Host hydrated barium phenylphosphonate/guest heterocyclic amine intercalation energetics by calorimetric titration

The heterocyclic amines 2,6-lutidine, pyrazine, piperazine and piperidine were intercalated into layered crystalline hydrated barium phenylphosphonate, Ba(HO₃PC₆H₅)₂·H₂O, through a batch method in ethanolic solution, to give the maximum amounts 0.39, 0.82, 2.80 and 5.50 mmol g⁻¹, respectively. The original host interlayer distance (d) of 1532 pm increased after intercalation for piperazine (1752 pm) and piperidine (2112 pm) molecules, while for 2,6-lutidine and pyrazine molecules d values were maintained. The enthalpy of intercalation gave −5.60 ± 0.10, −1.00 ± 0.02, −9.55 ± 1.00 and −30.70 ± 0.68 kJ mol⁻¹ for the sequence of heterocyclic amines. The Gibbs free energies are negative and entropies are positive for intercalation.