Crystal Structures of a Series of Novel Alkylammonium Phosphates and Their Formation in Aluminophosphate Synthesis Mixtures

The crystal structures of several novel alkylammonium phosphate salts were determined by single-crystal X-ray
methods:  cyclopentylammonium monohydrogen phosphate (CMP) ([C5H9NH3+]2[HPO42-], monoclinic, space
group P21/n, Z = 4, a = 14.197(3) Å, b = 5.992(1) Å, c = 16.580(3) Å, β = 98.57(2)°); octylammonium
dihydrogen phosphate (ODP) ([CH3(CH2)7NH3+][H2PO4-], monoclinic, space group P21/c, Z = 4, a = 4.554(1)
Å, b = 34.652(3) Å, c = 7.328(1) Å, β = 90.66(1)°); and decylammonium dihydrogen phosphate (DDP)
([CH3(CH2)9NH3+][H2PO4-], monoclinic, space group P21/n, Z = 4, a = 7.358(2) Å, b = 39.749(12) Å, c =
9.131(4) Å, β = 90.45(2)°). Each are composed of anionic layers of hydrogen-bonded phosphate molecules,
separated by charge-balancing alkylammonium cations. The long-chain alkylammoniums in ODP and DDP are
interdigitated, while the cyclopentylammoniums in CMP define a bilayer-like arrangement. Large crystals were
grown by recrystallization, but the materials were also observed to form in the corresponding solvothermal
aluminophosphate synthesis mixtures. We have isolated phosphate salt compounds in aluminophosphate synthesis
mixtures containing a variety of different alkylamines and suggest they are initially present in such experiments
whenever the alkylamine is primary or secondary.