Draw all the isomers of an octahedral complex that has three identical bidentate ligands.

Draw the energy level diagrams and indicate the occupancy of the orbitals in the following complexes.

(a) ${\mathrm{d}}^6$, octahedral, low spin
(b) ${\mathrm{d}}^{\text{9}}$, octahedral with tetragonal elongation
(c) ${\mathrm{d}}^8$, square planar
(d) ${\mathrm{d}}^6$, tetrahedral

Calculate the difference in crystal field stabilization energy (in unit of ${\mathrm{\Delta }}_{\mathrm{o}}$) between the complexes (a) and (d), assuming that the ligands are strong field ligands.

(Answer: octahedral $-2.4 {\mathrm{\Delta }}_{\mathrm{o}}$, tetrahedral $-0.27 {\mathrm{\Delta }}_{\mathrm{o}}$, difference $-2.13 {\mathrm{\Delta }}_{\mathrm{o}}$)