We present herein the development of a new polycationic molecular receptor, inspired by the ubiquitous cyclobis­(paraquat-p-phenylene)­cyclophane (“blue box”). Our analogue, the “white box”, has been easily self-assembled on a preparative scale in water, using a template-assisted process by acyl hydrazone bonding of complementary bis­(pyridinium)­xylylene tweezers, followed by kinetic trapping of the empty receptor. The obtained macrocycle was found to display a marked pH responsiveness in water, because of an abnormal acidity of the amide protons within its structure. Consequently, and because of the concurrence of rotational isomerism under acidic conditions (fixed at higher pH values), the compound was found to display a dual behavior as a conformationally locked/flexible molecular host, being able to recognize appropriate aromatic substrates, in a lock and key or induced fit fashion, by a conjunction of π–π, C–H···π, and, crucially, the hydrophobic effect.

The adsorption mechanism of SO2 in the Hofmann-like coordination polymer Fe­(pz)­[Pt­(CN)4] is studied using inelastic neutron scattering and density functional theory calculations. We find that the most important spectral change upon gas adsorption is the blue shift of the low-energy peak found at 100 cm–1, a feature that is fully confirmed by the computed neutron-weighted phonon density of states. Our calculations suggest that the origin of this change is twofold: (i) an increase in the force constant of the cyanide out-of-plane movement due to the binding of the gas onto the Pt­(CN)4 plane and (ii) the hampered rotation of the pyrazine due to steric hindrance. The high-energy region of the neutron scattering data whose spectral weight is dominated by the internal vibrations of the pyrazine is negligibly affected by the presence of the gas as expected from a physisorption type of binding.