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A novel family of redox-active dinuclear copper(II)-based macrocycles self-assembled from dithiocarbamate ligands has been synthesised; a naphthyl-spaced complex exhibits selective electrochemical recognition of perrhenate and dihydrogenphosphate anions.

Chemical oxidation of two preformed dinuclear copper(II) dithiocarbamate macrocycles leads to the formation of a novel mixed-valence tetranuclear copper(II)/copper(III) dithiocarbamate [2]catenane in near quantitative yield. Structural (see X-ray crystal structure), magnetic susceptibility, electrospray mass spectrometry, and electrochemical studies all support the formation of a CuII CuIII CuII CuIII tetranuclear catenane dication.

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−3nBu4NClO4 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.

The Cu2+ complex of the ligand L1 (L1 = [Ru(tpycyclam)(mtpy)]2+, tpycyclam = 1-[4′-p-tolyl-(2,2′:6′,2′′-terpyridyl)]-1,4,8,11-tetraazacyclotetradecane and mtpy = 4′-methyl-2,2′:6′,2′′-terpyridine) is able to display a selective sensing response against anions such as ATP. The L1−Cu2+ system contains a Ru(tpy)22+ fluorescent core and a cyclam−Cu2+ subunit. The fluorescent response of the Ru(tpy)22+ core in an aqueous environment (acetonitrile/water, 70:30) is governed by the quenching produced by the Cu2+ cation. In the presence of anions the L1−Cu2+ system shows a rich emission fluorescent response. Electrochemical studies on the Cu(cyclam)2+ complex in propylene carbonate in the presence of certain anions allowed us to conclude that the interaction with the anions sulfate, phosphate, ATP, ADP and GMP is mainly electrostatic whereas chloride and bromide form axial covalent bonds with the copper atom in the Cu(cyclam)2+ complex. The addition of anions that coordinate at the axial positions of the square-planar Cu2+−cyclam subunit (such as Cl−, Br− and OH−) produced an enhancement of the emission intensity. This enhancement is attributed to the occupation of the apical positions of copper in the Cu2+−L1 complex that might reduce the probability of an interaction between the Cu2+ ions and the Ru(tpy)22+ groups reducing the quenching process and, consequently, resulting in an enhancement of the fluorescence. A prediction of the fluorescent behaviour with the anions sulfate, phosphate, ATP, ADP and GMP that give electrostatic interactions with the positively charged cyclam−Cu2+ and/or Ru(tpy)22+ centres is rather difficult. Potentiometric studies on the L1−Cu2+−H+−ATP system suggested that the [Cu(L1)(ATP)] complex is responsible for the quenching observed at basic pH in the presence of ATP. It is noticeable that the quenching of the intensity of the fluorescence due to ATP in the pH range 9 to 10 is selective and no other anion studied is able to quench the emission of the Ru(tpy)22+ core in this pH range.

The selective sensing of the ATP anion in an aqueous environment over phosphate, sulfate, and chloride using a fluorescence chemosensor based on Ru(tpy)22+ cores attached to polyammonium groups is reported.

Macrocyclic ligands L1–L4 containing biphenyl units have been synthesized. Potentiometric and voltametric studies in the presence and the absence of transition metal cations have been carried out. The relationship between the conformation of the ligand and oxidation states has been also considered. The crystal structure of [HgL2(CN)2]·2Hg(CN)2 has been elucidated by X-ray diffraction techniques.

Two new ligands 4 and 5 , containing in their structures aza-crown ethers moieties in addition to tetramethylbenzidine units, have been prepared. Their ability to complex transition metal cations has been studied by NMR and electrochemical techniques. Ligand 5 gives rise to two diastereoisomeric complexes with Cd(NO 3 ) 2 .

The reaction of 2,2′:6′,2″-terpyridinyl-4′-carboxaldehyde with the diamine N-methyl-1,3-propanediamine yields the terpyridine derivative containing amino groups 1-(2,2′:6′,2″-terpyridin-4′-yl)-2,6-diaza-2-methylcyclohexane (L1), whereas under similar experimental conditions the reaction of 2,2′:6′,2″-terpyridinyl-4′-carboxaldehyde with N,N-dimethylethylenediamine yields the expected 1-(2,2′:6′,2″-terpyridin-4′-yl)-2,5-diaza-5-methyl-hexa-1-ene (L2) imine and the [4′-COO-tpy][H3NCH2CH2N(CH3)2] salt (L3). The crystal structure of L3 was determined by X-ray single-crystal analysis. The structure consists of terpyridine carboxylate and protonated diamines linked together by ionic and hydrogen bonding interactions. The homoleptic complexes [Co(L1)2]2+ and [Fe(L1)2]2+ have been prepared. These contain peripheral amino groups and their interactions with protons and the anions ATP, chloride, sulphate and phosphate have been studied in acetonitrile and in THF:water (70:30 v/v) using electrochemical techniques.

The interaction of the ferrocene-functionalised polyaza receptor 1,4,8,11-tetrakis(4-ferrocenyl-3-azabutyl)-1,4,8,11-tetraazacyclotetradecane (L1) with sulfate, phosphate and ATP has been studied potentiometrically in THF–water 70∶30 v/v (0.1 mol dm–3 tetrabutylammonium perchlorate, 25 °C). The molecular structure of the free receptor has been determined by single-crystal X-ray procedures. An electrochemical study on L1 as a function of the pH has been carried out in THF–water 70∶30 v/v in the presence of the sulfate, phosphate and ATP anions. The potential use of L1 as an anion sensing receptor is discussed in terms of the electrochemical and potentiometric data and its behaviour is compared with those of related redox-active polyammonium receptors.

A new family of aza-oxa open-chain and macrocyclic molecules functionalised with ferrocenyl groups have been synthesized and characterised. The crystal structures of the [HL1][PF6], [H2L3][PF6]2, [H2L4][PF6]2 and [H2L5][PF6]2 salts have been determined by single crystal X-ray procedures {L1 = 10-ferrocenylmethyl- 1,4,7-trioxa-10-azacyclododecane, L3 = 7,13-bis(ferrocenyl)-1,4,10-trioxa-7,13-diazacyclopentadecane, L4 = 1,8-bis[bis(ferrocenylmethylamino)]-3,6-dioxaoctane, L5 = 1,8-bis(ferrocenylmethylamino)-3,6-dioxaoctane}. They consist of cationic protonated amines linked via ionic interactions with hexafluorophosphate anions. Additionally hydrogen-bonding interactions have also been found. The receptors have been designed to promote discrimination, using electrochemical techniques, between toxic heavy metal ions such as Hg2+ over other commonly water present cations in aqueous environments. The presence in the receptors of oxygen and nitrogen donor atoms has been used to control the selectivity of large metal ions over small ones. Potentiometric and electrochemical studies have been mainly carried out to find pH ranges of selective electrochemical recognition. Potentiometric titrations were carried out in water (25°C, 0.1 mol dm-3 potassium perchlorate) for L1 and L2 [1,1′-(5,8-dioxa-2,11-diazadodecane-1,12-diyl)-ferrocene] and in 1,4-dioxane-water (25°C, 0.1 mol dm-3 potassium nitrate) for L3 and L5 with Ni2+, Cu2+, Zn2+, Cd2+, Pb2+ and Hg2+. All receptors show larger stability constants with Hg2+ than with the remaining metal ions studied. This is especially so for L1 and L2. The receptors L1, L2 and L5 are able electrochemically and selectively to sense the presence of Hg2+, whereas maximum electrochemical shifts are produced in L3 upon addition of Pb2+. Of importance is the large and selective electrochemical shift monitored in water for L2 and Hg2+ with an anodic displacement of the oxidation potential of ca. 130 mV which is one of the largest shifts ever reported in electrochemical cation sensing in water using related receptors. A good agreement has been found between potentiometric and electrochemical results. Selective electrochemical response against Hg2+ appears to be associated with (i) pH ranges of selective complexation or (ii) the existence of strong predominant receptor-metal complexes in a wide pH range. Additionally the electrochemical behaviour of receptors L1 and L2 in the presence of metal ions can be roughly predicted from potentiometric data. The stability constants of the complexes between L1 and Cu2+, Cd2+, Pb2+ and Hg2+ were also determined in the presence of Cl-. Whereas there is no important change in the stability constants of the L-H+-M2+ systems when M2+ = Cu2+, Cd2+ or Pb2+, there is a decrease of the co-ordination ability of L1 towards Hg2+. This is also reflected in electrochemical studies which demonstrate that [Hg(L1)]2+ electrochemically sense Cl- at pH 7. To the best of our knowledge this is the first time it has been shown that metal complexes functionalised with ferrocenyl groups can electrochemically sense anions.

The reaction of 4′-methyl-2,2′:6′,2″-terpyridine with ferrocenecarbaldehyde in the presence of lithium di-isopropyl-amide allowed us to isolate the ferrocene-functionalised terpyridine derivative 4′-[2-ferrocenyl-2-hydroxyethyl]-2,2′:6′,2″-terpyridine (L1) in a 80% yield. Dehydration of L1 with pyridinium toluene-p-sulphonate yielded the corresponding ferrocenylvinyl derivative 4′-ferrocenylvinyl-2,2′:6′,2″-terpyridine, (L2). Their spectroscopic and electrochemical characterisation and the synthesis of homoleptic complexes of L1 and L2 in acetonitrile has been carried out. The oxidative electropolymerisation of L2 and the enhancement or inhibition of the polymerisation process due to the presence of different transition metal ions is also reported.

New open-chain polyazaalkane N-terminal ferrocene-functionalised receptors, L1, L2 and L3, have been synthesized and characterised and their potential use as selective anion and cation sensing receptors in aqueous solution investigated. Solution studies by potentiometric methods have been carried out in the presence of H+ and Cu2+ in water (25 °C, 0.1 mol dm–3 KNO3). The results have been compared with those of the analogous non-functionalised receptors triethylenetetramine (L4), tetramethylenepentamine (L5) and N,N″‴-dimethylpentaethylenehexamine (L6). Compounds L1–L3 form both mono- and di-nuclear complexes with Cu2+. The electrochemical responses as a function of the pH in the presence of the Ni2+, Cu2+, Zn2+, Cd2+ or Pb2+ cations in water and the ATP, phosphate, sulfate and nitrate anions in thf–water (7∶3 v/v, 25 °C, 0.1 mol dm–3 [Bun4N][ClO4]) for L1, L2, L3 and for 1,4,7,10,13,16-hexaferrocenyl-1,4,7,10,13,16-hexaazacyclooctadecane (L7) in 1,4-dioxane–water (7∶3 v/v, 25 °C, 0.1 mol dm–3 KNO3) have also been determined. The studies have been directed to determine the pH ranges of selectivity in the electrochemical recognition of cations and anionic guests, pointing out the ability of molecules L1–L3 and L7 to act as selective anion-sensing or cation-sensing receptors. The anion ATP can be selectively detected using the L2 receptor in the presence of the competing anions phosphate and nitrate.

Chemical oxidation of two preformed dinuclear copper(II) dithiocarbamate macrocycles leads to the formation of a novel mixed-valence tetranuclear copper(II)/copper(III) dithiocarbamate [2]catenane in near quantitative yield. Structural (see X-ray crystal structure), magnetic susceptibility, electrospray mass spectrometry, and electrochemical studies all support the formation of a Cu

The redox-active polyazacyloalkane 1,4,8,11-ferrocenylmethyl-1,4,8,11-tetraazacyclotetradecane L 1 is a versatile receptor for the quantitative electrochemical determination of metal ions (Cu 2+ , Zn 2+ , Cd 2+ ) and ATP in aqueous solution.

A synthetic strategy has been devised for the preparation of new compounds in which terpyridyl fragments are linked to 1,4,8,11-tetraazacyclotetradecane (cyclam). Reaction of excess cyclam with 4′-[(4-bromomethyl)phenyl]-2,2′:2″,6′-terpyridine afforded the ligand 1-[4′-p-tolyl-(2,2′:6′,2″-terpyridyl)]-1,4,8,11-tetraazacyclotetradecane (L1) in which the tetraaza macrocycle was covalently attached to one benzyl-terpyridyl fragment. Under similar conditions reaction of cyclam with excess 4′-[(4-bromomethyl)phenyl]-2,2′:2″,6′-terpyridine gave the tetra substituted cyclam derivative 1,4,8,11-[4′-p-tolyl-(2,2′:6′,2″-terpyridyl)]-1,4,8,11-tetraazacyclotetradecane (L2). The multidentate ligand L2 was crystallographically characterised by single-crystal X-ray diffraction techniques. Reaction of L1 with [Ru(mtpy)Cl3] gave the heteroleptic ruthenium(II) complex [Ru(L1)(mtpy)][PF6]2 (mtpy = 4′-methyl-2,2′:6′2″-terpyridine). The fluorescent intensity of the metallo-receptor [Ru(L1)(mtpy)][PF6]2 was quenched selectively in the presence of copper(II) in an aqueous environment. To gain insight into the nature of this interaction, potentiometric titrations on [Ru(L1)(mtpy)]2+ in the presence of Cu2+ were carried out. The quenching of the emission intensity was associated with the presence of the copper {Cu[Ru(L1)(mtpy)]}4+ complex in solution. The receptor 1-[4′-methyl-(2,2′:6′,2″-terpyridyl)]-1,4,8,11-tetraazacyclotetradecane (L3), in which the cyclam fragment is separated from the terpyriyl by a methylene group, has also been synthesised by reaction of 4′-bromomethyl-2,2′:2″,6′-terpyridine and cyclam. With L3 as starting material, the ruthenium complex [Ru(L3)(mtpy)]2+ was prepared in order to evaluate the effect that the nature of the spacer has on the quenching of the fluorescence upon addition of Cu2+.

The redox-functionalised polyazacycloalkane receptor 1,4,7,10,13,16-hexa(ferrocenylmethyl)-1,4,7,10,13,16-hexaazacyclooctadecane (L1) has been designed and synthesized and its binding, electrochemical and metal extraction properties studied. The results have been compared to those obtained for the parent redox-active polyazacycloalkane 1,4,8,11-tetra(ferrocenylmethyl)-1,4,8,11-tetraazacyclotetradecane, L3. The cadmium complex of L1 and the free receptor L3 have been crystallographically characterised. The structure of [CdL1][PF6]2·4CH3CN·4H2O consists of cationic [CdL1]2+ units in which the cadmium ion exhibits a distorted octahedral environment. Solution studies by potentiometric methods have also been carried out in the presence of H+ and Cu2+ in 1,4-dioxane–water (70∶30 v/v, 25 °C, 0.1 mol dm–3 KNO3) for L1 and thf–water (70∶30 v/v, 25 °C, 0.1 mol dm–3 [NBun4][ClO4]) for L3. Electrochemical experiments as a function of the pH in the presence of Ni2+, Cu2+, Zn2+, Cd2+ or Pb2+ have been carried out for L1 and L3. The solvent extraction properties of L1 have also been studied.

Reactions of 4′-[4-(bromomethyl)phenyl]-2,2′:6′,2′′-terpyridine with 4,10-diaza-15-crown-5 and 1-aza-12-crown-4 in dichloromethane yielded the ligands L1 and L3, respectively. Reaction of an excess of 4′-[4-(bromomethyl)phenyl]-2,2′:6′,2′′-terpyridine with 4,10-diaza-15-crown-5 yielded L2, while treatment of the same terpyridine ligand with 1,4,7,10,13-pentaazacyclopentadecane afforded L4. Reactions of L1, L3, and L4 with Ru(mtpy)Cl3 (mtpy = 4′-methyl-2,2′:6′,2′′-terpyridine) in methanol yielded the metallo receptors [Ru(L1)(mtpy)][PF6]2, [Ru(L3)(mtpy)][PF6]2, and [Ru(L4)(mtpy)][PF6]2 after precipitation with ammonium hexafluorophosphate and column chromatography. On treating L3 with RuCl3, the homoleptic ruthenium complex [Ru(L3)2][PF6]2 was obtained. The synthesized metallo receptors contain oxa-aza crown or polyazacycloalkane moieties as recognition sites and [Ru(tpy)2]2+ cores as the signal-generating centre. The electronic spectra of the complexes are as expected for an Ru(tpy)22+ chromophore, with the main Ru[d(π)] tpy(π*) MLCT transition at ca. 484 nm and intense ligand-centred transitions in the UV region. One of the most interesting aspects of these ruthenium complexes is their multicomponent nature, as they contain both coordination sites and fluorescent Ru(tpy)22+ cores. The cations [Ru(L1)(mtpy)]2+, [Ru(L3)(mtpy)]2+, and [Ru(L3)2]2+ display an emission maximum at ca. 650 nm, the intensity of which is pH dependent, showing an enhancement upon protonation. The metallo receptor [Ru(L1)(mtpy)]2+ selectively senses Hg2+ in preference to Cu2+, Cd2+, and Pb2+. The emission intensity vs. pH curve for [Ru(L2)(mtpy)]2+ in the presence of Cu2+ and Hg2+ ions is close to that of the free receptor, but the presence of Cd2+ or Pb2+ enhances the emission intensity in the range pH 4−6. For the [Ru(L3)2]2+ complex, Cd2+, Pb2+, and Hg2+ induce an enhancement of the fluorescence of the Ru(tpy)22+ core in the range pH 3.5−7.5. These results are compared with those obtained for the metallo receptor [Ru(L4)(mtpy)]2+ containing a polyazacycloalkane moiety as the binding domain.