Modulation of iron spin in ethane-bridged diiron(III) porphyrin dimer: anion dependent spin state switching

  • Firoz Shah Tuglak Khan
  • Anjani Kumar Pandey
  • Sankar Prasad Rath
Regular Article


The multiheme cytochrome c involves extensive interaction among the heme centers to enable them to perform a wide variety of enzymatic activities. In an attempt to exploit such heme–heme interactions in the synthetic diheme, an ethane-bridged diiron(III) porphyrin dimer has been utilized that can switch easily between syn and anti conformations due to highly flexible nature of the bridge. Upon protonation using 5% aqueous Brønsted acid, the dichloromethane solution of diiron(III)-\(\upmu \)-oxo porphyrin dimer immediately changes its color from green to red leading to the formation of a series of \(\upmu \)-hydroxo complexes. However, long exposure of the Brønsted acid converts the \(\upmu \)-hydroxo complex to five-coordinate diiron(III) porphyrin dimer in which the counter anion switches its position to act as an axial ligand. In the present study, the investigation has been extended further using Brønsted acids containing strongly coordinating anions such as \(\hbox {HN}_{3}\), HNCS and l-(+)-Lactic acid (HLA) in which the anions eventually coordinate to iron centers directly as axial ligands. A comprehensive account of the anion-mediated spin state change in the ethane-bridged diiron(III) porphyrin dimer has also been presented here.

Graphical Abstract

SYNOPSIS Anion has been found to induce dramatic change in the structure and properties in the ethane-bridged diiron(III) porphyrin dimer including the spin state of the central metal ion. A brief comprehensive account of such anion-dependent spin state change has also been presented here.


Diiron(III) porphyrin dimer spin state axial ligand counter anion structure elucidation 



We are thankful to the Department of Science and Technology, Government of India and Council of Scientific and Industrial Research (CSIR), New Delhi for financial support. F.S.T.K. thanks University Grants Commission (UGC), India and A.K.P. thanks CSIR, India for their fellowships.


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Copyright information

© Indian Academy of Sciences 2018

Authors and Affiliations

  1. 1.Department of ChemistryIndian Institute of Technology KanpurKanpurIndia

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