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Colloidal bismuth therapeutics have been used for hundreds of years, yet remain mysterious. Here we report an X-ray pair distribution function (PDF) study of the solvolysis of bismuth disalicylate, a model for the metallodrug bismuth subsalicylate (Pepto-Bismol). This reveals catalysis by traces of water, followed by multistep cluster growth. The ratio of the two major species, {Bi 9 O 7 } and {Bi 38 O 44 }, depends on exposure to air, time, and the solvent. The solution-phase cluster structures are of significantly higher symmetry in comparison to solid-state analogues, with reduced off-center Bi 3+ displacements. This explains why such "magic-size" clusters can be both stable enough to crystallize and sufficiently labile for further growth.

The AMnO 2 delafossites (A = Na, Cu) are model frustrated antiferromagnets, with triangular layers of Mn 3+ spins. At low temperatures ( T N = 65 K), a C 2/ m → P 1̅ transition is found in CuMnO 2 , which breaks frustration and establishes magnetic order. In contrast to this clean transition, A = Na only shows short-range distortions at T N . Here, we report a systematic crystallographic, spectroscopic, and theoretical investigation of CuMnO 2 . We show that, even in stoichiometric samples, nonzero anisotropic Cu displacements coexist with magnetic order. Using X-ray/neutron diffraction and Raman scattering, we show that high pressures act to decouple these degrees of freedom. This manifests as an isostuctural phase transition at ∼10 GPa, with a reversible collapse of the c -axis. This is shown to be the high-pressure analogue of the c -axis negative thermal expansion seen at ambient pressure. Density functional theory (DFT) simulations confirm that dynamical instabilities of the Cu + cations and edge-shared MnO 6 layers are intertwined at ambient pressure. However, high pressure selectively activates the former, before an eventual predicted reemergence of magnetism at the highest pressures. Our results show that the lattice dynamics and local structure of CuMnO 2 are quantitatively different from nonmagnetic Cu delafossites and raise questions about the role of intrinsic inhomogeneity in frustrated antiferromagnets.

The structures and properties of vanadium oxides are often related to the formation of molecule-like clusters of vanadium cations through direct V-V bonding. GaV 2 O 4 , a new vanadium spinel, was synthesized. Powder diffraction and X-ray total scattering studies, complemented by magnetization and resistivity measurements, reveal that the low-temperature phase of this material is structurally distorted and features ordered pairs of three- and four-atom vanadium clusters. These clusters persist into a disordered cubic phase above the charge-ordering transition at T CO = 415 K. Furthermore, quasi-elastic neutron scattering indicates that the disordered clusters remain well-defined and static to 1100 K.