DOUBLE Ge(IV)-Co(ІІ) COMPLEXES WITH 1-HYDROXYETHYLIDENEDIPHOSPHONIC ACID AND 2,2-BIPYRIDINE

Abstract

The novel developed synthesis methods allowed to obtain three Ge(IV)-Co(II) coordination compounds  with 1- hydroxyethylidenediphosphonic acid and 2,2`-bipyridine [{Co(bipy)3}2{Co(bipy)(H2O)4}2][{Ge(μ-OH)(μ-hedp)}6Cl2]∙2H2O (1), [Co(bipy)3]4[{Ge(μ-OH)(μ-hedp)}6Cl2]∙30H2O (2), [Co(bipy)3]3[{Ge(μ-OH)(μ-hedp)}6]⋅20Н2О⋅2CH3COOH (3). Complexes are characterized by the methods of elemental analysis, IR-, Diffuse Reflectance spectroscopy,  thermogravimetric analysis. All absorption bands presented in the IR-spectra of compounds 1-3 are highlighted in the Table 2. Absorption bands of the P-O bond are 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–Ophosph), d(Ge–OH)  bands characteristic for all the previously synthesized compounds with [Ge6(m-OH)6(m-hedp)6]6-anion is detected in the IR spectra of 1-3. Presence of the crystal water molecules is confirmed by the ν(OH) at 3400 сm-1. A set of the bands usual for the aromatic molecules (n(C–Harom), n(C–Carom), das(CH3),  ds(CH3), n(С–N)) is assigned with 2,2`-bipyridine in  the structure of all compounds. A special feature of the IR-spectra of 1 is presence of COOH absorption band at 1700 сm-1, that indicates the location of  solvated acetic acid. Complex 1 also contains coordination water molecules, confirmed by the d(H2O) at 1642 сm-1 in its IR-spectrum. Absorption bands of Co–N and Со-О bonds evidence that 2,2`-bipyridine and H2O molecules are coordinated to the cobalt atom. Thermal decomposition of 1-3 differs a lot. Variable interval and temperature of the first  endoeffect is explained by the different nature of  water in them – crystal (1-3) and coordinated (1). In the diffuse reflection spectra of compounds 1-3, two bands corresponding to the following transitions are observed: 4T1g(F)→ 4T2g (1 – 7250, 2 – 7100, 3 – 7300 сm-1), 4T1g(F)→ 4T1g(P) (1 – 13800, 2 – 14200, 3 – 14000 сm-1). Such results confirm an octahedral  configuration of cobalt atom. There was also established, how composition and structure of the  synthesized compounds depend from the molar ratio of the reagents and anion of the initial Co(II) salt (chloride, acetate).