COOPERATIVE INTERACTIONS BETWEEN LONE AND WATER IN THE CHLORIDE-ION AND WATER COORDINATION TO A SQUARE-PLANAR NICKEL-COMPLEX ION IN CONCENTRATED AQUEOUS-SOLUTIONS

In concentrated aqueous solutions (1-6 mot dm(-3)) of various kinds of salts such as sodium chloride, calcium chloride, tetramethylammonium chloride and sodium perchlorate, salt effects on coordination of the c hloride ion and water to [Ni(tmc)](2+) (tmc: ,11-tetramethyl-1,4,8,11- tetraazacyclotetradecane) have been investigated spectrophotometricall y. In water at 25 degrees C 63% of the nickel complex is coordinated b y water as a five-coordinate species. Addition of perchlorates to the complex solution decreases the fraction of the five-coordinate complex without shifting the absorption peaks and 6.5 mol dm(-3) perchlorate gives 100% of the four-coordinate species. With sodium chloride, the f raction of the four-coordinate species is increased with concomitant r ed shifts in wavelength and decreases in absorbance at the absorption peaks for the five-coordinate species. On the other hand, tetramethyla mmonium chloride decreases the fraction of the four-coordinate species with similar red shifts of the five-coordinate peaks. The red shift i s attributed to coordination of the chloride ion. The different effect caused by sodium chloride compared with tetramethylammonium chloride is discussed in terms of the difference in cooperative interactions be tween the chloride ion and the counter-cations through hydrated water molecules.