Crystal engineering as a tool for directed radiationless energy transfer in layered {Λ-[Ru(bpy)3]Δ- [Os(bpy)3]}(PF6)4

New types of crystal structures with new physical properties such as energy harvesting can be engineered by exploiting the potentiality of chiral recognition. In the proposed strategy one takes advantage of the possibility that in true racemates one enantiomeric component in the crystal packing may be replaced by a different molecule of the same chirality and similar shape. This opens the path to a number of new properties. In the present investigation, we demonstrate that a system can be engineered, in which homochiral layers of Λ-[Ru(bpy)3]2+ rigorously alternate with homochiral layers of Δ-[Os(bpy)3]2+. This arrangement is realized in {Λ-[Ru(bpy)3]Δ- [Os(bpy)3]}(PF6)4. Due to the deliberately introduced lower dimensionality, the new crystalline system exhibits fascinating properties, in particular with respect to an interplay of processes of interlayer and intralayer radiationless energy transfer. Interestingly, in this system it is possible to achieve a controlled accumulation of excitation energy on a single crystallographic Δ-[Os(bpy)3]2+ site. Moreover, the excitation energy is absorbed in a wide range from the UV to the red side of the visible by both Λ-[Ru(bpy)3]2+ and Δ-[Os(bpy)3]2+ units, and one observes an intense red/infrared and highly resolved emission only of the low-energy Δ-[Os(bpy)3]2+ site, irrespective of the excitation wavelength used. The crystal structure of this newly engineered compound is determined for both the room-temperature phase (P32, a = 10.7012(5) angstroms, c = 16.3490(10) angstroms) as well as for the low-temperature phase (P3, a = 18.4189(10) angstroms, c = 16.2309(9) angstroms.)