Anion-exchange separations of metal ions in thiocyanate media

The analytical potential of a weak-base macroreticular anion-exchange resin for the quantitative separation of metal ions in thiocyanate media is investigated and demonstrated. Distribution data are given for the sorption of some 25 metal ions from aqueous mixtures of potassium thiocyanate (1.0M or less) and 0.5M hydrochloric acid. The magnitude of the distribution data suggests many possible separations, some of which were quantitatively performed by procedures which are fast, simple and require only mild conditions. Representative separations are removal of traces of iron(III) and copper(II) from water samples prior to the determination of water hardness (calcium and magnesium), separation of nickel(II) from vanadium(IV) and the separation of thorium(IV) from titanium(IV). Some multicomponent separations are the separation of rare earths(III) and thorium(IV) from scandium(III) and the separation of rare earths(III) from iron(III) and uranium(VI).     

Cerimetric determination of metals forming pyridine thiocyanate complexes

Summary A new procedure for the quantitative determination of Cu, Co, Ni and Cd has been described. It is based on the precipitation of the metals as pyridine thiocyanate complexes and titrating the excess thiocyanate with ceric sulphate using dead stop end point method or the usual visual end point method with vigorous stirring.

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Zusammenfassung Ein neues Verfahren zur Bestimmung von Kupfer, Kobalt, Nickel und Cadmium beruht auf der Fällung der Metalle als Pyridinthiocyanatkomplex und Rücktitration überschüssigen Thiocyanats mit Cer(IV)-sulfat. Der Endpunkt kann nach der Dead stop-Methode oder visuell bestimmt werden.

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See also Z. analyt. Chem. 185, 376 (1962).

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Authors thanks are due to Prof. G. B. Singh for the facilities provided during the above work. The award of a fellowship by U.G.C. to one of us (A.L.J.R.) is also acknowledged.     

Thermodynamics of ion association. Part XXIII. Copper,zinc, and cadmium complexes of some dipeptides

Calorimetric and potentiometric studies have been made at 25°C of the formation of zinc and cadmium complexes of diglycine and of the copper complexes of glycylsarcosine, glycineamide, glycylproline, glycyl-l-alanine, -alanylglycine, and glycyl--aminobutyric acid. In addition, a potentiometric investigation has been made of the formation of copperl-alanyl-l-alanine complexes. The data have been used to calculate G, H, and S values for all the equilibria involved and, in the case of copper, these data strongly support a common structure for all the mono complexes at lower pH in which the copper is bound to the terminal—NH₂ and the oxygen of the peptide group. At higher pH, thermodynamic functions have been determined for the dissociation of the peptide hydrogen atom which is labilized by the copper atom.     

Extraction of zinc thiocyanate complexes by high molecular weight amines and quaternary ammonium salt

The extraction of Zn(II) thiocyanate complexes by various high molecular weight amines and quaternary ammonium salts has been studied. The extraction efficiency of various amines and the dependence of extraction on thiocyanate concentration, pH of the aqueous phase and on metal and amine concentration have been investigated. An attempt has also been made to identify the extracted species by extraction isotherms and log-log plots of amine concentration vs distribution ratio.     

An infrared and Raman spectroscopic study of some metal pyridine tetracyanonickelate complexes

The results of an infrared and Raman spectroscopic study are presented for seven new metal pyridine tetracyanonickelate complexes, M(py)₂Ni(CN)₄, M = Mn, Co, Fe, Ni, Cu, Zn and Cd. It is shown that the spectra are consistent with a proposed crystal structure for these complexes derived from X-ray diffraction measurements. The spectra can be clearly distinguished from those of analogous Hofmann-type clathrates with which the nickel complex had been previously confused. The copper complex has spectral features different from the other six compounds and an explanation is proposed in terms of a distortion of the general crystal structure due to the Jahn-Teller effect. Analysis of the single, sharp bands of coordinated pyridine offers a method of resolving some difficulties in earlier assignments of the normal modes of the free base. Several modes of coordinated pyridine have upward shifts in frequency compared to those in the free molecule and the shifts are metal dependent. An explanation, supported by a simple normal coordinate analysis on a model, is provided in terms of coupling with low frequency vibrations, particularly the M-N stretching frequency. Other vibrations of the Ni(CN)₄ group, which coordinates to the metals M to form a two-dimensional coordination polymer, are also metal dependent. It is similarly suggested that coupling with low frequency modes is the principal cause of the upward shifts in frequency.     

The sorption behaviour and separation of some metal thiocyanate complexes on polyether-based polyurethane foam

The preliminary screening tests on the preconcentration of lanthanum(III), aluminium(III), molybdenum(VI), gallium(III) and tungsten(VI) thiocyanate complexes in aqueous media by unloaded foam indicated a reasonable percentage of metal ions were retained on the foam. The influence of various parameters affecting the retention of these complex species from the aqueous media by the foam were critically studied and the possible mechanisms of the sorption of the compounds were suggested. However, owing to the complex chemical nature of the polyether-polyurethane foam, several mechanisms may be involved simultaneously. Attempts for the quantitative retention and recovery of the tested complexes by the foam columns were also made and satisfactory results were obtained. The height equivalent to theoretical plates (HETP) of the foam columns were calculated from the chromatograms and break through capacity curve and were found in the range 1.8-2.3 mm at flow rates up to 15 cm(3)/min. The proposed foam column method has been successfully used for the separation of a series of complex mixtures of the tested metal thiocyanate complexes in aqueous media. The membrane properties of the foam sorbents offer unique advantages over conventional bulk type granular sorbents in rapid, versatile effective separations and preconcentrations of different complexes from fluid samples.     

Study on the synergistic extraction of cobalt(II) with lower fatty acids in the presence of heterocyclic amines and some metal ion separations

The synergistic extraction of cobalt(II) with a chloroform solution of propionic, butyric or valeric acid in the presence of beta-picoline, pyridine or quinoline has been investigated. The effect of different variables, such as pH of the aqueous phase, and concentration of metal ion, acid and amine, is reported. On the basis of slope analysis the species extracted were generally found to be CoA(2).2HA.2B where HA is the acid and B the base, but CoA(2).HA.2B.H(2)O for the butyric acid-quinoline system. The extraction constants were used to assess the relative effectiveness of the amines as synergists. From the extraction data, methods for separation of Co(II) from Mn(II), Cr(III), Fe(III), Zn(II), Cd(II) and Hg(II), with fairly high separation factors, have been worked out.     

Structures of bisphosphonate metal complexes: zinc and cadmium complexes of clodronate and its partial ester derivatives

Four new zinc and cadmium bisphosphonates [{NaZn(Cl2CP2O6H)(H2O)5}]n (1), [{Cd2(Cl2CP2O6)(H2O)4}.H2O]n (2), [{Zn(Cl2CP2O6Pri2)(H2O)3}.H2O]n (3), and [{Cd2(Cl2CP2O6Pri2)2(MeOH)2(H2O)2}.H2O]2 (4) have been prepared and their crystal structures determined by single-crystal X-ray diffractometry. Two bisphosphonate ligands were used: clodronate, (dichloromethylene)bis(phosphonate) and its symmetrical P,P'-diisopropyl ester derivative. The structure of the Zn complex 1 is three-dimensional, consisting of one-dimensional Zn-clodronate chains connected to the three-dimensional network by Na+ ions. The structure of Cd complex 2 consists of double layers, and a unique bond was found between the Cd2+ cation and a Cl atom of clodronate. Zn complex 3 consists of one-dimensional chains, but the binding of the bisphosphonate ligands is unique: in 3 the bisphosphonate ligand is only bidentate. Compound 4 is a tetramer, and hydrogen bonds hold the tetramers together, forming a layered structure.     

Solvent and metal ion effects in condensation reactions between semicarbazides and pyridine derivatives and study of the complexes with metal chlorides

Co, Ni, Cu, Zn, Cd and Hg chloride complexes of 3-acetylpyridinesemicarbazone, 3-acetylpyridinethiosemicarbazone 4-pyridinesemicarbazone and 4-pyridinethiosemicarbazone have been obtained, and have the general formulae [MLCl₂], [ML₂Cl₂], [MLCl₂]H₂O, [ML₂Cl₂]-H₂O, [ML_xCl₂] (L=3-apsc, 3-aptsc, 4-psc or 4-ptsc). The reaction product of 4-pyridinecarbaldehyde with semicarbazide has properties consistent with 4-pyridinecarbaldehyde·semicarbazide, without condensation, but this condensation may be obtained by solvent or metal template effects using Cd or Hg. The products have been characterized by physicochemical and spectroscopic methods.     

Unloaded polyurethane foams as solid extractants for some metal thiocyanate complexes from aqueous solution

Zinc, mercury, and indium are quantitatively extracted with unloaded polyurethane foams from aqueous thiocyanate solution. The unloaded polyester type foam will extract the thiocyanate complexes of the three metals as well as the polyether type. The extraction is strongly dependent on the thiocyanate concentration and is quantitative over a wide pH range.     

Extraction of zinc thiocyanate complex by tributyl phosphate in benzene

The species extracted is shown to be Zn(SCN)X.2TBP, where X is a common anion. Good separation factors are obtained for extraction of zinc from solutions containing silver(I), manganese(II), cobalt(II), cadmium(II), mercury(II) and thallium(III).     

Bromination of pyridine in the presence of some lewis acids

The bromination of pyridine in the form of complexes with some Lewis acids and in the presence of catalytic amounts of the latter was studied. It is shown that bromination takes place readily at 100 °C in the presence of catalysts such as AlCl₃, ZnCl₂, CuCl₂, SbCl₃, InCl₃, TeCl₄, and HgCl₂. The principal bromination products are 3-bromopyridine and 3,5-dibromopyridine. The problem of the possibility of so-called back-bonding in the case of elements of the higher periods (particularly In, Te, and Sb) is discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1236–1239, September, 1981.     

Creatinine complexes of zinc,cadmium and mercury

Zinc, cadmium and mercury(II) complexes of creatinine of the composition M(Creat)₂X₂ (X = Cl, Br or I) are prepared. The complexes are characterized by analytical and spectral methods. The increase in cyclic NH stretching frequency in the case of complexes (3350 cm^?1) from that of the free ligand (3300 cm^?1) suggested that secondary nitrogen is involved in coordination. The shift in the resonances of cyclic NH proton in the ¹H NMR and carbonyl and imine carbons in ¹³C NMR when compared to the ligand indicated that cyclic nitrogen coordinates. Conductivity measurements in N, N-dimethylformamide suggested that the complexes are non-electrolytes. Thermal decomposition behaviour of the complexes is also discussed.     

Extraction of zinc, cadmium and mercury salicylates

A systematic study of the solvent extraction of Zn, Cd and Hg salicylates is reported. Optimum conditions for extraction and separation of Zn, Cd and Hg are evaluated from a critical study of pH, sodium salicylate concentration, mesityl oxide concentration, period of equilibration, and effect of diverse ions. A separation scheme is described and results are reported for analysis of synthetic mixtures and commercial samples.     

Polarographic studies of complexes of cadmium with chloride and thiocyanate ions in aqueous medium

This is a polarographic study of the system Cd(II)?NaCl?NaSCN in aqueous medium of a constant ionic strength of μ=1.0 M with NaClO₄. Reduction takes place through a reversible bielectronic process. The diffusion magnitudes I_d and D have been determined, and the formation of the mixed complexes CdClSCN, [CdCl₂SCN]^? and [CdCl(SCN)₂]^?, with stability constants of β₁₁=106±101² mol^?2, β₂₁=156±101³ mol^?3 and β₁₂=484±801³ mol^?3, respectively, has been demonstrated. The values of these constants are discussed in the light of statistical aspects and Watters equations.     

Electrochemical approach to monitoring metal exchange reaction of acetylacetonate complexes with cadmium, copper and zinc ions

Metal exchange reactions of acetylacetonate complexes with Cd(II), Cu(II) and Zn(II) ions were investigated by using cadmium and copper ion selective electrodes. Changes in the electrode potential and pH of the solutions were monitored upon adding the pertinent metal Zn(II) of the acetylacetonate (AA) complexes. In the reverse system in which a stable Cu-AA complex exists in the solution prior to adding a secondary metal ion (Cd(II) or Zn(II)), no Cu(II) was replaced by either ion. In the systems containing Cd(II) and Zn(II) as a complexed form with AA or as free ions, the exchange reactions were not explained by considering the equilibrium stability constants of the Cd-AA and Zn-AA complexes.     

Extraction separation of cadmium and zinc with tetra-n-butylammonium iodide

Tetra-n-butylammonium iodide (TBAI) forms associations in chloroform and aqueous solutions. A TBAI solution in chloroform extracts hydroiodic acid by addition. From 0.5M hydroiodic acid medium cadmium is quantitatively extracted into a TBAI solution in chloroform. Under these conditions zinc is not extracted. This makes possible the extractive separation of cadmium from zinc in micro-or macroamounts.