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.

The chemical industry is dependent on the olefin/paraffin separation, which is mainly accomplished by using energy-intensive processes. We report the use of reticular chemistry for the fabrication of a chemically stable fluorinated metal-organic framework (MOF) material (NbOFFIVE-1-Ni, also referred to as KAUST-7). The bridging of Ni(II)-pyrazine square-grid layers with (NbOF5)2– pillars afforded the construction of a three-dimensional MOF, enclosing a periodic array of fluoride anions in contracted square-shaped channels. The judiciously selected bulkier (NbOF5)2– caused the looked-for hindrance of the previously free-rotating pyrazine moieties, delimiting the pore system and dictating the pore aperture size and its maximum opening. The restricted MOF window resulted in the selective molecular exclusion of propane from propylene at atmospheric pressure, as evidenced through multiple cyclic mixed-gas adsorption and calorimetric studies.

http://science.sciencemag.org/content/sci/353/6295/137.full.pdf

A metal-organic framework-based splitter for separating propylene from propane.

A new noncentrosymmetric (NCS) and polar material containing two lone-pair cations, Bi3+ and I5+, and exhibiting an Aurivillius-type (Bi2O2)2+ layer has been synthesized and structurally characterized. The material, BiO(IO3), exhibits strong second-harmonic generation (SHG), ∼12.5 × KDP (or ∼500 × α-SiO2), using 1064 nm radiation, and is found in the NCS polar orthorhombic space group Pca21 (No. 29). The structure consists of (Bi2O2)2+ cationic layers that are connected to (IO3)− anions. The macroscopic polarity, observed along the c-axis direction, may be attributed to the alignment of the IO3 polyhedra. In addition to the crystal structure and SHG measurements, polarization and piezoelectric measurements were performed, as well as electronic structure analysis.

BiO(IO3): a new polar iodate that exhibits an aurivillius-type (Bi2O2)2+ layer and a large SHG response.

The development of functional solid-state materials for carbon capture at low carbon dioxide (CO2) concentrations, namely, from confined spaces (<0.5%) and in particular from air (400 ppm), is of prime importance with respect to energy and environment sustainability. Herein, we report the deliberate construction of a hydrolytically stable fluorinated metal–organic framework (MOF), NbOFFIVE-1-Ni, with the appropriate pore system (size, shape, and functionality), ideal for the effective and energy-efficient removal of trace carbon dioxide. Markedly, the CO2-selective NbOFFIVE-1-Ni exhibits the highest CO2 gravimetric and volumetric uptake (ca. 1.3 mmol/g and 51.4 cm3 (STP) cm–3) for a physical adsorbent at 400 ppm of CO2 and 298 K. Practically, NbOFFIVE-1-Ni offers the complete CO2 desorption at 328 K under vacuum with an associated moderate energy input of 54 kJ/mol, typical for the full CO2 desorption in conventional physical adsorbents but considerably lower than chemical sorbents. Noticeably, the contra...

/pdf/a-fine-tuned-fluorinated-mof-addresses-the-needs-for-trace-42g6ogtugh.pdf

A Fine-Tuned Fluorinated MOF Addresses the Needs for Trace CO2 Removal and Air Capture Using Physisorption

Nonlinear optical (NLO) crystals are essential materials for generation of coherent UV light in solid state lasers. KBBF is the only material that can achieve coherent light below 200 nm by direct second harmonic generation (SHG). However, its strong layer habits and the high toxicity of the beryllium oxide powders required for synthesis limit its application. By substituting Be with Zn and connecting adjacent [Zn2BO3O2] ∞ layers by B3O6 groups, a new UV nonlinear optical material, Cs3Zn6B9O 21, was synthesized. It overcomes the processing limitations of KBBF and exhibits the largest SHG response in the KBBF family.

Cs3Zn6B9O21: A Chemically Benign Member of the KBBF Family Exhibiting the Largest Second Harmonic Generation Response

A new phase of Cd(py)4NbOF5 (py = pyridine) (A) is a rare example of a mixed metal oxide fluoride in an ordered linear chain structure. This phase is of particular interest because it is a polymorph of a previously reported Cd(py)4NbOF5 phase (B) that crystallizes in disordered linear chains. The ordered polymorph A contains two distinct Cd2+ sites:  one which is coordinated to the oxide ligands from two [NbOF5]2- units, and another that is coordinated to two trans fluoride ligands. As a result, the structure of polymorph A features nonpolar linear chains with locally ordered [NbOF5]2- anions. This ordering is explained in terms of the inherent electronic differences between oxide and fluoride ligands. The stabilization provided by π-stacking interactions between pyridine ligands on neighboring chains, as well as the effects of reactant stoichiometry on the general structure of the products in the CdO·1/2Nb2O5/(HF)x·py/H2O system, is also discussed. Crystal data for the ordered Cd(py)4NbOF5 polymorph:  mo...

/pdf/evidence-for-nonpolar-alignment-of-nbof5-2-anions-in-cd-1e9g8fs1hp.pdf

Evidence for Nonpolar Alignment of [NbOF5]2- Anions in Cd(pyridine)4NbOF5 Chains

The face-sharing bioctahedral molybdenum(VI) oxide fluoride anion [Mo 2 O 6 F 3 ] 3 - has been isolated in the new compound [Cu(3-apy) 4 ] 3 (Mo 2 O 6 F 3 ) 2 (3-apy = 3-aminopyridine) and has been characterized by experimental and computational techniques. Single-crystal X-ray diffraction studies show that the structure of the [Mo 2 O 6 F 3 ] 3 - anion resembles two distorted face-sharing octahedra, each with three short terminal metal-ligand bonds and three long metal-ligand-metal bridging interactions. Aspects of the electronic structure, as well as geometric comparisons of the bond lengths and angles in [Mo 2 O 6 F 3 ] 3 - with those in the similarly distorted [MoO 3 F 3 ] 3 - anion, suggest that the six terminal ligand positions of the confacial bioctahedra are occupied exclusively by oxide ligands and that the three bridging sites are occupied by fluorides. Crystal data for [Cu(3-apy) 4 ] 3 (Mo 2 O 6 F 3 ) 2 : trigonal space group R3 (No. 148) with hexagonal axes of a = 13.881(1) A and c = 31.783(3) A (Z = 3).

/pdf/synthesis-and-characterization-of-the-face-sharing-4jvjzdzrzg.pdf

Synthesis and Characterization of the Face-Sharing Bioctahedral [Mo2O6F3]3- Anion.

Out-of-center “primary” electronic distortions are inherent to the oxide fluoride anions of the early d0 transition metals. In the [NbOF5]2- anion, the Nb5+ moves from the center of the octahedron toward the oxide ligand to form a short NbO bond and long trans Nb−F bond. The combined results of single-crystal X-ray diffraction and electronic structure calculations indicate that the primary distortion of the [NbOF5]2- anion is affected by the coordination environment that is created by the three-dimensional extended structure. The formation of bonds between an M(L)42+ (M = Cd2+, Cu2+; L = 3-aminopyridine, 4-aminopyridine) cation and the oxide and/or trans-fluoride ligands of the [NbOF5]2- anion weakens the π component of the NbO bond. At the same time, hydrogen bond interactions between the equatorial fluorides and the aminopyridine groups both lengthen the equatorial Nb−F bonds and can further reduce the symmetry of the [NbOF5]2- anion. These combined three-dimensional bond network interactions that serve...

/pdf/examining-the-out-of-center-distortion-in-the-nbof5-2-anion-4djafok2ua.pdf

Examining the out-of-center distortion in the [NbOF5]2- anion.

Synthesis and characterization of the face-sharing bioctahedral [Mo2O6F3]3- anion.

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Evidence for Nonpolar Alignment of [NbOF5]2- Anions in Cd(pyridine)4NbOF5 Chains

Synthesis and Characterization of the Face-Sharing Bioctahedral [Mo2O6F3]3- Anion.

Examining the out-of-center distortion in the [NbOF5]2- anion.

Synthesis and characterization of the face-sharing bioctahedral [Mo2O6F3]3- anion.