Isomerism in . Write the formulas for the following coordination compounds: (i) Tetraamminediaquacobalt(III) chloride (ii) Potassium tetracyanidonickelate(II) (iii) Tris(ethane– , –diamine) chromium(III) chloride (iv) Amminebromidochloridonitrito-N-platinate(II) (v) Dichloridobis(ethane– , –diamine)platinum(IV) nitrate (vi) Iron(III) hexacyanidoferrate(II) . Write the IUPAC names of the following coordination compounds: (i) [Co(NH ) ]Cl (ii) [Co(NH ) Cl]Cl (iii) K [Fe(CN) ] (iv) K [Fe(C O ) ] (v) K [PdCl ] (vi) [Pt(NH ) Cl(NH CH )]Cl . .
Geometric Isomerism Fig. . : Geometrical isomers (cis and trans) of Pt [ NH ) Cl ] Co Cl Cl N H N H N H N H + Co Cl Cl N H N H N H N H + cis trans Fig. .
: Geometrical isomers (cis and trans) of [ Co ( NH ) Cl ] + This type of isomerism also arises when didentate ligands L – L [ e.g., NH CH CH NH (en)] are present in complexes of formula [MX (L – L) ] (Fig. . ). Another type of geometrical isomerism occurs in octahedral coordination entities of the type [Ma b ] like [Co(NH ) (NO ) ].
If three donor atoms of the same ligands occupy adjacent positions at the corners of an octahedral face, we have the facial (fac) isomer . When the positions are around the meridian of the octahedron, we get the meridional (mer) isomer (Fig. . ).
Fig. . : Geometrical isomers (cis and trans) of [CoCl (en) ] Why is geometrical isomerism not possible in tetrahedral complexes having two different types of unidentate ligands coordinated with the central metal ion ? Tetrahedral complexes do not show geometrical isomerism because the relative positions of the unidentate ligands attached to the central metal atom are the same with respect to each other.
Optical isomers are mirror images that cannot be superimposed on one another. These are called as enantiomers . The molecules or ions that cannot be superimposed are called chiral . The two forms are called dextro (d) and laevo (l) depending upon the direction they rotate the plane of polarised light in a polarimeter ( d rotates to the right, l to the left).
Optical isomerism is common in octahedral complexes involving didentate ligands (Fig. . ). In a coordination entity of the type [PtCl (en) ] + , only the cis -isomer shows optical activity (Fig.
Optical Isomerism Fig. . : Optical isomers (d and l) of [Co(en) ] + Fig. .
Optical isomers (d and l) of cis- [PtCl (en) ] + Fig. . The facial (fac) and meridional (mer) isomers of [Co(NH ) (NO ) ]