Good correlation between the calculated gas-phase first proton macroaffinities of some triazacycloalkanes ([X]aneN3, XÂ =Â 9-12) with their protonation constants in solution

A theoretical study on first protonation step of a series of triazacycloalkanes with general formula {([X]aneN3, X = 9-12)} (X = 9, L222; X = 10, L223; X = 11, L233; X = 12, L333) is reported. The geometry of all ligands and their monoprotonated forms were fully optimized at both the Hartree-Fock and DFT (B3LYP) levels of theory using 6-31+G∗ basis set. Then the first proton macroaffinities were calculated from the proton microaffinities according to defined equations. It is shown that there are good correlations between the calculated gas-phase first proton macroaffinities of these ligands with their protonation constants in solution.