Self-Assembly of Luminescent Molecular Squares Featuring Octahedral Rhenium Corners.

The self-assembly of rigid inorganic cyclophanes comprising cis bridging metal centers connected by aromatic edges has emerged as a promising new area within the realm of hostguest chemistry.1-5 By utilizing the power and simplicity of molecular self-assembly which enables components to arrange themselves into square host cavities, chemists have synthesized a large number of new species with recognition capabilities. In nearly all previous examples of square self-assemblies, PdII or PtII materials with leaving groups cis to one another have served in some capacity to drive the process. We report herein the extension of the chemistry of self-assembled6 molecular squares to include compounds incorporating solely octahedral metal centers (1-3).7,8 It should be noted that the synthetic methods used to construct the 4,4′-bipyridine square, 1, have been generalized with the synthesis of pyrazine (2) and 1,2-bis(4pyridyl)ethylene (3) molecular squares. Squares 1 and 2 luminesce at room temperature, making them potentially useful as small-molecule sensors; unfortunately, the excited state for square 3 decays exclusively via nonradiative pathways.