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.