2D metal–organic frameworks

e.g. Ni₃(HITP)₂, Cu₃(HHTP)₂

Also called conductive MOFs, Ni₃(HITP)₂, Cu₃(HHTP)₂

nanosheet depends on form

Porous crystals assembled from metal atoms and organic molecules, like molecular scaffolding. Most MOFs are insulators used to store gases, but flat, conjugated ones stack into layered sheets that conduct electricity – combining a huge internal surface with electrical access to it. That makes them candidates for chemical sensors, supercapacitors and electrocatalysts designed molecule by molecule.

Data sheet

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Kind of sheet: nanosheet
Made by chemistry or cut from a solid, not peeled as a clean crystal layer
Behaves as: depends on form
Band gap: From insulating to metallic depending on metal and linker; Ni₃(HITP)₂ films conduct at ~40 S/cm
Thickness: ~0.33 nm interlayer spacing in π-stacked conductive MOFs; nanosheets typically a few nanometres thick
Structure: Metal nodes linked by flat, conjugated organic molecules into porous sheets that stack like graphite; in-plane π–d conjugation makes some of them electrically conductive
Stability: Varies widely. Many conductive π-stacked MOFs are stable in air and water, but some frameworks lose crystallinity when solvent is removed, and strongly acidic or basic electrolytes degrade them.
First made: Highly conductive 2D MOF Ni₃(HITP)₂ reported in 2014 (Sheberla, Dincă and colleagues, MIT)

Compare with other materials

Key properties

Pore size and chemistry designable through the choice of metal node and organic linker
Ni₃(HITP)₂ conducts at ~40 S/cm as a film and ~2 S/cm as a pressed pellet, and single-crystal rods reach ~150 S/cm – rare for a porous material
Ni₃(HITP)₂ electrodes work as supercapacitors without conductive additives
Chemiresistive detection of gases such as ammonia at ppm levels

How it is made

Solvothermal or interfacial (liquid/liquid, air/liquid) synthesis of films and nanosheets
Layer-by-layer liquid-phase epitaxy on substrates
Top-down exfoliation of layered MOF crystals

Uses, and how close they are

Chemiresistive gas sensorsprototype
Supercapacitor electrodes and electrocatalystslab
Gas-separation membraneslab

Readiness runs lab → prototype → pilot → deployed.

Open problems

Is conduction in π-stacked MOFs band-like or hopping, and how much is limited by grain boundaries rather than intrinsic properties?
Can large, single-crystalline, few-layer films be grown to measure intrinsic transport?
Can conductive MOFs survive the chemistry of real electrochemical devices for long periods?

Going deeper

Short notes for specialists. Choose a lens in the header and yours comes first.

For theoreticians · your lens

Large unit cells with metal d–ligand π hybridisation need DFT+U or hybrid functionals, and stacking (eclipsed versus slipped) changes band dispersion dramatically – whether a framework is predicted metallic or semiconducting can hinge on the assumed stacking. Solvent and counter-ions affect results; correlations matter for magnetic metal nodes.

For experimentalists · your lens

State whether conductivity was measured on pellets, films or single crystals – values differ by orders of magnitude. Confirm porosity by gas adsorption after activation and crystallinity by PXRD or GIWAXS, and check for residual solvent and metal impurities.

For engineers · your lens

Designable at the molecular level but costly and batch-synthesised; sensors, where small quantities suffice, are the most plausible near-term application.

Key references

High electrical conductivity in Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2, a semiconducting metal-organic graphene analogueSheberla et al. · Journal of the American Chemical Society 136, 8859 (2014)cited by 1,174doi:10.1021/ja502765n
Cu₃(hexaiminotriphenylene)₂: an electrically conductive 2D metal–organic framework for chemiresistive sensingCampbell et al. · Angewandte Chemie International Edition 54, 4349 (2015)cited by 1,067doi:10.1002/anie.201411854
Conductive MOF electrodes for stable supercapacitors with high areal capacitanceSheberla et al. · Nature Materials 16, 220 (2017)cited by 2,411doi:10.1038/nmat4766
Single crystals of electrically conductive two-dimensional metal–organic frameworks: structural and electrical transport propertiesDay et al. · ACS Central Science 5, 1959 (2019)cited by 410doi:10.1021/acscentsci.9b01006