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Chiral tripodal ligands having an asymmetric center are used as chiral solvating agents for sulfoxides and metal ion sensing. Tetradentate TPA coordination compounds have solid state structures containing 5-, 6-, and 7-coordinate metal ions exhibiting coordination geometries. A set of tripodal ligands were studied to provide a detailed analysis of their conformational behavior and to determine factors dictating the axial chirality of the complexes.

The enthalpies of ionization of zinc-bound water in the complexes (ZntrenOH2)2+ and (ZnMe6trenOH2)2+ are determined by titration calorimetry and potentiometric methods. The difference in the zinc-water acidity is due to enthalpic effects. High acidity of the complex (ZnMe6trenOH2)2+ compared to (ZntrenOH2)2+ is due to the low inonization enthalpy of the former. The observed enthalpic control denotes the ability of coordination complex to stabilize charge.

The crystallographic analysis indicates that Zn(II) and Cu(II) complexes of tripodal ligands containing an alkyl substituent on one arm posses helical asymmetry with the handedness characterized by the configuration of the chiral carbon atom. The study investigates a means to control the direction of the propeller twist, providing a route to coordination with highly asymmetric environments around the electrophilic coordination site of the metal ion. The asymmetric, propeller-like conformation of TPA derivatives when complexed with Zn(II) and Cu(II) ions is studied.