Copper(II) complexes with tridentate O,N,O-chelate dianions and additive monodentate donor ligands I. Crystal structures and EPR results of urea adducts of N-salicylidene- α-aminoacidato-copper(II) compared with N-salicylideneglycinato-thiourea-copper(II)

Abstract

Dinuclear Cu(II) complexes with the tridentate N-salicylideneglycinate (saa 2−) or N-salicylidenemethylalaninate dianion (sab 2−) and urea (Ur) or thiourea (Tu) as additional monodentate donor ligand were prepared and characterised, namely [(saa)Cu(Ur)] 2 ( 1). [(sab)Cu(Ur)] 2(Ur) 2 ( 2) and [(saa)Cu(Tu)] 2 ( 3). The urea adducts crystallise in the triclinic space group P l with a = 7.611 ( 1), b=7.815(1), c=10.078(1) A ̊ ; α=98.06( 1), β=110.31(1), γ=95.91(1)° for 1 and a=8.820(1), b=9.712(1), c=10.317(1) A ̊ ; α=66.208(5), β=88.722(5), γ=83.364(6)° for 2; in each case Z=2 refering to the mononuclear constituents of centrosymmetric dimers. In the crystal structure of the thiourea derivative (monoclinic space group l2 a ; a=12.353(1), b=14.315(1), c=13.670(1) A ̊ ; β=91.62(1)°; Z=8), however, the dimers have C 2 symmetry due to a shift of the ligands into cis position. In all three cases the phenoxy-O ligands act as bridges in connecting monomeric units. Each one of them is part of the basal plane of one Cu ion and acts as an apical ligand to the copper centre of the second monomeric complex. The copper ions adopt (4 + 1) square-pyramidal geometry with relatively short apical CuO distances of about 2.4 Å in the case of 1 and 2 compared to about 2.8 Å for 3. Minor structural alterations in changing from 1 to 2 give rise to a significant impact in spectroscopic data, especially in the EPR parameters. The results are interpreted as consequences of (i) the electron inducing effect due to alkylation of the tridentate ligand and (ii) the intercalation of urea dimers in the case of 2 stabilised by hydrogen bonds.