Crystal and magnetic structures of the Bi1 ? xSrxFeO3 ? δ and Bi1 ? xAxFe1 ? xMnxO3 (A = Sr, Ca) solid solutions

Bi_{1 − x} Sr _x FeO_{3 − x/2} (I), Bi_{1 − x} Sr _x Fe_{1 − x} MnxO₃ (II), and Bi_{1 − x} Ca _x Fe_{1 − x} Mn _x O₃ (III) solid solutions have been obtained. Their magnetization has been measured by X-ray and neutron diffraction and M?ssbauer spectroscopy. According to the M?ssbauer spectroscopy data, iron ions are in the trivalent state in system I. Near the concentration x ≈ 0.2, rhombohedral distortions (sp. gr. R3c) are transformed into tetragonal (P4/mmm). The symmetry of system II changes at x > 0.2 (R3c → R3c), whereas orthorhombic distortions (R3c → Pbnm) arise in system III at x > 0.2. The magnetic structure is antiferromagnetic (of G type). The samples of systems II and III exhibit weak ferromagnetism at x > 0.2 due to the Dzyaloshinski-Moriya interaction.     

Hydrogen-Bonding Networks in Heterocyclic Thioureas

Abstract The synthesis of heterocyclic thioureas from heterocyclic amines with phenyl- or methylisothiocyanate or CS₂ is described. Seven new X-ray crystal structures are reported: In N-(3-pyridyl)-N′-phenylthiourea (Pna2₁, a = 10.1453(3), b = 17.6183(5), c = 6.4787(2), V = 1158.02(6), Z = 4) hydrogen-bonding results in formation of a 3D network consisting of helices, which form channels parallel to the c-axis. In N-(4-pyridyl)-N′-phenylthiourea (P2₁/c, a = 16.9314(3), b = 10.3554(2), c = 13.5152(3), β = 106.5080(10), V = 2271.96(8), Z = 4, two independent molecules) hydrogen-bonding results in N–H···S bridged dimers and N–H···Py chains, forming a 2D sheet network. In N-(2-pyrimidyl)-N′-phenylthiourea (P2₁/c, a = 5.45900(10), b = 13.8559(2), c = 14.3356(3), β = 94.9800(10), V = 1080.24(3), Z = 4) and N-(2-pyrimidyl)-N′-methylthiourea (P2₁/c, a = 8.8159(5), b = 11.2386(5), c = 7.7156(4), β = 95.629(2), V = 760.76(7), Z = 4) pairs of intra- and intermolecular N–H···N interactions produce dimers. Dimer formation through N–H···S occurs for N-(2-thiazolyl)-N′-methylthiourea (C2/c, a = 17.9308(3), b = 7.78260(10), c = 10.8686(2), β = 105.3740(10), V = 1462.42(4), Z = 8). Two symmetrically disubstituted thioureas were examined: N,N′-bis(2-pyridyl)thiourea (Fdd2, a = 15.1859(2), b = 30.1654(3), c = 9.44130(10), V = 4324.95(8), Z = 16) forms intra- and intermolecular N–H···Py hydrogen-bonds, forming a 1D zigzag chain and N,N′-bis(3-pyridyl)thiourea (P2₁/c, a = 13.2461(2), b = 6.26170(10), c = 12.3503(2), β = 96.0160(10), V = 1018.73(3), Z = 4) forms intermolecular N–H···Py hydrogen-bonds, resulting in 2D sheets. Index abstract Hydrogen-Bonding Networks in Heterocyclic Thioureas. Aakarsh Saxena and Robert D. Pike* The synthesis and hydrogen bonded structures of various pyridyl-, pyrimidyl-, and thiazolyl-substituted thioureas is presented.      

Pressure Effects of Nematic Liquid Crystals

There exists a variety of important new phenomena and plenty of experimental data on the pressure effects of liquid crystals. Yet, no systematic phenomenological or microscopic theory is available. In this paper, the ordinary Landau-deGennes theory is generalized so that the free energy becomes G = G _o(P, T) + a/2 [T - T*(P)]S ² - B(P)/3 S ³ + C(P)/4 S ⁴, T*(P) = T _o + bP - eP ². All the known pressure experiments of nematic PAA (where B and C are independent of P) are explained in one stroke and all parameters are determined. New results including reentrant I phase (I represents isotropic phase), and the independence of T _c—T* and T*—T _c on P, etc., are predicted. Simple methods of experimental confirmation are proposed. Similar discussions on the cases of MBBA, EBBA, etc. are also given. Our theory differs from that of Lin-Keyes-Daniels but agrees better with experiments. Results related to G _O(P, T) will be reported in a separate paper.     

Molecular Statistical Theory of the Frank Elastic Constants of Liquid Crystals

Abstract

The Frank elastic constants K ₁, K ₂, K ₃ are calculated in the mean field approximation by assuming that the intermolecular force is the sum of hard rod repulsion (length L and width D) and Maier-Saupe's type attraction. The main conclusions are as follows. (1) the inequlaities K ₃? K ₁ > K ₂ necessarily hold. (2) All the K'_is are nearly proportional to the square of the orientational order parameter S. (3) In thermotropic system, K ₁/S ², K ₁/K and K ₂/K(K: mean elastic constant) increase slowly and K _3/K, K ₃/K ₁ decreases with L/D, whereas K/kT _c is nearly constant for L/D = 3 ～ 5. These tendecies agree fairly well with the observations on liquid crystals with almost rigid structure. (4) In the lyotorpic system in which L/D ? 1, K ₁/3 = K ₂ = cLk _T/3π D ² and k ₁/K ₃ = 4D/5cL are obtained (c: packing fraction). The estimate for PBLG solution nearly agrees with recent experimental data.     

Structure of antitumor agents 2-acetylpyridinethiosemicarbazone hemihydrate and 2-acetylpyridinethiosemicarbazone hydrochloride

The structures of two antitumor agents, 2-acetylpyridinethiosemicarbazone hemihydrate (1), C₁₈H₁₁N₄O_0.5S, colorless,M _r 203.3, monoclinic,P2₁ lc,a=16.713(3),b=9.460(2),c=12.642(2) ?, β=97.60(1)°,V=1981.2(6) ?³,Z=8,R=0.054,R _w =0.085 and 2-acetylpyridinethiosemicarbazone hydrochloride (2), C₁₈H₁₂N₄SCl, yellow,M _r =230.7, monoclinic,P2₁ ln,a=7.676(2),b=7.889(1),c=17.452(4), ?, β=100.96(2)°,V=1037.5(4) ?³ Z=4,R=0.041,R _w =0.076, have been determined. Both compounds exhibit an E configuration(S atomtrans to the N atom of the hydrazine group). Three hydrogen bonds link the two crystallographically independent molecules in a pairwise fashion in the hemihydrate. An intramolecular N−H...Cl bond lends extra conformational stability to the hydrochloride salt.     

Relationship between the lengths of covalent and intermolecular bonds in <Emphasis Type="Italic">X</Emphasis>-H...<Emphasis Type="Italic">Y</Emphasis> bridges

The formula exp(−ln2((r ^XH − r ₀ ^XH)/(r _sym ^XH − r ₀ ^XH))^5/3) + exp(−ln2((r ^YH − r ₀ ^YH)/(r _sym ^YH − r ₀ ^YH))^5/3) = 1 is proposed, which relates the lengths of both covalent and hydrogen bonds in homo- and heterobridges. This formula is justified by the experimental data from the CSD bank, which was obtained by neutron diffraction for 108 O-H...N hydrogen bridges with bond angles exceeding 170°.     

Synthesis and crystal structures of complexes of Ni (II) to chiral Schiff bases of (R)- and (S)-serine with (S)- and (R)-2-N-(N′-benzylprolyl)-aminobenzophenone

The three-dimensional molecular and crystal structures of a pair of enantiopure mirror complexes of Ni (II) to chiral Schiff bases of (R)- and (S)-serine with (S)- and (R)-2-N-(N′-benzylprolyl)-aminobenzophenone (BPB), denoted as (S,R)-BPB-Ser-Ni and (R,S)-BPB-Ser-Ni, respectively, have been determined by X-ray diffraction. The complexes crystallize in the orthorhombic space group P2 ₁ 2 ₁ 2 ₁ with unit cell parameters: a = 10.050(2) Å, b = 10.100(2) Å, c = 26.514(5) Å, V = 2691.3(9) ų, and Z = 4 for (S,R)-BPB-Ser-Ni; and a = 9.878(2) Å, b = 10.130(2) Å, c = 26.304(5) Å, V = 2632.1(9) ų, and Z = 4 for (R,S)-BPB-Ser-Ni. The Ni atom is square-planar-coordinated to N(1), N(2), O(4), and N(3) of the Schiff base with minor distortion. The hydroxymethyl group on the serine moiety is axial to the coordination plane and parallel to the neighboring phenyl group.     

Antisolvent crystallization of aqueous ammonium dihydrogen phosphate solutions by addition of acetone at different rates

Results of an investigation of in situ measurements of laser‐beam intensity I_s and I_m transmitted through aqueous ammonium dihydrogen phosphate (ADP) solutions saturated at 30 °C and water, respectively, and temperature T_s of solution and T_m of water during feeding of antisolvent acetone at different rates R_A, using an indigenously designed experimental setup, are presented and discussed. It was found that: (1) for the measurement of MSZW, defined as the maximum volume fraction of acetone content Δx_max in the solution, obtained from temperature measurements are more reliable than transmitted laser‐beam intensity measurements for solutions, (2) two minima ΔT_min1 and ΔT_min2 associated with endothermic reactions, separated by a maximum ΔT_max due to exothermic reactions appear in the plots of temperature difference ΔT = T_s−T_m against acetone feeding time t, and (3) in the ΔT(t) plots there are time intervals Δt of constant rates R_T of increase in ΔT of aqueous ADP solutions, and these values of R_T increase linearly with acetone feeding time rate R_A. The experimental data on the observed dependence of MSZW on antisolvent feeding rate R_A, the appearance of minima ΔT_min1 and ΔT_min2 and maximum ΔT_max and their dependence on R_A, and the relationship between R_T and R_A are discussed from consideration of processes of nucleation and growth of crystallites.     

Sequence of phase transitions in PbHfO<Subscript>3</Subscript>

The temperature changes in the PbHfO₃ structure in the temperature range of 20 < t < 400°C have been studied by X-ray powder diffraction. The sequence of phase changes with an increase in temperature was found to be as follows: orthorhombic phase Pbam (O1), orthorhombic phase C2mm (O2), tetragonal phase P4mm (T), and cubic phase Pm3m (C). The C2mm and P4mm phases are ferroelectric, which is confirmed by measuring the dependences ɛ(t). The similarity of the transition pattern obtained with the known transition sequences for ferroelectric (barium titanate, potassium niobate, and lead titanate) and antiferroelectric (lead zirconate) oxides is analyzed.     

The Syntheses and Crystal Structures of Metronidazole-derived Compounds

Abstract Metronidazole (MET-OH), widely used as an antibacterial agent, is found to have some side effects on human bodies. Due to these disadvantages, people have been looking for its modification compounds for substituents. In this article, four MET-OH derivatives were designed, prepared, and structurally characterized by single crystal X-ray diffraction. These compounds are MET-OTs (1), MET-Br (2), MET-Cl (3), and MET-I (4). X-ray structure analyses revealed that, 1 crystallized in the monoclinic system with space group P2 ₁ /c, with a = 16.1178, b = 7.5473, c = 13.4161 ?, V = 1520.3 ?³, β = 111.3210^o and Z = 4. 2 crystallized in the monoclinic system with space group P2 ₁ /c, with a = 12.079, b = 11.089, c = 6.380 ?, V = 847.1 ?³, β = 97.57^o and Z = 4. 3 crystallized in the monoclinic system with space group P2 ₁ /c, with a = 12.098, b = 11.007, c = 6.295 ?, V = 830.3 ?³, β = 97.886^o and Z = 4. 4 crystallized in the triclinic system with space group P1, with a = 6.192, b = 7.740, c = 10.001 ?, V = 457.9 ?³, α = 89.073, β = 86.903, γ = 73.097^o and Z = 2. Index Abstract In this article, metronidazole-derived compounds were prepared and structurally characterized by single crystal X-ray diffraction      

Synthesis,Separation and Crystal Structures of <Emphasis Type="Italic">E</Emphasis> and <Emphasis Type="Italic">Z</Emphasis> Isomers of 3-(2,5-Dimethoxyphenyl)-2-(4-Methoxyphenyl)Acrylic Acid

Abstract Synthesis, separation and X-ray crystal structures of E and Z isomers of 3-(2,5-dimethoxyphenyl)-2-(4-methoxyphenyl)acrylic acid are reported. Separation of E and Z isomers from a 1:1 mixture has been carried out by selective acidification of their sodium salts carefully controlling the pH of the solution. The structures of E and Z isomers were confirmed by determining crystal structures of these isomers using single crystal X-ray diffraction. The E isomer crystallizes in the P2₁/c space group with a = 11.493(2) ?, b = 5.5456(11) ?, c = 24.900(5) ?, α = 90°, β = 92.36(3)°, γ = 90°, Z = 4. The Z isomer crystallizes in the P2₁/c space group with a = 10.192(2) ?, b = 12.893(3) ?, c = 13.948(3) ?, α = 90°, β = 92.18(3)°, γ = 90°, Z = 4. Details of the synthesis and structural characterization and X-ray crystal structure determination of the title compounds are presented. Index Abstract Synthesis, Separation and Crystal Structures of E and Z Isomers of 3-(2,5-Dimethoxyphenyl)-2-(4-Methoxyphenyl)Acrylic Acid Balachandra Chenna, Bidhan A. Shinkre, Shweta Patel, Samuel B. Owens Jr., Gary M. Gray, Sadanandan E. Velu* Separation of E and Z isomers of 3-(2,5-dimethoxyphenyl)-2-(4-methoxyphenyl)acrylic acid from a 1:1 mixture has been carried out by selective acidification of their sodium salts and the structures of the individual isomers have been determined by X-ray single crystal diffraction.      

Sequential reaction of p-toluidine with 2,3-dichloromaleic anhydride: Synthesis and molecular structure of 2-chloro-3-p-toluidino-N-p-tolylmaleimide

The reaction of equimolar amounts of p-toluidine with 2,3-dichloromaleic anhydride in refluxing toluene affords 2,3-dichloro-N-p-tolylmaleimide (1) and 2-chloro-3-p-toluidino-N-p-tolylmaleimide (2), as the major and minor products, respectively. While increasing the amount of p-toluidine relative to 2,3-dichloromaleic anhydride yields the latter compound as the major product, the replacement of the chloro group in 2-chloro-3-p-toluidino-N-p-tolylmaleimide by added p-toluidine was not observed in refluxing toluene. Both 1 and 2 were isolated by column chromatography and characterized in solution by IR and NMR spectroscopies. The solid-state structure of 2-chloro-3-p-toluidino-N-p-tolylmaleimide was solved by X-ray crystallography. Further, 2-Chloro-3-p-toluidino-N-p-tolylmaleimide crystallizes in the monoclinic space group C2/c, a = 33.191(8) Å, b = 4.037(1) Å, c = 24.876(6) Å, = 107.050(4)°, V = 3187(1) ų, Z = 8, and d _calc = 1.362 mg/m³; R = 0.0561, R _w = 0.1246 for 2087 reflections with I > 2 (I).     

Peculiarities of the initial transient process of binary melt crystallization

The time dependence of the crystallization rate V(t) in the transient process that occurs during crystal pulling into a cold zone at a constant rate W has been investigated within the one-dimensional time-dependent model of binary melt solidification using numerical and analytical approaches. It is shown that the character of the dependence V(t) in this process is mainly determined by the parameter B _w = V _c /W, where V _c is the crystallization rate at which the constitutional supercooling zone is formed in the melt. At B _w ≥ 1, the function V(t) monotonically approaches its steady-state value W, while at B _w < 1 V(t) is generally nonmonotonic. The nonmonotonic character of V(t) can manifest itself both as aperiodic damping and in the form of damping oscillations. At B _w ∼ 0.1, the vibrational amplitude of the crystallization rate in the initial transient process may reach several tens of a percent of W.     

Stereospecific Ligands and Their Complexes. III. Oxalato and Malonato-(ethylenediamine- N , N ′-di- S , S -2-propionato)-Chromate(III) Complexes. Crystal Structure of the Δ-(–)589- s - cis -K[Cr( S , S -eddp)(ox)]?·?0.5H2O

Abstract  The s-cis-[Cr(S,S-eddp)L]⁻ complexes (S,S-eddp = S,S-ethylenediamine-N,N′-di-2-propionate ion; L = oxalate or malonate ions) were prepared. The complexes were purified by ion-exchange chromatography. The geometry of the complexes has been supposed on the basis of the electronic absorption spectra, and the absolute configurations of the isolated s-cis-[Cr(S,S-eddp)L]⁻ complexes have been predicted on the basis of their circular dichroism (CD) spectra and confirmed by X-ray analysis of the crystal structure of the Δ-(–)₅₈₉-s-cis-K[Cr(S,S-eddp)(ox)] 0.5H₂O complex. Index Abstract  The title compound, s-cis-potassium-(ethylenediamine-N,N’-di-S,S-2-propionato) (oxalato)chromate(III) semihydrate was synthesized by passing the corresponding sodium salt through cation exchange-resin Merck I in potassium form and its crystal structure determined. Single crystal X-ray diffraction analysis reveals s-cis geometry of the complex cation. For Part II see Glodjović VV, Trifunović SR (2008) J Serb Chem Soc 73:541.     

Nanostructured crystals of fluorite phases Sr1 ? xRxF2 + x (R are rare-earth elements) and their ordering: IV. Study of the optical transmission spectra in the 2–17-μm wavelength range

Transmission spectra of two-component crystals of Sr_1−x R _x F_2+x (R = Y, La-Lu; 0 ≤ x ≤ 0.5) in the 1–17-μm wavelength range were studied. The spectral characteristics of these crystals and of single-component crystals of MF₂ (M = Ca, Sr, or Ba) and RF₃ (R = La-Nd) were compared. The transmission cutoff of Sr_1−x R _x F_2+x crystals is shifted to shorter wavelengths with increasing x. The same tendency is observed with the increasing atomic number R of rare-earth elements for two isoconcentration series of Sr_1−x R _x F_2+x (x ∼ 0.10 and 0.28). This tendency is pronounced at large x. The transmission cutoff of Sr_1−x R _x F_2+x crystals can be varied in the range of from 10.7 to 12.2 μm by changing their qualitative (R) and quantitative (x) composition. Hence, these crystals can be assigned to multicomponent fluoride optical materials with controlled optical characteristics. The Sr_1−x R _x F_2+x crystals, where R = Ce-Sm, were shown to be promising materials for the design of selective optical filters in the 2–10-μm spectral range.     

Crystal and molecular structures of 1-phenyl-4,6-dimethylpyrimidine-2-thionetetraaquacobalt(II) dinitrate complex and of two pyrimidine thiones

The crystal structures of 1-phenyl-4,6-dimethylpyrimidine-2-thionetetraaquacobalt(II) dinitrate (I)a=9.032(2),b=12.458(2),c=18.067(3)Å,=103.25(3)°,Z=4;P2₁/c,R=0.049; 1-phenyl-4,6-dimethylpyrimidine-2-thione (II)a=12.005(3),b=10.090(2),c=9.649(2)Å,=104.4(1)°,Z=4;P2₁/n,R=0.038; and 4,6-dimethylpyrimidine-2-thione (III)a=15.485(3),b=13.255(3),c=7.127(2)Å,=104.3(1)°,Z=8,C2/c,R=0.041 are reported. In (I) the coordination around the cobalt(II) is distorted octahedral involving one ligand moleculevia sulphur and nitrogen atoms and four water molecules. It is relevant that the parameters in the complexed ligand are not different from those found in the uncomplexed one (II), excepting the distances on the nitrogen atom directly involved in the coordination. Bond distances and angles in compound (III) agree with those found in (II).     

Heterophase states and a bridging phase in (1‐x)BiScO3 − xPbTiO3

Heterophase ferroelectric solid solutions of (1‐x)BiScO₃ − xPbTiO₃ are studied near the morphotrpic phase boundary (0.60 ≤ x ≤ 0.64). The role of non‐180° domain types of the P4mm and R3m phases in heterophase structures is studied in the context of the phase content. It is shown that the bridging Cm phase coexists with the adjacent phase (either P4mm or R3m), and different variants of an elastic matching ‘single‐domain Cm phase–polydomain P4mm phase’, ‘single‐domain Cm phase–polydomain R3m phase’ and ‘single‐domain Cm phase–near single‐domain R3m phase’ promote the complete stress relief. Based on these concepts and considering a minimum number of the domain types in the coexisting phases, we find a molar‐concentration dependence of the volume fraction of the Cm phase in the heterophase states. A correlation between the predicted volume fraction of the Cm phase and ratios of its unit‐cell parameters is first revealed. The role of the intermediate R3m phase in the phase sequence R3c − R3m − Pm$\overline 3$m and in the stress relief at x = 0.60 is discussed. Good agreement between the predicted and experimental data on the phase content is reached near the morphotrpic phase boundary.     

Electron diffraction study of 1<Emphasis Type="Italic">M</Emphasis> illites with interstratified <Emphasis Type="Italic">trans</Emphasis>- and <Emphasis Type="Italic">cis</Emphasis>-vacant 2 : 1 layers

Illites from the volcanogenic Zn-Au-Ag sulfide deposit Galkinskoe (Northern Urals) have been investigated using oblique-texture electron diffraction patterns in combination with the simulation of diffraction effects. Along with single-phase tv/cv1M illites, the structures of which are formed by statistically interstratified dioctahedral 2: 1 layers with vacant trans- or cis-octahedra, illites in the form of a mixture of two interstratified tv/cv1M phases, with the dominance of tv- or cv layers, are identified. It is shown that in the latter case the diffraction pattern can also be interpreted within the single-phase tv/cv model, provided that the tv- and cv layers are distributed with some tendency to segregate. The structural features indicating the preference of the two-phase model are analyzed.     

Crystal structures of 2,4,9-trimethyl-(3ar,4c,9c,9ac)-3a,4,9,9a-tetrahydro-benzo[?] isoindole-1,3-dione(endo), C15H17NO2 (1), and 2-methyl-(3ac,9ac)-3a,4,9,9a-tetrahydro-4r,9c-ethano-benzo[?]isoindole-1, 3-dione(endo), C15H15NO2 (2)

The title compounds crystallize in the space group P-1 (compound 1), with a = 7.198(2) Å, b = 7.965(2) Å, c = 12.707(2) Å, α = 72.05(1)^∘, β = 87.65(2)^∘, γ = 65.18(2)^∘ and Pbca (compound 2), with a = 8.156(3) Å, b = 13.177(3) Å, c = 22.742(4) Å. The chiral centers in both compounds C3a, C4, C9, C9a are either R, S, R, S or S, R, S, R (compound 1) and either R, R, S, S or S, S, R, R (compound 2) because of the centric space group.