Binuclear copper complexes based on the 6,6'-bis[[bis(2-pyridylmethyl)amino]methyl]-2,2'-bipyridine ligand

The tripodal tetradentate ligand TMPA (tris (2-pyridylmethyl) amine) has provided a wealth of valuable new Cu(I) and Cu(II) chemistry, in particular associated with copper(I)/dioxygen reactivity studies (Karlin, K. D.; Kaderli, S.; Zuberbiihler, A. D. Ace. Chem. Res. 1997, 30, 139-147). Dinucleating analogues have also been recently investigated, and here we describe new copper complexes of the 6,6'-bis[[bis(2-pyridylmethyl)amino]meth 2,2'-bipyridine ligand(bTMPA). The synthesis and X-ray crystallographic characterization of [(bTMPA)Cu-2(II)(CH3CN)(2)(ClO4)(2)](2+) (1, as ClO4- salt) and [(bTMPA)Cu-2(II)(N-3)(2)(ClO4)(2)] (2) are provided. [1: space group C2/c; a = 15.907(4) Angstrom, b = 29.268(7) Angstrom, c = 13.941(2) Angstrom; beta = 97.79(2)degrees; Z = 4; volume = 6431(2) Angstrom(3). 2: space group P2(1)/c; a = 8.118(5) Angstrom, b = 29.743(8) Angstrom, c = 9.120(6) Angstrom; beta = 114.00(5)degrees; Z = 2; volume = 2012(2) Angstrom(3).] Both solid state structures possess six-coordinate copper(II) ions, and in neither case does the 2,2'-bipyridine (bipy) moiety within bTMPA chelate to a single metal ion. Dissociation of bound perchlorate and the presence of pentacoordinate solution structures are suggested by spectroscopic (UV-vis with two d-d absorptions; axial EPR spectral along with conductivity data (1, 1:4 electrolyte; 2, 1:2 electrolyte). Electrochemical measurements by cyclic volammetry have been carried out, and for a dicopper(I) analogue, [(bTMPA)Cu-2(1)](ClO4)(2)(3(ClO4)(2)), a single quasireversible redox wave is observed; E-1/2 = +199 mV (versus Ag/AgCl in dimethylformamide), which is similar to 280 mV more positive than that observed for the simple ''parent'' compound [Cu-1(TMPA)(CH3CN)I(ClO4). Unlike [Cu-1(TMPA)(CH3CN)](ClO4), 3 does not readily form dioxygen adducts.