Dimensional Compounds Research Articles

Recent advances in tailoring the aggregation of heavier alkaline earth metal halides, alkoxides and aryloxides from non-aqueous solvents

This overview on one of the subjects treated in our group deals with the synthesis and study of low-dimensional polymer and molecular solid state structures formed with alkaline earth metal ions in non-aqueous solvents. We have chosen several synthetic approaches in order to obtain such compounds. The first concept deals with the "cutting out" of structural fragments from a solid state structure of a binary compound, which will be explained with reference to BaI2. Depending on the size and concentration of oxygen donor ligands, used as chemical scissors on BaI2, three-, two-, one- and zero-dimensional derived adducts of BaI2 are obtained, comparable to a structural genealogy tree for BaI2. A second part deals with the supramolecular approach for the synthesis of low dimensional polymeric compounds based on alkaline earth metal iodides, obtained by the combination of metal ion coordination with hydrogen bonding between the cationic complexes and their anions. Certain circumstances allow rules to be established for the prediction of the dimensionality of a given compound, contributing to the fundamental problem of structure prediction in crystal engineering. A third section describes a synthetic approach for generating pure alkaline earth metal cage compounds as well as alkali and alkaline earth mixed metal clusters. A first step deals with different molecular solvated alkaline earth metal iodides which are investigated as a function of the ligand size in non-aqueous solvents. These are then reacted with some alkali metal compound in order to partially or totally eliminate alkali iodide and to form the targeted clusters. These unique structures of ligand stabilized metal halide, hydroxide and/or alkoxide and aryloxide aggregates are of interest as potential precursors for oxide materials and as catalysts. Approaches to two synthetic methods of the latter, sol-gel and (MO)CVD (metal-organic chemical vapour deposition), are investigated with some of our compounds. (D. C. Bradley, Chem. Rev., 1989, 89, 1317-22; K. G. Caulton and L. G. Hubert-Pfalzgraf, Chem. Rev., 1990, 90, 969-95; T. P. Hanusa, Coord. Chem. Rev., 2000, 210, 329-367; T. P. Hanusa, in Comprehensive Coordination Chemistry II, ed. J. A. McCleverty and T. J. Meyer, Elsevier, Amsterdam, 2004, vol. 3, 1-92). Finally, the physical properties of some of our compounds are described qualitatively in order to show the wide spectrum of possibilities and potential applications for chemistry in this field.

Raman spectroscopic study of two dimensional polymer compounds of 2-aminopyrimidine

The Raman spectra of the two dimensional layered polymer compounds, M(2APM) 2M′(CN) 4 {where M=Mn or Cd; and M′=Ni or Pt; 2APM=2-aminopyrimidine} are reported in the 70–4000 cm −1 region. Vibrational data suggests that compounds are similar in structure to the Hofmann type two dimensional coordination polymer compounds, formed with M ′ ( CN ) 4 − 2 ions bridged by M ( 2 APM ) 2 + 2 cations. 2-Aminopyrimidine was coordinated to M(II) through one of the nitrogen atom of its heterocycle ring. Vibrational assignments are given for the bands arising from the tetracyanometallate layers and coordinated 2APM.

Superconducting phase in κ‐(BEDT‐TTF) 2 X compounds

We study within a mean field theory the superconducting phase of κ-(BEDT-TTF)2X organic superconductors. These two dimensional compounds can be described by a two-band model which depends on two parameters t1 and t2. We have considered that the superconducting state is induced by spin fluctuations and the gap symmetry is of dxy type. We have then determined the dependence of the energy gap on the ratio t1/t2, which gives us the behavior of the superconducting transition temperature. We show that t1/t2 may mimics either a chemical pressure or a hydrostatic one. Our results are in a good agreement with recent experiments suggesting a dxy wave symmetry. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

One dimensional compounds with large thermoelectric power: Ca 3Co 2O 6 and Ca 3CoMO 6 with M=Ir 4+ and Rh 4+

In the Ca–Co–O system, there exists at least two identified phases, Ca 3Co 4O 9 and Ca 3Co 2O 6 exhibiting 2D CoO 2 planes and 1D Co–Co chains, respectively. Both oxides are characterized by large thermopower values at room temperature, the largest value being obtained for Ca 3Co 2O 6 (Seebeck coefficient, S 300 K=450 μV K −1). However, the electrical resistivity of the latter is too large (typically 50 Ω cm) for applications as thermopower materials. Interestingly, the substitutions of Ir 4+ or Rh 4+ for one cobalt out of two in the chain do not greatly affect the electronic properties in contrast to the substitution by Sc 3+ (3d 0). This emphasizes that the Ir or Rh cations can play a similar role to that of the Co cations. This opens a new route for the search of new thermoelectric materials alternative to the cobaltites.

Infrared properties of W-doped charge-density-wave material K0.3MoO3

The optical conductivity spectra of quasi-one dimensional compounds K0.3Mo1−xWxO3 (x=0, 0.03 and 0.15) have been studied over broad frequencies. While the DC resistivity measurements indicate no sign of CDW transition in heavily W-doped blue bronze, the optical conductivity spectra still show a single particle gap at around 0.2eV for E parallel to the chain direction. Such impurity effect challenges our understanding about the occurrence of the optical gap with the CDW transition.

The FT-IR spectra of pyrazinamide complexes of transition metal(II) tetracyanonickelate

M(PZA) 2Ni(CN) 4 {where M=Mn, Co, Fe, Ni or Cd; PZA=pyrazinamide} complexes have been prepared for the first time and their FT-IR spectra are reported in the 400–4000 cm −1 region. The spectral features suggest that the compounds are similar in structure to the Hofmann type two dimensional coordination polymer compounds, formed with Ni(CN) 4 −2 ions bridged by M(PZA) 2 +2 cations. PZA is coordinated to M(II) through the oxygen atom of the carbonyl group.

The FT-IR spectroscopic investigation of two dimensional polymeric complexes of 2-aminopyrimidine

The coordination polymeric compounds, M(2APM) 2Ni(CN) 4 (where M=Mn, Co, Ni or Cd; 2APM=2-aminopyrimidine) have been prepared for the first time and their FT-IR spectra are reported in the 400–4000 cm −1 region. The spectral features suggest that the compounds are similar in structure to the Hofmann type two dimensional coordination polymeric compounds, formed with Ni(CN) 4 −2 ions bridged by M(2APM) 2 +2 cations. 2APM is coordinated to M(II) through one of the pyrimidine ring nitrogen atoms; the amino group is not involved in the complex formation. The coordination effect on the 2APM vibrational wavenumbers is analysed.

Conventional analytical methods for chemical warfare agents

Abstract Analytical methods that are currently used for the detection and identification of chemical warfare agents are reviewed and classified by the number of dimensions of information they provide. Single dimensional sensors target specific compounds or classes of compounds. Although they can be less expensive and more portable than multidimensional sensors, multidimensional sensors detect a broader threat spectrum with greater precision and accuracy. The recommendation for analytical field verification during inspections under the Chemical Weapons Convention (CWC) is to use simple two-dimensional analytical methods, such as gas chromatography (GC) or ion mobility spectrometry (IMS), for on-site screening of chemical weapons (CW) agents or to fully equip a modern, mobile analytical laboratory located in an airplane, which can be moved rapidly throughout the world to each inspection site and provide high-quality analytical data on-site.

H-bonded polymer structures of different dimensionality: syntheses and crystal structures of [Ca(DME) n(H 2O) m]I 2·(DME) x ( 1: n=3, m=3, x=1; 2: n=2, m=4, x=0) and [Ca{CH 3(OCH 2) 3OCH 3}(H 2O) 4]I 2

From the non-covalent binding modes used in supramolecular chemistry, metal ion complexation and hydrogen bonding are combined in order to synthesise new inorganic polymers as precursors for thin layer deposition. With the same coordinating ligands, DME and water, but in varying stoichiometries, two different dimensional compounds are obtained. The synthesis and crystal structures of the one- and three-dimensional polymers are described together with a third example for better control of the supramolecular products formed.

Preparation and characterization of natural lower dimensional layered perovskite-type compounds

Thin films of layered perovskite compounds (CnH2n+1NH3)2(CH3NH3)m−1PbmBr3m+1 (m=1, 2 and 3) were prepared by the spin-coating method from their DMF (N,N-dimethylformamide) solutions. The control of the inorganic layer thickness in layered perovskites can be achieved by changing the ratio of the two amines (CnH2n+1NH3/CH3NH3). The layered perovskite films showed a strong, clear exciton absorption peak at room temperature due to their large exciton binding energy. With increasing numbers of inorganic layers, a red shift of the exciton absorption was observed due to the decrease in transfer energy. X-ray diffraction patterns clearly demonstrated that the spin-coated film was highly oriented normal to the surface, which is consistent with ‘mono’, ‘bi’, and ‘tri’ layer structures, respectively. The effect of the alkyl chain length of the organic part was also investigated.

Synthesis and characterisation of novel layered compounds, Cs2MP3O10 (M = Al or Ga), containing triphosphate groups †

The compounds Cs2AlP3O10 and Cs2GaP3O10 have been synthesized by solid state reactions and structurally characterised by single crystal X-ray diffraction. They are two dimensional compounds possessing corrugated [MP3O10]2− anionic layers interleaved with Cs+ ions. The layers are built from MO6 octahedra and bent triphosphate groups. Solid state NMR studies corroborate the presence of crystallographically distinct phosphorus atoms of triphosphate groups.

Magnetic Materials Based on Nitronyl Nitroxide Radicals Complexes: From Mononuclear Building Blocks to One- and Two-Dimensional Compounds

In this paper is reported a series of Mn(II) complexes with nitronyl nitroxides specifically design to act as bis-chelating ligands. Starting with the mononuclear complexes used as molecular building blocks it is shown how they may polymerise to afford either one dimensional or two dimensional layered compounds exhibiting long-range magnetic ordering.

High pressure structure of (DIDCNQI) 2Cu

X-ray“monochromatic” Laue photo with diamond anvil pressure cell revealed c */3 satellite reflections indicating 2 k F CDW formation in the low dimensional compounds (DIDCNQI) 2Cu in the low pressure insulating(=I) phase around 11–20 kbar but no satellite reflections in the middle pressure metallic(=M) phases around 23–26 kbar.

High Pressure Structures of Organic Low Dimensional Conductor DCNQI Compounds.

Using X-ray and DAC, room-temperature crystal structures under physical pressure (PP) were solved for DCNQI-Cu compounds which exhibit particular metal-insulator (M-I) transition owing to their electronic low dimensionality (CDW) and strong correlation (Mott). This M-I transition is known to be triggered with moderate (=small) PP or chemical substitution (chemical pressure:CP). Observed high pressure structures were compared with theoretical structure determinations. From the structural viewpoint, relation between PP and CP effects on the M-I transition was discussed.

Transverse transport in organic conductors: possible evidence for a Luttinger liquid

We present c-axis resistivity measurements performed on the organic conductors and under pressure. The aim is to probe the density of states of quasi-one dimensional compounds the high temperature properties of which are those of a Luttinger liquid. It is found that the 1-D Luttinger description breaks down below a specific pressure-dependent temperature, giving rise to a transient regime. The Fermi liquid behaviour is however restored at low temperature i.e. around 10 K, as evidenced by NMR measurements. Accordingly, two different energy scales 100 K and 10 K are required to get a fair understanding of all observed physical phenomena. Our interpretation supports the picture of a power law exponent for the correlation functions of the order of 0.25–0.30.

Spectral functions of one-dimensional models of correlated electrons

Using the Ogata-Shiba wave function, the spectral functions of the one-dimensional infinite U Hubbard model are calculated for various concentrations. It is shown that the ``shadow band'' feature due to 2k_F fluctuations becomes more intense close to half-filling. Comparing these results with exact diagonalization data obtained on finite clusters for the finite U Hubbard model and for the t-J model, it is also shown that this feature remains well-defined for physically reasonable values of the parameters (U/t\simeq 10, J/t\simeq 0.4). The ``shadow'' structure in the spectral functions should thus be observable in angle-resolved photoemission experiments for a variety of quasi-one dimensional compounds.

Stochastic models for guest–guest interactions in one–dimensional inclusion compounds

The intrinsic relative preferences of XX, XY and YY interactions between functional groups X and Y can be obtained by considering a set of onedimensional inclusion compounds containing guest molecu...

Single crystal epr studies on mixed systems of copper dipyridine dibromide and copper dipyridine dichloride

X-band EPR measurements on the magnetically one dimensional (1D) mixed compounds CuPy 2 ( Cl x Br 1− x ) 2 (with 0 < x < 1) are performed in the temperature range 77–300 K. Principal ionic g -factors and their orientation in the crystals are determined. The EPR lineshape is found to be Lorentzian in all cases. Linewidth anisotropies in different planes of these crystals are satisfactorily analysed on the basis of the anisotropic exchange theories of McGregor K. T. and Soos Z. G., ( J. Chem. Phys. 64 , 2506 (1976).) and Ritter M. B., Drumheller J. E., Kite T. M., Snively L. O. and Emerson K. ( Phys. Rev. B28 , 4949 (1983).) for Cu(II) systems. Principal findings are the following: (i) Peak-to-peak derivative linewidth as well as the anisotropic symmetric exchange (a.e.) parameter D e follows a linear relationship with the concentration (i.e., increases as the Br content in the compound increases), (ii) The orthorhombic components of the a.e. tensor in the mixed compounds as well as in the pure bromine compound have identical magnitude. (iii) In explaining the linewidth anisotropy in the (100) planes of the mixed systems, an additional term of the form AδH 2 (arising out of interchain exchange and magnetic inequivalence of Cu 2+ ions in the neighbouring chains) needs to be incorporated in the linewidth formula.

The application of the 2-amino-4-pyrimidones to supramolecular synthesis

A strategy for preparation of two dimensional layered compounds is introduced. This strategy explores the possibility of using the 2-amino-4( H)-pyrimidone ring system as a host for dicarboxylic acids guests. This strategy is successful for the orientation of adipic acid into a two dimensional β-network with a molecular repeat distance of 6.5 Å.

The amazing story of semiconductor surface structures

A brief indication of the history of the determination and prediction of the structure of semiconductor surfaces is given. Only clean surfaces are considered, although adsorbate structures exhibit analogous features. Many of these surfaces are reconstructed, i.e., the symmetry of their surface structure is lower than that of the corresponding bulk lattice plane. During the 1980s and 1990s, the detailed atomic geometries of many of these structures were determined. They exhibit a wide variety of atomic motifs, many of which are not familiar from either small molecule geometries or solid state structures. Theoretical predictions exist for a few of the most heavily studied structures, but even in these cases not all the details of the structures are accepted. The enormous literature on this topic can be comprehended by recognizing that the surface regions of semiconductors constitute a new class of two dimensional chemical compounds, restricted by the requirement that they fit epitaxically on the bulk crystalline substrate. Five principles govern the formation of these compounds for clean tetrahedrally coordinated semiconductors, guiding even a novice to a rudimentary understanding of the origin of the observed rich variety of surface structures. In the case of the cleavage surfaces additional scaling laws are satisfied which further buttress the concept that these surfaces are two dimensional compounds governed by coordination chemistry considerations which are distinct from those appropriate for either molecules or bulk solids.