Rhombic symmetry

Hassel and Luzanski obtained quadratic tabular crystals on evaporation of an aqueous solution containing excess hydrogen fluoride. Laue photographs with the incident beam normal to the basal plane showed rhombic symmetry, with, however, appreciable approximation to ditetragonal symmetry. The unit of structure has the dimensions... 

Preliminary X-ray work on CrSBr crystals, probably formed via a chemical-transport reaction, shows rhombic symmetry (181). Powder patterns of the iodides can be indexed with respect to a hexagonal lattice, and are similar to those of Cris (17, 181). 

A hysteresis cycle in the molar susceptibility measurements has been observed for [Ni2(Medpt)2(N3)2(/r-N3)2] (883). This has been ascribed to a phase transition caused by an asymmetrization process of the rhombus-like centrosymmetric [Ni-(N3)2-Ni] core that occurs with falling temperature. The asymmetrization transition can be explained in terms of a second-order Jahn-Teller distortion, taking into account the local symmetry of the dinuclear [Ni-(N3)2-Ni] entity (D2h, rhombic symmetry) before the arrangement.2128... 

Asymmetry in the ligand environment, either geometric or in charge distribution (or both), affect the asymmetry parameter, tp An r = 0 value corresponds to complete axial symmetry, whereas r = 1 corresponds to pure rhombic symmetry. Electric monopole interactions between the nuclear charge distributions and the electrons at the nucleus cause a shift of the nuclear ground and excited states. These interactions are known as the isomer shift, 8. Both the Mossbauer source and the absorber (the sample of interest) experience an isomer shift, and it is customary to quote 8 relative to a standard, usually Fe metal or Na2[Fe(CN)5NO] 2H2O at... 

EPR. The frozen solution EPR spectrum of 75 shown in Fig. 13 exhibits rhombic symmetry typical of a Ni(III) bis(dithiolene) complex (126), with g-tensor values of gx = 2.13, gy = 2.04, g, = 1.99. The nickel dimer can thus be viewed as a classical bis(dithiolene) moiety with a 3B3g ground state where the odd electron orbital composed primarily of a metal dyZ orbital and sulfur 2pz orbitals. The Ni(II) in the pz, as expected, is EPR silent (19, 122). 

UV/VIS/NIR spectroscopy and ESR spectroscopy. The UV/VIS/NIR spectrum shows a sharp peak at 983 nm and a broad peak at 846 nm. These two absorbances are attributed to allowed NIR-transitions and these values are consistent with spectra of the cation obtained with other methods [2]. EPR spectroscopy of Cgg-cations, produced by different methods, leads to a broad distribution of measured g-values. These differences are caused by the short lifetime of the cation, the usually low signal-noise ratio and the uncertainty of the purity. The most reliable value imtil now is probably the one obtained by Reed and co-workers for the salt Cgg"(CBiiHgClg)-(g= 2.0022) [2,9] (see also Section 8.5). Ex situ ESR spectroscopy of above-mentioned bulk electrolysis solutions led to a g-value of2.0027 [8], which is very close to that of the salt, whereas the ESR spectra of this electro lyticaUy formed cation shows features not observed earlier. The observed splitting of the ESR signal at lower modulation amplitudes was assigned to a rhombic symmetry of the cation radical at lower temperatures (5-200 K). 

Figure 27 (a) The splitting of the one-electron energy levels of the copper(II) ion in crystal fields of axial and rhombic symmetry (b) The splitting of the one-electron energy levels of the copper(II) ion in crystal fields of tetrahedral, cu-distorted octahedral, trigonal octahedral and trigonal bipyramidal symmetry... 

Figure 3.11 Illustrations of the distortions to an octahedron that generate (a) tetragonal, (b) trigonal and (c) rhombic symmetries around a metal ion.

In the second example, consider the case of a paramagnetic species with rhombic symmetry x y z), characterized by three g values of gi, g2 and g. The variation in the g values now depends on the two polar angles of 0 and (Equation 1.29) and a typical example of the absorption and first derivative profiles for such a... 

After the catalyst has been treated with a mixture of AlEt3 and methyl-p-toluate, a new strong signal appears with gM = 1.967. The author attributes it to a species with rhombic symmetry containing both the Al-alkyl and the Lewis base, and having the following possible structures C and C ... 

An important example of an inherently rhombic symmetry SMM is [Ee802(OH)i2(tacn)6]Br8, which has an S = 10 ground state (like Mni2 ) with D = -0.20 cm . The symmetry of the cation is only Ci and lE/Dl is in the range 0.15-0.19 from EPR and The effect of this large rhombic... 

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