Thermodynamic and kinetic effects of 12-membered macrocycles. Polarographic studies of 1,4,7,10-tetra-azacyclododecanecopper(II)
- 1 January 1976
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in J. Chem. Soc., Dalton Trans.
- No. 2,p. 116-120
- https://doi.org/10.1039/dt9760000116
Abstract
Thermodynamic parameters and reaction rates for complex formation between Cu2+ and 1,4,7,10-tetra-azacyclododecane (tcdd) have been determined polarographically. The stability constants (log K 24.8 at 25 °C) for the 1 : 1 complex is more than 104-fold greater than that for the corresponding open-chain tetra-amine, 3,6-diazaoctane-1,8-diamine (3,6NH-od). The enhanced stability with tcdd is entirely due to a more favourable entropy change, which is in sharp contrast to the 14-membered macrocyclic effect attributed to a more favourable enthalpy change by Hinz and Margerum. The rate constants are 1.84 × 106 and 1.80 × 10–1 dm3 mol–1 s–1 for the reaction of [Cu(O2CMe)]+ with Htcdd+ and H2tccd2+, respectively. The sluggishness with which the diprotonated species reacts suggests that the rate-determining step is an associative process, probably proton loss preceding second-bond formation. The increased stability constant of the 12-membered macrocyclic complex is reflected most in the dissociation rate constants.Keywords
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