SCHEDULED MAINTENANCE
Recognition of fractional non-innocent feature of osmium coordinated 2,2′-biimidazole or 2,2′-bis(4,5-dimethylimidazole) and their interactions with anions†
Abstract
Mononuclear complexes [OsII(bpy)2(H2L1)](ClO4)2 ([1](ClO4)2) and [OsII(bpy)2(H2L2)](ClO4)2 ([2](ClO4)2) incorporating two free NH protons at the back face of the coordinated H2L, and deprotonated L2− bridged symmetric dinuclear complexes [(bpy)2OsII(μ-L12−)OsII(bpy)2)](ClO4)2 ([3](ClO4)2) and [(bpy)2OsII(μ-L22−)OsII(bpy)2)](ClO4)2 ([4](ClO4)2) (bpy = 2,2′-bipyridine, H2L1 = 2,2′-biimidazole and H2L2 = 2,2′-bis(4,5-dimethylimidazole)) have been characterised. Crystal structures of [1](ClO4)2 and the meso (ΔΛ) diastereomeric form of [3](ClO4)2 have been determined. The crystal structure of [1](ClO4)2 also reveals the hydrogen bonding interactions between its free acidic NH protons and the oxygen atoms of the perchlorate anion in the nearby asymmetric unit. Experimental and DFT/TD-DFT calculations have divulged the non-innocent feature of the doubly deprotonated L2− in 33+ and 43+, leading to the resonating formulation of {OsII(μ-L2−)OsIII} ↔ {OsII(μ-L˙−)OsII}, instead of a simple mixed valent situation {OsII(μ-L2−)OsIII}. The dinuclear complexes 33+ and 43+ display one broad and moderately intense near-IR transition near 1000 nm corresponding to a mixed Os(dπ)/L(π) → Os(dπ)/L(π*) MLLMCT (metal/ligand to ligand/metal charge transfer) transition. Different experimental studies have also established the interaction of 12+ and 22+ with the selective anions.
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