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1.
Dalton Trans ; 43(19): 7263-8, 2014 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-24681873

RESUMO

The hydrothermal reaction of cobalt(II) acetate tetrahydrate, 4-aminophenyl tetrazole and water at 135 °C for 48 hours provided orange crystals of [Co3(OH)2(H2O)2(aptet)4] (1) (aptet = 4-aminophenyltetrazolate). The three-dimensional structure of compound 1 is constructed from chains of corner- and edge-sharing Co(II) octahedra linked into a framework through the dipodal ligand tethers. The cobalt sites of the chain are linked through tetrazolate groups in the N2,N3-bridging mode, as well as through µ3-hydroxyl groups into trinuclear Co3 substructures. The magnetic properties are consistent with a ferrimagnetic chain with the non-compensating resultant moment of one Co(II) per trinuclear Co(II) subunit. The temperature dependence of the ac magnetic susceptibility indicates glassy-like magnetic behavior.

2.
J Phys Chem A ; 116(30): 8051-7, 2012 Aug 02.
Artigo em Inglês | MEDLINE | ID: mdl-22784643

RESUMO

Terahertz spectroscopy is sensitive to the interactions between molecules in the solid-state and recently has emerged as a new analytical tool for investigating polymorphism. Here, this technique is applied for the first time to the phenomenon of tautomeric polymorphism where the crystal structures of anthranilic acid (2-aminobenzoic acid) have been investigated. Three polymorphs of anthranilic acid (denoted Forms I, II and III) were studied using terahertz spectroscopy and the vibrational modes and relative polymorph stabilities analyzed using solid-state density functional theory calculations augmented with London dispersion force corrections. Form I consists of both neutral and zwitterionic molecules and was found to be the most stable polymorph as compared to Forms II and III (both containing only neutral molecules). The simulations suggest that a balance between steric interactions and electrostatic forces is responsible for the favoring of the mixed neutral/zwitterion solid over the all neutral or all zwitterion crystalline arrangements.

3.
J Phys Chem A ; 115(40): 11039-44, 2011 Oct 13.
Artigo em Inglês | MEDLINE | ID: mdl-21923096

RESUMO

The terahertz (THz) spectra of crystalline solids are typically uniquely sensitive to the molecular packing configurations, allowing for the detection of polymorphs and hydrates by THz spectroscopic techniques. It is possible, however, that coincident absorptions may be observed between related crystal forms, in which case careful assessment of the lattice vibrations of each system must be performed. Presented here is a THz spectroscopic investigation of citric acid in its anhydrous and monohydrate phases. Remarkably similar features were observed in the THz spectra of both systems, requiring the accurate calculation of the low-frequency vibrational modes by solid-state density functional theory to determine the origins of these spectral features. The results of the simulations demonstrate the necessity of reliable and rigorous methods for THz vibrational modes to ensure the proper evaluation of the THz spectra of molecular solids.


Assuntos
Ácido Cítrico/química , Ácido Cítrico/análogos & derivados , Cristalografia por Raios X , Modelos Moleculares , Espectroscopia Terahertz , Água/química
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