Cobalt complex compounds ammines

Under general headings such as Cobalt(III) complexes and Ammines, used for grouping coordination complexes of similar types having names considered unsuitable for individual headings, formulas or names of specific compounds are not usually given. Hence it is imperative to consult the Formula Index for entries for specific complexes. 

These cobaltous addition compounds, therefore, resemble the preceding group of additive substances rather than the eobaltic salts, and the series illustrate the statement previously made that the most highly saturated compounds of an element have greater capacity for the formation of complex addition compounds. In this connection, for example, one might compare the relative instability of hexammino-cobaltous chloride, [Co(NH3)6]Cl2, with the high stability of the ammine of the more saturated eobaltic chloride, hexammino-cobaltic chloride, [Co(NH3)6]C13.2... 

Molecular shapes and 1H chemical shift patterns for chloro-ammine cobalt(III) compounds. Different environments for ammonia molecules in some complexes are defined by eq and ax subscripts, with the two types opposite different types of ligand leading to different magnetic environments and chemical shifts (8). 

As just stated, rubeanic acid reacts to give colored complex compounds, not only with nickel, but also with cobalt and copper salts. Nevertheless, within certain concentration limits, nickel can be detected in the presence of these metals. Use is made of the different diffusion velocities of the metal ammine salts in thin filter paper, the diffusion velocity of nickel being the greatest. When a drop of an ammoniacal solution of copper, cobalt and nickel salts is placed on paper, or a drop of a neutral solution on paper is held over ammonia, the nickel accumulates in the outer zone of the spot. If a drop of the alcoholic reagent solution is then placed at the side and the drops coalesce, a blue ring of nickel rubeanate forms around the brown to green or brown circle due to the cobalt and copper compoimds. 

Ammonia forms a great variety of addition or coordination compounds (qv), also called ammoniates, ia analogy with hydrates. Thus CaCl2 bNH and CuSO TNH are comparable to CaCl2 6H20 and CuSO 4H20, respectively, and, when regarded as coordination compounds, are called ammines and written as complexes, eg, [Cu(NH2)4]S04. The solubiHty ia water of such compounds is often quite different from the solubiHty of the parent salts. For example, silver chloride, AgQ., is almost iasoluble ia water, whereas [Ag(NH2)2]Cl is readily soluble. Thus silver chloride dissolves ia aqueous ammonia. Similar reactions take place with other water iasoluble silver and copper salts. Many ammines can be obtained ia a crystalline form, particularly those of cobalt, chromium, and platinum. 

Cobalt exists in the +2 or +3 valence states for the majority of its compounds and complexes. A multitude of complexes of the cobalt(III) ion [22541-63-5] exist, but few stable simple salts are known (2). Werner s discovery and detailed studies of the cobalt(III) ammine complexes contributed gready to modem coordination chemistry and understanding of ligand exchange (3). Octahedral stereochemistries are the most common for the cobalt(II) ion [22541-53-3] as well as for cobalt(III). Cobalt(II) forms numerous simple compounds and complexes, most of which are octahedral or tetrahedral in nature cobalt(II) forms more tetrahedral complexes than other transition-metal ions. Because of the small stabiUty difference between octahedral and tetrahedral complexes of cobalt(II), both can be found in equiUbrium for a number of complexes. Typically, octahedral cobalt(II) salts and complexes are pink to brownish red most of the tetrahedral Co(II) species are blue (see Coordination compounds). 

In the complex [Co(NH3)6]Cl3, the cation is [Co(NH3)6]3+, and it is named first. The coordinated ammonia molecules are named as ammine, with the number of them being indicated by the prefix hexa. Therefore, the name for the compound is hexaamminecobalt(III) chloride. There are no spaces in the name of the cation. [Co(NH3)5C1]C12 has five NH3 molecules and one CN coordinated to Co3+. Following the rules just listed leads to the name pentaamminechlorocobalt(III) chloride. Potassium hexacyanoferrate(III) is K3[Fe(CN)6j. Reinecke s salt, NH4[Cr(NCS)4(NH3)2], would be named as ammonium diamminetetrathiocyanatochro mate (III). In Magnus s green salt, [Pt(NH3)4][PtCl4], both cation and anion are complexes. The name of the complex is tetraammineplatinum(II) tetrachloroplatinate(II). The compound [Co(en)3](N03)3 is named as tris(ethylenediamine)cobalt(III) nitrate. 

Hydrate Isomerism.—As its name implies, this depends on the position of water in the molecule, just as in the case of the acido compounds. If two or more molecules of water are present in a molecule of ammine, the water may be present within the co-ordination complex or outside of it. For instance, the compound Cr en2.(H20)2.Br3 exists in isomeric forms. It may have all the water within the complex, in which case the formula will be [Cr en2(H20)2]Br3. In solution the whole of the bromine is precipitated by silver nitrate. On the other hand, the compound may have one molecule of water in the complex and the other outside, in which case the formula is [Cr en2(IT20)Br]Br2.H20, and only two-thirds of the bromine are precipitated by silver nitrate. Another example of this kind occurs in the cobalt series chloro-aquo-tetrammino-cobaltic chloride, [Co(NTI3)4Cl.H20]Cl2, is violet in colour, and is isomeric with dichloro-tetrammino-cobaltie chloride monohydrate, [Co(N1I3)4CI2]C1.H20, which is green. 

After the resolution of 1-2-chloro-ammino-diethylenediamino-cobaltie chloride many analogous resolutions of optically active compounds of octahedral symmetry were carried out, and active isomers of substances containing central cobalt, chromium, platinum, rhodium, iron atoms are known. The asymmetry is not confined to ammines alone, but is found in salts of complex type for example, potassium tri-oxalato-chromium, [Cr(Ca04)3]K3, exists in two optically active forms. These forms were separated by Werner2 by means of the base strychnine. More than forty series of compounds possessing octahedral symmetry have been proved to exist in optically active forms, so that the spatial configuration for co-ordination number six is firmly established. 

Although iron, cobalt, and nickel occur in the same triad in Group VIII., the three elements differ considerably in their ability to form addition compounds with ammonia. Iron forms few ammino-salts, most of which are unstable, and its tendency to complex-salt formation of the ammine type appears in the complex cyanides and not in the ammines themselves. 

The best known of these compounds is potassium cobalti-nitrite, [Co(N02)6]K3.1 This salt was originally regarded as a double salt of cobaltic nitrite with potassium nitrite, and represented by the formula Co(NQ2)3.3KNOa. Such a formula, however, does not represent the reactions of the substance, as the nitrite radicle is held firmly, and nitrous aeid is not liberated when the compound is treated with cold dilute acids, as it would be if it were a double salt as the formula indicates. Molecular conductivity measurements also indicate that it is a complex salt comparable with the metal-ammines. Many compounds of cobalt of this type are known. They may be regarded as the salts of the complex acid hexanitrito-cobaltic acid, [Co (N02)6]H3. 

There are still some complex polynuclear cobalt-ammines to which satisfactory constitutional formulas have not yet been assigned. These are, for example, the Fusko salts described by Fremy 1 a class of compounds containing sulphur prepared by Hofmann 2 by the action... 

These hydroxo-salts are all sulphur-yellow crystalline substances. The acid residues are hydrolysable and hence outside the co-ordination complex, and the aqueous solutions, unlike the hydroxo-salts of chromium-and cobalt-ammines, are neutral to litmus, a fact which Werner suggests is due to the smaller tendency of the hydroxo-radicle attached to ruthenium to combine with hydrogen ions. This tendency is much less than in the case of the ammines of cobalt and chromium, but that it still exists is indicated by the increased solubility of these hydroxo-compounds in water acidified with mineral acids, and from such solutions aquo-nitroso-tetrammino-ruthenium salts are obtained thus ... 

Ammonia unites readily with iridium salts, giving rise to complex ammino-derivatives. The first compounds described appear to be ammines analogous to those of palladium and platinum, to which they were compared by Berzelius 8 and Skoblikoff.4 A further series were described by Claus 5 wliich he represented like those of ammino-rhodium salts, as they bore a marked resemblance to these. After Jorgensen had established the constitution of the ammines of rhodium, cobalt, and chromium salts, Palmaer gave similar constitution to the iridium compounds. 

At high initial [Fe2+] in the absence of added substrates, the stoichiometric ratio [Fe3+]oo/[L(H20)Rh00H2+]0 approaches 2.0. At lower concentrations of Fe2+, the overall reaction produces less Fe2+ because some of the newly formed L(H20)Rh02+ decomposes, presumably by loss of NH3 from the ammine complex and intramolecular ligand oxidation in the macrocyclic compounds, as observed for similar complexes of high-valent nickel, cobalt, and iron (58,118-120). Competition experiments were carried out at sufficiently high [Fe2+] to ensure that no L(H20)Rh02 + was lost in self-decay. 

The chlorides of the other polyhasic ammine complexes with cobalt described in (II) may easily be prepared in solution by a similar procedure, but only the ethylenedi-amine compound can be directly isolated as a solid. The other chlorides must be made indirectly from the nitrates, bromides, or iodides of the respective series,... 

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