The elastic constants of the triclinic crystals, ammonium and potassium tetroxalate dihydrate

Elastic and thermoelastic constants of triclinic thallium trihydrogen Oxalate dihydrate, TlH3(C2O4)2 · 2 H2O

The elastic constants of triclinic TlH3(C2O4)2 · 2 H2O and their temperature derivatives have been determined from ultrasonic resonance frequencies of thick plane-parallel plates. The elastic constants differ only slightly from those of the isotypic potassium salt. However, a distinct difference in respect to the deviation from Cauchy's relations occurs similar to the situation in many other isotypic potassium and thallium salts. The thermoelastic constants show an almost isotropic behaviour in contrast to the very large elastic anisotropy.

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.

Crystal structure, elastic properties and phase transition of triclinic ammonium hydrogen succinate, NH4HC4H4O4

Large optical quality, single crystals of triclinic ammonium hydrogen succinate have been grown from aqueous solutions. An X-ray structure analysis yields space group P[unk], a = 7.484(2), b = 8.876(2), c = 4.726(1) Å, α = 91.25(2), β = 93.26(2), γ = 100.26(3)°, Z = 2, ϱcalc = 1.456(1), ϱobs = 1.454(2) g cm−3. The structure contains strong hydrogen bonds between adjacent succinate ions which form a periodic bond chain along [110]. Another strong bond chain results from hydrogen bonds and ionic interactions between NH4 ions and the carboxylic groups along [001]. The succinate ion exhibits no intrinsic symmetry as found in most other acid salts of succinic acid. In the final refinement one hydrogen atom had to be split into two positions related by a centre of symmetry. Complete elastic and thermoelastic tensors have been determined from ultrasonic resonance frequencies of thick plates and their temperature dependence, respectively. Further, the tensor of thermal expansion has been studied in a wide temperature range. The existence of a second-order phase transition has been observed by thermal expansion and DSC measurements at about 169 K.