| Popis: |
In coordinating solvents, the complex 1, 4, 8, 11- tetramethyl-1, 4, 8, 11-tetraazacyclotetradecane nickel(II) bisperchlorate exists as an equilibrium mixture involving four coordinate R,S,R,S-[Ni(tmc)]2+ and five coordinate R,S,R,S-[Ni(tmc)(solvent)]2+ species. Spectrophotometric measurements of this equilibrium in a number of solvents have been conducted over a range of temperatures and pressures. The stability order for the five coordinate complex in the solvents investigated is CH3CN>DMF>DMSO>C6H5CN> H2O>ClCH2CN at 25 °C. Differences in stability are considered in terms of the measured thermodynamic parameters ΔH° and ΔS°. Both steric and electronic factors were found to influence solvent coordination with the macrocyclic complex. For the equilibrium in CH3CN, C6H5CN, DMF and H2O, reaction volumes, ΔV°, of −3.2±0.5, −4.2±0.5, −0.2±0.5 and −0.5±0.5 cm3 mol−1 respectively have been determined. Each is significantly smaller than the corresponding solvent molar volume. The ΔV° for the equilibrium in CH3CN is comparable with the previously determined activation volume for exchange of this solvent on R, S, R, S- [Ni(tmc)(CH3CN)]2+. The equilibrium and measured volume parameters are discussed in relation to the mechanism for solvent exchange. |
