Cobalt complexes with ammonia

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. 

Upon adsorption of excess ammonia in a Co(II)Y zeolite a white, high-spin cobalt(Il)-ammonia complex with a spin configuration of (fe )5-(eg)2 is formed. According to studies of cobalt (II) complexes in solutions, salts, and in zeolites, a hexacoordinate Co(II)-ammonia complex is the most likely form when an excess of ammonia is present (3, 4> ) Indeed,... 

Although a statistical factor contributes to the equilibrium constants for many types of reactions, it is in reactions of the type being considered here—the replacement of one neutral ligand by another neutral ligand— that this factor may be the principal factor in causing variation of Kn with n. Other series of reactions of this type are the formation of ammonia complexes in aqueous solution. The variation of Kn with n observed for the chromium (III)/water-methyl alcohol system is slightly smaller than observed for ammonia complexes of cobalt(II) (18) and nickel(II) (19) ... 

Kinetically inert low-spin cobalt (III) clathrochelates are reversibly reduced by accepting one electron to yield kinetically labile cobalt(II) complexes. In the case of the usual amines (for instance, ammonia), the reduction is, as a rule, accompanied by irreversible decay of the amine cobalt complex. This reaction is slower for chelating amines macrocyclic and especially macrobicyclic amines produce complexes with cobalt(II) ion that are stable over a long time. This fact facilitates the study of the reduction of cobalt(III) complexes to cobalt(II) ones. In most cases, the reactions of macrobicyclic ligands do not interfere with this process. 

A test first described by Parri in 1924 in which the barbiturate gives a colored complex with cobalt(II) has been adapted by the pharmacopoeia. The test parameters of the determination have been modified several times through the years, but the presence of a number of elements constitutes the essence of the procedure a ion, normally cobalt(II) or copper(II) an organic solvent, preferably one with a Lewis base character and an alkaline reaction and the absence of water in the test solution. Furthermore ammonia, or an organic amine, is sometimes added. 

Similarity with cobalt is also apparent in the affinity of Rh and iH for ammonia and amines. The kinetic inertness of the ammines of Rh has led to the use of several of them in studies of the trans effect (p. 1163) in octahedral complexes, while the ammines of Ir are so stable as to withstand boiling in aqueous alkali. Stable complexes such as [M(C204)3], [M(acac)3] and [M(CN)5] are formed by all three metals. Force constants obtained from the infrared spectra of the hexacyano complexes indicate that the M--C bond strength increases in the order Co < Rh < [r. Like cobalt, rhodium too forms bridged superoxides such as the blue, paramagnetic, fCl(py)4Rh-02-Rh(py)4Cll produced by aerial oxidation of aqueous ethanolic solutions of RhCL and pyridine.In fact it seems likely that many of the species produced by oxidation of aqueous solutions of Rh and presumed to contain the metal in higher oxidation states, are actually superoxides of Rh . ... 

Numerous d cobalt(III) complexes are known and have been studied extensively. Most of these complexes are octahedral in shape. Tetrahedral, planar and square antiprismatic complexes of cobalt(lII) are also known, but there are very few. The most common ligands are ammonia, ethylenediamine and water. Halide ions, nitro (NO2) groups, hydroxide (OH ), cyanide (CN ), and isothiocyanate (NCS ) ions also form Co(lII) complexes readily. Numerous complexes have been synthesized with several other ions and neutral molecular hgands, including carbonate, oxalate, trifluoroacetate and neutral ligands, such as pyridine, acetylacetone, ethylenediaminetetraacetic acid (EDTA), dimethylformamide, tetrahydrofuran, and trialkyl or arylphosphines. Also, several polynuclear bridging complexes of amido (NHO, imido (NH ), hydroxo (OH ), and peroxo (02 ) functional groups are known. Some typical Co(lll) complexes are tabulated below ... 

The valency of the complex radicle is the same as that of the central metallic atom when the complex contains only ammonia, substituted ammonia, water, or other neutral group. For example, cobalt in eobaltie. salts is trivalent, and the cobalt complex with ammonia, Co(NI13)8 ", is likewise trivalent copper in cupric sulphate is divalent, and the copper complex, [Cu(NH3)4] , is also divalent. In the same wn.y [Co(NH3)5.H30] " and [Co(NII3)4.(II20)2] " are trivalent, as also [Co(NH3)2.en2]" and [Co.en3] ", where en represents cthyleucdiamine, CH NH2... 

The unsymmetrical nature of / -mercaptoethylamine should lead to geometric isomerism among its metal complexes, cis and trans isomers might be expected with the square planar nickel (II) and palladium (II) derivatives and facial and peripheral isomers with cobalt (III). However, during the course of the preparation of various samples in which the procedure and experimental conditions were varied, no evidence of such isomerism was apparent (6, 15). This is particularly evident in the case of the cobalt (III) complex, CoL3. Samples prepared by the addition of cobalt (II) chloride 6-hydrate to strongly basic aqueous solution of the ligand and by displacement of ammonia and (ethylenedinitrilo)-... 

In this work, 1 1 oxygenated low-spin cobalt(II)-ammonia complexes were synthesized within the zeolite framework by the adsorption of NH3 and 02 in Co(II)Y zeolites with differing cobalt(II) content. Spin densities and the nature of the superoxide anion (02 ) were estimated by introducing oxygen-17 in the ammoniated Co(II) zeolites. Questions concerning the equivalence of the two oxygen atoms have arisen in studies on oxygen adducts of Co (II) Schiff base compounds (7), and it was of interest to study this problem in cobalt(II) ammonia complexes. 

As shown in Table I, the magnetic parameters of the oxygenated Co (Il)-ammonia complex in the zeolite are comparable with other mononuclear Co(II)-02 complexes, regardless of the nature of the cobalt (II) ligands. The very similar spectrum observed by Fujiwara et ah (9) for... 

The complications which result from the hydrolysis of alkali metal cyanides in aqueous media may be avoided by the use of non-aqueous solvents. The one most often employed is liquid ammonia, in which derivatives of some of the lanthanides and of titanium(III) may be obtained from the metal halides and cyanide.13 By addition of potassium as reductant, complexes of cobalt(O), nickel(O), titanium(II) and titanium(III) may be prepared and a complex of zirconium(0) has been obtained in a remarkable disproportion of zirconium(III) into zirconium(IV) and zirconium(0).14 Other solvents which have been shown to be suitable for halide-cyanide exchange reactions include ethanol, methanol, tetrahydrofuran, dimethyl sulfoxide and dimethylformamide. With their aid, species of different stoichiometry from those isolated from aqueous media can sometimes be made [Hg(CN)3], for example, is obtained as its cesium salt form CsF, KCN and Hg(CN)2 in ethanol.15... 

A cobalt(III) ion forms a complex with four ammonia molecules and two chloride ions. What is the formula of the complex ... 

K2[Fe(NO)2(CN)2]. My former co-worker R. Nast (83) showed that the reaction of carbon monoxide with K4[Ni2I(CN)6] and K4[Ni°(CN)4] in liquid ammonia gave nickel cyanocarbonyl complexes with monovalent and zero-valent metal atoms. The isoelectronic hexacyanoiron(III) or tetra-cyanonickel(II) complexes correspond to the cyanocarbonyls [Feu(CN)5 CO]3-, [Ni (CN)3CO]2-, or [Ni°(CN)2(CO)2]2-. Cobalt is analogous to nickel in forming the complex [Co(CN)3CO]2-. According to our earlier work, [Fe"(CN)5CO]3- and [Fem(CN)6]3- are isosteric (87). Other structural investigations were concerned with tetracyano and tetracarbonyl complexes (88). 

QuinoxaIinedithiolate was first prepared in 1956 by Morrison and Furst (4) who observed that qdt formed colored complexes with metals in aqueous ammonium hydroxide. Nickel was first quantitated using qdt in 1958 by Skoog et al. (26) in liquid ammonia. Silver, copper, cobalt, and manganese were found to interfere with nickel detection. In particular, under the conditions of Skoog et al., the absorbance of [Co(qdt)3]3- (A.max = 475 nm) significantly overlapped with the absorbance of [Ni(qdt)2]2 at 520 nm. 

The synthesis of pentaammine(carbonato)cobalt(III) salts is readily accomplished by an air-oxidation method starting with cobalt(II) nitrate and ammonium carbonate in aqueous ammonia.1 However, a suitable general method for making other types of monodentate amino(carbonato) metal salts is not available in the literature. The air-oxidation technique can be applied only to complexes where the ligands are all ammonia molecules or where the central metal ion is cobalt. 

The ammines of cobalt(II) are much less stable than those of cobalt(III) thermal decomposition of [Co(NH3)6]Cl2 is characterized by reversible loss of ammonia, whereas that of [Co(NH3)6]Cl3 is not. In his classic dichotomy of complexes, Biltz regarded [Co (NH 3)3] Cl 2 as the prototype of the normal complex and [Co(NH3)6]Cl3 as that of the Werner or penetration complex. Hexaamminecobalt-(II) chloride has been prepared by the action of gaseous ammonia on anhydrous cobalt (II) chloride or by displacing water from cobalt(II) chloride 6-hydrate with gaseous ammonia. It may also be synthesized in nonaqueous solvents by passing dry ammonia through solutions of cobalt(II) chloride in ethanol, acetone, or methyl acetate. Syntheses in the presence of water include heating cobalt(II) chloride 6-hydrate in a sealed tube with aqueous ammonia and alcohol and the treatment of aqueous cobalt(II) chloride with aqueous ammonia followed by precipitation of the product with ethanol. The latter method is used in this synthesis. Inasmuch as the compound is readily oxidized by air, especially when wet, the synthesis should be performed in an inert atmosphere. 

Direct methods for making the complex starting with cobalt(II) chloride involve preparation of a carbonatotetra-ammine salt by air oxidation and subsequent reaction with ammonia and hydrochloric acid. The procedure is time-consuming but gives excellent yields. A more rapid and simpler synthesis, which utihzes the reaction of hydrogen... 

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