Redox thermodynamics of dinuclear transition-metal complexes. Unusual entropy and electronic coupling effects in mixed solvents

Jeff C. Curtis, Robert L. Blackbourn, Kelly S. Ennix, Shixu Hu, Jody A. Roberts, Joseph T Hupp

Research output: Contribution to journalArticle

37 Citations (Scopus)

Abstract

As a guide to the thermodynamics of intramolecular electron-transfer processes, the redox thermodynamics of three dinuclear transition-metal systems have been investigated in mixtures of acetonitrile and dimethyl sulfoxide (DMSO) as solvent. The specific systems are (2,2′-bipyridine)2ClRu-L-Ru(NH3) 4(pyridine)5+/4+/3+, where L is pyrazine, 4,4′-bipyridine, or bis(pyridyl)ethane. A special feature is that the tetraammineruthenium redox site in each interacts specifically with hydrogen-bond-accepting (electron-pair-donating) solvents (as demonstrated by various optical and electrochemical measurements (Curtis et al. Inorg. Chem. 1986, 25, 4233; 1987, 26, 2660)) whereas the (polypyridyl)ruthenium site does not. Thus, the formal potential (Ef) for the ammine fragment is shifted to progressively less positive values as the solvent is enriched in DMSO. Measurements of Ef for the RuIII/II-polypyridyl fragment demonstrate that the solvational effects are readily transmitted electronically from the ammine fragment when pyrazine is the bridge. Variable-temperature Ef measurements reveal a sharp positive "spike" in plots of the half-reaction entropy for each of the tetraammine couples versus mixed-solvent composition. A statistical calculation shows that the entropy spike is a direct consequence of the unsymmetrical preferential solvation of (2,2′-bipyridine)2RuII-L-RuIII(NH 3)4(pyridine)4+ versus (2,2′-bipyridme)2RuII-L-RuII(NH 3)4(pyridine)3+, as found elsewhere for monomeric redox couples and as earlier predicted from optical intervalence studies. Further examination shows that the entropy effects also are transmitted electronically from the tetraammine site to the polypyridyl site and are detectable in both the pyrazine- and 4,4′-bipyridine-bridged cases. An evaluation of the overall intervalence thermodynamics reveals that ΔSdeg;"leads" ΔG°on a solvent molar composition coordinate. This suggests that unusual mixed-solvent-induced variations in activation parameters might also be observed in related kinetic experiments.

Original languageEnglish
Pages (from-to)3791-3795
Number of pages5
JournalInorganic Chemistry
Volume28
Issue number20
Publication statusPublished - 1989

Fingerprint

Coordination Complexes
Transition metals
Entropy
transition metals
Thermodynamics
entropy
Pyrazines
thermodynamics
pyrazines
electronics
ammines
pyridines
fragments
Dimethyl Sulfoxide
spikes
Ethane
Ruthenium
Electrons
Solvation
Chemical analysis

ASJC Scopus subject areas

  • Inorganic Chemistry

Cite this

Redox thermodynamics of dinuclear transition-metal complexes. Unusual entropy and electronic coupling effects in mixed solvents. / Curtis, Jeff C.; Blackbourn, Robert L.; Ennix, Kelly S.; Hu, Shixu; Roberts, Jody A.; Hupp, Joseph T.

In: Inorganic Chemistry, Vol. 28, No. 20, 1989, p. 3791-3795.

Research output: Contribution to journalArticle

Curtis, Jeff C. ; Blackbourn, Robert L. ; Ennix, Kelly S. ; Hu, Shixu ; Roberts, Jody A. ; Hupp, Joseph T. / Redox thermodynamics of dinuclear transition-metal complexes. Unusual entropy and electronic coupling effects in mixed solvents. In: Inorganic Chemistry. 1989 ; Vol. 28, No. 20. pp. 3791-3795.
@article{52cff85de0ee409a983189830d192f0d,
title = "Redox thermodynamics of dinuclear transition-metal complexes. Unusual entropy and electronic coupling effects in mixed solvents",
abstract = "As a guide to the thermodynamics of intramolecular electron-transfer processes, the redox thermodynamics of three dinuclear transition-metal systems have been investigated in mixtures of acetonitrile and dimethyl sulfoxide (DMSO) as solvent. The specific systems are (2,2′-bipyridine)2ClRu-L-Ru(NH3) 4(pyridine)5+/4+/3+, where L is pyrazine, 4,4′-bipyridine, or bis(pyridyl)ethane. A special feature is that the tetraammineruthenium redox site in each interacts specifically with hydrogen-bond-accepting (electron-pair-donating) solvents (as demonstrated by various optical and electrochemical measurements (Curtis et al. Inorg. Chem. 1986, 25, 4233; 1987, 26, 2660)) whereas the (polypyridyl)ruthenium site does not. Thus, the formal potential (Ef) for the ammine fragment is shifted to progressively less positive values as the solvent is enriched in DMSO. Measurements of Ef for the RuIII/II-polypyridyl fragment demonstrate that the solvational effects are readily transmitted electronically from the ammine fragment when pyrazine is the bridge. Variable-temperature Ef measurements reveal a sharp positive {"}spike{"} in plots of the half-reaction entropy for each of the tetraammine couples versus mixed-solvent composition. A statistical calculation shows that the entropy spike is a direct consequence of the unsymmetrical preferential solvation of (2,2′-bipyridine)2RuII-L-RuIII(NH 3)4(pyridine)4+ versus (2,2′-bipyridme)2RuII-L-RuII(NH 3)4(pyridine)3+, as found elsewhere for monomeric redox couples and as earlier predicted from optical intervalence studies. Further examination shows that the entropy effects also are transmitted electronically from the tetraammine site to the polypyridyl site and are detectable in both the pyrazine- and 4,4′-bipyridine-bridged cases. An evaluation of the overall intervalence thermodynamics reveals that ΔSdeg;{"}leads{"} ΔG°on a solvent molar composition coordinate. This suggests that unusual mixed-solvent-induced variations in activation parameters might also be observed in related kinetic experiments.",
author = "Curtis, {Jeff C.} and Blackbourn, {Robert L.} and Ennix, {Kelly S.} and Shixu Hu and Roberts, {Jody A.} and Hupp, {Joseph T}",
year = "1989",
language = "English",
volume = "28",
pages = "3791--3795",
journal = "Inorganic Chemistry",
issn = "0020-1669",
publisher = "American Chemical Society",
number = "20",

}

TY - JOUR

T1 - Redox thermodynamics of dinuclear transition-metal complexes. Unusual entropy and electronic coupling effects in mixed solvents

AU - Curtis, Jeff C.

AU - Blackbourn, Robert L.

AU - Ennix, Kelly S.

AU - Hu, Shixu

AU - Roberts, Jody A.

AU - Hupp, Joseph T

PY - 1989

Y1 - 1989

N2 - As a guide to the thermodynamics of intramolecular electron-transfer processes, the redox thermodynamics of three dinuclear transition-metal systems have been investigated in mixtures of acetonitrile and dimethyl sulfoxide (DMSO) as solvent. The specific systems are (2,2′-bipyridine)2ClRu-L-Ru(NH3) 4(pyridine)5+/4+/3+, where L is pyrazine, 4,4′-bipyridine, or bis(pyridyl)ethane. A special feature is that the tetraammineruthenium redox site in each interacts specifically with hydrogen-bond-accepting (electron-pair-donating) solvents (as demonstrated by various optical and electrochemical measurements (Curtis et al. Inorg. Chem. 1986, 25, 4233; 1987, 26, 2660)) whereas the (polypyridyl)ruthenium site does not. Thus, the formal potential (Ef) for the ammine fragment is shifted to progressively less positive values as the solvent is enriched in DMSO. Measurements of Ef for the RuIII/II-polypyridyl fragment demonstrate that the solvational effects are readily transmitted electronically from the ammine fragment when pyrazine is the bridge. Variable-temperature Ef measurements reveal a sharp positive "spike" in plots of the half-reaction entropy for each of the tetraammine couples versus mixed-solvent composition. A statistical calculation shows that the entropy spike is a direct consequence of the unsymmetrical preferential solvation of (2,2′-bipyridine)2RuII-L-RuIII(NH 3)4(pyridine)4+ versus (2,2′-bipyridme)2RuII-L-RuII(NH 3)4(pyridine)3+, as found elsewhere for monomeric redox couples and as earlier predicted from optical intervalence studies. Further examination shows that the entropy effects also are transmitted electronically from the tetraammine site to the polypyridyl site and are detectable in both the pyrazine- and 4,4′-bipyridine-bridged cases. An evaluation of the overall intervalence thermodynamics reveals that ΔSdeg;"leads" ΔG°on a solvent molar composition coordinate. This suggests that unusual mixed-solvent-induced variations in activation parameters might also be observed in related kinetic experiments.

AB - As a guide to the thermodynamics of intramolecular electron-transfer processes, the redox thermodynamics of three dinuclear transition-metal systems have been investigated in mixtures of acetonitrile and dimethyl sulfoxide (DMSO) as solvent. The specific systems are (2,2′-bipyridine)2ClRu-L-Ru(NH3) 4(pyridine)5+/4+/3+, where L is pyrazine, 4,4′-bipyridine, or bis(pyridyl)ethane. A special feature is that the tetraammineruthenium redox site in each interacts specifically with hydrogen-bond-accepting (electron-pair-donating) solvents (as demonstrated by various optical and electrochemical measurements (Curtis et al. Inorg. Chem. 1986, 25, 4233; 1987, 26, 2660)) whereas the (polypyridyl)ruthenium site does not. Thus, the formal potential (Ef) for the ammine fragment is shifted to progressively less positive values as the solvent is enriched in DMSO. Measurements of Ef for the RuIII/II-polypyridyl fragment demonstrate that the solvational effects are readily transmitted electronically from the ammine fragment when pyrazine is the bridge. Variable-temperature Ef measurements reveal a sharp positive "spike" in plots of the half-reaction entropy for each of the tetraammine couples versus mixed-solvent composition. A statistical calculation shows that the entropy spike is a direct consequence of the unsymmetrical preferential solvation of (2,2′-bipyridine)2RuII-L-RuIII(NH 3)4(pyridine)4+ versus (2,2′-bipyridme)2RuII-L-RuII(NH 3)4(pyridine)3+, as found elsewhere for monomeric redox couples and as earlier predicted from optical intervalence studies. Further examination shows that the entropy effects also are transmitted electronically from the tetraammine site to the polypyridyl site and are detectable in both the pyrazine- and 4,4′-bipyridine-bridged cases. An evaluation of the overall intervalence thermodynamics reveals that ΔSdeg;"leads" ΔG°on a solvent molar composition coordinate. This suggests that unusual mixed-solvent-induced variations in activation parameters might also be observed in related kinetic experiments.

UR - http://www.scopus.com/inward/record.url?scp=33845183050&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=33845183050&partnerID=8YFLogxK

M3 - Article

VL - 28

SP - 3791

EP - 3795

JO - Inorganic Chemistry

JF - Inorganic Chemistry

SN - 0020-1669

IS - 20

ER -