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Please use this identifier to cite or link to this item: http://repository.iitr.ac.in/handle/123456789/3408
Title: Lattice-dictated conformers in bis(pyrazolyl)pyridine-based iron(II)complexes: Mössbauer, NMR, and magnetic studies
Authors: Manikandan P.
Padmakumar K.
Justin Thomas K.R.
Varghese B.
Onodera H.
Manoharan P.T.
Published in: Inorganic Chemistry
Abstract: Iron(II) complexes [FeL2](ClO4)2·CH3CN, [FeL2](BPh4)2·2CH3CN, and [FeL2](PF6)2 with an FeN6 chromophore of the same ligand L (2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine) and differing counterions have been made and their crystal and molecular structures determined. The first two crystallized in triclinic space group P 1, and the third, with PF6- anion in Ibca space group. The FeL2 complex ions in all lattices have similarly distorted octahedral geometry. Variable-temperature Mössbauer spectra of [FeL2](ClO4)2·CH3CN and [FeL2](PF6)2 measured in the temperature range 1.7-300 K reveal temperature-dependent populations of two different spin states with increased amount of low-spin form at high temperatures, a phenomenon unlike the normal spin crossover behavior; this abnormal behavior is interpreted here as due to the presence of two different conformations. It is very interesting to note that the two different compounds have similar spectra, Mössbauer parameters, and temperature dependence. But the variable-temperature Mössbauer spectra of [FeL2](Bob4)2·2CH3CN in the range 20-300 K do not show the presence of such different species but exhibit a clear phase transition at ̃200 K. This phase transition is further supported by SQUID measurements. The results of variable-temperature 1H NMR in CD3CN and the solution susceptibility measurement of all complexes also support the presence of high-spin and low-spin forms in solution. Hence, the complex ion [FeL2]2+ exhibits a thermally driven interconversion between low-spin and a high-spin structural forms - A phenomenon observed in the solid and solution states due to ligand dynamics. This is not due to the well-known spin crossover phenomenon. These results are compared with the case of normal spin crossover seen in [FeL′2](C1O4)2 (L′ = 2,6-(bis(pyrazol-1-ylmethyl)pyridine)).
Citation: Inorganic Chemistry (2001), 40(27): 6930-6939
URI: https://doi.org/10.1021/ic010655g
http://repository.iitr.ac.in/handle/123456789/3408
Issue Date: 2001
ISSN: 201669
Author Scopus IDs: 55767788400
39161676800
57203389297
14016867200
57188835057
15120961900
Author Affiliations: Manikandan, P., Department of Chemistry, Regional Sophisticated Instrumentation Centre, Indian Institute of Technology/Madras, Chennai-600 036, India
Padmakumar, K., Department of Chemistry, Regional Sophisticated Instrumentation Centre, Indian Institute of Technology/Madras, Chennai-600 036, India, JNCASR, Bangalore, India
Justin Thomas, K.R., Department of Chemistry, Regional Sophisticated Instrumentation Centre, Indian Institute of Technology/Madras, Chennai-600 036, India
Varghese, B., Department of Chemistry, Regional Sophisticated Instrumentation Centre, Indian Institute of Technology/Madras, Chennai-600 036, India
Onodera, H., Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
Manoharan, P.T., Department of Chemistry, Regional Sophisticated Instrumentation Centre, Indian Institute of Technology/Madras, Chennai-600 036, India, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India
Corresponding Author: Manoharan, P.T.; Department of Chemistry, Reg. Sophisticated Instrum. Centre, Indian Inst. of Technol. and Madras, Chennai-600 036, India; email: ptm@magnet.iitm.ernet.in
Appears in Collections:Journal Publications [CY]

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