The crystal structures of tetramethylammonium tetrachloro-cobaltate(II), -nickelate(II), and -zincate(II)

Wiesner, J.; Srivastava, Ritu; Kennard, C. H. L.; Vaira, Massimo Di; Lingafelter, E. C.

doi:10.1107/s0365110x67003214

Cited by 181 publications

(47 citation statements)

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“…The paraelectric phase of ((C H^N^ZnC U . At temperatures above 297.6 K the structure of ((CHa^N^ZnCLt is orthorhombic and centrosymmetric (Wiesner et al 1967). The space group is Pcmn.…”

Section: The Samplesmentioning

confidence: 99%

The interpretation of HAUP measurements: a study of the systematic errors

Kremers¹,

Meekes²

1995

J. Phys. D: Appl. Phys.

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Please be advised that this information was generated on 2018-05-10 and may be subject to change. j Phys. d : Appl. Phys. 28 (1995) 1195-1211. Printed in the UK T h e i n t e r p r e t a t i o n o f h a u p m e a s u r e m e n t s : a s t u d y o f t h e s y s t e m a t i c e r r o r sM IntroductionThe merits of the high-accuracy universal polarimeter (HAUP), introduced by Kobayashi and Uesu (1983), lie in the possibility of measuring very accurately and simultaneously the optical activity and birefringence of crystals. In addition, the rotation of the optical indicatrix is detected with a high sensitivity. The measurements require optically transparent, birefringent platelets of single crystals, with flat (polished) plane-parallel faces. It is very important to perform the measurements as a function of some external parameter in order to separate systematic errors from the optical properties, In the experiments described in this paper, the wavelength k of the light is the external parameter* Additional parameters can be temperature, electric fields (electro-optics) or magnetic fields (magneto-optics).The presence and nature of structural phase transitions can often be revealed by the birefringence (Ivanov 1991, Gehring 1977). The point symmetry of a specific phase can be studied by measuring the optical activity in several directions in a crystal, since optical activity is a tensorial property, which is sensitive to the symmetry (Nye 1985). The HAUP is, therefore, a powerful instrument in crystal optics.A very interesting problem in this field is encountered for incommensurately modulated crystals, with a centrosymmetric paraelectric phase (Cummins 1990). The incommensurate phase is often a (small) periodic deformation of the centrosymmetric paraelectric phase. The wavelengths of the periodic deformation is incommensurate with the lattice of the average structure. Therefore, the lattice translational symmetry is broken in at least one direction. Of course, the question arises of whether this phase can be optically active, because optical activity is forbidden in a centrosymmetric crystal (Nye 1985 In order to exclude the possibility that these differences are caused by the way of measuring or the way of interpreting the measurements, we feel . it necessary to reconsider very precisely the working principles of the HAUP method. In this paper, we re-derive rigorously the HAUP intensity formula (section 2 ). Experiments have been performed both on a centrosymmetric crystal with zero optical activity and on the non-centrosymmetric room-temperature phase of quartz, which has a large optical activity (section 3). In section 4 the obtained results are used to re consider critically the fitting procedures with which the optical properties are extracted from the measurements. Moreover, in section 5, the behaviour and origin of the systematic errors will be studied thoroughly. The quality and sensitivity of HAUP measurements is addressed in section 6 . For all aspects of the HAUP method, we discuss and take into accoun...

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“…The paraelectric phase of ((C H^N^ZnC U . At temperatures above 297.6 K the structure of ((CHa^N^ZnCLt is orthorhombic and centrosymmetric (Wiesner et al 1967). The space group is Pcmn.…”

Section: The Samplesmentioning

confidence: 99%

The interpretation of HAUP measurements: a study of the systematic errors

Kremers¹,

Meekes²

1995

J. Phys. D: Appl. Phys.

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“…Each of the CI-Fe-CI angles deviates significantly from the tetrahedral value (Table 5), the angular distortion being best described in terms of a compression or 'flattening' of the tetrahedron along the direction of the crystallographic C2 axis together with a 3 ° twist about this axis, resulting in a 93 ° dihedral angle between the planes CI(1)-Fe-CI(I') and CI(2)-Fe-CI(2'). Distortions of similar magnitude have been observed in (COC14) z-and (ZnCI4) 2- (Figgis, Gerloch & Mason, 1964;Wiesner, Srivastava, Kennard, Di Vaira & Lingafelter, 1967), both of which have orbitally non-degenerate ground states, and more recently in the (FeC14) 2-ion in [Fe(hS-CsHs)(CO)z]3SbCIa(FeCI4). CH2CI 2 (Trinh-Toan & Dahl, 1971).…”

Section: Geometry Of the (Feci4) 2-ionsmentioning

confidence: 71%

The structure of bis-(3,5-dimethyl-1,2-dithiolium) tetrachloroferrate(II): a comparison of structural details derived from two independent diffractometer analyses

Freeman¹,

Milburn²,

Nockolds³

et al. 1974

Acta Crystallogr Sect B

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We wish to thank Dr E. R. Clark of the Pharmacology Department of Leeds University for valuable discussions, Mr D. Akrigg for technical assistance and the Leeds University Computing Laboratory for the provision of computing facilities.Note added in proof:-The structure of TM1 has been congrmed as TTTT. The structure of ome TM1 has recently been determined as TTGT (manuscripts in preparntion).References CHOTHIA, C. t~ PAULING, P. (1969) Results from two independent X-ray diffraction studies are discussed. Both analyses are based on threedimensional diffractometer data with least-squares refinement of the scattering model. In other details the experimental and refinement techniques employed are substantially different. The mean difference between corresponding parameters derived from the two analyses is ca.

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“…Although the crystal structure of (TMA)2HgBr4 and (TMA)2HgI4 is reported (Kamenar and Nagl 1976) to be orthorhombic at room temperature as for (TMA)2ZnCI 4 (Wiesner et al 1967), the latter compound undergoes five successive phase transitions (Sawada et al 1978). The 7"1 minima observed in (TMA)2ZnCI4 were ascribed (Niemela and Heinila 1981) to arise from two inequivalent r~l^ ions.…”

Section: Resultsmentioning

confidence: 99%