The coordination behaviour of the ditopic receptor of 1‐[p‐(2,2′:6′,2′′‐terpyrid‐4′‐yl)tolyl]‐1,4,8,11‐tetraazacyclotetradecane (L1) towards Co2+ in acetonitrile/water (70:30, v/v) has been investigated. At acidic pH values, the L1−H+−Co2+ system shows an oxidation wave at 150 mV vs. SCE, characteristic of Co2+ in a bis(terpyridine) environment. Upon addition of OH−, a reduction in the intensity of the wave at 150 mV is observed and a new oxidation wave appears at 1.30 V. This new wave is close to that found for [Co(cyclam)]2+ under similar working conditions. The electrochemical data thus suggest that there is a pH‐controlled translocation of the Co2+ ion from the bis(terpyridine) to the cyclam environment. A similar inference can be made from the results of UV/Vis studies. A thermodynamic characterization of the L1−H+−Co2+ system has also been carried out. Stability constants have been determined in acetonitrile/water (70:30, v/v, containing 0.1 mol dm−3 nBu4NClO4 at 25 °C) using potentiometric techniques. The following species were found: [Co(L1)2H4]6+, [Co(L1)2H3]5+, [Co(L1)H]3+, [Co(L1)]2+, and [Co(L1)(OH)]+. The 2:1 ligand‐to‐metal species [Co(L1)2H4]6+ and [Co(L1)2H3]5+ are assigned to complexes where Co2+ is coordinated by two terpyridine units. The [Co(L1)H]3+, [Co(L1)]2+, and [Co(L1)(OH)]+ species are assigned to complexes where the Co2+ cation is in the cyclam binding domain. The pH‐induced Co2+ jumping between coordination sites is discussed in terms of the different basicities of cyclam and terpyridine. Co2+ jumping between coordination sites has also been studied by the sequential acidification of basic mixtures of L1 and Co2+. Under these conditions, the translocation was observed at a different pH value than when an acid‐to‐basic path was followed. The effect of anions such as phosphate and chloride on the translocation process has also been studied. In the presence of phosphate, translocation occurs at pH = 11 rather than at pH ≈︁ 8. The phosphate−L1 and phosphate−L1−Co2+ systems have been characterized by potentiometry and a remarkably good agreement has been found between the electrochemical and potentiometric data.

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The reaction of 1,1'-ferrocene-bis(methylenepyridinium) salt with 1,4,8,11-tetraazacyclotetradecane-5,12-dione, followed by LiAlH4 reduction results in the formation of FcCyclam. Metal complexes of FcCyclam with M2+ = Co2+, Ni2+, Cu2+, and Zn2+ were synthesized from FcCyclam and the respective metal triflates. The complexation of Cu2+ and FcCyclam in CH3CN is preceeded by a rapid electron transfer, followed by a slower complex formation reaction and a reverse electron transfer. The protonation constants of FcCyclam and the stability constants for the Cu2+ complex of FcCyclam (logK = 9.26(4) for the formation of the [Cu(FcCyclam)]2+ complex) were determined in 1,4-dioxane/water 70:30 v/v, 0.1 moldm(-3), KNO3, 25 degrees C. By using FcCyclam one can selectively sense the presence of Cu2+ ions in the presence of Ni2+, Zn2+, Cd2+, Hg2+, and Pb2+ with a very large deltaE approximately 200 mV, depending on pH. The X-ray crystal structures of FcCyclam and of complexes with Co2+, Ni2+, Cu2+, and Zn2+ were determined and Fe-M2+ distances obtained: Fe-Co2+ 395.9, Fe-Ni2+ 385.4, Fe-Cu2+ 377.7, and Fe-Zn2+ 369.0 pm. The redox potential of FcCyclam is influenced in a characteristic manner by the complexation of M2+. A linear correlation of 1/r approximately/= deltaE [r = distance Fe-M2+ from crystal data, deltaE=-E1/2([M(FcCyclam)]2+) - E1/2(FcCyclam)] was found; this is indicative of a mainly Coulomb type interaction between the two metal centers. The nature of the Fe...M2+ interaction was also investigated by determining deltaE in several solvents (mixtures) of different dielectric constants epsilon. The expected relation of deltaE approximately/= 1/epsilon was only found at very high values of epsilon. At epsilon < 40 increased ion-pairing appears to reduce the effective positive charge at M2+ leading to progessively smaller values of deltaE with lowered epsilon. The dependence of deltaE and epsilon can be calculated semiquantitatively by combining the Fuoss ion-pairing theory with the Coulomb model.

The new ligands 13-anthrylmethyl-7-ferrocenylmethyl-1,4,10-trioxa-7,13-diaza-cyclopentadecane (L 1 ) and 1-anthrylmethyl-4,8,11-ferrocenylmethyl-1,4,8,11-tetraaza-cyclotetradecane (L 2 ) have been synthesised, characterised, and their potential activity as chemosensors towards the metal cations Ni 2+ , Cu 2+ , Zn 2+ , Cd 2+ , Hg 2+ and Pb 2+ studied in 1,4-dioxane/water (70:30, v/v). Both ligands L 1 and L 2 are difunctionalised receptors containing redox-active (ferrocene) and fluorescent (anthracene) signalling subunits. The crystal structures of [H 2 L 1 ][PF 6 ] 2 and [CuL 2 ][PF 6 ] 2 were determined by single-crystal X-ray procedures. Potentiometric experiments in dioxane/water (70:30, v/v; 0.1 M KNO 3 ; 25.0 ± 0.1°C ) for L 1 and L 2 allowed the determination of protonation constants and complex stability constants with the Cu 2+ and Pb 2+ metal ions. They form stable complexes with both ligands and show stability constants with values close to those reported for similar complexes. The electrochemical and fluorescence behaviour of L 1 and L 2 was studied as a function

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