Solubility of coordination compounds

Chapter 2. THE SOLUBILITY OF COORDINATION COMPOUNDS RELATIONSHIP TO COMPOSITION AND STRUCTURE... 

Feigl has suggested that systematic modification of the solubilities of coordination compounds may be achieved by alteration of the hydrophilic-lipophilic balance (HLB) of the molecuks. Hydrophilic-lipophilic balance is a specific relationship between polar and nonpolar groups in a compound. By increasing the lipophilicity of a molecule, decreased solubility in water and increased solubility in organic solvents usually results. Similarly, increasing the hydrophilicity of a molecule usually results in decreased solubility in organic solvents and increased solubility in water... 

Thus, [PtMe(RCN)L2] , on addition of NaBPh4, forms a precipitate of [PtMe(RCN)L2)[BPh4] in methanol. These [PtMe(RCN)L2][BPh4l salts are freely soluble in dichloromethane. Clearly, the precipitation of the complexes from aqueous solution by lipophilic counterions and the simultaneous increase in solubility of the complexes in organic solvents are closely related to one another. Accordingly, it is helpful to consider existing ideas about the solubilities of coordination compounds ionized in water. 

Solubility appears to depend less on the non-aqueous or aqueous solvent in use and more on two pertinent factors that are important in considerations of the solubility of coordination compounds in all solvents the polarity of the solvent and its ability to function as a ligand or ottierwise interact with a metal complex. Essentially, the behavior of water as a solvent for the synthesis of coordination compounds is consistent with the general behavior exhibited by other solvents. Therefore, there appears to be little... 

Forms a number of coordination compounds (ammonia complex) with several metals adds to AgCl forming soluble complex [Ag(NH3)2]Cl forms tetraamine complex [Cu(NH3)4]S04 with CUSO4 and forms many hexaamine complexes with cobalt, chromium, palladium, platinum and other metals. 

I2]. The substantial solubilities of these compounds in chloroform and other less polar organic solvents are in agreement with their formulation as nonelectrolytes. In methanol at 25° C., the molar conductivities of 166 and 167 ohm-1 for [Ni-(NH2CH2CH2S-CH3)2I2] and [Ni(NH2CH2CH2S-CH2C6H5)2I2], respectively, are characteristic of di-univalent electrolytes in this solvent, indicating almost complete solvolysis of the coordinated iodide ions in this relatively polar solvent. Decomposition of these complexes was observed upon dissolving in water. Visible and near-infrared spectra results are also consistent with structure VI. 

Solvated transition metal cations containing weakly bonded organic ligands are potentially useful as intermediates in preparative coordination chemistry. The coordinated solvent molecules provide solubility of the compounds in various organic solvents, and they can be replaced readily by other ligands with better donor properties.1, 2 The preparation of mononuclear transition metal complexes with weakly bonded anions has been described previously3 and preparative applications of such complexes have been reviewed.4... 

The coverage has been limited to the applications of coordination compounds or of the coordination chemistry of relatively soluble ligands and metal species. Numerous chemical agents in photographic systems function by means of adsorption on silver halide grains and silver metal surfaces. Such chemical interactions lie outside the confines of coordination chemistry defined for this work and have not been discussed. 

The use of borane-containing monomers clearly presents an effective and general approach in the functionalisation of polyolefins, which has the following advantages stability of the borane moiety to coordination catalysts, solubility of borane compounds in hydrocarbon solvents (such as hexane and toluene) used as the polymerisation medium, and versatility of borane groups, which can be transformed to a remarkable variety of functionalities as well as to free radicals for graft-form polymerisations. The functionalised polymers are very effective interfacial modifiers in improving the adhesion between polyolefin and substrates and the compatibility in polyolefin blends and composites [518],... 

The first successful resolution of coordination compounds was reported by Werner in 1911 and involved two series of complexes, the cw-chloroammine-bis(ethylenediamine)cobalt(III) series (with V. L. King) and the m-bromo-amminebis(ethylenediamine)cobalt(III) series (with E. Scholze). Of the two, the bromoammine series is easier to resolve because of the greater difference in solubility between the diastereoisomers that are formed with the resolving agent, silver ( + )-octahedral configuration first postulated by Werner for cobalt(III) in 1893. 

Due to the good solubility of organometallic compounds, ionic liquids have been used as reaction media, replacing traditional molecular solvents, or as the catalyst-supporting phase in a biphasic system. Influences of the ionic liquid on the reaction rate and selectivity can mostly be explained by the reactivity of the anion, which can be noncoordinating or coordinating as well as Lewis-acidic, Lewis-basic or neutral. The cation, in contrast, is considered to be essentially noncoordinating and innocent. 

The formation of coordination complexes can have a large effect on the solubility of a compound in water. Silver bromide is only very weakly soluble in water,... 

The process can be reversed, with the precipitate dissolving in the aqueous phase when the activities of the precipitate species in the aqueous phase are less than the solubility of the precipitate or when the environmental conditions such as pH and redox are changed. For example, typical A sp values of various lead compounds (e.g., Pb(OH)2 = 10"PbSO4 = 10 PbS = IQ- o and PbCOa = 10 ) indicate that the least soluble of the four compounds is PbS, while the most soluble is PbSO4. Although A sp provides an indication of the solubility of the compound, metal ions in wastewater interact with other ions or molecules to form complex ions or coordination compounds, and this may also affect their solubilities. Examples of complexes formed include hydro-, cyano-, and ammonium complexes when cyanide and ammonium ions are present. 

Before we travel too far, however, it may be valuable to look back to the beginnings of coordination chemistry. While examples of coordination compounds were slowly developed during the nineteenth century, it wasn t until the twentieth century that the nature of these materials was understood. They were at a very early stage named complex compounds , a reflection of their unexplained structures, and we still call them complexes today. Around the beginning of the twentieth century, the wealth of instrumental methods we tend to take for granted today simply didn t exist. Chemists employed chemical tests, including elemental analyses, to probe formulation and structure, augmented by limited physical measurements such as solubility and conductivity in solution. Analyses defined the components, but not their structure. As a consequence, it became usual to represent... 

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