Mu-7, a New Layered Aluminophosphate [CH₃NH₃]₃[Al₃P₄O₁₆] with a 4 × 8 Network:  Characterization, Structure, and Possible Crystallization Mechanism

The title compound, Mu-7, is a new layered aluminophosphate. It was obtained from a quasi-nonaqueous system involving methylformamide (MF) as solvent in addition to restricted amounts of water. MF is decomposed into methylamine during synthesis and the latter is occluded into the interlayer spacing of the material. The structure was determined by single-crystal X-ray diffraction. The symmetry is triclinic, space group P 1̄, a = 8.368(7), b = 11.274(10), c = 11.462(12) Å, α = 72.40(7), β = 89.45(8), and γ = 85.37(7)°. Mu-7 is built from zigzag ladder-type chains connected to form layers containing only four- and eight-membered rings. Mu-7 is the first lamellar aluminophosphate having such a 4 × 8 network. Characterization of the new compound by 13 C, 27 Al, and 31 P solid-state NMR spectroscopy, bulk chemical analysis and TG/DSC is reported. A possible crystallization mechanism based on the condensation between “parent” ([AlP 2 O 8 H 2 ] - ) and zigzag ladder-type ([Al 4 P 4 O 20 H 4 ] 4 - ) chains is proposed.