Proton Magnetic Resonance and Optical Spectroscopy of [Ni(MeOH)5Cl]+ in Methanol

Abstract

A proton magnetic resonance and optical spectroscopy study of the complex formation of Ni2+ with Cl− in methanol is reported. NMR studies were made between − 70° and + 100°C. At low temperatures (below − 20°C) in solutions containing both Ni2+ and Cl− it is possible to detect an NMR signal due to a superposition of the solvation shells of [Ni(MeOH)6]2+ and of [Ni(MeOH)5Cl]+. Between − 15° and + 30°C fast exchange smears out the part of the peak due to the monochloro complex; from the decrease in the intensity of the remaining signal, equilibrium constants as function of temperature are determined. From the variation of the bulk-methanol NMR linewidth and frequency shift with temperature the following kinetic parameters and hyperfine interaction constants for the solvation-shell molecules of [Ni(MeOH)5Cl]+ are found: specific rate of exchange at 25°C, 2.3 × 105sec−1; activation energy for the exchange reaction, 15.8 kcal mole−1; hyperfine interaction constants for the methyl and hydroxyl protons, + 0.51 and + 0.37 Mc/sec, respectively. Optical spectroscopy measurements were made at − 40°, + 23°, and + 50°C. Analysis of these data provided evidence that the nickel–chlorine complex formed is a monochloro pseudo-octahedral complex, i.e. [Ni(MeOH)5Cl]+.