171 research outputs found
Negative linear compression and expanding NH N bonds in an imidazoline compound.
The 3-dimensional network of NHN hydrogen bonds and ClCl hydrogen contacts in the crystal structure of 2-(3′-chlorophenyl)imidazoline exhibits an anomalous hydrostatic compression. The lengthening of hydrogen bonds NHN and some CHN contacts as well as their supramolecular architecture lead to anomalous expansion of the crystal along [x] and [y] on increasing pressure to 0.1 GPa. The mechanism of this phenomenon is due to the ‘stiffness’ of the NHN and ClCl interactions and ‘softness’ of other van der Waals contacts. Above 0.1 GPa all crystal directions become compressed. However, up to 1.20 GPa, the crystal remains in the same orthorhombic phase of polar space group Fdd2
Peierls Instabilities in Quasi-One-Dimensional Quantum Double-Well Chains
Peierls-type instabilities in quarter-filled () and half-filled
() quantum double-well hydrogen-bonded chain are investigated
analytically in the framework of two-stage orientational-tunnelling model with
additional inclusion of the interactions of protons with two different optical
phonon branches. It is shown that when the energy of proton-phonon coupling
becomes large, the system undergoes a transition to a various types of
insulator states. The influence of two different transport amplitudes on ground
states properties is studied. The results are compared with the pressure effect
experimental investigations in superprotonic systems and hydrogen halides at
low temperatures.Comment: 7 pages, RevTeX, 9 eps figure
4-Chloroanilinium 4-methylbenzenesulfonate
In the crystal structure of the title salt, C6H7ClN+·C7H7O3S−, the cations and anions are linked via N—H⋯O hydrogen bonds into double chains in [101]. Weak intermolecular C—H⋯π-ring interactions link these chains into layers parallel to the ac plane
Thermodynamic Behavior of a Model Covalent Material Described by the Environment-Dependent Interatomic Potential
Using molecular dynamics simulations we study the thermodynamic behavior of a
single-component covalent material described by the recently proposed
Environment-Dependent Interatomic Potential (EDIP). The parameterization of
EDIP for silicon exhibits a range of unusual properties typically found in more
complex materials, such as the existence of two structurally distinct
disordered phases, a density decrease upon melting of the low-temperature
amorphous phase, and negative thermal expansion coefficients for both the
crystal (at high temperatures) and the amorphous phase (at all temperatures).
Structural differences between the two disordered phases also lead to a
first-order transition between them, which suggests the existence of a second
critical point, as is believed to exist for amorphous forms of frozen water.
For EDIP-Si, however, the unusual behavior is associated not only with the open
nature of tetrahedral bonding but also with a competition between four-fold
(covalent) and five-fold (metallic) coordination. The unusual behavior of the
model and its unique ability to simulation the liquid/amorphous transition on
molecular-dynamics time scales make it a suitable prototype for fundamental
studies of anomalous thermodynamics in disordeered systems.Comment: 48 pages (double-spaced), 13 figure
A high-pressure crystallographic and magnetic study of Na5[Mn(l-tart)2]·12H2O (l-tart = l-tartrate)
The crystal structure and magnetic properties of the compound Na5[Mn(L-tart)2]•12H2O (1, L-tart = L-tartrate) have been investigated over the pressure range 0.34 – 3.49 GPa. The bulk modulus of 1 has been determined as 23.9(6) GPa, with a compression of the coordination spheres around the Na+ ions observed. 1 is therefore relatively incompressible, helping it to retain its magnetic anisotropy under pressure
Enforcing Multifunctionality: A Pressure-Induced Spin-Crossover Photomagnet
Photomagnetic compounds are usually
achieved by assembling preorganized
individual molecules into rationally designed molecular architectures
via the bottom-up approach. Here we show that a magnetic response
to light can also be enforced in a nonphotomagnetic compound by applying
mechanical stress. The nonphotomagnetic cyano-bridged Fe<sup>II</sup>–Nb<sup>IV</sup> coordination polymer {[Fe<sup>II</sup>(pyrazole)<sub>4</sub>]<sub>2</sub>[Nb<sup>IV</sup>(CN)<sub>8</sub>]·4H<sub>2</sub>O}<sub><i>n</i></sub> (<b>FeNb</b>) has been
subjected to high-pressure structural, magnetic and photomagnetic
studies at low temperature, which revealed a wide spectrum of pressure-related
functionalities including the light-induced magnetization. The multifunctionality
of <b>FeNb</b> is compared with a simple structural and magnetic
pressure response of its analog {[Mn<sup>II</sup>(pyrazole)<sub>4</sub>]<sub>2</sub>[Nb<sup>IV</sup>(CN)<sub>8</sub>]·4H<sub>2</sub>O}<sub><i>n</i></sub> (<b>MnNb</b>). The <b>FeNb</b> coordination polymer is the first pressure-induced spin-crossover
photomagnet
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