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1.
Chemistry ; 21(3): 1036-47, 2015 Jan 12.
Artigo em Inglês | MEDLINE | ID: mdl-25370384

RESUMO

Diatrizoic acid (DTA), a clinically used X-ray contrast agent, crystallises in two hydrated, three anhydrous and nine solvated solid forms, all of which have been characterised by X-ray crystallography. Single-crystal neutron structures of DTA dihydrate and monosodium DTA tetrahydrate have been determined. All of the solid-state structures have been analysed using partial atomic charges and hardness algorithm (PACHA) calculations. Even though in general all DTA crystal forms reveal similar intermolecular interactions, the overall crystal packing differs considerably from form to form. The water of the dihydrate is encapsulated between a pair of host molecules, which calculations reveal to be an extraordinarily stable motif. DTA presents functionalities that enable hydrogen and halogen bonding, and whilst an extended hydrogen-bonding network is realised in all crystal forms, halogen bonding is not present in the hydrated crystal forms. This is due to the formation of a hydrogen-bonding network based on individual enclosed water squares, which is not amenable to the concomitant formation of halogen bonds. The main interaction in the solvates involves the carboxylic acid, which corroborates the hypothesis that this strong interaction is the last one to be broken during the crystal desolvation and nucleation process.


Assuntos
Diatrizoato/química , Varredura Diferencial de Calorimetria , Cristalografia por Raios X , Ligação de Hidrogênio , Conformação Molecular , Difração de Nêutrons , Solventes/química , Termodinâmica , Termogravimetria , Água/química
2.
J Am Chem Soc ; 134(48): 19772-81, 2012 Dec 05.
Artigo em Inglês | MEDLINE | ID: mdl-23130914

RESUMO

Neutron diffraction studies have been carried out to shed light on the unprecedented order-disorder phase transition (ca. 155 K) observed in the mixed-valence iron(II)-iron(III) formate framework compound [NH(2)(CH(3))(2)](n)[Fe(III)Fe(II)(HCOO)(6)](n). The crystal structure at 220 K was first determined from Laue diffraction data, then a second refinement at 175 K and the crystal structure determination in the low temperature phase at 45 K were done with data from the monochromatic high resolution single crystal diffractometer D19. The 45 K nuclear structure reveals that the phase transition is associated with the order-disorder of the dimethylammonium counterion that is weakly anchored in the cavities of the [Fe(III)Fe(II)(HCOO)(6)](n) framework. In the low-temperature phase, a change in space group from P31c to R3c occurs, involving a tripling of the c-axis due to the ordering of the dimethylammonium counterion. The occurrence of this nuclear phase transition is associated with an electric transition, from paraelectric to antiferroelectric. A combination of powder and single crystal neutron diffraction measurements below the magnetic order transition (ca. 37 K) has been used to determine unequivocally the magnetic structure of this Néel N-Type ferrimagnet, proving that the ferrimagnetic behavior is due to a noncompensation of the different Fe(II) and Fe(III) magnetic moments.

3.
Phys Chem Chem Phys ; 14(38): 13273-83, 2012 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-22918382

RESUMO

The phenomenon of solid-state proton migration within molecular complexes containing short hydrogen bonds is investigated in two dimethylurea-oxalic acid complexes. Extensive characterisation by both X-ray and neutron diffraction shows that proton migration along the hydrogen bond can be induced in these complexes as a function of temperature. This emphasises the subtle features of the hydrogen bond potential well in such short hydrogen bonded complexes, both intrinsically and in the effect of the local crystalline environment. Based on these findings, the synthesis and analysis of a series of solid-state molecular complexes is shown to be a potential route to designing materials with tuneable proton migration effects.


Assuntos
Compostos de Metilureia/química , Ácido Oxálico/química , Cristalização , Ligação de Hidrogênio , Conformação Molecular , Difração de Nêutrons , Prótons , Temperatura , Difração de Raios X
4.
Org Biomol Chem ; 10(12): 2464-9, 2012 Mar 28.
Artigo em Inglês | MEDLINE | ID: mdl-22349254

RESUMO

(+)-syn-Benzotriborneol forms stable complexes with one molecule of water. This is due to the ability of the host to form three hydrogen bonds with water, to act simultaneously as a hydrogen-bond acceptor and donor, and to a perfect geometrical match between the pair. We report experimental (X-ray and neutron diffraction, VT NMR, DSC, TGA) and stereochemical studies carried out to elucidate and quantify the molecular and thermodynamic aspects of this supramolecular complex.


Assuntos
Canfanos/síntese química , Água/química , Ligação de Hidrogênio , Modelos Moleculares , Estrutura Molecular , Oxigênio/química , Soluções , Estereoisomerismo , Termodinâmica
5.
Angew Chem Int Ed Engl ; 50(35): 8184-7, 2011 Aug 22.
Artigo em Inglês | MEDLINE | ID: mdl-21744449

RESUMO

Squaring the circle: the novel dienamido pincer ligand N(CHCHPtBu(2))(2)(-) affords the isolation of the unusual square-planar iridium(II) and iridium(III) amido complexes [IrCl{N(CHCHPtBu(2))(2)}](n) (n=0 (1), +1 (2)). In contrast, the corresponding iridium(I) complex of the redox series (n=-1) is surprisingly unstable. The diamagnetism of 2 is attributed to strong N→Ir π donation.

7.
J Am Chem Soc ; 131(37): 13508-15, 2009 Sep 23.
Artigo em Inglês | MEDLINE | ID: mdl-19754191

RESUMO

We have determined the crystal structure of ammonia monohydrate phase II (AMH II) employing a combination of ab initio computational structure prediction and structure solution from neutron powder diffraction data using direct space methods. Neutron powder diffraction data were collected from perdeuterated AMH II using the D2B high-resolution diffractometer at the Institut Laue-Langevin. AMH II crystallizes in space-group Pbca with 16 formula units in a unit-cell of dimensions a = 18.8285(4) A, b = 6.9415(2) A, c = 6.8449(2) A, and V = 894.61(3) A3 [rho(calc)(deuterated) = 1187.56(4) kg m(-3)] at 502 MPa, 180 K. The structure is characterized by sheets of tessellated pentagons formed by orientationally ordered O-D...O, O-D...N, and N-D...O hydrogen-bonds; these sheets are stacked along the a-axis and connected by N-D...O hydrogen bonds alone. With the exception of the simple body-centered-cubic high-pressure phases of ammonia monohydrate and ammonia dihydrate, this is the first complex molecular structure of any of the high-pressure stoichiometric ammonia hydrates to be determined. The powder structure solution is complemented by an ab initio structure prediction using density functional theory which gives an almost identical hydrogen bonding network.

8.
J Chem Phys ; 131(15): 154503, 2009 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-20568868

RESUMO

We describe the results of a neutron powder diffraction study of perdeuterated ammonia monohydrate (AMH, ND(3).D(2)O) carried out in the range 102

9.
Phys Rev Lett ; 99(15): 156407, 2007 Oct 12.
Artigo em Inglês | MEDLINE | ID: mdl-17995198

RESUMO

Diffuse x-ray data for mixed-stack organic charge-transfer crystals approaching the neutral-ionic phase transition can be quantitatively explained as due to the softening of the optical phonon branch. The interpretation is fully consistent with vibrational spectra, and underlines the importance of electron-phonon coupling in low-dimensional systems with delocalized electrons.

10.
Science ; 300(5619): 612-5, 2003 Apr 25.
Artigo em Inglês | MEDLINE | ID: mdl-12714737

RESUMO

We report the direct observation by x-ray diffraction of a photoinduced paraelectric-to-ferroelectric structural phase transition using monochromatic 100-picosecond synchrotron pulses. It occurs in tetrathiafulvalene-p-chloranil, a charge-transfer molecular material in which electronic and structural changes are strongly coupled. An optical 300-femtosecond laser pulse switches the material from a neutral to an ionic state on a 500-picosecond time scale and, by virtue of intrinsic cooperativity, generates self-organized long-range structural order. The x-ray data indicate a macroscopic ferroelectric reorganization after the laser irradiation. Refinement of the structures before and after laser irradiation indicates structural changes at the molecular level.

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