CORRELATION OF THE ASYMMETRIC AND SYMMETRICAL POO- FREQUENCIES WITH THE IONIC POTENTIAL OF THE METAL-ION IN COMPOUNDS OF ORGANOPHOSPHORUS ACID EXTRACTANTS - A SHORT REVIEW

The correlation between [(nu(asym)(POO-) - nu(sym)(POO-)], Delta nu, a nd the ionic potential of the metal ion in metal compounds of alkylsub stituted diphosphonic acid extractants is reviewed. Similar correlatio ns of the ionic potential of the metal ion with Delta v in organosubst ituted monophosphate, organosubstituted monophosphonate, carbonate and nitrate compounds have been previously demonstrated. In this paper, w e discuss the origin, general validity, and utility of the correlation for organophosphorus compounds. Far-infrared and Fe-54-labeled data w ere used to identify metal-oxygen stretching vibrations and establish that for some metal ions, e.g., Fe(III) and possibly Th(IV), the metal -oxygen interaction has substantial covalent character. The correlatio n appears to be valid not only for materials in which the metal-oxygen interaction is predominantly ionic, but also for compounds characteri zed by a covalent metal-oxygen bonding as well as for polymeric materi als, providing the POO- stretching vibrations are assignable. The corr elation is useful in identifying changes in M-O bonding across a serie s of complexes containing similar metals (i.e., lanthanides and actini des), as well as in making comparisons for differences in M-O bonding when the charge on the metal ion changes. The correlation becomes part icularly useful for compounds where no X-ray data are available.