Azide interaction with 4f and 5f ions in aqueous solutions. I. Trivalent ions

Solvent extraction and UV, Raman, and NMR spectroscopic studies were carried out on trivalent actinide and lanthanide aqueous azido complexes. Unlike trivalent d transition ions (β11 approx. = 105) 5f and 4f aqueous azido complexes are weak (β11 approx. = 2.5 for neodymium azide complexes [Nd(N3)2+)], but the trivalent actinides exhibit formation constants 1 order of magnitude higher than the lanthanides. All the spectroscopic methods indicate that we are dealing with inner-sphere complexes and actinide-lanthanide differences must be attributed to higher covalent contributions in the 5f azides. 15N NMR combined with 1H NMR served to investigate the azide binding properties. With the trivalent 5f and 4f ions the binding occurs by one of the terminal nitrogen atoms. The M-N bond distance is close to 2.75 A. The lanthanide(III)-(linear azide) moieties are bent with a bond angle close to 1350, unlike the homologous linear thiocyanate complexes. 7 figures, 4 tables