Transition metal complexes facial isomers

The preference for the cis and facial structures has been explained as arising from strong 4,-t4 bonding between the metal and sulfur atoms transition metal ions can form two 7t-bonds at 90° and, consequently, of the isomeric cis and irons structures, wherein only the two sulfur atoms of the four donor atoms can form d -d bonds, the cis isomer is the more stable. An alternative explanation is that the cis configuration is due to weak non-bonded S—S interaction. Recent dipole moment and and F NMR data on Ga and In complexes indicate a facial-meridional (cis-trans) equiUbrium in solution. For these non-transition elements d -d bonding cannot arise consequently, the explanation of d -d stabilization of the configurations for transition metal complexes appears to be the correct one. 

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