square planar

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The general structure of a square planar molecule, with the central atom labelled pink.
The square planar molecular geometry in chemistry describes the stereochemistry (spatial arrangement of atoms) that is adopted by certain chemical compounds. As the name suggests, molecules of this geometry have their atoms lying in a square about a central atom.

Relatively few compounds adopt this geometry, but these species are often notable and even useful, examples being the first noble gas compound XeF4 and the anticancer drug Cisplatin (PtCl2(NH3)2).

This geometry can be visualised as resulting from the removal of a pair of ligands from the z-axis of an octahedron, leaving four ligands in the x-y plane. For transition metal compounds, the orbital splitting diagram for square planar geometry can thus be derived from the octahedral diagram. The removal of the two ligands stabilizes the dz2 level, leaving the dx2-y2 level as the most destabilized. Consequenly the dx2-y2 remains unoccupied in complexes of metals with the d8 configuration. These compounds typically have 16 valence electrons (eight from ligands, eight from the metal). Examples include Vaska's complex, Zeise's salt and Crabtree's catalyst.[1]

See also

  • For the other possible molecular geometries: AXE method.

References

1. ^ G. L. Miessler and D. A. Tarr “Inorganic Chemistry” 3rd Ed, Pearson/Prentice Hall publisher, ISBN 0-13-035471-6.
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Xenon tetrafluoride, XeF4, is one of the few chemical compounds involving a noble gas. It was the first discovered binary compound containing a noble gas. It is formed by the reaction of Xe and F2 in the ratio of 1 mol Xe to 2 mol F2.
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Cisplatin, cisplatinum or cis-diamminedichloroplatinum(II) (CDDP) is a platinum-based chemotherapy drug used to treat various types of cancers, including sarcomas, some carcinomas (e.g. small cell lung cancer, and ovarian cancer), lymphomas and germ cell tumors.
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In chemistry, a ligand is an atom, ion, or molecule (see also: functional group) that generally donates one or more of its electrons through a coordinate covalent bond to, or shares its electrons through a covalent bond with, one or more central atoms or ions (these ligands act as
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An octahedron (plural: octahedra) is a polyhedron with eight faces. A regular octahedron is a Platonic solid composed of eight equilateral triangles, four of which meet at each .

The octahedron's symmetry group is Oh, of order 48.
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Electron counting is a formalism used for classifying compounds and for explaining or predicting electronic structure and bonding. Many rules in chemistry rely on electron-counting:

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Vaska's complex is the trivial name for trans-chlorocarbonylbis(triphenylphosphine)iridium(I) with the formula IrCl(CO)[P(C6H5)3]2.
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Zeise's salt is the chemical compound with the formula K[PtCl3(C2H4)].H2O. This air-stable, yellow, coordination complex contains an η2-ethylene ligand.
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Crabtree's catalyst is the name given to a complex of iridium with 1,5-cyclooctadiene, tris-cyclohexylphosphine, and pyridine. It is a homogeneous catalyst for hydrogenation reactions, developed by Robert H. Crabtree, a professor at Yale University.
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In chemistry, the AXE method is commonly used in formatting molecules to fit the VSEPR model that aims to explain molecular geometry.

The A represents the central atom and always has an implied subscript one.
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