Shielding Effect of Ortho-Substituents on Magnetic Moments and d-d Bands in Chloro-N-phenylsalicylideneiminatocopper(II)

Abstract

Complexes with the formula, Cu (O.CBH4. CH=N-Ph-X)Cl, where Ph-X is a mono-or disubstituted phenyl group, were prepared. A dimeric structure was postulated for these complexes based on the observed subnormal magnetic moments and the chemical formula. For these comwavelengths than those with m-or p-substituents irrespective of the polar nature of the substituents. A similar ortho-effect was also observed for the magnetic moments; complexes with o-substituents were observed to have smaller moment values than those with m-or p-substituents.The ortho-effect was also observed in the d-d bands of the monomeric bis-complexes Cu(O. CaH4 CH=N-Ph-X)2 and their d-d bands when X=o-substituents appeared at shorter wavelengths than those with m-or psubstituents. These ortho-effects decreased for the solution spectra of the monomeric complexes.moments of the d-d band positions. The breakdown of Hammett's rule in these dimeric systems was correlated to a steric effect of the substituents on the central metal atom overlapped by their polar effect. The substituents in the aromatic ring which rotates around the N-C bond perpendicular to the coordination plane, will, depending on their size or positions, shield the fifth coordinating site of the central metal atom from the influences of other molecules or ions. This type of shielding effect makes the d-d bands shift towards shorter wavelengths and lowers the magnetic moments compared to those of the parent complexes. In order to test the validity of these observations for other dimeric complexes, we have prepared copper(II) complexes with the formula, Cu(Sal.NPh-X)Cl*2 and studied their magnetic and spectral properties. Spectral measurements were also made for the parent bis-complexes Cu(Sal.N-Ph-X)2.

1H NMR Studies on Strongly Antiferromagnetically Coupled Dicopper(II) Systems

“…The relatively high magnetic moment observed for 2 is due to the displacement of the Cu atom from the mean plane. Generally, the more planar is the geometry around the Cu(II) ion, the larger is the magnetic exchange interaction between the Cu(II) ions . Least-squares plane (see Table ) calculations show that complex 1 is more planar than complex 2 .…”