The contrasted structural and magnetic behaviour of two single-component paramagnetic dithiolene complexes

The neutral organometallic/dithiolene radical complexes [CpNi(oxddt)] and [CpNi(bddt)] were prepared, respectively, from the reactions of [Ni(oxddt)2] with [Cp2Ni] and (NBu4)[Ni(bddt)2] with [CpNi(cod)](BF4) (oxddt = o-xylenediyldithioethylene-1,2-dithiolato, bddt = 1,4butanediyldithioethylene-1,2-dithiolato). Both complexes exhibit reversible oxidation and reduction waves to the cation and anion forms, respectively. A NIR absorption is observed around lmax = 825 for [CpNi(oxddt)] and 774 nm for [CpNi(bddt)] in dichloromethane solution. The X-ray crystal structures of the two complexes show two-legged piano-stool geometries around the central nickel atom (formally Ni) and strong distortions from planarity of the eightmembered ring moieties. In the solid state, the stronger rigidity of [CpNi(oxddt)] allows for a face-to-face p–p stacking of the radicals into dyads, confirmed by a singlet–triplet magnetic behaviour while the more flexible [CpNi(bddt)] radical complexes only interact through a lateral antiferromagnetic interaction giving rise to Heisenberg-type uniform spin chains.