Tin(II) Lone Pair Stereoactivity: Influence on Structures and Properties and Mössbauer Spectroscopic Properties

Dénès, Georges; Muntasar, Abdualhafed; Madamba, M. Cecilia; Mérazig, Hocine

doi:10.1002/9781118714614.ch11

Cited by 2 publications

(2 citation statements)

References 84 publications

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“…In the other model, the Galy-Andersson model, it is shown that the lone pair in Te(IV) occupies the same space as an oxide ion or a fluoride ion, and the lone pair forms with the O 2-and/or F -ions form a compact polyhedron containing the central Te(IV), that is shifted towards the lone pair [23]. We showed in an earlier work that the same is true for Sn(II) fluorides, oxides and oxide fluorides [24]. It should be noted that when the lone pair reduces the coordination number and distorts the polyhedron of coordination, it is located on an axial orbital that is a hybrid orbital.…”

Section: Introductionsupporting

confidence: 50%

The Unique Case of Tin(ii) Fluoride Containing Unexpected Substitutional Solid Solutions: Local Structure Versus Global Structure

Dénès¹,

Muntasar²,

Madamba³

et al. 2017

Materials and Contact Characterisation VIII

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Solid solutions provide the means of tailoring the properties of materials by adjusting their chemical composition without phase demixing. A solid solution is a compound with a variable composition. Substitutional solid solutions are formed by replacing some atoms/ions by other atoms/ions. In order to be energetically favored, this replacement is possible only if certain criteria are met: (1) size criterion: there should be no more than 15% difference between the radius of the atoms/ions that are replacing each other, and (2) bonding type criterion: the replacing atom/ion should be able to accept the bonding type of the host. If these criteria are not met, the substitution will create an unacceptable level of stress at and around the substitution sites. In our studies of the SnF2/MF2 systems, where (M = Ca, Sr, Ba or Pb), we have found a M1−xSnxF2 solid solution for M = Ca and Pb, with a wide range of composition in the case of Pb. In addition, the investigation of the SnF2/MF2/MCl2 systems revealed an even more complicated type of solid solution. All should be forbidden according to accepted criteria: the alkaline earth metal fluorides and chlorides have ionic structures, while SnF2 has three allotropes, all which are characterized by strongly covalent bonding with a significant amount of polymerization. In addition, the similar size criterion is grossly violated, Sn 2+ being much smaller than the alkaline earth metal, well beyond the accepted limit of about 15% for ion substitution. Furthermore, the wider solid solutions are formed with PbF2 and BaClF, i.e. for the cations that have the largest size difference. The Ba1−xSnxCl1+yF1-y solid solution is by far the most unusual, and it is probably unique since it is a doubly disordered solid solution (simultaneous disorder on the cationic sita and on the anionic sites). The combined use of X-ray diffraction and Mössbauer spectroscopy was necessary in order to understand these solid solutions.

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Section: Introductionsupporting

confidence: 50%

The Unique Case of Tin(ii) Fluoride Containing Unexpected Substitutional Solid Solutions: Local Structure Versus Global Structure

Dénès¹,

Muntasar²,

Madamba³

et al. 2017

Materials and Contact Characterisation VIII

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“…Figure b shows the room-temperature 119 Sn Mössbauer spectrum for our c-BaSnF 4 sample. The spectrum features an asymmetric quadrupole doublet with an isomer shift of around 3 mm s –1 , characteristic of covalently bonded Sn(II), and a large quadrupole splitting parameter (Δ > 1.5 mm s –1 ), indicating that Sn exhibits a stereoactive lone pair. , The experimental spectrum can be reconstructed using two quadrupole doublets with distinct isomer shift and quadrupole-splitting parameters (see the Supporting Information for details), indicating some degree of variation in Sn–F bonding interactions and in the coordination geometry around individual tin cations.…”

Section: Resultsmentioning

confidence: 99%

Dynamic Lone Pairs and Fluoride-Ion Disorder in Cubic-BaSnF₄

Mercadier,

Coles,

Duttine

et al. 2023

J. Am. Chem. Soc.

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Introducing compositional or structural disorder within crystalline solid electrolytes is a common strategy for increasing their ionic conductivity. (M,Sn)F2 fluorites have previously been proposed to exhibit two forms of disorder within their cationic host frameworks: occupational disorder from randomly distributed M and Sn cations and orientational disorder from Sn(II) stereoactive lone pairs. Here, we characterize the structure and fluoride-ion dynamics of cubic BaSnF4, using a combination of experimental and computational techniques. Rietveld refinement of the X-ray diffraction (XRD) data confirms an average fluorite structure with {Ba,Sn} cation disorder, and the 119Sn Mössbauer spectrum demonstrates the presence of stereoactive Sn(II) lone pairs. X-ray total-scattering PDF analysis and ab initio molecular dynamics simulations reveal a complex local structure with a high degree of intrinsic fluoride-ion disorder, where 1/3 of fluoride ions occupy octahedral “interstitial” sites: this fluoride-ion disorder is a consequence of repulsion between Sn lone pairs and fluoride ions that destabilizes Sn-coordinated tetrahedral fluoride-ion sites. Variable-temperature 19F NMR experiments and analysis of our molecular dynamics simulations reveal highly inhomogeneous fluoride-ion dynamics, with fluoride ions in Sn-rich local environments significantly more mobile than those in Ba-rich environments. Our simulations also reveal dynamical reorientation of the Sn lone pairs that is biased by the local cation configuration and coupled to the local fluoride-ion dynamics. We end by discussing the effect of host-framework disorder on long-range diffusion pathways in cubic BaSnF4.

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Tin(II) Lone Pair Stereoactivity: Influence on Structures and Properties and Mössbauer Spectroscopic Properties

Cited by 2 publications

References 84 publications

The Unique Case of Tin(ii) Fluoride Containing Unexpected Substitutional Solid Solutions: Local Structure Versus Global Structure

The Unique Case of Tin(ii) Fluoride Containing Unexpected Substitutional Solid Solutions: Local Structure Versus Global Structure

Dynamic Lone Pairs and Fluoride-Ion Disorder in Cubic-BaSnF₄

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Tin(II) Lone Pair Stereoactivity: Influence on Structures and Properties and Mössbauer Spectroscopic Properties

Cited by 2 publications

References 84 publications

The Unique Case of Tin(ii) Fluoride Containing Unexpected Substitutional Solid Solutions: Local Structure Versus Global Structure

The Unique Case of Tin(ii) Fluoride Containing Unexpected Substitutional Solid Solutions: Local Structure Versus Global Structure

Dynamic Lone Pairs and Fluoride-Ion Disorder in Cubic-BaSnF4

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Dynamic Lone Pairs and Fluoride-Ion Disorder in Cubic-BaSnF₄