Metallocene-coupled cumulenes: a quest for chiral single-molecule magnets

In this work, we computationally investigated nickelocene and chromocene-coupled linear carbon chains. The designed systems are [Ni]-C_n-Ni], [Cr]-C_n-[Cr] and [Cr]-C_n-[Ni] (n = 3 to 9), where [Ni], [Cr] and C_n represent nickelocene (NiCp₂, Cp = cyclopentadienyl), chromocene (CrCp₂) and linear carbon chains respectively. The magnetic properties of these systems were computationally investigated by a density functional theory-based method. Ferromagnetic ground states were observed for [Ni]-C_n-[Ni] and [Cr]-C_n-[Cr] complexes for couplers with odd numbers of carbon atoms (n = 3, 5, 7 and 9), whereas antiferromagnetic ground states result for couplers with even numbers of carbon atoms (n = 4, 6 and 8). However, a totally opposite trend is followed by [Cr]-C_n-[Ni] complexes due to the spin polarization inside the chromocene. The calculation and study of magnetic anisotropy for all the ferromagnetic complexes suggest that the [Ni]-C_n-[Ni] complexes with coupler of odd number of carbon atoms will be suitable for the synthesis of single-molecule magnets among the designed complexes.