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, OdC(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 center dot center dot center dot Cp face to face sigma overlap, an original feature in organometallic radical complexes.