Ammines, of chromium

The ammines of chromium were first obtained by E. Fremy i in 1858, and they were soon afterwards studied by P. T. Cleve, and then by J. Morland, A. Eeineoke, and S. M. Jorgensen. A. Werner showed that as in the case of the cobalt, and platinum ammines, most of the chromium ammines fitted into the system based on his co-ordination theory—-8. 49, 19. I. I. ChernyefE studied the inner structure of the chromium ammines. Extensive investigations on the chromium ammines have been made by P. Pfeiffer and his fellow-workers, and the following summary is based on his reports ... 

Thermally, ammine complexes of chromium(III) containing a coordinated ligand X (where X is CL, CNS , etc.) undergo substitution of X by H20 in aqueous solution with retention of stereochemistry ... 

The chromi-ammines containing one atom of chromium in the molecule form by far the largest class of these additive compounds. 

A. Mononuclear Chromi-ammines containing One Atom of Chromium in the Molecule. 

The chromi-ammines show - very clearly the parallelism between hydrated salts and ammino-salts. It has been proved that water may be gradually substituted for ammonia in the metal-ammines, and in the hexammino-salts of chromium all degrees of substitution, with, the... 

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. 

Platinum forms both platinous and platinie salts, in which the metal is divalent and tetravalent respectively. Both series of salts are capable of uniting with ammonia, forming complex ammines. The co-ordination number in the platinous series is four and in the platinie series six. The latter series correspond in many respects to the chromic and cobaltic ammino-salts, but as the metal is tetravalent, the maximum number of radicles outside the complex is four instead of three. Also, the ammino-bases from which the salts are derived are much more stable than those of chromium or cobalt. 

Polynuclear chromium(III) ethylenediamine complexes have been synthesized by methods similar to those applied for the ammine systems by using the combined catalytic effect of chromium(II) and charcoal on aqueous ethylenediamine buffer solutions (pH -8) of chromium(III) (40, 42, 60). As mentioned above, the use of catalysts is important when equilibration between the mononuclear species is required, but it is unnecessary when the aim is to produce polynuclear species. In fact, identical polynuclear species are formed in approximately the same ratio when buffered chromium(III) solutions ([Cr] =0.1 M, [en = 0., i M) without catalyst are kept for a few days at 40 50 C (40). 

The difference in acid strength of the cis and trans isomers of (NH3)5Cr(0H)Cr(NH3)4(H20)5+ may be explained as an effect of the ligand trans to water. A comparison with the effect of trans ligand on the water ligand acidity observed for mononuclear ammine and amine complexes of chromium(III) or rhodium(III) (346) leads to the sequence Hi OH) < OH NH3 < H20 for increasing acidity due to the trans ligand. 

Abstract A brief review of my work with Carl Ballhausen in 1967-1968 and subsequent work. The assignments of the vibronic sidebands in the emission spectra of chromium ammine complexes are given with some comments on the Jahn-Teller effect in the emissive state. Energy transfer and cross relaxation phenomena are discussed and the shell model for this processes in lanthanide elpasolites is presented... 

---