Electron microscopy
P21/c (P21/n, 14) space group
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Table 1886. P21/c (P21/n, 14) space group.

Name in the International Tables for Crystallography
P21/c, P21/n (The 'n' indicates that the glide plane translates molecules in a direction that is a diagonal on a plane perpendicular to screw axis) P
10 2/m
Crystal system
Monoclinic (Pharmaceutically common monoclinic space group) 2/m
0≤ x ≤ 1 and 0 ≤ y ≤ 1/4 and 0 ≤ z ≤ 1
4 Reflection conditions h0l: h + l = 2n; 0k0: k = 2n; h00: h = 2n; 00l: l = 2n.
The forbidden reflections are caused by 21-screw axis and n-glide plane.
(0 k 0): k = 2n + 1 due to the presence of a two-fold axis.
(h 0 l): h + l = 2n + 1 due to the presence of a glide plane.
Is diagonal in the direction of ac plane, rather than parallel to c-axis.
Symmetry (atomic coordinates)

X, Y, Z; -X, -Y, -Z; -X, 1/2+Y, 1/2-Z; X, 1/2-Y, 1/2+Z

Crystal symmetry
Is centrosymmetric because it has -x, -y, -z in its symmetry.
Crystal examples
Yb(IO3)3, Lu(IO3)3
LiHMaleate·2H2O: a = 5.858, b = 6.051, c = 18.800, α = 90, β = 91.47, γ = 90.

For a monoclinic crystal, if the systematic absence shows the presence of 21 screw axis and c-glide, then the possible space group can be P21/c.







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