Alfred Stock hydrates study pioneer for Boron, Silicon

Alfred Stock – pioneer in boron hydrides studies

Article on Alfred Stock  pioneer studying  hydrates

Biography & contributions

Alfred Stock, a German inorganic chemist born on July 16, 1876 – died on August 12, 1946. Alfred was pioneer in the fields of research on the hydrides of boron and silicon, coordination chemistry, mercury, and mercury poisoning.

Alfred prepared metallic beryllium by electrolyzing a fused mixture of sodium and beryllium fluorides. Alfred in the year of 1916 coined the term in ligand in coordination chemistry field. Other important topics in coordination chemistry which he worked are bite angle and chelation concepts.

Alfred was extensively worked on boron hydrogen chemical compounds and hydrides of silicon and also he was the co-discoverer of silicon boride.


Ligands are ions or neutral molecules that bond to a central metal atom or ion. Ligands act as Lewis bases (electron donors), and the central atom acts as a Lewis acid (electron acceptor). Ligands have at least one donor atom with an electron pair used to form covalent bonds with the central atom. Anions, cations, or neutral molecules can act as ligands.

Ligands nomenclature includes following patterns

[1] If a complex has an ion ligand, an "-o" ending is added.


"-ide" is changed to "-o," "-ite" is changed to "-ito", and "-ate" to "-ato."

Bromide ion (Br-) – bromo

Nitrite ion (NO2-) - nitrito

Sulfate ion (SO42-) - sulfato

[2] When a complex has a neutral molecule ligand, the molecule keeps its original name.


Ethylenediamine is a ligand, and the ligand is still called ethylendiamine.

[3] Prefixes mono=1, di=2, tri=3, tetra=4, penta=5, and hexa=6, are used to specify the number of ligands.

[4] If a ligand name has a prefix within itself such as ethylendiamine, place a parenthesis around the name and add bis=2, tris=3, tetrakis=4, in front of the molecule.


If there was 2 (en) molecules, the name would be bis(ethylenediamine).

[5] When naming a complex, ligands are the first to be named. If there is more than one ligand, list them in alphabetical order, next comes the metal ion or atom. The oxidation state follows the name in roman numerals.

Types of ligands

Ligands are classified based on number of donor which allows them to bind to a central metal atom or ion.

  • Monodentate ligands
  • Ambidentate Ligands
  • Bidentate ligands
  • Tridentate ligands
  • Polydentate ligands

Monodentate Ligands

A monodentate ligand has only one donor atom used to bond to the central metal atom or ion. The term "monodentate" can be translated as "one tooth," referring to the ligand binding to the center through only one atom.


  • Chloride ions
  • Fluorine ions
  • Bromide ions
  • Hydroxide ions
  • Cyanide ions
  • Ammine ions

Ambidentate Ligands

Ambidentate ligands are monodentate ligands that have can bind in two possible places.


[1] Nitrate ion NO2- can bind to the central metal atom/ion at either the nitrogen atom or one of the oxygen atoms

[2] Thiocyanate ion, SCN- can bind to the central metal at either the sulfur or the nitrogen.

Bidentate Ligands

Bidentate ligands have two donor atoms which allow them to bind to a central metal atom or ion at two points.



Tridentate Ligands


Tridentate ligands have three atoms capable of binding to a central metal atom or ion.



Polydentate Ligands

Polydentate ligands range in the number of atoms used to bond to a central metal atom or ion.


EDTA - EDTA, a hexadentate ligand / polydentate ligand that has six donor atoms with electron pairs that can be used to bond to a central metal atom or ion.


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