Orthorhombic crystal system

Summary

In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a rectangular base (a by b) and height (c), such that a, b, and c are distinct. All three bases intersect at 90° angles, so the three lattice vectors remain mutually orthogonal. Bravais lattices There are four orthorhombic Bravais lattices: primitive orthorhombic, base-centered orthorhombic, body-centered orthorhombic, and face-centered orthorhombic. For the base-centered orthorhombic lattice, the primitive cell has the shape of a right rhombic prism; it can be constructed because the two-dimensional centered rectangular base layer can also be described with primitive rhombic axes. Note that the length a of the primitive cell below equals \frac{1}{2} \sqrt{a^2+b^2} of the conventional cell above. C

Official source

https://en.wikipedia.org/wiki/Orthorhombic_crystal_system

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The alpha(2)-polymorph of salicylideneaniline

Gervais Chapuis, Philip Pattison

N-Salicylideneaniline (SA), C13H11NO, belongs to the large family of aromatic Schiff bases. It is of particular importance owing to its reversible photoreactivity. SA forms two photochromic polymorphs, both with two non-coplanar benzene rings. In addition, we have recently discovered a planar polymorph, named the β-polymorph, which will be discussed in a subsequent paper. We report here the structure of the α(2)-polymorph in the orthorhombic crystal system. This compound exhibits a strong intramolecular O-H&BULL;&BULL;&BULL; N hydrogen bond and the dihedral angle between the two rings varies with temperature.

2005

Insights into the Origin of Cooperative Effects in the Spin Transition of [Fe(NH(2)trz)(3)](NO3)(2): the Role of Supramolecular Interactions Evidenced in the Crystal Structure of [Cu(NH(2)trz)(3)](NO3)(2)center dot H2O

Christine Neuhausen

The thermally induced hysteretic spin transition (ST) that occurs in the polymeric chain compound Fe(NH(2)trz)(3)(2) (1) above room temperature (T-c(sic) = 347 K, T-c(sic) = 314 K) has been tracked by Fe-57 Mossbauer spectroscopy, SQUID magnetometry, differential scanning calorimetry (DSC), and X-ray powder diffraction (XPRD) at variable temperatures. From the XRPD pattern indexation, an orthorhombic primitive cell was observed with the following cell parameters: a = 11.83(2) angstrom, b = 9.72(1) angstrom, c = 6.361(9) angstrom at 298 K (low-spin state) and a = 14.37(2) angstrom, b = 9.61(4) angstrom, c = 6.76(4) angstrom at 380 K (high-spin state). The enthalpy and entropy variation associated to the ST of 1, have been evaluated by DSC as Delta H = 23(1) kJ mol(-1) and Delta S = 69.6(1) J mol(-1) K-1. These thermodynamic data were used within a two-level Ising like model for the statistical analysis of First Order Reversal Curve (FORC) diagram that was recorded for 1, in the cooling mode. Strong intramolecular cooperative effects are witnessed by the derived interaction parameter of J = 496 K. The crystal structure of Cu(NH(2)trz)(3)(2) center dot H2O (2) was obtained thanks to high quality single crystals prepared by slow evaporation after hydrothermal pretreatment. The catena poly[mu-tris(4-amino-1,2,4-triazole-N1,N2) copper.(II)] dinitrate monohydrate (2) crystallizes in the monoclinic space group C2/c, with a = 16.635(6) angstrom, b = 13.223(4) angstrom, c = 7.805(3) angstrom, beta = 102.56(3)degrees, Z = 4. Complex 2 is.a 1D infinite chain containing triple N1,N2-1,2,4-triazole bridges with an intra-chain distance of Cu center dot center dot center dot Cu = 3.903(1) angstrom. A dense H-bonding network with the nitrate counteranion involved in intra-chain and inter-chain interactions is observed. Such a supramolecular network could be at the origin of the unusually large hysteresis loop displayed by 1 (Delta T similar to 33 K), as a result of an efficient propagation of elastic interactions through the network. This hypothesis is strengthened by the crystal structure of 2 and by the absence of crystallographic phase transition for 1 over the whole temperature range of investigation as shown by XRPD.

2010

Competing Jahn-Teller distortions combined with geometrical frustration give rise to a rich phase diagram as a function of x(Cu) and temperature in the spinel system Ni1-xCuxCr2O4. The Jahn-Teller distortion of the end members acts in opposite ways, with an elongation of the NiO4 tetrahedra resulting in a structural transition at T-S1 = 317K in NiCr2O4, but a flattening in the CuO4 tetrahedra at T-S1 = 846K in CuCr2O4. In both cases the symmetry is lowered from cubic (Fd (3) over barm) to tetragonal (I4(1)/amd) on cooling. In order to follow the influence of Jahn-Teller active Ni2+ and Cu2+ ions on the structural and magnetic properties of chromium spinels, we have investigated a series of samples of Ni1-xCuxCr2O4 by x-ray and neutron powder diffraction. In the critical range 0.10 < x(Cu) < 0.20, strong orthorhombic distortions were observed, where competing Jahn-Teller activities between the Cu2+ and Ni2+ ions result in distortions along both the a and c axes. For Ni0.85Cu0.15Cr2O4, the orthorhombic structure (Fddd) is stabilized up to T-S2 = 368(2) K, close to the first structural phase transition at T-S1 = 374(2) K. A ferrimagnetic spin alignment of the Ni/Cu and chromium atoms sets in at much lower temperature TC = 95K in this compound. The end members NiCr2O4 and CuCr2O4 undergo this ferrimagnetic transition at TC = 74 and 135 K, respectively. These transitions are accompanied by the structural change to the orthorhombic symmetry which relieves the frustration. NiCr2O4 and Ni0.85Cu0.15Cr2O4 undergo a second magnetic transition at TM2 = 24 and 67K due to a superimposed antiferromagnetic ordering of the Cr moments resulting in a noncollinear magnetic structure. In the system Ni1-xCuxCr2O4, the magnetic transitions TC and TM2 merge with increasing copper content up to x(Cu) similar to 0.5. For the Ni-rich chromites, geometrical frustration causes a strong reduction of the chromium moments, where magnetic long-range order coexists with a disordered spin-liquid-like or a reentrant-spin-glass-like state. This paper provides insight into the interplay between the Jahn-Teller effect, geometrical frustration, and long-range magnetic order in these complex systems.

Amer Physical Soc2015

Insights into the Origin of Cooperative Effects in the Spin Transition of [Fe(NH(2)trz)(3)](NO3)(2): the Role of Supramolecular Interactions Evidenced in the Crystal Structure of [Cu(NH(2)trz)(3)](NO3)(2)center dot H2O

Christine Neuhausen

2010

Amer Physical Soc2015