Homoleptic copper(II) and copper(I) complexes of 5,6-dihydro-5,6-epoxy-1,10-phenanthroline. Six-coordinate copper(I) in solution
摘要:
Reaction of 5,6-dihydro-5,6-epoxy-1,10-phenanthroline (L) with Cu(ClO4)(2)center dot 6H(2)O in methanol in 3:1 M ratio at room temperature yields light green [CuL3](ClO4)(2)center dot H2O (1). The X-ray crystal structure of the hemi acetonitrile solvate [CuL3](ClO4)(2)center dot 0.5CH(3)CN has been determined which shows Jahn-Teller distortion in the CuN6 core present in the cation [CuL3](2+). Complex 1 gives an axial EPR spectrum in acetonitrile-toluene glass with g(parallel to) = 2.262 (A(parallel to) = 169 x 10 (4) cm (1)) and g(perpendicular to) = 2.069. The Cu(II/I) potential in 1 in CH2Cl2 at a glassy carbon electrode is 0.32 V versus NHE. This potential does not change with the addition of extra L in the medium implicating generation of a six-coordinate copper(I) species [CuL3](+) in solution. B3LYP/LanL2DZ calculations show that the six Cu-N bond distances in [CuL3](+) are 2.33, 2.25, 2.32, 2.25, 2.28 and 2.25 angstrom while the ideal Cu(I)-N bond length in a symmetric Cu(I)N-6 moiety is estimated as 2.25 angstrom. Reaction of L with Cu(CH3CN)(4)ClO4 in dehydrated methanol at room temperature even in 4:1 M proportion yields [CuL2]ClO4 (2). Its H-1 NMR spectrum indicates that the metal in [CuL2](+) is tetrahedral. The Cu(II/I) potential in 2 is found to be 0.68 V versus NHE in CH2Cl2 at a glassy carbon electrode. In presence of excess L, 2 yields the cyclic voltammogram of 1. From H-1 NMR titration, the free energy of binding of L to [CuL2](+) to produce [CuL3](+) in CD2Cl2 at 298 K is estimated as -11.7 (+/-0.2) kJ mol (1). (C) 2010 Elsevier B.V. All rights reserved.