Subrata Tewary - Academia.edu (original) (raw)

Papers by Subrata Tewary

Research paper thumbnail of CCDC 925600: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Research paper thumbnail of Theoretical Perspectives on Redox “Non-Innocent” Oxazolidine N -Oxide Iron Nitroxide Complexes

European Journal of Inorganic Chemistry, 2013

One-electron redox processes in ligands that exhibit noninnocent behaviour invariably leads to th... more One-electron redox processes in ligands that exhibit noninnocent behaviour invariably leads to the generation of radical species, which, when coupled with redox-active metal centres, can lead to strong magnetic exchange, ambiguous electronic structures and even spin crossover (SCO). We have chosen two iron complexes [Fe II (L · ) 2 ](BF 4 ) 2 (1) and [Fe III (L -) 2 ]-(BPh 4 ) (2) [with L · = 4-dimethyl-2,2-di(2-pyridyl)oxazolidine N-oxide] as the basis for an extensive theoretical study to determine the influence and interplay of the strong magnetic [a]

Research paper thumbnail of A synthetic strategy for switching the single ion anisotropy in tetrahedral Co( ii ) complexes

Chem. Commun., 2015

Four novel mononuclear tetrahedral cobalt(II) complexes containing exocyclic mesoionic ligands of... more Four novel mononuclear tetrahedral cobalt(II) complexes containing exocyclic mesoionic ligands of molecular formulae [Co II (L 1 )(X) 2 (MeCN)] X = Cl (1) or Br (2) and [Co II (L 2 )(X) 2 (MeCN)], X = Cl (3) or Br (4) have been reported. It is found that simple substitution of L 1 (O donor in 1 and 2) by L 2 (S donor in 3 and 4) results in switching of the single ion magnetic anisotropy parameter (D) from positive to negative, with a significant change in magnitude.

Research paper thumbnail of Solvate-dependent spin crossover and exchange in cobalt(II) oxazolidine nitroxide chelates

Inorganic chemistry, Jan 19, 2014

Two oxazolidine nitroxide complexes of cobalt(II), [Co(II)(L(•))2](B(C6F5)4)2·CH2Cl2 (1) and [Co(... more Two oxazolidine nitroxide complexes of cobalt(II), [Co(II)(L(•))2](B(C6F5)4)2·CH2Cl2 (1) and [Co(II)(L(•))2](B(C6F5)4)2·2Et2O (2), where, L(•) is the tridentate chelator 4,4-dimethyl-2,2-bis(2-pyridyl)oxazolidine N-oxide, have been investigated by crystallographic, magnetic, reflectivity, and theoretical (DFT) methods. This work follows on from a related study on [Co(II)(L(•))2](NO3)2 (3), a multifunctional complex that simultaneously displays magnetic exchange, spin crossover, and single molecule magnetic features. Changing the anion and the nature of solvation in the present crystalline species leads to significant differences, not only between 1 and 2 but also in comparison to 3. Structural data at 123 and 273 K, in combination with magnetic data, show that at lower temperatures 1 displays low-spin Co(II)-to-radical exchange with differences in fitted J values in comparison to DFT (broken symmetry) calculated J values ascribed to the sensitive influence of a tilt angle (θ) formed...

Research paper thumbnail of Characterization of a Robust Co II Fluorescent Complex Deposited Intact On HOPG

Chemistry - A European Journal, 2014

The new diimine fluorescent ligand ACRI-1 based on a central acridine yellow core is reported alo... more The new diimine fluorescent ligand ACRI-1 based on a central acridine yellow core is reported along with its coordination complex [Co2 (ACRI-1)2 ] (1), a fluorescent weak ferromagnet. Due to the strong fluorescence of the acridine yellow fluorophore, it is not completely quenched when the ligand is coordinated to Co(II) . The magnetic properties of bulk complex 1 and its stability in solution have been studied. Complex 1 has been deposited on highly ordered pyrolitic graphite (HOGP) from solution. The thin films prepared have been characterized by AFM, time-of-flight secondary ion mass spectrometry (TOF-SIMS), grazing incidence X-ray diffraction (GIXRD), X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD) and theoretical calculations. The data show that the complex is robust and remains intact on the surface of graphite.

Research paper thumbnail of Enhancing the double exchange interaction in a mixed valence {VIII–VII} pair: a theoretical perspective

Dalton Transactions, 2013

The magnetic interaction between V(II)-V(II) is calculated using the Hamiltonian, J is the isotro... more The magnetic interaction between V(II)-V(II) is calculated using the Hamiltonian, J is the isotropic coupling constant and S v 2+ is the spin of V(II) centres. J values are computed from the energy differences between the high spin (HS) state, which is calculated using single determinant wave functions and low spin (BS) state, determined using Broken Symmetry (BS) approach developed by Noodleman.1 ,2 The BS approach was proved to be handy in evaluating the J values to a good estimate in variety of complexes. All the calculations for V 2+ -V 2+ complex has been done using B3LYP3 functional and TZV4 basis set.

Research paper thumbnail of CCDC 925600: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Research paper thumbnail of Theoretical Perspectives on Redox “Non-Innocent” Oxazolidine N -Oxide Iron Nitroxide Complexes

European Journal of Inorganic Chemistry, 2013

One-electron redox processes in ligands that exhibit noninnocent behaviour invariably leads to th... more One-electron redox processes in ligands that exhibit noninnocent behaviour invariably leads to the generation of radical species, which, when coupled with redox-active metal centres, can lead to strong magnetic exchange, ambiguous electronic structures and even spin crossover (SCO). We have chosen two iron complexes [Fe II (L · ) 2 ](BF 4 ) 2 (1) and [Fe III (L -) 2 ]-(BPh 4 ) (2) [with L · = 4-dimethyl-2,2-di(2-pyridyl)oxazolidine N-oxide] as the basis for an extensive theoretical study to determine the influence and interplay of the strong magnetic [a]

Research paper thumbnail of A synthetic strategy for switching the single ion anisotropy in tetrahedral Co( ii ) complexes

Chem. Commun., 2015

Four novel mononuclear tetrahedral cobalt(II) complexes containing exocyclic mesoionic ligands of... more Four novel mononuclear tetrahedral cobalt(II) complexes containing exocyclic mesoionic ligands of molecular formulae [Co II (L 1 )(X) 2 (MeCN)] X = Cl (1) or Br (2) and [Co II (L 2 )(X) 2 (MeCN)], X = Cl (3) or Br (4) have been reported. It is found that simple substitution of L 1 (O donor in 1 and 2) by L 2 (S donor in 3 and 4) results in switching of the single ion magnetic anisotropy parameter (D) from positive to negative, with a significant change in magnitude.

Research paper thumbnail of Solvate-dependent spin crossover and exchange in cobalt(II) oxazolidine nitroxide chelates

Inorganic chemistry, Jan 19, 2014

Two oxazolidine nitroxide complexes of cobalt(II), [Co(II)(L(•))2](B(C6F5)4)2·CH2Cl2 (1) and [Co(... more Two oxazolidine nitroxide complexes of cobalt(II), [Co(II)(L(•))2](B(C6F5)4)2·CH2Cl2 (1) and [Co(II)(L(•))2](B(C6F5)4)2·2Et2O (2), where, L(•) is the tridentate chelator 4,4-dimethyl-2,2-bis(2-pyridyl)oxazolidine N-oxide, have been investigated by crystallographic, magnetic, reflectivity, and theoretical (DFT) methods. This work follows on from a related study on [Co(II)(L(•))2](NO3)2 (3), a multifunctional complex that simultaneously displays magnetic exchange, spin crossover, and single molecule magnetic features. Changing the anion and the nature of solvation in the present crystalline species leads to significant differences, not only between 1 and 2 but also in comparison to 3. Structural data at 123 and 273 K, in combination with magnetic data, show that at lower temperatures 1 displays low-spin Co(II)-to-radical exchange with differences in fitted J values in comparison to DFT (broken symmetry) calculated J values ascribed to the sensitive influence of a tilt angle (θ) formed...

Research paper thumbnail of Characterization of a Robust Co II Fluorescent Complex Deposited Intact On HOPG

Chemistry - A European Journal, 2014

The new diimine fluorescent ligand ACRI-1 based on a central acridine yellow core is reported alo... more The new diimine fluorescent ligand ACRI-1 based on a central acridine yellow core is reported along with its coordination complex [Co2 (ACRI-1)2 ] (1), a fluorescent weak ferromagnet. Due to the strong fluorescence of the acridine yellow fluorophore, it is not completely quenched when the ligand is coordinated to Co(II) . The magnetic properties of bulk complex 1 and its stability in solution have been studied. Complex 1 has been deposited on highly ordered pyrolitic graphite (HOGP) from solution. The thin films prepared have been characterized by AFM, time-of-flight secondary ion mass spectrometry (TOF-SIMS), grazing incidence X-ray diffraction (GIXRD), X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD) and theoretical calculations. The data show that the complex is robust and remains intact on the surface of graphite.

Research paper thumbnail of Enhancing the double exchange interaction in a mixed valence {VIII–VII} pair: a theoretical perspective

Dalton Transactions, 2013

The magnetic interaction between V(II)-V(II) is calculated using the Hamiltonian, J is the isotro... more The magnetic interaction between V(II)-V(II) is calculated using the Hamiltonian, J is the isotropic coupling constant and S v 2+ is the spin of V(II) centres. J values are computed from the energy differences between the high spin (HS) state, which is calculated using single determinant wave functions and low spin (BS) state, determined using Broken Symmetry (BS) approach developed by Noodleman.1 ,2 The BS approach was proved to be handy in evaluating the J values to a good estimate in variety of complexes. All the calculations for V 2+ -V 2+ complex has been done using B3LYP3 functional and TZV4 basis set.