title: [(Cyclen)(4)Ru(4)(pz)(4)](9+): a Creutz-Taube square.
abstract: The use of cyclen (1,4,7,10-tetraazacyclododecane) as a blocking ligand enables assembly of the mixed-valence square complex [(cyclen)4Ru4(pz)4]9+ (pz = pyrazine). A crystal structure determination shows the molecule to possess a regular square geometry wherein each Ru atom has an equivalent coordination environment. Consistent with the presence of one RuIII and three RuII centers, cyclic voltammetry reveals a single reversible reduction wave and three successive oxidation waves. The separation between the first oxidation and reduction waves indicates a comproportionation constant of Kc = 108.9 for the [(cyclen)4Ru6(pz)4]9+ square, suggesting a greater extent of electron delocalization than that observed for the Creutz-Taube ion. The closer spacing between oxidation waves suggests a lesser degree of delocalization in the [(cyclen)4Ru6(pz)4]10+ (Kc = 102.0) and [(cyclen)4Ru6(pz)4]11+ (Kc = 103.0) species, bearing the higher average oxidation states of Ru2.5+ and Ru2.75+, respectively.
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720-1460, USA.
authors.forename: Victor C
authors.initials: VC
authors.lastname: Lau
authors.forename: Louise A
authors.initials: LA
authors.lastname: Berben
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Long