The infrared absorption spectra of metal ammine complexes and related compounds.

The infrared absorption spectra of many metal ammine complexes of differing stabilities and steric configurations have been studied in the frequency range 4000 to 400 cm-1. The use of deuteration techniques has provided a direct means of identifying the nitrogen-hydrogen vibrations, and by com-paring the spectra of the ammines with those of simple molecules whose frequency assignments are definitely known, it has been possible to assign all the observed absorption bands to fundamental vibrations of the molecule. The metal-nitrogen vibration frequencies proved difficult to detect as the absorption bands produced were extremely weak, but these frequencies have now been identified for several of the more stable ammines, the assignment being confirmed by comparison with the Raman spectra of the same compounds. The variations in the absorption frequencies found for the ammines have been compared with their stabilities and it has been shown that with few exceptions the two properties show similar trends. The metal-nitrogen stretching frequencies are directly related to the strength of bonding of the ammonia group, and the effect of other substituents in the molecule on this bond has been examined. In this way it has been shown that some groups weaken the bonding of an ammonia molecule in the trans position, and this may contribute to the increased ease of substitution of the group. Other ligands where an almost complete frequency assignment of the absorption bands has been made include the nitro group and ethylene, the same method being used as for the metal ammines, i.e. comparison of the spectra of the complexes with those of simple molecules. Insufficient compounds of this type have been examined to observe any regularities in the spectra obtained. A preliminary study has also been made of ethylenediamine complexes