Abstract The crystal structures of Cr 2B 3, Cr 3B 4, and CrB, of which Cr 2B 3 is a new compound, were investigated by single-crystal X-ray diffractometry. Cr 2B 3 crystallizes in the orthorhombic space group Cmcm witha = 3.0264(5), b = 18.115(4), c = 2.9542(4)A˚, Z = 4. The intensity data were collected on a four-circle diffractometer with graphite-monochromatizedMoKα radiation. The structure was solved by the Patterson method and refined with a full-matrix least-squares program to anR value (= Σ|ΔF|Σ|F o|) of 0.021 for 1310 reflections. The structures of Cr 3B 4 and CrB were refined starting from published data; theR values were 0.032 (Cr 3B 4) and 0.022 (CrB). The structure of Cr 2B 3 can be described by stacking sheets of the AlB 2 structure type in the same manner as in the cases of Cr 3B 4 and CrB. The fusion of two neighboring sheets is performed by a 5Cr tetragonal pyramid and a Cr-B direct bond at their boundary. The essential difference between the structures of these compounds is only in the widths of the sheets. The relations of the widths of the sheets to the bond distances and angles of boron atoms are discussed.