Coordination sphere geometry changes of lanthanoid(III) nitrate complexes with hexamethylenetetramine

Abstract

The 1 : 2 adducts of lanthanoid nitrate complexes with hexamethylenetetramine (hmta) have been synthesized and characterized by X-ray crystallography, IR spectroscopy, and bond valence calculations. The effect of lanthanoid contraction is observed. The lanthanoids create three isostructural groups: La–Nd (group I), Sm–Gd (group II), and Dy–Lu (group III). As an example, one structure for each group is presented in detail. There is a change in the composition of the lanthanoid coordination sphere, geometry, and coordination number with changing size of the lanthanoid. As the ionic radii decrease, the number of water molecules increases, whereas the nitrate ions move outside the inner coordination shell forming three isostructural groups. The hmta molecules are not coordinated to the central atom. Group I is formed by 10-coordinate complexes with the nitrate ions and water molecules in the inner and outer coordination sphere ([Ln(NO3)2(H2O)6]+ · · 2hmta · 2H2O). Group II includes the adducts of general formula ([Ln(NO3)(H2O)7]2+ · 2 · 2hmta · 3H2O) with nine-coordinate lanthanoid. Group III consists of eight-coordinate lanthanoid with general formula [Ln(H2O)8]3+ · 3 · 2hmta · 2H2O].