Chloro complexes of cobalt(II) in aprotic solvents: stability and structural modifications due to solvent effect

Cobalt(II) chloro complexes were studied in aprotic solvents, namely, dimethylsulfoxide (DMSO), dimethylformamide (DMF), and propylene carbonate (PC). The measurements were performed spectrophotometrically in UV–visible–IR region at 25°C and at constant ionic strength: I = 1 mol L−1 in DMSO and DMF, and 0.1 mol L−1 in PC. Different models were tested and the model 1, 2, 3, 4, i.e., that of four mononuclear successive complexes was retained. Stability constants of the identified complexes were determined and they increase inversely with the Gutmann\u27s donor number of the solvents. Calculated electronic spectra are reported and the effect of solvents on the spectral properties are discussed. The symmetry of tetrachlorocobaltate is strictly Td

pH-metric study of the complexation equilibria of alkaline-earth cations with [1]- and [2]- cryptands in methanol

The stability constants of the complexes of the alkaline-earth cations Mg2+, Ca2+, Sr2+ and Ba2+ with the monocyclic cryptands 11, 21 and 22 and the bicyclic cryptands 211, 221 and 222 were determined by pH-metry at 25 °C. The results confirm, within experimental uncertainties, most of those which were previously established by a competitive potentiometric method using Ag+. or estimated. Selectivity, size charge and solvent effects, as well as the magnitude and thermodynamic origin of the macrobicyclic effect, are discussed