Pulse radiolysis and laser flash photolysis have been used to generate and characterize Ni(cyclam)+, where cyclam is 1,4,8,11-tetraazacyclotetradecane, in aqueous solution. Reduction of Ni(cyclam)2+ was carried out at ambient temperature (22 ± 2 °C) by solvated electrons, eaq", hydrogen atoms, H", and carbon dioxide radical anions, C02-. Reduction by eaq~o ccurs with a rate constant of (4.1 ± 0.2) x 1010 M_1 s_1 (7 < 2 x -4 M). Reduction by C02*_ and H' proceeds via an inner-sphere mechanism to yield [Ni(cyclam)(C02)]+ and [Ni(cyclam)(H)]2+, with rate constants of (6.7 ± 0.2) x 109 and (5 ± 2) x 109 M_l s_1, respectively. Decomposition of the adducts, to yield Ni(cyclam)+ and C02 or H+, proceeds with rate constants of (2.0 ± 0.2) x 106 and (5.3 ± 0.7) x 105 s_l, respectively.Carbon dioxide and proton dissociation constants for [Ni(cyclam)(C02)]+ and [Ni(cyclam)(H)]2+ were found to be (6.2 ± 0.3) x 10-2 and (1.6 ± 0.4) x 10-2 M, respectively. The rate constants for the addition of C02 and H+ to Ni(cyclam)+ were calculated to be (3.2 ± 0.4) x 107 and (3 ± 1) x 107 M-1 s_1, respectively. The selective reduction of C02 by Ni(cyclam)+ in the presence of protons at pH 4 is rationalized.

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The reduction of CO 2 and H + by Ni(cyclam) + in aqueous solution was found to proceed by the reduction of Ni(cyclam)(CO 2 ) + or Ni(cyclam)(H) 2+ by Ni(cyclam) + . At ambient temperature the rate constants for the bimolecular reactions are 1.6 × 10 8 and 7.2 × 10 7 M -1 s -1 , respectively. Continuous γ-radiolysis studies have demonstrated nearly quantitative formation of CO from two Ni(cyclam) + at pH 5.2 under 1 atm of CO 2 and in the presence of formate. Under the same conditions, but at low CO 2 concentration, the reduction of protons was found to compete with CO 2 reduction.

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The new heteronuclear complexes Rum(CoL3)2X3 (L = 2-mercaptoethylamine( 1 -); X = I~, BPha") have been prepared and characterized and found to be analogous to the previously prepared Fe(III) complexes. A study of the electron spin resonance of these unique Fe(III) and Ru(III) species indicates that they are severely distorted from octahedral geometry, a fact responsible in part for their room-temperature spectra and that substantial metal-metal interaction occurs via direct metal orbital-metal orbital overlap. Ffyperfine structure from two equivalent Co nuclei indicates that the unpaired electron is delocalized over all three metal ions in the complex. A comparison with other systems is given.