Solubility of d-element salts in organic and aqueous–organic solvents: II. Effect of halocomplex formation on solubility of cobalt bromide and chloride and nickel chloride

Abstract

Solubility of salts in the systems MCl 2 -H 2 O-Solv (M = Co, Ni) and CoBr 2 -H 2 O-Solv (Solv = dimethyl sulfoxide, dimethyl formamide, and dimethyl acetamide) at 25°C was measured experimentally. Dominating species of cobalt and nickel halides existing in various concentration regions were identified by analysis of electron absorption spectra. It was shown that the major factor defining solubility is the interaction of halocomplexes of metal ions with solvent molecules. 1 For communication I, see [1].In absence of complexation with anions (in the systems with cobalt, cadmium and copper sulfates in organic and mixed aqueous-organic solvents) ionic association is the dominating process in concentrated solutions and, as a consequence, solubility is determined mainly by the solvent dielectric permittivity [1]. This paper presents results of studying systems consisting of cobalt and nickel halides in aqueous-organic mixtures with various content of non-aqueous oxygendonor solvents: dimethyl sulfoxide (DMSO), dimethyl acetamide (DMA), and dimethyl formamide (DMF). All organic solvents used in the work are miscible continuously with water, values of their dielectric permittivity and donor ability [2] (Table 1) decrease in rather broad ranges, which makes it possible to reveal the influence of these factors on solubility of salts in the systems under study.The formation of several coordination compounds (rather stable halocomplexes in solution and various solid crystal solvates) makes the behavior of aqueousorganic solutions of such salts more diverse than that of the systems containing sulfates of d-elements, where ionic association is the dominating process [1]. The study of solubility in the systems copper(II) halideaqueous-organic solvent [3] has shown that the formation of halocomplexes along with resolvation leads to the fact that the stability of formed halocomplexes [4, 5], but not dielectric permittivity of a solvent, becomes the major factor defining the solubility.The formation of halocomplexes in ternary systems leads to the increase in the number of species present in the solution. In this case the solubility should be influenced by not so much by macroparameters of separate components (properties of salt and solvents) as by a combination of reactions proceeding between a solute and a solvent.We have carried out the following research to check this hypothesis. Solubility of cobalt and nickel salts in aqueous-organic solutions was measured experimentally, and compositions of the equilibrium

Co(iii) 2-ethylhexanoate, a hydrophobic and highly soluble Co(iii) precursor for thin coatings for water electrolysis

“…The entire spectrum of readily available Co(III) compounds is insoluble in extremely apolar media such as alkanes. [1][2][3][4][5] Inorganic Co(III) salts are soluble in water and polar solvents only, 1,2 while Co(III) carboxylates and several metal-organic complexes, such as the frequently used Co(III) acetylacetonate, are soluble in many common organic solvents but are only moderately soluble or insoluble in strongly apolar solvents. [3][4][5] This is due to the particularly hard character of the Co 3+ center, i.e.…”

“…the high positive charge concentrated in a small ionic radius. 1,2 The lack of such a Co(III) precursor showing high affinity for markedly apolar environments hinders the development of easy and direct synthetic protocols for Co(III)-based metal-organic frameworks (MOFs), 6,7 hydrophobic nanoparticles, 8 and solvogels, [9][10][11] which frequently require anhydrous, non-reactive, apolar conditions. A precursor soluble in highly apolar (hence highly volatile) solvents is also one of the most desirable features to prepare Co(III)-based coatings in environmental conditions via chemical solution deposition (CSD) processes.…”