Characterization of complexes formed between [Me2Sn(IV)]2+ and carboxymethylcelluloses.

Abstract

Complexes formed between carboxymethylcellulose (CMC) and the [Me2Sn(IV)]2+ cation have been prepared in the solid state and characterized by FTIR and Mössbauer spectroscopy. The complexes contained CMC with varying molar weight and degree of carboxylation, and the complexes were isolated both from acidic and from neutral solutions at varying metal-to-ligand ratios. The characteristic vibration bands of the ligands were identified from their pH-dependent FTIR spectra. In the organotin(IV) complexes obtained at pH ∼2, the –COO− moieties were found to be coordinated in a monodentate manner, and the band characteristic of the protonated (unbound) –COO− group(s) was also identified. The broad –OH band can be interpreted as the sum of the contributions of the alcoholic –OH groups of the anhydroglucose units and the mixed organotin aqua complexes. In complexes obtained at pH ∼7, the broad –OH band significantly sharpens, which is probably due to the metal-ion induced deprotonation and subsequent coordination of the alcoholic –OH groups. At the same time, –COO− groups are also involved in the coordination of the metal ions, resulting in a complicated network that forms through inter- and intramolecular bridges. Quadrupole splitting (∣Δexp∣) values observed by Mössbauer spectroscopy revealed that the valence state of tin is four in all of the complexes. The ∣Δexp∣ values were compared with the calculated ones, obtained from the pqs theory. From these data, trigonal bipyramidal (Tbp) and octahedral (Oh) geometries have been suggested for the complexes obtained. It has also been concluded that the structure of the complexes prepared depends mainly on the pH of the solution, and it is relatively insensitive to the other parameters, like molar mass or degree of carboxylation of the ligand, or the metal-to-ligand ratio in the reaction mixture