Novel tetrahedral tetranickel cluster with alkylidyne ligand (NiCp)4(μ3-CR)

A novel tetrahedral (μ3-alkylidyne)tetranickel cluster (NiCp)4(μ3-C(CH2)4CH3) (4) was obtained in the reaction of nickelocene with potassium and 1-hexene. Compound 4 was characterised by means of MS and X-ray diffraction analysis. It crystallizes in the orthorhombic crystal system and Pna21 (No. 33) space group. Unit cell dimensions: a = 28.406(6) Å, b = 8.928(2) Å, c = 9.541(2) Å; Z = 4. The compound possesses 63 valence electrons, three more than the expected “magic number” for such type of clusters, and three of the four nickel atoms do not fulfil the 18VE rule. It is paramagnetic with the magnetic moment 3.54 μB, what corresponds to three unpaired electrons per molecule. This was confirmed by molecular orbital calculations using the density functional theory (DFT).