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Krogmann's salt is a
Krogmann's salt is a series of partially
linear chain compound
222px, Magnus's green salt is an example of a linear chain compound.
In chemistry and materials science, linear chain compounds are materials composed of one-dimensional arrays of metal-metal bonded molecules or ions. Such materials exhibit ...
consisting of stacks of tetracyanoplatinate. Sometimes described as molecular wires, Krogmann's salt exhibits highly anisotropic electrical conductivity. For this reason, Krogmann's salt and related materials are of some interest in nanotechnology
Nanotechnology, also shortened to nanotech, is the use of matter on an atomic, molecular, and supramolecular scale for industrial purposes. The earliest, widespread description of nanotechnology referred to the particular technological goal ...
.
History and nomenclature
Krogmann's salt was first synthesized by Klaus Krogmann in the late 1960s. Krogmann's salt most commonly refers to a platinum metal complex of the formula K2 t(CN)4X0.3where X is usuallybromine
Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table ( halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simi ...
(or sometimes chlorine
Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...
). Many other non-stoichiometric
Stoichiometry refers to the relationship between the quantities of reactants and products before, during, and following chemical reactions.
Stoichiometry is founded on the law of conservation of mass where the total mass of the reactants equ ...
metal salts containing the anionic
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
complex t(CN)4sup>n− can also be characterized.
Structure and physical properties
Krogmann's salt is a series of partially oxidized
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
tetracyanoplatinate complexes linked by the platinum-platinum bonds on the top and bottom faces of the planar t(CN)4sup>n− anions. This salt forms infinite stacks in the solid state based on the overlap of the dz2 orbitals.
Krogmann's salt has a tetragonal
In crystallography, the tetragonal crystal system is one of the 7 crystal systems. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a squar ...
crystal structure with a Pt-Pt distance of 2.880 angstroms, which is much shorter than the metal-metal bond distances in other planar platinum complexes such as Ca t(CN)4·5H2O (3.36 angstroms), Sr t(CN)4·5H2O (3.58 angstroms), and Mg t(CN)4·7H2O (3.16 angstroms). The Pt-Pt distance in Krogmann's salt is only 0.1 angstroms longer than in platinum metal.Heger, G.; Deiseroth, H.J.; Schulz, H. "Combined X-ray and neutron diffraction study of K2 (Pt(CN)4)X0.3.3(H2O) with X= Br, Cl (KCP) between 31 K and room temperature" Acta Crystallographica B 1982, volume 24,1968-38. (1978) 34, p725-p731.
Each unit cell
In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector, for example) does not necessaril ...
contains a site for Cl−, corresponding to 0.5 Cl− per Pt. However, this site is only filled 64% of the time, giving 0.32 Cl− per Pt in the actual compound. Because of this, the oxidation number
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...
of Pt does not rise above +2.32.
Krogmann's salt has no recognizable phase range and is characterized by broad and intense intervalence bands in its electronic spectra.
Chemical properties
One of the most widely researched properties of Krogmann's salt is its unusual electric conductance. Because of its linear chain structure and overlap of the platinum orbitals, Krogmann's salt is an excellent conductor ofelectricity
Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as describe ...
. This property makes it an attractive material for nanotechnology.
Preparation
The usual preparation of Krogmann's salt involves the evaporation of a 5:1 molar ratio mixture of the salts K2 t(CN)4and K2 t(CN)4Br2in water to give copper-colored needles of K2 t(CN)4r0.32·2.6 H2O. ::5K2 t(CN)4+ K2 t(CN)4Br2+ 15.6 H2O → 6K2 t(CN)4r0.32·2.6 H2O Because excess PtII or PtIV complex crystallizes out with the product when the reactant ratio is changed, the product is therefore well defined, although non-stoichiometric.Uses
Krogmann's salt nor any related material has found any commercial applications.References