[Ni(R2pipdt)2](BF4)2 (R2pipdt = 1,4-disubstituted-piperazine-3,2-dithione) as useful precursors of mixed–ligand dithiolenes of interest for non-linear optics

A simple method to obtain in high yields mixed-ligand nickel–dithiolene complexes, which show strong negative solvatochromism and negative first molecular hyperpolarizability, and the use of Raman spectroscopy to establish the extent of electronic delocalisation in these complexes, are reported.