resorcinarene and acetonitrile

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 Ti(3+) 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 Ti(3+) 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 (ΔH(c)(0), ΔS(c)(0)) for formation of the CMCR-Ti(3+) 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.

Topics: Acetonitriles; Calixarenes; Coordination Complexes; Electric Conductivity; Phenylalanine; Solutions; Solvents; Thermodynamics; Titanium; Water

Solid C-methylcalix[4]resorcinarene solvated by acetonitrile and water (CAL-Me) and then modified by slow solvent evaporation (CAL-Me*) was studied using single-crystal and powder X-ray diffraction, FT-IR, and (13)C CP/MAS NMR. The CAL-Me solvate crystallizes in the monoclinic P2(1)/n space group with three CH(3)CN and two H(2)O molecules in the asymmetric part of the unit cell. The CAL-Me molecules adopt a typical crown conformation with all of the hydroxyl groups of the aryl rings oriented up and all of the methyl groups disposed down (the rccc isomeric form). The crystalline network is formed by resorcinarene, CH(3)CN, and H(2)O molecules and assembled by intermolecular hydrogen bonds and weak C-H...A or C-H...pi interactions. The desolvated CAL-Me* loses its crystalline character and becomes partly amorphous. It is devoid of CH(3)CN and deficient in water. However, the resorcinarene molecules still remain in the crown conformation supported by intramolecular hydrogen bonds, while intermolecular hydrogen bonds are considerably disintegrated. The work directs general attention to the problem of stability and polymorphism of resorcinarene solvates. It shows that the joint use of diffractometric and spectroscopic methods is advantageous in the structural studies of complex crystalline macromolecular systems. On the other hand, the solid-state IR and NMR spectroscopic analyses applied in tandem have been found highly beneficial to elucidate the disordered structure of poorly crystalline, desolvated resorcinarene.

Topics: Acetonitriles; Calixarenes; Crystallography, X-Ray; Hydrogen Bonding; Molecular Structure; Nuclear Magnetic Resonance, Biomolecular; Phenylalanine; Solvents; Spectroscopy, Fourier Transform Infrared; X-Ray Diffraction