Synthesis, crystal structure, and solid-state NMR spectroscopy of K2[Ga4(C2O4)(PO4)4]·2H2O, a new gallium phosphatooxalate with an intersecting tunnel structure

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Abstract

A new gallium phosphatooxalate, K2[Ga4(C2O4)(PO4)4]·H2O, has been synthesized hydrothermally and characterized by single-crystal X-ray diffraction and solid-state NMR spectroscopy. It crystallizes in the triclinic space group P-1 (No. 2) with a = 7.9863(4), b = 8.2458(5), and c = 8.7631(5) Å, α = 116.075(1)°, β = 100.825(1)°, and γ = 104.033(1)°, V = 473.3(1) Å 3, and Z = 1. The structure consists of GaO6 octahedra and GaO4 tetrahedra connected by coordinating C2O42- and PO43- anions to generate intersecting channels in the three-dimensional framework with guest water molecules and the charge compensating K+ cations within the channels. The water molecules and K+ cations sites are half occupied. 1H MAS NMR confirms two different sites for water molecules and also shows that one is more mobile than the other. Three 31P resonances at -10.9, -12.3, and -14.9 ppm are observed at room temperature; the resonance at -14.9 ppm splits into two peaks at 375 K. These four 31P resonances, which have nearly the same intensity, result from different local environments due to the ordering of the water molecules and K+ cations. The information obtained from 1H → 31P CP/MAS experiments provides insight into the interaction between the guest water molecules in the structural tunnels and the phosphates in the framework. 71Ga MAS NMR confirms the presence of four- and six-coordinated Ga atoms.

Original languageEnglish
Pages (from-to)2411-2417
Number of pages7
JournalChemistry of Materials
Volume12
Issue number8
DOIs
StatePublished - 2000

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