From a paramagnetic, mononuclear supersulfidonickel(II) complex to a diamagnetic dimer with a four-sulfur two-electron bond

The first isolable "side-on" supersulfidonickel(II) complex 1(1) with the elusive S2-. ligand has been synthesized by facile oxidation of the corresponding nickel(I) precursor LNi] with elemental sulfur. Remarkably, paramagnetic 1(1) associates voluntarily to give the diamagnetic dimer 1(2) with a four-sulfur two-electron bond as proven by X-ray diffraction analysis, spectroscopic measurements (1H NMR, EPR, SQUID), and DFT calculations. Gentle sulfur transfer of 1(1) to Ph3P or its reaction with LNi] affords solely the genuine disulfide complex 3 having a Ni2(mu-mu2:mu2-S2) core.