Hydrophilic and Hydrophobic Channels of Flexible Crystal Lattice: (Guanidinium)₂(Benzene-1,4-disulfonate)·n(XC₆H₅)

The −NH₂···[SO₃^–]– electrostatic hydrogen bonding interaction between guanidinium (G⁺) and benzene-1,4-disulfonate (BS^2–) formed the two-dimensional hydrogen-bonding network linked by benzene pillars, which formed a host–guest crystal with a halobenzene derivative (XC₆H₅) as a guest. When X = F, the (G⁺)₂(BS^2–)·3(FC₆H₅) crystals were obtained in the same type as the benzene inclusion (G⁺)₂(BS^2–)·3(C₆H₆) crystals. On the contrary, the size of the guest molecule increases for X = Cl and Br, and a hydrophilic channel with nine H₂O molecules and a hydrophobic channel with two XC₆H₅ molecules coexist in (G⁺)₂(BS^2–)·2(XC₆H₅)·9(H₂O) crystals. The crystal structure with X = I returned to that of the crystals with FC₆H₅ as the guest, and the number of guest molecules decreased from three to two. Crystals with hydrophilic channels in a highly symmetric hexagonal lattice appear at X = Cl and Br, which are the boundary region between X = F and I. (G⁺)₂(BS^2–)·2(ClC₆H₅)·9(H₂O) crystals changed to guest-free crystals by heat at 373 K, which showed only gate H₂O adsorption–desorption behavior at 298 K. The original host–guest crystals were recovered by the vapor diffusion of the ClC₆H₅–H₂O mixture. However, once the crystal is heated to 420 K, it changes to a different host crystal (G⁺)₂(BS^2–), where XC₆H₅ cannot be adsorbed again.