Growth Environment-Driven Structural Adaptability Enabling Chirality in a Spin-Crossover Framework

Controllable induction of chiral and achiral topological
isomers
in metal–organic frameworks (MOFs) from achiral tectons remains
a challenge. This study demonstrates the tunable growth of an achiral
two-dimensional (2D) spin-crossover MOF (SCO-MOF) and a chiral three-dimensional
(3D) SCO-MOF by systematically modifying the growth environment. In
the C2Cl4–CH3OH system, planar
C2Cl4 molecules template the formation of the
achiral 2D SCO-MOF. Replacing C2Cl4 with CHCl3 in the CHCl3–CH3OH system induces
the sequential growth of achiral 2D and chiral 3D SCO-MOFs, while
reducing the CHCl3 proportion suppresses the achiral 2D
framework, yielding pure chiral 3D SCO-MOF. In the H2O–CH3OH system, devoid of bulky solvents, chiral 3D samples are
rapidly and selectively synthesized at 363 K. Enantiopure agents ((S)-(−)-PET and (R)-(+)-PET) further
control the chiral orientation of the 3D samples. Single-crystal X-ray
diffraction (SC-XRD) data reveal that the chiral 3D structure features
oppositely handed large and small double helices in an ABAB packing
mode, homologous to the ABAB-stacked supramolecular structure of its
achiral 2d isomer. The denser 3D framework enhances thermal
and chemical stability and exhibits pressure-induced and guest-loss
abolition of SCO properties.