Concise template syntheses of gallium phosphates driven by in situ direct alkylation of aliphatic and aromatic precursors by methanol

Abstract

A family of open-framework gallium phosphates (GaPOs), namely [dmdabco]_0.5[Ga(HPO₄)₂] (1, dmdabco = N,N′-dimethyl-1,4-diazabicyclo[2,2,2]octane), [tmpip]_0.5[Ga₃(OH)(PO₄)₃]·(H₂O)_0.25 (2, tmpip = N,N,N′,N′-tetramethyl-piperazinium), [mpy][Ga₃F(PO₄)₃]·(H₂O)_0.25 (3, mpy = N-methyl-pyridine), [dmbpy]_0.5[Ga₂(HPO₄)₂(PO₄)] (4, dmbpy = N,N′-dimethyl-4,4′-bipyridine), and [Hmpip]₂[Ga₇(OH)(PO₄)₆(HPO₄)₂] (5, mpip = N-methylpiperazine) have been fabricated under hydro(solvo)thermal conditions and structurally characterized. The in situ-template-synthesis strategy is firstly used to construct the gallium phosphates. The in situ generated dmdabco²⁺, tmpip²⁺, mpy⁺ and dmbpy²⁺ templates were derived from the methylation of two distinct types of organic-amine precursors under methanol media: aliphatic 1,4-diazabicyclo[2,2,2]octane (dabco) in 1, 1,4-dimethylpiperazine or 1-methylpiperazine or piperazine (pip) in 2, and aromatic pyridine (py) in 3 and 4,4′-bipyridine (bpy) in 4. Such a unique in situ methylation feature is different from classic Eschweiler–Clarke methylation in which excessive formic acid and formaldehyde is needed. Compound 1 exhibits infinite inorganic chains connected by hydrogen bonds to generate a 3D supramolecular framework; compounds 2 and 3 are isomorphous and constructed from a Ga₆P₆ secondary building unit (SBUs), forming a 3D pcu architecture with intersecting 8-membered channels; compound 4 possesses an inorganic layered structure and compound 5 features an interesting 3D open-framework architecture with helical channels.