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 ($\bar{n}=1/2$) and half-filled ($\bar{n}=1$) 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^II–Nb^IV coordination polymer {[Fe^II(pyrazole)₄]₂[Nb^IV(CN)₈]·4H₂O}_<i>n</i> (<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^II(pyrazole)₄]₂[Nb^IV(CN)₈]·4H₂O}_<i>n</i> (<b>MnNb</b>). The <b>FeNb</b> coordination polymer is the first pressure-induced spin-crossover photomagnet