H. W. Rotter

Structural and scanning microscopy studies of layered compounds MCl3 (M = Mo, Ru, Cr) and MOCl2 (M = V, Nb, Mo, Ru, Os)

Abstract Structural investigations on trichlorides (α- and β-MoCl3, solid solutions Ru1−5CrxCl3) and oxide dichlorides MOCl2 (M = V, Nb, Mo, Ru, Os) show that layer structures with stacking faults can be solved without evaluation of the diffuse parts of scattering. The combination of X-ray methods and atomic scale STM/AFM imaging yields information about the pattern of the surface atoms and the metal sublattice between the halide layers. Metal-metal bonds, structural distortions of coordination polyhedra and cation distribution in solid solutions have been determined. The correct layer symmetry, obtained by STM/AFM methods, was used in the X-ray structure analysis by single crystal and powder diffraction. Disorder problems due to stacking faults of the layers could be treated in that way.

Isotopic effects on the phonon modes in boron carbide

The effect of isotopes ((10)B-(11)B; (12)C-(13)C) on the infrared- and Raman-active phonons of boron carbide has been investigated. For B isotopes, the contributions of the virtual crystal approximation, polarization vector and isotopical disorder are separated. Boron and carbon isotope effects are largely opposite to one another and indicate the share of the particular atoms in the atomic assemblies vibrating in specific phonon modes. Some infrared-active phonons behave as expected for monatomic boron crystals.

Atomic scale surface studies of conductive organic compounds 2. Scanning tunneling microscopy and crystal structure of the charge transfer complex of 4-ethylpyridine-TCNQ2 (4-EP-TCNQ2)

Abstract The scanning tunneling microscopy (STM) studies of the conductive charge transfer complex of 4-ethylpyridine (4EP) with tetracyanoquinodimethane (TCNQ) were combined with X-ray diffraction measurements. The existence of two different crystalline modifications of the complex was revealed. The block-type monocrystals have a triclinic crystallographic structure with the following parameters: a=7.112 2 A , b=7.862 7 A , c=13.954 4 A , a=72.95 4 °, β=78.40 2 ° and γ=69.92 3 ° . The existence of a columnar structure of TCNQ molecules with diadic repeat unit is shown. The interplanar distances between neighboring TCNQ molecules in stack is 3.21 A. The STM images of one of the surfaces of such monocrystals correspond well with the distribution of TCNQ atoms in the surface layer constructed from the crystallographic ( a , b ) plane. The quality of needle-shaped monocrystals does not permit detailed crystallographic measurements. Only the triclinic crystal system and the lattice constants were determined: a=3.865 2 A , b=6.658 9 A , c=26.386 7 A , α=92.63 5 °, β=94.12 3 ° and γ=106.80 8 ° . STM images provide additional structural information about this crystal modification. The formation of stacks of TCNQ molecules with the average parameters of 4.1 A (periodicity in stack) and 13.1 A (distance between neighboring stacks) seems to be the characteristic feature of this structure. Observed structures are compared with the known crystallographic data of other charge transfer systems. The peculiarities of STM imaging in charge transfer systems are discussed in due course.

Structural and spectroscopic characterisation of the mixed valence platinum complex PtdabI3 (dab=o-diaminobenzene) ☆

Abstract The new mixed valence platinum complex PtdabI3 (dab=o-diaminobenzene) (1) has been prepared and characterised. The crystal structure consists of separate units of planar Pt(II)dabI2 and octahedral Pt(IV)dabI4 molecules. The latter are arranged in linear chains with rather short intermolecular I⋯I-contacts (3.478 A) which are responsible for charge transfer interactions. In the resonance Raman spectrum strong intensity enhancements and extended overtone progressions of the symmetric I–Pt–I stretching mode have been observed.

Über Caesiumtrichloromercurat(II) CsHgCl3: Lösung einer komplexen Überstruktur und Verhalten unter hohen Drücken

Bei der Losung der Kristallstruktur von CsHgCl3 wurde eine neue, ungewohnliche Verzerrungsvariante des kubischen Perowskit-Typs mit extrem (2 + 2 + 2)-verzerrten HgCl6-Baugruppen gefunden. Es liegt eine trigonale Uberstruktur mit der Raumgruppe P32 und neunfachem Zellinhalt vor, bei der im Vergleich zum Aristotyp lediglich 2/3 der verbruckenden Cl-Atome derart verschoben sind, das jeweils zwei kurzere (ca. 2,35 A), mittlere (ca. Hg–Cl: 2,70 A) und langere (ca. 3,15 A) Hg–Cl-Bindungen resultieren. Die Kationen Cs+ und Hg2+ und die Cl-Atome mit mittleren Abstanden behalten nahezu die idealen Positionen bei. Weil die kurzen, mittleren und langen Hg–Cl-Bindungen in den drei Raumrichtungen gleich verteilt sind, bleibt die kubische Metrik der Struktur trotz der extremen Verzerrungen des HgCl6-Gerusts nahezu unverandert. Hochdruckexperimente bis ca. 5 GPa ergaben, das die Struktur mit zunehmendem Druck entzerrt wird. Verschiebungen der Banden des FT-Raman-Spektrums zeigen in Einklang mit Kraftkonstantenrechnungen, das die Hg–ClBindungen in Richtung auf eine regular-oktaedrische Koordination der Hg-Atome angeglichen werden. Das Verschwinden des Raman-Spektrums bei P > 3,4 GPa deutet an, das in der Hochdruckphase von CsHgCl3 bei einer Gitterkonstante a = 5,204(1) A eine kubische Perowskit-Anordnung mit Hg–Cl = 2,60 A vorliegt. About Cesium Trichloromercurate(II) CsHgCl3: Solution of a Complex Superstructure and Behaviour under High Pressure By solving the crystal structure of CsHgCl3 a new uncommon distortion variant of the cubic perovskite type with extremely (2 + 2 + 2)-distorted HgCl6 octahedra has been found. The trigonal superstructure with space group P32 and ninefold cell contents differs from the aristotype only so far, as 2/3 of the Cl-atoms are moved away from their ideal positions leading to 3 pairs of different Hg–Cl distances with about 2.35 A, 2.71 A and 3.15 A. The cations Cs+ and Hg2+ and the chloride ions with medium Hg–Cl distance keep the ideal positions of a cubic perovskite lattice. Due to the evenly distribution of the three different bonds in the three directions of cubic space the cell shows an almost perfect cubic metric. Raman spectra and powder diffraction experiments up to pressures of 5 GPa demonstrated that the ideal perovskite arrangement is stabilized with increasing pressure. The shift of the FT-Raman bands show in agreement with spectra simulations that the Hg–Cl bonds are equalized, leading to a regular octahedral co-ordination of the Hg atoms. The disappearance of the Raman spectrum at P > 3.4 GPa indicates that the high pressure phase forms an ideal cubic perovskite (a = 5.204(1) A, Hg–Cl = 2.60 A).

Structure analysis of conductive polymer systems: Poly-4-vinylpyridine and poly(butadiene-b-4-vinylpyridine) with 7,7′,8,8′-tetracyanoquinodimethane

SummaryThe structure analysis of two conductive polymer systems-poly-4-vinylpyridine and poly(butadiene-b-4-vinylpyridine) with 7,7′,8,8′-tetracyanoquinodimethane (TCNQ)-was done by X-ray diffraction, scanning tunneling microscopy (STM) and FTIR. The charge transfer complex formed between the pyridine group and the known electron acceptor, TCNQ, is supposed to be the conductive element in these systems. In order to understand the structure of this complex, a model compound, the complex of 4-ethylpyridine (4EP) with TCNQ, 4EP/TCNQ2, was studied by the mentioned methods. It appears that there are two crystalline modifications of the model compound with different type of stacks of the TCNQ molecules. In polymer systems only one type of the complex is dominant as revealed by joint analysis of X-ray diffraction diagrams, STM and FTIR data. In the STM image of the polymer surface one can distinguish that molecular stacks with periodicities of 4.1 Å in a row are separated (12.5Å) from each other. Such organization is similiar to the one observed in conductive charge transfer complexes such as tetrathiofulvalene (TTF) with TCNQ. The ordered molecular domains are scattered on the polymer surface and take part in the formation of the conductive network.

Molekulare gemischtvalente Platin-Iod-Amin-Komplexe: Das dreikernige Pt3I8(NHEt2)2 mit kantenverknüpften planaren und oktaedrischen Baugruppen

PtI2 · NHEt2 wurde durch Umsetzung von K2PtCl4 mit KI und NEt2H in wasriger Losung erhalten. Die Kristallstruktur der monoklinen Verbindung (a = 20,558(4) A; b = 7,254(1) A; c = 13,790(3) A; β = 100,47(3)°; Raumgruppe C2/c) wird aufgebaut aus zweikernigen Komplexen [{Pt(NHEt2)I}2(μ-I)2]. Bei der Oxidation der Platin(II)-Verbindung mit I2 in CH2Cl2 entstanden Gemische, die den gemischtvalenten Komplex Pt3I8(NHEt2)2 und den zweikernigen Platin(IV)-Komplex [{Pt(NHEt2)I3}2(μ-I)2] enthielten. Die monokline Kristallstruktur von Pt3I8(NHEt2)2 (a = 20,278(4) A; b = 10,627(2) A, c =14,232(3) A; β = 115,66(3)° Raumgruppe C2/c) besteht aus dreikernigen Molekulen, bei denen zwei planare Baugruppen PtII(NEt2H)I3 mit einem zentralen PtIVI6-Oktaeder uber I-Kanten verbunden sind. Mixed Valence Molecular Platinum Iodide Amin Complexes: The Trinuclear Pt3I8(NHEt2)2 with Edgeshared Planar and Octahedral Building Groups PtI2 · NHEt2 was prepared by reaction of K2PtCl4 with KI and NEt2H in aqueous solution. The crystal structure of the monoclinic compound (a = 20.558(4) A; b = 7.254(1) A; c = 13.790(3) A; β = 100.47(3)°; space group C2/c) consists of binuclear molecules of [{Pt(NH(Et)2)I}2(μ-I)2]. On oxidation of this Pt(II) compound by I2 in CH2Cl2 mixtures of the trinuclear mixed-valence compound Pt3I8(NHEt2)2 and of the binuclear PtIV complex [{Pt(NHEt2)I3}2(μ-I)2] were obtained. The monoclinic crystal structure of Pt3I8(NHEt2)2 (a = 20.278(4) A; b = 10.627(2) A, c = 14.232(3) A; β = 115.66(3)° space group C2/c) is built up by trimeric units of two planar PtIII3(NHEt2) groups sharing edges with a central PtIVI6-octhedron.

CRYSTAL STRUCTURES AND VIBRATIONAL SPECTROSCOPY OF NEUTRAL PLATINUM(IV) AMINE IODO COMPLEXES

Abstract A series of platinum(IV) amine iodo complexes of the type [PtL 2 I 4 ] was synthesized for the first time and their infrared and Raman spectra were recorded. The crystal structures of cis -[Pt(net) 2 I 4 ], (net=ethylamine) (space group Pnma, a =14.668(3), b =8.787(2), c =11.433(2) A), trans -[Pt(net) 2 I 4 ] (space group C2/c, a =11.276(2), b =8.866(2), c =12.542(3) A, β =114.86(3)°) and [Pt(en)I 4 ] (en=ethylendiamine) (space group P1, a =6.780(1), b =11.613(2), c =14.703(3) A, α =71.87(3), β =80.78(3), γ =80.08 (3)°) were determined. Formation of linear chains of molecules with short intermolecular I–I distances was observed for cis -[Pt(net) 2 I 4 ]. The spectroscopic behavior is discussed according to these results.

Raman and resonance Raman spectroscopy of iodoplatinate(II), iodoplatinate(IV) and mixed-valence iodoplatinate(II,IV) salts

Abstract The Raman and resonance Raman spectra of a number of new iodoplatinate(II), iodoplatinate(IV) and mixed valence iodoplatinate(II,IV) salts are presented. Previous X-ray structure determination showed that the building blocks of all these compounds consist of PtI 6 octahedra and/or PtI 4 squares, which can be isolated or connected to dimeric units or polymeric chains. The Raman spectra show that the different coordination polyhedra and oxidation states of the platinum atoms have only a small influence on the wavenumbers of bands attributable to the Pt-I stretching modes. Due to the presence of intervalence transitions in the region probed the mixed-valence compounds show stronger resonance effects then the single-valence parent compounds. The resonance Raman spectra are determined not only by A-term activity but also by B-term activity.

Fehlordnung von Kationen und Kristallwasser bei kubischen Alkalitetrabromo- und -iodothallaten(III)/Disorder of Cations and Water Molecules in Cubic Tetrabromo- and -iodothallates

Abstract Tetrabromo- and -iodothallates(III) of the alkali cations crystallise from aqueous solutions as cubic hydrates MTlX4·nH2O (M = Li, Na, K, Rb, Cs, NH4; X = Br, I; n = 1-2). The tetraiodothallates retain their cubic structure on dehydratisation, while the tetrabromothallates undergo structural changes. The X-ray structure analyses of RbTlBr4 · H2O, NH4TlBr4 · 2H2O and KTlBr4 · 2H2O (-50 °C) showed that these compounds consist of a three-dimensional framework of TlBr4 tetrahedra and MBr12 ikosahedra which reminds of zeolites. In cavities of this framework 2/3 of the alkali cations and the crystal water molecules are accommodated in a disordered manner.