Synthesis and stability of the dirhenium(III) cluster compounds with isoleucine, serine and proline in aqueous solutions

Abstract

The previously developed methods for the synthesis of cis-tetrachlorodi--carboxylates of dirhenium(III) were modified, due to which the derivatives of Re26+ with proteinogenic amino acids (AA) isoleucine, serine and proline were synthesized for the first time. The composition and structure of these substances with the general formula cis-[Re2(АA)2Cl4(CH3CN)2]Cl2 were confirmed by elemental analysis, electron adsorption and IR spectroscopy. The presence of a characteristic peak, which corresponds to the *-electronic transition of the Re–Re quadruple bond for compounds with the cis-arrangement of two bridging-coordinated carboxylate groups in the ligand environment of the Re26+ cluster, was showed by using the data on the electronic absorption spectra of solutions of the synthesized compounds. The IR spectrum contains an intense, weakly split band in the region of 1466–1458 cm–1, which is attributed to the s(CO) coordinated carboxyl group and indicates its bridging coordination to the binuclear Re26+ fragment. The spectra exhibited the presence of bands of stretching (NH3+) and bending vibrations (NH3+) of protonated amino groups in complex compounds of isoleucine and serine and the presence of bands of stretching (NH2+) and bending vibrations (NH2+) of the protonated imino group of proline. The stability of the prepared complex compounds in aqueous solutions was investigated. It is shown that the hydrolysis of the synthesized substances occurs within 9–14 days with a decrease in the pH of the reaction solution due to a gradual replacement of labile chloride ligands by OH–-groups at the first stages of interaction with water. The resistance to hydrolysis is an important parameter of biologically active substances; the determination of the resistance to hydrolysis will expand understanding of the possible mechanisms of their specific biological activity.