Chiral MOF incorporating chiral guests: Structural studies and enantiomer-dependent luminescent properties

Two new inclusion compounds of chiral guest molecules in chiral metal–organic framework (MOF) were obtained by soaking the crystalline [Zn ₂ (dmf)(bdc)(S-lac)]·DMF (dmf = N,N-dimethylformamide; bdc = terephthalate; S-lac = S-lactate) in neat R-1,2-propanediol (R-pd) or S-1,2-propanediol (S-pd). Single crystal X-ray analysis for [Zn ₂ (dmf)(bdc)(S-lac)]·R-pd (1) and [Zn ₂ (S-pd) ₂ (bdc)(S-lac)]·S-pd (2) showed that two enantiomers of the same alcohol react quite differently with the chiral porous framework, occupying different positions and form different types of interactions with the host. While the R-pd acts only as a guest molecule inside the channels, the S-pd coordinates to zinc cations of the framework and substitutes both guest and coordinated DMF of the original MOF. The chirality of 1,2-propanediol guest molecules has a considerable effect on luminescent properties of the [Zn ₂ (dmf)(bdc)(S-lac)] host. The luminescence spectra of [Zn ₂ (S-pd) ₂ (bdc)(S-lac)]·S-pd and the original [Zn ₂ (dmf)(bdc)(S-lac)]·DMF are almost identical while the luminescence spectra of [Zn ₂ (dmf)(bdc)(S-lac)]·R-pd features new peak, compared with the original host. Also, the incorporation of alcohol guest molecules has different impact on quantum yields of the luminescence of the host, depending on the chirality of the isomer. In a more general prospect, such enantiomer-dependent luminescent properties of [Zn ₂ (dmf)(bdc)(S-lac)] represent a chiral luminescence sensing, which is quite an extraordinary and rare phenomenon for chiral MOFs.