The literature on open-framework materials has shown numerous examples of porous solids with additional structural, chemical, or physical properties. These materials show promise for applications ranging from sensing, catalysis and separation to multifunctional materials. This critical review provides an up-to-date survey to this new generation of multifunctional open-framework solids. For this, a detailed revision of the different examples so far reported will be presented, classified into five different sections: magnetic, chiral, conducting, optical, and labile open-frameworks for sensing applications. (413 references.)

Old materials with new tricks: multifunctional open-framework materials.

In the paragraph following eq 28, the average bond valence was incorrectly referred to as V/R. It has been corrected to V/N. The paper originally posted to the web on September 3, 2009, and was reposted on September 24, 2009.

http://pubs.acs.org/doi/pdf/10.1021/cr900053k

Recent developments in the methods and applications of the bond valence model.

Clathrate hydrates, ice-like host–guest systems containing guest molecules in cages of hydrogen-bonded water molecules exist in three well-characterized cubic forms, and a less well-characterized tetragonal form1,2 On the basis of 2H and l29Xe NMR measurements and X-ray and neutron powder diffraction results, we now report a new hexagonal hydrate structure requiring both large and small guest molecules to stabilize the structure This hydrate is expected to be isostructural with the hexagonal clathrasil dodecasil-lH (see ref 14 for clathrasil nomenclature) As for the cubic clathrate hydrates, the new hydrate structure may occur naturally

A new clathrate hydrate structure

Changes in the lattice parameters of fluorite type MO2 oxides (M = Hf4+, Zr4+, Ce4+, Th4+, U4+) due to the formation of solid solutions can be predicted by proposed empirical equations. The equations show the generalized relationship between dopant size and ionic conductivity in the binary systems of these oxides, illustrating that the smaller the difference between the dopant ionic radius and the critical dopant radius, the higher the conductivity. The solubility limit of the same periodic group elements in fluorite-structure MO2 oxides decreaes linearly with the square of Vegard's slope for each solute as determined from the proposed equations.

Lattice Parameters, Ionic Conductivities, and Solubility Limits in Fluorite-Structure MO2 Oxide [M = Hf4+, Zr4+, Ce4+, Th4+, U4+] Solid Solutions

Recent advances in the synthesis of (hetero)aryl-substituted heteroarenes via transition metal-catalysed direct (hetero)arylation of heteroarene C–H bonds with aryl halides or pseudohalides, diaryliodonium salts, and potassium aryltrifluoroborates

Hydrothermal syntheses were made mainly in the binary system SiO2-H2O in a temperature range between 300 ° C and 500 ° C and pressures from 0.2 kbar up to 4.0 kbar with various starting materials. In this way the transformation behavior of different amorphous silicas via cristobalite and keatite to quartz were observed. This behavior depends mainly on the parameters: pressure, temperature, run duration and state of the starting material. Four reaction paths have been observed: in most experiments the complete reaction sequence “amorphous silica→cristobalite→keatite→quartz” took place. Less often the reactions: “amorphous silica→cristobalite→quartz” and: “amorphous silica→keatite→quarts” were observed. Very few samples were found with a direct transition of amorphous silica into quartz at high pressures. A kinetic model is given in form of a pressure-temperature-time diagram of the system SiO2-H2O under hydrothermal conditions.

The transformation of amorphous silica to crystalline silica under hydrothermal conditions

Die Silikate haben schon friihzeitig das Interesse der Mineralogen und Chemiker erregt. Der Grund hierffir ist einmal in der weiten Verbreitung der Silikate in der Natur und zum anderen in ihrer grol3en technischen Bedeutung zu suchen. W~thrend die erstere am besten darin zum Ausdruck kommt, dab die feste Erdkruste zu etwa 90% aus Silikaten und Siliciumdioxyd besteht, dtirfte die letztere schon daran zu erkennen sein, dab Zement, Bausteine, Glas, Porzellan, Steinzeug und zahlreiche andere Produkte, yon denen j~ihrlich ungeheure Mengen hergestellt und verbraucht werden, ausschlieBlich oder zum gr6Bten Teil aus Silikaten und SiO 2 bestehen.

Die Systematik der Silikate

In the present bond-valence concept the bond-valence parameter ro is treated as constant for a given pair of atoms, and it is assumed that the bond valence sij is a function of the corresponding bond length Dij, and that the atomic valence is an integer equal to the formal oxidation number forVi derived from stoichiometry. However, from a statistical analysis of 76 [SbIIISn] and 14 [SbIIISen] polyhedra in experimentally determined structures, it is shown that for SbIII—X bonds (X = S, Se), ro is correlated with {\bar \alpha}i, the average of the X—Sb—X angles between the three shortest Sb—X bonds. This is interpreted as a consequence of a progressive retraction of the 5s lone-electron pair from the SbIII nucleus, which can be considered as continuous change of the actual atomic valence actVi of Sb from +3 towards +5. A procedure is derived to calculate an effective atomic valence effVi of SbIII from the geometry, {\bar \alpha}i and Dij, of the [SbIIIXn] polyhedra, which approximates actVi and is a better description of the actual valence state of SbIII than the formal valence forVi. Calculated effVSbIII are found to vary between +2.88 and +3.80 v.u. for [SbIIISn] and between +2.98 and +3.88 v.u. for [SbIIISen] polyhedra. It is suggested that a corresponding modification of the present bond-valence concept is also required for other cations with lone-electron pairs.

/pdf/studies-on-bond-and-atomic-valences-i-correlation-between-1otp94wx00.pdf

Studies on bond and atomic valences. I. correlation between bond valence and bond angles in SbIII chalcogen compounds: the influence of lone‐electron pairs

According to the current bond-valence concept, the valence V i of an atom A i is a function of the distances D ij to its neighbors X j and can be calculated using V i = ΣS ij = Σexp[(r o -D ij )/0.37] , where the bond-valence parameter r o is considered to be constant for each element pair A-X. A statistical analysis based on 1924 [LX m ] polyhedra is presented, where L are cations having one electron lone-pair and X=O, S or Se. According to this analysis, for i r o for each individual [LX m ] polyhedron is dependent on the stereochemical influence of the lone-pair electrons on the geometry of the polyhedron. This influence is expressed by a vector Φ i = Φ(LX j -L i -X j , D ij ). As a result, the formal bond-valence sum for an individual lone-pair cation L i can be calculated with ΣS ij = Σexp[(E|Φ i |+F-D ij )/0.37] where E and F are constants.

Friedrich Liebau

Papers

The transformation of amorphous silica to crystalline silica under hydrothermal conditions

Die Systematik der Silikate

Studies on bond and atomic valences. I. correlation between bond valence and bond angles in SbIII chalcogen compounds: the influence of lone‐electron pairs

Influence of lone-pair electrons of cations on bond-valence parameters

Synthesis and Structure of [CH3NH3]2Sb8S13: A Nanoporous Thioantimonate(III) with a Two-Dimensional Channel System