Properties of the tetraphenylcyclobutadienecyclopentadienylnickel(II) cation
1 and its tetra-
o-fluoro derivative
1a have been measured and calculated. The B3LYP/TZP optimized geometry of the free cation
1 agrees with a single-crystal X-ray diffraction structure except that in the crystal one of the phenyl substituents is strongly twisted to permit a close-packing interaction of two of its hydrogens with a nearby BF
4– anion. The low-energy parts of the solution electronic absorption and magnetic circular dichroism (MCD) spectra of
1 and
1a have been interpreted by comparison with TD-DFT (B3LYP/TZP) results. Reduction or pulse radiolysis lead to a neutral 19-electron radical, whose visible absorption and MCD spectra have been recorded and interpreted as well. The reduction is facilitated by ∼0.1 V upon going from
1 to
1a. Unsuccessful attempts to prepare several other aryl substituted derivatives of
1 by the classical synthetic route are described in the
Supporting Information.