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1.
IUCrJ ; 6(Pt 5): 884-894, 2019 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-31576221

RESUMO

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).

2.
IUCrJ ; 5(Pt 5): 647-653, 2018 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-30224967

RESUMO

In this study, the nature and characteristics of a short Br⋯π interaction observed in an ebselen derivative, 2-(2-bromophenyl)benzo[d][1,2]selenazol-3(2H)-one, has been explored. The electronic nature of this Br⋯π interaction was investigated via high-resolution X-ray diffraction and periodic density functional theory calculations using atoms-in-molecules (AIM) analysis. This study unravels the simultaneous presence of σ-hole and π-hole bonding characteristics in the same interaction. The dual characteristics of this unique Br⋯π interaction are further established via molecular electrostatic potentials (MESPs) and natural bond orbitals (NBOs).

3.
J Chem Phys ; 148(16): 164106, 2018 Apr 28.
Artigo em Inglês | MEDLINE | ID: mdl-29716230

RESUMO

In this paper, we propose a simple cluster model with limited basis sets to reproduce the unpaired electron distributions in a YTiO3 ferromagnetic crystal. The spin-resolved one-electron-reduced density matrix is reconstructed simultaneously from theoretical magnetic structure factors and directional magnetic Compton profiles using our joint refinement algorithm. This algorithm is guided by the rescaling of basis functions and the adjustment of the spin population matrix. The resulting spin electron density in both position and momentum spaces from the joint refinement model is in agreement with theoretical and experimental results. Benefits brought from magnetic Compton profiles to the entire spin density matrix are illustrated. We studied the magnetic properties of the YTiO3 crystal along the Ti-O1-Ti bonding. We found that the basis functions are mostly rescaled by means of magnetic Compton profiles, while the molecular occupation numbers are mainly modified by the magnetic structure factors.

4.
Acta Crystallogr B Struct Sci Cryst Eng Mater ; 73(Pt 4): 544-549, 2017 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-28762966

RESUMO

Joint refinement of X-ray and polarized neutron diffraction data has been carried out in order to determine charge and spin density distributions simultaneously in the nitronyl nitroxide (NN) free radical Nit(SMe)Ph. For comparison purposes, density functional theory (DFT) and complete active-space self-consistent field (CASSCF) theoretical calculations were also performed. Experimentally derived charge and spin densities show significant differences between the two NO groups of the NN function that are not observed from DFT theoretical calculations. On the contrary, CASSCF calculations exhibit the same fine details as observed in spin-resolved joint refinement and a clear asymmetry between the two NO groups.

5.
Acta Crystallogr Sect E Struct Rep Online ; 70(Pt 9): o1061-2, 2014 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-25309226

RESUMO

In the title mol-ecule, C18H21Cl2N3, the tri-aza-cyclo-hexane ring adopts a chair conformation with both 4-chloro-phenyl substituents in axial positions and the propyl group in an equatorial site. The dihedral angle between the planes of the benzene rings is 49.5 (1)°. In the crystal, mol-ecules are arranged in a head-to-tail fashion, forming columns along [010], and pairs of weak C-H⋯π inter-actions form inversion dimers between columns.

6.
IUCrJ ; 1(Pt 3): 194-9, 2014 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-25075338

RESUMO

Since the 1980s it has been possible to probe crystallized matter, thanks to X-ray or neutron scattering techniques, to obtain an accurate charge density or spin distribution at the atomic scale. Despite the description of the same physical quantity (electron density) and tremendous development of sources, detectors, data treatment software etc., these different techniques evolved separately with one model per experiment. However, a breakthrough was recently made by the development of a common model in order to combine information coming from all these different experiments. Here we report the first experimental determination of spin-resolved electron density obtained by a combined treatment of X-ray, neutron and polarized neutron diffraction data. These experimental spin up and spin down densities compare very well with density functional theory (DFT) calculations and also confirm a theoretical prediction made in 1985 which claims that majority spin electrons should have a more contracted distribution around the nucleus than minority spin electrons. Topological analysis of the resulting experimental spin-resolved electron density is also briefly discussed.

7.
Acta Crystallogr A ; 68(Pt 6): 675-86, 2012 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-23075610

RESUMO

New crystallographic tools were developed to access a more precise description of the spin-dependent electron density of magnetic crystals. The method combines experimental information coming from high-resolution X-ray diffraction (XRD) and polarized neutron diffraction (PND) in a unified model. A new algorithm that allows for a simultaneous refinement of the charge- and spin-density parameters against XRD and PND data is described. The resulting software MOLLYNX is based on the well known Hansen-Coppens multipolar model, and makes it possible to differentiate the electron spins. This algorithm is validated and demonstrated with a molecular crystal formed by a bimetallic chain, MnCu(pba)(H(2)O)(3)·2H(2)O, for which XRD and PND data are available. The joint refinement provides a more detailed description of the spin density than the refinement from PND data alone.

8.
Acta Crystallogr B ; 67(Pt 4): 324-32, 2011 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-21775811

RESUMO

The experimental charge-density distribution of the dinuclear cobalt(II) complex [Co(2)(sym-hmp)(2)](BPh(4))(2)·2H(2)O·2C(3)H(6)O was determined at 100 K. When decreasing the temperature, the magnetic susceptibility of this complex deviates from Curie law because of anti-ferromagnetic exchange interactions, but the susceptibility increases sharply at low temperature (< 20 K). To explain this magnetic behaviour a tilt angle between the Co-atom environments was previously theoretically predicted. The structure and experimental charge density determined in this study show a tilt angle. The calculated value, based on the 100 K experimental d-orbital model, is in agreement with the theoretical one.

9.
Acta Crystallogr B ; 64(Pt 6): 713-24, 2008 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-19029701

RESUMO

The crystal structure of a new phase consisting of the inclusion of the hyperpolarizable molecule p-N,N-dimethylnitroaniline (dimethyl-para-nitroaniline or dmpNA) in the large-pore zeolite mordenite (MOR) has been determined from high-resolution synchrotron powder diffraction at 300 and 90 K. The unit-cell parameters and space group at 300 K are similar to those of as-synthesized mordenite. The crystallographic study indicates that the MOR straight channels are almost fully loaded with molecules that are disordered over eight symmetry-related sites. As expected, the molecules are located in the large 12-membered ring channel, at the intersection with the secondary eight-membered channel with which they might form hydrogen bonds. The elongation axes (and then the dipole moments) of the molecules are slightly tilted (28.57 degrees ) from [001]. The configuration found suggests an interaction of dmpNA with framework O atoms through its methyl groups.


Assuntos
Silicatos de Alumínio/química , Compostos de Anilina/química , Síncrotrons , Zeolitas/química , Modelos Moleculares , Difração de Pó , Temperatura
10.
Faraday Discuss ; 135: 217-35; discussion 237-59, 503-6, 2007.
Artigo em Inglês | MEDLINE | ID: mdl-17328431

RESUMO

High-resolution X-ray diffraction experiments and state-of-the-art density functional theory calculations have been performed. The validity of the atoms-in-molecules approach is tested for the neutral-ionic transition of TTF-CA which involves a transfer of less than one electron between the donor and acceptor molecules. Foremost, crystallographical data have been reassessed along the temperature-induced neutral-ionic phase transition undergone by this charge transfer complex. Based on accurate X-ray structures at 105 and 15 K, topological analysis of both DFT and the experimental multipolar electron densities allowed detailed characterization of intra- and interstack intermolecular interactions. Direct quantification of the intermolecular charge transfer and the dipole moment are discussed.

11.
J Am Chem Soc ; 128(42): 13921-31, 2006 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-17044720

RESUMO

An experimental electron density (ED) analysis of the spin crossover coordination complex Fe(btr)(2)(NCS)(2).H(2)O has been performed in the ground low-spin (LS) state and in the metastable thermally quenched high-spin (HS) state at 15 K by fitting a multipolar model to high-resolution X-ray diffraction measurements. The ED has been quantitatively analyzed using the quantum theory of atoms in molecules. This is the first time the ED distribution of a molecular metastable state has been experimentally investigated. The electron deformation densities and derived Fe 3d orbital populations are characteristic of LS (t(2g)(6) e(g)(0)) and HS (t(2g)(4) e(g)(2)) electron configurations and indicate significant sigma donation to the Fe d(x)2(-)(y)2 and d(z)2 atomic orbitals. The Fe-N(NCS) and Fe-N(btr) coordination interactions are characterized using the laplacian distribution of the ED, the molecular electrostatic potential, and the fragment charges obtained by integration over the topological atomic basins. A combination of electrostatic and covalent contributions to these interactions is pointed out. Interlayer interactions are evidenced by the presence of bond critical points in N...H hydrogen bonds involving the non-coordinated water molecule. Systematic differences in the atomic displacement parameters between the LS and HS states have been described and rationalized in terms of modifications of bond force constants.

12.
Acta Crystallogr A ; 60(Pt 5): 455-64, 2004 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-15477685

RESUMO

For more than forty years, the experimental determination and analysis of electron densities have played a fundamental role in advances in the chemical bond concept. The present paper illustrates the application of this approach to the field of molecular magnetism with examples that recently appeared in the literature. Particular attention is attached to several classes of materials, purely organic free radicals, coordination compounds and organometallic complexes, which exhibit specific magnetic behaviors. It is shown to what extent the electron-density analysis can shed light on bonding aspects that are closely related to magnetic couplings. Relations between spin delocalization, spin polarization, superexchange and the characteristics of the electron density are described. The use of the topological theory of 'atoms in molecules' allows the possible magnetic interaction pathways to be located and defined, especially through weak intermolecular contacts. The complementarity with polarized neutron diffraction and spin-density modeling techniques is particularly evident from the chosen examples.

13.
J Am Chem Soc ; 126(39): 12604-13, 2004 Oct 06.
Artigo em Inglês | MEDLINE | ID: mdl-15453793

RESUMO

A nitronyl-nitroxide (NIT) biradical D-NIT2 linked by a single double bond has been engineered and investigated in the solid state by a combination of X-ray diffraction, magnetic susceptibility measurement, EPR, as well as solid-state (1)H and (13)C NMR spectroscopies, and experimental electron density distribution. All techniques reveal that a double bond is a very efficient coupling unit for exchange interactions between two radical moieties. Using a Bleaney-Bowers model dimer (H = -JS(1)S(2)), a singlet-triplet energy gap of J = -460 K was found with the singlet state being the ground state. This very strong intramolecular interaction was confirmed by EPR measurements in CH(2)Cl(2) solution (6 10(-4) M) or dispersed in a polymer matrix at low concentration. In keeping with these unusual interactions, solid-state NMR signals of the biradical were found to be considerably less shifted than those found for related monoradicals. Temperature-dependent solid-state (13)C NMR spectra of D-NIT2 confirmed the very strong intramolecular coupling constant (J = -504 K). The electron density distribution of D-NIT2 was measured by high resolution X-ray diffraction, which also revealed that this biradical is an ideally conjugated system. The in-depth characterization includes the deformation maps and the observed electron density ellipticities, which exhibit a pronounced sigma-pi character of the O-N-C=C-N-O cores in keeping with an efficient electronic delocalization along the alkene spacer.

14.
J Am Chem Soc ; 126(4): 1219-28, 2004 Feb 04.
Artigo em Inglês | MEDLINE | ID: mdl-14746494

RESUMO

The electron density distribution of the ferrimagnetic MnCu(pba)(H2O)3.2H2O chain compound, where pba stands for 1,3-propylenebis(oxamato), has been derived from high resolution X-ray diffraction measurements at 114 K using a multipolar model. The analysis of the chemical bonding has been carried out through the "Atoms in Molecules" formalism and thoroughly interpreted with regards to the strong intrachain and weak interchain magnetic couplings. The topological properties of the electron density on the oxamato bridge indicate large electron delocalization and conjugation effects, in addition to high charge transfer from both metals to the bridge. The resulting positive charges on Mn (+1.45 e) and Cu (+1.56 e) induce charge polarization of the bridge, leading to a shift of electron density from the central C atoms to the metal coordinating O and N atoms. The Mn-bridge interactions are mainly closed-shell interactions with low electron density at the corresponding bond critical points, whereas the Cu-bridge interactions exhibit significant covalent character. The Cu-N bonds are moreover stronger than the Cu-O bonds. The 3d Cu and Mn orbital populations are consistent with pyramidal and regular octahedral environments, respectively, in agreement with the loss of degeneracy due to ligand field effects. Interchain interaction pathways are evidenced by the existence of four bond critical points in hydrogen bond regions. Finally, these intrachain and interchain bonding features are correlated to the results of experimental and theoretical spin density distributions, as well as magnetic measurements.

15.
Acta Crystallogr B ; 59(Pt 6): 687-700, 2003 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-14634246

RESUMO

The electron-density distribution of AlPO4-15 has been determined using high-resolution single-crystal X-ray diffraction, and the topological properties of the charge density have been calculated using the 'atoms in molecules' (AIM) theory. Analysis of the topological properties at the bond critical points has been used to characterize the interactions within the framework, and between the framework and the extra-framework species (ammonium ions and water molecules), and to define atomic properties, such as volume and net charges, uniquely. A comparison between procrystal and multipolar representations of the density was performed in order to explore to what extent the former representation is likely to reflect the interactions in the solid. Correlation with geometrical properties (P-O and Al-O bond lengths, and Al-O-P angle) is found for topological charges obtained from the multipolar model, but not for the results from the procrystal representation.

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