Setting ambiguity in C2/c with dibromidotetrakis(1H-pyrazole-kappaN2)manganese(II) as an example.
trans-Dibromidotetrakis(1H-pyrazole-kappaN(3))manganese(II), [MnBr2(C3H4N2)4], crystallizes in the C2/c space group with the Mn atom located on a centre of inversion. As a result, there is just one half-molecule in the asymmetric unit. Geometric parameters are in the usual ranges. The Mn centre is octahedrally coordinated by four pyrazole residues in the equatorial plane and by two bromide ligands in the axial positions. The molecular conformation is stabilized by N-H...Br hydrogen bonds. The structure of the title compound had already been described [Lumme & Lindell (1987). J. Coord. Chem. 15, 383-392] in a different setting, with the Mn atoms located on inversion centres on Wyckoff position d (1/4, 1/4, 1/2; 3/4, 1/4, 0; 3/4, 3/4, 1/2; 1/4, 3/4, 0). In the conventional setting, however, the Mn atoms are situated on Wyckoff position a (0, 0, 0; 0, 0, 1/2; 1/2, 1/2, 0; 1/2, 1/2, 1/2). In this special case, if the c axis has the same length as the short diagonal of the ac plane, the transformation from one setting into the other yields almost indistinguishable cell parameters, and the possibility of confusion arises. This setting ambiguity could be the reason why two structures in different settings might be taken as polymorphs even though they can easily be transformed. As a result of this, care should always be taken to use the conventional setting.
Ruth
Kai
K
Institut für Anorganische Chemie, J. W. Goethe-Universität Frankfurt, Max-von-Laue-Strasse 7, 60438 Frankfurt/Main, Germany.
Kunz
Kerstin
K
Lerner
Hans-Wolfram
HW
Bolte
Michael
M