Journal of Photochemistry and Photobiology, A: Chemistry, 49 (1989) 195 - 202 195 PHOTODECARBOXYLATION OF CITRATE THROUGH ION PAIR PHOTOCHEMISTRY: THE Co( Sep)3+- CITgATE” - (n = 1,2,3) SYSTEM JOAO SOTOMAYOR Faculdade de Cie’ncias e Tecnologia da Universidade Nova de Lisboa, 2825 Monte de Caparica (Portugal) and Centro de Quimica Estrutural, Lisbon (Portugal) JtiLIA C. COSTA Faculdade de Ci&zcias e Tecnologia da Universidade Nova de Lisboa, 2825 Monte de Caparica (Portugal) QUINT0 G. MULAZZANI Istituto FRAE-CNR, Bologna (Italy) FERNANDO PINA Faculdade de Ci&acias e Tecnologia da Universidade Nova de Lisboa, 2825 Monte de Caparica (Portugal) and Centro de Qulinica Estrutural, Lisbon (Portugal) (Received December 8, 1988; in revised form March 14, 1989) Summary The Co( Sep)3+ complex (Sep = sepulchrate = 1,3,6,8,10,13,16,19-octa- azabicyclo [ 6.6.6leicosane) forms ion pairs with citrate in aqueous solution at @H 4.0, 5.6 and 8.5, where the forms CIT-, CIT2- and CIT3- (CIT = citrate) predominate respectively. Irradiation in the ion pair charge transfer band for the three pH values leads to the decarboxylation of citrate with the production of CO2 and Co(Sep) 2+ In the presence of colloidal platinum, . CO2 and H, are evolved. The quantum yields for formation of C02, Co( Sep)2f and H, were obtained and are discussed in terms of their depen- dence on pH. 1. Introduction Ion pair photochemistry may constitute a useful method for the devel- opment of photocatalysis using coordination compounds that do not meet the normal requirements, such as a long excited state lifetime, of a photo- sensitizer [ 1, 2 1. We have previously described the ion pair photochemistry of the Co(Sep)3+= C20e2- system [ 1] (Sep = sepulchrate = 1,3,6,8,10,13,16,19-octa- azabicyclo [ 6.6.61 eicosane). Hydrogen is evolved and the photocatalytic con- version of oxalate to carbon dioxide occurs, in the presence of platinum lOlO-6030/89/$3.50 @ Elsevier Sequoia/Printed in The Netherlands