Ligational properties of two new phenolic aza cages towards proton and alkali metal ions - a theoretical and an experimental approach

Molecular Dynamics (MD) simulations were performed on several species (anio n, zwitterion, and neutral metal complexes) of two phenolic aza cages (L1 a nd L2) in aqueous solution. The anionic species of the smaller L1 ligand ap pears to be able to selectively encapsulate Lif, while the other alkaline m etal ions tested (Na+ and K+) are too large to be encapsulated. The larger cage L2 does not show any selectivity; the anion binds all the alkaline met al ions. The two aza cages L1 and La were synthesized. Both basicity and al kali metal complex formation were studied in aqueous solution at 25 degrees C in 0.15 mol dm(-3) Me4NCl, using potentiometric, W/Vis- and NMR-spectrosc opic techniques. Both cages behave as triprotic bases in the pH range inves tigated; logK(1) = 12.15(6), logK(2) = 7.39(5), logK(3) = 1.4(1) for L1 and logK(1) = 11.76(5) logK(2) = 8.24(5), logK(3) = 2.9(2) for L2. The last pr oton cannot be removed because both compounds are strongly basic under the experimental conditions studied. Proton localization was studied by UV/Vis and NMR spectroscopy, both in water and nonaqueous solutions. The crystal s tructures of [HL1](ClO4) and [NaL2](ClO4) were determined by X-ray analysis . The crystals of [HL1](ClO4) are triclinic, space group P(I); cell paramet ers are a = 10.3628(8), b = 11.938(1), c = 12.201(4) Angstrom, alpha = 117. 53(1), beta = 101.25(1), gamma = 102.774 degrees. The crystals of [NaL2](Cl O4) are monoclinic, space group P2(1)/n; cell parameters are a = 10.6154(7) , b = 17.0418(9), c = 14.9452(9) Angstrom, beta = 95.634(6)degrees.