Amine-capped gold nanoparticles: reaction steps during the synthesis and the influence of the ligand on the particle size

Alkylamine-capped gold nanoparticles were synthesised using the Leff method. In order to investigate the influence on the complexes formed during the synthesis and the final size of the protected nanoparticles the chain length of the stabilizing ligands varied. Phase transfer and amine complex formation were studied in solution with X-ray absorption spectroscopy. The phase transfer complexes retain the quadratic planar conformation whilst all alkyl amines form a linear coordinated gold(I) complex. After reduction, the particles were characterised in solution with EXFAS, UV-Vis spectroscopy, and compared to TEM measurements. The size of the particles was determined from the coordination number of the first gold shell. The position of the UV-Vis plasmon band and the distance of the first gold shell were used to qualitatively compare the effects of the ligands on the particle size. The size of the particles decreases with increasing chain length.