Enriching the Reticular Chemistry Repertoire: Merged Nets Approach for the Rational Design of Intricate Mixed-Linker Metal–Organic Framework Platforms

Rational design and construction
of metal–organic frameworks
(MOFs) with intricate structural complexity are of prime importance
in reticular chemistry. We report our latest addition to the design
toolbox in reticular chemistry, namely the concept of merged nets
based on merging two edge-transitive nets into a minimal edge-transitive
net for the rational construction of intricate mixed-linker MOFs.
In essence, a valuable net for design enclosing two edges (not related
by symmetry) is rationally generated by merging two edge-transitive
nets, namely (3,6)-coordinated spn and 6-coordinated hxg. The resultant merged-net, a (3,6,12)-coordinated sph net with net transitivity [32] enclosing three nodes and
two distinct edges, offers potential for deliberate design of intricate
mixed-linker MOFs. We report implementation of the merged-net approach
for the construction of isoreticular rare-earth mixed-linker MOFs, sph-MOF-1 to -4, based on the assembly of 12-c hexanuclear
carboxylate-based molecular building blocks (MBBs), displaying cuboctahedral
building units, 3-c tritopic ligands, and 6-c hexatopic ligands. The
resultant sph-MOFs represent the first examples of MOFs
where the underlying net is merged from two 3-periodic edge-transitive
nets, spn and hxg. Distinctively, the sph-MOF-3 represents the first example of a mixed-linker MOF
to enclose both trigonal and hexagonal linkers. The merged-nets approach
allows the logical practice of isoreticular chemistry by taking into
account the mathematically correlated dimensions of the two ligands
to afford the deliberate construction of a mixed-linker mesoporous
MOF, sph-MOF-4. The merged-net equation and two key parameters,
ratio constant and MBB constant, are disclosed. A merged-net strategy
for the design of mixed-linker MOFs by strictly controlling the size
ratio between edges is introduced.