Solid-State Structure of a Degradation Product Frequently Observed on Historic Metal Objects

In the course of the investigation of glass-induced metal corrosion processes, a microcrystalline sodium copper formate hydroxide oxide hydrate, Cu₄Na₄O­(HCOO)₈­(H₂O)₄(OH)₂, was detected on a series of antique works of art, and its crystal structure was determined ab initio from high-resolution laboratory X-ray powder diffraction data using the method of charge flipping, simulated annealing, and difference-Fourier analysis (<i>P</i>4₂/<i>n</i>, <i>a</i> = 8.425 109(97) Å, <i>c</i> = 17.479 62(29) Å, <i>V</i> = 1240.747(35) ų, <i>Z</i> = 8). In the crystal structure, the metal cations are interconnected in a two-dimensional metal–organic framework via the oxygen atoms of the formate, hydroxide, and oxide anions. Doublets of face-sharing square pyramidal Cu²⁺ polyhedra are linked via a single, central oxide oxygen atom to give a paddle-wheel arrangement, while the Na⁺ cations are organized in Na₂O₁₁ moieties with highly disordered, edge-sharing octahedral coordination. In addition, hydrogen bonding plays an important role in stabilizing the crystal structure

Healthnet News v.16:no.4 Winter 2001

A newsletter for public librarians and others interested in consumer health information services

Perpetually Self-Propelling Chiral Single Crystals

When heated, single crystals of enantiomerically pure d- and l-pyroglutamic acid (PGA) are capable of recurring self-actuation due to rapid release of latent strain during a structural phase transition, while the racemate is mechanically inactive. Contrary to other thermosalient materials, where the effect is accompanied by crystal explosion due to ejection of debris or splintering, the chiral PGA crystals respond to internal strain with unprecedented robustness and can be actuated repeatedly without deterioration. It is demonstrated that this superelasticity is attained due to the low-dimensional hydrogen-bonding network which effectively accrues internal strain to elicit propulsion solely by elastic deformation without disintegration. One of the two polymorphs (β) associated with the thermosalient phase transition undergoes biaxial <i>negative</i> thermal expansion (α_<i>a</i> = −54.8(8) × 10^–6 K^–1, α_<i>c</i> = −3.62(8) × 10^–6 K^–1) and exceptionally large uniaxial thermal expansion (α_<i>b</i> = 303(1) × 10^–6 K^–1). This second example of a thermosalient solid with anomalous expansion indicates that the thermosalient effect can be expected for first-order phase transitions in soft crystals devoid of an extended 3D hydrogen-bonding network that undergo strongly anisotropic thermal expansion around the phase transition

Synthesis, Structures, Polymorphism, and Magnetic Properties of Transition Metal Thiocyanato Coordination Compounds

Reaction of manganese, iron, and nickel thiocyanate with 4-ethylpyridine leads to the formation of single crystals of compounds with composition M­(NCS)₂(L)₄ (<b>1</b>), M­(NCS)₂(L)₂(H₂O)₂ (<b>2-Mn</b>), and M­(NCS)₂(L)₂ (<b>3</b>) with M = Mn, Fe, and Ni and L = 4-ethylpyridine. For most compounds, different polymorphic modifications are observed, and their transition behavior and thermodynamic stability was investigated. Additionally, compounds of composition M­(NCS)₂(L)₂ (M = Mn or Ni) were prepared from solution and by thermal decomposition of compounds <b>1</b> and <b>2</b>, which lead to different stable and metastable modifications. The crystal structures of most compounds were determined by single crystal X-ray diffraction and some of them by Rietveld refinements. Compounds <b>1</b> and <b>2</b> consist of octahedrally coordinated discrete complexes with terminal N-bonded thiocyanato anions. In compounds <b>3</b>, the metal cations are linked by pairs of μ-1,3-bridging thiocyanato anions into chains. Surprisingly, thermal decomposition of Ni­(NCS)₂(4-ethylpyridine)₄ leads to the formation of a new compound of composition Ni­(NCS)₂(4-ethylpyridine) (<b>4-Ni</b>). Magnetic measurements reveal that <b>3-Mn/II</b> and <b>3-Mn/III</b> show antiferromagnetic ordering at <i>T</i>_N = 21.5 and 23.9 K and that <b>4-Ni</b> is a metamagnet with a critical field of 1.4 kOe at 2 K. All other compounds show Curie or Curie–Weiss behavior with no magnetic anomalies

La Croix du Nord : supplément régional à la Croix de Paris ["puis" grand journal quotidien du Nord de la France]

16 juillet 19101910/07/16 (A21,N7196).Appartient à l’ensemble documentaire : NordPdeC

Crystal Structure of Thecotrichite, an Efflorescent Salt on Calcareous Objects Stored in Wooden Cabinets

The crystal structure of thecotrichite, Ca₃(CH₃COO)₃­Cl­(NO₃)₂·6H₂O, an efflorescent salt occurring on surfaces of porous calcareous objects stored in wooden cabinets, was solved <i>ab initio</i> from high-resolution, laboratory X-ray powder diffraction data. The compound was found to contain one water molecule per formula unit less than what was previously reported. The crystal structure of thecotrichite (<i>P</i>2₁/<i>a</i>, <i>Z</i> = 4, <i>a</i> = 23.5933(4), <i>b</i> = 13.8459(3), <i>c</i> = 6.8010(1) Å, β = 95.195(2)°, <i>V</i> = 2212.57(7) ų) consists of a network of calcium ions, connected through acetate and nitrate ions, forming a metal–organic framework. In addition, five of the six chemically different water molecules are directly coordinated to the calcium ions, with the remaining water molecule located in the interstitial space, together with the chloride ion. The needle-like morphology of the microcrystals was rationalized from the crystal structure. It is suggested that the crystallite growth mechanism depends heavily on the porous nature of the crystal structure. The thermal characteristics and stability of the material were studied. Structural and spectroscopic information on this efflourescent salt are provided to ease its characterization and identification, especially in museums and art collections worldwide

Ultrahigh Damping Capacities in Lightweight Structural Materials

The demand to outperform current technologies pushes scientists to develop novel strategies, which enable the fabrication of materials with exceptional properties. Along this line, lightweight structural materials are of great interest due to their versatile applicability as sensors, catalysts, battery electrodes, and acoustic or mechanical dampers. Here, we report a strategy to design ultralight (ρ = 3 mg/cm³) and hierarchically structured ceramic scaffolds of macroscopic size. Such scaffolds exhibit mechanical reversibility comparable to that of microscopic metamaterials, leading to a macroscopically remarkable dynamic mechanical performance. Upon mechanical loading, these scaffolds show a deformation mechanism similar to polyurethane foams, and this resilience yields ultrahigh damping capacities, tan δ, of up to 0.47

Record High Hydrogen Storage Capacity in the Metal–Organic Framework Ni2(m‑dobdc) at Near-Ambient Temperatures

Hydrogen holds promise as a clean alternative automobile fuel, but its on-board storage presents significant challenges due to the low temperatures and/or high pressures required to achieve a sufficient energy density. The opportunity to significantly reduce the required pressure for high density H2 storage persists for metal-organic frameworks due to their modular structures and large internal surface areas. The measurement of H2 adsorption in such materials under conditions most relevant to on-board storage is crucial to understanding how these materials would perform in actual applications, although such data have to date been lacking. In the present work, the metal-organic frameworks M2(m-dobdc) (M = Co, Ni; m-dobdc4- = 4,6-dioxido-1,3-benzenedicarboxylate) and the isomeric frameworks M2(dobdc) (M = Co, Ni; dobdc4- = 1,4-dioxido-1,3-benzenedicarboxylate), which are known to have open metal cation sites that strongly interact with H2, were evaluated for their usable volumetric H2 storage capacities over a range of near-ambient temperatures relevant to on-board storage. Based upon adsorption isotherm data, Ni2(m-dobdc) was found to be the top-performing physisorptive storage material with a usable volumetric capacity between 100 and 5 bar of 11.0 g/L at 25 °C and 23.0 g/L with a temperature swing between -75 and 25 °C. Additional neutron diffraction and infrared spectroscopy experiments performed with in situ dosing of D2 or H2 were used to probe the hydrogen storage properties of these materials under the relevant conditions. The results provide benchmark characteristics for comparison with future attempts to achieve improved adsorbents for mobile hydrogen storage applications

Ultrahigh Damping Capacities in Lightweight Structural Materials

The demand to outperform current technologies pushes scientists to develop novel strategies, which enable the fabrication of materials with exceptional properties. Along this line, lightweight structural materials are of great interest due to their versatile applicability as sensors, catalysts, battery electrodes, and acoustic or mechanical dampers. Here, we report a strategy to design ultralight (ρ = 3 mg/cm³) and hierarchically structured ceramic scaffolds of macroscopic size. Such scaffolds exhibit mechanical reversibility comparable to that of microscopic metamaterials, leading to a macroscopically remarkable dynamic mechanical performance. Upon mechanical loading, these scaffolds show a deformation mechanism similar to polyurethane foams, and this resilience yields ultrahigh damping capacities, tan δ, of up to 0.47

A Diaminopropane-Appended Metal–Organic Framework Enabling Efficient CO₂ Capture from Coal Flue Gas via a Mixed Adsorption Mechanism

A new diamine-functionalized metal–organic framework comprised of 2,2-dimethyl-1,3-diaminopropane (dmpn) appended to the Mg²⁺ sites lining the channels of Mg₂(dobpdc) (dobpdc^4– = 4,4′-dioxidobiphenyl-3,3′-di­carboxylate) is characterized for the removal of CO₂ from the flue gas emissions of coal-fired power plants. Unique to members of this promising class of adsorbents, dmpn–Mg₂(dobpdc) displays facile step-shaped adsorption of CO₂ from coal flue gas at 40 °C and near complete CO₂ desorption upon heating to 100 °C, enabling a high CO₂ working capacity (2.42 mmol/g, 9.1 wt %) with a modest 60 °C temperature swing. Evaluation of the thermodynamic parameters of adsorption for dmpn–Mg₂(dobpdc) suggests that the narrow temperature swing of its CO₂ adsorption steps is due to the high magnitude of its differential enthalpy of adsorption (Δ<i>h</i>_ads = −73 ± 1 kJ/mol), with a larger than expected entropic penalty for CO₂ adsorption (Δ<i>s</i>_ads = −204 ± 4 J/mol·K) positioning the step in the optimal range for carbon capture from coal flue gas. In addition, thermogravimetric analysis and breakthrough experiments indicate that, in contrast to many adsorbents, dmpn–Mg₂(dobpdc) captures CO₂ effectively in the presence of water and can be subjected to 1000 humid adsorption/desorption cycles with minimal degradation. Solid-state ¹³C NMR spectra and single-crystal X-ray diffraction structures of the Zn analogue reveal that this material adsorbs CO₂ via formation of both ammonium carbamates and carbamic acid pairs, the latter of which are crystallographically verified for the first time in a porous material. Taken together, these properties render dmpn–Mg₂(dobpdc) one of the most promising adsorbents for carbon capture applications