Coordination Compounds-2 Flashcards
Coordination entity
A coordination entity constitutes a central metal atom or ion bonded
to a fixed number of ions or molecules.
example of Coordination entity
[CoCl3(NH3)3 ]
is a coordination entity in which the cobalt ion is surrounded by
three ammonia molecules and three chloride ions.
Coordination sphere
The central atom/ion and the ligands attached to it are enclosed in
square bracket and is collectively termed as the coordination
sphere.
The ionisable groups are written outside the bracket and
are called counter ions.
Example for coordination sphere and counter ion
For example, in the complex K4
[Fe(CN)6 ],
the coordination sphere is [Fe(CN)6]4– and the counter ion is K+.
Coordination polyhedron
The spatial arrangement of the ligand atoms which are directly
attached to the central atom/ion defines a coordination
polyhedron about the central atom. The most common
coordination polyhedra are octahedral, square planar and
tetrahedral.
example for Coordination polyhedron
For example, [Co(NH3)6]3+ is octahedral, [Ni(CO)4 ] is
tetrahedral and [PtCl4]2– is square planar.
Oxidation number of central atom
The oxidation number of the central atom in a complex is defined
as the charge it would carry if all the ligands are removed along
with the electron pairs that are shared with the central atom.
Homoleptic complexes
Complexes in which a metal is bound to only one kind of donor
groups, e.g., [Co(NH3)6]3+, are known as homoleptic.
Central atom/ion
In a coordination entity, the atom/ion to which a fixed number
of ions/groups are bound in a definite geometrical arrangement
around it, is called the central atom or ion
These central atoms/ions are also referred to as Lewis acids.
Ligands
The ions or molecules bound to the central atom/ion in the
coordination entity are called ligands.
unidentate
When a ligand is bound to a metal ion through a single donor
atom, as with Cl–, H2
O or NH3
, the ligand is said to be unidentate.
didentate
When a ligand is bound to a metal ion through two donor atoms, as with (ethane-1,2-diamine) or (oxalate)
, the ligand is said to be didentate.
polydentate
When a ligand is bound to a metal ion through several donor atoms, as as in N(CH2CH2NH2)3
, the ligand is said to be polydentate.
chelate ligand
When a di- or polydentate ligand uses its two or more donor
atoms simultaneously to bind a single metal ion, it is said to be a
chelate ligand.
denticity of the ligand
The number of such ligating groups is called the
denticity of the ligand.
