Equatorial ligand plane perturbations lead to a spin-state change in an iron(iii) porphyrin dimer.

A complete reversal of the spin state of iron(iii) is observed upon a small change to the diporphyrin bridge from ethane to ethene by keeping all other factors intact. Combined analysis using single crystal X-ray structure determination, Mossbauer, variable-temperature magnetic, H-1 NMR and EPR studies has confirmed the spin states of iron(iii) complexes both in solid and solution phases.