Planar tetracoordinate carbon CNi4H4 cluster and its nanoribbon complexes [(CNi4H2)n(C4H6)n+1] (n=1-4) stabilized using aromatic butadiene ligands

We report a density-functional study on planar tetracoordinate carbon (ptC) cluster CNi4H4 and its nanoribbon complexes [(CNi4H2)(n)(C4H(6))(n+1)] (n = 1-4), in which ptC CNi4 units are separated, interconnected, and stabilized via aromatic butadiene ligands. Simplified as an 18-electron system, ptC CNi4H4 cluster features four peripheral Ni-H-Ni three-center two-electron (3c -2e) sigma bonds and three-fold (2 pi, 2 sigma, and 6 sigma) aromaticity. The 2 pi subsystem is situated on inner CNi4 core, 2 sigma is located at peripheral Ni4H4 ring and oriented tangentially, and 6 sigma sextet is global in nature and oriented radially. The [(CNi4H2)(n)(C4H6)(n+1)] (n = 1-4) nanoribbons span from 6.60 to 25.69 angstrom in length, which contain isolated ptC CNi4H2 units, being interconnected edge-by-edge via butadiene ligands. Chemical integrity of CNi4H2 and butadiene are maintained in the nanoribbons, except for two Ni-C sigma bonds per ligand. Nanoribbon complexes represent a new type of extended low -dimensional nanomaterials using the ptC CNi4 unit. (C) 2018 Elsevier B.V. All rights reserved.