Size-Controlled Synthesis of Ag Nanoparticles Functionalized by Heteroleptic Dipyrrinato Complexes Having meso-Pyridyl Substituents and Their Catalytic Applications

The syntheses of heteroleptic dipyrrinato nickel­(II) complexes [Ni­(4-pydpm)­(dedtc)] (1) and [Ni­(4-pydpm)­(dipdtc)] (2) [4-pydpm = 5-(4-pyridyl)­dipyrromethene; dedtc = diethyldithiocarabamate; and dipdtc = diisopropyldithiocarbamate] and the thorough characterization of these complexes by satisfactory elemental analyses, electrospray ionization mass spectrometry, Fourier-transform infrared, NMR (1H, 13C), and UV–vis spectroscopies, and electrochemical studies was achieved. Structure of 1 was authenticated by X-ray single-crystal analysis. Both the complexes 1 and 2 were successfully utilized as a capping agent in the preparation of silver nanoparticles. Availability of free pyridyl nitrogen on the dipyrrin core of these complexes was meticulously exploited in functionalization and stabilization of the silver nanoparticles (AgNPs). Morphological and structural investigations on colloidal nanoparticles were followed by UV–vis spectroscopy and transmission electron microscopy (TEM). Overall results revealed that average size of the silver nanoparticles (∼10, 15, 20 nm, and aggregation) is strongly influenced by ratio of Ag/[1/2] (03, 06, 10, 20). Correlation between particle size and capping agents was realized by UV–vis and TEM studies. Catalytic activity of the AgNPs obtained through this route was successfully employed in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). It was established that reduction process follows a pseudo-first-order kinetics.