Structure, Optical and Magnetic Properties of Two Isomeric 2-Bromomethylpyridine Cu(II) Complexes [Cu(C 6 H 9 NBr) 2 (NO 3 ) 2 ] with Very Different Binding Motives

Two isomeric 2-bromomethylpyridine Cu(II) complexes [Cu(C H NBr) (NO ) ] with 2-bromo-5-methylpyridine (L ) and 2-bromo-4-methylpyridine (L ) were synthesized as air-stable blue materials in good yields. The crystal structures were different with [Cu(L ) (NO ) ] ( ) crystallizing in the monoclinic space group 2 /c, while the 4-methyl derivative was solved and refined in triclinic 1¯. The orientation of the Br substituents in the molecular structure ( ( ) vs. ( ) conformations) and the geometry around Cu(II) in an overall 4 + 2 distorted coordination was very different with two secondary (axially elongated) Cu-O bonds on each side of the CuN O basal plane in or both on one side in . The two Br substituents in come quite close to the Cu(II) centers and to each other (Br⋯Br ~3.7 Å). Regardless of these differences, the thermal behavior (TG/DTA) of both materials is very similar with decomposition starting at around 160 °C and CuO as the final product. In contrast to this, FT-IR and Raman frequencies are markedly different for the two isomers and the UV-vis absorption spectra in solution show marked differences in the π-π* absorptions at 263 ( ) or 270 ( ) nm and in the ligand-to-metal charge transfer bands at around 320 nm which are pronounced for with the higher symmetry at the Cu(II) center, but very weak for . The -dependent susceptibility measurements also show very similar results ( = 1.98 µ for and 2.00 µ for and very small Curie-Weiss constants of about -1. The EPR spectra of both complexes show axial symmetry, very similar averaged values of 2.123 and 2.125, respectively, and no hyper-fine splitting.