Symbiosis (chemical)
Encyclopedia
The biological term Symbiosis
Symbiosis
Symbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...

 was adopted for chemistry by Jøergensen in 1964, who applied it to the process by which, say, a hard
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....

 ligand on a metal predisposes the metal to receive another hard
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....

 ligand rather than a soft
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....

 ligand. In fact, two superficially antithetical phenomena occur: symbiosis and antisymbiosis.

Chemical antisymbiosis

This is found principally with soft
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....

 metals. Two soft
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....

 ligands in mutual trans
Trans effect
In inorganic chemistry, the trans effect is the labilization of ligands that are trans to certain other ligands, which can thus be regarded as trans-directing ligands...

 position will have a destabilizing effect on each other. The effect is also found with borderline metals in the presence of high trans effect
Trans effect
In inorganic chemistry, the trans effect is the labilization of ligands that are trans to certain other ligands, which can thus be regarded as trans-directing ligands...

 ligands. As illustration, the Selenocyanate ion trans
Trans effect
In inorganic chemistry, the trans effect is the labilization of ligands that are trans to certain other ligands, which can thus be regarded as trans-directing ligands...

 to the soft
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....

 carbon dioxide in trans
Trans effect
In inorganic chemistry, the trans effect is the labilization of ligands that are trans to certain other ligands, which can thus be regarded as trans-directing ligands...

-Rh(PPh3)2(CO)(NCSe) bonds via the Nitrogen, the harder
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....

 of its two donors. The phenomenon may be explained in terms of a trans influence
Trans effect
In inorganic chemistry, the trans effect is the labilization of ligands that are trans to certain other ligands, which can thus be regarded as trans-directing ligands...

:
“With two π-acid ligands in mutual trans positions
Trans effect
In inorganic chemistry, the trans effect is the labilization of ligands that are trans to certain other ligands, which can thus be regarded as trans-directing ligands...

 at a class-b metal, there would be a destabilizing competition for the dπ electrons on the metal. A π-acid bonded to a soft
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....

 metal thus makes a metal a harder
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....

 Lewis acid. Similarly a soft
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....

 σ-donor will tend to polarize the electron density on a soft
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....

 metal, causing it to favour an electrovalently bonded ligand in the trans position
Trans effect
In inorganic chemistry, the trans effect is the labilization of ligands that are trans to certain other ligands, which can thus be regarded as trans-directing ligands...

.”

Chemical symbiosis

This effect occurs with class-a metals such as Iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

(II). The Cyclopentadienyl complex (C5H5)Fe(CO)2(SCN is a typical example. The Cyclopentadienyl directing the Selenocyanate to bond through its softer
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....

 Selenium donor. A more definitive example are the Halopentamminocobalt(III) ions, Co(NH3)5X2+, which are more stable when the halogen, X, is Fluoride
Fluoride
Fluoride is the anion F−, the reduced form of fluorine when as an ion and when bonded to another element. Both organofluorine compounds and inorganic fluorine containing compounds are called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are...

 than with [Iodine], and the Halopentcyanocobalt(III) ions, Co(CN)5X3-, which are most stable when the halogen is [Iodine].
Hard
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....

 bases (electronegative donor atoms) retain their valence (outer shell) electrons when attached to a given central metal ion, thus enabling the metal ion to retain more of its positive charge, making it a hard
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....

 Lewis acid. With soft
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....

 bases the central metal atom is made a softer
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....

 Lewis acid, because the metal’s positive charge is reduced by delocalization of electron density from the ligand into the ligand-metal bond. But we have the distinction that with a class-a metal there is little concomitant polarization of the electron density away from the trans position
Trans effect
In inorganic chemistry, the trans effect is the labilization of ligands that are trans to certain other ligands, which can thus be regarded as trans-directing ligands...

 of the metal. In addition, symbiosis, unlike antisymbiosis, is probably not specifically trans
Trans effect
In inorganic chemistry, the trans effect is the labilization of ligands that are trans to certain other ligands, which can thus be regarded as trans-directing ligands...

directional, and is just as effective in, say, tetrahedral complexes.”
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