Cadmium halide complexes

Some Formation Constants of Zinc and Cadmium Halide Complexes (at 25°)... 

Nickel halide complexes with amines give mixtures of linear polymer and cychc trimers (30). Nickel chelates give up to 40% of linear polymer (31). When heated with ammonia over cadmium calcium phosphate catalysts, propargyl alcohol gives a mixture of pyridines (32). 

Cadmium(II) and zinc(II) systems other than cyanides Among the i acceptors of the zinc group, the softness rapidly decreases from the markedly soft Hg2+ to the mildly soft Cd2+ and to the distinctly hard Zn2+. As mentioned above, only very soft ligands such as CN are coordinated to Cd2+ or Zn + by bonds which are essentially covalent. Nevertheless, covalent bonding is still important for the formation of the Cd2+ halide complexes. This is evident from the fact that the values of AHn become more exothermic as the halide becomes larger and consequently more polarizable and susceptible to covalent bonding. This trend results in the (6) or soft sequence for the halide systems of... 

Cadmium is a member of Group 12 (Zn, Cd, Hg) of the Periodic Table, having a filled d shell of electrons 4valence state of +2. In rare instances the +1 oxidation state may be produced in the form of dimeric Cd2+2 species [59458-73-0], eg, as dark red melts of Cd° dissolved in molten cadmium halides or as diamagnetic yellow solids such as (Cd2)2+ (AlCl [79110-87-5] (2). The Cd + species is unstable in water or other donor solvents, immediately disproportionating to Cd2+ and Cd. In general, cadmium compounds exhibit properties similar to the corresponding zinc compounds. Compounds and properties are listed in Table 1. Cadmium(TT) [22537 48-0] tends to favor tetrahedral coordination in its compounds, particularly in solution as complexes, eg, tetraamminecadmium(II) [18373-05-2], Cd(NH3)2+4. However, solid-state cadmium-containing oxide or halide materials frequently exhibit octahedral coordination at the Cd2+ ion, eg, the rock-salt structure found for CdO. 

Metal complexes of several zinc, cadmium and mercury salts with 2-, 3- and 4-cyanopyridine have been reported.495 In none of the complexes was cyanide coordination observed. Zinc halides react with 3- and 4-cyanopyridine, but not with 2-cyanopyridine, to give 1 2 complexes which are assigned a monomeric tetrahedral structure on the basis of IR evidence. The cadmium halides also form 1 2 complexes with all the cyanopyridines, except cadmium chloride, which reacts with 2-cyanopyridine to give a 1 1 complex. The former contain... 

The stability constants in melts of NH4N03- H20 of ZnX+, ZnX2 (n = 1-3 X = Cl or Br), CdX+, CdX2 (n = 1.5-3 X = Cl or Br) and HgX HgX2 (n = 2.5 X = Cl or Br) have been determined.950,931 The behaviour of zinc is peculiar if the Ki and K2 values are compared with those of cadmium and mercury. The stability constants increase with temperature and the bromide is more stable than the chloride, trends which are opposite to those normally observed for the halide complexes of most metals in anhydrous or aqueous melts. The data also show... 

An EMF method has been used to study the interaction of ZnCl2 with chloride ion in methanol. It is found that Kx (7.76 x 103 M) is less than K2 (1.74 x 104 M), a finding which is interpreted in terms of passing from an octahedral [ZnCl(MeOH)5]+ species to a tetrahedral [ZnCl2(MeOH)2] complex.967 Related studies have shown that the solubility of cadmium halides in water decreases with increasing pressure.968 969 Anionic [ZnCl3] and [ZnCU]2-species are present in zinc chloride battery electrolyte, and are responsible for the observed negative transference numbers for zinc in aqueous acidic chloride medium.970 In neutral... 

Raman measurements on concentrated aqueous solutions of cadmium halides show the presence of chloro complexes of tetrahedral and octahedral symmetry, but the formation of only tetrahedral bromo complexes.978 A combination of solution and solid state 113CdNMR spectroscopic results have allowed the compilation of 113Cd chemical shifts for the complexes [CdX]+, [CdX2], [CdX3] and [CdXJ2-, for X = Cl, Br or I.979... 

Much work has been devoted to the halide complexation of these elements in non-aqueous media. Equilibrium and calorimetric measurements for the formation of the [MX ](n-2) (M = Zn or Cd X = Cl, Br, I or SCN n = 1-4) anions in dimethyl sulfoxide (DMSO) have shown that stability constants follow the same order, but are much larger than those found for aqueous solution zinc exhibits an enhanced hardness as an acceptor in DMSO as compared to cadmium. Calorimetric measurements indicate a change from octahedral to tetrahedral coordination with increasing halide concentrations.1002-1006... 

In general, the cadmium halides show in their crystal structure the relation between polarizing effect and si/e of anion. The tluoride has tile smallest and least polarizable anion of Ihe lour and forms a cubic structure, while the mure polarizable heavy halides have hexagonal layer structures, increasingly covalent and al increasing distances apart in inxler down tire periodic table, in solution the halides exhibit anomalous thermal and transport properties, due primarily to the presence of complex ions, such as CDlr and CdBr r. especially in concentrated solutions or those containing excess halide ions. 

The 2,2 -bipyridylamine complexes of some zinc, cadmium, and mercury salts have been reported.29 All the metal halide complexes isolated are of the stoicheiometry MLX2 (M = Zn, Cd, or Hg X = Cl, Br, or I), and are assigned a monomeric, tetrahedral structure on the basis of i.r. evidence. The complexes ML(SCN)2 (M = Zn, Cd, or Hg) are also monomeric. Only mercuric cyanide reacts to give the monomeric HgL(CN)2, whereas zinc sulphate forms 1 1 and 1 1.5 complexes which possess highly polymeric structures. Zinc and cadmium acetates form 1 1 complexes having pseudo-octahedral structures with bidentate, symmetrically chelating acetates. Cadmium also forms a 1 3 complex which is best formulated as [CdL3] [OAc]2. 

The same coordination geometry was also inferred from the analysis of the lowest energy LMCT bands (see Ligand-to-Metal Charge Transfer) in the far-UV absorption spectra of Zu7- and Cd7-MT, and those of corresponding tetrahedral halide complexes (see Cadmium Inorganic Coordination Chemistry see Zinc Inorganic Coordination Chemistry) Further support came from... 

Cadmium halides form auto-complex ions in concentrated solution. The anomedous transport number of Cd in Cdig solution was noticed by Hittorf (1859) and correctly attributed to the equilibrium ... 

A number of salts of narcotine were prepared 41-50)—some for oral use, since they are less bitter 47-49). Regeneration from its picrate with an anion-exchange resin proceeds with an almost quantitative yield 41). Fluorescence of complexes of narcotine with manganese chloride and cadmium halides was studied 51, 52). 

A number of stannyl-zinc and -cadmium compounds have been prepared by reaction of a tin-alkali metal compound with a zinc or cadmium halide, or a tin hydride with an alkyl-zinc or -cadmium compound. The coordination of a ligand such as a triphenyl-phosphine, TMEDA, or bipyridyl, or a solvating solvent such as DME, both enhances the nucleophilicity of the alkyl group in the alkylmetallic compounds and stabilises the stannylmetallic product. Thus triphenyltin hydride reacts with diethylzinc or diethylcad-mium in pentane or benzene with separation of metallic zinc or cadmium, but with a preformed complex, or in a coordinating solvent, the distannylmetallic compound is formed (e.g. equation 19-32). 

D. Inman, Complex Ions in Molten Salts A Potentiometric Study of the Halide Complexes of Cadmium in Molten Equimolar NaN03-KN03 at 250 °C, Electrochim. Acta 10 (1965) 11-21. 

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