Cr ammines

Asa rule, the colors of Co and Cr ammines are largely independent of the nature of the metal, but depend on the number of neutral and acidic radicals. For instance hexammines are yellow(luteo), chioropentammines are purple-red(purpureo) and aquopentammines are pink(roseo). The compd [Co(NH )4 Cl2]Cl is green(praseo) and the compd [Co(NH3)4 (NOa)2]CI is called the flavo- or coceo salt... 

CA 351636(1941 )(Nonsetting expls obtained by coating AN grains with tetram-minezinc nitrate) 29)O.Schmitz-Dumont, ZElektrochem 47, 221-2(1941) CA 35, 5052(I941)(Interaction of Co and Cr ammines with alkali metal amides results in formation of Co and Cr amides) 30)W.V,Smith, CanP 401,643(1941) CA 36, 1744(1942)(Prepn of... 

Co and Cr ammines were among the first to be investigated by Reinecke, Jmgensen, Werner (Nobel prize, 1912), and Pfeiffer in the early days of coordination chemistry see Coordination Chemistry History), and this work continues today (Taube, Nobel Prize, 1984). [MX(NH3)5]"+ (X = anionic or neutral group) is particularly well-studied and has even been used as a protecting group in peptide synthesis. Variation of M has a considerable influence on the rate of the Solvolysis of X (Table 4). 

Measurements have been made of the room-temperature luminescence quantum yields of various Cr ammine and ethylenediamine complexes in water. Most emission was phosphorescence, but some fluorinated complexes emitted delayed fluorescence. The range of quantum yields was accounted for in terms of processes degrading the state. Radiationless decay rates for the transition... 

Decomposition of the metal ammines have probably been most extensively investigated. Some qualitative features of the thermal decomposition of metal ammine compounds are conveniently illustrated [1116— 1118] by the somewhat contrasting behaviour of the compounds [Cr(NH3)6]X3 and [Co(NH3)6]X3 where X is Cl- or Br . During decomposition of the chromium compound, the oxidation number of the metal remains unchanged, viz. 

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. 

The importance of knowing the stoichiometry of a reaction can be simply illustrated by considering the aquation of c -Cr(en)2(NCS)Cl+ ion.Is Cl or NCS replaced in the initial step and is the product cis or trans or both Does the product of this first step aquate further, and if so what groups are then replaced Chemical and spectral analysis answers these questions. The results reveal the surprising fact that the bidentate ligand en is lost at one stage, a behavior that appears more common with ammines of Cr(III) than with Co(III), where its occurrence is only occasionally noted. 

Powder reflectance spectra have shown that PCl5,CrCl3 involves an octahedral CrClg chromophore. The preparation, unit cells, and vibrational spectra of the hexa-ammine metal(iii) salts [M(NH3)g][CrCl6] (M = Cr, Co, or Rh) have been reported. ... 

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. 

Chromium in the trivalent state forms a variety of salts, the most important and the simplest being the violet salts, which liberate in aqueous solution chromium cation Cr" A green series of chromic salts, isomeric with the violet salts, liberate in aqueous solution some chromium cation, whilst part of the chromium is present as a complex ion. With weak acids, sulphurous, hydrocyanic, or thiocyanic acids, the chromic ion forms complex ions of great stability. Finally, a very large group of salts exists where chromium associated with ammonia forms the complex ion, the chromi-ammines. 

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