Magnetic Moments and d–d Bands of Copper(II) Halide Complexes with Substituted Pyridine <i>N</i>-Oxides and Some Related Ligands

Abstract

Abstract In order to test the substituent effect or the effect of variations in chemical structures on the demagnetization and d–d band shift in dimeric copper(II) halide complexes with pyridine N-oxides and some related ligands, a variety of electron-donating or electron-withdrawing substituents attached in 2-, 3- and 4-positions in the pyridine ring of the ligand were extensively studied. In these dimeric complexes, no correlation was observed between the Hammett’s σ constants and the observed d–d band positions or magnetic moments. However, irrespective of the nature of the substituents, a linear relation was observed to exist between the d–d band positions and the magnetic moments, indicative of a magnetochemical support for the interpretation of the spectrochemical series through the idea of symmetry-restricted covalency. For the monomeric complexes with the same ligands, a linear relation exists between Hammett’s constants and the d–d band positions for each series of the electron-donating and electron-withdrawing substituents. Experimental results indicate that the most important factor determining the non-applicability of Hammett’s Rule in these dimeric complexes is the steric condition of the metal ions which shields them from the influence of other molecules or ions. The larger demagnetization effect of the bromide ion compared to the chloride ion has been interpreted as due to its larger nephelauxetic effect. On the basis of the established structure of the parent compound, two pathways for superexchange interaction have been proposed. The importance of a σ type orbital overlap compared to the π type is discussed.