title: Localization and delocalization in a mixed-valence dicopper helicate.
abstract: The coordination chemistry of the tetradentate pyridyl-thiazole (py-tz) N-donor ligand 6,6'-bis(4-phenylthiazol-2-yl)-2,2'-bipyridine (L1) has been investigated. Reaction of L1 with equimolar copper(II) ions results in the formation of the single-stranded mononuclear complex [Cu(L1)(ClO4)2] (1), whereas reaction with copper(I) ions results in the double-stranded dinuclear helicate [Cu2(L1)2][PF6]2 (2). Both complexes were characterized by X-ray crystallography, UV-vis spectroscopy, and electrospray ionization mass spectroscopy (as well as 1H NMR spectroscopy for diamagnetic 2). Complex 2 is redox-active and, upon one-electron oxidation, forms the stable tricationic mixed-valence helicate [Cu2(L1)2]3+ (3). This species can also be prepared in situ by combining [Cu(MeCN)4][BF4], [Cu(H2O)6][BF4]2, and L1 in a 1:1:2 ratio in nitromethane. X-ray crystallographic analysis of 3 provides structural evidence for the presence of an internuclear Cu-Cu bond, with an even distribution of spin density across the two Cu centers. Room-temperature UV-vis spectroscopy is consistent with this finding; however, frozen-glass EPR spectroscopic investigations suggest solvatochromic behavior at 110 K, with the [Cu2]3+ core varying from localized to delocalized depending on the solvent polarity.
authors.affiliation: School of Chemistry, University of Bristol, Bristol BS8 1TS, UK.
authors.forename: John C
authors.initials: JC
authors.lastname: Jeffery
authors.forename: Thomas
authors.initials: T
authors.lastname: Riis-Johannessen
authors.forename: Callum J
authors.initials: CJ
authors.lastname: Anderson
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Adams
authors.forename: Adam
authors.initials: A
authors.lastname: Robinson
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Argent
authors.forename: Michael D
authors.initials: MD
authors.lastname: Ward
authors.forename: Craig R
authors.initials: CR
authors.lastname: Rice
mesh_terms: D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure
chemical_list: D008024:Ligands; D003300:Copper