
TY  - JOUR
A1  - Hambley, TW 
A1  - Lawrance, GA 
A1  - Sangster, DF 
A1  - Ward, CB 
T1  - Characterization, Redox Properties and Pulse-Radiolysis Study of Dichloro-(Tetraazacyclotetradecane)Manganese(III) Complexes, and X-Ray Crystal-Structure of the <I>meso</I>-5,7,7,12,14,14-Hexamethyl-1,4,8,11-Tetraazacyclotetradecane Complex
JF  - Australian Journal of Chemistry
JO  - Aust. J. Chem.
Y1  - 1987
VL  - 40
IS  - 5
SP  - 883
EP  - 893
KW  - 
UR  - https://doi.org/10.1071/CH9870883 
N2  - The complexes [Mn ( mac )Cl2]+ [ mac = 1,4,8,1l-tetraazacyclotetradecane (cyclam), meso and rac-5,7,7,12,14,14-hexamethylcyclam ( teta and tetb respectively)] have been prepared. The trans-[ Mn ( teta )Cl2] Cl.3H2O complex crystallizes in the monoclinic space group P21 /c, Z 2, a 8.4006(8), b 12.465(2), c 11 .659(2) Å, &#946; 103.20(1)º. The geometry about the manganese(III) is close to octahedral with the macrocycle coordinated to four equatorial sites ( Mn -N 2.043(2), 2.074(2) Å) and chlorides in trans axial sites (Mn -Cl 2.549(1) Å. Since electronic spectra of the cyclam and teta complexes are similar, the ions should exist in similar geometries; however, the tet b analogue is spectroscopically unique, and the complex may adopt a different geometry. All complexes in water exhibit quasi-reversible one-electron couples near O V at a mercury electrode; irreversible reductions of manganese(II) are also observed before the solvent limit near -1.5 V for the teta  and tet b complexes. No metal-centred oxidation waves are seen before the solvent limit (c.+ 1 V) at a platinum electrode. However, pulse radiolytic oxidation (with OH) of all complexes is observed with formation kf > 109 dm3mol-1 s-1; apparently d3 manganese(IV) monomers with electronic spectra qualitatively similar to d3 chromium(III) complexes are formed. Decay of these intermediates is first-order, with all kd  &#8805; 5&#215;103 s-1, but varying with the macrocyclic ligand present. Alkyl substitution on the cyclam stabilizes the manganese(IV) oxidation state, the intermediate cyclam complex decaying 25 times faster than the teta analogue. The final decay product appears to be MnO2, and rate-determining ligand loss is presumed. 
ER  -

