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Sarkar S, Tiwari RK, Samanta D, Guchhait T, Sañudo EC, Rajaraman G, Rath SP. Unusual Stabilisation of Remarkably Bent Tetra-Cationic Tetra-radical Intermolecular Fe(III) μ-Oxo Tetranuclear Complexes. Angew Chem Int Ed Engl 2024; 63:e202402344. [PMID: 38478415 DOI: 10.1002/anie.202402344] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2024] [Indexed: 04/24/2024]
Abstract
A hitherto unknown series of air stable, π-conjugated, remarkably bent tetra-cation tetra-radical intermolecular Fe(III) μ-oxo tetranuclear complex, isolated from the dication diradical diiron(III) porphyrin dimers, has been synthesised and spectroscopically characterised along with single crystal X-ray structure determination of two such molecules. These species facilitate long-range charge/radical delocalisation through the bridge across the entire tetranuclear unit manifesting an unusually intense NIR band. Assorted spin states of Fe(III) centres are stabilised within these unique tetranuclear frameworks: terminal six-coordinate iron centres stabilise the admixed intermediate spin states while the central five-coordinate iron centres stabilise the high-spin states. Variable temperature magnetic susceptibility measurements indicated strong antiferromagnetic coupling for the Fe(III)-O-Fe(III) unit while the exchange interactions between the Fe centres and the porphyrin π-cation radicals are weaker as supported both by magnetic data and DFT calculations. The nature of orbital overlap between the SOMOs of Fe(III) and π* orbital of the porphyrin was found to rationalise the observed exchange coupling, establishing such a complex magnetic exchange in this tetranuclear model with a significant bioinorganic relevance.
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Affiliation(s)
- Sabyasachi Sarkar
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
| | - Rupesh Kumar Tiwari
- Department of Chemistry, Indian Institute of Technology Bombay, Mumbai, 400076, India
| | - Deepannita Samanta
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
| | - Tapas Guchhait
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
| | - E Carolina Sañudo
- Secció de Química Inorgànica, Department de Química Inorgànica i Orgànica, Facultat de Química, Universitat de Barcelona, C/Martí i Franqués 1-11, 08028, Barcelona, Spain
- Institut de Nanociència i Nanotecnologia, IN2UB, Universitat de Barcelona, C/Martí i Franqués 1-11, 08028, Barcelona, Spain
| | - Gopalan Rajaraman
- Department of Chemistry, Indian Institute of Technology Bombay, Mumbai, 400076, India
| | - Sankar Prasad Rath
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
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Sanfui S, Chakraborty P, Garribba E, Rath SP. Diheme cytochromes: Effect of mixed-axial ligation on the electronic structure and electrochemical properties with cobalt porphyrin dimer. J Inorg Biochem 2023; 240:112109. [PMID: 36592509 DOI: 10.1016/j.jinorgbio.2022.112109] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Revised: 12/11/2022] [Accepted: 12/15/2022] [Indexed: 12/24/2022]
Abstract
A series of six-coordinate diCo(III) porphyrin dimers, as synthetic analogues of diheme cytochromes, have been reported here having bis(imidazole), bis(pyridine) and mixed thiophenolate-pyridine/imidazole axial ligands. In the X-ray structures of bis(imidazole) and bis(pyridine) complexes, the axial ligands are in perpendicular orientation while they are parallelly oriented in their monomeric analog. The porphyrin rings are also highly ruffle-distorted in dimer but planar in monomer which reflect the effect of intramolecular interaction between two Co(porphyrin) units in dimers. In the X-ray structure of diCo(III) thiophenolate-pyridine mixed-ligated complex, the axial Co-S and Co-N(py) distances are 2.256(1) and 2.063(2) Å, respectively. The Co-N(py) distance of 2.063(2) Å is much longer than the distances of 1.961(3) and 1.972(3) Å observed in bis(pyridine) complex and the Co-S distance is larger than Co-N(py) in the mixed ligated complex which results in a displacement of Co by 0.15 Å towards the pyridine ligand from the mean porphyrin plane. Indeed, this is the first X-ray structure of a metalloporphyrin with mixed thiophenolate-pyridine axial ligands. The effect of mixed-axial ligation is demonstrated by a blue-shift of the Soret band in the UV-visible spectroscopy and also a positive shift of the Co(III)/Co(II) redox couple as compared to their bis(pyridine) analogue. The redox potentials are shifted to a large negative value just upon replacing the metal from iron to cobalt. The present investigation emphasizes the role of axial ligation, metal ions, and also the effect of heme-heme interaction in controlling the spectral and electrochemical properties.
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Affiliation(s)
- Sarnali Sanfui
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
| | - Paulami Chakraborty
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
| | - Eugenio Garribba
- Dipartimento di Medicina, Chirurgia e Farmacia, Università di Sassari, Viale San Pietro, I-07100 Sassari, Italy
| | - Sankar Prasad Rath
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India.
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Sarkar S, Shah Tuglak Khan F, Guchhait T, Rath SP. Binuclear complexes with single M-F-M bridge (M: Fe, Mn, and Cu): A critical analysis of the impact of fluoride for isoelectronic hydroxide substitution. Coord Chem Rev 2023. [DOI: 10.1016/j.ccr.2022.215003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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Pandit YA, Usman M, Sarkar A, Shah SJ, Rath SP. Control of spin coupling through a redox-active bridge in a dinickel(II) porphyrin dimer: step-wise oxidations enable isolations of a chlorin-porphyrin heterodimer and a dication diradical with a singlet ground state. Dalton Trans 2023; 52:877-891. [PMID: 36464989 DOI: 10.1039/d2dt03283j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
A dinickel(II)porphyrin dimer has been used here in which the redox-active pyrrole-moiety, similar to the tryptophan residue in diheme enzymes such as MauG and bCcP, has been placed between two Ni(II)porphyrin centers connected via a flexible, but unconjugated methylene bridge. This arrangement provides a large physical separation between the two metal centers and thus displays almost no communication between them through the bridge. Upon treatment with DDQ as an oxidant, the dinickel(II) porphyrin dimer slowly gets converted into an indolizinium-fused chlorin-porphyrin heterodimer. However, oxidations of the dinickel(II) porphyrin dimer up to two oxidizing equivalents using oxidants such as AgSbF6 and FeCl3 resulted in the formation of a dication diradical complex. Interestingly, in order to stabilize such a highly oxidized dication diradical, two non-conjugated methylene spacers undergo facile 2e-/-2H+ oxidation to make the bridge fully π-conjugated for promoting through-bond communication. Through the oxidized and conjugated bridge, two porphyrin π-cation radicals display considerable communications leading to an efficient intramolecular spin coupling to form a singlet state. Interestingly, the redox-active nature of the bridge controls the electronic communication just by simple oxidation or reduction, and thereby, acts as a molecular switch for efficient magnetic relay.
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Affiliation(s)
- Younis Ahmad Pandit
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur-208016, India.
| | - Mohammad Usman
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur-208016, India.
| | - Anindya Sarkar
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur-208016, India.
| | - Syed Jehanger Shah
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur-208016, India.
| | - Sankar Prasad Rath
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur-208016, India.
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Sanfui S, Usman M, Sarkar S, Pramanik S, Garribba E, Rath SP. Highly Oxidized Cobalt Porphyrin Dimer: Control of Spin Coupling via a Bridge. Inorg Chem 2022; 61:8419-8430. [PMID: 35613476 DOI: 10.1021/acs.inorgchem.1c03807] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A cobalt porphyrin dimer is constructed in which two Co(II)porphyrins are connected covalently through a redox-active diethylpyrrole moiety via a flexible but "nonconjugated" methylene bridge. Upon oxidation with even a mild oxidant such as iodine, each cobalt(II) center and porphyrin ring undergo 1e- oxidation, leading to the formation of a 4e--oxidized cobalt(III)porphyrin dication diradical complex. Other oxidants such as Cl2 and Br2 also produce similar results. To stabilize such highly oxidized dication diradicals, the "nonconjugated" methylene spacer undergoes a facile and spontaneous oxidation to form a methine group with a drastic structural change, thereby making the bridge fully π-conjugated and enabling through-bond communication. This results in a strong spin coupling between two π-cation radicals which stabilizes the singlet state. The experimental observations are also strongly supported by extensive density functional theory calculations. The present study highlights the crucial role played by the nature of the bridge in the long-range electronic communication.
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Affiliation(s)
- Sarnali Sanfui
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
| | - Mohammad Usman
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
| | - Sabyasachi Sarkar
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
| | - Subhadip Pramanik
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
| | - Eugenio Garribba
- Dipartimento di Scienze Mediche, Chirurgiche e Sperimentali, Università di Sassari, Viale San Pietro, Sassari I-07100, Italy
| | - Sankar Prasad Rath
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
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Pandit YA, Shah SJ, Usman M, Sarkar S, Garribba E, Rath SP. Long-Range Intramolecular Spin Coupling through a Redox-Active Bridge upon Stepwise Oxidations: Control and Effect of Metal Ions. Inorg Chem 2022; 61:5270-5282. [PMID: 35323011 DOI: 10.1021/acs.inorgchem.1c03945] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Dinickel(II) and dicopper(II) porphyrin dimers have been constructed in which two metalloporphyrin units are widely separated by a long unconjugated dipyrrole bridge. Two macrocycles are aligned somewhat orthogonally to each other, while oxidation of the bridge generates a fully π-conjugated butterfly-like structure, which, in turn, upon stepwise oxidations by stronger oxidants result in the formation of the corresponding one- and two-electron-oxidized species exhibiting unusual long-range charge/radical delocalization to produce intense absorptions in the near-infrared (NIR) region and electron paramagnetic resonance (EPR) signals of a triplet state due to interaction between the unpaired spins on the Cu(II) ions. Although the two metal centers have a large physical separation through the bridge (more than 16 Å), they share electrons efficiently between them, behaving as a single unit rather than two independent centers. Detailed UV-vis-NIR, electrospray ionization mass spectrometry, IR, variable-temperature magnetic study, and EPR spectroscopic investigations along with X-ray structure determination of unconjugated, conjugated, and one electron-oxidized complexes have been exploited to demonstrate the long-range electronic communication through the bridge. The experimental observations are also supported by density functional theory (DFT) and time-dependent DFT calculations. The present study highlights the crucial roles played by a redox-active bridge and metal in controlling the long-range electronic communication.
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Affiliation(s)
- Younis Ahmad Pandit
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
| | - Syed Jehanger Shah
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
| | - Mohammad Usman
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
| | - Sabyasachi Sarkar
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
| | - Eugenio Garribba
- Dipartimento di Scienze Mediche, Chirurgiche e Sperimentali, Università di Sassari, Viale San Pietro, Sassari I-07100, Italy
| | - Sankar Prasad Rath
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
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