New 1,4,7,10-tetraazacyclotridecane-11,13-dione ligands appended with additional donor(s) 8-methylquinoline(s): crystal structures and characterization of their copper(II) complexes

Abstract

Two macrocyclic dioxotetraamine ligands 4-(quinolin-8-ylmethyl)-1,4,7,10-tetraazacyclotridecane-11,13-dione (H₂L¹) and 4,7-bis(quinolin-8-ylmethyl)-1,4,7,10-tetraazacyclotridecane-11,13-dione (H₂L²) have been synthesized. The resulting dioxomacrocycles readily co-ordinate Cu²⁺ with concomitant double deprotonation of the ligands. The solution behaviour of the copper(II) complexes [CuL¹]1 and [CuL²]2 has been studied by ESR, UV/VIS and cyclic voltammetric techniques. Remarkable red shifts were observed for the absorption band maxima of the electronic spectra of these copper(II) complexes (598 nm for 1 and 600 nm for 2) in comparison to that of unsubstituted (1,4,7,10-tetraazacyclotridecane-11,13-dione)copper(II) species (516 nm). The crystal structures of 1 and 2(which crystallised in the form [(CuL²)₂]·3H₂O·MeCN) have been determined by X-ray diffraction analysis. Crystallographic data: 1, orthorhombic, space group Pcab, a= 16.260(3), b= 7.739(2), c= 27.530(9)Å, Z= 8, R′= 0.061 for 2594 observed reflections with l > 3σ(l); 2, triclinic, space group P, a= 12.288(3), b= 14.734(4), c= 18.005(4)Å, α= 102.26(2), β= 104.26(2), γ= 107.02(2)°, Z= 2, R′= 0.090 for 2284 observed reflections with l > 3σ(l). In complex 1, the Cu atom is five-co-ordinate and forms a distorted square pyramid in which N(11) of the quinoline pendant is at the apical site. The Cu–N(11) bond [2.266(3)Å] is longer than the basal Cu–N bond lengths [average 1.985(3)Å]. In complex 2, the Cu^II centre is also five-co-ordinate, with one of the quinoline pendants co-ordinating to Cu^II from the apical position and the other pendant remaining unco-ordinated.