Copper(II) Nitrate
Properties
| State | Solid (blue, deliquescent crystals; usually as trihydrate) |
| Color | Blue |
| Solubility | Very soluble in water (381 g/L at 20°C); soluble in ethanol and acetone |
| Melting Point | 114.5°C (trihydrate); 255°C (anhydrous decomposes) |
| Boiling Point | Decomposes at ~170°C (trihydrate) |
About Copper(II) Nitrate
Cu(NO₃)₂ is what most chemists actually reach for when they need a clean source of Cu²⁺ in solution — sulfate carries a complexing counterion, chloride forms [CuClₙ]²⁻ⁿ species at any decent concentration, but nitrate is essentially a spectator ion in water, so you get a clean [Cu(H₂O)₆]²⁺ aquo ion and all of its bright blue d-d absorption around 800 nm. The hydrates are the form you typically weigh out: the trihydrate Cu(NO₃)₂·3H₂O melts around 114.5°C in its own water of crystallization, and the hexahydrate is what crystallizes from cold solution. Heating any of these does something visually striking — the blue crystals lose water, then around 170–200°C the salt decomposes via 2 Cu(NO₃)₂ → 2 CuO + 4 NO₂ + O₂, giving a black solid and a plume of brown NO₂. Anhydrous Cu(NO₃)₂ is much weirder: it sublimes around 150°C in vacuum (rare for an ionic-looking salt) because it's actually molecular in the gas phase, with bidentate η²-nitrate ligands chelating Cu — a structure that wasn't pinned down until the 1960s and was a small surprise at the time. In synthesis, Cu(NO₃)₂ supported on bentonite clay (Laszlo's "Claycop") gives a mild, regioselective nitrating agent for activated arenes that doesn't need fuming HNO₃, and Cu(NO₃)₂/Ac₂O does selective benzylic nitration. In pyrotechnics it gives blue-green flame color from CuO* and CuOH* emission.
Where you'll encounter it
If you've ever seen the classic "blue crystals to black powder with brown smoke" decomposition demo, the starting material was almost always Cu(NO₃)₂·3H₂O scooped onto a watch glass over a hot plate. In a research lab, the trihydrate is the go-to source of Cu²⁺ when you need to avoid sulfate or chloride coordination — for example when running EPR on Cu(II) complexes where extra ligands would mess up the spectrum, or when synthesizing copper carboxylate paddlewheel dimers and you need bare Cu²⁺.
Common Uses
- Non-coordinating Cu²⁺ source for synthesis of copper coordination complexes and MOFs
- Precursor for CuO and Cu/CuO catalyst materials via thermal decomposition under air
- Claycop reagent (Cu(NO₃)₂ on bentonite) for regioselective nitration of activated arenes
- Selective oxidant in Sakurai–Hosomi-type allylations and benzylic C–H nitrooxylation
- Blue-green colorant in pyrotechnic stars via CuOH* and CuCl* emission with chloride donor
- Mordant in textile dyeing for fixing acid dyes onto wool and silk fibers
- Patina solution component for chemically aging copper, brass, and bronze sculptures
- Source of Cu(II) for electroless plating bath formulations on plastics
Safety Information
GHS: H272 (oxidizer), H302 (harmful if swallowed), H315/H319 (skin/eye irritation), H410 (very toxic to aquatic life). DOT class 5.1 oxidizer, UN1479. The oxidizer hazard is real — do not store with paper, sawdust, organic solvents, or reducing agents; spills onto cellulose can ignite spontaneously after drying. Thermal decomposition releases NO₂, which is the actually dangerous part if you heat it in a closed space. NO₂ is immediately dangerous to life at low ppm concentrations. Copper dust carries its own exposure limit, expressed as Cu. Skin contact gives the characteristic blue-green stain plus low-grade nitric acid burn from acidic hydrolysis.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals. We deliberately do not publish occupational exposure limits or other regulatory thresholds: those values are revised over time and differ between jurisdictions, so the only correct source is the current SDS and the regulations that apply where you work.