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Structural characterization is developed to determine crystallographic site-specific metal disorder. Anomalous scattering at the Zn and Cu edges is used for determining that there is no Zn occupation of the intralayer Cu sites within the kagome layer, however there is Cu present on the Zn intersite, which has led to a structural formula of ([Zn.sub.0.85][Cu.sub.0.15])[Cu.sub.3][(OH).sub.6][Cl.sub.2].

The synthesis and magnetic properties of a new series of magnetically frustrated materials [Mg.sub.x][Cu.sub.4-x][(OH).sub.6][Cl.sub.2] are described. The studies have shown that site disorder within the kagome layers is minimized because of the different ligand-field chemistry of [Mg.sup.2+] and [Cu.sup.2+].

The mechanism of autoreduction is understood by studying the thermal reduction of the Pd-Co cyanogel system formed by the reaction of Pd[Cl.sub.4.sup.2-] and Co[(CN).sub.6.sup.3-] in an inert atmosphere. Pt-Co cyanogel is also shown to autoreduce via a similar route and CoPt[(CN).sub.4] is confirmed as an intermediate.

Here, we study the nature of metal-metal bonding in the ThCr2Si2 structure type by probing the rate-limiting steps in the oxidative deintercalation of KNi2Se2. For low extents of oxidation, alkali ions are removed exclusively to form K1-xNi2Se2. For greater extents of oxidation, the rate of the reaction decreases dramatically, concomitant with the extraction of both potassium and nickel to form K1-xNi2-ySe2. The appreciable mobility of transition metal ions is unexpected, but illustrates the relative energy scales of different defects in the ThCr2Si2 structure type. Furthermore, the fully oxidized compounds, K0.25Ni1.5Se2, spontaneously convert from the tetrahedral [NiSe4]-containing ThCr2Si2 structure to a vacancy-ordered NiAs structure with [NiSe6] octahedra. From analysis of the atom positions and kinetic data, we have determined that this transformation occurs by a continuous, low-energy pathway via subtle displacements of Ni atoms and buckling of the Se sublattice. These results have profound implications for our understanding of the stability, mobility, and reactivity of ions in materials. [ABSTRACT FROM AUTHOR]

The article presents a study which characterized the structural and magnetic properties of MgxCu4-x(OH)6Cl2, an isostructural series of compounds with paratacamite. The study investigated the synthesis of the compounds, and the presence of Cu2+ atoms. It showed that the compounds exhibited an unconventional magnetic ground state due to the absence of magnetic order and disorder in the minimal site at the kagomé planes.

Structural characterization, exploiting X-ray scattering differences at elemental absorption edges, is developed to quantitatively determine crystallographic site-specific metal disorder. We apply this technique to the problem of Zn-Cu chemical disorder in ZnCu3(OH)6Cl2. This geometrically frustrated kagomé antiferromagnet is one of the best candidates for a spin-liquid ground state, but chemical disorder has been suggested as a mundane explanation for its magnetic properties. Using anomalous scattering at the Zn and Cu edges, we determine that there is no Zn occupation of the intralayer Cu sites within the kagomé layer; however there is Cu present on the Zn intersite, leading to a structural formula of (Zn0.85Cu0.15)- Cu3(OH)6Cl2. The lack of Zn mixing onto the kagomé lattice sites lends support to the idea that the electronic ground state in ZnCu3(OH)6Cl2 and its relatives is nontrivial. [ABSTRACT FROM AUTHOR]

The design of novel quaternary materials can be a chemically challenging endeavor. Here, we show that a new tolerance factor, we herein call the quaternary tolerance factor (QTF), akin to the Goldschmidt ratio, can be applied to a homologous series of quaternary materials to aid in the prediction of structural stability in new phases. Single crystals of nine new members of the A 2 Ln 4 Cu 2 n Q 7+ n homologous series were synthesized ( A = K, Rb, Cs, Ln = Sm, Gd, Tb, Dy, Er, Yb, Lu, Q = S, Se) for n = 1, 2, and 3 using a reactive KCl flux method as the sole potassium source. This homologous series is notable for being the largest of all known chalcogenide homologies and thus serves as a case study for understanding quaternary structural relationships. We present a thorough structural analysis of these newly synthesized compounds and place them in the context of all previously reported members of the homologous series. We then report a generalizable tolerance factor capable of predicting structurally interrelated quaternary materials from an a priori sphere-packing approach for the design of new materials.