The Structure of Three-Coordinated Copper(II) Complexes and the Infrared C=O Stretching Vibration

A new type of binuclear structure having copper atoms of ligancy 4 is proposed on the basis of infrared C=O stretching vibrations for the so-called three-coordinated copper(II) complexes showing a normal magnetic moment. In this binuclear structure, copper atoms are bridged in pairs by two Cu-O-C-O-Cu links of syn-anti arrangement. Suggestion is made that "three-coordinated" copper(II) complexes in the literal sense of the word do not exist regardless of whether the complexes show normal or subnormal magnetic moments.

Magnetic susceptibility and the structure of Tri-coordinated copper(II) Complexes

The magnetic susceptibilities of 2-hydroxynaphthaldehyde-(1)-[2-hydroxyanil] Cu(II), 5-nitrosalicylalanthranilic acid Cu(II), 5-bromosalicylalanthranilic acid Cu(II), 2-hydroxyformazylbenzene Cu(II), and 2-oarboxyformazylbenzene Cu(II), as well as their monopyridino-compounds, have been measured by the Gouy method at 25 �C. From the data of magnetic susceptibility, the effective magnetic moments were calculated per one copper atom in these chelates. Some of the pyridine-free complexes show magnetic moments that are smaller than the theoretical moment, 1.73 B.M., for one odd electron, while others have normal magnetic moments. Taking into account four other tri-coordinated copper chelates reported in a preceding paper, two alternative suggestions were made as follows. First, the subnormal moments resulting from the close distance of approach of two copper atoms in dimer molecules can be correlated with the planar configuration of chelate rings involving a copper atom. On the other hand, when a three-dimensional ring exists, the approach of two copper atoms to such a small distance as to cause an appreciable exchange effect is hindered by steric effects, resulting in the normal magnetic moment for this type of tri-coordinated complexes. Secondly, those pyridine-free tri-coordinated copper complexes showing normal moments have a carbonyl group, the oxygen atom of which may take part in the coordination about a copper atom.

Magnetic susceptibility of Tri-Coordinated copper(II) complexes

The magnetic susceptibilities of salicylal-o-hydroxybenzylamine Cu(II), salicylal-o-hydroxyanil Cu(II), acetylacetone-mono-(0-hydroxyanil) Cu(II), and benzoylacetone- mono-(0-hydroxyanil) Cu(II), as well as their pyridinates, have been measured by the Gouy method at room temperature. The effective magnetic moments calculated from the . data of the pyridine-free complexes per one copper atom are smaller than the theoretical moment, 1.73 B.M., for one odd electron. Although it has been presumed from the method of synthesis, the chemical analysis of the complexes, and the tridentate nature of the ligand molecules that the copper atoms of the chelates have the unusual coordination number 3, the subnormal magnetic moments suggest the presence of dimeric molecules, in which two copper atoms are very close to each other as in cupric acetate monohydrate. On the other hand, the pyridinates have normal magnetic moments expected for tetra-coordinated copper complexes.