Microhardness of tetrahedrally bonded elemental and binary semiconductors

An analysis of experimental microhardness data shows that the microhardness at room temperature of the diamond, zincblende and wurtzite structure compounds follows the simple relation H = h_oa^−xT_m(1 –g_of_i) where a is the lattice parameter T_m the melting temperature, f_i the spectroscopically defined bond ionicity and h_o, x, and g_o are constants having the same values for all compounds. The close relation between microhardness and bulk modulus is discussed.     

Bulk modulus — volume relationship in alkali halides with rocksalt structure

It is shown that the bulk modulus of the alkali halides with rocksalt structure follows the simple relation B = b₀(1 — b₁f_c) V where V₀ is the unit cell volume, f_c the spectroscopically defined covalency of the chemical bond, and b₀, b₁, and n are constants having the same values for all compounds. This result is compared with the bulk modulus scaling law found for the tetrahedral semiconductors.     

2-phenyl thiazolidine — its growth and characterisation

The importance of 2-phenyl thiazolidine lies in its being a model for penicillin, as the five-membered thiazolidine ring happens to be the moiety of penicillin. This material is synthesised and crystallised (Tsukerman). The crystals are white in colour, transparent, needle-shaped and of dimensions (0.2 × 0.3 × 0.4 mm³). Employing X-ray diffraction studies, it is found that the crystal belongs to the orthorhombic system with the unit cell parameters a = 8.388(1), b = 18.114(2) and c = 5.625(1) Å. The space group is P 2₁2₁2₁ and Z = 4. The absorption peaks pertaining to NH, NCS, methylene CH₂ and aromatic C₆H₄ have been identified from the infrared absorption spectrum of the sample. The Proton Magnetic Resonance (PMR) spectrum fully accounts for the hydrogens in the sample thereby unambigiously supporting the proposed structure.     

The structure of 2-amino-3-cyano-4-(4-methylphenyl)-6-methoxyl-1,4,9,10-tetrahydrobenzo[<Emphasis Type="Italic">f</Emphasis>]chromene

The X-ray crystal structure of 2-amino-3-cyano-4-(4-methylphenyl)-6-methoxyl-1,4,9,10-tetrahydrobenzo [f]chromene 1, C₂₂H₂₀N₂O₂, is determined. The crystals of compound 1 are triclinic, space group P-1, a = 10.120(1), b = 13.127(1), c = 15.203(2) Å, = 67.841(9), = 80.81(1), = 77.58(1), Z = 4, V = 1819.7(4) ų. It is interesting that all the atoms of the pyran ring are coplanar, which is different from other similar compounds. The structure is stabilized by intermolecular hydrogen bonds.     

Refined Crystal and Molecular Structure of Andrographolide — Diterpene

A refined crystal structure of andrographolide has been obtained by X-ray anaysis using CuKα radiation. It crystallizes in the monoclinic crystal system with unique b-axis in space group P2₁. The unit cell parameters are a = 6.552(2) Å, b = 8.009(1) Å, c = 17.989(1) Å and interaxial angle β = 97.32(1)°. The structure has been solved by direct methods and was refined up to R = 0.041, ωR = 0.0464. Both the cyclohexane rings are in chair conformation with the furan ring in twist conformation. The crystal structure is stabilized by hydrogen bonding.     

Crystal structure of lithium magnesium phosphate,LiMgPO4: Crystal chemistry of the olivine-type compounds

LiM_gPO₄ is orthorhombic, space groupPnma,a=10.147(2),b=5.909(2),c=4.692(2)×10^–10 m,D _m =3000(8),D _x =2980 kg m^–3,Z=4,R=4.8% for 1262 observed reflections. The structure contains tetrahedral PO₄ and octahedral LiO₆ and MgO₆ groups. It belongs to the ordered olivine-type structures, since the inversion site is occupied by Li⁺ ions and the mirror site is taken by Mg²⁺ ions. The distortion of polyhedra is caused mainly by the adjustment stresses between the different polyhedral dimensions and by the sharing of edges. Octahedral LiO₆ share six and MgO₆ share three common edges. The sharing of the O-O edges contributes to the stability of the bridging arrangements. The corresponding average distances of the O-O bridges are 2.432, 2.479, 2.883, and 3.028×10^–10 m, while the average O-O distances in the PO₄, MgO₆, and LiO₄ polyhedra are 2.512,2.921, and 3.015 × 10^–10 m, close to the ideal values 2.531, 2.970, and 3.026×10^–10 m respectively. The structure field of the olivine-type compounds plotted as a function of ionic radii in radius space is specified in relation to the-K₂SO₄, spinel, and K₄NiF₄ type structures. From the overlap of the structure fields, the high-pressure transformations of the olivine compounds are considered.     

Crystal Structure of 14-Deoxy-11,12-Didehydroandrographolide — A Diterpenoid

The crystal structure of 14-deoxy-11,12-didehydroandrographolide has been determined by X-ray structure analysis. The compound crystallizes in the trigonal space group P3₁ with cell parameters a = b 15.860(3), c = 6.437(2) Å. The structure has been solved by direct methods and refined to R = 0.048. The six-membered rings are trans-fused and both are in the chair conformation. The furan ring is planar with maximum deviation −0.011 (4) Å for C(14). Molecular are held together by hydrogen bonds.     

Synthesis and Crystal Structures of Two <Emphasis Type="Italic">N</Emphasis>-Heterocyclic Carbene Adducts of CrCl<Subscript>2</Subscript>

Abstract  

The reactions of CrCl₂ with two N-heterocyclic carbenes (NHC) have afforded the complexes, trans-[CrCl₂(NHC)₂] (NHC = :C{N(C₆H₃Pr₂ⁱ-2,6)C(H)}₂ 1 or :C{N(Prⁱ)C(Me)}₂ 2). The cell parameters of the compounds are 1: P2₁2₁2₁, a = 12.9445(4), b = 20.7364(5), c = 21.2841(6); 2: Pca2₁, a = 21.7583(14), b = 9.9465(8), c = 11.4414(9). The crystal structures of the complexes are the first for NHC adducts of CrCl₂, and both exhibit square planar chromium centers.     

Crystal Structure of N-methyl Crotananinium Iodide — A Pyrrolizidine Alkaloid

The crystal structure of N-methyl crotananinium iodide has been determined by X-ray structure analysis. The compound crystallizes in the orthorhombic space group P2₁2₁2₁ with cell parameters a = 19.37(2), b = 7.70(2), c = 13.38(2) Å. The structure has been solved by Patterson and successive Fourier methods and refined by full matrix least-squares methods to an R-index of 0.075. The structural features of the title compound are noted and are compared with those of similar others of such pyrrolizidine alkaloids.     

Crystal structure of the gold(I) complex [Au(tfp)Cl] with tfp = (C<Subscript>4</Subscript>H<Subscript>3</Subscript>O)<Subscript>3</Subscript>P

The Au(I) complex [Au(tfp)Cl] with tfp = (C₄H₃O)₃P has been prepared and characterised. It crystallises in the monoclinic P2₁/n space group with z = 4, a = 9.837(3), b = 12.684(4), c = 11.103(5)Å, = 91.58(2)° and V = 1384.8(2)ų. The structure of the complex consists of molecules connected in head-to-tail dimers by a metal-halogen contact as generally found in analogus complexes of lighter coinage metals. The typical feature of halogen gold compounds, the Au–Au interaction, seems prevented by the bulk of the tfp ligand.     

Crystal and molecular structure of 3‐phenyl‐4‐(p‐chlorobenzylamino)‐4,5‐dihydro‐1‐H‐1,2,4‐triazol‐5‐on

The structure of the title compound, C₁₅H₁₃N₄OCl was determined by single crystal X‐ray diffraction technique. The structure consists of a p‐chlorobenzylamino moiety and triazol and phenyl rings. The title compound crystallizes in the monoclinic space group P2₁/c with a = 14.368(3), b = 6.255(3), c = 17.631(3) Å, β = 113.24(3)°, Z = 4, V = 1455.8(8) ų and D_x = 1.372 gcm^‐3. The structure was solved by direct methods and refined by full‐matrix least‐squares method (R=0.0477). The dihedral angle between the triazole moiety and the phenyl ring is 28.8(3)°. The molecular packing is stabilized by N‐H…N and N‐H…O types of inter molecular hydrogen bonds. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal structure,thermal and compositional deformations of β‐CsB5O8

The crystal structure of β‐CsB₅O₈ has been determined from X‐ray powder diffraction data using synchrotron radiation: Pbca, a = 7.8131(3) Å, b = 12.0652(4) Å, c = 14.9582(4) Å, Z = 8, ρ_calc = 2.967 g/cm³, R‐p = 0.076, R‐wp = 0.094. β‐CsB₅O₈ was found to be isostructural with β‐KB₅O₈ and β‐RbB₅O₈. The crystal structure consists of a double interlocking framework built up from B‐O pentaborate groups. The crystal structure exhibits a highly anisotropic thermal expansion: α_a = 53, α_b = 16, α_c = 14 · 10^‐6/K; the anisotropy may be caused by partial straightening of the screw chains of the pentaborate groups. The similarity of the thermal and compositional (Cs‐Rb‐K substitution) deformations of CsB₅O₈ is revealed: increasing the radius of the metal by 0.01 Å leads to the same deformations of the crystal structure as increasing the temperature by 35°C. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Molecular and Crystal Structure of 3β-O-(2′,3′ -O-isoropylidene-α-L-rhamnopyranosyl) — digitoxigenin

3β-O-(2′,3′ -O-isoropylidene-α-L-rhamnopyranosyl) — digitoxigenin crystallizes in the monoclinic space group P 2₁ with two molecules C₃₂H₄₈O₈ per unit cell and the lattice constants a = 7.865, b = 6.470, c = 29.803 Å, β = 93.95°. The structure was solved by direct methods of phases determination and subsequently refined by least squares technique to the final R-value 0.06. The position of the lactone ring is disordered in the crystal.     

Crystal structure of 2‐(2'‐hydroxyphenyl)‐6‐tributylstannyl‐4‐(3H )‐quinazolinone and 2‐(2'‐hydroxyphenyl)‐6‐iodo‐4‐(3H)‐quinazolinone

The structures of the title compounds C₂₆H₃₇N₂O₂Sn ( I ) and C₁₄H₉IN₂O₂ ( II ) were determined by single‐crystal X‐ray diffraction technique. Compound I crystallizes in the triclinic space group P1 with a = 9.560(3) Å, b = 16.899(6) Å, c = 17.872(5) Å, α = 65.957(7)°, β = 83.603(5)°, γ ( = 75.242(5)°, V = 2549.8(13) ų, Z = 4, and D =1.374 g/cm³. The compound consists of a quinazolinone ring with phenol and tributylstannyl moieties. Compound II crystallizes in the monoclinic space group P2₁/c with a = 7.6454(12) Å, b = 5.9270(9) Å, c = 27.975(4) Å; α = 90°, β = 95.081(3)°, γ = 90°, V = 1262.7(3) ų, Z = 4, and D = 1.915 g/cm³. The compound consists of a quinazolinone ring with phenol and iodine substituents. For both I and II , the short intramolecular O–H…N and two long intermolecular N–H…O hydrogen bonds are highly effective in holding the molecular system in a stable state. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure types – a review

Structures of binary inorganic A_xB_y compounds with A and B on two Wyckoff positions are characterized by the self‐coordination numbers T_i, i = 1–3, of A and B atoms. The T₁ = 0–12 values of 122 structure types can be correlated with different topologies, A–A interactions and densities. High T₁ values like T₁ = 12 are obtained for fcc or hcp sphere packing with maximum density of A atoms and interstitial B atoms. Hexagonal or tetragonal layered compounds are recognized by the T_i values 6 6 6 or 4 4 4. The T₁ = 2 values are found for chains, T₁= 1 for ordered molecules like N₂ or Br₂. The A and B atoms of few compounds like NaCl or CsCl form a pc or bcc sphere packing. The T₁ = 0 values of Na or Cs atoms indicate repulsive Na–Na or Cs–Cs interactions. Distorted structures of a structure type are recognized, if atoms with slightly different A–A or B–B distances are included in the proper coordination shells. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal and Molecular structure of 3,3-Diethyl–2,4,6–[1 H,3 H,5 H] Pyrimidine Trione

C₈H₁₂O₃N₂, M_r = 184.19, Trigonal, R3 (hexagonal axes) a = b = 26.800(1) Å, c = 6.828(3) Å, α = β = 90°, γ = 120°, V = 4247.11 ų, Z = 18, D_m = 1.297 Mg m⁻³, D_c = 1.296 Mg m⁻³, mu = 0.79 mm⁻¹, F(000) = 1764, T = 293 K, final R = 0.080 for 1205 observed reflections. There are two crystallographically independent molecules in the unit cell of the title compound.     

On the morphology of <100>-textured Germanium Crystallites in Zn—Ge Eutectic Alloy

Different geometry parameters for the cross-like germanium crystallites (eutectic dendrites) of the Zn-Ge eutectic alloys unidirectionally solidified have been related to the growth rate R and liquid temperature gradient G using linear regression analysis. It has been found that for eutectic dendrite spacing λ, balk length d and balk thickness b follow the relationship of the type w = C_wR^−rwG^−gw; C_w is a constant. The spacing relationship of eutectic dendrites (r_λ = 0.21; g_λ = 0.48) shows a similarity with published experimental and theoretical results on primary dendrite arm spacing (r_λ = 0.25; g_λ = 0.5). It has been shown in terms of a profile ration λ/d that for geometrical similar morphologies the relationship λ²R = const. is valid.     

The crystal and molecular structure of three homologue 1,4-terephthalylidene-bis-N-(4′-alkylanilines) (TBAA-n)

The three homologue compounds with the general formula (TBAA-n) crystallize in the following space groups: TBAA-0 : monoclinic, P 2₁ c. a = 7.656(3), b = 6.073(1), c = 16.403(7) Å, β = 91.60(2)°; TBAA-1 : monoclinic, P 2₁ c. a = 7.656(3), b = 6.073(1), c = 16.403(7) Å, β = 91.60(2)°; TBAA-1 : monoklin, P 2₁/n, a = 6.0426(11), b = 7.84171(4), c = 18.2147(31) Å, β = 92.32(1)°; TBAA-2 : orthorhombic, P ben, a = 20.9390(8), b = 14.8876(7), c = 6.2069(1) Å. The structures have been solved by direct methods and refined to R = 0.029, 0.044, and 0.049, respectively. Despite the different conformation of the terminal phenyl rings relative to the central core of the coplanar azomethine groups and the phenyl ring, the molecular packing of the three compounds obeys the same principles in forming the crystal structure.     

Crystal structure of syn-1-acetyl-9′aH-8′- methoxyspiro[indole-3,2′-oxeto[3′,2′:4,5]furo[3,2-g][1] benzopyran]2,6′-dione

The crystal structure of syn-1-acetyl-9a-hydro-8-methoxyspiro[3H-indole-3,2(2aH) oxeto[3,2-g]furo[3,2-g]benzo[ b]pyran-2,6-dione 1 was determined by X-ray diffraction analysis. It possesses P2(1)/c space group symmetry, with a = 12.391(3), b = 15.035(3), c = 9.5435(19) Å, = 93.66(3), and D _calc. = 1.517 Mg/m³ for Z = 4.     

Synthesis and structure of new Am ? 1Bi2BmO3m + 3 (m = 3) phases

Six new polycrystalline bismuth-containing layered perovskite-like oxides described by the general formula A _m − 1Bi₂B _m O_{3m + 3} (m = 3) were synthesized by high-temperature solid-state reactions. The unit-cell parameters of these compounds were determined as a = 5.438(9) Å, b = 5.462(7) Å, and c = 33.08(6) Å for Bi₄Ti₂Nb_0.5Fe_0.5O₁₂; a = 5.408(6) Å, b = 5.425(9) Å, and c = 32.85(6) Å for Ca_0.5Bi_3.5Ti_2.75W_0.25O₁₂; a = 5.457(0) Å, b = 5.482(2) Å, and c = 32.75(2) Å for NaCaBi₂Nb₃O₁₂; a = b = 3.826(2) Å and c = 32.82(6) Å for Ca_0.25Th_0.25Bi_3.5Ti₃O₁₂; a = b = 3.816(2) Å and c = 32.81(5) Å for Nd_0.5Gd_0.5Bi₃Ti₃O₁₂; and a = b = 3.826(4) Å and c = 32.95(8) Å for Th_0.5Bi_3.5Ti_2.5Ga_0.5O₁₂. The compositions of these compounds are based on the composition of the basic Bi-containing layered perovskite-like Bi₄Ti₃O₁₂ oxide in which Bi^III and Ti^IV atoms are partially or completely replaced with other atoms. The experimental and calculated interplanar spacings determined from X-ray diffraction patterns and the reliability factors of their indexing are reported. __________ Translated from Kristallografiya, Vol. 48, No. 3, 2003, pp. 450–457. Original Russian Text Copyright ? 2003 by Geguzina, Shuvayev, Vlasenko, Shuvayeva, Shilkina. This study was presented at the symposium “Order, Disorder, and Properties of Oxides” (ODPO), Sochi, Russia, 2002.