Syntheses and structures of two open-framework zinc phosphites with extra-large 24-ring channels

Two new three-dimensional open-framework zinc phosphites, [HCHA]2[Zn3(HPO3)4] (1) and [HCHPA]2[Zn3(HPO3)4] (2), have been synthesized under hydrothermal conditions, where CHA = cyclohexylamine and CHPA = cycloheptylamine. Both compounds are isostructural and exhibit a similar three-dimensional 3, 4-connected framework constructed by strictly alternating ZnO4 tetrahedra and HPO32−HPO32− pseudopyramids. The occurrence of extra-large tubular channels constructed by the concatenation of 24- and 30-ring windows along the [001] direction in the two structures is very unusual in known extra-large micropore materials. Crystal data: 1, rhombohedral, R-3, a = 32.9618(5) Å, c = 13.2818(3) Å, V = 12497.1(4) Å3, Z = 18, R1 = 0.0445, wR2 = 0.1068; 2, rhombohedral, R-3, a = 33.2184(4) Å, c = 13.1697(6) Å, V = 12585.3(6) Å3, Z = 18, R1 = 0.0401, wR2 = 0.0974.

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► Two open-framework zinc phosphites were synthesized under hydrothermal conditions.
► Extra-large 24-ring channels were observed in the structures.
► The extra-large tubular channels widen and shrink periodically.
► Sizable openings coexist even with the extra-framework cations present.