%0 Journal Article %A Lawrance, GA %A Suvachittanont, S %T The preparation, aquation kinetics and activation volumes of trans-chloro-and trans-bromo-azido(meso-5,12-dimethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene)cobalt(III) perchlorate %J Australian Journal of Chemistry %D 1980/02/01 %V 33 %N 2 %P 273-278 %K %R https://doi.org/10.1071/CH9800273 %U https://www.publish.csiro.au/paper/CH9800273 %X The macrocyclic complexes trans-[Co(dtcd)(N3)X]ClO4 (dtcd = meso-5,12- dimethyl-1,4,8,11-tetra-azacyclotetradeca-4,11-diene; X = Cl- or Br-) have been prepared and characterized. Halide aquation in 0.1 M HNO3 at 25°C proceeds at rates of 4.6 × 10-4 s-1, ΔH‡ 77(±2) kJ mol-1, ΔS?-51(±6) J K-1 mol-1 (X = Cl-) and 10.2x10-4 s-1, ΔH‡ 80(±3) kJ mol-1, ΔS‡ -34(±10) J K-1 mol-1 (X = Br-). The pressure dependence of the aquation rate at elevated pressures yields ΔV‡ +8.3(±0.5) cm3 mol-1 (X = Cl-) and ΔV‡ +5.3(±0.7) cm3 mol-1 (X = Br-). While the observed positive ΔV‡ values are consistent with a dissociative mechanism they differ markedly from reported negative ΔV‡ values for acid hydrolysis of [Co(NH3)5X]2+ ions.