Number Of Formula Units Research Articles

Synthesis, crystallographic, spectroscopic, magnetic, and DFT characterization of a new strandberg-type polyoxometalate: (H2AEP)4[CoP2Mo5]2 ̶ first principles calculations

This work reports the synthesis of a novel diphosphopentamolybdate compound with the formula (C6H17N3)4[Co(H2O)4P2Mo5O23]2‧8·74H2O abbreviated as (H2AEP)4[CoP2Mo5]2. Characterization of this compound was carried out using various techniques, including X-ray diffraction, thermal analysis (TGA), and spectroscopies such as FT-IR, Raman, UV–visible, and fluorescence. The structural study reveals that the studied material crystallizes in the orthorhombic system Pca21 with lattice parameters of a = 18.6348(16) Å, b = 11.8613(10) Å, c = 35.074(3) Å, and volume V = 7752.5(11) Å3, and a number of formula units per primitive cell Z = 4. The crystal structure study reveals that the Strandberg anions (P2Mo5O23)6− are connected to Co(II) octahedra through the terminal oxygen atoms of the PO4 tetrahedra, creating 1-D anionic chains in the crystallographic direction [101]. The 1-(2-Aminoethyl)piperazinium (AEP) cations are located within the anionic framework to neutralize its negative charge. The magnetic characteristics of the compound were investigated by examining the temperature-dependent molecular susceptibility over the range of 2–300 K. The analysis revealed the presence of an antiferromagnetic exchange interaction. Moreover, the material's refractive index exhibited significant dispersive behavior within the visible spectrum, indicating its potential for use in visible optical communication devices. A first-principles density functional theory (DFT)-based computational study confirms the semiconducting behavior of (H2AEP)4[CoP2Mo5]2, revealing that in the ground state, high-spin octahedrally coordinated Co2+ cations exhibit a very weak antiferromagnetic coupling along the [Co(H2O)4P2Mo5O23]∞4−chains running in the crystal a direction.

Crystal Structure Prediction and Lattice Dynamical Calculations for the Rare Platinum-Group Mineral Zaccariniite (RhNiAs)

The crystal structures of newly found minerals are routinely determined using single-crystal techniques. However, many rare minerals usually form micrometer-sized aggregates that are difficult to study with conventional structural methods. This is the case for numerous platinum-group minerals (PGMs) such as, for instance, zaccariniite (RhNiAs), the crystal structure of which was first obtained by studying synthetic samples. The aim of the present work is to explore the usefulness of USPEX, a powerful crystal structure prediction method, as an alternative means of determining the crystal structure of minerals such as zaccariniite, with a relatively simple crystal structure and chemical formula. We show that fixed composition USPEX searches with a variable number of formula units, using the ideal formula of the mineral as the only starting point, successfully predict the tetragonal structure of a mineral. Density functional theory (DFT) calculations can then be performed in order to more tightly relax the structure of the mineral and calculate different fundamental properties, such as the frequency of zone-center Raman-active phonons, or even their pressure behavior. These theoretical data can be subsequently compared to experimental results, which, in the case of newly found minerals, would allow one to confirm the correctness of the crystal structure predicted by the USPEX code.

Ontology, archetypes and the definition of ‘mineral species’

AbstractOntologydeals with questions concerning what things exist, and how such things may be associated according to similarities and differences and related within a hierarchy. Ontology provides a rigorous way to develop a general definition of a mineral species. Properties may be divided into two principal groups: anintrinsic propertyis characteristic of the object and is independent of anything else; anextrinsic propertydepends on the relation between the object and other things. Auniversalis an entity that is common to all objects in a set. Here the objects are mineral samples, each entity is a specific property of these minerals, and the set of objects is all mineral samples of that mineral species. The key intrinsic properties of a mineral species are its name, its end-member formula andZ(the number of formula units in the unit cell), its space group and the bond topology of the end-member structure. These are also universals as they are common to all mineral samples belonging to that mineral species. An archetype is a pure form which embodies the fundamental characteristics of an object. Thus the archetype of a mineral species embodies the above set of universals. Real mineral samples of this mineral species are imperfect copies of that archetype, with a range of chemical composition defined by the boundaries between end-member formulae of this and other end members of the same bond topology. The result is a formal definition of a mineral species: A specific mineral species is the set of imperfect copies of the corresponding archetype and is defined by the following set of universals: name, end-member formula andZ, space group, and bond topology of the end-member structure, with the range of chemical composition limited by the compositional boundaries between end members with the same bond topology.

High-throughput design of Peierls and charge density wave phases in Q1D organometallic materials.

Soft-phonon modes of an undistorted phase encode a material's preference for symmetry lowering. However, the evidence is sparse for the relationship between an unstable phonon wavevector's reciprocal and the number of formula units in the stable distorted phase. This "1/q*-criterion" holds great potential for the first-principles design of materials, especially in low-dimension. We validate the approach on the Q1D organometallic materials space containing 1199 ring-metal units and identify candidates that are stable in undistorted (1 unit), Peierls (2 units), charge density wave (3-5 units), or long wave (>5 units) phases. We highlight materials exhibiting gap-opening as well as an uncommon gap-closing Peierls transition and discuss an example case stabilized as a charge density wave insulator. We present the data generated for this study through an interactive publicly accessible Big Data analytics platform (https://moldis.tifrh.res.in/data/rmq1d) facilitating limitless and seamless data-mining explorations.

Polymorphic transformations of CaSi2 and CaGe2

The control of CaSi2 and CaGe2 polymorphic transformations is important for their use as raw materials to prepare widely applicable 2D materials. CaSi2 and CaGe2 have several polymorphs, such as 2H, 3R, 4H, and 6R, having layered structures with different stacking of Ca and Si or Ge layers. In this study, CaSi2 and CaGe2 ingots were synthesized by melting and solidifying Ca with Si or with Ge, respectively, and their polymorphs and polymorphic transformations were investigated using X-ray diffraction and transmission electron microscopy. The most stable CaSi2 polymorph, 6R, was formed by solidifying at a 10 ​°C/min cooling rate, whereas the metastable 3R polymorph was formed with slow cooling of 0.167 ​°C/min because the formation of 3R–CaSi2 was promoted by tensile stress. After fluorine diffusion, 6R–CaSi2 was transformed into 3R–CaSi2, and 4H-CaGe2 and 6R–CaGe2 were transformed into 3R–CaGe2 with the largest unit cell volume/Z value (where Z is the number of formula units in a unit cell). Polymorphic transformations occurred owing to the occupation of F− ions in interstitial sites because the volume/Z values for the polymorphs of CaSi2 and CaGe2 are in the following order: 3R ​> ​4H ​> ​2H ​> ​6R. The c lattice constant of each polymorph remained constant after fluorine diffusion. Thus, the formation of the polymorphs of CaSi2 (and CaGe2) can be governed by controlling the unit cell volume of CaSi2 (and CaGe2).

Structural chemistry of fluoride and mixed-ligand fluoride complexes of gallium(III)

AbstractThis article covers the structural chemistry of fluoride and mixed-ligand fluoride complexes of gallium(III), discusses more than 140 known crystal structures of anionic fluoride and mixed-ligand fluoride complexes and continues the discussion initiated in previous reviews dedicated to the stereochemistry and structural chemistry of group III–V metals fluoride complexes. Most of these structures have been established by single-crystal X-ray diffraction techniques, but some were characterized by powder X-ray diffraction methods. This paper offers a discussion of the geometry of gallium and outer sphere cation coordination polyhedra, the association of gallium atoms in dimer and polymer formations, types of cation-anion interactions, and their contributions in actual three-dimensional crystal structures. The structural information has been compiled in a single table containing phase compositions and the corresponding standard crystallographic data (such as crystal system, space group, unit cell parameters, number of formula units per cell [Z], reliability factors [R1], Ga-F, and Ga-O bond lengths).

Structural chemistry of anionic fluoride and mixed-ligand fluoride complexes of indium(III)

AbstractA total of 88 crystal lattice structures of indium(III) anionic fluoride and mixed-ligand fluoride complexes have been discussed and systematized. Most of these structures have been established by single-crystal X-ray diffraction techniques, but some were characterized by powder X-ray diffraction methods. The presented crystallography data were compared with known isotypical compounds. This paper offers a discussion of the geometry of indium and outer sphere cation coordination polyhedra; the association of indium atoms in dimer, oligomer, and polymer formations (chains, layers, frameworks); types of cation-anion interactions; and their contributions in actual three-dimensional crystal structures including types of the crystal lattices formed. We also used structural examples of potassium fluoroindates(III) to describe the basics of the structural depolymerization model for fluoride compounds, which is used to depict the formation and transformation of complex metal fluorides and predict structural types of novel or uncharacterized fluorides in the corresponding compound series. For the readers’ convenience, we have compiled structural information in a single table containing phase compositions and corresponding standard crystallographic data (such as crystal system, space group, unit cell parameters, number of formula units per cell [

Crystallographic parameters and composition of unit cells of macrocyclic complexes of Zn and Co with polygalacturonic acid

Zinc and cobalt(II) pectinates are found to crystallize in hexagonal syngony. The parameters of unit cells of zinc (a = 10.72 A, c = 3.79 A) and cobalt(II) (a = 29.89 A, c = 10.57 A) pectinates are determined. The correctness of indexing is confirmed by the agreement between the experimental and calculated values of the crystallographic parameters, and by the number of formula units per unit cell.

Cation substitution in synthetic meridianiite (MgSO4·11H2O) II: variation in unit-cell parameters determined from X-ray powder diffraction data

We have prepared aqueous MgSO4 solutions doped with various divalent metal cations (Ni2+, Zn2+, Mn2+, Cu2+, Fe2+, and Co2+) in proportions up to and including the pure end-members. These liquids have been solidified into fine-grained polycrystalline blocks of metal sulfate hydrate + ice by rapid quenching in liquid nitrogen. In a companion paper (Fortes et al., in Phys Chem Min 39) we reported the identification of various phases using X-ray powder diffraction, including meridianiite-structured undecahydrates, melanterite- and epsomite-structured heptahydrates, novel enneahydrates and a new octahydrate. In this work we report the changes in unit-cell parameters of these crystalline products where they exist over sufficient dopant concentrations. We find that there is a linear relationship between the rate of change in unit-cell volume as a function of dopant concentration and the ionic radius of the dopant cation; large ions such as Mn2+ produce a substantial inflation of the hydrates’ unit-cell volume, whereas smaller ions such as Ni2+ produce a modest reduction in unit-cell volume. Indeed, when the data for all hydrates are normalised (i.e., divided by the number of formula units per unit-cell, Z, and the hydration number, n), we find a quantitatively similar relationship for different values of n. Conversely, there is no relationship between the degree of unit-cell inflation or deflation and the limit to which a given cation will substitute into a certain hydrate structure; for example, Co2+ and Zn2+ affect the unit-cell volume of MgSO4·11H2O to a very similar degree, yet the solubility limits inferred in our companion paper are >60 mol. % Co2+ and <30 mol. % Zn2+.

ChemInform Abstract: Structure, Electrical Transport and Magnetic Properties of the Misfit Layer Compound (SmS)1.19TaS2 “SmTaS3”.

Abstract Single-crystal X-ray diffraction has shown that (SmS)1.19TaS2 is a misfit layer compound built alternately of double layers of SmS, an approximately {100} slice of NaCl-type SmS and sandwiches of TaS2 with tantalum in slightly distorted trigonal prisms of sulfur. The two structural units are both described in the orthorhombic space group Fm2m, a 1 = 5.552(3) A , b 1 = 5.679(4) A , c 1 = 22.50(4) A , Z = 8 for the SmS part and a 2 = 3.293(1) A , b 2 = 5.679(4) A , c 2 = 22.50(4) A , Z = 4 for the TaS2 part. Corresponding axes are parallel and the layer stacking direction is c. The composition is determined by the ratio a 1 a 2 and the number of formula units in each cell. Sm-S distances in the SmS double layer are close to those in SmS in the metallic high-pressure form with the scheme Sm3+ (e−)S2−. The electrical transport properties are in agreement with an almost filled 5dz2 band of the TaS2 part of the structure, indicating electron donation from the SmS to the TaS2 part. The magnetic susceptibility χ does not follow a Curie-Weiss law; χ−1 goes to zero with decreasing temperature after a small discontinuous drop at about 50 K.

Properties of Polyvinyl Alcohol Oligomers: A Molecular Dynamics Study

AbstractMD studies of liquid isopropyl alcohol and melts of short poly(vinyl alcohol) (PVA) oligomers are described. The specific volume was found to depend inversely on the number N of repeat units. If the chain length is enhanced, the viscosity of the PVA melt increases and the peaks in the radial distribution function become sharper. Additional peaks that appear in melts of PVA chains are of pure intramolecular origin. The calculated radius of gyration was found to depend on the number of formula units via $N^{0.65 \pm 0.03}$. The orientation correlation functions showed that all molecular vectors of PVA melts with chain lengths N = 1, 2, 3 relax completely within a few nanoseconds. The relaxation times for the OH bond vector as obtained via the Kohlrausch‐Williams‐Watts expression showed an exponential dependence on the number of repeat units.magnified image

Phase behaviour and thermoelastic properties of perdeuterated ammonia hydrate and ice polymorphs from 0 to 2 GPa

The results are described of a series of neutron powder diffraction experiments over the pressure and temperature ranges 0 &lt;P&lt; 2 GPa, 150 &lt;T&lt; 240 K, which were carried out with the objective of determining the phase behaviour and thermoelastic properties of perdeuterated ammonia dihydrate (ND3·2D2O). In addition to the low-pressure cubic crystalline phase, ADH I, two closely related monoclinic polymorphs of ammonia dihydrate have been identified, which commonly occur as a composite in the range 450–550 MPa at 175 K; these are labelled ADH IIaand IIb, and each has unit-cell volumeV≃ 310 Å3and number of formula units per unit cellZ= 4. It has been determined that this composite dissociates to a mixture of ammonia monohydrate (ND3·D2O) phase II (AMH II) and ice II when warmed to ∼190 K at 550 MPa, which in turn partially melts to ice II + liquid atT= 196 K; AMH II has a large orthorhombic unit cell (V≃ 890 Å3,Z= 16). Above 600 MPa, an orthorhombic polymorph of ammonia dihydrate (withV≃ 530 Å3,Z= 8), which has been referred to previously as ADH IV, persists to pressures greater than 2 GPa and appears to be the liquidus phase over this whole pressure range. This phase has been observed co-existing with ice II, ice VI and AMH II. The most plausible synthesis of the high-pressure phase behaviour is described here. This model explains the reported observations, and provides measurements of the densities, thermal expansion, bulk moduli and crystal growth kinetics of the high-pressure ammonia dihydrate, ammonia monohydrate and ice polymorphs.

Dependences of Space-Group Type Incidences of Organic and Metal-Organic Compounds on Reduced Unit-Cell Volumes

The dependences of occurrences of the most frequent space-group types P, P2 1 , P2 1 /c, C2/c, P2 1 2 1 2 1 and Pbca on reduced (primitive) unit-cell volumes up to 8000 Å3 were investigated for organic and metal-organic compounds with different number of residues (1–3), i.e. for the compounds with different number of molecular constituents. The dependences for these space-group types are similar, single-peaked; their maxima are proportional to the number of asymmetric units (a compact symmetry-independent part of the unit cell) affected by Z′ (number of formula units per asymmetric unit) in the pertinent space-group types. The dependences of Z′ < 1, Z′ = 1, Z′ > 1 within each space group type on reduced unit-cell volumes are also similar in shape. From these dependences it can be inferred that ability for crystallization of organic and metal-organic molecules ceases for the structures with the reduced unit-cell volumes above 8000 Å 3 . This volume corresponds roughly to 450 non-hydrogen atoms.

Combinatorial modular design of the structures of spinel-type phases

A review is presented of studies dealing with spinelloids, i.e., phases with spinel-type structures. Structures of one-dimensional and two-dimensional spinelloids, ordered solid solutions, polytypes, homologues, and hybrid spinelloids (phases with structures that can be constructed using fragments of a spinel or any other structure type) are analyzed in comparison with the spinel structure. The spinelloid structures are calculated using the developed combinatorial modular design method. It is revealed that the constructed modular spinelloid structures are in reasonable agreement with those described in the literature. The proposed crystal chemical description of the modular structures of spinelloids (composition, symmetry, relative sizes of unit cells, and the number of formula units in the unit cell) can be used to identify new phases with spinel-type structures. The results of the combinatorial modular design provide the basis for the controlled search for new spinelloids with a specified set of physical and physicochemical properties.

Self-propagating, high-temperature combustion synthesis of rhombohedral AlPt thin films

Sputter-deposited, Al/Pt multilayer thin films of various designs exhibited rapid, self-propagating, high-temperature reactions. With reactant layers maintained at ∼21 °C prior to ignition and films adhered to oxide-passivated silicon substrates, the propagation speeds varied from approximately 20 to 90 m/s depending on bilayer dimension and total film thickness. Contrary to current Al–Pt equilibrium phase diagrams, all multilayers reacted in air and in vacuum transformed into rhombohedral AlPt having a space groupR-3(148). Rietveld refinement of AlPt powder (generated from thin film samples) yielded trigonal/hexagonal unit cell lattice parameters ofa= 15.634(3) Å andc= 5.308(1) Å; the number of formula units = 39. Rhombohedral AlPt was stable to 550 °C with transformation to a cubic FeSi-type structure occurring above this temperature.

39K NMR spectra of the powder and single crystal of potassium titanyl phosphate

The powder and single crystal of potassium titanyl phosphate KTiO(PO4) have been studied by 39K NMR. The quadrupole coupling and 39K isotropic chemical shift parameters have been calculated. The number of formula units in the unit cell of potassium titanyl phosphate is suggested to be equal to the number of magnetically nonequivalent positions of potassium atoms in the lattice.

Characterization of an electroactive polymer for overcharge protection in secondary lithium batteries

The optical, electronic, and electrochemical properties of thin films of the electroactive polymer, poly(3-butylthiophene) (P3BT), were studied in a lithium hexafluorophosphate electrolyte. Upon extraction of n electrons per polymer formula unit, anions are taken up to balance the charge, forming a polymer cation salt, (P3BT) mn+ (PF 6 −) mn ( m is the number of formula units in the polymer chain), whose state of charge (SOC) varies with n. An in situ ac impedance method was developed to determine the electronic conductivity of the polymer at different states of charge. On oxidation of the insulating neutral P3BT polymer, the conductivity increased by eight orders of magnitude. The electrochemical potential, electronic conductivity, and optical spectrum at each state of charge were correlated, producing a color index of these primary characteristics. This allowed determination of the potential and state of charge as a function of location in transparent polymer films during propagation of an oxidation front across the film and during passage of steady-state currents through the polymer film.

Thermal conductivity of spinels and olivines from vibrational spectroscopy: Ambient conditions

The damped harmonic oscillator model for thermal conductivity of insulators is improved, lead­ing to a formula that predicts thermal conductivity at ambient conditions (k 0 ) from various physical properties, most of which are commonly measured. Specifically, k 0 = [ρ/(3ZM)] C v [(u P + u s )/2] 2 / &lt;Γ&gt;, where ρ is density, Z is the number of formula units in the primitive unit cell, M is the molar weight, C v is heat capacity, u is the sound speed (P denotes compression; S denotes shear), and &lt;Γ&gt; is the average of the damping coefficients determined from peak widths in infrared reflectivity spec­tra, or from suitable Raman and Brillouin spectra. The classical physics and quantum-mechanical basis for this model is discussed, with emphasis on the effect of phonon-phonon interactions on mode properties. The calculated values of k 0 all lie within the experimental uncertainty of the mea­surements for all samples with the spinel or olivine structure examined by Horai (1971) with known or approximately correct chemical compositions. Other divergent measurements of k for MgAl 2 O 4 are discounted for various reasons. Early studies of Fe-bearing spinels are not generally reliable, but rough estimates from the above equation are consistent with all data, and good agreement is ob­tained for samples such as Mg 0.5 Fe 0.5 Al 2 O 4 and γ-Fe 2 SiO 4 for which the previous authors obtained chemical data, and for which IR reflectivity data exist. The theory reproduces the measured depen­dence of k 0 on composition and structure. Anisotropy in k 0 results mainly from differences in lattice constants (j): the equation for olivine is kj/k 0 =(V ⅓ /j) 0.73 which predicts the ratios within 3%. For solid solutions between Fe and Mg, the model provides a non-linear dependence of k 0 on mol% Fe, with the damping coefficient being the key factor producing non-linearity. Predicted ambient values are 11.3 ± 0.4 W/m-K for γ-Mg 2 SiO 4 , 6.5 ± 0.7 W/m-K for γ-Mg 12 Fe 0.8 SiO 4 , and 6.9 ± 0.3 W/m-K for β-Mg 2 SiO 4 . The high k 0 for ringwoodite suggests that heat in Earth’s transition zone should be conducted twice as efficiently as in the adjacent upper and lower mantles: this discontinuous depth dependence of k could impact thermal models of conduction in subducting slabs and of mantle convection

Determinationof the structure of IIIa-ZnIn2S4 usingconvergent-beam electron diffraction and single-crystal x-raydiffraction

The crystal structure of the ternary semiconductor IIIa-ZnIn2S4 was investigated using convergent-beamelectron diffraction (CBED) and single-crystal x-ray diffractionto elucidate whether the structure is fully ordered, asdescribed by the acentric R3m space group, or has somedegree of disorder as described by the centric R3̅m space group. The CBED technique, based upon dynamicaldiffraction, permitted the unique identification of the truestructural symmetry, while x-ray diffraction could notdiscriminate between the two space groups. CBED patternsperpendicular to the [001] crystal direction showed the 6mmsymmetry characteristic of the R3̅m space group.This result agrees with early Raman and photoluminescencespectroscopy measurements. The structure is best described bythe R3̅m space group, with cell parameters a = 3.8728(6) Å and c = 37.0664(1) Å and unit-cell volumeV = 481.4(1) Å3. The length of the c axiscan be described by the expression c = N(3.086±0.003) Å, where N is the number of sulfur layers in theunit cell and Z = N/4 the number of formula units; for ourstructure N = 12 and Z = 3. The crystal structure consistsof a close-packed arrangement of S atoms, with Zn and half ofthe In atoms distributed in a disorderly fashion in tetrahedral sites, andthe other half of the In atoms located in octahedral sites. Theatomic positions and an isotropic temperature factor arereported.

Crystal structures of copper(II) compounds with racemic threonine

Crystals structures of two modifications of the copper(II) compound with racemic threonine Cu(D-Tre)(L-Tre) are determined by the electron diffraction technique. The unit cell parameters, space group, and number of formula units per unit cell for the crystals of two modifications are as follows: a = 11.10(3) A b = 9.56(2) A, c = 5.11(2) A, γ = 92.6(2)°, space group P21/b, and Z = 2 (I); and a = 22.20(3) A, b = 9.56(2) A, c = 5.11(2) A, γ = 92.6(2)°, space group C21/b, and Z = 4 (II). The structures are polytypic modifications of the same compound.