DALTON FULL PAPER DOI: 10.1039/b000079p J. Chem. Soc., Dalton Trans., 2000, 1805–1812 1805 This journal is © The Royal Society of Chemistry 2000 Anion interaction with ferrocene-functionalised cyclic and open-chain polyaza and aza-oxa cycloalkanes Paul D. Beer,* a James Cadman, a José Manuel Lloris, b Ramón Martínez-Máñez,* b Juan Soto, b Teresa Pardo b and M a Dolores Marcos c a Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, UK OX1 3QR. E-mail: paul.beer@inorganic.chemistry.oxford.ac.uk b Departamento de Química, Universidad Politécnica de Valencia, Camino de Vera s/n, 46071 Valencia, Spain. E-mail: rmaez@qim.upv.es c Institut de Ciència dels Materials de la Universitat de València (ICMUV), PO Box 2085, 46071 Valencia, Spain Received 6th January 2000, Accepted 24th March 2000 A family of ferrocene-functionalised receptors of different topologies have been used as receptors for anions. The compounds have been designed to contain both amine nitrogen and ether oxygen atoms and comprises from monoaza to pentaaza derivatives both open-chain (L 1 , L 2 , L 3 ) or cyclic (L 4 , L 5 ) and having from one to five ferrocenyl groups. Solution studies directed to determine the protonation constants of L 1 , L 2 and L 3 have been carried out in water (0.1 mol dm -3 KNO 3 , 25 °C) and those of L 4 and L 5 in 1,4-dioxane–water (70:30 v/v, 0.1 mol dm -3 KNO 3 , 25 °C). The protonation behaviour of the receptors can be explained taking into account electrostatic considerations. Speciation studies in the presence of phosphate have been carried out in water for L 1 , L 2 and L 3 and in dioxane–water for L 4 and L 5 . Speciation studies have also been performed in the presence of ATP with L 1 , L 2 and L 3 in water. Selectivity of a mixture of receptors against a certain anion is discussed in terms of ternary diagrams. The shift of the redox potential of the ferrocenyl groups as a function of the pH has been studied. The difference between the oxidation potentials at basic and acidic pH has been determined experimentally and is compared with that theoretically predicted using an electrostatic model previously reported. The electrochemical shift in the presence of ATP and phosphate has been measured in water for L 1 , L 2 and L 3 and in the presence of phosphate and sulfate in 1,4-dioxane–water for L 4 and L 5 as a function of the pH. The electrochemical response found against those anions is quite poor with maximum cathodic shifts of ca. 30–40 mV. The electrochemical response induced by HSO 4 - and H 2 PO 4 - has also been studied in acetonitrile solutions where a large cathodic shift for H 2 PO 4 - up to ca. 200 mV was found. Introduction Designing of molecules containing appropriate signalling subunits has been a synthetic strategy for the development of new sensing receptors of application in sensor technologies. In these systems, co-ordination of the target guest to the binding sites followed by a further interaction of the complex with the covalently attached signalling subunits allows transformation of chemical information into a measurable signal. The possibil- ity of modulation of the co-ordination sites, the nature and number of signalling units (bearing in mind that external fac- tors such as for example the solvent may also influence) makes the number of potential receptors very large and the search for selective receptors against target substrates a challenge. Among different signalling subunits described in the literature there is an increasing interest for redox-active groups. 1–7 In these sys- tems the signalling effect is based on the fact that co-ordination can induce a shift of the redox potential of the electroactive subunits. A number of works have allowed the synthesis of suitable and selective receptors that electrochemically can recognise cationic, 8–16 anionic 17–21 and neutral 22,23 molecules. New advances in this area would probably involve the use of different not well studied redox-active units and the search for potential applications as electrochemical sensors based on amperometric measurements. With the aim of advance in the knowledge of redox-active ferrocene-functionalised systems and taking into account that relatively little effort has been devoted to the study of their anion sensing ability in water, 24–39 we report here a solution and electrochemical study on a family of new receptors in the presence of some anions such as ATP, phosphate and sulfate. The receptors have been designed to contain both amine nitrogen and ether oxygen atoms and com- prise from monoaza to pentaaza derivatives both open-chain or cyclic, having from one to five ferrocenyl groups. Experimental Physical measurements Potentiometric titrations were carried out in water (0.1 mol dm -3 KNO 3 ) for L 1 , L 2 and L 3 and in 1,4-dioxane–water (70 : 30 v/v, 0.1 mol dm -3 KNO 3 ) for L 4 and L 5 using a reaction vessel water-thermostatted at 25.0 ± 0.1 °C under a nitrogen atmos- phere. Experimental potentiometric details have been published previously. 36 The concentration of the metal ions was deter- mined using standard methods. The computer program SUPERQUAD 40 was used to calculate the protonation and stability constants. The titration curves for each system (ca. 250 experimental points corresponding to at least three titration curves, pH = -log [H] range investigated 2.5–10, concentration of the ligand and metal ion being ca. 1.2 × 10 -3 mol dm -3 ) were treated either as a single set or as separated entities without significant variations in the values of the stability constants. Finally the data sets were merged and treated simultaneously to give the stability constants. Electrochemical data were obtained in water, 1,4-dioxane–water (70:30 v/v) and in dry acetonitrile, with a programmable function generator Tacussel IMT-1, connected to a Tacussel PJT 120–1 potentiostat. The working electrode was platinum with a saturated calomel reference electrode separated from the test solution by a salt bridge