Fragmenting the\nKagome Lattice: Pressure-Tuned\nAnisotropy of Cu<sup>2+</sup> Triangles in a Novel Atacamite Relative\nCaCu(OH)<sub>3</sub>Cl

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