[Ni(R(2)pipdt)(2)](BF4)(2)(R(2)pipdt=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 com plexes, which show strong negative solvatochromism and negative first molec ular hyperpolarizability, and the use of Raman spectroscopy to establish th e extent of electronic delocalisation in these complexes, are reported.