Spin resolved electron density study of YTiO3 in its ferromagnetic phase: signature of orbital ordering.

The present work reports on the charge and spin density modelling of YTiO3 in its ferromagnetic state (T C = 27 K). Accurate polarized neutron diffraction and high-resolution X-ray diffraction (XRD) experiments were carried out on a single crystal at the ORPHÉE reactor (LLB) and SPRING8 synchrotron source. The experimental data are modelled by the spin resolved pseudo-atomic multipolar model (Deutsch et al., 2012 ▸). The refinement strategy is discussed and the result of this electron density modelling is compared with that from XRD measured at 100 K and with density functional theory calculations. The results show that the spin and charge densities around the Ti atom have lobes directed away from the O atoms, confirming the filling of the t 2g orbitals of the Ti atom. The d xy orbital is less populated than d xz and d yz , which is a sign of a partial lift of degeneracy of the t 2g orbitals. This study confirms the orbital ordering at low temperature (20 K), which is already present in the paramagnetic state above the ferromagnetic transition (100 K).

A new copper(II) coordination polymer containing chains of interconnected paddle-wheel antiferromagnetic clusters.

The construction of supramolecular architectures based on inorganic-organic coordination frameworks with weak noncovalent interactions has implications for the rational design of functional materials. A new crystalline binuclear copper(II) one-dimensional polymeric chain, namely catena-poly[[[tetrakis(µ-4-azaniumylbutanoato-κ2O:O')dicopper(II)(Cu-Cu)]-µ-chlorido-[diaquadichloridocopper(II)]-µ-chlorido] bis(perchlorate)], {[Cu3Cl4(C4H9NO2)4(H2O)2](ClO4)2}n, was obtained by the reaction of 4-aminobutyric acid (GABA) with CuCl2·2H2O in aqueous solution. The structure was established by single-crystal X-ray diffraction and was also characterized by IR spectroscopy and magnetic measurements. The crystal structure consists of [{Cu2(GABA)4}{CuCl4(H2O)2}]+ cations and isolated perchlorate anions. Two symmetry-related CuII centres are bridged via carboxylate O atoms into a classical paddle-wheel configuration, with a Cu...Cu distance of 2.643 (1) Å, while bridging Cl atoms complete the square-pyramidal geometry of the metal atoms. The Cl atoms connect the paddlewheel moieties to a second CuII atom lying on an octahedral site, resulting in infinite helical chains along the c axis. The packing motif exhibits channels containing free perchlorate anions. The crystal structure is stabilized by hydrogen bonds between the perchlorate anions, the coordinated water molecules and the ammonium groups of the polymeric chains. The magnetic analysis of the title compound indicates a nontrivial antiferromagnetic behaviour arising from alternating weak-strong antiferromagnetic coupling between neighbouring CuII centres.

Syntheses and crystal structures of two magnesium-tetrazole compounds in salt and polymeric forms.

Two alkaline earth-tetrazole compounds, namely catena-poly[[[triaquamagnesium(II)]-µ-5,5'-(azanediyl)ditetrazolato-κ(3)N(1),N(1'):N(5)] hemi{bis[µ-5,5'-(azanediyl)ditetrazolato-κ(3)N(1),N(1'):N(2)]bis[triaquamagnesium(II)]} monohydrate], {[Mg(C(2)HN(9))(H(2)O)(3)][Mg(2)(C(2)HN(9))(2)(H(2)O)(6)]0.5·H(2)O}n, (I), and bis[5-(pyrazin-2-yl)tetrazolate] hexaaquamagnesium(II), (C(5)H(3)N(6))[Mg(H(2)O)(6)], (II), have been prepared under hydrothermal conditions. Compound (I) is a mixed dimer-polymer based on magnesium ion centres and can be regarded as the first example of a magnesium-tetrazolate polymer in the crystalline form. The structure shows a complex three-dimensional hydrogen-bonded network that involves magnesium-tetrazolate dimers, solvent water molecules and one-dimensional magnesium-tetrazolate polymeric chains. The intrinsic cohesion in the polymer chains is ensured by N-H...N hydrogen bonds, which form R(2)(2)(7) rings, thus reinforcing the propagation of the polymer chain along the a axis. The crystal structure of magnesium tetrazole salt (II) reveals a mixed ribbon of hydrogen-bonded rings, of types R(2)(2)(7), R(2)(2)(9) and R(2)(4)(10), running along the c axis, which are linked by R(2)(4)(16) rings, generating a 4,8-c flu net.

XPAD X-ray hybrid pixel detector for charge density quality diffracted intensities on laboratory equipment.

The new generation of X-ray detectors, the hybrid pixel area detectors or `pixel detectors', is based on direct detection and single-photon counting processes. A large linearity range, high dynamic and extremely low noise leading to an unprecedented high signal-to-noise ratio, fast readout time (high frame rates) and an electronic shutter are among their intrinsic characteristics which render them very attractive. First used on synchrotron beamlines, these detectors are also promising in the laboratory, in particular for pump-probe or quasi-static experiments and accurate electron density measurements, as explained in this paper. An original laboratory diffractometer made from a Nonius Mach3 goniometer equipped with an Incoatec Mo microsource and an XPAD pixel area detector has been developed at the CRM2 laboratory. Mo Kα accurate charge density quality data up to 1.21 Å(-1) resolution have been collected on a sodium nitroprusside crystal using this home-made diffractometer. Data quality for charge density analysis based on multipolar modelling are discussed in this paper. Deformation electron densities are compared to those already published (based on data collected with CCD APEXII and CAD4 diffractometers).

Two-dimensionally stacked heterometallic layers hosting a discrete chair dodecameric ring of water clusters: synthesis and structural study.

The stacked two-dimensional supramolecular compound catena-{Co(amp)3Cr(ox)3·6H2O} (amp = 2-picolylamine, ox = oxalate) has been synthesized from the bimolecular approach using hydrogen bonds. It is built from layers in which both Co(amp)(3+) (D) and Cr(ox)(3-) (A) ions are bonded in a repeating DADADA… pattern along the a and c axes by multiple hydrogen bonds. These layers host a well resolved R12 dodecameric discrete ring of water clusters built by six independent molecules located around the 2c centrosymmetric Wyckoff positions of the P21/n space group in which the compound crystallizes. These clusters are ranged along the [001] direction, occupy 733.5 Å(3) (22.0%) of the unit cell and have a chair conformation via 12 hydrogen bonds. The water molecules of the cluster are linked with stronger hydrogen bonds than those between the cluster and its host, which explains the single continuous step of the dehydration process of the compound.

Di-aqua-bis-[5-(2-pyrazin-2-yl)tetra-zolato]copper(II)-pyrazine-2-carbo-nitrile (1/2).

The title compound, [Cu(C5H3N6)2(H2O)2]·2C5H3N3, is a 1:2 co-crystal between the mononuclear complex di-aqua-bis-[5-(pyrazin-2-yl)tetra-zolato]copper(II) and the reagent pyrazine-2-carbo-nitrile which was used in the synthesis. The Cu(II) atom is located on an inversion centre and has a distorted octa-hedral [4 + 2]-coordination environment formed by four N atoms of two chelating bidentate 5-(pyrazin-2-yl)tetra-zolate ligands at shorter distances and two water O atoms at longer distances. The Cu(II) complex molecules are held together by O-H⋯N hydrogen bonds and π-π stacking inter-actions [centroid-centroid distance 3.6139 (8) Å], forming layers parallel to (100). These layers alternate with layers of pyrazine-2-car-bo-nitrile mol-ecules and both are held together via C-H⋯N hydrogen bonds and further π-π stacking inter-actions.

A new heteroleptic oxalate-based compound: poly[[2-(aminomethyl)pyridine]di-µ6-oxalato-chromium(III)potassium(I)].

The title compound, [KCr(C2O2)2(C6H8N2)]n, was obtained from aqueous solution and analyzed with single-crystal X-ray diffraction at 100 K. It crystallizes in the monoclinic space group C2/c and displays a three-dimensional polymeric architecture built up by bimetallic oxalate-bridged Cr(III)-K helical chains linked through centrosymmetric K2O2 units to yield a sheet-like alternating P/M arrangement which looks like that of the previously described two-dimensional [NaCr(ox)2(pyim)(H2O)]·2H2O [pyim is 2-(pyridin-2-yl)imidazole; Lei et al. (2006). Inorg. Chem. Commun. 9, 486-488]. The Cr(III) ions in each helix have the same chirality. The infinite neutral sheets are eclipsed with respect to each other and are held together by a hydrogen-bonding network involving 2-(aminomethyl)pyridine H atoms and oxalate O atoms. Each sheet gives rise to channels of Cr4K4 octanuclear rings and each resultant hole is occupied by a pair of 2-(aminomethyl)pyridine ligands with partial overlap. The shortest Cr...Cr distance [5.593 (4) Å] is shorter than usually observed in the K-M(III)-oxalate family.

Inter-layer charge disproportionation in the dual-layer organic metal (tTTF-I)2ClO4 with unsymmetrical I···O halogen bond interactions.

A mixed-valence salt of tTTF-I with ClO4(-), formulated as (tTTF-I)2ClO4, is characterized by the presence of two crystallographically independent donor molecules, segregated in different layers and linked together through I···O interactions with the ClO4(-) anion disordered at room temperature. The tTTF-I donor molecule was prepared by metallation of tTTF (trimethylene tetrathiafulvalene) followed by reaction with iodine to afford the mono and diiodo derivatives tTTF-I and tTTFI2, respectively. The crystal structure of the latter neutral tTTFI2 shows the occurrence of strong type II, II halogen bond interactions. Band structure calculations of the dual-layer structure of the 2 : 1 salt (tTTF-I)2ClO4 show co-existence of both 1D open and 2D closed Fermi surfaces. The salt undergoes a metal-insulator phase transition at T(MI) = 90 K, associated with an electronic dimensionality decrease, since already at 100 K, the 2D part of the Fermi surface transforms into 1D corrugated planes. High resolution X-ray investigations performed at 100 K, combined with multipolar refinements, indicate an approximately equivalent +0.5e charge in both donor molecules, as also deduced from the intramolecular bond distances. On the other hand, Raman spectroscopic investigations show that at ambient temperature the charge is actually distributed non-uniformly in conducting layers of tTTF-I molecules, with the identification of molecules with charges +1, +0.5, 0e, while at low temperature the charge distribution becomes essentially uniform (+0.5e), as confirmed from the X-ray high resolution data. These apparently contradictory behaviors are actually a consequence of a partial electron transfer between the two independent slabs to reach a common Fermi level in the metallic phase.

Poly[di-µ-aqua-di-aqua-bis-(µ7-oxalato-κ(9) O (1):O (1):O (1),O (2):O (2):O (2'):O (2'),O (1'):O (1'))calciumdicaesium].

In the title compound, [CaCs2(C2O4)2(H2O)4] n , the Ca(2+) ion, lying on a twofold rotation axis, is coordinated by four O atoms from two oxalate ligands and two bridging water mol-ecules in an octa-hedral geometry. The Cs(+) ion is coordinated by seven O atoms from six oxalate ligands, one bridging water and one terminal water mol-ecule. The oxalate ligand displays a scarce high denticity. The structure contains parallel chain units runnig along [10-1], formed by two edge-sharing Cs polyhedra connected by CsO9 polyhedra connected by a face-sharing CaO6 octahedron. These chains are further linked by the oxalate ligands to build up a three-dimensional framework. O-H⋯O hydrogen bonds involving the water mol-ecules and the carboxyl-ate O atoms enhance the extended structure.

Charge-assisted halogen bonding: donor-acceptor complexes with variable ionicity.

Charge-assisted halogen bonding is unambiguously revealed from structural and electronic investigations of a series of isostructural charge-transfer complexes derived from iodinated tetrathiafulvalene and tetracyanoquinodimethane derivatives, (EDT-TTFI2)2(TCNQF(n)), n=0-2, which exhibit variable degrees of ionicity. The iodinated tetrathiafulvalene derivative, EDT-TTFI2, associates with tetracyanoquinodimethane (TCNQ) and its derivatives of increasing reduction potential (TCNQF, TCNQF2) through highly directional C-I⋅⋅⋅N≡C halogen-bond interactions. With the less oxidizing TCNQ acceptor, a neutral and insulating charge-transfer complex is isolated whereas with the more oxidizing TCNQF2 acceptor, an ionic, highly conducting charge-transfer salt is found, both of 2:1 stoichiometry and isostructural with the intermediate TCNQF complex, in which a neutral-ionic conversion takes place upon cooling. A correlation between the degree of charge transfer and the C-I⋅⋅⋅N≡C halogen-bond strength is established from the comparison of the structures of the three isostructural complexes at temperatures from 300 to 20 K, thus demonstrating the importance of electrostatics in the halogen-bonding interaction. The neutral-ionic conversion in (EDT-TTFI2)2(TCNQF) is further investigated through the temperature dependence of its magnetic susceptibility and the stretching modes of the C≡N groups.

l-Leucinium fluoride monohydrate.

The asymmetric unit of the title hydrated salt, C(6)H(14)NO(2) (+)·F(-)·H(2)O, contains a discrete cation with a protonated amino group, a halide anion and one water mol-ecule. The crystal structure is composed of double layers parallel to (010) held together by N-H⋯O, N-H⋯F, O-H⋯F and C-H⋯F hydrogen bonds, forming a two-dimensional network, and stacked along the c axis, viz. hydro-philic layers at z = 0 and 1/2 and hydro-phobic layers at z = 1/3 and 2/3.

Intra- and supra-molecular inter-actions in cis,mer-diaqua-tris-(1H-imidazole-κN(3))(terephthalato-κO)cobalt(II) monohydrate.

In the title compound, [Co(C(8)H(4)O(4))(C(3)H(4)N(2))(3)(H(2)O)(2)]·H(2)O, the cisoid angles are in the range 85.59 (5)-93.56 (5)°, while two equal transoid angles deviate significantly from the ideal linear angle, the third being almost linear. One carboxyl-ate group is almost coplanar [1.23 (13)°] with the plane of its parent aromatic ring, although it has one O-atom donor involved in one coordination and one hydrogen bond as acceptor. The other carboxyl-ate group does not coordinate and is rotated out of this plane with a torsional twist of 17.27 (20)°. The coordination neutral entity, based on aqua ligands and two cyclic co-ligands seems, at first sight, monomeric. Strongly tight, via one intra-molecular hydrogen bond between aqua and carboxyl-ate O atoms, it brings out a quasi-planar six-membered ring around the Co(II) atom, turning the CoN(3)O(3) coordination octa-hedron into a new building block. The rigidity of this feature associated with several hydrogen-bonded arrays yields an extended structure. In the resulting supra-molecular packing, a binuclear hydrated Co(II) assembly, built up from triple strands driven by different heterosynthons, embodies the synergy of coordination, covalent and hydrogen bonds.

Bis(adeninium) bis-(hydrogensulfate) sulfate.

The title compound, 2C5H7N5(2+)·2HSO4(-)·SO4(2-), was synthesized from adenine and sulfuric acid. The asymmetric unit contains two diprotonated adeninium cations, two bis-ulfate anions and one sulfate anion. The crystal structure is stabilized by classical N-H⋯O and O-H⋯O hydrogen bonds, and weak C-H⋯O and C-H⋯N hydrogen bonds, generating a three-dimensional network.

dl-Tyrosinium chloride dihydrate.

In the title compound, C(9)H(12)NO(3) (+)·Cl(-)·2H(2)O, the cation has a protonated amino group resulting from proton transfer from chloridric acid. The structure displays double layers parallel to the [010] direction held together by N-H⋯O, N-H⋯Cl, O-H⋯O and O-H⋯Cl hydrogen bonds. These layers are stacked along the c axis at b = 1/2; within each layer, the tyrosinium cations are arranged in an alternating head-to-tail sequence, forming inversion dimers [R(2) (2)(10) motif]. The water mol-ecules allow for the construction of a three-dimensional hydrogen-bonded network formed by centrosymmetric R(6) (6)(28) and R(8) (8)(34) motifs.

Periodic projector augmented wave density functional calculations on the hexachlorobenzene crystal and comparison with the experimental multipolar charge density model.

The projector augmented wave (PAW) methodology has been used to calculate a high precision electron density distribution ρ(r) for the hexachlorobenzene crystal phase. Implementing the calculation of the crystallographic structure factors in the VASP code has permitted one to obtain the theoretical multipolar ρ(r). This electron density is compared with both the DFT electron density and the experimental multipolar model obtained from high-resolution X-ray diffraction data. This comparison has been carried out in intra- and intermolecular regions within the framework of the quantum theory of atoms-in-molecules (QTAIM) developed by Bader and co-workers. The characterization of the electron density in both C-Cl and Cl···Cl regions, as well as within the atomic basins, shows similar features for the three models. As a consequence, the observation of charge depletion and charge concentration regions around the halogen nuclei (along the C-Cl bonding axis and in the perpendicular plane, respectively) underlines the nature of halogen bonding in terms of electrophilic and nucleophilic interactions.

Intermolecular interactions and charge transfer in the 2:1 tetrathiafulvalene bromanil complex, (TTF)2-BA.

The crystal structure of the 2:1 charge-transfer complex of tetrathiafulvalene [2,2'-bis(1,3-dithiolylidene)] and bromanil (tetrabromo-1,4-benzoquinone) [(TTF)(2)-BA, (C(6)H(4)S(4))(2)-C(6)Br(4)O(2)] has been determined by X-ray diffraction at room temperature, 100 and 25 K. No structural phase transition occurs in the temperature range studied. The crystal is made of TTF-BA-TTF sandwich trimers. A charge-transfer estimation between donor and acceptor (0.2 e) molecules is proposed in comparison to the molecular geometries of TTF-BA and TTF and BA isolated molecules. Displacement parameters of the molecules have been modeled with the TLS formalism.

Poly[diaquadi-µ6-oxalato-µ5-oxalato-chromium(III)rubidium(I)]: a new supramolecular isomer.

The title compound, [CrRb(C(2)O(4))(2)(H(2)O)(2)](n), obtained under hydrothermal conditions and investigated structurally at 100 K, is a three-dimensional supramolecular isomer of the layered structure compound studied at room temperature. This novel polymer is built up from crosslinked heterobimetallic units. The linkage of alternating edge- and vertex-shared RbO(7)(H(2)O)(2) and CrO(4)(H(2)O)(2) polyhedra running along three different directions gives a dense packing. The two independent ligands display two η(4)-chelation modes and two conventional carboxylate bridges. However, the pentadentate ligand connects the Cr(III) and Rb(I) ions through one O-atom bridge, while the hexadentate ligand exhibits an additional η(3)-chelation and two O-atom bridges. Each coordinated water molecule forms an O-atom bridge between the two metals. Moreover, in the absence of protonated ligands, these water molecules act as donors through their four H atoms in strong-to-weak hydrogen bonds. This results in zigzag chains of alternating oxalate and aqua ligands parallel to the twofold screw axis. The six double oxalates known to date containing an alkali and Cr(III) all present layered two-dimensional structures. In the series, this supramolecular isomer is the first three-dimensional framework.

Nickel(II)-dipeptidoamine-based tetrameric complex: structural study in solution and in solid state.

The coordination structure of M(4)L(4)H(-8) macromolecules (M = Ni(II), Cu(II), Pd(II)) containing small peptidic ligands (L = Xaa-His or Xaa-His-Yaa) has been predicted primarily on the basis of spectroscopic and potentiometric data in the literature. In this work, the neutral tetranuclear nickel(II) complex 1 formed with four double-deprotonated ligands (L = α-methyl-alanyl-histamine) was prepared, and its crystal structure was determined (C(36)H(56)N(16)Ni(4)O(4)·4.5CH(3)OH·1.5H(2)O: a = 11.2645(4) A, b = 23.5003(8) A, c = 20.9007(7) A, ß = 102.321(1)°, monoclinic, P2(1)/c, Z = 4). In complex 1, the metal ions have a square planar geometry with 4N donor set consisting of the N-terminal amino nitrogen, the deprotonated amide nitrogen, the imidazole N(3) atom, and the deprotonated imidazole N(1) atom of the adjacent ligand. The latter nitrogen atom provides the connection of the four NiLH(-2) units forming a C(1) symmetrical saddle-like shape. The complexation of L with Ni(II) ion has been studied by a potentiometric method combined with UV-visible spectrophotometric titration. At pH 8.0, the predominant species is M(4)L(4)H(-8) with pK(4)(oligomerization) = 5.73. The tetranuclear structure of complex 1 was also studied in solution by (1)H and (13)C NMR spectroscopy suggesting a structure of symmetry S(4). DFT calculations on optimized structure in symmetry C(1) and S(4) have been performed to explain the observed differences in solution and in solid state. The nuclearity was also confirmed in solution by ESI-HRMS analysis.

Influence of anion substitution on hydrogen-bonding patterns of salt compounds: cytosinium hydrogen sulfate and cytosinium perchlorate.

In the two title compounds, cytosinium hydrogen sulfate, C(4)H(6)N(3)O(+).HSO(4)(-), (I), and cytosinium perchlorate, C(4)H(6)N(3)O(+).ClO(4)(-), (II), the asymmetric units comprise a cytosinium cation with hydrogen sulfate and perchlorate anions, respectively. The crystal structures of (I) and (II) are similar; that of (I) is characterized by a three-dimensional N-H...O, O-H...O and C-H...O hydrogen-bonded network. In (I) and (II), two-dimensional layers are formed by N-H...O and C-H...O hydrogen bonds and, in the case of (I), they are linked by O-H...O hydrogen bonds where the anion acts as a donor and the cation as an acceptor. The hydrogen-bonded sheets in (II) form an angle of 87.1 degrees.

The nature of halogen...halogen interactions: a model derived from experimental charge-density analysis.

Slightly attractive: The attractive and anisotropic nature of the ClCl interaction in C(6)Cl(6) is experimentally demonstrated from an expansion of the electron density rho(r) around the chlorine nuclei. The interaction is explained in a model in which there is a bonding attraction involving electron-deficient (see picture, blue) and electron-rich (red) regions of adjacent Cl atoms.