Quantitative evaluation of Ln(III) pyridine N-oxide carboxylic acid spectra under chemometric and metrological aspects

Abstract

The interaction of Nd(III) with four carboxylated pyridine N-oxide derivatives in aqueous solutions is studied by UV–vis absorption spectroscopy. From factor analysis in combination with computer-intensive bootstrap resampling methods the empirical probability distributions of the formation quotients of the 1:1 Nd(III) complexes with nicotinic acid N-oxide ( I), picolinic acid N-oxide ( II), pyridine 2,4 dicarboxylic acid N-oxide ( III), and dicarboxylic acid 2,6 N-oxide ( IV) are evaluated. The strength of the interaction was found to correlate with the charge density around the coordinating groups. Charge density was calculated by ab initio methods using a polarised continuum model to account for solvation effects. Evidence for a 1:2 species with IV is presented. A speciation diagram for this model is obtained from the probabilistic speciation code LJUNGSKILE, which visualises the rather weak evidence for a two-species system. Thus, the formation quotients lg β 11 = 2.3 ± 0.0 5 ( I), lg β 11 = 2.7 ± 0.0 4 ( II), lg β 11 = 2.8 ± 0.0 5 ( III), and lg β 11 = 3.0 ± 0.0 5 ( IV) are found to describe the chemical systems satisfactorily.