The range of complexes is extremely wide.According to their structural characteristics, complexes can be divided into the following types: simple complexes, chelates, polynuclear complexes, carbonyl complexes, metal cluster complexes, sandwich complexes, and macrocyclic ligand complexes.
Sandwich complexes usually refer to organometallic complexes consisting of metal atoms and conjugated ligands on both sides, with a plate core plate structure.The anti sandwich complex is composed of a conjugated ligand in the center and metal atoms on both sides of the ligand, with a core plate core structure.[1]
First synthesis
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The first sandwich complex prepared in 1951 was dicyclopentadienyl iron (II).
structure
Cyclopentadiene is a planar molecule with delocalized π bond, CfiveHfiveNa is its sodium salt, cyclopentadiene ion (CfiveHfive-) is also called Mao, so (CfiveHfive）twoFe (II) is commonly known as ferrocene, and its structure is determined by X-ray as: ferrous ion is sandwiched between two opposite parallel cyclopentadienes to form the so-called sandwich complex.
nature
It is a kind of non-polar and very stable solid, as aromatic as benzene.Ferrocene is an orange crystal with a melting point of 173-174 degrees. It is easy to sublimate, insoluble in water and soluble in organic solvents.
application
Ferrocene and its derivatives can be used as additives for rocket fuel, shock absorber for gasoline, curing agent for silicone resin and rubber, and ultraviolet light absorber.[1]
Knowledge expansion
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Definition of complex
To illustrate what is a complex, let's first look at the experiment of dropping excessive ammonia into copper sulfate solution.Drop ammonia into the test tube containing copper sulfate solution, shake while adding. At the beginning, a large amount of sky blue precipitates are generated. When you continue to drop ammonia, the precipitates gradually disappear, and a dark blue transparent solution is obtained.If NaOH solution is added to this dark blue solution, no azure copper hydroxide precipitates, but if a small amount of barium chloride solution is added to this solution, white barium sulfate precipitates.This indicates that sulfate ion exists in the solution, but copper ion can hardly be detected.
Add ethanol to the dark blue solution, and dark blue crystals will precipitate immediately.According to X-ray analysis, the chemical composition of the dark blue crystal is [Cu (NHthree)four]S0four·Htwo0。It can be completely dissociated into negative divalent [Cu (NHthree)four]Ion and sulfate ion, while the former is a complex ion formed by the combination of one copper ion and four ammonia molecules.Such complex ions are called coordination individuals.
Generally, complex ions (or molecules) that are not easy to dissociate formed by coordination bonds between central atoms or cations with empty orbits and ligands (possibly anions or neutral molecules) that can provide lone electron pairs are called coordination individuals.The coordination individuals can be neutral molecules or charged ions.The neutral coordination individual without charge is also called coordination molecule, which is itself a complex.The charged coordination individuals are called coordination ions, and the positively charged coordination individuals are called coordination cations;The anion with negative charge is called anion.
The corresponding compounds and neutral coordination individuals formed by charged coordination individuals are collectively referred to as complexes (the charged coordination individuals are also known as complexes).Such as [Cu (NHthree)four]S0fourIt is a complex.
Composition of complexes
The complex is composed of inner and outer parts.The inner boundary is the characteristic part (i.e. coordination individual) of the complex, which is a relatively stable whole in solution, and is indicated in square brackets in the chemical formula of the complex.The ions outside the square brackets form the outside of the complex, and the inside and outside are bound by ionic bonds.The total charge of the inner boundary and the external ions is equal, but the sign is opposite.Obviously, neutral coordination individuals have only internal boundaries and no external boundaries.With [Cu (NHthree)four]S0fourFor example, its composition can be expressed as
