Low-temperature magnetic properties of the kagome MOF system Cu₃(HOTT)₂

The metal-organic framework (MOF) system Cu₃(HOTT)₂ coordinates Cu²⁺ with HOTT (2,3,7,8,12,13-hexaoxytetraazanaphthotetraphene), a conjugated polyaromatic tetraazanaphthotetraphene ligand, resulting in stacked 2D graphene-like honeycomb grids. The HOTT ligand is in a formal oxidation state of 3, and this generates an S = 1/2 radical state. The HOTT molecules form a honeycomb lattice, while the S = 1/2 Cu²⁺ ions each coordinate to two HOTT ligands, establishing a kagome lattice. Magnetic susceptibility indicates that the radical spins are paired, leading to magnetic properties that reflect one spin 1/2 per Cu on the kagome lattice. This arrangement creates a frustrated quantum magnetic system, making Cu₃(HOTT)₂ a compelling material for further investigation as a candidate quantum spin liquid (QSL). The exchange interactions between kagome sites are estimated to be of order 5 K. We propose to explore the magnetic properties of this compound at low temperatures using ZF and LF muon spin relaxation and compare these results with similar measurements that we made previously on the kagome MOF system Cu₃(HOTP)₂, whose properties were found to be consistent with a Z₂-linear Dirac QSL.