Hydrogen bond energies and cooperativity in substituted calix[n]arenes (n = 4, 5)

Hydrogen-bonded interactions in para-substituted calix[n]arenes (CX[n]) (n = 4, 5) and their thia analogues are analyzed using the recently proposed molecular tailoring approach. The cooperative contribution toward the hydrogen-bonding network within the CX[5] host is shown to be nearly 5 times larger than that in its thia analogue. Hydrogen bond strengths in the O-H···O network are enhanced on substitution of an electron-donating group. The cooperativity contributions are reflected in the electron density at the bond critical point in the quantum theory of atoms in molecules.