analysis. (c) 2006 Published by Elsevier B.V.