Mixed-Ligand Germanium–lanthanide Complexes With 1-Hydroxyethylidenediphosphonic Acid and 2,2’-Bipyridine

Abstract

There were developed the novel methods for the synthesis of six mixed- metal and mixed-ligand complexes of germanium and rare earth metals (Pr, Nd, Dy, Ho, Tm, Lu) with 1-hydroxyethylidenediphosphonic acid and 2,2´-bipyridine. The compounds have been characterized using various research methods: elemental analysis, mass spectrometry, electrical conductivity, thermogravimetry, IR spectroscopy. It has proved that all complexes are crystal hydrates, belong to heterometallic mixed ligand compounds [Ln(H2O)4(bipy)2]2 [Ge(m-hedp) (m- OH)]6⸱nH2O, Ln=Pr (1); Nd (2); Dy (3); Ho (4); Tm (5); Lu (6); n = 22 (1, 2), 21 (3), 20 (4, 5), 19 (6). Their formation occurs due to the electrostatic interaction of complex cations [Ln(H2O)4(bipy)2]3+ with hexanuclear anions [Ge(m-hedp)(m- OH)]66-. According to the results of measuring the electrical conductivity of dimethylformamide solutions 1–6, it has been established that they belong to triionic electrolytes: λ (in Ohm-1∙сm2∙mol-1) for 1 = 131,3; 2 = 138,8; 3 = 145,8; 4 = 151,1; 5 = 158,3; 6 = 162,7. The cation-anionic type of complexes 1–6 has been confirmed as a result of the analysis of their mass spectrum. The analysis of the mass spectrum showed that the main decomposition direction of the complex is related to the formation of the complex cation fragment [Ln(H2O)4(bipy)2]3+, which corresponds to the most intense peak (m/z = 136, I = 55%). The thermal decomposition of compounds 1–6 includes dehydration, deaquatation, oxidative thermal destruction and the formation of final products as a mixture of Ln2O3 and GeP2O7. On the DTA curves in the interval 70–200 °C the first endothermic effect can be traced, which is accompanied by the removal of a certain number of crystallization and coordination water molecules into the gas phase. Absorption bands of the P-O bond have been detected at ~1053 and ~970 сm-1, that indicates the presence of the fully deprotonated PO32- groups in the composition of complexes. Furthermore, n(OH), ν(Ge–O), d(Ge–OH) bands characteristic for all the previously synthesized compounds with [Ge6(m-OH)6(m-hedp)6]6- anion have been detected in the IR spectra of 1–6. A set of the bands usual for the aromatic molecules n(C–C), das(CH3), ds(CH3), n(Сar=N) has been assigned with 2,2`-bipyridine in the structure of all compounds.