Bioinorganic Laboratory
Department of Chemistry
Indian Institute of Technology Kanpur

Selected Publications

1.     Silver(III)···Silver(III) Interaction Stabilizes the Syn-form in a Porphyrin Dimer Upon Oxidation

         A. K. Singh, F. S. T. Khan and S. P. Rath*

         Angew. Chem. Int. Ed. 2017, 56, 8849-8854. Full Article

Meeting at the bridge: Ethane-bridged silver(III) porphyrin dimer exhibits significant metallophilic interaction that brings two porphyrin rings on top of each other with short Ag(III)···Ag(III) distance attributed to the overlap of dz2 metal orbital. The complex displays an intense emission peak at 546 nm at 77 K in the photoluminescence study.

2.    A Highly Oxidized Cobalt Porphyrin Dimer: Spin Coupling and Stabilization of the Four-Electron Oxidation Product

         S. Dey, D. Sil and S. P. Rath*

         Angew. Chem. Int. Ed. 2016, 55, 996-1000. Full Article

Four to be sure: The oxidation of a cobalt(II) porphyrin dimer with iodine readily produced a cobalt(III) porphyrin π-cation radical dimer. Extensive π conjugation through the ethylene bridge led to several unusual spectral and geometrical features of this four-electron oxidized complex and stabilized the singlet state by enabling strong antiferromagnetic coupling between the π-cation radicals.

3.    Hydrogen Bonding Interactions Trigger a Spin-Flip in Iron(III)-Porphyrin Complexes

        D. Sahoo, M. G. Quesne, S. P. de Visser* and S. P. Rath*

        Angew. Chem. Int. Ed. 2015, 54, 4796-4800. Full Article

Spin control: The electronic structure of a five-coordinate iron(III) porphinato chloride has been found to depend on the presence of hydrogen-bonding interactions, with the iron center switching reversibly between a high (S=5/2) and intermediate spin (S=3/2) state. Computational calculations clearly support the experimentally assigned spin state.

4.     A Remarkably Bent Diiron(III)-μ-Hydroxo Bisporphyrin: Unusual Stabilization of Two Spin States of Iron in a Single Molecular Framework

         S. K. Ghosh and S. P. Rath*

         J. Am. Chem. Soc. 2010132, 17983-17985. Full Article

A novel diiron(III) bisporphyrin bridged by a single hydroxo group between two Fe-centers is reported in which the Fe-O(H)-Fe angle becomes the smallest ever reported in a Fe-porphyrin and two different spin states of Fe are stabilized in a single molecular framework, for the first time, although both cores have exactly the same chemical entity.

 5.    Oxidation Triggers Extensive Conjugation and Unusual Stabilization of Two Di-heme Dication Diradical Intermediates: Role of Bridging Group for Electronic Communication

         D. Sil, S. Dey, A. Kumar, S. Bhowmik and S. P. Rath*

         Chem. Sci. 2016, 7, 1212-1223. (Edge Article) Full Article

Unlike bis-Fe(IV) state in MauG, the 2e-oxidation has stabilized two ferric hemes, each coupled with a porphyrin cation radical. The extensive π-conjugation enables the generation of a charge resonance band ~1200 nm and allows antiferromagnetic coupling between iron and porphyrin radical spins of both rings.

6.  Oxo- and hydroxo-bridged diiron(III) porphyrin dimers: inorganic and bio-inorganic perspectives and effects of intermacrocyclic interactions        

          T. Guchhait, S. Sasmal, F. S. T. Khan and S. P. Rath *

          Coord. Chem. Rev. 2017, 337, 112-144.  Full Article

The fascinating chemistry of the oxo and hydroxo-bridged diheme centers, covalently connected through bridges varying in lengths and flexibility, has attracted much attention in recent times and a comprehensive review on their syntheses, structures and spectral properties is presented here.

7.    Multiheme Proteins: Effect of Heme-Heme Interactions

        D. Lai, F. S. T. Khan, and S. P. Rath*

        Dalton Trans. 2018, 47, ASAP  Full Article (Invited Frontier article)

This Frontier illustrates a brief personal account on the effect of heme-heme interaction in dihemes which thereby discloses some of the evolutionary design principles involved in multiheme proteins for its diverse structures and functions.

8.    Hydroxo-bridged diiron(III) and dimanganese(III) bisporphyrins: modulation of metal spins by counter anions

        F. S. T. Khan, T. Guchhait, S. Sasmal and S. P. Rath *

        Dalton Trans. 2017, 46, 1012-1037. (Invited Perspective and Front Cover Article) Full Article

A brief account has been presented on how the inter-heme interactions in μ-hydroxo diiron(III) bisporphyrins and counter anions can induce significant change in the structure and properties including the iron spin state without affecting the overall topology.

9.    An Ethane-bridged Porphyrin Dimer as Model of Di-heme Proteins: Inorganic and Bioinorganic Perspectives and Consequences of Heme-Heme Interactions

        D. Sil and S. P. Rath *

        Dalton Trans. 2015, 44, 16195-16211. (Invited Perspective Article)  Full Article

A brief account of our recent efforts on how inter-heme interactions can possibly change the structure and functional properties of the individual heme centers in a highly flexible ethane-bridged porphyrin dimer has been presented.

10.    Controlled generation of highly saddled (porphyrinato) iron(III) iodide, tri-iodide and one-electron oxidized complex

        D. Sahoo and S. P. Rath*

        Chem. Commun. 2015, 51, 16790-16793. Full Article

Three iron(III) porphyrinato complexes have been isolated selectively just by varying iodine concentration which eventually form admixed-intermediate (iodo complex), pure intermediate (tri-iodide complex) and high-spin (1e-oxidized complex) states of iron where iodide and/or tri-iodide used as axial ligands. Computational calculations clearly support the experimentally assigned spin state.

11.    Metal-coordination-driven Mixed Ligand Binding in Supramolecular Bisporphyrin Tweezers

        Sk. A. Ikbal, A. Dhamija and S. P. Rath*

        Chem. Commun. 2015, 51, 14107-14110. Full Article

The mixed ligand polymers of Mg(II)bisporphyrin with heterogeneous guest pairs have been synthesized just by mixing host and guests in one pot and structurally characterized. The guest ligands are bound selectively between inside and outside the bisporphyrin cavity.

12.    Step-wise induction, amplification and inversion of molecular chirality through the coordination of chiral diamines with Zn(II)bisporphyrin

          Sk. A. Ikbal, S. Brahma and S. P. Rath*

          Chem. Commun. 2015, 51, 895-898. Full Article

A clear structural rationalization of the origin of chirality transfer from an optically active diamine guest to an achiral Zn(II)bisporphyrin host in a 1:1 and 2:3 host-guest supramolecular complex has been demonstrated for the first time. During the process, chirality inversion along with amplification was observed.

13.    Transfer and Control of Molecular Chirality in the 1:2 Host-Guest Supramolecular Complex Consisting of Mg(II) bisporphyrin and Chiral Diols: Effect of H-bonding on Rationalization of Chirality

          Sk. A. Ikbal, S. Brahma and S. P. Rath*

          Chem. Commun. 2014, 50, 14037-14040. Full Article

Chiral diol substrate binds to Mg(II)bisporphyrin in an unusual endo-endo fashion due to inter- ligand H-bonding which eventually results in remarkably high amplitude bisignate CD signal.

14.    Induction of Supramolecular Chirality in Di-Zinc(II) Bisporphyrin via Tweezer Formation: Synthesis, Structure and Rationalization of Chirality

            S. Brahma, Sk. A. Ikbal, S. Dey and S. P. Rath*

            Chem. Commun. 201248, 4070-4072.  Full Article (Invited article in a special thematic issue 'Porphyrins and Phthalocyanines')


Two new supramolecular complexes consisting of an achiral bisporphyrin host and a chiral diamine guest are reported. One shows remarkably high amplitude of bisignate CD signal while other one shows very low value.

15.    Control of Spins by Ring Deformation in a Diiron(III)bisporphyrin: Reversal of ClO4- and CF3SO3- Ligand Field Strength on the Magnetochemical Series.

          S. Bhowmik, S. K. Ghosh and S. P. Rath*

          Chem. Commun. 201147, 4790-4792. Full Article

The complete reversal of the ligand field strength between ClO4- and CF3SO3- on the ‘magnetochemical’ series is observed in a diiron(III)bisporphyrin. While ClO4- gives typical high-spin complex, just by twisting the conformation of the macrocycle shows properties with pure intermediate-spin state with CF3SO3- although the axial ligand strengths suggest the reverse order of spin stabilization.

16.    Intermacrocyclic Interaction Triggers Facile One-pot Synthesis of a Chlorin-Porphyrin Heterodimer

          Y. A. Pandit, S. Sanfui and S. P. Rath *

          Chem. Eur. J. 2017, 23, 13415-13422.  Full Article

Highly reactive π-cation radicals: Intermacrocyclic interaction stimulates the quantitative one-pot synthesis of a new series of fully π-conjugated unsymmetric chlorin-porphyrin heterodimers by using mild oxidants such as iodine at room temperature.

17.    Probing Bis-FeIV MauG: Isolation of Highly Reactive Radical Intermediates

          T. Guchhait, S. Sarkar, Y. A. Pandit and S. P. Rath*

          Chem. Eur. J. (Communication) 2017, 23, 10270-10275. Full Article

Step-wise oxidations: Step-wise oxidations of a synthetic analog of diheme MauG enable isolation and structural characterizations of dication diradical, indolizinium-fused chlorin-porphyrin heterodimer and spiro-porphyrinato heterodimer. The active role played by the bridge in the electronic communication has been explored.

18. Cyclic Bisporphyrin Based Flexible Molecular Containers: Controlling Guest Arrangements and  Supramolecular Catalysis by Tuning Cavity Size

          P. Mondal, S. Sarkar and S. P. Rath*

          Chem. Eur. J. 2017, 23, 7093-7103. Full Article Highlighted in Synfacts 2017, 13, 816

Accommodating substrates: Three cyclic zinc(II) bisporphyrins (CB) with flexible linkers are employed as artificial molecular containers. Interestingly, the arrangements of the guests and the reactivity inside the containers are significantly influenced by the cavity size.

19.    Remarkable Anion Dependent Spin state Switching in Diiron(III)-μ-Hydroxo Bisporphyrins: What role do Counter ions play?

          F. S. T. Khan, A. K. Pandey and S. P. Rath*

          Chem. Eur. J. 2016, 22, 16124-16137. Full Article

All about the spin: The possible roles of the counter ion in controlling the spin state of iron in μ-hydroxo bisporphyrins are demonstrated. The counter ion has been shown to perturb the spin-state ordering through, for example, hydrogen-bonding interactions, switching between counter ion and axial ligand positions, ion-pair interactions, and charge polarization.

20.    Effect of Inter-porphyrin Distance on Spin-state in Diiron(III) μ-Hydroxo Bisporphyrins

          D. Sil, F. S. T. Khan and S. P. Rath*

          Chem. Eur. J. 2016, 22, 14585-14597. Full Article

Spot the difference: A series of diethyl pyrrole-bridged diiron(III) μ-hydroxo bisporphyrins that stabilize two equivalent iron(III) centers, unlike previously reported ethane-bridged analogues, are reported. Experimental evidence and DFT calculations indicate the increased inter-porphyrin distance in the diethyl pyrrole-bridged complexes as a factor for rendering the two iron(III) centers equivalent.

21.    Diiron(III)-μ-Fluoro Bisporphyrins: Effect of Bridging Ligand on the Metal Spin State

          D. Sil, A. Kumar and S. P. Rath*

          Chem. Eur. J. 2016, 22, 11214-11223. [Highlighted as Frontispiece (Hot Paper)] Full Article

Metalloporphyrins: A hitherto unknown family of diiron(III)-μ-fluoro bisporphyrins have been synthesized and structurally characterized, for the first time.

22.    Cyclic Zn(II)bisporphyrin Based Molecular Switch: Supramolecular Control of Complexation Mediated Conformational Switching and Photoinduced Electron Transfer

           P. Mondal and S. P. Rath*

           Chem. Eur. J. 2016, 22, 5607-5619. Full Article

Molecular switch: A cyclic zinc(II) bisporphyrin was employed as an efficient molecular switch under the regulation of π-acceptors and bidentate guests, which ultimately control the molecular orientation and charge-transfer process. During the process, two porphyrin rings also reversibly change their relative orientation between perpendicular and parallel.

23.    Unusual Stabilization of an Intermediate Spin of Iron upon Axial Phenoxide Coordination on a Diiron(III)bisporphyrin: Effect of Heme-Heme Interactions

           S. Bhowmik, S. Dey and S. P. Rath*

           Chem. Eur. J. 201319, 13732-13744. Full Article

Spin city: Five new phenolate complexes of diiron(III)bisporphyrin, in which 2,4,6-trinitrophenol stabilizes the pure intermediate-spin state (S=3/2) of iron, are reported for the first time. Similar coordination with the corresponding FeIII monoporphyrin only resulted in stabilization of the high-spin state.

24.    Effect of Heme-Heme Interactions and Modulation of Metal Spins by Counter Anions in a Series of Diiron(III)-μ-hydroxo Bisporphyrins: Unusual Stabilization of Two Different Spins in a Single Molecular Framework

          S. K. Ghosh, S. Bhowmik and S. P. Rath*

          Chem. Eur. J. 201319, 17846-17859. Full Article

Anion effect on diiron-bisporphyrin properties: A new family of five ethene-bridged diiron(III)-μ-hydroxo bisporphyrins with the same core structure but different counter anions is reported herein. In these complexes, two different spin states of Fe are stabilized in a single molecular framework.

25.    Protonation of an oxo-Bridged Diiron Unit Makes Two Iron Centers Different: A New Class of Diiron(III)-μ-hydroxo Bisporphyrin and Control of Spins by Counter Anions

          S. Bhowmik, S. K. Ghosh and S. P. Rath*

          Chem. Eur. J. 201218, 13025-13037. Full Article

The core of the matter: A previously unknown family of diiron(III)-μ-hydroxo bisporphyrins in which two different spin states of Fe are stabilized in a single molecular framework, even though both cores have identical molecular structures, is presented. The spin states were found to be dependent on the counterion.

26.  Encapsulation of TCNQ and Acridinium Ion within Bisporphyrin Cavity: Synthesis, Structure, Photophysical and HOMO-LUMO Gap Mediated Electron Transfer Properties

          A. Chaudhary and S. P. Rath*

          Chem. Eur. J. 201218, 7404-7417. Full Article

Donor-acceptor complexes: Donor–acceptor complexes, which were constructed from free base bisporphyrin (H4DEP) as a host, strongly encapsulated two electron-deficient guests, TCNQ and the acridinium ion, in its clefts. The extremely low electrochemically evaluated HOMO–LUMO gap in H4DEP•TCNQ led to facile electron transfer from the host to the guest at room temperature, whilst partial electron transfer took place in [H4DEP•AcH]ClO4.

27.    Efficient Complexation of Pyrrole-bridged Di-Zinc(II) Bisporphyrin with Fluorescent Probe Pyrene: Synthesis, Structure, and Photoinduced Singlet-Singlet Energy Transfer

          A. Chaudhary and S. P. Rath*

          Chem. Eur. J. 201117, 11478-11487. Full Article

Fluoroscent guest!: A dizinc(II) bisporphyrin encapsulates the fluorescent probe pyrene (guest) within the bisporphyrin clefts. The solid-state assembly is very robust in solution for days. Spectroscopic studies indicate significant photoinduced singlet–singlet energy transformation from guest to host.