Low temperature properties of a super-honeycomb S=1/2 frustrated magnet

The MOF (Metal-organic framework) system Cu3(HHTP)2 coordinates Cu with HHTP, a conjugated polyaromatic tricatecholate ligand, resulting in stacks of extended 2D graphene-like honeycomb grids. The HHTP ligand is triply oxidized with a formal oxidation state of −3 after 6-fold deprotonation of the hydroxy groups producing an S=1/2 radical state. The HTTP molecules form a honeycomb lattice and the S=1/2 Cu2+ ions each coordinate to two HHTP molecules forming a kagome lattice. The Cu and HHTP taken together form a super-honeycomb lattice of S=1/2 spins which is characterized by a nearest-neighbour Cu-HHTP exchange interaction and two further frustrating interactions between next-nearest-neighbours. This material therefore provides an interesting new frustrated quantum magnetic system and we wish to explore the magnetic properties of Cu3(HHTP)2 down to low temperatures using muSR.