Single Crystal and Magnetic Characterization of Iodobarlowite Cu ₄ (OH) ₆ FI: A Kagomé Lattice Synthesized from a 2-D Triangular Precursor

High Resolution Image Download MS PowerPoint Slide A single-step synthetic method to produce single crystals of the barlowite structural family is disclosed with iodobarlowite as a focus. The kagomé lattice of iodobarlowite, Cu 4 (OH) 6 FI, is furnished by removal of 1/4 of the triangular lattice sites of iodobotallackite, Cu 2 (OH) 3 I. Single-crystal structures have been solved at 100 and 300 K, both of which show I – vacancies within the lattice with no attendant Cu vacancies. X-ray absorption spectroscopy and diffraction studies reveal only the presence of Cu(II), no F – substitution at the I – site, and no Cu vacancies, suggesting that the charge balance to accommodate the I – deficiency occurs through loss of protons from the bridging hydroxide ligands during hydrothermal synthesis. Unlike microcrystalline powders, single-crystalline Cu 4 (OH) 6 FI exhibits a single magnetic transition at 15 K, which contrasts with the large Weiss constant of θ = −163(5) K, highlighting the key role of geometric spin frustration in the kagomé lattice to lower the critical temperature of the magnetically ordered state. Temperature-dependent susceptibility measurements indicate that the low temperature magnetic phase is associated with an uncompensated antiferromagnetic ordered state arising from the competing interactions between the four S = 1/2 Cu(II) spins of the iodobarlowite lattice.