Hydrothermal Synthesis and Characterization of Two New Microporous Zinc-Substituted Gallium Phosphates Templated by Diaminocyclohexane:  (H₂DACH)₂[Zn₄Ga₂(HPO₄)₃(PO₄)₄] and (H₂DACH)[Zn₂Ga₂(PO₄)₄]

Abstract

Two new zinc-substituted gallophosphates, (H2DACH)2[Zn4Ga2(HPO4)3(PO4)4] (1) and (H2DACH)[Zn2Ga2(PO4)4] (2), have been synthesized under mild hydrothermal conditions and characterized by single-crystal X-ray diffraction, solid-state NMR spectroscopy, and thermogravimetric analysis. Both structures are built up with MO4 (M = Zn, Ga) and PO4 (or HPO4) tetrahedra. Compound 1 adopts a novel microporous framework which contains the highest transition-metal concentration of any MGaPO. The structure may be viewed as stacking of [Zn2Ga(HPO4)2(PO4)2]2 layers along a linked by extra HPO4 tetrahedra as pillars to generate intersecting 12-ring channels with dimensions ∼8.1 × 8.1 Å. Compound 2 has a CGS framework topology but a higher divalent-metal content than the isostructural materials of (C7NH14)[MGa3P4O12] (M = Co, Zn). Diprotonated 1,2-diaminocyclohexane (DACH) cations are ordered at the intersections of two interconnected channels in both 1 and 2. They represent the first zinc-substituted gallophosphate templated by dibasic amine and showing distinguishable Zn sites. The solid-state 31P MAS NMR spectrum of 1 showed a resonance for the HPO42- group that was shifted downfield by ∼8 ppm relative to the PO43- group. On the basis of the results of TG/DT analyses, both frameworks can be thermally stable up to ∼300 °C. Crystal data: 1, monoclinic, C2/c, a = 23.568(1) Å, b = 10.242(1) Å, c = 16.235(1) Å, β = 108.115(1)°, Z = 4; 2, monoclinic, P21/c, a = 14.320(1) Å, b = 16.255(1) Å, c = 8.855(1) Å, β = 90.134(1)°, Z = 4.