We present the results of first-principle calculations using the Vienna Ab initio Simulation Package (vasp) for a class of organometallics labeled ${\mathit{TM}}_3{\mathrm{C}}_6{\mathrm{O}}_6$ ($\mathit{TM}=\mathrm{Sc}$, Ti, V, Cr, Fe, Co, Ni, and Cu) in the form of planar, two-dimensional, periodic freestanding layers. These materials, which can be produced by on-surface coordination on metallic surfaces, have a kagome lattice of $\mathit{TM}$ ions. Calculating the structural properties, we show that all considered materials have local magnetic moments in the ground state, but four of them (with Fe, Co, Ni, and Cu) show spin-crossover behavior or switch between magnetic and nonmagnetic states by changing the lattice constant, which could be valuable for possible epitaxy routes on various substrates. Surprisingly, we find a very large richness of electronic and magnetic properties, qualifying these materials as highly promising metal-organic topological quantum materials. We find semiconductors with nearest-neighbor ferromagnetic (FM) or antiferromagnetic (AFM) couplings for V, and Sc, Ti, and Cr, respectively, being of potential interest to study spin ice or spin liquids on the 2D kagome lattice. Other $\mathit{TM}$ ion systems combine AFM couplings with metallic behavior (Fe and Ni) or are ferromagnetic kagome metals like ${\mathrm{Cu}}_3{\mathrm{C}}_6{\mathrm{O}}_6$ with band crossings at the Fermi surface. For the latter compound, the spin-orbit coupling is shown to be responsible for small gaps which makes them a candidate material to observe the quantum anomalous Hall effect.

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• Electronic structure
• First-principles calculations
• Flat bands
• Magnetic interactions
• Topological materials
• 2-dimensional systems