# HKUST-1: copper paddlewheels and open metal sites

> HKUST-1 (Cu-BTC) forms in high yield when copper(II) nitrate and trimesic acid are heated in water and ethanol. Pairs of Cu²⁺ ions bridged by four carboxylates (paddlewheels) are joined by the triangular trimesate into a cubic framework with 1 nm channels. Each copper carries a water molecule; heating under vacuum removes it and leaves an open metal site that binds guests, and pyridine can take its place.

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- Updated: 2026-10-14
- Category: Metal–organic frameworks
- Method: Solvothermal synthesis, bottom-up
- Starting materials: Copper(II) nitrate trihydrate and trimesic acid (benzene-1,3,5-tricarboxylic acid, H₃BTC) in water/ethanol (1:1)
- Product: Turquoise octahedral crystals of [Cu₃(BTC)₂(H₂O)₃]ₙ (cubic, a ≈ 26.3 Å)
- Key result: Stable up to 240 °C by thermogravimetry and high-temperature single-crystal diffraction (Chui et al. 1999)
- Figure: 1920 × 1080 px, 81 editable layers (15 generated objects with settings)

## Steps

1. **Solvothermal**: Cu(NO₃)₂·3H₂O and H₃BTC in H₂O/EtOH, Teflon-lined autoclave, 180 °C for 12 h; 80% yield (Chui et al. 1999)
2. **Paddlewheels**: Cu₂(CO₂)₄ units, Cu···Cu 2.63 Å, one water on each copper
3. **Framework**: Paddlewheels joined by BTC (tbo net): 1 nm channels, about 40% accessible porosity
4. **Activation**: Heating under vacuum removes the axial water: open Cu²⁺ sites, darker crystals (Prestipino et al. 2006)
5. **Exchange**: The aqua ligands can be replaced by pyridines (Chui et al. 1999)

## Strengths

- High-yield synthesis from inexpensive reagents
- Open Cu²⁺ sites that bind small molecules
- Channel linings that can be functionalized

## Limitations

- Takes up water from air; moisture slowly degrades it
- Open sites must be kept dry after activation

## Uses

- Gas storage and separation
- Catalysis at open copper sites
- Sensing

## References

1. Chui et al., “A Chemically Functionalizable Nanoporous Material [Cu₃(TMA)₂(H₂O)₃]ₙ”, Science 1999. https://doi.org/10.1126/science.283.5405.1148 (primary)
2. Prestipino et al., “Local Structure of Framework Cu(II) in HKUST-1 Metallorganic Framework: Spectroscopic Characterization upon Activation and Interaction with Adsorbates”, Chem. Mater. 2006. https://doi.org/10.1021/cm052191g (further reading)

Credit: Redrawn and simplified after Chui et al., Science 1999 (doi:10.1126/science.283.5405.1148) and Prestipino et al., Chem. Mater. 2006 (doi:10.1021/cm052191g). Models built at the bond lengths of the crystal structure.

## Questions

**What does the “HKUST-1: copper paddlewheels and open metal sites” template show?** HKUST-1 (Cu-BTC) forms in high yield when copper(II) nitrate and trimesic acid are heated in water and ethanol. Pairs of Cu²⁺ ions bridged by four carboxylates (paddlewheels) are joined by the triangular trimesate into a cubic framework with 1 nm channels. Each copper carries a water molecule; heating under vacuum removes it and leaves an open metal site that binds guests, and pyridine can take its place.

**What are the steps shown in “HKUST-1: copper paddlewheels and open metal sites”?** 1. Solvothermal: Cu(NO₃)₂·3H₂O and H₃BTC in H₂O/EtOH, Teflon-lined autoclave, 180 °C for 12 h; 80% yield (Chui et al. 1999). 2. Paddlewheels: Cu₂(CO₂)₄ units, Cu···Cu 2.63 Å, one water on each copper. 3. Framework: Paddlewheels joined by BTC (tbo net): 1 nm channels, about 40% accessible porosity. 4. Activation: Heating under vacuum removes the axial water: open Cu²⁺ sites, darker crystals (Prestipino et al. 2006). 5. Exchange: The aqua ligands can be replaced by pyridines (Chui et al. 1999).

**What are the starting materials and the product?** Starting materials: Copper(II) nitrate trihydrate and trimesic acid (benzene-1,3,5-tricarboxylic acid, H₃BTC) in water/ethanol (1:1). Product: Turquoise octahedral crystals of [Cu₃(BTC)₂(H₂O)₃]ₙ (cubic, a ≈ 26.3 Å).

**Which papers is “HKUST-1: copper paddlewheels and open metal sites” based on?** Chui et al., “A Chemically Functionalizable Nanoporous Material [Cu₃(TMA)₂(H₂O)₃]ₙ”, Science 1999 (doi:10.1126/science.283.5405.1148); Prestipino et al., “Local Structure of Framework Cu(II) in HKUST-1 Metallorganic Framework: Spectroscopic Characterization upon Activation and Interaction with Adsorbates”, Chem. Mater. 2006 (doi:10.1021/cm052191g).

**Can I edit the “HKUST-1: copper paddlewheels and open metal sites” template?** Yes. Open it in the LabCanvas editor: all 81 layers are editable, including 15 generated objects (structures, plots, equipment) with their own settings. Change the text, colours and layout, then export PNG, TIFF, SVG or PDF.

**Do I need an account to use this template?** Not to view it here. To open and edit it, sign in to LabCanvas or create a free account (the free plan keeps one design of each kind). Downloading the figure is part of LabCanvas Pro (US$19 a month or US$199 a year).