Bis(imino)pyridine iron dinitrogen compounds revisited: Differences in electronic structure between four- and five-coordinate derivatives.

S. Chantal E. Stieber; Carsten Milsmann; Jordan M. Hoyt; Zoë R. Turner; Kenneth D. Finkelstein; Karl Wieghardt; Serena Debeer; Paul J. Chirik

doi:10.1021/ic202750n

Bis(imino)pyridine iron dinitrogen compounds revisited: Differences in electronic structure between four- and five-coordinate derivatives.

S. Chantal E. Stieber
, Carsten Milsmann
, Jordan M. Hoyt
, Zoë R. Turner
, Kenneth D. Finkelstein
, Karl Wieghardt
, Serena Debeer
, Paul J. Chirik

Chemistry

Research output: Contribution to journal › Article › peer-review

118 Scopus citations

Abstract

The electronic structures of the four- and five-coordinate aryl-substituted bis(imino)pyridine iron dinitrogen complexes, ( ^iPrPDI)FeN ₂ and ( ^iPrPDI)Fe(N ₂) ₂ ( ^iPrPDI = 2,6-(2,6- ⁱPr ₂-C ₆H ₃-N=CMe) ₂C ₅H ₃N), have been investigated by a combination of spectroscopic techniques (NMR, Mössbauer, X-ray Absorption, and X-ray Emission) and DFT calculations. Homologation of the imine methyl backbone to ethyl or isopropyl groups resulted in the preparation of the new bis(imino)pyridine iron dinitrogen complexes, ( ^iPrRPDI) FeN ₂ ( ^iPrRPDI = 2,6-(2,6- ⁱPr ₂-C ₆H ₃-N=CR) ₂C ₅H ₃N; R = Et, ⁱPr), that are exclusively four coordinate both in the solid state and in solution. The spectroscopic and computational data establish that the ( ^iPrRPDI)FeN ₂ compounds are intermediate spin ferrous derivatives (S _Fe = 1) antiferromagnetically coupled to bis(imino)pyridine triplet diradical dianions (S _PDI = 1). While this ground state description is identical to that previously reported for ( ^iPrPDI)Fe(DMAP) (DMAP = 4-N,N-dimethylaminopyridine) and other four-coordinate iron compounds with principally σ-donating ligands, the d-orbital energetics determine the degree of coupling of the metal-chelate magnetic orbitals resulting in different NMR spectroscopic behavior. For ( ^iPrRPDI)Fe(DMAP) and related compounds, this coupling is strong and results in temperature independent paramagnetism where a triplet excited state mixes with the singlet ground state via spin orbit coupling. In the ( ^iPrRPDI)FeN ₂ family, one of the iron singly occupied molecular orbitals (SOMOs) is essentially dz ² in character resulting in poor overlap with the magnetic orbitals of the chelate, leading to thermal population of the triplet state and hence temperature dependent NMR behavior. The electronic structures of ( ^iPrRPDI)FeN ₂ and ( ^iPrPDI)Fe(DMAP) differ from ( ^iPrPDI)Fe(N ₂) ₂, a highly covalent molecule with a redox noninnocent chelate that is best described as a resonance hybrid between iron(0) and iron(II) canonical forms as originally proposed in 2004.

Original language	English (US)
Pages (from-to)	3770-3785
Number of pages	16
Journal	Inorganic Chemistry
Volume	51
Issue number	6
DOIs	https://doi.org/10.1021/ic202750n
State	Published - Mar 19 2012

All Science Journal Classification (ASJC) codes

Inorganic Chemistry
Physical and Theoretical Chemistry

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10.1021/ic202750n

Cite this

@article{6d720aa2799d45dd9d6110c85978e8b7,

title = "Bis(imino)pyridine iron dinitrogen compounds revisited: Differences in electronic structure between four- and five-coordinate derivatives.",

abstract = "The electronic structures of the four- and five-coordinate aryl-substituted bis(imino)pyridine iron dinitrogen complexes, ( iPrPDI)FeN 2 and ( iPrPDI)Fe(N 2) 2 ( iPrPDI = 2,6-(2,6- iPr 2-C 6H 3-N=CMe) 2C 5H 3N), have been investigated by a combination of spectroscopic techniques (NMR, M{\"o}ssbauer, X-ray Absorption, and X-ray Emission) and DFT calculations. Homologation of the imine methyl backbone to ethyl or isopropyl groups resulted in the preparation of the new bis(imino)pyridine iron dinitrogen complexes, ( iPrRPDI) FeN 2 ( iPrRPDI = 2,6-(2,6- iPr 2-C 6H 3-N=CR) 2C 5H 3N; R = Et, iPr), that are exclusively four coordinate both in the solid state and in solution. The spectroscopic and computational data establish that the ( iPrRPDI)FeN 2 compounds are intermediate spin ferrous derivatives (S Fe = 1) antiferromagnetically coupled to bis(imino)pyridine triplet diradical dianions (S PDI = 1). While this ground state description is identical to that previously reported for ( iPrPDI)Fe(DMAP) (DMAP = 4-N,N-dimethylaminopyridine) and other four-coordinate iron compounds with principally σ-donating ligands, the d-orbital energetics determine the degree of coupling of the metal-chelate magnetic orbitals resulting in different NMR spectroscopic behavior. For ( iPrRPDI)Fe(DMAP) and related compounds, this coupling is strong and results in temperature independent paramagnetism where a triplet excited state mixes with the singlet ground state via spin orbit coupling. In the ( iPrRPDI)FeN 2 family, one of the iron singly occupied molecular orbitals (SOMOs) is essentially dz 2 in character resulting in poor overlap with the magnetic orbitals of the chelate, leading to thermal population of the triplet state and hence temperature dependent NMR behavior. The electronic structures of ( iPrRPDI)FeN 2 and ( iPrPDI)Fe(DMAP) differ from ( iPrPDI)Fe(N 2) 2, a highly covalent molecule with a redox noninnocent chelate that is best described as a resonance hybrid between iron(0) and iron(II) canonical forms as originally proposed in 2004.",

author = "Stieber, \{S. Chantal E.\} and Carsten Milsmann and Hoyt, \{Jordan M.\} and Turner, \{Zo{\"e} R.\} and Finkelstein, \{Kenneth D.\} and Karl Wieghardt and Serena Debeer and Chirik, \{Paul J.\}",

year = "2012",

month = mar,

day = "19",

doi = "10.1021/ic202750n",

language = "English (US)",

volume = "51",

pages = "3770--3785",

journal = "Inorganic Chemistry",

issn = "0020-1669",

publisher = "American Chemical Society",

number = "6",

}

TY - JOUR

T1 - Bis(imino)pyridine iron dinitrogen compounds revisited

T2 - Differences in electronic structure between four- and five-coordinate derivatives.

AU - Stieber, S. Chantal E.

AU - Milsmann, Carsten

AU - Hoyt, Jordan M.

AU - Turner, Zoë R.

AU - Finkelstein, Kenneth D.

AU - Wieghardt, Karl

AU - Debeer, Serena

AU - Chirik, Paul J.

PY - 2012/3/19

Y1 - 2012/3/19

N2 - The electronic structures of the four- and five-coordinate aryl-substituted bis(imino)pyridine iron dinitrogen complexes, ( iPrPDI)FeN 2 and ( iPrPDI)Fe(N 2) 2 ( iPrPDI = 2,6-(2,6- iPr 2-C 6H 3-N=CMe) 2C 5H 3N), have been investigated by a combination of spectroscopic techniques (NMR, Mössbauer, X-ray Absorption, and X-ray Emission) and DFT calculations. Homologation of the imine methyl backbone to ethyl or isopropyl groups resulted in the preparation of the new bis(imino)pyridine iron dinitrogen complexes, ( iPrRPDI) FeN 2 ( iPrRPDI = 2,6-(2,6- iPr 2-C 6H 3-N=CR) 2C 5H 3N; R = Et, iPr), that are exclusively four coordinate both in the solid state and in solution. The spectroscopic and computational data establish that the ( iPrRPDI)FeN 2 compounds are intermediate spin ferrous derivatives (S Fe = 1) antiferromagnetically coupled to bis(imino)pyridine triplet diradical dianions (S PDI = 1). While this ground state description is identical to that previously reported for ( iPrPDI)Fe(DMAP) (DMAP = 4-N,N-dimethylaminopyridine) and other four-coordinate iron compounds with principally σ-donating ligands, the d-orbital energetics determine the degree of coupling of the metal-chelate magnetic orbitals resulting in different NMR spectroscopic behavior. For ( iPrRPDI)Fe(DMAP) and related compounds, this coupling is strong and results in temperature independent paramagnetism where a triplet excited state mixes with the singlet ground state via spin orbit coupling. In the ( iPrRPDI)FeN 2 family, one of the iron singly occupied molecular orbitals (SOMOs) is essentially dz 2 in character resulting in poor overlap with the magnetic orbitals of the chelate, leading to thermal population of the triplet state and hence temperature dependent NMR behavior. The electronic structures of ( iPrRPDI)FeN 2 and ( iPrPDI)Fe(DMAP) differ from ( iPrPDI)Fe(N 2) 2, a highly covalent molecule with a redox noninnocent chelate that is best described as a resonance hybrid between iron(0) and iron(II) canonical forms as originally proposed in 2004.

AB - The electronic structures of the four- and five-coordinate aryl-substituted bis(imino)pyridine iron dinitrogen complexes, ( iPrPDI)FeN 2 and ( iPrPDI)Fe(N 2) 2 ( iPrPDI = 2,6-(2,6- iPr 2-C 6H 3-N=CMe) 2C 5H 3N), have been investigated by a combination of spectroscopic techniques (NMR, Mössbauer, X-ray Absorption, and X-ray Emission) and DFT calculations. Homologation of the imine methyl backbone to ethyl or isopropyl groups resulted in the preparation of the new bis(imino)pyridine iron dinitrogen complexes, ( iPrRPDI) FeN 2 ( iPrRPDI = 2,6-(2,6- iPr 2-C 6H 3-N=CR) 2C 5H 3N; R = Et, iPr), that are exclusively four coordinate both in the solid state and in solution. The spectroscopic and computational data establish that the ( iPrRPDI)FeN 2 compounds are intermediate spin ferrous derivatives (S Fe = 1) antiferromagnetically coupled to bis(imino)pyridine triplet diradical dianions (S PDI = 1). While this ground state description is identical to that previously reported for ( iPrPDI)Fe(DMAP) (DMAP = 4-N,N-dimethylaminopyridine) and other four-coordinate iron compounds with principally σ-donating ligands, the d-orbital energetics determine the degree of coupling of the metal-chelate magnetic orbitals resulting in different NMR spectroscopic behavior. For ( iPrRPDI)Fe(DMAP) and related compounds, this coupling is strong and results in temperature independent paramagnetism where a triplet excited state mixes with the singlet ground state via spin orbit coupling. In the ( iPrRPDI)FeN 2 family, one of the iron singly occupied molecular orbitals (SOMOs) is essentially dz 2 in character resulting in poor overlap with the magnetic orbitals of the chelate, leading to thermal population of the triplet state and hence temperature dependent NMR behavior. The electronic structures of ( iPrRPDI)FeN 2 and ( iPrPDI)Fe(DMAP) differ from ( iPrPDI)Fe(N 2) 2, a highly covalent molecule with a redox noninnocent chelate that is best described as a resonance hybrid between iron(0) and iron(II) canonical forms as originally proposed in 2004.

UR - https://www.scopus.com/pages/publications/84858636125

UR - https://www.scopus.com/pages/publications/84858636125#tab=citedBy

U2 - 10.1021/ic202750n

DO - 10.1021/ic202750n

M3 - Article

C2 - 22394054

AN - SCOPUS:84858636125

SN - 0020-1669

VL - 51

SP - 3770

EP - 3785

JO - Inorganic Chemistry

JF - Inorganic Chemistry

IS - 6

ER -

Bis(imino)pyridine iron dinitrogen compounds revisited: Differences in electronic structure between four- and five-coordinate derivatives.

Abstract

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