Why is geometrical isomers not possible in tetrahedral complexes having two different types of unidentate ligands?

Geometrical isomerism in complexes of co-ordination number 4:• Complexes having co-ordination number 4 adopt tetrahedral or square planar geometry.  • Geometrical isomerism is not possible in tetrahedral complexes.  • Square planar complexes of the type MA2X2, MA2XY, MABX2, MABXY can exist as geometrical isomers.  www.sakshieducation.comwww.sakshieducation.com(Here A and B are neutral ligands such as H2O, NH3, CO, NO, C2H5N whereas X and Y are anionic ligands such as Cl–, NO2–, CN–, SCN–1 etc.) 1) [PtCl2(NH3)2]    Trans (Dark yellow)PtNH3ClClH3NPtNH3NH3ClClCis-(Pale yellow)2) [PtCl(C5H5N)2(NH3)]   PtNH3PyPyClTransPtNH3ClPyPyCis   • Geometrical isomerism is also shown by o

Geometrical isomerism is also shown by octahedron complexes in which the co-ordination number of the central metal atom is 6. • MA2X4, MA4X2, MA4XY etc. types of complexes exhibit geometrical isomerism. Ex:  [CoCl2(NH3)4]+ClNH3PtClNH3H3NH3NCis-(Violet)ClPtNH3NH3H3NH3NTrans(Green)Cl2) [Fe(CN)4 (NH3)2]– FeNH3CNNCNCCisNH3CN NH3FeCNCNNCNCTransNH3• Octahedral complexes of the type [MA3B3] like [Co(NO2)3(NH3)3] also exist in two geometrical isomers.  • When the three ligands (with same donor atoms) are on the same triangular face of the octahedron, the isomer is called facial or fac isomer. • When the three ligands are on the same equatorial plane of the octahedron i.e. around the meridian of the octahedron, the isomer is called meridional or merisomer. Ex : [CoCl3(NH3)3]

Tetrahedral complexes do not show geometrical isomerism because the relative positions of unidentate ligands attached to the central atom are same with respect to each other.