Two-Dimensional Honeycomb Lattice Consisting of a New Organic Radical 2-Cl-6-F-V

We have successfully synthesized new organic radical crystals of 2-Cl-6-F-V [= 3-(2-chloro-6-fluorophenyl)-1,5-diphenylverdazyl]. Two types of dominant intermolecular interactions forming a honeycomb lattice are deduced from the molecular packing in the crystal, and ab initio molecular orbital calculation also indicate such an exchange network. We analyzed the magnetic and thermodynamic properties by using the quantum Monte Carlo method and successfully explained these properties as an S = 1/2 Heisenberg honeycomb lattice with ferromagnetic chain interactions. Our results indicate that 2-Cl-6-F-V is one of the few examples of a purely organic radical compound that forms two-dimensional lattices, and this paper presents the first complete, quantitative description of an actual honeycomb lattice material.