(Becher, 1966) give the space group as $C222$ #20, but their Wyckoff positions are obviously from space group $Cmmm$ #65, a result which was confirmed by (Ade, 2015).
$- a x_{3} \,\mathbf{\hat{x}}+\frac{1}{2}c \,\mathbf{\hat{z}}$
(4h)
Mn I
References
H. J. Becher, K. Krogmann, and E. Peisker, Über das ternáre Borid Mn$_{2}$AlB$_{2}$, Z. Anorganische und Allgemeine Chemie 344, 140–147 (1966), doi:10.1002/zaac.19663440304.
K. Cenzual, L. M. Gelato, M. Penzo, and E. Parthé, Inorganic structure types with revised space groups. I, Acta Crystallogr. Sect. B 47, 433–439 (1991), doi:10.1107/S0108768191000903.
M. Ade and H. Hillebrecht, Ternary Borides Cr$_{2}$AlB$_{2}$, Cr$_{2}$AlB$_{4}$, and Cr$_{4}$AlB$_{6}$: The First Members of the Series (CrB$_{2}$)$_{n}$CrAl with $n = 1, 2, 3$ and a Unifying Concept for Ternary Borides as MAB-Phases, Inorg. Chem. 54, 6122–6135 (2015), doi:10.1021/acs.inorgchem.5b00049.
Found in
M. Ade and H. Hillebrecht, Ternary Borides Cr$_{2}$AlB$_{2}$, Cr$_{2}$AlB$_{4}$, and Cr$_{4}$AlB$_{6}$: The First Members of the Series (CrB$_{2}$)$_{n}$CrAl with $n = 1, 2, 3$ and a Unifying Concept for Ternary Borides as MAB-Phases, Inorg. Chem. 54, 6122–6135 (2015), doi:10.1021/acs.inorgchem.5b00049.
D. Hicks, C. Toher, D. C. Ford, F. Rose, C. D. Santo, O. Levy, M. J. Mehl, and S. Curtarolo, AFLOW-XtalFinder: a reliable choice to identify crystalline prototypes7, 30 (2021), doi:10.1038/s41524-020-00483-4.
First cited in
H. Eckert, S. Divilov, M. J. Mehl, D. Hicks, A. C. Zettel, M. Esters, X. Campilongo, and S. Curtarolo, The AFLOW Library of Crystallographic Prototypes: Part 4, Comp. Mat. Sci. 240, 112988 (2024). (doi=10.1016/j.commatsci.2021.110450)