X-ray structures and properties of five-coordinate copper(II) complexes with a quadridentate N 4 ligand and with a quinquedentate N 5 ligand

Abstract

Complexes Cu(biquinen)(H 2O)(BF 4) 2 ( 1), Cu(biquinen)(H 2O)(ClO 4) 2 ( 2) and Cu(biquidien)(ClO 4) 2 ( 3) with the N 4 Schiff base biquinen (1,2-bis(8-quinolylmethyleneimino)ethane) and with the N 5 Schiff base biquidien (1,5-bis(8-quinolylmethyleneimino)-3-aza-pentane) were prepared. 1 crystallizes in the trigonal space group P3 2 with a=1018.0(3), c=2032.2(7) pm and Z=3; 2 in the monoclinic space group Cc with a=1865.7(9), b=995.1(5), c=1715.7(8) pm, β=128.59(2)° and Z=4; 3 in the triclinic space group P 1 with a=1419.6(8), b=1095.8(6), c=917.7(6) pm, α=74.16(2), β=75.55(2), γ=88.95(2)° and Z=2. In all three complexes the copper is five-coordinate with a N 4O set of donor atoms in 1 and 2 and a N 5 set of donor atoms in 3. The coordination geometry of the chromophors Cu(biquinen)(H 2O) 2+ in 1 and 2 and Cu(biquidien) 2+ in 3 is distorted trigonal bipyramidal, with the water in 1 and 2 being coordinated in an equatorial position. In aqueous solution 1 and 2 give the same Vis absorption spectrum with a broad band at 609 nm, whereas for 3 this weak dd band is shifted to 578 nm. In water/dioxane (3:1) the imine nitrogens of the Schiff base biquinen have p K a values of 9.25 and 6.63, respectively ( I=0.5 M NaClO 4; T=25 °C).