Litharge – issue with coordinates

[Rob2026]

I landed on the wikipidia page where it shows that litharge it’s a tetragonal crystal of PbO and space structure P 4/n m m :1.

In the COD database I get multiple PbO CIF files, with different structures and space groups. Without the information from wikipidia I wouldn’t be able to identify the correct one just from the name.
I downloaded file COD ID 1010977 with space group P 4/n m m.

space group IT number is 129
Pb and O positions are:
Pb1 Pb2+ 2 c 0. 0.5 0.24 1. 0 d
O1 O2- 2 a 0. 0. 0. 1. 0 d

we can check the coordinates of the Wyckoff number from Bilbao database (IT number 129: 2c, 2a)
2 c 4mm
(1/4,1/4,z) (3/4,3/4,-z)
2 a -4m2
(3/4,1/4,0) (1/4,3/4,0)

However, they don’t match coordinates in the CIF file. Same information can be derived from CIF file COD ID 1537982.

[Rob2026]

Judging from the CIF files we can see these coordinates, which would belong to the Wyckoff letter k, with multiplicity 16:

_symmetry_equiv_pos_as_xyz
x,y,z
-x,-y,z
1/2+x,1/2+y,-z
1/2-x,1/2-y,-z
-x,y,z
x,-y,z
1/2-x,1/2+y,-z
1/2+x,1/2-y,-z
-y,x,-z
y,-x,-z
1/2-y,1/2+x,z
1/2+y,1/2-x,z
y,x,-z
-y,-x,-z
1/2+y,1/2+x,z
1/2-y,1/2-x,z

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