CLUSTER COMPLEXES OF RHENIUM WITH CARBONYL AND AMINE CONTAINING LIGANDS

Abstract

Methods for the synthesis of rhenium cluster complexes based on carbonyl and amine containing organic bifunctional ligands have been developed. The structure of the obtained cluster combinations were determined on the basis of IR spectroscopy data, methods of thermogravimetry and elemental analysis. Samples of ligands I and II were obtained by condensation of cyclopentane and cyclohexane carboxylic acids chloroanhydrides with ethylene, followed by the replacement of the chlorine atom by amine groups. To obtain cluster complexes of rhenium with the synthesized ligands, an ultradisperse solution of rhenium in distilled water was prepared in advance. To this end, the rhenium trichloride salt (ReCl3) was dissolved in water and the calculated amount of sodium borohydride in a nitrogen atmosphere was added in portions to the resulting solution with vigorous stirring. Rapidly arising black dispersed nanoparticles of metallic rhenium were not deposited. When organic ligands I and II are added, the corresponding cluster compounds III and IV are formed, which gradually over 30 minutes. precipitated from aqueous solution. The resulting black-brown precipitates were washed with distilled water and dried in a nitrogen atmosphere at a temperature of 35-40 °C. The melting points of the synthesized compounds are determined, which are components for cluster III-195 °С and cluster IV- 212 °С (with decomposition). In the IR spectra of cluster compounds, intense absorption bands were found, which characterize the presence of both a ketone carbonyl group (1718 sm–1, 1720 sm–1) and an amine fragment (2727 sm–1, 2720 sm–1 and 2613 sm–1, 2609 sm–1). The absorption bands of ketone groups in cluster compounds are shifted toward higher frequencies compared to the initial ligands. A similar picture is observed when comparing IR vibrations of C – N bonds in the initial ligands and the corresponding cluster compounds. The results of elemental analysis confirm the structure of cluster compounds and are in complete agreement with the notion that the reduction of rhenium salts with metal hydrides in an aqueous solution forms cluster compounds. Apparently, in this case, the most stable rhenium clusters with a tetrahedral structure are formed. Thermogravimetric analysis made it possible to establish the presence of a peak at a temperature of 318 °С with a mass number of 744.8 c.u. corresponding to the cluster combination of four rhenium atoms. At each stage of decomposition, the experimental mass loss agrees well with the calculated values.