Metallacarborane-Based Metal–Organic Framework with a Complex Topology

The
long, linear cobalt­(III) bis­(dicarbollide)-based bis­(isophthalic
acid) anion was synthesized as a tetraphenylphosphonium salt in five
steps from 8-iodo-closo-1,2-C2B10H11. The solvothermal reaction between the anionic bis­(isophthalic
acid) linker and copper­(II) nitrate in acidified DMF yielded single
crystals. Despite the tendency for copper­(II) and analogous linear
tetraacids to form members of an isoreticular family of metal–organic
frameworks (MOFs) with the fof topology, single-crystal
X-ray diffraction analysis revealed the growth of three different
frameworks. These MOFs, NU-150, NU-151,
and NU-152, have three distinct topologies: fof, sty, and hbk, respectively. NU-152 has a novel quadrinodal topology in which cuboctahedral coordination
polyhedra are each connected to 10 neighboring polyhedra via the cobalt
bis­(dicarbollide) portions of the linkers. The formation of these
frameworks illustrates the limitations of structure prediction in
MOF chemistry and the possibility of using flexible linkers to generate
unexpected topologies. Furthermore, this work represents the first
example of the incorporation of an anionic bis­(dicarbollide) unit
into a MOF.