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The outer-sphere redox behaviour of a series of [L n Co IIINCFe II (CN) 5 ] − (L n = n-membered pentadentate aza-macrocycle) complexes have been studied as a function of pH and oxidising agent. All the dinuclear complexes show a double protonation process at pH ഠ 2 that produces a shift in their UV/Vis spectra. Oxidation of the different non-protonated and diprotonated complexes has been carried out with peroxodisulfate, and of the non-protonated complexes also with trisoxalatocobaltate ( oxidants, has been carried out as a function of pH, temperature, and pressure. As a whole, the values found for the activation volumes, entropies, and enthalpies are in the follow-

The cyano-bridged complexes [L14CoIIINCFeII(CN)5]-, [L14CoIIINCFeIII(CN)5], [L15CoIIINCFeII(CN)5]-, and [L15CoIIINCFeIII(CN)5] (L14 = 6-methyl-1,4,8,11-tetraazacyclotetradecan-6- amine, L15 = 10-methyl-1,4,8,12-tetraazacyclopentadecan-10-amine) are prepared and characterized both structurally and spectroscopically. In each complex, the pendant amine is trans to the bridging CN ligand, as determined by spectroscopy and X-ray crystallography: Na(trans-[L14CoIIINCFeII(CN)5]).8H2O, monoclinic space group P2(1)/c, a = 15.58(1) A, b = 19.797(4) A, c = 19.830(6) A, beta = 91.62(4) degrees, Z = 8; trans-[L14CoIIINCFeIII(CN)5].4H2O, monoclinic space group P2(1)/m, a = 9.9690(9) A, b = 13.316(1) A, c = 10.1180(8) A, beta = 90.720(6) degrees, Z = 2; [L15CoIIINCFeIII(CN)5].4H2O, triclinic space group P1, a = 9.454(1) A, b = 9.778(1) A, c = 9.865(2) A, alpha = 60.37(1) degrees, beta = 62.60(1) degrees, gamma = 65.82(1) degrees, Z = 1. A precursor to the 14-membered macrocyclic complexes is prepared for the first time, and its crystal structure is also reported: trans-I [CoL14Cl](ClO4)2, orthorhombic space group Pbca, a = 11.833(3) A, b = 13.363(2) A, c = 26.015(2) A, Z = 8. These compounds form part of a novel series of discrete CN-bridged dinuclear compounds. The mixed-valent CoIII-FeII compounds exhibit metal-to-metal charge-transfer (MMCT) transitions in the region 510-530 nm.

The cyano-bridged complexes cis-[L 14 Co III NCFe II (CN) 5 ] Ϫ and cis-[L 14 Co III NCFe III (CN) 5 ] (L 14 = 6-methyl-1,4,8,11tetraazacyclotetradecan-6-amine) are prepared and characterised spectroscopically, electrochemically and structurally: Na{cis-[L 14 Co III NCFe II (CN 1), b = 14.709(2), c = 18.760(3) Å, Z = 4. In both complexes, the pendant amine is cis to the bridging cyanide ligand. An analysis of the metal-to-metal charge transfer (MMCT) transition in these systems with Hush theory has been carried out. This has revealed that the change in the configuration of the macrocycle both decreases the redox isomer energy difference (∆E 1/2 ) and increases the reorganisational energy (λ) of the cis-[L 14 Co III NCFe II -(CN) 5 ] Ϫ complex with respect to the trans-[L 14 Co III NCFe II (CN) 5 ] Ϫ complex, the result being that both isomers display an MMCT transition of similar energy. The variation in redox isomer energy differences of the configurational isomers has been related to strain energy differences by molecular mechanics analysis of the [CoL 14 Cl] 2ϩ/ϩ precursor complexes. DALTON