title: Influence of ancillary ligands on the electronic structure and anion sensing features of ligand bridged diruthenium complexes.
abstract: The present article deals with a newer class of ligand bridged asymmetric complexes incorporating ancillary ligands (AL) with varying electronic characteristics: [(bpy)2Ru(II)(μ-HL(2-)) Ru(II)(bpy)2](ClO4)2·([1](ClO4)2); [(pap)2Ru(II)(μ-HL(2-))Ru(II)(pap)2](ClO4)2 ([2](ClO4)2); [(bpy)2Ru(II)(μ-HL(2-))Ru(II)(pap)2](ClO4)2 ([3](ClO4)2); [(acac)2Ru(III)(μ-HL(2-))Ru(III)(acac)2] (4) and [(bpy)2Ru(II)(μ-HL(2-))Ru(III)(acac)2]ClO4 ([5]ClO4) (H3L: 5-(1H-benzo[d]imidazol-2-yl)-1H-imidazole-4-carboxylic acid, bpy = moderately π-accepting 2,2'-bipyridine, pap = strongly π-accepting 2-phenylazopyridine, acac(-) = σ-donating acetylacetonate). The molecular identity of [1](ClO4)2 was established by its single crystal X-ray structure. A large shift in Ru(II)/Ru(III) potential of 0.7-2.0 V took place on switching the ancillary ligands from AL = bpy to pap to acac(-), leading to the stabilisation of ruthenium(II) and ruthenium(III) states in 1(2+), 2(2+), 3(2+), 4 and 5(+), respectively. The detailed magnetic studies revealed that the paramagnetic Ru(III)Ru(III) state in 4 essentially behaves as a system with two independent S = 1/2 spins and it exhibits an anisotropic EPR at 77 K (<g> = 2.192, Δg = g1-g3 = 0.70) but without any half-field signal near g∼ 4. The isolated mixed valent Ru(II)Ru(III) state in 5(+) exhibits weak antiferromagnetic coupling of -0.25 cm(-1) and anisotropic EPR with <g> = 2.155, Δg = 0.704 but fails to show a Ru(II)→ Ru(III) IVCT (intervalence charge transfer) transition in the near-IR region up to 2000 nm. The complexes 1(2+), 2(2+) and 4 encompassing identical metal fragments, exhibited weak to moderate electrochemical coupling at the intermediate mixed valent states with Kc values of 10(2)-10(5). The coulometrically generated mixed valent Ru(II)Ru(III) state in 1(3+) or 4(-) also failed to display any prominent absorption in the near-IR region, but exhibited Ru(III) based rhombic EPR, implying valence localised situation with negligible intermetallic electronic coupling. The complexes 2(2+), 3(2+), 4 and 5(+) having one NH proton associated with the bridging ligand HL(2-) do not show any interaction with the anions F(-), Cl(-), Br(-), I(-), HSO4(-), H2PO4(-), OAc(-) and SCN(-) in CH3CN, though 1(2+) selectively recognises the fluoride ion.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai-400076, India.
authors.forename: Ankita
authors.initials: A
authors.lastname: Das
authors.forename: Tanaya
authors.initials: T
authors.lastname: Kundu
authors.forename: Shaikh M
authors.initials: SM
authors.lastname: Mobin
authors.forename: José Luis
authors.initials: JL
authors.lastname: Priego
authors.forename: Reyes
authors.initials: R
authors.lastname: Jiménez-Aparicio
authors.forename: Goutam Kumar
authors.initials: GK
authors.lastname: Lahiri
mesh_terms: D000838:Anions / Q000737:chemistry; D004583:Electrons; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D012428:Ruthenium / Q000737:chemistry*
chemical_list: D000838:Anions; D008024:Ligands; D009942:Organometallic Compounds; D012428:Ruthenium