Substituted phenols as ligands. Part IV. Six- and four-co-ordinate copper(II) complexes with nitrogen bases. X-Ray crystal structure analysis of bis-(2-methoxy-4-nitrophenolato)bis(pyridine)copper(II)

Abstract

Two groups of six-co-ordinate copper(II) complexes of chloro- or alkoxy-phenolates and a nitrogen base (pyridine, ammonia, or NNN′N′-tetramethylethylenediamine) have been identified from their diffuse reflectance electronic spectra. Bis-(2-methoxy-4-nitrophenolato)bis(pyridine)copper(II), (I), has been characterised by an X-ray structure analysis [orthorhombic, a= 37·54(2), b= 16·76(1), c= 7·947(5)Å, Z= 8, space group Pbca]. Both methoxy-oxygen atoms are co-ordinated at non-equivalent distances [2·46(2) and 2·58(2)Å] with the phenolic oxygen atoms [1·93(2) and 1·95(2)Å] and the pyridine nitrogen atoms [2·05(2) and 2·08(2)Å] completing the co-ordination sphere. This chromophore gives a relatively intense absorption at 13·2 kK in the diffuse reflectance spectrum.

A second group of compounds gives rise to two d–d transitions (ca. 14 and 17 kK); one of these, (II), bis-(4-formyl-2-methoxyphenolato)bis(pyridine)copper(II) hydrate, is known to be six-co-ordinate and contains two molecular types. Both have symmetrically placed methoxy-oxygen atoms [2·321(6) and 2·413(6)Å]. The smaller mean tetragonal distortion is considered to be the determining factor influencing the spectra.

The strong, broad, low-lying charge-transfer absorption (ca. 20 kK) obscuring most of the d–d transitions, which characterises a third group of compounds with similar ligands, is absent in the above cases. In the third group, bis-(2,4,6-trichlorophenolato)-(NNN′N′-tetramethylethylenediamine)copper(II), (III) is known to be square planar. An isomer of bis-(4-formyl-2-methoxyphenolato)(NNN′N′-tetramethylethylenediamine)copper(II) has a large tetrahedral distortion.