Electrochemical Synthesis of Complex Compounds of Transition Elements with Carboxyl- and Carbonyl-containing Ligands

Abstract

Complex compounds of d-and f-elements with carboxyl-and carbonyl-containing ligands were synthesized by the electrochemical method. The influence exerted by a number of factors on the process course was studied. The dependence of the electrosynthesis parameters on the composition of the forming compounds was established. The composition of these compounds was determined. A new method for anodic synthesis of these compounds was developed.The electrochemical method simplifies synthesis of known compounds [135] and makes it possible to synthesize compounds that cannot be obtained otherwise [6]. Moreover, the advantage of the anodic synthesis is in that the process can be controlled and performed in mild conditions with a high yield and purity of the final products [7].Despite that the electrosynthesis is one of the oldest methods for synthesis of coordination compounds [8], the analysis of the anodic synthesis methods in [137, 9 313] shows that many problems concerning the theory and practical application of the method have not been studied.Transition-metal carboxylates of composition M(O 2 CR) n (M = Cr; R = C 2 H 5 or C 6 H 5 ; n = 3; M = Mn, Fe, or Ni; R = CH 3 , C 2 H 5 , C 6 H 5 , or n-C 7 H 15 ; n = 2) have been prepared [14] by electrochemical oxidation of the corresponding metals in solutions of carboxylic acids RCOOH in acetonitrile. In [15317], monocarboxylic acids containing one to four atoms in the carbon chain were successfully used to synthesize M(O 2 CR) 2 salts. Oxalate complexes of iron and copper were synthesized by the electrochemical method in [18]. On the whole, publications devoted to carboxylate complexes are scarce and analyze a rather small number of the ligands.The goal of this study was to develop new original methods that would enable application of the electrochemical synthesis in a wider range and to a larger number of objects and make it possible to perform directed syntheses in which the composition of the forming products is controlled by varying the process conditions (ligand concentration, temperature, solvent, and electrode potential), and also to compare the properties of compounds synthesized by electrochemical methods with those produced by chemical methods. Acetylacetonates of rare-earth elements (REE) were synthesized to confirm the suggestion that substances exhibiting a tendency toward sublimation, which could not be synthesized previously by other methods [19,20], can be obtained by electrochemical synthesis. EXPERIMENTALThe installation for anodic synthesis (Fig. 1) comprised a three-electrode cell, PI-50-1 potentiostat, Fig. 1. Schematic of a three-electrode cell for electrochemical anodic synthesis (1) Thermostating jacket, (2) stirrer, (3) outlet, (4) inlet, (5) separator, (6) working electrode, (7) auxiliary electrode, and (8) reference electrode.