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Bagchi S, Kamilya S, Mehta S, Mandal S, Bandyopadhyay A, Narayan A, Ghosh S, Mondal A. Spin-state switching: chemical modulation and the impact of intermolecular interactions in manganese(III) complexes. Dalton Trans 2023; 52:11335-11348. [PMID: 37530419 DOI: 10.1039/d3dt01707a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/03/2023]
Abstract
A series of mononuclear manganese(III) complexes [Mn(X-sal2-323)](ReO4) (X = 5 Cl, 1; X = 5 Br, 2; X = 3,5 Cl, 3; X = 3,5 Br, 4; and X = 5 NO2, 5), containing hexadentate ligands prepared using the condensation of N,N'-bis(3-aminopropyl)ethylenediamine and 5- or 3,5-substituted salicylaldehyde, has been synthesized. Variable temperature single-crystal X-ray diffraction, magnetic, spectroscopic, electrochemical, and spectroelectrochemical analyses, and theoretical calculations have been used to explore the role of various ligand substituents in the spin-state switching behavior of the prepared manganese(III) complexes. All five complexes consist of an analogous distorted octahedral monocationic MnN4O2 surrounding offered by the flexible hexadentate ligand and ReO4- as the counter anion. However, a disordered water molecule was detected in complex 4. Complexes 1 (X = 5 Cl) and 5 (X = 5 NO2) show gradual and complete spin-state switching between the high-spin (HS) (S = 2) and the low-spin (LS) (S = 1) state with T1/2 values of 146 and 115 K respectively, while an abrupt and complete transition at 95 K was observed for complex 2 (X = 5 Br). Alternatively, complex 3 (X = 3, 5 Cl) exhibits an incomplete and sharp transition between the HS and LS states at 104 K, while complex 4 (X = 3, 5 Br) (desolvated) remains almost LS up to 300 K and then displays gradual and incomplete SCO at a higher temperature. The nature of the spin-state switch and transition temperature suggest that the structural effect (cooperativity) plays a more significant role in comparison with the electronic effect coming from various substituents (Cl, Br, and NO2), which is further supported by the detailed structural, electrochemical, and theoretical studies.
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Affiliation(s)
- Sukanya Bagchi
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
| | - Sujit Kamilya
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
| | - Sakshi Mehta
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
| | - Subhankar Mandal
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
| | - Arka Bandyopadhyay
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
| | - Awadhesh Narayan
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
| | - Subrata Ghosh
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
| | - Abhishake Mondal
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
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Ghosh S, Ghosh S, Kamilya S, Mandal S, Mehta S, Mondal A. Impact of Counteranion on Reversible Spin-State Switching in a Series of Cobalt(II) Complexes Containing a Redox-Active Ethylenedioxythiophene-Based Terpyridine Ligand. Inorg Chem 2022; 61:17080-17088. [PMID: 36264687 DOI: 10.1021/acs.inorgchem.2c02313] [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
The self-assembly of a redox-active ethylenedioxythiophene (EDOT)-terpyridine-based tridentate ligand and cobalt(II) unit with different counteranions has led to a series of new cobalt(II) complexes [Co(L)2](X)2 (X = BF4 (1), ClO4 (2), and BPh4 (3)) (L = 4'-(3,4-ethylenedioxythiophene)-2,2':6',2″-terpyridine). The impact of various counteranions on stabilization and spin-state switching of the cobalt(II) center was explored through detailed magneto-structural investigation using variable temperature single-crystal X-ray diffraction, magnetic, spectroscopic, electrochemical, and spectroelectrochemical studies. All three complexes 1-3 consisted of an isostructural dicationic distorted octahedral CoN6 coordination environment offered by the two L ligands in a bis-meridional fashion and BF4-, ClO4-, and BPh4- as a counteranion, respectively. Complex 2 with ClO4- counteranion showed a reversible, gradual, and nearly complete spin-state switching between low-spin (LS) (S = 1/2) and high-spin (HS) (S = 3/2) states, while an incomplete spin-state switching behavior was observed for complexes 1 (BF4-) and 3 (BPh4-) in the measured temperature range of 350-2 K. The non-covalent cation-anion interactions played a significant role in stabilizing the spin-state in 1-3. Additionally, complexes 1-3 also exhibited interesting redox-stimuli-based reversible paramagnetic HS cobalt(II) (S = 3/2) to diamagnetic LS cobalt(III) (S = 0) conversion, offering an alternate way to switch the magnetic properties.
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Affiliation(s)
- Subrata Ghosh
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India
| | - Sounak Ghosh
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India
| | - Sujit Kamilya
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India
| | - Subhankar Mandal
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India
| | - Sakshi Mehta
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India
| | - Abhishake Mondal
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India
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Investigations on the Spin States of Two Mononuclear Iron(II) Complexes Based on N-Donor Tridentate Schiff Base Ligands Derived from Pyridine-2,6-Dicarboxaldehyde. INORGANICS 2022. [DOI: 10.3390/inorganics10070098] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Iron(II)-Schiff base complexes are a well-studied class of spin-crossover (SCO) active species due to their ability to interconvert between a paramagnetic high spin-state (HS, S = 2, 5T2) and a diamagnetic low spin-state (LS, S = 0, 1A1) by external stimuli under an appropriate ligand field. We have synthesized two mononuclear FeII complexes, viz., [Fe(L1)2](ClO4)2.CH3OH (1) and [Fe(L2)2](ClO4)2.2CH3CN (2), from two N6–coordinating tridentate Schiff bases derived from 2,6-bis[(benzylimino)methyl]pyridine. The complexes have been characterized by elemental analysis, electrospray ionization–mass spectrometry (ESI-MS), Fourier-transform infrared spectroscopy (FTIR), solution state nuclear magnetic resonance spectroscopy, 1H and 13C NMR (both theoretically and experimentally), single-crystal diffraction and magnetic susceptibility studies. The structural, spectroscopic and magnetic investigations revealed that 1 and 2 are with Fe–N6 distorted octahedral coordination geometry and remain locked in LS state throughout the measured temperature range from 5–350 K.
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Ghosh S, Kamilya S, Mehta S, Herchel R, Kiskin M, Veber S, Fedin M, Mondal A. Effect of Ligand Chain Length for Tuning of Molecular Dimensionality and Magnetic Relaxation in Redox Active Cobalt(II) EDOT Complexes (EDOT = 3,4-Ethylenedioxythiophene). Chem Asian J 2022; 17:e202200404. [PMID: 35617522 DOI: 10.1002/asia.202200404] [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: 04/18/2022] [Revised: 05/17/2022] [Indexed: 11/07/2022]
Abstract
Four cobalt(II) complexes, [Co(L1)2(NCX)2(MeOH)2] (X = S (1), Se (2)) and {[Co(L2)2(NCX)2]}n (X = S (3), Se (4)) (L1 = 2,5dipyridyl-3,4,-ethylenedioxylthiophene and L2 = 2,5diethynylpyridinyl-3,4-ethylenedioxythiophene), were synthesized by incorporating ethylenedioxythiophene based redox-active luminescence ligands. All these complexes have been well characterized using single-crystal X-ray diffraction analyses, spectroscopic and magnetic investigations. Magneto-structural studies showed that 1 and 2 adopt a mononuclear structure with CoN4O2 octahedral coordination geometry while 3 and 4 have a 2D [4 x 4] rhombic grid coordination networks (CNs) where each cobalt(II) center is in a CoN6 octahedral coordination environment. Static magnetic measurements reveal that all four complexes displayed a high spin (HS) (S = 3/2) state between 2 and 280 K which was further confirmed by X-band and Q-band EPR studies. Remarkably, along with the molecular dimensionality (0D and 2D) the modification in the axial coligands lead to a significant difference in the dynamic magnetic properties of the monomers and CNs at low temperatures. All complexes display slow magnetic relaxation behavior under an external dc magnetic field. For the complexes with NCS- as coligand observed higher energy barrier for spin reversal in comparison to the complexes with NCSe- as coligand, while mononuclear complex 1 exhibited a higher energy barrier than that of CN 3. Theoretical calculations at the DFT and CASSCF level of theory have been performed to get more insight into the electronic structure and magnetic properties of all four complexes.
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Affiliation(s)
- Subrata Ghosh
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C. V. Raman Road, 560012, Bangalore, India
| | - Sujit Kamilya
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C. V. Raman Road, 560012, Bangalore, India
| | - Sakshi Mehta
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C. V. Raman Road, 560012, Bangalore, India
| | - Radovan Herchel
- Department of Inorganic Chemistry, Faculty of Science, Palacký University, CZ-771 46, Olomouc, Czech Republic
| | - Mikhail Kiskin
- N. S. Kurnakov Institute of General and Inorganic Chemistry of the Russian Academy of Sciences, Leninsky Prosp. 31, 119991, Moscow, Russia
| | - Sergey Veber
- International Tomography Center of the Siberian Branch of the Russian Academy of Sciences, Institutskaya Str. 3a, 630090, Novosibirsk, Russia
- Novosibirsk State University, Pirogova Str. 1, 630090, Novosibirsk, Russia
| | - Matvey Fedin
- International Tomography Center of the Siberian Branch of the Russian Academy of Sciences, Institutskaya Str. 3a, 630090, Novosibirsk, Russia
- Novosibirsk State University, Pirogova Str. 1, 630090, Novosibirsk, Russia
| | - Abhishake Mondal
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C. V. Raman Road, 560012, Bangalore, India
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Ghosh S, Bagchi S, Kamilya S, Mehta S, Sarkar D, Herchel R, Mondal A. Impact of counter anions on spin-state switching of manganese(III) complexes containing an azobenzene ligand. Dalton Trans 2022; 51:7681-7694. [PMID: 35521740 DOI: 10.1039/d2dt00660j] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Four mononuclear manganese(III) complexes coordinated with photo-active hexadentate azobenzene ligands, [Mn(5azo-sal2-323)](X) (X = Cl, 1; X = BF4, 2; X = ClO4, 3; X = PF6, 4), were prepared. The impact of various counter anions on the stabilization and switching of the spin state of the manganese(III) center was explored through detailed magneto-structural investigation using variable temperature single-crystal X-ray diffraction, magnetic, spectroscopic, and spectroelectrochemical studies, along with theoretical calculations. All four complexes consisted of an isostructural monocationic distorted octahedral MnN4O2 coordination environment offered by the hexadentate ligand and Cl-, BF4-, ClO4-, and PF6- as counter anions respectively. Complex 1 with a spherical Cl- counter anion showed a reversible and gradual spin-state switching between low-spin (LS) (S = 1) and high-spin (HS) (S = 2) states above 400 K, where non-covalent cation-anion interactions played a significant role in stabilizing the LS state. While, irrespective of the shape of the counter anion, complexes 2-4 remained in the HS state throughout the measured temperature range of 300-2 K, where strong π-π interaction between the azobenzene motifs among cationic units played a substantial role in stabilizing the HS state. Furthermore, magnetic data analyses revealed significantly large zero-field splitting in the S = 1 state for 1 (D = 19.4 cm-1, E/D = 0.008) in comparison with that in the S = 2 state for 2-4 (D = 3.99-4.97 cm-1, E/D = 0.002-0.195). Spectroelectrochemical investigations revealed the quasi-reversible reduction and oxidation of the manganese(III) center to manganese(II) and manganese(IV), respectively. A detailed theoretical calculation at the DFT and CASSCF level of theory was carried out to better understand the magneto-structural correlation.
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Affiliation(s)
- Subrata Ghosh
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
| | - Sukanya Bagchi
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
| | - Sujit Kamilya
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
| | - Sakshi Mehta
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
| | - Debopam Sarkar
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
| | - Radovan Herchel
- Department of Inorganic Chemistry, Faculty of Science, Palacký University, CZ-771 46 Olomouc, Czech Republic
| | - Abhishake Mondal
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
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Ghosh S, Kamilya S, Pramanik T, Mohanty A, Rouzières M, Herchel R, Mehta S, Mondal A. Thermo- and photoinduced spin state switching in an iron(II) 2D coordination network associated with large light-induced thermal hysteresis and tuning of dimensionality via ligand modulation. Dalton Trans 2021; 50:7725-7735. [PMID: 33988205 DOI: 10.1039/d1dt00212k] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Three iron(ii) complexes, [Fe(L1)2(NCS)2(MeOH)2] (1), [Fe(L1)2(NCSe)2(MeOH)2] (2), and [Fe(L2)2(NCS)2]n (3) (L1 = 2,5-dipyridyl-3,4-ethylenedioxythiophene and L2 = 2,5-diethynylpyridinyl-3,4-ethylenedioxythiophene), have been synthesized using redox-active luminescent ethylenedioxythiophene (EDOT)-based ligands, and characterized by variable temperature single-crystal X-ray diffraction, (photo)magnetic, optical reflectivity, and spectroscopy studies. Magneto-structural investigations revealed that 1 and 2 are mononuclear with a FeN4O2 octahedral coordination geometry and remain in a high-spin (HS) (S = 2) state in a temperature range of 2-280 K. Interestingly, a 2D coordination network structure with FeN6 surrounding each iron center was observed for 3, which exhibits reversible thermo-induced spin-state switching between the paramagnetic high-spin (HS) (S = 2) and diamagnetic low-spin (LS) (S = 0) states at around 105 K (T1/2). Furthermore, optical reflectivity and photomagnetic measurements at low temperature confirmed that 3 shows reversible ON/OFF switching between the photoinduced excited paramagnetic HS metastable state and diamagnetic LS state under light irradiation (ON mode using red light and OFF mode using green light). Finally, the photoinduced excited HS state can be reversibly relaxed back to the diamagnetic ground LS state by heating the system at ca. 88 K (TLIESST = 88 K) (light-induced excited spin state trapping (LIESST) effect). Furthermore, 3 also showed an exciting and unique 18 K wide light-induced thermal hysteresis (LITH) effect above liquid nitrogen temperature (100 K). DFT and CASSCF level theoretical calculations were utilized to better understand the magneto-structural correlations of these complexes.
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Affiliation(s)
- Subrata Ghosh
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
| | - Sujit Kamilya
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
| | - Titas Pramanik
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
| | - Ashutosh Mohanty
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
| | - Mathieu Rouzières
- Univ. Bordeaux, CNRS, Centre de Recherche Paul Pascal, UMR 5031, 33600 Pessac, France
| | - Radovan Herchel
- Department of Inorganic Chemistry, Faculty of Science, Palacký University, CZ-771 46 Olomouc, Czech Republic
| | - Sakshi Mehta
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
| | - Abhishake Mondal
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
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Kaushik K, Ghosh S, Kamilya S, Rouzières M, Mehta S, Mondal A. Reversible Photo- and Thermo-Induced Spin-State Switching in a Heterometallic { 5d-3d} W 2Fe 2 Molecular Square Complex. Inorg Chem 2021; 60:7545-7552. [PMID: 33929177 DOI: 10.1021/acs.inorgchem.1c01014] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Following the complex-as-a-ligand strategy, self-assembly of [W(CN)8]3- and iron(II) with bidentate nitrogen donor ligand bik (bik = bis(1-methyl-1H-imidazol-2-yl)ketone) ligand affords a cyanide-bridged [W2Fe2] molecular square complex [HNBu3]2{[W(CN)8]2[Fe(bik)2]2}·6H2O·CH3OH (1). The complex was characterized by single-crystal X-ray diffraction analyses, (photo)magnetic studies, optical reflectivity, electrochemical studies, and spectroscopic studies. Structural analyses revealed that in the [W2Fe2] square motif tungsten(V) and iron(II) centers reside in an alternate corner of the square and are bridged by the cyanide ligands. Complex 1 exhibits thermo-induced spin crossover (SCO) between {WV (S = 1/2) - FeIILS (S = 0)} and {WV (S = 1/2) - FeIIHS (S = 2)} pairs near room temperature and photoinduced spin-state switching with TLIESST = 70 K under light irradiation at low temperature. To the best of our knowledge, 1 represents the first complex containing iron(II) and [WV(CN)8]3- units exhibiting both SCO and photomagnetic effect.
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Affiliation(s)
- Krishna Kaushik
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C. V. Raman Road, Bangalore 560012, India
| | - Subrata Ghosh
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C. V. Raman Road, Bangalore 560012, India
| | - Sujit Kamilya
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C. V. Raman Road, Bangalore 560012, India
| | - Mathieu Rouzières
- Univ. Bordeaux, CNRS, Centre de Recherche Paul Pascal, CRPP, UMR 5031, 33600 Pessac, France
| | - Sakshi Mehta
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C. V. Raman Road, Bangalore 560012, India
| | - Abhishake Mondal
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C. V. Raman Road, Bangalore 560012, India
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Ghosh S, Bagchi S, Kamilya S, Mondal A. Effect of ligand substituents and tuning the spin-state switching in manganese(iii) complexes. Dalton Trans 2021; 50:4634-4642. [PMID: 33720257 DOI: 10.1039/d1dt00284h] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Three mononuclear manganese(iii) complexes based on flexible hexadentate ligands obtained from the condensation of N,N'-bis(3-aminopropyl)ethylenediamine and salicylaldehyde or salicylaldehyde with substitutions at the 5 or 3,5 positions, namely [Mn(X-sal2-323)](BPh4) (X = 5 H, 1; X = 5 Br, 2, and X = 3,5 Br, 3) have been synthesized. The impact of ligand substituents has been studied by variable temperature single-crystal X-ray diffraction analyses, and magnetic, spectroscopic and electrochemical investigations. The complexes have an analogous monocationic MnN4O2 surrounding offered by the flexible hexadentate ligand in a distorted octahedral geometry. Complex 1 remains in the high spin state over the entire temperature range, while complex 2 shows a reversible and complete two-step thermo-induced spin-state switching. An incomplete spin-state switching from a high spin to an intermediate high-spin low-spin (1 : 1) state was observed for complex 3. Single-crystal X-ray structural studies show the presence of three different spin states in 2 during the occurrence of the spin-state switching process. Electrochemical investigations showed that the reduced state of manganese(iii) centers in 3 is easily accessible in comparison to complexes 1 and 2.
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Affiliation(s)
- Subrata Ghosh
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
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Molecular S = 2 High-Spin, S = 0 Low-Spin and S = 0 ⇄ 2 Spin-Transition/-Crossover Nickel(II)-Bis(nitroxide) Coordination Compounds. INORGANICS 2021. [DOI: 10.3390/inorganics9020010] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Heterospin systems have a great advantage in frontier orbital engineering since they utilize a wide diversity of paramagnetic chromophores and almost infinite combinations and mutual geometries. Strong exchange couplings are expected in 3d–2p heterospin compounds, where the nitroxide (aminoxyl) oxygen atom has a direct coordination bond with a nickel(II) ion. Complex formation of nickel(II) salts and tert-butyl 2-pyridyl nitroxides afforded a discrete 2p–3d–2p triad. Ferromagnetic coupling is favored when the magnetic orbitals, nickel(II) dσ and radical π*, are arranged in a strictly orthogonal fashion, namely, a planar coordination structure is characterized. In contrast, a severe twist around the coordination bond gives an orbital overlap, resulting in antiferromagnetic coupling. Non-chelatable nitroxide ligands are available for highly twisted and practically diamagnetic complexes. Here, the Ni–O–N–Csp2 torsion (dihedral) angle is supposed to be a useful metric to describe the nickel ion dislocated out of the radical π* nodal plane. Spin-transition complexes exhibited a planar coordination structure in a high-temperature phase and a nonplanar structure in a low-temperature phase. The gradual spin transition is described as a spin equilibrium obeying the van’t Hoff law. Density functional theory calculation indicates that the energy level crossing of the high- and low-spin states. The optimized structures of diamagnetic and high-spin states well agreed with the experimental large and small torsions, respectively. The novel mechanism of the present spin transition lies in the ferro-/antiferromagnetic coupling switch. The entropy-driven mechanism is plausible after combining the results of the related copper(II)-nitroxide compounds. Attention must be paid to the coupling parameter J as a variable of temperature in the magnetic analysis of such spin-transition materials. For future work, the exchange coupling may be tuned by chemical modification and external stimulus, because it has been clarified that the parameter is sensitive to the coordination structure and actually varies from 2J/kB = +400 K to −1400 K.
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Ghosh S, Kamilya S, Rouzières M, Herchel R, Mehta S, Mondal A. Reversible Spin-State Switching and Tuning of Nuclearity and Dimensionality via Nonlinear Pseudohalides in Cobalt(II) Complexes. Inorg Chem 2020; 59:17638-17649. [PMID: 33174721 DOI: 10.1021/acs.inorgchem.0c02887] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The self-assembly of a macrocyclic tetradentate ligand, cobalt(II) tetrafluoroborate, and nonlinear pseudohalides (dicyanamide and tricyanomethanide) has led to two cobalt(II) complexes, {[Co(L)(μ1,5-dca)](BF4)·MeOH}n (1) and [Co2(L)2(μ1,5-tcm)2](BF4)2 (2) (L = N,N'-di-tert-butyl-2,11-diaza[3,3](2,6)pyridinophane; dca- = dicyanamido; tcm- = tricyanomethanido). Both complexes were characterized by single-crystal X-ray diffraction, spectroscopic, magnetic, and electrochemical studies. Structural analyses revealed that 1 displays a one-dimensional (1D) coordination polymer containing [Co(L)]2+ repeating units bridged by μ1,5-dicyanamido groups in cis positions, while 2 represents a discreate dinuclear cobalt(II) molecule bridged by two μ1,5-tricyanomethanido groups in a cis conformation. Both complexes have a CoN6 coordination environment around each cobalt center offered by the tetradentate ligand and cis coordinating bridging ligands. Complex 1 exhibits a high-spin (S = 3/2) state of cobalt(II) in the temperature range of 2-300 K with a weak ferromagnetic coupling between two dicyanamido-bridged cobalt(II) centers. Interestingly, complex 2 exhibits reversible spin-state switching associated with spin-spin coupling. Complexes 1 and 2 also exhibit interesting redox-stimuli-based reversible paramagnetic high-spin cobalt(II) to diamagnetic low-spin cobalt(III) conversion, offering an additional way to switch magnetic properties. A detailed theoretical calculation was consistent with the stated results.
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Affiliation(s)
- Subrata Ghosh
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India
| | - Sujit Kamilya
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India
| | - Mathieu Rouzières
- Univ. Bordeaux, CNRS, Centre de Recherche Paul Pascal, CRPP, UMR 5031, 33600 Pessac, France
| | - Radovan Herchel
- Department of Inorganic Chemistry, Faculty of Science, Palacký University, 17. listopadu 12, CZ-771 46 Olomouc, Czech Republic
| | - Sakshi Mehta
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India
| | - Abhishake Mondal
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India
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Ghosh S, Bagchi S, Das M, Kamilya S, Mondal A. Stepwise spin-state switching in a manganese(III) complex. Dalton Trans 2020; 49:14776-14780. [PMID: 33078798 DOI: 10.1039/d0dt02746d] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A mononuclear manganese(iii) complex containing a flexible hexadentate chelating ligand has been prepared and characterized by performing, at various temperatures, single-crystal X-ray diffraction analyses and magnetic, spectroscopic, and electrochemical studies. The complex was shown to consist of an MnN4O2 octahedral coordination environment, and to exhibit reversible two-step thermally induced spin-state switching, a gradual one at 168 K and an abrupt one at 103 K. Structural analyses revealed the existence of three spin-states, namely high-spin, low-spin, and intermediate states, during the spin-state switching process. Electrochemistry studies showed the quasi-reversible reduction and oxidation of the manganese(iii) center with a comparatively easily accessible reduced state.
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Affiliation(s)
- Subrata Ghosh
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
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Contribution of the Multiplicity Fluctuation in the Temperature Dependence of Phonon Spectra of Rare-Earth Cobaltites. Molecules 2020; 25:molecules25184316. [PMID: 32962303 PMCID: PMC7570745 DOI: 10.3390/molecules25184316] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Revised: 09/14/2020] [Accepted: 09/17/2020] [Indexed: 11/17/2022] Open
Abstract
We have studied, both experimentally and theoretically, the unusual temperature dependence of the phonon spectra in NdCoO3, SmCoO3 and GdCoO3, where the Co3+ ion is in the low-spin (LS) ground state, and at the finite temperature, the high-spin (HS) term has a nonzero concentration nHS due to multiplicity fluctuations. We measured the absorption spectra in polycrystalline and nanostructured samples in the temperature range 3–550 K and found a quite strong breathing mode softening that cannot be explained by standard lattice anharmonicity. We showed that the anharmonicity in the electron–phonon interaction is responsible for this red shift proportional to the nHS concentration.
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Kyoden Y, Ishida T. A Hidden Coordination-Bond Torsional Deformation as a Sign of Possible Spin Transition in Nickel(II)-Bis(nitroxide) Compounds. Molecules 2020; 25:E3790. [PMID: 32825395 PMCID: PMC7503645 DOI: 10.3390/molecules25173790] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2020] [Revised: 08/13/2020] [Accepted: 08/18/2020] [Indexed: 11/17/2022] Open
Abstract
Complex formation of nickel(II) tetrafluoroborate and tert-butyl 5-phenyl-2-pyridyl nitroxide (phpyNO) in the presence of sodium cyanate gave a discrete molecule [Ni(phpyNO)2(X)2] (X = NCO). The Ni-O-N-Csp2 torsion angles were reduced on heating; 33.5(5)° and 36.2(4)° at 100 K vs. 25.7(10)° and 32.3(11)° at 400 K. The magnetic behavior was almost diamagnetic below ca. 100 K, and the χmT value reached 1.04 cm3 K mol-1 at 400 K. An analysis using the van't Hoff equation indicates a possible spin transition at T1/2 >> 400 K. Density functional theory calculation shows that the singlet-quintet energy gap decreases as the structural change from 100 to 400 K. The geometry optimization results suggest that the diamagnetic state has the Ni-O-N-Csp2 torsion angles of 32.7° while the Stotal = 2 state has those of 11.9°. The latter could not be experimentally observed even at 400 K. After overviewing the results on the known X = Br, Cl, and NCS derivatives, the magnetic behavior is described in a common phase diagram. The Br and Cl compounds undergo the energy level crossing of the high-/low-spin states, but the NCS and NCO compounds do not in a conventional experimental temperature range. The spin transition mechanism in this series involves the exchange coupling switch between ferro- and antiferromagnetic interactions, corresponding to the high- and low-spin phases, respectively.
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Affiliation(s)
| | - Takayuki Ishida
- Department of Engineering Science, The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan;
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14
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Kashiro A, Kohno W, Ishida T. Odd–Even Effect on the Spin-Crossover Temperature in Iron(II) Complex Series Involving an Alkylated or Acyloxylated Tripodal Ligand. Inorg Chem 2020; 59:10163-10171. [DOI: 10.1021/acs.inorgchem.0c01296] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Affiliation(s)
- Atsushi Kashiro
- Department of Engineering Science, The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan
| | - Wakana Kohno
- Department of Engineering Science, The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan
| | - Takayuki Ishida
- Department of Engineering Science, The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan
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15
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Kyoden Y, Ishida T. An indication of spin-transition accompanied by an order-disorder structural transformation in [Ni(phpyNO)2(NCS)2] (phpyNO = tert-butyl 5-phenyl-2-pyridyl nitroxide). RSC Adv 2020; 10:16009-16015. [PMID: 35493632 PMCID: PMC9052934 DOI: 10.1039/d0ra02041a] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2020] [Accepted: 04/03/2020] [Indexed: 11/29/2022] Open
Abstract
Reaction of nickel(ii) thiocyanate and tert-butyl 5-phenyl-2-pyridyl nitroxide (phpyNO) afforded a 2p–3d–2p heterospin triad [Ni(phpyNO)2(NCS)2]. The compound crystallizes in the orthorhombic Pbcn space group. The whole molecule is crystallographically independent. The torsion angles around Ni–O–N–C2py are 26.8(4) and 27.3(4)° at 400 K, indicating appreciable orbital overlaps of the radical π* and nickel(ii) 3dx2−y2/3dz2 orbitals. In a low-temperature region, the torsion was enhanced, and the space group changed to monoclinic P21/c with a doubled asymmetric unit volume. The χmT value was practically null below ca. 140 K and, on heating to 400 K, gradually increased and reached 1.30 cm3 K mol−1. A van't Hoff analysis suggests a spin transition at T1/2 = 530(20) K. Density functional theory calculation reproduced ground Stotal = 0 with singlet-triplet gaps of 910 and 1263 K for the 140 K structure, and the gap was reduced to 297 K at 400 K. Consequently, the present compound can be considered as an incomplete spin-crossover material, as a result of T1/2 located above the experimental temperature window. The exchange coupling in [Ni(phpyNO)2(NCS)2] is strongly antiferromagnetic in a low-temperature structure whilst moderately antiferromagnetic in a high-temperature structure.![]()
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Affiliation(s)
- Yukiya Kyoden
- Department of Engineering Science
- The University of Electro-Communications
- Chofu
- Japan
| | - Takayuki Ishida
- Department of Engineering Science
- The University of Electro-Communications
- Chofu
- Japan
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16
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Ghosh S, Selvamani S, Mehta S, Mondal A. Reversible thermo-induced spin crossover in a mononuclear cis-dicyanamido-cobalt(ii) complex containing a macrocyclic tetradentate ligand. Dalton Trans 2020; 49:9208-9212. [DOI: 10.1039/d0dt01888k] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
For the first time, a mononuclear cobalt(ii) complex with dicyanamide coligands exhibiting reversible spin crossover behavior at high temperature is reported.
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Affiliation(s)
- Subrata Ghosh
- Solid State and Structural Chemistry Unit
- Indian Institute of Science
- Bangalore 560012
- India
| | - Subramani Selvamani
- Solid State and Structural Chemistry Unit
- Indian Institute of Science
- Bangalore 560012
- India
| | - Sakshi Mehta
- Solid State and Structural Chemistry Unit
- Indian Institute of Science
- Bangalore 560012
- India
| | - Abhishake Mondal
- Solid State and Structural Chemistry Unit
- Indian Institute of Science
- Bangalore 560012
- India
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17
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Ghosh S, Selvamani S, Kamilya S, Mehta S, Mondal A. Tuning of Spin Crossover Properties in a Series of Mononuclear Cobalt(II) Complexes Based on Macrocyclic Tetradentate Ligand and Pseudohalide Coligands. Dalton Trans 2020; 51:9642-9652. [DOI: 10.1039/d0dt02546a] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The three mononuclear cobalt(II) complexes, [Co(L)(NCX)2] (L = N,N'-di-tert-butyl-2,11-diaza[3,3](2,6)pyridinophane, and X = S (1), Se (2), and [C(CN)2] (3)), have been synthesized and characterized using variable temperature single-crystal X-ray crystallography,...
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18
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Kyoden Y, Homma Y, Ishida T. High-Spin and Incomplete Spin-Crossover Polymorphs in Doubly Chelated [Ni(L) 2Br 2] (L = tert-Butyl 5-Phenyl-2-pyridyl Nitroxide). Inorg Chem 2019; 58:10743-10755. [PMID: 31368687 DOI: 10.1021/acs.inorgchem.9b00885] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Complexation of nickel(II) bromide with tert-butyl 5-phenyl-2-pyridyl nitroxide (phpyNO) gave two morphs of doubly chelated [Ni(phpyNO)2Br2] as a 2p-3d-2p heterospin triad. The α phase crystallizes in the orthorhombic space group Pbcn. An asymmetric unit involves a half-molecule. The torsion angle around Ni-O-N-C2py is as small as 6.5(3)° at 100 K and 7.0(6)° at 400 K, guaranteeing an orthogonal arrangement between the magnetic radical π* and metal 3dx2-y2 and 3dz2 orbitals. Magnetic study revealed the high-spin ground state with the exchange coupling constant 2J/kB = +288(5) K, on the basis of a symmetrical spin Hamiltonian. The β phase crystallizes in the monoclinic space group P21/n. The whole molecule is an independent unit. The Ni-O-N-C2py torsion angles are 24.2(6) and 37.2(5)° at 100 K and 10.4(7) and 25.9(6)° at 400 K. A magnetic study revealed a very gradual and nonhysteretic spin transition. An analysis based on the van't Hoff equation gave a successful fit with the spin-crossover temperature of 134(1) K, although the susceptibility did not reach the theoretical high-spin value at 400 K. Density functional theory calculation on the β phase showed ground Stotal = 0 in the low-temperature structure while Stotal = 2 in the high-temperature structure, supporting the synchronized exchange coupling switch on both sides. Consequently, the β phase can be recognized as an "incomplete spin crossover" material, as a result of conflicting thermal depopulation effects in a high-temperature region.
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Affiliation(s)
- Yukiya Kyoden
- Department of Engineering Science , The University of Electro-Communications , Chofu, Tokyo 182-8585 , Japan
| | - Yuta Homma
- Department of Engineering Science , The University of Electro-Communications , Chofu, Tokyo 182-8585 , Japan
| | - Takayuki Ishida
- Department of Engineering Science , The University of Electro-Communications , Chofu, Tokyo 182-8585 , Japan
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Kashiro A, Kyoden Y, Okazawa A, Ishida T. Moving Organic Molecules in Crystalline Solids: Gradual Structural Transition and Spin Transition/Crossover. J SYN ORG CHEM JPN 2019. [DOI: 10.5059/yukigoseikyokaishi.77.684] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
| | | | | | - Takayuki Ishida
- Department of Engineering Science, The University of Electro-Communications
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20
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Kashiro A, Some K, Kobayashi Y, Ishida T. Iron(II) and 1,1,1-Tris(2-pyridyl)nonadecane Complex Showing an Order-Disorder-Type Structural Transition and Spin-Crossover Synchronized over Both Conformers. Inorg Chem 2019; 58:7672-7676. [PMID: 31185543 DOI: 10.1021/acs.inorgchem.9b01146] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The title compound (Me4N)[Fe{(2-py)3C- n-C18H37}(NCS)3] having a C18 chain underwent spin-crossover (SCO). There are two crystallographically independent molecules in a triclinic cell at 100 K but only one in a monoclinic cell at 300 K. The complex showed a gradual one-step SCO in the same temperature region as that of the structural transition. The SCO is supported with the 57Fe Mössbauer spectroscopy. The molecules are differentiated on cooling, but the SCO was synchronized.
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Affiliation(s)
- Atsushi Kashiro
- Department of Engineering Science , The University of Electro-Communications , Chofu , Tokyo 182-8585 , Japan
| | - Kanako Some
- Department of Engineering Science , The University of Electro-Communications , Chofu , Tokyo 182-8585 , Japan
| | - Yoshio Kobayashi
- Department of Engineering Science , The University of Electro-Communications , Chofu , Tokyo 182-8585 , Japan
| | - Takayuki Ishida
- Department of Engineering Science , The University of Electro-Communications , Chofu , Tokyo 182-8585 , Japan
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Kimura A, Ishida T. Spin-Crossover Temperature Predictable from DFT Calculation for Iron(II) Complexes with 4-Substituted Pybox and Related Heteroaromatic Ligands. ACS OMEGA 2018; 3:6737-6747. [PMID: 31458846 PMCID: PMC6644749 DOI: 10.1021/acsomega.8b01095] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/23/2018] [Accepted: 06/08/2018] [Indexed: 06/10/2023]
Abstract
Spin-crossover (SCO) is a reversible transition between low and high spin states by external stimuli such as heat. The SCO behavior and transition temperature (T 1/2) of a series of [FeII(X-pybox)2](ClO4)2 were studied to establish a methodology for ligand-field engineering, where X-pybox stands for 2,6-bis(oxazolin-2-yl)pyridine substituted with X at the 4-position of the pyridine ring. We utilized X = MeO, Me, 3-thienyl, Ph, H, MeS, 2-thienyl, N3, Cl, Br, 3-pyridyl, and 4-pyridyl. The solution susceptometry on five new derivatives with X = Me, 2-thienyl, N3, Br, and 3-pyridyl was performed in acetone, giving the SCO temperatures of 220, 260, 215, 280, and 270 K, respectively. The density-functional-theory molecular orbital (MO) calculation was performed on the ligands with geometry optimization. The atomic charge on the pyridine nitrogen atom [ρ(Npy)] was extracted from the natural orbital population analysis. Positive correlation appeared in the T 1/2 versus ρ(Npy) plot with R 2 = 0.734, being consistent with the analysis using the Hammett substituent constants (σp and σp +). This finding well agrees with the mechanism proposed: the rich electron density lifts the t2g energy level through the dπ-pπ interaction, resulting in a narrow t2g-eg energy gap and favoring the high-spin state and low T 1/2. The MO method was successfully applied to the known SCO-active iron(II) compounds involving 4-substituted 2,6-bis(pyrazol-1-yl)pyridines. A distinct positive correlation appeared in the T 1/2 versus ρ(Npy) plot. The comparison of correlation coefficients indicates that ρ(Npy) is a more reliable parameter than σp or σp + to predict a shift of T 1/2. Furthermore, this method can be more generalized by application to another known SCO family having 3-azinyl-4-p-tolyl-5-phenyl-1,2,4-triazole ligand series, where azinyl stands for a 2-azaaromatic ring. A good linear correlation was found in the T 1/2 versus ρ(NA) plot (NA is the ligating nitrogen atom in the azaaromatic ring). Finally, we will state a reason why the present treatment is competent to predict the SCO equilibrium position only by consideration on the electronic perturbation.
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