Chiral Supramolecular Frameworks Based on Chiral Metallocycles: Crystal Structures and Photophysical Properties

Abstract

AbstractFour purely chiral supramolecular frameworks were constructed from a new chiral terpyridyl ligand, (S)‐2{4‐[2,6‐bis(pyridin‐2‐yl)pyridin‐4‐yl]benzylamino}propanoic acid (H2ptpy). The resulting compounds 1–4, namely [Cd2(Hptpy)2(Ac)2]·3CH3OH·H2O (1) [Ni2(Hptpy)2(CH3OH)(H2O)](ClO4)2·CH3OH·H2O (2), [Ni2(Hptpy)2(H2O)2](SCN)2 (3), and [Cu2(Hptpy)2](dca)2·4H2O (4) (Ac = acetate and dca = dicyanamide) all consist of those chiral metallocyclic units. As expected, those chiral nanometallocycles not only induced a chiral array or helicates but also amplified chirality through hydrogen‐bonding interactions, and finally aggregated into complicated higher‐dimensional chiral supramolecular architectures with chiral voids for further use. The formation of the metallocyclic units is easily monitored by UV/Vis spectra. Spectrophotometric titrations were performed by titrating Na(Hptpy) with a soltution of Cd(Ac)2 in methanol, and the global stability constants of [Cd2(Hptpy)2]2+ (log β = 17.60) were calculated. In combination with the structural analyses and UV/Vis and ES mass spectra, it is tentatively deduced that metallocycle units in 1–4 are the thermodynamically favored species in solution. Both the chiral H2ptpy ligand and 1 in the solid state and in solution display purple emission. The bathochromic shift of 1 is mainly due to the bichelation and intrametallocyclic π–π interactions.