Boris I. Kharisov

DIRECT ELECTROSYNTHESIS OF METAL COMPLEXES: STATE OF THE ART

Abstract Recent results on the electrosynthesis of metal complexes are reviewed. The basic principles of such syntheses and the main factors that influence the process quality are covered. The main structural characteristics of each type of coordination compound obtained by this method are discussed. The large number of publications testify to the wide application of direct electro-synthesis to obtain molecular complexes and metal chelates. In addition, this manuscripts shows the necessity of developing this technique to obtain π-complexes, compounds with macro-cyclic ligands and lanthanides complexes.

CRYOSYNTHESIS OF COORDINATION AND ORGANOMETALLIC COMPOUNDS: HISTORY AND PRESENT STATE

Abstract Interactions of metals with inorganic and organic ligands including polymers are reviewed. Direct methods of synthesis have many possibilities in comparison to conventional synthetic methods. However, cryosyntheses with chelate-forming ligands have not been sufficiently devel—oped at the present time. Cryosyn thesis is especially recommended for preparation of compounds difficult to obtain by traditional methods.

Oxidative Dissolution of Metals and Metal Oxides in a Liquid Phase

This chapter focuses on the oxidative dissolution of metals and metal oxides in a liquid phase. Studies of the theory of solid-liquid interaction are becoming more essential in view of the necessity to increase the productivity of technological processes in the chemical, hydrometallurgical, chemopharmaceutical and other branches of industry. Several methods are employed to study solid dissolution kinetics. The most applicable are the two techniques that involve powder samples or samples of some definite shape—such as pressed pellets, plates, cylinders or disks—with a known surface. The methods based on the use of a compact sample, however, do not produce unambiguous results to characterize the kinetics of a real hydrometallurgy process. The methods using powder samples reveal more exactly the character of hydrometallurgy process kinetics. The chapter discusses the kinetics of dissolution of metal powders and metal oxides and describes the processes of direct synthesis using halogenated hydrocarbons, direct synthesis with solutions of ammonium salts, and direct synthesis in solutions of proton-donor reagents. The chapter also discusses about the interaction of metals with Quinones and Phthalocyanine precursors..

Chapter 2 – Direct Electrosynthesis of Metal Complexes

Publisher Summary Electrosynthesis is not only the oldest but also the best method to obtain complex compounds starting from bulk zero-valent metals. It is the optimal method for carrying out redox reactions, because it works at normal temperature and has the following advantages: the addition of redox species to the reaction mixture is unnecessary, compounds are produced by metal dissolution in soft conditions and with simple equipment, it is possible to produce compounds that are very difficult to obtain by the classical route, the electrosynthesized compounds are more reactive than those obtained by conventional methods, and the working conditions required permit minimum contamination. The chapter focuses on electrosynthesis at sacrificial anodes, highlighting the processes of electrosynthesis of molecular complexes, metal chelates, di- and polymetallic complexes, and π- and σ-organometallic complexes. The chapter emphasizes that the combination of the electrochemical dissolution of metals with simultaneous ultrasonic treatment of the reaction system could help to avoid the typical problems of electrochemical procedures and to increase the yields. The chapter ends with the discussion on electrosynthesis at sacrificial cathodes.

Chapter 1 – Cryosynthesis of Metal Complexes

Publisher Summary This chapter focuses on the process of cryosynthesis of metal complexes. The use of metal vapors in organic and inorganic chemistry has led to the creation of a new area of synthetic coordination chemistry: the “direct synthesis” of metal complexes starting from metal vapors in the gas phase. Coordination compounds can be obtained in the gas phase by direct interaction of vaporized atomic metals and ligands. However, the scope of this approach is strongly limited by the instability of complexes at high temperatures. The highest efficiency in gas-phase syntheses is attained by co-condensation of metal vapors and ligands at low temperature. The types of apparatus used for direct synthesis of metal complexes in the gas phase differ according to the methods of metal evaporation used and of the introduction of the ligand into the reaction chamber. Various organic and inorganic ligands are used in cryosynthesis with the participation of atomic metals at low temperatures, and pure gas-phase reactions without a condensed phase at high temperatures hold many possibilities for the synthesis of various types of complex, especially π-complexes of aromatic and cyclodiene ligands. The chapter discusses the processes of synthesis of metal complexes with simple inorganic ligands, cryosynthesis of metal π- and σ-complexes, and vapor synthesis of metal chelates, highlighting the advantages and disadvantages of cryosynthesis.

Chapter 5 – Some Peculiarities of the Crystal Structures of Complexes Obtained by Direct Synthesis

Publisher Summary One of the peculiar properties of the compounds obtained by direct synthesis is their uncommon composition. The complexes obtained directly from metal powders or metal oxides and ammonium salt solutions illustrate peculiarities of crystal structures. Most complexes have two types of different polyhedra: a distorted square pyramid and a trigonal pyramid. The formation of the coordination sphere of the metal during complex formation in the conditions of direct synthesis does make it possible to obtain compounds with unusual spatial structures. These peculiarities of crystal structures can be illustrated by the complexes obtained directly from metal powders or metal oxides and ammonium salt solutions. This chapter focuses on these specific peculiarities of the crystal structure.

Mechanosynthesis of Coordination Compounds

Among various methods of activation of chemical reactions, mechanical activation has its own characteristics and it is used for increasing the chemical transformation of inorganic and high-molecular compounds. Mechanical treatment of compact metal surfaces in the presence of complex-forming compounds leads to the formation of various complexes of different compositions and structures. An immediate mechanical activation of the “compact metal-ligand” system could contribute to the complex–formation process. The effects accompanying frictional interaction of solid substances are a primary cause of activation of the system “compact metal–ligand” under friction conditions. The study of this process is important in the analysis of the mechanisms of lubricant action in the processes of friction and wear of solid bodies, in particular of friction in conditions of self-organization of frictional systems. This chapter highlights the complex formation in the metal–carbon tetrachloridedimethyl sulfoxide system. It also discusses about interaction of copper with salicylic aldehyde, o-azomethinic ligands, Schiff bases, o-hydroxyazo compounds, 8-hydroxyquinoline and its derivatives, acetylacetone, n-acylsalicylamide solutions, and disalicylamide.