The electron density of the α form of boron has been obtained by multipole refinement against high-resolution, single-crystal x-ray diffraction data measured on a high-quality single crystal at a temperature of 100 K. Topological properties of this density have been used to show that all chemical bonds between B 12 clusters in α-B 12 are formed due to one orbital on each boron atom that is oriented perpendicular to the surface of the cluster. It is shown that the same orbital order on B 12 clusters persists in both α-B 12 and γ-B 28 polymorphs and in several dodecaboranes, despite the fact that in every case the B 12 clusters participate in entirely different kinds of exocluster bonds. It is likely that the same orbital order of B 12 clusters can explain bonding in other boron polymorphs and boron-rich solids.

The first-order charge density wave (CDW) phase transition of Er 2 Ir 3 Si 5 is characterized by a crystal structure analysis, and electrical resistivity, magnetic susceptibility and specific heat measurements. The incommensurate CDW is accompanied by a strong lattice distortion, from which it is shown that the CDW resides on zigzag chains of iridium atoms. The CDW transition affects the magnitude of the local magnetic moments on Er 3+ , implying strong coupling between CDW and magnetism. This could account for the observation that magnetic order is suppressed down to at least 0.1 K in the high-quality single crystal presently studied. Any disorder in the crystallinity, as in ceramic material, broadens and suppresses the CDW transition, while magnetic order appears at 2.1 K.

No abstract

Correlated variations of chemical bonds demonstrate stabilization by the resonance of the chloranilic acid anion. Proton transfer in some of the intermolecular hydrogen bonds is responsible for the ferroelectic properties.

The three-dimensional charge density wave (CDW) compound Lu 2 Ir 3 Si 5 undergoes a first-order CDW phase transition at around 200 K. An atypical CDW state is found, that is characterized by an incommensurate CDW with q = [0.2499(3), 0.4843(4), 0.2386(2)] at 60 K, and a large orthorhombic-to-triclinic lattice distortion with β = 91.945(2) • . We present the modulated crystal structure of the incommensurate CDW state. Structural analysis shows that the CDW resides on the zigzag chains of iridium atoms along c. The structural distortions are completely similar between nonmagnetic Lu 2 Ir 3 Si 5 and previously studied isostructural magnetic Er 2 Ir 3 Si 5 with the small differences explained by the different values of the atomic radii of Lu and Er. Such a similarity is unique to R 2 Ir 3 Si 5 (R = rare earth). It differs from, for example, the rare-earth CDW compounds R 5 Ir 4 Si 10 for which Lu 5 Ir 4 Si 10 and Er 5 Ir 4 Si 10 possess entirely different CDW states. We argue that the mechanism of CDW formation, thus, is different for R 2 Ir 3 Si 5 and R 5 Ir 4 Si 10 .