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Host-guest inclusion complex formation of tetraoxacalix[2]arene[2]triazine (1) with anions X(CH 3 COO−, ClO 4 −, BrO 4 −, IO 4 −, SO 4 2−, SO 3 2−, CO 3 2−, SiO 3 2−) was studied by DFT calculations at M062X/6-311+G** level, together with their equilibrium geometries, binding energies and electronic structures. MESP, NCI-RDG and AIM topography analysis were performed to explore underlying interactions. The inclusion complexes in 1:1 ratio were stabilized through a cooperative effect of non-covalent interactions, including anion-π, σ-interactions, hydrogen bonds and van der Waals interactions. The recognition process of anions within 1 was spontaneous both thermodynamically and dynamically. The structure of molecule 1 changed slightly after encapsulation, reflected in IR and NMR spectra. After complexation, the red shifts of C H stretching and triazine rings bending in IR were attributed by hydrogen bonds and anion-π interactions. Anions encased in the host cavity exhibited magnetic shielding; those bifurcate hydrogen bonds could cause chemical shifts signals in 1H NMR spectra. • Tetraoxa[2]arene[2]triazine can selectively recognize anions. • The anion-π interactions and hydrogen bonds maintain the stability of the system. • The recognition process accompanied with electron transfer and redistribution. • The solvents weaken the binding interaction significantly. • The shifts of IR and NMR spectra are obvious makers of the combination. [ABSTRACT FROM AUTHOR]

Two novel cocrystals were successfully constructed by 1(2H)-Phthalazinone (PHT) and Tetrafluoroterephthalic acid (TETA) based on O–H⋯O, N–H⋯O, C–H⋯O, C–H⋯F, N–H⋯N and C–H⋯N hydrogen bonding networks, and were well depicted by single crystal diffraction analysis. As predicted by electrostatic potential analysis, the stoichiometry of PHT to TETA is 2:1 and stabilized by O–H⋯O and N–H⋯O hydrogen bonds. The single crystal X-ray diffraction characterized that the two cocrystals were all made up by 2PHT-TETA motif in different ways. AIM analysis and Hirshfeld surfaces indicated the adjacent 2PHT-TETA units assemble through C–H⋯O, C–H⋯F and C–H⋯N hydrogen bonds, producing a 2D plane structure in cocrystal I. Meanwhile, the C–H⋯F, N–H⋯N and C–H⋯O hydrogen bonds between 2PHT-TETA units were the stabilizing factors in cocrystal II. Topological parameters such as ∇ 2 ρ and H revealed the strength of hydrogen bonds were moderate in nature except O31⋯H32–O34 (1.704Å, −60.336 kJ mol−1) in compound I. The hydrogen bonding interactions, cocrystal stability and electron donor-acceptor interactions were investigated using natural bonding orbital analysis. It showed that electron transfer of n(O) σ*(O–H) and n(O) σ*(N–H) between PHT and TETA influence the packing characteristics significantly. Structural changes accompanying cocrystal process have been rationalized through the IR spectrum along with the quantum chemical calculations. The frequency downshifts of C O, N–H and O–H stretching after cocrystallization have been attributed to hydrogen bonding interactions. Image 1 • Cocrystals of 1(2H)-Phthalazinone and Tetrafluoroterephthalic acid have been found. • 2PHT-TET motif contains N–H⋯O, O–H⋯O intermolecular hydrogen bonds. • Two cocrystals are made up by 2PHT-TET motif in different ways. • DFT calculations are performed to analysis the characteristics hydrogen bonds. • Downshifts of C O, N–H and O–H are attributed to the hydrogen bonding interactions. [ABSTRACT FROM AUTHOR]