Affiliation:
1. Department of Chemistry Indian Institute of Technology Bombay Powai, Mumbai 400076 India
2. Departamento de Química Inorgánica Facultad de Ciencias Químicas Universidad Complutense de Madrid Ciudad Universitaria 28040 Madrid Spain
Abstract
AbstractThe article dealt with the structurally validated L2− (H2L=epindolidione=5,11‐dihydroquinolino[3,2‐b]quinoline‐6,12‐dione, a heteroatom‐modified tetracene and a structural isomer of indigo dye) bridged {(acac)2RuIII}2(μ‐L2−) 1/2 (S=1, acac=acetylacetonate) and [{(bpy)2OsII}2(μ‐L2−)](ClO4)2 [3](ClO4)2/[(pap)2OsII}2(μ‐L2−)](ClO4)2 [4](ClO4)2 (S=0, bpy=2,2′‐bipyridine, pap=2‐phenylazopyridine). 1/2 and [3](ClO4)2/[4](ClO4)2 with a metal‐metal separation of ≈7 Å stabilized selectively in meso(ΔΛ)/rac(ΔΔ/ΛΛ) and meso diastereomeric forms, respectively, in spite of calculated minor difference in energy between the diastereomers in each case. Though 2, [3](ClO4)2/[4](ClO4)2) exhibited intermolecular π–π interactions, no such non‐covalent interaction was perceived in 1. RuIIIRuIII derived 1/2 (S=1, 2.63/2.57 μB at 300 K) attributed to non‐interacting two Ru(III) (S=1/2) spins with an intermolecular through space weak antiferromagnetic exchange interaction below 12 K and its variable temperature 1H NMR revealed Fermi and pseudo‐contact shifts. Multiple redox steps of the complexes varied as a function of metal ion (Ru versus Os), its oxidation state (III versus II) and ancillary ligand (acac versus bpy versus pap). A collective consideration of DFT calculated MOs and Mulliken spin densities suggested delicate electronic forms along the redox chain due to the participation of bridge largely in the oxidation processes as a consequence of its redox non‐innocent feature. Reductions were however mostly centered around the metal (RuIII to RuII) and ancillary ligands (bpy/pap) in 1/2 and 32+/42+, respectively. 1n/2n, [3]2+/[4]2+ displayed mixed metal/ligand based weak low‐energy (800‐1400 nm) transitions in addition to intense visible bands as corroborated by TD‐DFT calculations.