Fragmenting the Kagomé Lattice: Pressure-Tuned Anisotropy of Cu2+ Triangles in a Novel Atacamite Relative CaCu(OH)3Cl

Abstract

The atacamite family of copper halide minerals contains several prominent quantum spin liquid candidate materials, chiefly herbertsmithite. Unfortunately, an intrinsic chemical disorder in herbertsmithite complicates attempts to perform magneto-structural correlations that deconvolute the fundamental magnetic exchange terms that underpin frustration. We sought to synthesize disorder-free zero-dimensional analogues of the atacamites that retain the basic local geometry required for frustration (i.e., triangular arrangements of spins) while avoiding the extended lattices that are prone to site disorder. We present here the synthesis of a novel trimetallic compound, CaCu(OH)₃Cl, that is reminiscent in composition and structure to the known atacamites. CaCu(OH)₃Cl features mildly Jahn–Teller distorted copper triangles that represent zero-dimensional analogues to the triangles that comprise the kagomé layers in herbertsmithite. We present a high-pressure synchrotron single crystal X-ray diffraction study of CaCu(OH)₃Cl up to 10.1(2) GPa and show that pressure counteracts the magnetic Jahn–Teller distortion of the square planar Cu(OH)₄ units that comprise the copper triangles, offering a new direction for optimizing magnetic frustration.