CpNi(dithiolene)] (and diselenolene) neutral radical complexes

Various preparations of the neutral radical CpNi(dddt)] complex (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate) were investigated with CpNi sources, Cp2Ni], Cp2Ni](BF4), CpNi(CO)]2, and CpNi(cod)](BF4), and dithiolene transfer sources, O=C(dddt), the naked dithiolate (dddt(2-)), the monoanion of square-planar Ni dithiolene complex (NBu4)Ni(dddt)2], and the neutral complex Ni(dddt)2]. The reaction of CpNi(cod)](BF4) with (NBu4)Ni(dddt)2] gave the highest yield for the preparation of CpNi(dddt)] (86%). CpNi(ddds)] (ddds = 5,6-dihydro-1,4-dithiin-2,3-diselenolate), CpNi(dsdt)] (dsdt = 5,6-dihydro-1,4-diselenin-2,3-dithiolate), CpNi(bdt)] (bdt = 1,2-benzenedithiolate), and CpNi(bds)] (bds = 1,2-benzenediselenolate) were synthesized by the reactions of Cp2Ni] with the corresponding neutral Ni dithiolene complexes Ni(ddds)2]2, Ni(dsdt)2], Ni(bdt)2], and Ni(bds)2], respectively. The five, formally Ni(III), radical complexes oxidize and reduce reversibly. They exhibit, in the neutral state, a strong absorption in the NIR region, from 1000 nm in the dddt/ddds/dsdt series to 720 nm in the bdt/bds series with epsilon values between 2500 and 5000 M(-1) cm(-1). The molecular and solid state structures of the five complexes were determined by X-ray structure analyses. CpNi(dddt)] and CpNi(ddds)] are isostructural, while CpNi(dsdt)] exhibits a closely related structure. Similarly, CpNi(bdt)] and CpNi(bds)] are also isostructural. Correlations between structural data and magnetic measurements show the presence of alternated spin chains in CpNi(dddt)], CpNi(ddds)], and CpNi(dsdt)], while a remarkably strong antiferromagnetic interaction in CpNi(bdt)] and CpNi(bds)] is attributed to a Cp...Cp face-to-face sigma overlap, an original feature in organometallic radical complexes.