EXO-LIGAND COMPLEXES OF DIETHYLENTRIAMINE-PENTAACETATOGERMANATIC(IV) ACID

Abstract

The synthesis of complexes based on diethylenetriaminepenta-acetategermanate(IV) acid and a number of exo-ligands was carried out. Their composition, thermal stability, method of coordination of diethylenetriaminepentaacetic acid (H5Dtpa) and protonation of exo-ligands (isoniazid Ind, diphenylguanidine Dphg, piracetam Pam, imidazole Im, cytosine Ctz, 1,10-phenanthroline Phen, 2,2´-bipyridine Bipy), were established. The structural scheme and molecular formula of the obtained compounds were proposed (HL)[Ge(OH)(HDtpa)]·nH2O, де L = Ind, n = 0 (1), Dphg, n = 8 (2), Pam, n = 4 (3), Im, n = 2 (4), Ctz, n = 2 (5), Phen, n = 5 (6), Bipy, n = 4 (7). Based on the elemental analysis of the synthesis products 1–7, it was determined that they exhibit a molar ratio of Ge:N = 1:6 (1, 2, 5), Ge:N = 1:5 (3, 4, 6, 7), therefore, Ge:Dtpa:Ind (Dphg, Pam, Im, Ctz, Phen, Bipy) = 1:1:1. The thermal decomposition of complexes 2–7 begins with an endothermic effect in the temperature range of 80–180 °C, during which a certain amount of crystallization water molecules is removed. The relatively high temperature of its removal is due to the formation of a broad system of intermolecular and intramolecular hydrogen bonds, which is characteristic of various metal complexonates. Thus, in the new compounds, the structure of the octahedral polyhedron of Germanium remains the same as in the original complex acid: the Ge atom is coordinated by two Nitrogen atoms and three Oxygen atoms of three Dtpa acetate groups. The coordination number of Germanium is complemented to 6 by the hydroxo-ligand. All carboxyl groups of the ligand are deprotonated, as evidenced by the presence of bands νas(COO⁻) at 1630–1690 cm⁻¹ and νs(COO⁻) at 1380–1420 cm⁻¹. The presence of Ge-N and Ge-O bonds in the synthesized complexes is confirmed by the bands of valence vibrations of these bonds in the range of 640–650 cm⁻¹ and 590–620 cm⁻¹, respectively. Particularly noteworthy is the band of deformation vibrations of the Ge-O-N group at 810–820 cm⁻¹. In complexes 1–7, a splitting of bands in the 3000 cm⁻¹ region (valence vibrations of the C-H bond) is observed, indicating that all nitrogen atoms in their molecules are coordinated or protonated. The obtained compounds are of interest as promising agents for biomedical applications.