Copper carboxylate salts, structures

Figure 9. Structures of Cu carboxylate salts, (a) monomeric Isolated complexes, (b) dimeric complex (monohydrated copper acetate type), and (c) dimeric complex (anhydrous copper formate tyjpe). (Reproduced with permission from ref. 10. Copyright 1966 Butterworth)...

The third spectrum (c) was obtained from copper chloride dissolved in hydrated trioctylammonium 2-ethylhexanoate in toluene (the mixed extractant). It has a broad maximum absorbance at 725 nm, its symmetry is similar to that of copper carboxylate, and bonding of copper can be assumed to occur via the carboxylic oxygens in a manner similar to that of the dimer. Spectrum (c) bears an even greater similarity to that of the Cu-EDTA complex, the maximum absorption being at 734 nm, and which is known to have a distorted octahedral structure [12]. It is easy to convert the carboxyT ate dimer into a mixed complex. On adding trioctylamine to copper carboxylate, the maximum absorption shifts gradually from 680 to 725 nm. It is assumed that the addition of the amine converts the dimer into a monomer in which copper is bound to four monomeric carboxylic ligands and two amine molecules are located farther away in an axial position. It is of interest to note that the anion of the salt coextracted with the metal ion has no effect on the visible spectrum i.e., it is immaterial whether copper fluoride, chloride, or nitrate is extracted they all have the same spectrum. 

Chemical analysis revealed that commercial food grade copper chlorophyllin is not a single, pure compound, but is a complex mixture of structurally distinct porphyrins, chlorin, and non-chlorin compounds with variable numbers of mono-, di-, and tri- carboxylic acid that may be present as either sodium or potassium salts. Although the composition of different chlorophyllin mixtures may vary, two compounds are commonly found in commercial chlorophyllin mixtures trisodium Cu (II) chlorin Cg and disodium Cu (II) chlorin which differ in the number of... 

Broadbent et al. [69] showed that ar-time curves for the decomposition of copper(II) oxalate (503 to 533 K) were sigmoidal and that data for the vacuum reaction fitted the Avrami-Erofeev equation with values of = 2.9 initially and later n = 3.5 ( , = 136 kJ mol ). Electron transfer was identified as the step controlling the reaction. There was no evidence from X-ray diffraction studies for the intervention of the Cu salt the orthorhombic structure was present until disappearance of the reactant and product copper metal was detected. However, many metal carboxylates, chilled after dehydration, yield anhydrous salts that are amorphous to X-rays or poorly crystalline, see, for example [70]. 

In contrast to the case of straight chain salts, complexation of the copper(II) branched chain carboxylate with a difunctional ligand as pyrazine or 4,4 -dipyridyl result in a liquid crystalline material whose mesophase structure has not been established [47]. 

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