Hole and Electron Doping of the 4d Transition‐Metal Oxyhydride LaSr3NiRuO4H4

Hole or electron doping of phases prepared by topochemical reactions (e.g. anion deintercalation or anion‐exchange) is extremely challenging as these low‐temperature conversion reactions are typically very sensitive to the electron counts of precursor phases. Herein we report the successful hole and electron doping of the transition‐metal oxyhydride LaSr₃NiRuO₄H₄ by first preparing precursors in the range La_xSr_4?xNiRuO₈ 0.5<x<1.4 and then converting into the corresponding La_xSr_4?xNiRuO₄H₄ phases. This is particularly noteworthy as the (Ni/Ru)H₂ sheets in the La_xSr_4?xNiRuO₄H₄ phases are structurally analogous to the CuO₂ sheets in cuprate superconductors and hole doping (Ni^1+/2+, Ru²⁺) or electron doping (Ni²⁺, Ru^1+/2+) yields materials with partial occupancy in Ni/Ru –H 1s bands which are analogous to the partially occupied Cu –O 2p bands present in the CuO₂ sheets of doped superconducting cuprates.     

Oxo-Hydroxoferrate K2−xFe4O7−x(OH)x: Hydroflux Synthesis,Chemical and Thermal Instability,Crystal and Magnetic Structures

The reaction of Fe(NO₃)₃⋅9 H₂O with KOH under hydroflux conditions at about 200 °C produces red crystals of K_2−xFe₄O_7−x(OH)_x in a quantitative yield. In the crystal structure, edge-sharing [FeO₆] octahedra form Fe₂O₆] honeycomb nets. Pillars consisting of pairs of vertex-sharing [FeO₄] tetrahedra link the honeycomb layers and form columnar halls in which the potassium ions are located. The trigonal (P 1m) and the hexagonal (P6₃/mcm) polytypes of K_2−xFe₄O_7−x(OH)_x show oriented intergrowth. The sub-stoichiometric potassium content (x≈0.3) is compensated by hydroxide ions. K_2−xFe₄O_7−x(OH)_x is an antiferromagnet above 2 K and its magnetic structure was determined by neutron powder diffraction. Under ambient conditions, K_2−xFe₄O_7−x(OH)_x hydrolyzes and K₂CO₃ ⋅ H₂O forms gradually on the surface of the K_2−xFe₄O_7−x(OH)_x crystals. Upon annealing at air at about 500 °C, the potassium atoms in the columnar halls start to order into a superstructure. The thermal decomposition of K_2−xFe₄O_7−x(OH)_x proceeds via a topotactic transformation into K_1+x′Fe₁₁O₁₇, adopting the rhombohedral β’’ or the hexagonal β-aluminate-type structure, before γ-Fe₂O₃ is formed above 950 °C, which then converts into thermodynamically stable α-Fe₂O₃.     

A Rational Approach to Crosslinking of Coordination Polymers Using the Photochemical [2+2] Cycloaddition Reaction

Summary: Polymerization as a result of photocrosslinking is one of the most versatile technologies for producing organic polymers. This article highlights the formation of crosslinking in metal coordination polymers in the solid‐state using a photochemical approach and its importance in material science. Past and current developments of solid‐state photochemical [2+2] cycloaddition in organic and inorganic systems relevant to the topic are reviewed. The challenges for the coordination chemist in utilising this rational approach to orient the coordination polymers and the scope of this work are delineated.

The CC‐containing molecules can be aligned by metal coordination bonds in such a way as to promote crosslinking by a photochemical [2+2] cycloaddition reaction.     

Diphenic acid as a general conformational lock in the design of bihelical structures

The bihelical (figure of "infinity") topology was examined from vantages of design, crystal structures, chirality, circular dichroism (CD) studies and molecular-orbital calculations. The minimalistic design envisaged the sequential linking of cystine to the anchor diphenic acid, which proved to be a general conformational lock. The bihelical compound 4 was obtained in two steps from diphenic anhydride 1 and cystine di-OMe. The chirality of 4 arises largely from the L-cystine. The bihelical compound 5 obtained from D-cystine di-OMe was found, by X-ray crystallography, CD studies, and optical rotation, to be the perfect mirror image of 4 prepared from L-cystine. The crystal structure of prototype 8, prepared by protocols used for 4 from the achiral cystine analogue cystamine, had a "U"-shaped conformation held together by intramolecular hydrogen bonds. Analysis of 4 and 5 show that the pairs of nine-membered beta-turn-like constructs made compact through hydrogen bonding with DMSO hold the key for the bihelical conformation. Another factor is the need for the presence of a ligand at the Calpha position. The absence of this, as in 8, allows major flexibility in the torsional angles around this critical region, promoting flexible alternatives. The CD analysis of 4, confirmed to be bihelical by X-ray crystallography, showed a typical negative band at about 210 A attributed to the beta-turn-like motif, and in the positive-band region a peak at about 227 A, generally related to the twist of the biphenyl unit. The cystamine analogue 8, which showed a "U"-type structure, presented a CD spectrum with no typical features. The total energy, derived from theoretical calculations by using the X-ray structure data, support the bihelical structure for 4 and a "U"-shaped one for 8. The limited utility of such calculations was tested with composite 9. Composite 9, in which the anchor diphenic acid is linked to cystamine on the one hand and to cystine on the other, showed a CD spectrum similar to that of 4, and this coupled with molecular-orbital calculations, using data from 4 and 8, predict a bihelical structure for this compound.     

3D Coordination Framework with Uncommon Two‐Fold Interpenetrated {33⋅59⋅63}‐lcy Net and Coordinated Anion Exchange

Unusual {3 ³ ?5 ⁹ ?6 ³ }‐lcy topology has been found in an uncommon 3D six‐connected, two‐fold interpenetrated {3³ ? 5⁹ ? 6³}‐lcy net (illustrated). The coordinated SO₄^2? anions in this framework can undergo a full exchange with Cl^? anions, in the course of which the crystals change color as shown. The process has a solvent‐mediated rather than a solid‐state mechanism.