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Crystals, Volume 2, Issue 3 (September 2012), Pages 730-1365

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Open AccessArticle Fluoride Ion as Ligand and Hydrogen Bond Acceptor: Crystal Structures of Two Dinuclear CuII Complexes Built on a Diazecine Template
Crystals 2012, 2(3), 1357-1365; https://doi.org/10.3390/cryst2031357
Received: 2 July 2012 / Revised: 15 August 2012 / Accepted: 23 August 2012 / Published: 18 September 2012
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Abstract
Two dinuclear CuII complexes based on a diazecine ligand were characterized by X-ray diffraction, one of which includes the rare CuII–F bond, resulting from dissociation of a BF4 ion. The F ligands actively participate in the crystal
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Two dinuclear CuII complexes based on a diazecine ligand were characterized by X-ray diffraction, one of which includes the rare CuII–F bond, resulting from dissociation of a BF4 ion. The F ligands actively participate in the crystal structure, behaving as acceptors for hydrogen bonding. Full article
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Open AccessArticle Temperature-Dependent Ordering of the Methyl Group in the Crystal Structure of 5-(2-Chlorophenyl)-7-ethyl-1H-thieno [2,3-E][1,4]diazepin-2(3H)-one
Crystals 2012, 2(3), 1347-1356; https://doi.org/10.3390/cryst2031347
Received: 15 May 2012 / Revised: 23 July 2012 / Accepted: 26 July 2012 / Published: 18 September 2012
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Abstract
5-(2-Chlorophenyl)-7-ethyl-1H-thieno[2,3-e][1,4]diazepin-2(3H)-one, a close analogue of clotiazepam (full agonist at GABA receptor), crystallizes in monoclinic P21/c space group with a = 15.6941(6) Å, b = 10.7909(4) Å, c = 8.6586(3) Å, and β = 102.184(4)° (at 125
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5-(2-Chlorophenyl)-7-ethyl-1H-thieno[2,3-e][1,4]diazepin-2(3H)-one, a close analogue of clotiazepam (full agonist at GABA receptor), crystallizes in monoclinic P21/c space group with a = 15.6941(6) Å, b = 10.7909(4) Å, c = 8.6586(3) Å, and β = 102.184(4)° (at 125 K). Seven-Membered diazepine ring has approximate mirror plane of symmetry, planar thieno and phenyl rings are almost perpendicular to one another, dihedral angle between their mean planes is 84.11(5)°. N–H···O hydrogen bonds connect molecules into centrosymmetric dimers which are further expanded into 3D crystal structure with the help of weaker C–H···O and C–H···π interactions. The methyl group is disordered at room temperature, but it gets gradually ordered at lower temperatures and becomes fully ordered at approximately 200 K. The changes in structure with temperature were studied between 125 and 380 K. The unit cell volume—as expected—increases almost monotonically when the temperature rises, but one of the parameters shortens significantly. Full article
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Open AccessReview Infrared and Raman Studies of Charge Ordering in Organic Conductors, BEDT-TTF Salts with Quarter-Filled Bands
Crystals 2012, 2(3), 1291-1346; https://doi.org/10.3390/cryst2031291
Received: 22 May 2012 / Revised: 4 July 2012 / Accepted: 20 July 2012 / Published: 18 September 2012
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Abstract
This paper reviews charge ordering in the organic conductors, β″-(BEDT-TTF) (TCNQ), θ-(BEDT-TTF)2X, and α-(BEDT-TTF)2X. Here, BEDT-TTF and TCNQ represent bis(ethylenedithio)tetrathiafulvalene and 7,7,8,8-tetracyanoquinodimethane, respectively. These compounds, all of which have a quarter-filled band, were evaluated using infrared and Raman spectroscopy
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This paper reviews charge ordering in the organic conductors, β″-(BEDT-TTF) (TCNQ), θ-(BEDT-TTF)2X, and α-(BEDT-TTF)2X. Here, BEDT-TTF and TCNQ represent bis(ethylenedithio)tetrathiafulvalene and 7,7,8,8-tetracyanoquinodimethane, respectively. These compounds, all of which have a quarter-filled band, were evaluated using infrared and Raman spectroscopy in addition to optical conductivity measurements. It was found that β″-(BEDT-TTF)(TCNQ) changes continuously from a uniform metal to a charge-ordered metal with increasing temperature. Although charge disproportionation was clearly observed, long-range charge order is not realized. Among six θ-type salts, four compounds with a narrow band show the metal-insulator transition. However, they maintain a large amplitude of charge order (Δρ~0.6) in both metallic and insulating phases. In the X = CsZn(SCN)4 salt with intermediate bandwidth, the amplitude of charge order is very small (Δρ < 0.07) over the whole temperature range. However, fluctuation of charge order is indicated in the Raman spectrum and optical conductivity. No indication of the fluctuation of charge order is found in the wide band X = I3 salt. In α-(BEDT-TTF)2I3 the amplitude of charge order changes discontinuously from small amplitude at high temperature to large amplitude (Δρmax~0.6) at low temperature. The long-range charge-ordered state shows ferroelectric polarization with fast optical response. The fluctuation of multiple stripes occurs in the high-temperature metallic phase. Among α-(BEDT-TTF)2MHg(SCN)4 (X = NH4, K, Rb, Tl), the fluctuation of charge order is indicated only in the X = NH4 salt. α′-(BEDT-TTF)2IBr2 shows successive phase transitions to the ferroelectric state keeping a large amplitude of charge order (Δρmax~0.8) over the whole temperature range. It was found that the amplitude and fluctuation of charge order in these compounds is enhanced as the kinetic energy (bandwidth) decreases. Full article
(This article belongs to the Special Issue Molecular Conductors)
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Open AccessArticle Structural and Electrical Properties of the τ-(P-S,S-DMEDT-TTF)2 (AuCl2) (AuCl2)y Compound with (y ≈ 0.9)
Crystals 2012, 2(3), 1283-1290; https://doi.org/10.3390/cryst2031283
Received: 24 May 2012 / Revised: 6 July 2012 / Accepted: 16 August 2012 / Published: 3 September 2012
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Abstract
The compound τ-(P-S,S-DMEDT-TTF)2(AuCl2) (AuCl2)y (where P-S,S-DMEDT-TTF is the compound pyrazino-(S,S)-dimethyl-ethylenedithio-tetrathiofulvale) crystallizes in the non-centrosymmetric space group I-42d, with a = 7.3260(1) Å and
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The compound τ-(P-S,S-DMEDT-TTF)2(AuCl2) (AuCl2)y (where P-S,S-DMEDT-TTF is the compound pyrazino-(S,S)-dimethyl-ethylenedithio-tetrathiofulvale) crystallizes in the non-centrosymmetric space group I-42d, with a = 7.3260(1) Å and c = 67.5487(12) Å (RT data) and remains tetragonal in the temperature range from RT to 100 K. This compound is a quasi-two-dimensional material and the relation of the lattice of the order part of the structure created by the donor molecules with that of the disordered anion lattice revealed by intense diffusion streaks give a value of y ≈ 0.9. In contrast to the Br and I analogs or the related compounds which contain the compound ethylenedioxy-S,S-dimethylenedithiotetrathiafulvalene (abbreviated as EDO-S,S-DMEDT-TTF) as donor and which exhibit anisotropic metallic behavior down to low temperature, this compound is anisotropic semiconductor in the same temperature range. The appearance of satellites on the diffraction images recorded below 110 K indicates a structural change. Resistivity measurements show that this material is a semiconductor with anisotropy σac of ca. 400–1400 at room temperature. Full article
(This article belongs to the Special Issue Molecular Conductors)
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Open AccessReview Electronic Principles of Hydrogen Incorporation and Dynamics in Metal Hydrides
Crystals 2012, 2(3), 1261-1282; https://doi.org/10.3390/cryst2031261
Received: 20 March 2012 / Revised: 14 July 2012 / Accepted: 18 July 2012 / Published: 30 August 2012
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Abstract
An approach to various metal hydrides based on electronic principles is presented. The effective medium theory (EMT) is used to illustrate fundamental aspects of metal-hydrogen interaction and clarify the most important processes taking place during the interaction. The elaboration is extended using the
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An approach to various metal hydrides based on electronic principles is presented. The effective medium theory (EMT) is used to illustrate fundamental aspects of metal-hydrogen interaction and clarify the most important processes taking place during the interaction. The elaboration is extended using the numerous existing results of experiment and calculations, as well as using some new material. In particular, the absorption/desorption of H in the Mg/MgH2 system is analyzed in detail, and all relevant initial structures and processes explained. Reasons for the high stability and slow sorption in this system are noted, and possible solutions proposed. The role of the transition-metal impurities in MgH2 is briefly discussed, and some interesting phenomena, observed in complex intermetallic compounds, are mentioned. The principle mechanism governing the Li-amide/imide transformation is also discussed. Latterly, some perspectives for the metal-hydrides investigation from the electronic point of view are elucidated. Full article
(This article belongs to the Special Issue Hydrogen Storage Alloys)
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Open AccessShort Note [Pr2(pdc)3(Hpdc)(H2O)4]n·n(H3hp)·8n(H2O), a One-Dimensional Coordination Polymer Containing PrO6N3 Tri-Capped Trigonal Prisms and PrO8N Mono-Capped Square Anti-Prisms (H2pdc = Pyridine 2,6-Dicarboxylic Acid, C7H5NO4; 3hp = 3-Hydroxy Pyridine, C5H5NO)
Crystals 2012, 2(3), 1253-1260; https://doi.org/10.3390/cryst2031253
Received: 15 May 2012 / Revised: 8 June 2012 / Accepted: 6 July 2012 / Published: 27 August 2012
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Abstract
The synthesis, structure and some properties of the one-dimensional coordination polymer, [Pr2(pdc)3(Hpdc)]n·n(H3hp)·8n(H2O), (H2pdc = pyridine 2,6-dicarboxylic acid, C7H5NO4; 3hp = 3-hydroxypyridine, C5
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The synthesis, structure and some properties of the one-dimensional coordination polymer, [Pr2(pdc)3(Hpdc)]n·n(H3hp)·8n(H2O), (H2pdc = pyridine 2,6-dicarboxylic acid, C7H5NO4; 3hp = 3-hydroxypyridine, C5H5NO) are described. One of the Pr3+ ions is coordinated by two O,N,O-tridentate pdc2− ligands and one tridentate Hpdc anion to generate a fairly regular PrO6N3 tri-capped trigonal prism, with the N atoms acting as the caps. The second Pr3+ ion is coordinated by one tridentate pdc2− dianion, four water molecules and two monodentate bridging pdc2− ligands to result in a PrO8N coordination polyhedron that approximates to a mono-capped square-anti-prism. The ligands bridge the metal-atom nodes into a chain, which extends in the [100] direction. The H3hp+ cation and uncoordinated water molecules occupy the inter-chain regions and an N–HLO and numerous O–HLO hydrogen bonds consolidate the structure. The H3hp+ species appears to intercalate between pendant pdc rings to consolidate the polymeric structure. Crystal data: 1 (C33H43N5O29Pr2), Mr = 1255.54, triclinic, (No. 2), Z = 2, a = 13.2567(1) Å, b = 13.6304(2) Å, c = 13.6409(2) Å, α = 89.695(1)°, β = 63.049(1)°, γ = 86.105(1)°, V = 2191.16(5) Å3, R(F) = 0.033, wR(F2) = 0.084. Full article
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Open AccessShort Note One-Pot Synthesis and Crystal Structure of Methyl 5-Hydroxy-1-phenyl-1H-pyrazole-3-carboxylate
Crystals 2012, 2(3), 1248-1252; https://doi.org/10.3390/cryst2031248
Received: 15 May 2012 / Revised: 31 July 2012 / Accepted: 14 August 2012 / Published: 27 August 2012
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Abstract
The title compound, Methyl 5-Hydroxy-1-Phenyl-1H-Pyrazole-3-Carboxylate (C11H10N2O3), was prepared by a one-pot, two-component reaction of an equimolar mixture of phenyl hydrazine and dimethyl acetylene dicarboxylate (DMAD) at reflux temperature for 2 h in a
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The title compound, Methyl 5-Hydroxy-1-Phenyl-1H-Pyrazole-3-Carboxylate (C11H10N2O3), was prepared by a one-pot, two-component reaction of an equimolar mixture of phenyl hydrazine and dimethyl acetylene dicarboxylate (DMAD) at reflux temperature for 2 h in a mixture of toluene and dichloromethane as solvent. C11H10N2O3 was crystallized from an ethanol solution in monoclinic space group P21/c with unit cell dimensions a = 9.5408(16), b = 9.5827(16), c = 11.580(2) Å, β = 105.838(3)°, V = 1018.5(3) Å3, Z = 4. Full article
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Open AccessArticle Crystal and Molecular Structure Studies of Ethyl 4-(4-Hydroxyphenyl)-6-(6-methoxy-2-naphthyl)-2-oxocyclohex-3-ene-1-carboxylate and Ethyl 4-(3-Bromophenyl)-6-(6-methoxy-2-naphthyl)-2-oxocyclohex-3-ene-1-carboxylate
Crystals 2012, 2(3), 1239-1247; https://doi.org/10.3390/cryst2031239
Received: 24 July 2012 / Revised: 8 August 2012 / Accepted: 15 August 2012 / Published: 27 August 2012
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Abstract
The crystal and molecular structures of the title compounds, ethyl 4-(4-hydroxyphenyl)-6-(6-methoxy-2-naphthyl)-2-oxocyclohex-3-ene-1-carboxylate (I) and ethyl 4-(3-bromophenyl)-6-(6-methoxy-2-naphthyl)-2-oxocyclohex-3-ene-1-carboxylate (II), are reported and confirmed by single crystal X-ray diffraction data. Compound (I), C26H24O5, crystallizes from
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The crystal and molecular structures of the title compounds, ethyl 4-(4-hydroxyphenyl)-6-(6-methoxy-2-naphthyl)-2-oxocyclohex-3-ene-1-carboxylate (I) and ethyl 4-(3-bromophenyl)-6-(6-methoxy-2-naphthyl)-2-oxocyclohex-3-ene-1-carboxylate (II), are reported and confirmed by single crystal X-ray diffraction data. Compound (I), C26H24O5, crystallizes from a methanol solution in the monoclinic C2/c space group with eight molecules in the unit cell. The unit cell parameters are: a = 25.4114(5) Å, b = 8.47440(10) Å, c = 20.6921(4) Å, β = 108.328(2)° and V = 4229.92(13) Å3. Disorder is observed throughout the entire molecule with an occupancy ratio 0.690(2):0.310(2). Compound (II), C26H23O4Br, crystallizes from an ethyl acetate solution in the monoclinic P21/c spacegroup with four molecules in the unit cell. The unit cell parameters are a = 17.8991(9) Å, b = 11.4369(6) Å, c = 10.8507(5) Å, β = 92.428(4)° and V = 2219.25(19) Å3. Disorder is observed in the cyclohexenone ring and the carboxylate group with an occupancy ratio 0.830(6):0.170(6). Weak O–H...O (I) or C–H...O (II) intermolecular interactions are observed which influence crystal packing stability. These chalcone derivative types of molecules are important in their ability to act as activated unsaturated systems in conjugated addition reactions of carbanions in the presence of basic catalysts which exhibit a multitude of biological activities. Full article
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Open AccessArticle Organic Semiconductors and Conductors with tert-Butyl Substituents
Crystals 2012, 2(3), 1222-1238; https://doi.org/10.3390/cryst2031222
Received: 12 May 2012 / Revised: 30 July 2012 / Accepted: 30 July 2012 / Published: 22 August 2012
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Abstract
Tetrathiafulvalene (TTF), pentacene, and quarterthiophene with tert-butyl substituents are synthesized, and the crystal structures and the transistor properties are investigated. The tetracyanoquinodimethane (TCNQ) complex of tert-butyl TTF constructs highly one-dimensional segregated columns with tetragonal crystal symmetry. Full article
(This article belongs to the Special Issue Molecular Conductors)
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Open AccessArticle Electronic Structure of Cu(tmdt)2 Studied with First-Principles Calculations
Crystals 2012, 2(3), 1210-1221; https://doi.org/10.3390/cryst2031210
Received: 13 April 2012 / Revised: 9 August 2012 / Accepted: 13 August 2012 / Published: 21 August 2012
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Abstract
We have studied the electronic structure of Cu(tmdt)2, a material related to single-component molecular conductors, by first-principles calculations. The total energy calculations for several different magnetic configurations show that there is strong antiferromagnetic (AFM) exchange coupling along the crystal a-axis. The
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We have studied the electronic structure of Cu(tmdt)2, a material related to single-component molecular conductors, by first-principles calculations. The total energy calculations for several different magnetic configurations show that there is strong antiferromagnetic (AFM) exchange coupling along the crystal a-axis. The electronic structures are analyzed in terms of the molecular orbitals near the Fermi level of isolated Cu(tmdt)2 molecule. This analysis reveals that the system is characterized by the half-filled pdσ(−) band whose intermolecular hopping integrals have strong one-dimensionality along the crystal a-axis. As the exchange splitting of the band is larger than the band width, the basic mechanism of the AFM exchange coupling is the superexchange. It will also be shown that two more ligand orbitals which are fairly insensitive to magnetism are located near the Fermi level. Because of the presence of these orbitals, the present calculation predicts that Cu(tmdt)2 is metallic even in its AFM state, being inconsistent with the available experiment. Some comments will be made on the difference between Cu(tmdt)2 and Cu(dmdt)2. Full article
(This article belongs to the Special Issue Molecular Conductors)
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Open AccessCommunication Synthesis and Crystal Structure of Benzyl [(1S)-1-(5-amino-1,3,4-oxadiazol-2-yl)-2-phenylethyl]carbamate
Crystals 2012, 2(3), 1201-1209; https://doi.org/10.3390/cryst2031201
Received: 6 June 2012 / Revised: 20 July 2012 / Accepted: 26 July 2012 / Published: 20 August 2012
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Abstract
The conversion of Z-phenylalanine hydrazide with cyanogen bromide resulted in the formation of the corresponding 2-amino-1,3,4-oxadiazole by spontaneous cyclization of the intermediary cyanohydrazide. The molecular structure of the product was confirmed by single crystal X-ray diffraction. Crystals of the title compound where obtained
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The conversion of Z-phenylalanine hydrazide with cyanogen bromide resulted in the formation of the corresponding 2-amino-1,3,4-oxadiazole by spontaneous cyclization of the intermediary cyanohydrazide. The molecular structure of the product was confirmed by single crystal X-ray diffraction. Crystals of the title compound where obtained from a saturated solution in a mixture of petroleum ether and ethyl acetate and belong to the monoclinic space group P21 with unit cell parameters a = 9.8152(2) Å, b = 9.6305(2) Å, c = 9.8465(2) Å, β = 116.785(1)°. The asymmetric unit contains one molecule. Full article
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Open AccessReview Theories on Frustrated Electrons in Two-Dimensional Organic Solids
Crystals 2012, 2(3), 1155-1200; https://doi.org/10.3390/cryst2031155
Received: 28 April 2012 / Revised: 9 July 2012 / Accepted: 26 July 2012 / Published: 20 August 2012
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Abstract
Two-dimensional quarter-filled organic solids are a promising class of materials to realize the strongly correlated insulating states called dimer Mott insulator and charge order. In their conducting layer, the molecules form anisotropic triangular lattices, harboring geometrical frustration effect, which could give rise to
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Two-dimensional quarter-filled organic solids are a promising class of materials to realize the strongly correlated insulating states called dimer Mott insulator and charge order. In their conducting layer, the molecules form anisotropic triangular lattices, harboring geometrical frustration effect, which could give rise to many interesting states of matter in the two insulators and in the metals adjacent to them. This review is concerned with the theoretical studies on such issue over the past ten years, and provides the systematic understanding on exotic metals, dielectrics, and spin liquids, which are the consequences of the competing correlation and fluctuation under frustration. Full article
(This article belongs to the Special Issue Molecular Conductors)
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Open AccessShort Note APA2[Zn3(HPO4)4(H2O)2], a Layered Zincophosphate Featuring Template-to-Framework N–H⋯O and “Synergic” Framework-to-Template O–H⋯N Hydrogen Bonds and C–H⋯O Interactions (APA = 2-Amino-1-phenyleneammonium, C6H9N2+)
Crystals 2012, 2(3), 1146-1154; https://doi.org/10.3390/cryst2031146
Received: 9 May 2012 / Revised: 7 August 2012 / Accepted: 8 August 2012 / Published: 16 August 2012
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Abstract
The crystal structure of APA2[Zn3(HPO4)4(H2O)2] (APA = 2-amino-1-phenylene-ammonium, C6H9N2+) (1), as prepared by a predominantly non-aqueous synthesis, is described and compared to related compounds.
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The crystal structure of APA2[Zn3(HPO4)4(H2O)2] (APA = 2-amino-1-phenylene-ammonium, C6H9N2+) (1), as prepared by a predominantly non-aqueous synthesis, is described and compared to related compounds. 1 is built up from an alternating array of ZnO4 and HPO4 tetrahedra sharing vertices as Zn–O–P bonds to generate infinite anionic sheets. Within these sheets, polyhedral 4-, 6- and 8-rings are apparent. The negative charge of the inorganic layer is balanced by singly-protonated APA template cations and water molecules are also present. The components are linked by Nt–H⋯Of, Of–H⋯Ow, Ow–H⋯Of and Of–H⋯Nt (t = template, f = framework, w = water) hydrogen bonds: the last of these represents an unusual framework-to-template interaction. Weak Ct–H⋯Of links may also play a role in consolidating the structure. Crystal data: 1 (C12H26N4O18P4Zn3), Mr = 834.36, monoclinic, C2/c (No. 15), Z = 4, a = 20.194 (8) Å, b = 8.682 (3) Å, c = 15.123 (6) Å, β = 91.510 (11)°, V = 2650.5 (17) Å3, R(F) = 0.048, wR(F2) = 0.112. Full article
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Open AccessArticle The Short Series of the Oxygen-Poor Lanthanide Oxide Selenides M10OSe14 with M = La–Nd
Crystals 2012, 2(3), 1136-1145; https://doi.org/10.3390/cryst2031136
Received: 6 June 2012 / Revised: 6 July 2012 / Accepted: 17 July 2012 / Published: 16 August 2012
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Abstract
Single crystals and phase pure samples of oxygen-poor ternary lanthanide oxide selenides with the composition M10OSe14 (M = La–Nd; tetragonal, I41/acd; a = 1592.0–1559.8 pm, c = 2106.5–2062.9 pm) could be obtained by reacting
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Single crystals and phase pure samples of oxygen-poor ternary lanthanide oxide selenides with the composition M10OSe14 (M = La–Nd; tetragonal, I41/acd; a = 1592.0–1559.8 pm, c = 2106.5–2062.9 pm) could be obtained by reacting the corresponding metals, selenium and selenium dioxide as oxygen source. Their crystal structures are isotypic with Pr10OS14 and thus contain isolated [OM4]10+ tetrahedra (d(O2–M3+) = 243–248 pm) embedded in a complex anionic {[M6Se14]10–} lanthanide selenide matrix (d(M3+–Se2–) = 288–358 pm). All three crystallographically independent M3+ cations exhibit eight contacts to chalcogenide anions (O2– and/or Se2–) resulting in the formation of bicapped trigonal prismatic coordination polyhedra. The optical band gaps of the oxide selenides M10OSe14 amount to values between 1.89 and 2.04 eV indicating wide band-gap semiconductors. Full article
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Open AccessReview 1H and 195Pt NMR Study of the Parallel Two-Chain Compound Per2[Pt(mnt)2]
Crystals 2012, 2(3), 1116-1135; https://doi.org/10.3390/cryst2031116
Received: 12 June 2012 / Revised: 23 July 2012 / Accepted: 23 July 2012 / Published: 16 August 2012
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Abstract
1H and 195Pt NMR are used to probe the spin ½ anion chain in the quasi-one-dimensional conductor Per2[Pt(mnt)2], which exhibits nearly simultaneous charge density wave (CDW) and spin-Peierls (SP) transitions at low temperatures (Tc ~ 8
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1H and 195Pt NMR are used to probe the spin ½ anion chain in the quasi-one-dimensional conductor Per2[Pt(mnt)2], which exhibits nearly simultaneous charge density wave (CDW) and spin-Peierls (SP) transitions at low temperatures (Tc ~ 8 K). Below Tc the [Pt(mnt)2] chain forms a spin-singlet state that is evident in 1H NMR spectra and spin relaxation (1/T1) rates; however minority unpaired Pt spins may remain in the SP ground state. With increasing magnetic field, the SP and CDW order parameters decrease in unison, indicating they are coupled up to a critical field Bc ~ 20 T. Above Bc, the spin singlet evolves into a spin-polarized configuration. The 195Pt NMR signals vanish as either Tc or Bc are approached from within the SP ground state, suggesting the hyperfine field of the Pt nucleus is significantly stronger than at the proton sites. Simulations yield a consistent picture of the angular, temperature, and magnetic field-dependent spectral features. Full article
(This article belongs to the Special Issue Molecular Conductors)
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