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Abstract:
A new framework cobalt(II) hydroxyl phosphate, Co2PO4OH, was prepared by
ionothermal synthesis using 1-butyl-4-methyl-pyridinium
hexafluorphosphate as the ionic liquid. As the formation of Co2PO4F
competes in the synthesis, the synthesis conditions have to be
judiciously chosen to obtain well-crystallized, single phase Co2PO4OH.
Single-crystal X-ray diffraction analyses reveal Co2PO4OH crystallizes
with space group I4(1)/amd (a = b = 5.2713(7) angstrom, c = 12.907(3)
angstrom, V = 358.63(10) angstrom(3), and Z = 4). Astonishingly, it does
not crystallize isotypically with Co2PO4F but rather isotypically with
the hydroxyl minerals caminite Mg-1.33[SO4(OH)(0.66)(H2O)(0.33)] and
lipscombite Fe2-yPO4(OH) (0 <= y <= 2/3). Phosphate tetrahedra groups
interconnect four rod-packed face-sharing (1)(infinity){CoO6/2}
octahedra chains to form a three-dimensional framework structure. The
compound Co2PO4OH was further characterized by powder X-ray diffraction,
Fourier transform-infrared, and ultraviolet-visible spectroscopy,
confirming the discussed structure. The magnetic measurement reveals
that Co2PO4OH undergoes a magnetic transition and presents at low
temperatures a canted antiferromagnetic spin order in the ground state.