Estimation of free energies of anion transfer from solid-state electrochemistry of alkynyl-based Au(I) dinuclear and Au(I)–Cu(I) cluster complexes containing ferrocenyl groups Antonio Doménech a, ⁎, Igor O. Koshevoy b , Noemí Montoya c , Tapani A. Pakkanen b a Departament de Química Analítica, Facultat de Química, Universitat de València, Dr. Moliner 50, 46100 Burjassot, Valencia, Spain b Department of Chemistry, University of Eastern Finland, FI-80101, Joensuu, Finland c Departament de Química Inorgànica, Facultat de Química, Universitat de València, Dr. Moliner 50, 46100 Burjassot, Valencia, Spain abstract article info Article history: Received 8 November 2010 Received in revised form 12 November 2010 Accepted 17 November 2010 Available online 25 November 2010 Keywords: Ion solvation Thermochemistry Electrochemical anion insertion Alkynyl metal complexes Heterometallic clusters Ferrocenyl units A method is presented to determine the free energy for anion transfer between two solvents. This is based on solid-state electrochemistry of alkynyl-based dinuclear Au(I) complexes (AuC 2 R) 2 PPh 2 C 6 H 4 PPh 2 (L1: R = Fc; L2:R=C 6 H 4 Fc) and heterometallic Au(I)–Cu(I) [{Au 3 Cu 2 (C 2 R) 6 }Au 3 (PPh 2 C 6 H 4 PPh 2 ) 3 ](PF 6 ) 2 (L3: R = Fc; L4: R=C 6 H 4 Fc) complexes. These compounds exhibit a reversible ferrocenyl-centred solid-state oxidation processes involving anion insertion in contact with aqueous, MeOH and MeCN electrolytes. Voltammetric data can be used for a direct measurement of the free energy of ion transfer using midpeak potentials in solutions of suitable salts in the solvents separately or in mixtures of the solvents. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The determination of Gibbs free energies of ion transfer between two solvents is of fundamental importance for understanding the behaviour of pharmacokinetics, biological ion channels, solvent extraction techniques, phase transfer catalysis, and ion-selective electrodes [1]. Such quantities are determinable from partition, solubility, etc. data only for electrolytes and electroneutral combinations of ions, so that the separation into contributions from individual ions is conventionally accomplished by using the single-ion solvation free energy of one reference ion; quantities for other individual ions are then obtainable from appropriate thermochemical cycles. Consequently, single-ion thermochemical properties can only be evaluated by introducing extra-thermodynamic assumptions [1]. These last usually consist of quantum mechanics calculations to describe the solvent portion in the vicinity of the ion and classical continuum modelling of the solvent relatively far from the ion [2–8]. Electrochemical measurements have been also widely used for determining individual ion thermochemical properties. The electrochemical methods all rely on extra-thermodynamic assumptions, which, however, are very well reasoned. Recent approaches involve, among others, membrane- modified liquid–liquid interfaces [9], micro/nanohole [10,11], and triple-phase boundary measurements [12–15]. Here we suggest a new approach to determine the free energy for anion transfer between two solvents. Partial (vide infra) overcoming of extra-thermodynamic assumptions is obtained by using the anion- insertion solid-state electrochemistry of a series of recently synthesized alkynyl-based dinuclear Au(I) complexes (AuC 2 R) 2 PPh 2 C 6 H 4 PPh 2 (L1: R=Fc; L2: R=C 6 H 4 Fc) and the heterometallic Au(I)–Cu(I) [{Au 3 Cu 2 (C 2 R) 6 }Au 3 (PPh 2 C 6 H 4 PPh 2 ) 3 ](PF 6 ) 2 (L3: R = Fc; L4:R=C 6 H 4 Fc) cluster complexes containing ferrocenyl units [16]. Using the voltammetry of microparticles approach developed by Scholz et al. [17], such complexes display a solid-state oxidation where the electron transfer process is accompanied by highly selective anion insertion [18] prompting their use as potentiometric sensors [19] using the methodology developed by Bond et al. [20]. 2. Experimental section Synthesis and characterization of L1-L4 complexes was performed as previously described [16]. Electrochemical measurements were performed at 0.10 M solutions of NaF, NaCl, NaBr, KBr, LiClO 4 , NaClO 4 , LiNO 3 , NaNO 3 , Et 4 NClO 4 , Bu 4 NOAc, Bu 4 NClO 4 , and Bu 4 NPF 6 in water, MeOH and MeCN. Voltammetry of microparticles experiments were performed at complex-modified paraffin-impregnated graphite elec- trodes using a CH I660 potentiostat. Electrode modification was Electrochemistry Communications 13 (2011) 96–98 ⁎ Corresponding author. Tel.: +34 963544533; fax: +34 96354436. E-mail address: antonio.domenech@uv.es (A. Doménech). 1388-2481/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2010.11.023 Contents lists available at ScienceDirect Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom