Dipyridinium dichromate: an achiral compound forming chiral crystals.

The title compound, (C(5)H(6)N)(2)[Cr(2)O(7)], crystallizes in one of the Sohncke space groups, viz. P2(1)2(1)2(1). Crystallization of dipyridinium dichromate is thus an example of spontaneous formation of a chiral crystal structure from achiral molecules. The dichromate anion adopts a virtually eclipsed achiral conformation, and the crystal structure is held together primarily by N-H...O and C-H...O interactions. The possibility of using dipyridinium dichromate as a reagent in enantioselective synthesis is discussed.