Ni(C5H5)2 belongs to a group of organometallic compounds called metallocenes. Metallocenes usually adopt structures in which a metal ion is sandwiched between two parallel cyclopentadienyl rings. This structure is relevant to the solubility in organic solvents and volatility. In the solid-state, the molecule has D5h symmetry, wherein the two rings are eclipsed.
The Ni center has a formal 2+ charge, and the Cp rings are usually assigned as cyclopentadienyl anions (Cp-), related to cyclopentadiene by deprotonation. The structure is similar to ferrocene. In terms of its electronic structure, three pairs of d electrons on nickel are allocated to the three d orbitals involved in Ni - Cp bonding: dxy, dx2–y2, dz2. One of the two remaining d-electrons resides in each of the dyz and dxz orbitals, giving rise to the molecule's paramagnetism. With 20 valence electrons, nickelocene has the highest electron count of the transition metal metallocenes. Cobaltocene, Co(C5H5)2, is, however, a stronger reducing agent.