Syntheses, X-ray crystal structures and properties of di- and tetra-ferrocenyl nickel-bis(1,4-dithiin-5,6-dithiolate) complexes

Tetra-n-butylammonium salts of nickel-bis(2-ferrocenyl-1,4-dithiin-5,6-dithiolate) (1; TBA[Ni(fcvdt)2]) and nickel-bis(2,3-diferrocenyl-1,4-dithiin-5,6-dithiolate) (2; TBA[Ni(dfcvdt)2]) have been successfully synthesized. The crystal structures of complex 1 and 2 were determined by X-ray analysis. The [Ni(fcvdt)2]− anion has a chair-like conformation with the two ferrocenyl groups folding up and down while the [Ni(dfcvdt)2]− anion has a boat-like conformation with four ferrocenyl groups folding up. Cyclic voltammograms of these complexes show two reversible redox peaks at around −0.9 V and −0.2 V (Ag/Ag+, THF) associated with the Ni(II) dithiolate complex and one quasi-reversible peak associated with the ferrocenyl moieties. The complexes exhibit a strong near-IR absorption at 1178 nm (log ε = 3.99) for complex 1 and at 1155 nm (log ε = 4.06) for complex 2. This suggests the possibility of utilizing these complexes as near-IR dyes for absorbing lower energy.