In-situ formation of copper nanoparticles using organometallic copper(II) formate-amine complexes

Copper(II) formate tetrahydrate is complexed with three amine ligands: amino-2-propanol, hexylamine and 2-(ethylamino)ethanol to develop copper particle-free inks for low-temperature (<130 °C) in-situ formation of copper nanoparticles for printed electronics. This study investigates how ligand structure influences complex formation, thermal decomposition behaviour and the resulting particle morphology. Fourier transform infrared spectroscopy confirms coordination between copper(II) formate and the amines through characteristic shifts in N-H and formate-related bands, indicating ligand-dependent coordination strength. Differential scanning calorimetry and thermogravimetric analysis show that complexation significantly reduces the decomposition temperature compared to pristine copper(II) formate, enabling formation below 150 °C. Activation energies determined using Kissinger and Ozawa methods range from 96 to 103 kJ/mol, lower than that of pristine copper(II) formate (∼115 ± 10 kJ/mol), demonstrating that amine ligands decrease the energy barrier for copper(II) reduction. Scanning electron microscopy reveals that thermal processing parameters (temperature, time and heating rate) and ligand structure strongly affect the formation of particles. Hexylamine produces uniform, densely packed spherical particles (0.3-1.2 μm) with low porosity across the investigated temperature range. Amino-2-propanol yields small particles (0.4-0.6 μm) only at 130 °C, whereas lower temperatures lead to agglomeration. In contrast, 2-(ethylamino)ethanol results in irregular and porous particles due to weaker coordination and higher volatility. Overall, ligand structure governs decomposition kinetics and particle morphology, providing a rational basis of designing low-temperature Cu particle-free inks for flexible printed electronics.