The stability of polymorphs of MgCl2 — an ab initio study

Barrera, Gustavo D.; Allan, Neil L.; Soriano, M.R.

doi:10.1016/s0009-2614(97)00985-8

Cited by 6 publications

(12 citation statements)

References 7 publications

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“…To the best of our knowledge, no high pressure experimental structural study has been reported on MgCl 2 , plausibly because of its extremely high hygroscopicity. A previous theoretical study 2 suggests that pressurized MgCl 2 ( α or β phases) transforms to the rutile structure at ≈17 GPa and the fluorite structure at ≈77 GPa i.e. trending towards higher connectivity or 3D-like structures as normally would be expected for AX 2 inorganic compounds.…”

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confidence: 75%

“…According to Pauling’s first rule, the ambient pressure crystal structure of divalent metal halides and oxides AX 2 is mainly determined by the cation-anion radius ratio R = r c / r a 1 2 . For R values > 1, 9-fold coordinated cations ionic structures like cotunnite ( α -PbCl 2 -type) are formed while for R > 0.73, 8-fold coordinated cations ionic structures like fluorite (CaF 2 and SrCl 2 ) are formed 3 .…”

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confidence: 99%

“…At ambient conditions, MgCl 2 with a R = 0.40 12 crystalizes into alternative crystalline polymorphs, which is a common aspect of this class of inorganic X-A-X layered compounds: (a) the most common is α -MgCl 2 , CdCl 2 -type SG R-3m (166) Z = 3 5 13 14 followed by the less common (b) β -MgCl 2 , CdI 2 -type SG P-3m1 (164) Z = 1 9 . The computed density-functional theory energy difference between these phases is on the order of vibrational contributions to the structure (e.g., only 0.02 eV per formula unit volume) 2 . Mechanically milling MgCl 2 can easily shift the polymorphic concentration ratio.…”

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confidence: 99%

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High-pressure X-ray diffraction, Raman and computational studies of MgCl2 up to 1 Mbar: Extensive pressure stability of the β-MgCl2 layered structure

Stavrou

Yao

Zaug

et al. 2016

Sci Rep

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Magnesium chloride (MgCl2) with the rhombohedral layered CdCl2-type structure (α-MgCl2) has been studied experimentally using synchrotron angle-dispersive powder x-ray diffraction and Raman spectroscopy using a diamond-anvil cell up to 100 GPa at room temperature and theoretically using first-principles density functional calculations. The results reveal a pressure-induced second-order structural phase transition to a hexagonal layered CdI2-type structure (β-MgCl2) at 0.7 GPa: the stacking sequence of the Cl anions are altered resulting in a reduction of the c-axis length. Theoretical calculations confirm this phase transition sequence and the calculated transition pressure is in excellent agreement with the experiment. Lattice dynamics calculations also reproduce the experimental Raman spectra measured for the ambient and high-pressure phase. According to our experimental results MgCl2 remains in a 2D layered phase up to 100 GPa and further, the 6-fold coordination of Mg cations is retained. Theoretical calculations of relative enthalpy suggest that this extensive pressure stability is due to a low enthalpy of the layered structure ruling out kinetic barrier effects. This observation is unusual, as it contradicts with the general structural behavior of highly compressed AB2 compounds.

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confidence: 75%

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confidence: 99%

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confidence: 99%

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High-pressure X-ray diffraction, Raman and computational studies of MgCl2 up to 1 Mbar: Extensive pressure stability of the β-MgCl2 layered structure

Stavrou

Yao

Zaug

et al. 2016

Sci Rep

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“…The hybrid density functional PBE0 24,25 and B3LYP 26,27 methods were combined with three basis sets optimized for the periodic treatment of MgCl 2 . A previously reported basis set was taken from the paper of Barrera et al, 28 ■ RESULTS AND DISCUSSION Method Evaluation. The catalytically relevant (104) and (110) surfaces of MgCl 2 were studied by a 1-D periodic approach described in Figure 2.…”

Section: ■ Computational Detailsmentioning

confidence: 99%

“…The hybrid density functional PBE0 , and B3LYP , methods were combined with three basis sets optimized for the periodic treatment of MgCl 2 . A previously reported basis set was taken from the paper of Barrera et al, namely, 8–5–11G* (Mg) and 8–6-311G* (Cl) of Harrison and Saunders with further optimized 3sp, 4sp, and 3d functions for Mg and 4sp, 5sp, and 3d functions for Cl, together with added 4d functions for Cl. In conjunction with Barrera’s basis set, the standard 6-31G(d) basis set was used for oxygen, carbon, and hydrogen.…”

Section: Computational Detailsmentioning

confidence: 99%

Modeling of Substitutional Defects in Magnesium Dichloride Polymerization Catalyst Support

et al. 2012

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We evaluate methods and models for the periodic quantum chemical treatment of defects in MgCl 2 polymerization catalyst support and demonstrate the applicability of the approach for a study of chemical substitution of chlorine with bromine. Effects of the defects are evaluated through binding of methanol to catalytically relevant MgCl 2 surfaces. Our results show that the hybrid density functional PBE0 method reproduces the MgCl 2 crystal structure in good agreement with experiments and that a triple-ζ quality basis set is required to evaluate the donor binding properties. Furthermore, the effects of the defects depend on their position in the crystal lattice, and destabilization of the crystal lattice results in increased donor binding energy. Therefore, substitutions at the coordinatively unsaturated edges typically stabilize the crystallites and lower the donor binding energies, whereas substitutions at the coordinatively saturated bulk typically destabilize the crystallites and increase the donor binding energies. The effects are stronger on the (104) than on the (110) surface. The study is readily extendable to other kinds of defects occurring in crystallites.

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Alkylation of titanium tetrachloride on magnesium dichloride in the presence of Lewis bases

Linnolahti

Pakkanen

Bazhenov

et al. 2017

Journal of Catalysis

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The stability of polymorphs of MgCl2 — an ab initio study

Cited by 6 publications

References 7 publications

High-pressure X-ray diffraction, Raman and computational studies of MgCl2 up to 1 Mbar: Extensive pressure stability of the β-MgCl2 layered structure

High-pressure X-ray diffraction, Raman and computational studies of MgCl2 up to 1 Mbar: Extensive pressure stability of the β-MgCl2 layered structure

Modeling of Substitutional Defects in Magnesium Dichloride Polymerization Catalyst Support

Alkylation of titanium tetrachloride on magnesium dichloride in the presence of Lewis bases

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