Definition: Coordination Compounds
Coordination compounds are those molecular compounds which retain their identity in solid as well as in aqueous solution. In these compounds, metals or atoms are bonded to a number of anions or neutral molecules by a coordinate bond.
Define Lewis bases and Lewis acids with respect to a coordination compound.
Lewis bases: The ligands being electron pair donors are Lewis bases.
Lewis acids: The central metal ion, as an electron-pair acceptor, serves as a Lewis acid. For example, in the coordination compound [Cu(NH3)4]2+, NH3 is a Lewis base, and Cu2+ is a Lewis acid.
Definition: Ligand
A ligand is a molecule, ion or group that is bonded to the metal atom or ion in a complex or coordination compound by a coordinate bond.
Define monodentate ligand.
A monodentate ligand is one in which a single donor atom shares an electron pair with the centre metal ion to create a coordinate bond.
In the coordination compound, the species surrounding the central metal atom or ion are called ligands.
Define Anionic sphere complex.
A negatively charged coordination sphere or a coordination compound having a negatively charged coordination sphere is called anionic complex or anionic sphere complex.
Define coordination number.
Coordination number is the number of ligand donor atoms directly bonded to the central metal atom or ion in a complex.
Example: In [Co(NH3)5Cl]2+, the coordination number of cobalt (Co) is 6 because 5 ammonia molecules and 1 chloride ion are attached to it.
Define coordination sphere. Give example.
The central metal ion and ligands linked to it are enclosed in a square bracket. This is called a coordination sphere. This is a discrete structural unit. The ionisable groups shown outside the bracket are the counter ions. For example, the compound K4[Fe(CN)6] has [Fe(CN)6]4- coordination sphere with the ionisable K⊕ ions representing counter ions.
Definition: Effective Atomic Number (EAN) Rule
The total number of electrons present on the central metal atom/ion, including those gained by it in bonding, is called EAN.
Definition: Isomerism
Isomerism is the phenomenon in which compounds have the same molecular formula but differ in their physical or chemical properties due to a different arrangement of atoms or groups in space or structure.
Define the term Hydrated isomers.
Isomers in which there is exchange of solvent (water) ligands between coordination and ionization spheres are called hydrate isomers.
Two or more coordination compounds which contain the same number and types of atoms, and bonds (i.e., the connectivity between atoms is the same), but which have different spatial arrangements of the atoms are called distereoisomers.
Define the term Co-ordination isomer.
Isomers which show interchange of ligands between cationic and anionic spheres of different metal ions are called co-ordination isomers.
Definition: Homoleptic complex
A complex containing only one type of ligand attached to the central metal ion is called a homoleptic complex.
Definition: Heteroleptic complex
A complex containing more than one type of ligand attached to the central metal ion is called a heteroleptic complex.
Definition: Cationic complex
A complex having a positively charged coordination sphere is called a cationic complex.
Definition: Strong field ligands
Ligands that cause large splitting of d-orbitals and pairing of electrons are called strong field ligands.
Definition: Weak field ligands
Ligands that cause small splitting of d-orbitals and do not cause pairing of electrons are called weak field ligands.
Definition: Effective atomic number (EAN)
The total number of electrons surrounding the central metal ion after complex formation is called the effective atomic number (EAN).
EAN = number of electrons of metal ion + total number of electrons donated by ligands
= atomic number of metal (Z) - number of electrons lost by metal to form the ion (X) + number of electrons donated by ligands (Y).
= Z - X + Y
Definition: Coordination compound
A compound in which a central metal atom or ion is surrounded by ligands bonded through coordinate bonds is called a coordination compound.
Definition: Ligand
An ion or molecule that donates a pair of electrons to the central metal atom or ion to form a coordinate bond is called a ligand.
Definition: Monodentate ligand
A ligand that contains only one donor atom and forms only one coordinate bond with the central metal ion is called a monodentate ligand.
Definition: Ambidentate ligand
A ligand that can coordinate to the metal through two different donor atoms but only one at a time is called an ambidentate ligand.
Definition: Coordination number
The number of ligand donor atoms directly bonded to the central metal ion in a complex is called the coordination number.
Definition: Coordination complex
A compound that retains its identity in solution and does not completely dissociate into simple ions is called a coordination complex.
Definition: Anionic complex
A complex having a negatively charged coordination sphere is called an anionic complex.
Definition: Neutral complex
A complex having no charge on the coordination sphere is called a neutral complex.
Definition: Linkage isomerism
Isomerism arising due to different donor atoms of the same ligand is called linkage isomerism.
Definition: Coordination isomerism
Isomerism arising due to interchange of ligands between cationic and anionic complexes is called coordination isomerism.
Definition: Solvate (hydrate) isomerism
Isomerism arising due to the presence of solvent molecules inside or outside the coordination sphere is called solvate (hydrate) isomerism.
Definition: Geometrical isomerism
Isomerism in which ligands differ in their spatial arrangement around the central metal ion is called geometrical isomerism.
Definition: Optical isomerism
Isomerism in which two compounds are non-superimposable mirror images of each other is called optical isomerism.
Definition: Chelation
The removal of metal ions from solution by forming stable coordination complexes is called chelation.
Definition: Electroplating
The process of depositing a thin layer of metal over another material using coordination compounds is called electroplating.
Definition: Ionization isomerism
Isomerism arising due to exchange of ligands between coordination sphere and ionization sphere is called ionization isomerism.
Definition: Polydentate ligand
A ligand that contains two or more donor atoms and forms multiple coordinate bonds with the central metal ion is called a polydentate ligand.
