# Heterometallic 3‑D Zn/Ca Metal–Organic Frameworks Based on V‑Shaped Angular Tetracarboxylic Ligands as Selective Fluorescence Sensors for Nitroaromatic Explosive Vapors

## TL;DR

Researchers developed a new type of metal-organic framework that can selectively detect explosive vapors using fluorescence.

## Contribution

The novel contribution is the design of heterometallic Zn/Ca MOFs with angular tetracarboxylic ligands for selective detection of nitroaromatic explosives.

## Key findings

- The MOFs exhibit high BET surface areas ranging from 1338 to 2134 m²/g.
- Thin films of selected MOFs show high selectivity for detecting 2,4,6-trinitrophenol and 2,4,6-trinitrotoluene vapors.
- Crystal structures reveal interactions between the MOFs and nitroaromatic molecules.

## Abstract

A family of heterometallic Zn/Ca MOFs based on angular
tetracarboxylic
ligands with formulas [ZnCa­(L)­(S)­(S′)]
n
(S, S′ = H2O or S = H2O, S′
= DMF) UCY-18(L) (H4L = 4,4′-hexafluoroisopropilidene
diphthalic acid (H4HFPD), 3,3′,4,4′-benzophenone
tetracarboxylic acid (H4BPTC), 4,4′-oxydiphthalic
acid (H4ODPA), 4,4′-azanediyl diphthalic acid (H4ADPA)) is reported. The crystal structures of UCY-18(L) comprise 3-D networks based on helical one-dimensional chain
SBUs [ZnCa­(L4–)] containing tetragonal channels
along the crystallographic a-axis. Gas sorption studies
on activated UCY-18(L) indicated appreciable BET surface
areas ranging from 1338 to 2134 m2 g–1. Selected vapor sorption studies indicated the affinity of these
materials toward representative C6-aromatic and nonaromatic
organic molecules. Thin films of UCY-18(HFPD), UCY-18(ODPA), and UCY-18(ADPA) embedded in poly­(vinylidene
fluoride) were fabricated and evaluated for their sensing capability
for vapors of selected nitroaromatic compounds. The thin films exhibit
high selectivity in detecting 2,4,6-trinitrophenol and 2,4,6-trinitrotoluene
vapors among other nitroaromatic compounds and interferents at equal
concentration. The crystal structures of UCY-18(HFPD)
loaded with nitrobenzene and 2-nitrotoluene provided useful information
about the interactions of the MOFs with these nitroaromatic molecules.
Overall, this work highlights the potential of heterometallic Zn/Ca
MOF chemistry to afford microporous MOFs containing highly accessible
metal centers and displaying the capability to recognize vapors of
selected analytes.