Diradicals as Topological Charge Carriers in Metal-Organic Toy Model Pt(HIB).

We explore the eclipsed stacking of a metal-organic Kagome lattice containing heavy-metal nodes. Our model is Pt(HIB), a hypothetical but viable member of a well-known family of hexaaminobenzene based metal-organic frameworks (MOFs). Applying space group theory, it is shown how molecular diradicals, brought into play by a noninnocent ligand, become topologically nontrivial bands when moving in a periodic potential. Three factors are required to enable this: (1) eclipsed stacking, which shifts the Fermi level near a symmetry-protected band crossing (2) the emergence of an electride-like band that renders the topological invariant equal to 1, thus nontrivial, and (3) Pt-induced spin-orbit coupling, to turn the crossing into a bulk band gap. The electride band, with its unforeseen role, bears kinship to the interlayer band in hexagonal superconductors. It places its charge density in the voids of the crystal, rather than around the atomic nuclei, and we name it a "pore band". While the synthesis of truly conductive MOFs has proven challenging, the analysis shows that intrinsically nonlocal physics may emerge from tunable molecular building blocks. With the richness of redox-active MOF chemistry, this offers a pathway to tailored topological electronics.