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Structure of iodine heptafluoride, an example of a molecule with the pentagonal-bipyramidal coordination geometry. In chemistry, a pentagonal bipyramid is a molecular geometry with one atom at the centre with seven ligands at the corners of a pentagonal bipyramid. A perfect pentagonal bipyramid belongs to the molecular point group D 5h.
The crystallographic restriction theorem in its basic form was based on the observation that the rotational symmetries of a crystal are usually limited to 2-fold, 3-fold, 4-fold, and 6-fold. However, quasicrystals can occur with other diffraction pattern symmetries, such as 5-fold; these were not discovered until 1982 by Dan Shechtman .
The more precise mathematical definition is that there is never translational symmetry in more than n – 1 linearly independent directions, where n is the dimension of the space filled, e.g., the three-dimensional tiling displayed in a quasicrystal may have translational symmetry in two directions.
In chemistry, absolute configuration refers to the spatial arrangement of atoms within a molecular entity (or group) that is chiral, and its resultant stereochemical description. [1] Absolute configuration is typically relevant in organic molecules where carbon is bonded to four different substituents .
[18]: 1165 Examples of this include the octacyanomolybdate (Mo(CN) 4− 8) and octafluorozirconate (ZrF 4− 8) anions. [18]: 1165 The nonahydridorhenate ion (ReH 2− 9) in potassium nonahydridorhenate is a rare example of a compound with a steric number of 9, which has a tricapped trigonal prismatic geometry. [13]: 254 [18]
In chemistry, a molecule or ion is called chiral (/ ˈ k aɪ r əl /) if it cannot be superposed on its mirror image by any combination of rotations, translations, and some conformational changes. This geometric property is called chirality (/ k aɪ ˈ r æ l ɪ t i /).
An antiphase domain (APD) is a type of planar crystallographic defect in which the atoms within a region of a crystal are configured in the opposite order to those in the perfect lattice system. Throughout the entire APD, atoms sit on the sites typically occupied by atoms of a different species.
Bent's rule can be extended to rationalize the hybridization of nonbonding orbitals as well. On the one hand, a lone pair (an occupied nonbonding orbital) can be thought of as the limiting case of an electropositive substituent, with electron density completely polarized towards the central atom.