Heat Capacity Study of the Abrupt Valence-detrapping Phase Transition of Mixed-valence [Mn3O(O2CCH3)6(py)3]⋅ Py

Motohiro Nakano; Michio Sorai; David N. Hendrickson; John B. Vincent; George Christou; Ho G. Jang

doi:10.1021/ic00325a014

Heat Capacity Study of the Abrupt Valence-detrapping Phase Transition of Mixed-valence [Mn₃O(O₂CCH₃)₆(py)₃]⋅ Py

Motohiro Nakano, Michio Sorai, David N. Hendrickson, John B. Vincent, George Christou, Ho G. Jang

College of Science

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Abstract

The heat capacity of the mixed-valence complex [Mn₃O(O₂CCH₃)₆(py)₃].py, where py is pyridine, has been measured with an adiabatic calorimeter between 13 and 300 K. A phase transition with a sharp heat capacity peak has been found at 184.65 K. The enthalpy and entropy of the phase transition are ΔH = 6460 J mol^-1and ΔS = 35.77 J K^_1mol^-1. From a comparison of the present calorimetric results with the results of single-crystal X-ray diffraction, magnetic susceptibility, and solid-state²H NMR studies, it is concluded that the phase transition is associated with the onset of rapid intramolecular electron transfer in the mixed-valence Mn₃0 complexes and the orientational disordering of the pyridine solvate molecules. The former contribution to ΔS is R In 4, while the latter is R In 18, where R is the gas constant. The total entropy gain from these two contributions, R In 72 (=35.56 J K^_1mol'¹), agrees well with the observed ΔS. In the high-temperature valence-detrapped phase each Mn₃0 complex is dynamically interconverting between four configurations, where in three cases the “extra” electron resides on one manganese ion and the Mn₃0 unit is distorted as an isosceles triangle and in the fourth configuration the Mn₃0 unit is a symmetric equilateral triangle that is electronically delocalized. The contribution of R In 18 results from the disordering of the pyridine solvate molecule about a pseudo-C₆axis perpendicular to the plane of the pyridine and 3-fold reorientations about the crystallographic C₃axis where the plane of the pyridine solvate molecule in each of its positions is tipped ~15° off the C₃axis. Together with the isostructural mixed-valence complex [Fe₃O(O₂CCH₃)₆(py)₃](CHCl₃), the present complex [Mn₃O(O₂CCH₃)₆(py)₃]⋅py is one of two R32 symmetry trinuclear mixed-valence complexes in which the static electron delocalization state has clearly been found to occur as a constituent in the valence-detrapped phase.

Original language	English
Pages (from-to)	4608-4614
Number of pages	7
Journal	Inorganic Chemistry
Volume	28
Issue number	26
DOIs	https://doi.org/10.1021/ic00325a014
Publication status	Published - 1989 Dec 1

ASJC Scopus subject areas

Physical and Theoretical Chemistry
Inorganic Chemistry

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@article{51d8c24497734fcea2b143c835f7ede2,

title = "Heat Capacity Study of the Abrupt Valence-detrapping Phase Transition of Mixed-valence [Mn3O(O2CCH3)6(py)3]⋅ Py",

abstract = "The heat capacity of the mixed-valence complex [Mn3O(O2CCH3)6(py)3].py, where py is pyridine, has been measured with an adiabatic calorimeter between 13 and 300 K. A phase transition with a sharp heat capacity peak has been found at 184.65 K. The enthalpy and entropy of the phase transition are ΔH = 6460 J mol-1and ΔS = 35.77 J K_1mol-1. From a comparison of the present calorimetric results with the results of single-crystal X-ray diffraction, magnetic susceptibility, and solid-state2H NMR studies, it is concluded that the phase transition is associated with the onset of rapid intramolecular electron transfer in the mixed-valence Mn30 complexes and the orientational disordering of the pyridine solvate molecules. The former contribution to ΔS is R In 4, while the latter is R In 18, where R is the gas constant. The total entropy gain from these two contributions, R In 72 (=35.56 J K_1mol'1), agrees well with the observed ΔS. In the high-temperature valence-detrapped phase each Mn30 complex is dynamically interconverting between four configurations, where in three cases the “extra” electron resides on one manganese ion and the Mn30 unit is distorted as an isosceles triangle and in the fourth configuration the Mn30 unit is a symmetric equilateral triangle that is electronically delocalized. The contribution of R In 18 results from the disordering of the pyridine solvate molecule about a pseudo-C6axis perpendicular to the plane of the pyridine and 3-fold reorientations about the crystallographic C3axis where the plane of the pyridine solvate molecule in each of its positions is tipped ~15° off the C3axis. Together with the isostructural mixed-valence complex [Fe3O(O2CCH3)6(py)3](CHCl3), the present complex [Mn3O(O2CCH3)6(py)3]⋅py is one of two R32 symmetry trinuclear mixed-valence complexes in which the static electron delocalization state has clearly been found to occur as a constituent in the valence-detrapped phase.",

author = "Motohiro Nakano and Michio Sorai and Hendrickson, {David N.} and Vincent, {John B.} and George Christou and Jang, {Ho G.}",

year = "1989",

month = dec,

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doi = "10.1021/ic00325a014",

language = "English",

volume = "28",

pages = "4608--4614",

journal = "Inorganic Chemistry",

issn = "0020-1669",

publisher = "American Chemical Society",

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T1 - Heat Capacity Study of the Abrupt Valence-detrapping Phase Transition of Mixed-valence [Mn3O(O2CCH3)6(py)3]⋅ Py

AU - Nakano, Motohiro

AU - Sorai, Michio

AU - Hendrickson, David N.

AU - Vincent, John B.

AU - Christou, George

AU - Jang, Ho G.

PY - 1989/12/1

Y1 - 1989/12/1

N2 - The heat capacity of the mixed-valence complex [Mn3O(O2CCH3)6(py)3].py, where py is pyridine, has been measured with an adiabatic calorimeter between 13 and 300 K. A phase transition with a sharp heat capacity peak has been found at 184.65 K. The enthalpy and entropy of the phase transition are ΔH = 6460 J mol-1and ΔS = 35.77 J K_1mol-1. From a comparison of the present calorimetric results with the results of single-crystal X-ray diffraction, magnetic susceptibility, and solid-state2H NMR studies, it is concluded that the phase transition is associated with the onset of rapid intramolecular electron transfer in the mixed-valence Mn30 complexes and the orientational disordering of the pyridine solvate molecules. The former contribution to ΔS is R In 4, while the latter is R In 18, where R is the gas constant. The total entropy gain from these two contributions, R In 72 (=35.56 J K_1mol'1), agrees well with the observed ΔS. In the high-temperature valence-detrapped phase each Mn30 complex is dynamically interconverting between four configurations, where in three cases the “extra” electron resides on one manganese ion and the Mn30 unit is distorted as an isosceles triangle and in the fourth configuration the Mn30 unit is a symmetric equilateral triangle that is electronically delocalized. The contribution of R In 18 results from the disordering of the pyridine solvate molecule about a pseudo-C6axis perpendicular to the plane of the pyridine and 3-fold reorientations about the crystallographic C3axis where the plane of the pyridine solvate molecule in each of its positions is tipped ~15° off the C3axis. Together with the isostructural mixed-valence complex [Fe3O(O2CCH3)6(py)3](CHCl3), the present complex [Mn3O(O2CCH3)6(py)3]⋅py is one of two R32 symmetry trinuclear mixed-valence complexes in which the static electron delocalization state has clearly been found to occur as a constituent in the valence-detrapped phase.

AB - The heat capacity of the mixed-valence complex [Mn3O(O2CCH3)6(py)3].py, where py is pyridine, has been measured with an adiabatic calorimeter between 13 and 300 K. A phase transition with a sharp heat capacity peak has been found at 184.65 K. The enthalpy and entropy of the phase transition are ΔH = 6460 J mol-1and ΔS = 35.77 J K_1mol-1. From a comparison of the present calorimetric results with the results of single-crystal X-ray diffraction, magnetic susceptibility, and solid-state2H NMR studies, it is concluded that the phase transition is associated with the onset of rapid intramolecular electron transfer in the mixed-valence Mn30 complexes and the orientational disordering of the pyridine solvate molecules. The former contribution to ΔS is R In 4, while the latter is R In 18, where R is the gas constant. The total entropy gain from these two contributions, R In 72 (=35.56 J K_1mol'1), agrees well with the observed ΔS. In the high-temperature valence-detrapped phase each Mn30 complex is dynamically interconverting between four configurations, where in three cases the “extra” electron resides on one manganese ion and the Mn30 unit is distorted as an isosceles triangle and in the fourth configuration the Mn30 unit is a symmetric equilateral triangle that is electronically delocalized. The contribution of R In 18 results from the disordering of the pyridine solvate molecule about a pseudo-C6axis perpendicular to the plane of the pyridine and 3-fold reorientations about the crystallographic C3axis where the plane of the pyridine solvate molecule in each of its positions is tipped ~15° off the C3axis. Together with the isostructural mixed-valence complex [Fe3O(O2CCH3)6(py)3](CHCl3), the present complex [Mn3O(O2CCH3)6(py)3]⋅py is one of two R32 symmetry trinuclear mixed-valence complexes in which the static electron delocalization state has clearly been found to occur as a constituent in the valence-detrapped phase.

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ER -

Heat Capacity Study of the Abrupt Valence-detrapping Phase Transition of Mixed-valence [Mn₃O(O₂CCH₃)₆(py)₃]⋅ Py

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