Three Novel Isomeric Zinc Metal–Organic Frameworks from a Tetracarboxylate Linker

Three porous supramolecular isomers (IZE-1, IZE-2, and IZE-3) with the same framework
component
[Zn2(EBTC)­(H2O)2] (EBTC = 1,1′-ethynebenzene-3,3′,5,5′-tetracarboxylate)
were successfully constructed by finely tuning the reaction condition.
Although both IZE-1 and IZE-2 are constructed
from the linear EBTC subunits and one kind of regular [Zn2(CO2)4] paddlewheels, their frameworks exhibit
two different (3,4)-c net of fof (sqc1575) and sqc1572,
respectively, resulting in cavities with different size and shape.
However, as for isomer IZE-3, the EBTC ligands are bent
and one-half of the [Zn2(CO2)4] paddlewheels
are distorted, leading to a novel (3,4,4)-c hyx net with
point symbol (6.72)4(62.82.102)­(72.82.112) and
vertex symbol (6.7.7)4(72.72.8.8.12.12)­(6.6.8.8.102.102). Quantum chemical calculations by DFT indicate
that the three isomers have very close thermodynamic stabilities,
which may explain that subtle condition change leads to variation
of the frameworks. Further theoretical semiempirical investigation
on the interactions between solvent molecules and compounds shows
different hydrogen binding patterns in good agreement with the experimental
observations. Furthermore, they exhibit good solid-state luminescence
properties with long lifetime.