sentences:  Of historical interest is the supposedly diamagnetic [Ni(diars)](ClO), obtained by heating nickel perchlorate with diars.Octahedral "d" complexes characteristically have triplet ground states, so the diamagnetism of this complex was puzzling.Later by X-ray crystallography, the complex was shown to be pentacoordinate with the formula [Ni(triars)(diars)](ClO), where triars is the tridentate ligand [CHAs(CH)]As(CH), arising from the elimination of trimethylarsine.