Ionic recognition by 7-nitro-1,3,5-triaza adamantane: first thermodynamic study.

A thermodynamic study involving 7-nitro-1,3,5-triaza adamantane, 1, and its interaction with metal cations in nonaqueous media is first reported. Solubility data of 1 in various solvents were used to derive the standard Gibbs energies of solution, DeltaG(s)o in these solvents. The effect of solvation in the different media was assessed from the Gibbs energy of transfer taking acetonitrile as a reference solvent. 1H NMR studies of the interaction of 1 and metal cations were carried out in CD3CN and CD3OD and the data are reported. Conductance measurements revealed that this ligand forms lead(II) or zinc complexes of 1:1 stoichiometry in acetonitrile. It also revealed a stoichiometry of two molecules of 1 per mercury(II) and two cadmium (II) ions per molecule of 1. The addition of silver salt to 1 led to the precipitation of the silver-1 complex which was isolated and characterized by X-ray crystallography. At variance with conductance measurements in solution, in the solid state the X-ray structure shows a 1:1 stoichiometry in the Hg(II) complex. The thermodynamics of complexation of 1 and these cations provide a quantitative assessment of the selective behavior of this ligand for ions of environmental relevance.