title: Cu(I) complexes of 3,3'-polymethylene bridged derivatives of 2,2'-bi-1,10-phenanthroline.
abstract: A series of 3,3'-polymethylene-2,2'-bi-1,10-phenanthrolines coordinate with Cu(I) to form dinuclear complexes [(CuL)(2)](2+). As the 3,3'-bridge is lengthened from two to four carbons, the ligand becomes more twisted about the 2,2'-bond, favoring dinuclear coordination. The distance between the two copper atoms varies from 2.92 A for the dimethylene-bridged system to 3.59 A for the tetramethylene bridge. Favorable pi-stacking interactions occur between opposing ligands and promote complex formation. Competition experiments indicate that self-recognition is important and only homoleptic complexes are observed. Under equilibrium conditions, formation of the tetramethylene-bridged complex appears to be the most favored while the dimethylene-bridged system is least favored. The intensity of the long wavelength metal-ligand charge-transfer absorption band decreases as the 3,3'-bridge is shortened. Interaction between the two copper centers is evidenced by a splitting of the oxidation wave, and this splitting increases as the Cu-Cu distance is decreased.
authors.affiliation: Department of Chemistry, University of Houston, Houston, Texas 77204-5641, USA.
authors.forename: Elvira C
authors.initials: EC
authors.lastname: Riesgo
authors.forename: Yi-Zhen
authors.initials: YZ
authors.lastname: Hu
authors.forename: Randolph P
authors.initials: RP
authors.lastname: Thummel