Conformational control through co-operative nonconventional C-H...N hydrogen bonds.

We report the design, synthesis, and crystal structure of a conjugated aryleneethynyl molecule, 2-(2-{4,5-dimethoxy-2-[2-(2,3,4-trifluorophenyl)ethynyl]phenyl}ethynyl)-6-[2-(pyridin-2-yl)ethynyl]pyridine, C30H17F3N2O2, that adopts a planar rhombus conformation in the solid state. The molecule crystallizes in the space group P-1, with Z = 2, and features two intramolecular sp2-C-H...N hydrogen bonds that co-operatively hold the arylethynyl molecule in a rhombus conformation. The H atoms are activated towards hydrogen bonding since they are situated on a trifluorophenyl ring and the H...N distances are 2.470 (16) and 2.646 (16) Å, with C-H...N angles of 161.7 (2) and 164.7 (2)°, respectively. Molecular electrostatic potential calculations support the formation of C-H...N hydrogen bonds to the trifluorophenyl moiety. Hirshfeld surface analysis identifies a self-complementary C-H...O dimeric interaction between adjacent 1,2-dimethoxybenzene segments that is shown to be common in structures containing that moiety.