O(1,4,8,11-TETRAAZACYCLOTETRADECANE)MANGANESE(III) CHLORIDE - CIS-TRANS ISOMERIZATION EVIDENCED BY INFRARED AND ELECTROCHEMICAL STUDIES

The isomers cis- and o(1,4,8,11-tetraazacyclotetradecane)manganese(III ) chloride have been synthesized and characterised. An isomerisation o f the type cis-Mn-III --> trans-Mn-III was observed by IR spectroscopy . Recrystallisation of the cis species gave systematically crystals of the trans derivative. The crystal structure of the latter complex has been determined. An electrochemical study of the trans-manganese(III) complex in dimethyl sulfoxide revealed a rare trans, cis isomerisatio n reaction which proceeds through an electrochemical step-chemical ste p mechanism. The overall first-order rate constant, k(iso), for this i somerisation was determined by simulation of the chronoamperometric da ta. Supplementary electrochemical information for the ti.ans-manganese (III) isomer was obtained through simulation of the cyclic voltammogra ms over a large range of scan rates. No influence of chloride ion conc entration was observed as determined by cyclic voltammetry using an in ternal chloride standard, [N(PPh3)(2)]Cl. The cyclic voltammogram of t he ro(1,4,8,11-tetraazacyclotetradecane)manganese(II) generated in sit u displays the usual cis --> trans isomerisation which also occurs via an electrochemical step-chemical step mechanism.