The monoclinic modification of dipotassium dichromate, β-K₂Cr₂O₇, has been synthesized in the K₂Cr₂O₇-H₂O system. The structure consists of K⁺ cations and Cr₂O₇^2- dimers. In contrast with triclinic α-K₂Cr₂O₇, the Cr₂O₇^2- groups in β-K₂Cr₂O₇ have twofold crystallographic symmetry and are parallel to each other.