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15N NMR Coordination Shifts in Transition Metal Chloride Complexes with Azines versus Type of Central Ion

Pazderski L.

Polish Journal of Chemistry

2006

Vol. 80, nr 7

1083-1093

15N NMR coordination shift is the difference between the 15N chemical shift of the concerned nitrogen atom in the complex and ligand molecules (Delta coord 15N =delta compl 15N - delta lig 15N ). Themeasurements, convenient for complexes with diamagnetic transition metal ions, allow to determinemetallation siteswithin potentially ambidentateN-donor heterocycles. In case of azines, the 15N coordination shifts of pyridine-type nitrogens are usually negative, i.e. the shielding is observed. Variable low-frequency 15N coordination shifts (ca. 70-140 ppm) were noted for a number of chloride complexes of Pd(II), Pt(II), Au(III), Pd(IV), Pt(IV), Co(III), Rh(III) and Zn(II) with pyridine, 2,2'-bipyridine, 1,10-phenanthroline, 2,2'-biquinoline, purine and 1,2,4-triazolo-[1,5a]-pyrimidine(s). Some dependencies between the magnitude of the shielding effect and such features of the concerned complex as the type of central ion, its electron configuration (oxidation state) and the coordination sphere geometry were discussed.