New series of asymmetrically substituted bis(1,2-dithiolato)-nickel(III) complexes exhibiting near IR absorption and structural diversity

Abstract

The synthesis, structural characterization, and properties of a new series of asymmetrically substituted bis(dithiolene) nickel(III) compounds [Bu₄N][Ni(Phdt)₂] (1) (Phdt = 2-Phenyl-1,2-dithiolate), [Bu₄N][Ni(NO₂Phdt)₂] (2) (NO₂Phdt = 2-(p-nitrophenyl)-1,2-dithiolate), [Bu₄N][Ni(FPhdt)₂] (3) (FPhdt = 2-(p-fluorophenyl)-1,2-dithiolate), [Bu₄N][Ni(ClPhdt)₂] (4) (ClPhdt = 2-(p-chlorophenyl)-1,2-dithiolate), and [Bu₄N][Ni(BrPhdt)₂] (5) (BrPhdt = 2-(p-bromophenyl)-1,2-dithiolate) have been described. All complexes 1-5 exhibit absorptions in the near-infrared region; the shift of these absorption bands can be tuned by the choice of the substituents on the relevant dithiolene moieties. The substituents on the dithiolene moiety are also responsible for their structural diversities. The nature of the substituents on the dithiolene moiety play an important role in tuning the redox potentials along this series. The nitro derivative (compound 2) exhibits several redox couples in its cyclic voltammogram in contrast to the other compounds in this series. The synthesis and characterization of two asymmetrically halogen substituted tetrathiafulvalene (TTF) derivatives 4,4'-bis(4-chlorophenyl)-tetrathiafulvalene ClPhTTF (6) and 4,4'-bis(4-bromophenyl)-tetrathiafulvalene (BrPhTTF) (7) have been described. One of these compounds has been structurally characterized. Iodine treatment of the monoanionic Ni(III) compound [Bu₄N][Ni(ClPhdt)₂] (4) results in the formation of a neutral Ni(IV) complex [Ni(ClPhdt)₂] (8). All monoanionic compounds 1-5 are Ni(III) complexes, as evidenced by electron spin resonance spectroscopy. Interestingly, strong Cl...Cl interactions are observed in the solid state structures of the chlorinated compounds 6 and 8. Finally, the structural features of compound [Ni(ClPhdt)₂] (8) and the TTF derivative ClPhTTF (6) are compared based on their enormous structural similarities, and the neutral compound [Ni(ClPhdt)₂] (8) is classed as the "an inorganic counterpart of TTF".