M-M bond-stretching energy landscapes for M 2(dimen) 4 2+ (M = Rh, Ir; Dimen = 1,8-diisocyanomenthane) complexes

Bryan M. Hunter, Randy M. Villahermosa, Christopher L. Exstrom, Michael G. Hill, Kent R. Mann, Harry B. Gray

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Abstract

Isomers of Ir 2(dimen) 4 2+ (dimen = 1,8-diisocyanomenthane) exhibit different Ir-Ir bond distances in a 2:1 MTHF/EtCN solution (MTHF = 2-methyltetrahydrofuran). Variable-temperature absorption data suggest that the isomer with the shorter Ir-Ir distance is favored at room temperature [K = ∼8; δH° = -0.8 kcal/mol; δS° = 1.44 cal mol -1 K -1]. We report calculations that shed light on M 2(dimen) 4 2+ (M = Rh, Ir) structural differences: (1) metal-metal interaction favors short distances; (2) ligand deformational-strain energy favors long distances; (3) out-of-plane (A 2u) distortion promotes twisting of the ligand backbone at short metal-metal separations. Calculated potential-energy surfaces reveal a double minimum for Ir 2(dimen) 4 2+ (∼4.1 Å Ir-Ir with 0° twist angle and ∼3.6 Å Ir-Ir with ±12° twist angle) but not for the rhodium analogue (∼4.5 Å Rh-Rh with no twisting). Because both the ligand strain and A 2u distortional energy are virtually identical for the two complexes, the strength of the metal-metal interaction is the determining factor. On the basis of the magnitude of this interaction, we obtain the following results: (1) a single-minimum (along the Ir-Ir coordinate), harmonic potential-energy surface for the triplet electronic excited state of Ir 2(dimen) 4 2+ (R e,Ir-Ir = 2.87 Å; F Ir-Ir = 0.99 mdyn Å -1); (2) a single-minimum, anharmonic surface for the ground state of Rh 2(dimen) 4 2+ (R e,Rh-Rh = 3.23 Å; F Rh-Rh = 0.09 mdyn Å -1); (3) a double-minimum (along the Ir-Ir coordinate) surface for the ground state of Ir 2(dimen) 4 2+ (R e,Ir-Ir = 3.23 Å; F Ir-Ir = 0.16 mdyn Å -1).

Original languageEnglish (US)
Pages (from-to)6898-6905
Number of pages8
JournalInorganic Chemistry
Volume51
Issue number12
DOIs
StatePublished - Jun 18 2012

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Stretching
Metals
metals
Potential energy surfaces
twisting
Ligands
Isomers
Ground state
ligands
energy
isomers
potential energy
Rhodium
ground state
interactions
Strain energy
rhodium
Excited states
analogs
harmonics

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

Cite this

M-M bond-stretching energy landscapes for M 2(dimen) 4 2+ (M = Rh, Ir; Dimen = 1,8-diisocyanomenthane) complexes. / Hunter, Bryan M.; Villahermosa, Randy M.; Exstrom, Christopher L.; Hill, Michael G.; Mann, Kent R.; Gray, Harry B.

In: Inorganic Chemistry, Vol. 51, No. 12, 18.06.2012, p. 6898-6905.

Research output: Contribution to journalArticle

Hunter, Bryan M. ; Villahermosa, Randy M. ; Exstrom, Christopher L. ; Hill, Michael G. ; Mann, Kent R. ; Gray, Harry B. / M-M bond-stretching energy landscapes for M 2(dimen) 4 2+ (M = Rh, Ir; Dimen = 1,8-diisocyanomenthane) complexes. In: Inorganic Chemistry. 2012 ; Vol. 51, No. 12. pp. 6898-6905.
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title = "M-M bond-stretching energy landscapes for M 2(dimen) 4 2+ (M = Rh, Ir; Dimen = 1,8-diisocyanomenthane) complexes",
abstract = "Isomers of Ir 2(dimen) 4 2+ (dimen = 1,8-diisocyanomenthane) exhibit different Ir-Ir bond distances in a 2:1 MTHF/EtCN solution (MTHF = 2-methyltetrahydrofuran). Variable-temperature absorption data suggest that the isomer with the shorter Ir-Ir distance is favored at room temperature [K = ∼8; δH° = -0.8 kcal/mol; δS° = 1.44 cal mol -1 K -1]. We report calculations that shed light on M 2(dimen) 4 2+ (M = Rh, Ir) structural differences: (1) metal-metal interaction favors short distances; (2) ligand deformational-strain energy favors long distances; (3) out-of-plane (A 2u) distortion promotes twisting of the ligand backbone at short metal-metal separations. Calculated potential-energy surfaces reveal a double minimum for Ir 2(dimen) 4 2+ (∼4.1 {\AA} Ir-Ir with 0° twist angle and ∼3.6 {\AA} Ir-Ir with ±12° twist angle) but not for the rhodium analogue (∼4.5 {\AA} Rh-Rh with no twisting). Because both the ligand strain and A 2u distortional energy are virtually identical for the two complexes, the strength of the metal-metal interaction is the determining factor. On the basis of the magnitude of this interaction, we obtain the following results: (1) a single-minimum (along the Ir-Ir coordinate), harmonic potential-energy surface for the triplet electronic excited state of Ir 2(dimen) 4 2+ (R e,Ir-Ir = 2.87 {\AA}; F Ir-Ir = 0.99 mdyn {\AA} -1); (2) a single-minimum, anharmonic surface for the ground state of Rh 2(dimen) 4 2+ (R e,Rh-Rh = 3.23 {\AA}; F Rh-Rh = 0.09 mdyn {\AA} -1); (3) a double-minimum (along the Ir-Ir coordinate) surface for the ground state of Ir 2(dimen) 4 2+ (R e,Ir-Ir = 3.23 {\AA}; F Ir-Ir = 0.16 mdyn {\AA} -1).",
author = "Hunter, {Bryan M.} and Villahermosa, {Randy M.} and Exstrom, {Christopher L.} and Hill, {Michael G.} and Mann, {Kent R.} and Gray, {Harry B.}",
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T1 - M-M bond-stretching energy landscapes for M 2(dimen) 4 2+ (M = Rh, Ir; Dimen = 1,8-diisocyanomenthane) complexes

AU - Hunter, Bryan M.

AU - Villahermosa, Randy M.

AU - Exstrom, Christopher L.

AU - Hill, Michael G.

AU - Mann, Kent R.

AU - Gray, Harry B.

PY - 2012/6/18

Y1 - 2012/6/18

N2 - Isomers of Ir 2(dimen) 4 2+ (dimen = 1,8-diisocyanomenthane) exhibit different Ir-Ir bond distances in a 2:1 MTHF/EtCN solution (MTHF = 2-methyltetrahydrofuran). Variable-temperature absorption data suggest that the isomer with the shorter Ir-Ir distance is favored at room temperature [K = ∼8; δH° = -0.8 kcal/mol; δS° = 1.44 cal mol -1 K -1]. We report calculations that shed light on M 2(dimen) 4 2+ (M = Rh, Ir) structural differences: (1) metal-metal interaction favors short distances; (2) ligand deformational-strain energy favors long distances; (3) out-of-plane (A 2u) distortion promotes twisting of the ligand backbone at short metal-metal separations. Calculated potential-energy surfaces reveal a double minimum for Ir 2(dimen) 4 2+ (∼4.1 Å Ir-Ir with 0° twist angle and ∼3.6 Å Ir-Ir with ±12° twist angle) but not for the rhodium analogue (∼4.5 Å Rh-Rh with no twisting). Because both the ligand strain and A 2u distortional energy are virtually identical for the two complexes, the strength of the metal-metal interaction is the determining factor. On the basis of the magnitude of this interaction, we obtain the following results: (1) a single-minimum (along the Ir-Ir coordinate), harmonic potential-energy surface for the triplet electronic excited state of Ir 2(dimen) 4 2+ (R e,Ir-Ir = 2.87 Å; F Ir-Ir = 0.99 mdyn Å -1); (2) a single-minimum, anharmonic surface for the ground state of Rh 2(dimen) 4 2+ (R e,Rh-Rh = 3.23 Å; F Rh-Rh = 0.09 mdyn Å -1); (3) a double-minimum (along the Ir-Ir coordinate) surface for the ground state of Ir 2(dimen) 4 2+ (R e,Ir-Ir = 3.23 Å; F Ir-Ir = 0.16 mdyn Å -1).

AB - Isomers of Ir 2(dimen) 4 2+ (dimen = 1,8-diisocyanomenthane) exhibit different Ir-Ir bond distances in a 2:1 MTHF/EtCN solution (MTHF = 2-methyltetrahydrofuran). Variable-temperature absorption data suggest that the isomer with the shorter Ir-Ir distance is favored at room temperature [K = ∼8; δH° = -0.8 kcal/mol; δS° = 1.44 cal mol -1 K -1]. We report calculations that shed light on M 2(dimen) 4 2+ (M = Rh, Ir) structural differences: (1) metal-metal interaction favors short distances; (2) ligand deformational-strain energy favors long distances; (3) out-of-plane (A 2u) distortion promotes twisting of the ligand backbone at short metal-metal separations. Calculated potential-energy surfaces reveal a double minimum for Ir 2(dimen) 4 2+ (∼4.1 Å Ir-Ir with 0° twist angle and ∼3.6 Å Ir-Ir with ±12° twist angle) but not for the rhodium analogue (∼4.5 Å Rh-Rh with no twisting). Because both the ligand strain and A 2u distortional energy are virtually identical for the two complexes, the strength of the metal-metal interaction is the determining factor. On the basis of the magnitude of this interaction, we obtain the following results: (1) a single-minimum (along the Ir-Ir coordinate), harmonic potential-energy surface for the triplet electronic excited state of Ir 2(dimen) 4 2+ (R e,Ir-Ir = 2.87 Å; F Ir-Ir = 0.99 mdyn Å -1); (2) a single-minimum, anharmonic surface for the ground state of Rh 2(dimen) 4 2+ (R e,Rh-Rh = 3.23 Å; F Rh-Rh = 0.09 mdyn Å -1); (3) a double-minimum (along the Ir-Ir coordinate) surface for the ground state of Ir 2(dimen) 4 2+ (R e,Ir-Ir = 3.23 Å; F Ir-Ir = 0.16 mdyn Å -1).

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