Heat capacity study of the abrupt valence-detrapping phase transition of mixed-valence [Mn3O(O2CCH3)6(py) 3]·py

Motohiro Nakano, Michio Sorai, John B. Vincent, George Christou, Ho G. Jang, Ho Gyeom Jang

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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-1 and ΔS = 35.77 J K-1 mol-1. From a comparison of the present calorimetric results with the results of single-crystal X-ray diffraction, magnetic susceptibility, and solid-state 2H NMR studies, it is concluded that the phase transition is associated with the onset of rapid intramolecular electron transfer in the mixed-valence Mn3O complexes and the orientational disordering of the pyridine solvate molecules. The former contribution to ΔS is R ln 4, while the latter is R ln 18, where R is the gas constant. The total entropy gain from these two contributions, R ln 72 (=35.56 J K-1 mol-1), agrees well with the observed ΔS. In the high-temperature valence-detrapped phase each Mn3O complex is dynamically interconverting between four configurations, where in three cases the "extra" electron resides on one manganese ion and the Mn3O unit is distorted as an isosceles triangle and in the fourth configuration the Mn3O unit is a symmetric equilateral triangle that is electronically delocalized. The contribution of R ln 18 results from the disordering of the pyridine solvate molecule about a pseudo-C6 axis perpendicular to the plane of the pyridine and 3-fold reorientations about the crystallographic C3 axis where the plane of the pyridine solvate molecule in each of its positions is tipped ∼15° off the C3 axis. 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 languageEnglish
Pages (from-to)4608-4614
Number of pages7
JournalInorganic Chemistry
Volume28
Issue number26
Publication statusPublished - 1989 Dec 1
Externally publishedYes

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Phase Transition
Specific heat
Hot Temperature
Phase transitions
specific heat
pyridines
valence
Entropy
Electrons
Molecules
triangles
entropy
molecules
manganese ions
Manganese
Calorimeters
Magnetic susceptibility
X-Ray Diffraction
Electron energy levels
electron states

ASJC Scopus subject areas

  • Inorganic Chemistry

Cite this

Heat capacity study of the abrupt valence-detrapping phase transition of mixed-valence [Mn3O(O2CCH3)6(py) 3]·py. / Nakano, Motohiro; Sorai, Michio; Vincent, John B.; Christou, George; Jang, Ho G.; Jang, Ho Gyeom.

In: Inorganic Chemistry, Vol. 28, No. 26, 01.12.1989, p. 4608-4614.

Research output: Contribution to journalArticle

Nakano, M, Sorai, M, Vincent, JB, Christou, G, Jang, HG & Jang, HG 1989, 'Heat capacity study of the abrupt valence-detrapping phase transition of mixed-valence [Mn3O(O2CCH3)6(py) 3]·py', Inorganic Chemistry, vol. 28, no. 26, pp. 4608-4614.
Nakano, Motohiro ; Sorai, Michio ; Vincent, John B. ; Christou, George ; Jang, Ho G. ; Jang, Ho Gyeom. / Heat capacity study of the abrupt valence-detrapping phase transition of mixed-valence [Mn3O(O2CCH3)6(py) 3]·py. In: Inorganic Chemistry. 1989 ; Vol. 28, No. 26. pp. 4608-4614.
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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-1 and ΔS = 35.77 J K-1 mol-1. From a comparison of the present calorimetric results with the results of single-crystal X-ray diffraction, magnetic susceptibility, and solid-state 2H NMR studies, it is concluded that the phase transition is associated with the onset of rapid intramolecular electron transfer in the mixed-valence Mn3O complexes and the orientational disordering of the pyridine solvate molecules. The former contribution to ΔS is R ln 4, while the latter is R ln 18, where R is the gas constant. The total entropy gain from these two contributions, R ln 72 (=35.56 J K-1 mol-1), agrees well with the observed ΔS. In the high-temperature valence-detrapped phase each Mn3O complex is dynamically interconverting between four configurations, where in three cases the {"}extra{"} electron resides on one manganese ion and the Mn3O unit is distorted as an isosceles triangle and in the fourth configuration the Mn3O unit is a symmetric equilateral triangle that is electronically delocalized. The contribution of R ln 18 results from the disordering of the pyridine solvate molecule about a pseudo-C6 axis perpendicular to the plane of the pyridine and 3-fold reorientations about the crystallographic C3 axis where the plane of the pyridine solvate molecule in each of its positions is tipped ∼15° off the C3 axis. 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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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-1 and ΔS = 35.77 J K-1 mol-1. From a comparison of the present calorimetric results with the results of single-crystal X-ray diffraction, magnetic susceptibility, and solid-state 2H NMR studies, it is concluded that the phase transition is associated with the onset of rapid intramolecular electron transfer in the mixed-valence Mn3O complexes and the orientational disordering of the pyridine solvate molecules. The former contribution to ΔS is R ln 4, while the latter is R ln 18, where R is the gas constant. The total entropy gain from these two contributions, R ln 72 (=35.56 J K-1 mol-1), agrees well with the observed ΔS. In the high-temperature valence-detrapped phase each Mn3O complex is dynamically interconverting between four configurations, where in three cases the "extra" electron resides on one manganese ion and the Mn3O unit is distorted as an isosceles triangle and in the fourth configuration the Mn3O unit is a symmetric equilateral triangle that is electronically delocalized. The contribution of R ln 18 results from the disordering of the pyridine solvate molecule about a pseudo-C6 axis perpendicular to the plane of the pyridine and 3-fold reorientations about the crystallographic C3 axis where the plane of the pyridine solvate molecule in each of its positions is tipped ∼15° off the C3 axis. 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-1 and ΔS = 35.77 J K-1 mol-1. From a comparison of the present calorimetric results with the results of single-crystal X-ray diffraction, magnetic susceptibility, and solid-state 2H NMR studies, it is concluded that the phase transition is associated with the onset of rapid intramolecular electron transfer in the mixed-valence Mn3O complexes and the orientational disordering of the pyridine solvate molecules. The former contribution to ΔS is R ln 4, while the latter is R ln 18, where R is the gas constant. The total entropy gain from these two contributions, R ln 72 (=35.56 J K-1 mol-1), agrees well with the observed ΔS. In the high-temperature valence-detrapped phase each Mn3O complex is dynamically interconverting between four configurations, where in three cases the "extra" electron resides on one manganese ion and the Mn3O unit is distorted as an isosceles triangle and in the fourth configuration the Mn3O unit is a symmetric equilateral triangle that is electronically delocalized. The contribution of R ln 18 results from the disordering of the pyridine solvate molecule about a pseudo-C6 axis perpendicular to the plane of the pyridine and 3-fold reorientations about the crystallographic C3 axis where the plane of the pyridine solvate molecule in each of its positions is tipped ∼15° off the C3 axis. 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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