Immobilisation of electroactive macrocyclic complexes within titania films

The 4-carboxyphenyl-appended macrocyclic ligand trans-6,13-dimethyl-6-((4-carboxybenzyl)amino)-1,4,8,11- tetraazacyclotetradecane-6-amine (HL¹⁰) has been synthesised and complexed with Co^III. The mononuclear complexes [Co(HL¹⁰)(CN)]²⁺ and [CoL¹⁰(OH)]⁺ have been prepared and the crystal structures of their perchlorate salts are presented, where the ligand is bound in a pentadentate mode in each case while the 4-carboxybenzylsubstituted pendent amine remains free from the metal. The cyano-bridged dinuclear complex [CoL¹⁰-μ-NCFe( CN)₅]²⁻ was also prepared and chemisorbed on titania-coated ITO conducting glass. The adsorbed complex is electrochemically active and cyclic voltammetry of the modified ITO working electrode in both water and MeCN solution was undertaken with simultaneous optical spectroscopy. This experiment demonstrates that reversible electrochemical oxidation of the Fe^II centre is coupled with rapid changes in the optical absorbance of the film.