Crystal structure of β′Mn3(PO4)2

Abstract

β′Mn3(PO4)2 crystallizes as a monoclinic crystal with lattice parameters a = 8.94(3) Å, b = 10.04(2) Å, c = 24.12(12) Å, β = 120.8(1)°, and Z = 12. The diffraction pattern shows a pronounced superlattice phenomenon with reflections generally weak if their l index ≠ 0 mod 3. The conventional R value for a total of 3516 reflections, of which 1637 were strong enough to be measured, was reduced to 0.09 by full matrix least squares procedures. This structure is related to that of βZn3(PO4)2 whose unit cell dimensions are comparable save for a tripled c axis in β′Mn3(PO4)2. In addition, the latter compound is isostructural with the low temperature form of Cd3(PO4)2. The PO43− groups are slightly irregular tetrahedra with a mean P—O bond distance of 1.54 ± 0.01 Å. The coordination numbers of the cations have increased on the average in comparison to βZn3(PO4)2 where they are 4, 5, and 5 for the three unique cations. In β′Mn3(PO4)2 each cation shows 5 strong Mn—O bonds and most cations have one additional bond of intermediate strength. The metal–oxygen atom bond distances in β′Mn3(PO4)2 range from 2.03 to 2.31 Å although there are some additional long ones ranging from 2.4 to 3.0 Å which can be correlated with normal bond lengths in βZn3(PO4)2.