Ions in Crystals:  The Topology of the Electron Density in Ionic Materials. III. Geometry and Ionic Radii

On the basis of a multipole refinement of single-crystal X-ray diffraction data collected using an Ag source at 90 K to a resolution of 1.63 Å−1, a quantitative experimental charge density distribution has been obtained for fluorite (CaF2). The atoms-in-molecules integrated experimental charges for Ca2+and F−ions are +1.40 e and −0.70 e, respectively. The derived electron-density distribution, maximum electron-density paths, interaction lines and bond critical points along Ca2+...F−and F−...F−contacts revealed the character of these interactions. The Ca2+...F−interaction is clearly a closed shell and ionic in character. However, the F−...F−interaction has properties associated with the recently recognized type of interaction referred to as `charge-shift' bonding. This conclusion is supported by the topology of the electron localization function and analysis of the quantum theory of atoms in molecules and crystals topological parameters. The Ca2+...F−bonded radii – measured as distances from the centre of the ion to the critical point – are 1.21 Å for the Ca2+cation and 1.15 Å for the F−anion. These values are in a good agreement with the corresponding Shannon ionic radii. The F−...F−bond path and bond critical point is also found in the CaF2crystal structure. According to the quantum theory of atoms in molecules and crystals, this interaction is attractive in character. This is additionally supported by the topology of non-covalent interactions based on the reduced density gradient.

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Ions in Crystals: The Topology of the Electron Density in Ionic Materials. 4. The Danburite (CaB2Si2O8) Case and the Occurrence of Oxide−Oxide Bond Paths in Crystals

The Journal of Physical Chemistry B ◽

10.1021/jp022374f ◽

2003 ◽

Vol 107 (21) ◽

pp. 4912-4921 ◽

Cited By ~ 23

Author(s):

Victor Luaña ◽

Aurora Costales ◽

Paula Mori-Sánchez ◽

A. Martín Pendás

Keyword(s):

Electron Density ◽

Ionic Materials

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Ions in crystals: The topology of the electron density in ionic materials. I. Fundamentals

Physical Review B ◽

10.1103/physrevb.55.4275 ◽

1997 ◽

Vol 55 (7) ◽

pp. 4275-4284 ◽

Cited By ~ 93

Author(s):

A. Martín Pendás ◽

Aurora Costales ◽

Víctor Luaña

Keyword(s):

Electron Density ◽

Ionic Materials

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A Universal Relation between Electron Density Minima and Atomic or Ionic Radii

A Quantum Approach to Alloy Design ◽

10.1016/b978-0-12-814706-1.00009-1 ◽

2019 ◽

pp. 179-184

Author(s):

Masahiko Morinaga

Keyword(s):

Electron Density ◽

Universal Relation ◽

Ionic Radii

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Structural dynamics of ionic materials mapped by femtosecond x-ray diffraction

Acta Crystallographica Section A Foundations and Advances ◽

10.1107/s2053273314092304 ◽

2014 ◽

Vol 70 (a1) ◽

pp. C769-C769

Author(s):

Thomas Elsaesser

Keyword(s):

Electron Density ◽

Time Resolution ◽

Theoretical Calculations ◽

Interaction Mechanism ◽

Electronic Charge ◽

X Ray Diffraction ◽

Optical Fields ◽

X Ray ◽

Photon Excitation ◽

Ionic Materials

Relocation of electronic charge plays a key role for functional processes in condensed-phase molecular materials. X-ray diffraction with a femtosecond time resolution allows for spatially resolving transient atomic arrangements and charge distributions [1]. In particular, time-dependent spatial maps of electron density have been derived from x-ray powder diffraction patterns measured with a 100 fs time resolution. In this talk, new results on electron dynamics in transition metal complexes and on field-driven charge relocations in elementary ionic materials will be presented. Crystals containing a dense array of Fe(II)-tris(bipyridine) complexes and their PF6 counterions display pronounced changes of electron density that occur within the first 100 fs after two photon excitation of a small fraction of the complexes [2]. Electron density maps reveal a transfer of electronic charge from the Fe atoms and - so far unknown - from the PF6 counterions to the bipyridine units. The charge transfer displays pronounced Coulomb-mediated many-body features, affecting approximately 30 complexes around the directly excited one. As a second topic, electron relocations induced by strong external optical fields will be discussed [1,3]. This interaction mechanism allows for generating coherent superpositions of valence and conduction band quantum states and inducing fully reversible charge dynamics. While the materials LiBH4 and NaBH4 display electron relocations from the (BH4)- ions to the neighboring Li+ and Na+ ions, LiH exhibits an electron transfer from Li to H. The latter is a manifestation of electron correlations and in agreement with theoretical calculations.

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Atomic and ionic radii: a comparison with radii derived from electron density distributions

Physics and Chemistry of Minerals ◽

10.1007/s002690050057 ◽

1997 ◽

Vol 24 (6) ◽

pp. 432-439 ◽

Cited By ~ 16

Author(s):

G. V. Gibbs ◽

Osamu Tamada ◽

M. B. Boisen Jr.

Keyword(s):

Electron Density ◽

Ionic Radii ◽

Density Distributions

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Electron density of KNiF3: analysis of the atomic interactions

Acta Crystallographica Section B Structural Science ◽

10.1107/s0108768199015529 ◽

2000 ◽

Vol 56 (2) ◽

pp. 197-203 ◽

Cited By ~ 8

Author(s):

Vladimir Tsirelson ◽

Yury Ivanov ◽

Elizabeth Zhurova ◽

Vladimir Zhurov ◽

Kiyoaki Tanaka

Keyword(s):

Electron Density ◽

Critical Points ◽

Topological Analysis ◽

Ionic Radii ◽

Bond Path ◽

Coordination Numbers ◽

Packed Layer ◽

Atomic Interactions ◽

Specific Shape ◽

Close Packed Layer

The topological analysis of the electron density in the perovskite KNiF3, potassium nickel trifluoride, based on the accurate X-ray diffraction data, has been performed. The topological picture of the atomic interactions differs from that resulting from the classic crystal chemistry consideration. The shapes of atoms in KNiF3 defined by zero-flux surfaces in the electron density are, in general, far from spherical. At the same time, their asphericity in the close-packed layer is very small. The topological coordination numbers of K and Ni are the same as the geometrical ones, whereas topological coordination for the F atom (6) differs from the geometrical value. The latter results from a specific shape of the Ni-atom basin preventing the bond-path formation between F atoms in the same atomic close-packed layer, in spite of the fact that the closest F—F distance is the same as K—F. Judging by the electron density value and curvature at the bond critical points, the K—F interaction in KNiF3 can be considered ionic, while the Ni—F bond belongs to the polar covalent type. No correlation of the topological ionic radii with crystal or ionic radii was found in KNiF3. Critical points in the electrostatic potential have also been studied.

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White-Light Coronal Structures: Streamers and CMEs

International Astronomical Union Colloquium ◽

10.1017/s0252921100025045 ◽

1994 ◽

Vol 144 ◽

pp. 82

Author(s):

E. Hildner

Keyword(s):

Emission Line ◽

Electron Density ◽

White Light ◽

Coronal Mass Ejections ◽

X Rays ◽

Solar Cycles ◽

Temperature Function ◽

X Ray ◽

Eclipse Observations ◽

Coronal Structures

AbstractOver the last twenty years, orbiting coronagraphs have vastly increased the amount of observational material for the whitelight corona. Spanning almost two solar cycles, and augmented by ground-based K-coronameter, emission-line, and eclipse observations, these data allow us to assess,inter alia: the typical and atypical behavior of the corona; how the corona evolves on time scales from minutes to a decade; and (in some respects) the relation between photospheric, coronal, and interplanetary features. This talk will review recent results on these three topics. A remark or two will attempt to relate the whitelight corona between 1.5 and 6 R⊙to the corona seen at lower altitudes in soft X-rays (e.g., with Yohkoh). The whitelight emission depends only on integrated electron density independent of temperature, whereas the soft X-ray emission depends upon the integral of electron density squared times a temperature function. The properties of coronal mass ejections (CMEs) will be reviewed briefly and their relationships to other solar and interplanetary phenomena will be noted.

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