Copper(II) Halide Complexes with Substituted Pyridine <i>N</i>-Oxides

Abstract

Abstract Pyridine N-oxide copper(II) chloride, the structure of which has recently been elucidated by X-ray analysis [J. C. Morrow and H. L. Schäfer, private communication], has a subnormal magnetic moment (0.85 b.m. [J. V.Quagliano, J. Fujita, G. Franz, D. J. Phillips, J. A. Walmsley and S. Y. Tyree (J. Am. Chem. Soc., 83, 3770 (1961)]). It consists of a binuclear molecule [Cu(C5H5NO)Cl2]2 in which copper atoms are bridged in pairs by two oxygen atoms. In this work, copper(II) complexes with the empirical formulae of CuX2L, CuX2L2 and CuX2LY (X=Cl, Br;L=pyridine N-oxide, 3-picoline N-oxide, 4-picoline N-oxide, 4-chloropyridine N-oxide, 2,4-lutidine N-oxide, 2,4,6-collidine N-oxide, 4-nitroquinoline N-oxide; Y=N,N′-dimethylformamide, dimethylsulfoxide) have been prepared, and magnetic and spectral studies of these complexes have been made. The room-temperature magnetic susceptibilities of CuX2L complexes have been found to be correlated with the pKa (acid-dissociation constant) values of the attached N-oxides. The absorption band in the 735–900 mμ region (the so-called copper band) in the solid-state reflectance spectra of CuX2L complexes has been found to shift towards a lower frequency as the ligand field strength decreases, and a good parallelism between the frequencies and the magnetic moments has been observed. The effect of the attached ligand on the magnetic interaction has been discussed in terms of the electronic effect of the substituent on the pyridine ring. The infrared spectral data on the N–O stretching frequency indicate the absence of Cu–O–Cu linkage in the CuX2L2 complexes with normal magnetic moments.