Solvent Effects for Spectroscopic Properties of Near-Infrared Absorbing Nickel-Dithiolene Complex [Ni(iPr(2)timdt)(2)] (iPr(2)timdt: Monoanion of 1,3-Diisopropylimidazolidine-2,4,5-trithione)

摘要

The near-infrared (NIR) absorption properties of a square planar nickel-dithiolene complex [Ni(iPr(2)timdt)(2)] in various organic solvents have been investigated (iPr(2)timdt denotes a monoanion of 1,3-diisopropylimidazolidine-2,4,5-trithione). In non-coordinating aprotic organic solvents of smaller relative permittivity (epsilon(r) < 10) such as dichloromethane (epsilon(r) = 8.9), the neutral complex [Ni(iPr(2)timdt)(2)] shows a huge and sharp NIR absorption band at ca. 1000 mn having the molar absorptivity of epsilon = 6-8 x 10(4)L mol(-1) cm(-1). In contrast, in strongly coordinating solvents such as pyridine (Gutmann's donor number, DN = 33.1), the NIR absorption of [Ni(iPr(2)timdt)(2)](0) disappears most probably, owing to the coordination of pyridine molecules onto the axial sites of this square-planar complex. In high relative permittivity solvents such as N,N-dimethylformamide (DMI, epsilon(r) = 36.71), [Ni(iPr(2)timdt)(2)](0) (lambda(max): ca. 1000nm) undergoes spontaneous reduction reactions yielding the ionic complexes of [Ni(iPr(2)timdt)(2)](-) (lambda(max): ca. 1400 nm) and [Ni(iPr(2)timdt)(2)](2-) (no NIR peaks), which is indeed reconciled with the results of the spectroelectrochemical measurements. It is stressed that the absorption properties of [Ni(iPr(2)timdt)(2)] in the NIR region are sensitive to the solvent properties, and these complex systems serve as NIR probes to report solvent properties.