Quantum Spin Liquid from a Three-Dimensional Copper-Oxalate Framework

The quantum spin liquid (QSL) state is of great interest in relation to quantum computation and superconductivity and the search for new QSL materials is a current challenge in chemistry. Existing inorganic and molecular QSL compounds have two-dimensional structures, with spins arranged on triangular and kagome lattices, whereas three-dimensional structures with QSL characteristics are rare. In the copper-oxalate framework compound [(C2H5)3NH]2Cu2(C2O4)3, Cu­(II) is coordinated with three bisbidentate oxalate bridges to form a three-dimensional (10,3) lattice and this produces a strong antiferromagnetic interaction between Cu2+ (S = 1/2) atoms (θ = −180 K). No long-range ordering (LRO) was observed in either magnetic susceptibility or specific heat measurements down to 2 K. Absence of LRO was further confirmed by μSR measurements down to 60 mK, indicating that it is a gapless QSL with f > 3000. Due to Jahn–Teller distortion and partial dimerization, the effective dimensionality of the magnetic lattice is reduced. This compound nevertheless highlights the great potential for obtaining QSLs of varying dimensionality from metal–organic frameworks.