Inter-ligand electronic coupling mediated through a dimetal bridge: dependence on metal ions and ancillary ligands. Issue 17 (8th February 2017)

• Record Type: Journal Article
• Authors: Majumdar, Moumita; Saha, Sayantani; Dutta, Indranil; Sinha, Arup; Bera, Jitendra K.
• Is Part Of: Dalton transactions. Volume 46:Issue 17(2017)
• Page Start: 5660
• Page End: 5669
• Publication Date: 2017-02-08
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/c6dt04679g
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : The metal–metal bond orbitals and the ancillary ligands influence inter-ligand charge transfer through the dimetal bridge. Abstract : A series of Mo2, Ru2, Rh2 and Cu2 complexes with redox-active NP-R [2-(2-R)-1, 8-naphthyridine; R = pyrazinyl (NP-pz, L 1 ) and thiazolyl (NP-tz, L 2 )] ligands have been synthesized and characterized by X-ray crystallography and spectroscopic methods. Two NP-R ligands wrap the dimetal core by occupying four equatorial positions and two axial sites. The remaining four equatorial sites are engaged by bridging acetates in quadruply bonded cis -[Mo2 (L 1 )2 (OAc)2 ][BF4 ]2 (1 ), cis -[Mo2 (L 2 )2 (OAc)2 ][BF4 ]2 (1A ), doubly bonded cis -[Ru2 (L 1 )2 (OAc)2 ][ClO4 ]2 (3 ), cis -[Ru2 (L 2 )2 (OAc)2 ][ClO4 ]2 (3A ) and singly bonded trans -[Rh2 (L 1 )2 (OAc)2 ][BF4 ]2 (5 ) and trans -[Rh2 (L 2 )2 (OAc)2 ][BF4 ]2 (5A ). Compounds cis -[Mo2 (L 1 )2 (CH3 CN)4 ][BF4 ]4 (2 ), cis -[Mo2 (L 2 )2 (CH3 CN)4 ][BF4 ]4 (2A ), cis -[Ru2 (L 1 )2 (CO)4 ][OTf]2 (4 ) and cis -[Ru2 (L 2 )2 (CO)4 ][ClO4 ]2 (4A ) contain acetonitriles or carbonyls as the ancillary ligands. The dicopper complexes trans -[Cu2 (CH3 CN)(L 1 )2 ][ClO4 ]2 (6 ) and trans -[Cu2 (L 2 )2 (ClO4 )2 ] (6A ) involve no bonding interaction between two Cu(i ) units. Cyclic voltammogram studies reveal that two one-electron processes corresponding to each of the two ligands bound to the metal–metal bonded dimetal core result in four reversible one-electron reductions, with the exception of dirhodium(ii, ii ) compounds5 and5A which show two one-electron reductions. The highest comproportionation constant ( K c ) values are obtained for inter-valence complexes originating from the diruthenium(ii, ii ) compounds3 and3A, whereas no electron delocalization is observed for dicopper(i, i ) complexes6 and6A . The dimetal bridge and the ancillary ligands tune the degree of inter-ligand electronic coupling in these complexes. DFT calculations reveal a π*(NP)–δ*(M2 )–π*(NP) orbital conduit for electron delocalization. For diruthenium(ii, ii ) compounds3 and3A, an additional π*(NP)–π*(M2 )–π*(NP) pathway is accessible contributing to high K c values. The ancillary π-ligands (acetates and carbonyls) reduce the extent of the electron flow through π*(NP)–δ*(M2 )–π*(NP) and thus lower the K c values. The absence of metal–metal bond orbitals and the reduced metal–ligand covalency in dicopper(i, i ) compounds are responsible for the lack of electron delocalization in these systems.