Lanthanide determination data interpretation

The interpretation of conductance data is complicated by the labile nature of the lanthanide complexes in solution which results in ligand exchange and dissociation reactions. It is difficult to understand the nature of the complex species present in solution. A combination of conductance data and molecular weight determination may be useful in determining the coordination number and structure of the complexes in solution. However, due to the poor solubility of lanthanide complexes in suitable solvents, molecular weight data have been obtained for only a few complexes. The dissociative reactions of lanthanide complexes in solution are well illustrated by the TPPO complexes of lanthanide isothiocyanates (202). In chloroform solution, the dissociation... 

The lanthanide compoimds imder consideration have a large number of excited electronic states (Kaledin et al., 1996a), which complicates the interpretation of spectroscopic data. In particular, the molecular constants for the groimd state cannot be always determined. The available data should be preliminarily tested for reliability, and missing data should be completed. To this end, a semiempirical approach is possible in which the results are checked for correspondence with the known principle of the change in a given parameter in a series of related compoimds. 

Thermodynamic data for the complexation of trivalent lanthanides by hexa-cyanoferrate(III) have been interpreted as supporting a model of outer-sphere ion-pairing of RFe(CN)j (Stampfli and Choppin, 1972). The stability constants for the interaction of Fe(CN)g and Co(CN)j ligands with selected R ions have been determined and for La at zero ionic strength the log values... 

---