Synthesis, crystal structure, and solid-state NMR spectroscopy of (4-HAP)(2)[Ga4O(PO4)(4)(H2O)(4)] (AP = aminopyridine), a gallophosphate containing discrete double-four-ring units

A new gallophosphate, (4-HAP)(2)[Ga4O(PO4)(4)(H2O)(4)] (designated NCUGa-1) , has been synthesized in the presence of 4-aminopyridine as the structure- directing agent. The structure consists of discrete Ga-4(PO4)(4)(H2O)(4) do uble-four-ring (D4R) units hosting O2- anions. Charge compensation is achie ved by the monoprotonated amine. Each D4R unit is linked to adjacent units and the organic cations via hydrogen bonding. Crystal data: (C5H7N2)(2)[Ga4 O(PO4)(4)(H2O)(4)], orthorhombic, space group Aba2 (no. 41), a = 18.879(4) Angstrom, b = 18,481(4) Angstrom, c = 7.469(1) Angstrom, V = 2606.1(9) Angs trom (3), Z = 4, R1 = 0.025, and wR2 = 0.062. H-1 MAS NMR confirms that pro tonation is on the pyridine nitrogen in aminopyridine. The proton-decoupled P-31 MAS NMR spectrum exhibits two resonances at 3.8 and 3.4 ppm with an i ntensity ratio of 1:1, corresponding to two distinct crystallographic P-31 sites. The information obtained from H-1 --> P-31 CP/MAS NMR experiments pr ovides insight into the interaction between the hydrogen atoms of the water molecules and/or the amine and the IT spins, and can be used to correlate P-31 resonances with crystallographic sites. In addition, Ga-71 MAS NMR con firms the presence of two, Ga sites.