The crystal structure of potassium binoxalate

Exploring short-wavelength birefringent crystals via triggering cooperative arrangement between different π-conjugated groups

We herein reported our strategy to assemble planar π-conjugated [B(OH)3] and [C2O4]2-/[HC2O4]-/[C4O4]2- functional groups to explore short-wavelength birefringent crystals. Three compounds, K2C2O4·B(OH)3, Cs4(HC2O4)2(C2O4)·[B(OH)3]2 and K(C4O4)0.5·B(OH)3, which all exhibit a layered structure favorable for generating large optical anisotropy, were synthesized and characterized. The strategy of assembling π-conjugated [B(OH)3] and C-O functional modules shows the potential to explore promising UV birefringent materials.

Characterization of the alkali metal oxalates (MC2O4-) and their formation by CO2 reduction via the alkali metal carbonites (MCO2-)

The reduction of carbon dioxide to oxalate has been studied by experimental Collisionally Induced Dissociation (CID) and vibrational characterization of the alkali metal oxalates, supplemented by theoretical electronic structure calculations. The critical step in the reductive process is the coordination of CO2 to an alkali metal anion, forming a metal carbonite MCO2- able to subsequently receive a second CO2 molecule. While the energetic demand for these reactions is generally low, we find that the degree of activation of CO2 in terms of charge transfer and transition state energies is the highest for lithium and systematically decreases down the group (M = Li-Cs). This is correlated to the strength of the binding interaction between the alkali metal and CO2, which can be related to the structure of the oxalate moiety within the product metal complexes evolving from a planar to a staggered conformer with increasing atomic number of the interacting metal. Similar structural changes are observed for crystalline alkali metal oxalates, although the C2O42- moiety is in general more planar in these, a fact that is attributed to the increased number of interacting alkali metal cations compared to the gas-phase ions.

Synthesis, Structure and Thermal Behavior of Oxalato-Bridged Rb+ and H3O+ Extended Frameworks with Different Dimensionalities

Correlative studies of three oxalato-bridged polymers, obtained under hydrothermal conditions for the two isostructural compounds {Rb(HC₂O₄)(H₂C₂O₄)(H₂O)₂}_∞¹, 1, {H₃O(HC₂O₄)(H₂C₂O₄).2H₂O}_∞¹, 2, and by conventional synthetic method for {Rb(HC₂O₄)}_∞³, 3, allowed the identification of H-bond patterns and structural dimensionality. Ferroïc domain structures are confirmed by electric measurements performed on 3. Although 2 resembles one oxalic acid sesquihydrate, its structure determination doesn’t display any kind of disorder and leads to recognition of a supramolecular network identical to hybrid s-block series, where moreover, unusual H₃O⁺ and NH₄⁺ similarity is brought out. Thermal behaviors show that 1D frameworks with extended H-bonds, whether with or without a metal center, have the same stability. Inversely, despite the dimensionalities, the same metallic intermediate and final compounds are obtained for the two Rb⁺ ferroïc materials.

The crystal structure of the decomposition product NH4HC2O4 from powder diffraction data

The crystal structure of anhydrous ammonium acid oxalate, NH4HC2O4, obtained from the thermal decomposition of the related hemihydrate has been determined from powder diffraction data collected with monochromatic laboratory X-rays, using the capillary technique. The crystal structure is monoclinic, P21/c, Z = 4, a = 4.3629(1) Å, b = 13.5657(1) Å, c = 7.7100(1) Å, β = 102.602(1)° and V = 445.3(1) Å3. The structure has been solved with the direct methods and refined with the Rietveld method, from which the agreement factors R wp = 8.19% and R B = 5.18% have been obtained. The crystal structure consists of corrugated layers built from seven-fold ammonium coordination polyhedra and connected by oxalate groups. The hydrogen atom positions have been located and the hydrogen bond network is extensively discussed.

Crystal and molecular structures of alkali oxalates: first proof of a staggered oxalate anion in the solid state

The molecular and crystal structures of solvent-free potassium, rubidium, and cesium oxalates have been determined ab initio from high-resolution synchrotron and X-ray laboratory powder patterns. In the case of potassium oxalate K(2)C(2)O(4) (a = 10.91176(7) A, b = 6.11592(4) A, c = 3.44003(2) A, orthorhombic, Pbam, Z = 2), the oxalate anion is planar, whereas in cesium oxalate Cs(2)C(2)O(4) (a = 6.62146(5) A, b = 11.00379(9) A, c = 8.61253(7) A, beta = 97.1388(4) degrees, monoclinic, P2(1)/c, Z = 4) it exhibits a staggered conformation. For rubidium oxalate at room temperature, two polymorphs exist, one (beta-Rb(2)C(2)O(4)) isotypic to potassium oxalate (a = 11.28797(7) A, b = 6.29475(4) A, c = 3.62210(2) A, orthorhombic, Pbam, Z = 2) and the other (alpha-Rb(2)C(2)O(4)) isotypic to cesium oxalate (a = 6.3276(1) A, b = 10.4548(2) A, c = 8.2174(2) A, beta = 98.016(1) degrees, monoclinic, P2(1)/c, Z = 4). The potassium oxalate structure can be deduced from the AlB(2) type, and the cesium oxalate structure from the Hg(99)As type, respectively. The relation between the two types of crystal structures and the reason for the different conformations of the oxalate anion are discussed.