Vibrational and structural mapping of [Os(bpy)3] and [Os(phen)3] |
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| Authors: | Konstantinos D Demadis Edward M Kober Peter S White |
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| Institution: | Department of Chemistry, Venable and Kenan Laboratories, CB 3290, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3290, USA |
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| Abstract: | Structural changes between OsIIL3]2+ and OsIIIL3]3+ (L: 2,2′-bipyridine; 1,10-phenanthroline) and molecular and electronic structures of the OsIII complexes OsIII(bpy)3]3+ and OsIII(phen)3]3+ are discussed in this paper. Mid-infrared spectra in the ν(bpy) and ν(phen) ring stretching region for OsII(bpy)3](PF6)2, OsIII(bpy)3](PF6)3, OsII(phen)3](PF6)2, and OsIII(phen)3](PF6)3 are compared, as are X-ray crystal structures. Absorption spectra in the UV region for OsIII(bpy)3](PF6)3 and OsIII(phen)3](PF6)3 are dominated by very intense absorptions (ε = 40 000-50 000 M−1 cm−1) due to bpy and phen intra-ligand π → π∗ transitions. In the visible region, relatively narrow bands with vibronic progressions of ∼1500 cm−1 appear, and have been assigned to bpy or phen-based, spin-orbit coupling enhanced, 1π → 3π∗ electronic transitions. Also present in the visible region are ligand-to-metal charge transfer bands (LMCT) arising from π(bpy) → t2g(OsIII) or π(phen) → t2g(OsIII) transitions. In the near infrared, two broad absorption features appear for oxidized forms OsIII(bpy)3](PF6)3 and OsIII(phen)3](PF6)3 arising from dπ-dπ interconfigurational bands characteristic of dπ5OsIII. They are observed at 4580 and 5090 cm−1 for OsIII(bpy)3](PF6)3 and at 4400 and 4990 cm−1 for OsIII(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 OsIII(bpy)3](PF6)3, the OsIII atom resides at a distorted octahedral site, as judged by ∠N-Os-N, which varies from 78.78(22)° to 96.61(22)°. Os-N bond lengths are also in general longer for OsIII(bpy)3](PF6)3 compared to OsII(bpy)3](PF6)2 (0.010 Å), and for OsIII(phen)3](PF6)3 compared to OsII(phen)3](PF6)2 (0.014 Å). Structural changes in the ligands between oxidation states are discussed as originating from a combination of dπ(OsII) → π∗ (bpy or phen) backbonding and charge redistribution on the ligands as calculated by natural population analysis. |
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| Keywords: | Osmium complexes X-ray crystal structures Bipyridine Phenanthroline Oxidation states |
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