Publisher Summary This review is concerned with the neglected class of inorganic compounds, which contain ions of the same element in two different formal states of oxidation. Although the number of references cited in our review show that many individual examples of this class have been studied, yet they have very rarely been treated as a class, and there has never before, to our knowledge, been a systematic attempt to classify their properties in terms of their electronic and molecular structures. In the past, systems containing an element in two different states of oxidation have gone by various names, the terms “mixed valence,” nonintegral valence,” “mixed oxidation,” “oscillating valency,” and “controlled valency” being used interchangeably. Actually, none of these is completely accurate or all-embracing, but in our hope to avoid the introduction of yet another definition, we have somewhat arbitrarily adopted the phrase “mixed valence” for the description of these systems. The concept of resonance among various valence bond structures is one of the cornerstones of modern organic chemistry.

Mixed Valence Chemistry-A Survey and Classification

This critical review presents a comprehensive study of transition-metal carboxylate clusters which may serve as secondary building units (SBUs) towards construction and synthesis of metal–organic frameworks (MOFs). We describe the geometries of 131 SBUs, their connectivity and composition. This contribution presents a comprehensive list of the wide variety of transition-metal carboxylate clusters which may serve as secondary building units (SBUs) in the construction and synthesis of metal–organic frameworks. The SBUs discussed here were obtained from a search of molecules and extended structures archived in the Cambridge Structure Database (CSD, version 5.28, January 2007) which included only crystals containing metal carboxylate linkages (241 references).

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Secondary building units, nets and bonding in the chemistry of metal–organic frameworks

Hydrogen bonding in solids correlation of spectroscopic and crystallographic data

The distribution of distances from atoms of a particular element E to a probe atom X (oxygen in most cases), both bonded and intermolecular non-bonded contacts, has been analyzed. In general, the distribution is characterized by a maximum at short E⋯X distances corresponding to chemical bonds, followed by a range of unpopulated distances – the van der Waals gap – and a second maximum at longer distances – the van der Waals peak – superimposed on a random distribution function that roughly follows a d3 dependence. The analysis of more than five million interatomic “non-bonded” distances has led to the proposal of a consistent set of van der Waals radii for most naturally occurring elements, and its applicability to other element pairs has been tested for a set of more than three million data, all of them compared to over one million bond distances.

/pdf/a-cartography-of-the-van-der-waals-territories-4rxnfp59yz.pdf

A cartography of the van der Waals territories

The electrochemical reaction of lithium with crystallized -Fe2O3 (hematite) has been studied by means of in situ X-ray diffraction. When reacting large particles (~0.5 µm), we observed the well-known transformation of the close-packed anionic array from hexagonal (hc) to cubic (ccp) stacking. At the early stage of the reduction, a very small amount of lithium (xc<0.1 Li/Fe2O3) can be inserted before this structural transformation occurs. Nanosize -Fe2O3 made of fine monolithic particles (200 A) behaves very different, since up to one Li per formula unit (-Li1Fe2O3,xc = 1) can be inserted in the corundum structure without phase transformation. To our knowledge, this is the first time this phase is maintained for such large xc values. This cationic insertion was found to come with a small cell volume expansion evaluated to 1%. Unsuccessful attempts to increase the xc values on large particles by decreasing the applied discharge current density suggest that the particle size is the only parameter involved. The better structural reversibility of this monophasic process compared to the biphasic one was confirmed by electrochemical cycling tests conducted with hematite samples of various particle sizes. Therefore, by using nanosize particles, we can drastically increase the critical Li concentration required to observe the hcccp transition. This work demonstrates that a careful control of the texture/particle size of electrochemically active oxide particles is likely an important variable that has been largely disregarded for such properties. ©2002 The Electrochemical Society. All rights reserved.

https://iopscience.iop.org/article/10.1149/1.1528941/pdf

Effect of Particle Size on Lithium Intercalation into α ­ Fe2 O 3

A single-crystal X-ray structural investigation of the material previously known as ‘Ag2O II’ has shown the correct empirical formula to be Ag3O.

X-Ray crystal structure of Ag6O2

Die Beziehung zwischen der Wellenzahl der OH-Valenzschwingung (νOH) und dem O…O-Abstand in Wasserstoffbrucken von festen Hydroxiden wurde erneut studiert. Es erscheint dabei zweckmasig, Hydroxide mit einer OH…OH- und solche mit einer OH…O-Gruppierung getrennt zu betrachten. Fur beide Klassen ergibt sich ein stetiger Zusammenhang zwischen νOH und dem O…O-Abstand in der Wasserstoffbrucke. Abweichungen davon werden diskutiert.



The relation between νOH and the O…O distance in hydrogenbonded solid hydroxides has been reinvestigated. The hydroxides are subdivided into those with OH…OH bonds and those having OH…O bonds. Deviations from the observed continuous relation are discussed.

Zusammenhang zwischen OH-Valenzfrequenzen und OH…OH- bzw. OH…OH-Abständen in festen Hydroxiden

Es wurde die Wasserbindung im Dihydrat und Monohydrat des Wolframtrioxids mit Hilfe von Ultrarotabsorptions- und Protonenresonanzspektren untersucht. In beiden Verbindungen liegt das Wasser als Kristallwasser vor.



IR- and proton resonance spectra have shown that wolfram trioxide di- and monohydrate contain the water as crystal water.

Zur Bindung des Wassers in den Hydraten des Wolframtrioxids

IR- und1H-Kernresonanzmessungen an InO(OH)

Abstract Au2(SeO2)2O was prepared from gold and excess selenic acid in a sealed tube at 533 K. The crystal structure [Pba2, a = 659.2(2), b = 1183.7(3), c = 399.8(1) pm, Z = 2,R = 0.087] was determined; gold atoms are bridged by oxide ions (lying on twofold axes) and selenite ions. The extended structure consists of polymeric layers parallel to the xy-plane. The light atom positions are inaccurate because of the presence of a heavy atom in a polar space group.

Darstellung und Kristallstruktur von Di-gold(III)bis(selenit)oxid, Au2(SeO3)2O / Preparation and Crystal Structure of Di-gold(III) Bis(selenite) Oxide, Au2(SeO3)2O

Einhard Schwarzmann

Papers

X-Ray crystal structure of Ag6O2

Zusammenhang zwischen OH-Valenzfrequenzen und OH…OH- bzw. OH…OH-Abständen in festen Hydroxiden

Zur Bindung des Wassers in den Hydraten des Wolframtrioxids

IR- und1H-Kernresonanzmessungen an InO(OH)

Darstellung und Kristallstruktur von Di-gold(III)bis(selenit)oxid, Au2(SeO3)2O / Preparation and Crystal Structure of Di-gold(III) Bis(selenite) Oxide, Au2(SeO3)2O