Control of supramolecular chirality in co-crystals of achiral molecules via stacking interactions and hydrogen bonding

Abstract

An approach is proposed to obtain non-centrosymmetric crystal structures using co-crystallization of specific achiral molecules. The co-formers, donors and acceptors of electron density are selected in such a way that they can form two types of supramolecular synthons: infinite H-bonded chains along a 2-fold screw axis and π-stacks propagating by translation. Geometry analysis shows that combination of these synthons in a co-crystal with a 1 : 1 molar ratio of the co-formers leads to a preference for the crystallization in two Sohncke space groups, P2₁ and P2₁2₁2₁, or, probably, in a polar Pna2₁ space group. Experimental data confirming this suggestion was obtained for co-crystals of 1H-3,5-dinitropyridine-2-one with five polyaromatic hyrdocarbons with different numbers of aromatic rings connected in a different manner. From seven crystal structures, three with a 1 : 1 composition crystallize in Sohncke groups, while four structures with different stoichiometries, including two polymorphs with anthracene, crystallize in the P2₁/c (or equivalent P2₁/n) group. The influence of molecular size and crystal composition on the geometry of supramolecular synthons and total crystal packing is discussed. The suggested approach allows constructing crystal structures not only with a specific packing pattern and symmetry, but, to some extent, with a predefined unit cell.