Unlocking New Topologies in Zr-Based Metal–Organic Frameworks by Combining Linker Flexibility and Building Block Disorder

The outstanding diversity of Zr-based frameworks is inherently
linked to the variable coordination geometry of Zr-oxo clusters and
the conformational flexibility of the linker, both of which allow
for different framework topologies based on the same linker–cluster
combination. In addition, intrinsic structural disorder provides a
largely unexplored handle to further expand the accessibility of novel
metal–organic framework (MOF) structures that can be formed.
In this work, we report the concomitant synthesis of three topologically
different MOFs based on the same M6O4(OH)4 clusters (M = Zr or Hf) and methane-tetrakis­(p-biphenyl-carboxylate) (MTBC) linkers. Two novel structural models
are presented based on single-crystal diffraction analysis, namely,
cubic c-(4,12)­MTBC-M6 and trigonal tr-(4,12)­MTBC-M6, which comprise 12-coordinated clusters and 4-coordinated
tetrahedral linkers. Notably, the cubic phase features a new architecture
based on orientational cluster disorder, which is essential for its
formation and has been analyzed by a combination of average structure
refinements and diffuse scattering analysis from both powder and single-crystal
X-ray diffraction data. The trigonal phase also features structure
disorder, although involving both linkers and secondary building units.
In both phases, remarkable geometrical distortion of the MTBC linkers
illustrates how linker flexibility is also essential for their formation
and expands the range of achievable topologies in Zr-based MOFs and
its analogues.