Abstract
Calixresorcinarenes have proved to be unique molecules for molecular recognition via hydrogen bonding, hydrophobic and ionic interactions with suitable substrates such as cations. The study of the interactions involved in the complexation of different cations with calixresorcinarenes in solvent mixtures is important for a better understanding of the mechanism of biological transport, molecular recognition, and other analytical applications. This article summarizes different aspects of the complexes of the Ti3+ metal cation with c-methylcalix[4]resorcinarene (CMCR) as studied by conductometry in acetonitrile (AN)–water (H2O) binary mixtures at different temperatures. Conductance data show that the metal cation/ligand (ML) stoichiometry of the complexes in solution is 1:1 in all cases. Non-linear behaviour was observed for the variation of logKf of the complexes vs. the composition of the binary solvent mixtures. Selectivity of CMCR for the Ti3+ cation is sensitive to solvent composition; in some cases and at certain compositions of the mixed solvent systems, the selectivity order is changed. Values of thermodynamic parameters (,) for formation of the CMCR–Ti3+ complexes in AN–H2O binary systems were obtained from the temperature dependence of stability constants, and the results show that the thermodynamics of complexation reactions are affected by the nature and composition of the mixed solvents.
Highlights
Investigations with calixarenes and calixresorcinarenes have demonstrated the versatility of these molecules in supermolecular host–guest chemistry [1]. c-Methylcalix[4]resorcinarene (CMCR, Figure 1) is an excellent building block for the construction of a variety of hydrogen-bonded networks, thanks to the large number of hydroxyl groups along its rim, allowing it to act as a hydrogen bond donor in producing extended structures or binding ligands to give an extended cavity capable of taking up large guests, such as ferrocene [2]
The results could be useful for applications such as the fabrication of ion selective electrodes (ISEs) based on macrocyclic ionophores for determining titanium ions in real samples [17,18,19]
Ti(OH)(OH2)52+ cation ([L]t/[M]t, where [L]t is the total concentration of the ligand and [M]t is the total concentration of the titanium (III) ion) for the complexation reactions were measured in pure AN and in AN–H2O binary systems at three different temperatures
Summary
Investigations with calixarenes and calixresorcinarenes have demonstrated the versatility of these molecules in supermolecular host–guest chemistry [1]. c-Methylcalix[4]resorcinarene (CMCR, Figure 1) is an excellent building block for the construction of a variety of hydrogen-bonded networks, thanks to the large number of hydroxyl groups along its rim, allowing it to act as a hydrogen bond donor in producing extended structures or binding ligands to give an extended cavity capable of taking up large guests, such as ferrocene [2]. Shivanyuk et al have reported the ability of CMCR to adopt the boat conformation without forming the brick walls described by Coppens in his investigations of bipyridyl-type ligands [4] In this instance, chloride ions served to extend the boat-shaped cavity to allow accommodation of the triethylammonium ion. Several groups have studied the novel resorcin[4]arenes, and their complexation with alkali metal ions, especially with potassium ions [6,7] Due to this fact, many researchers have examined a wide range of applications for these macrocyclic compounds in different areas, such as the construction of ion selective electrodes (ISEs) [8], separation of metal cations [9], as stationary phases in chromatography columns [10], in the design of chemical sensors [11], recognition of isomers [12], and chemical analysis [13]
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