Neutral Bis(-iminopyridine)metal Complexes of the First-Row Transition Ions (Cr, Mn, Fe, Co, Ni, Zn) and Their Monocationic Analogue
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- 作者：Connie C. Lu ; Eckhard Bill ; Thomas Weyhermü ; ller ; Eberhard Bothe ; Karl Wieghardt
- 刊名：Journal of the American Chemical Society
- 出版年：2008
- 出版时间：March 12, 2008
- 年：2008
- 卷：130
- 期：10
- 页码：3181 - 3197
- 全文大小：857K
- 年卷期：v.130,no.10(March 12, 2008)
- ISSN：1520-5126
文摘
A series of bis(
fchars/alpha.gif" BORDER=0>-iminopyridine)metal complexes featuring the first-row transition ions (Cr, Mn,Fe, Co, Ni, and Zn) is presented. It is shown that these ligands are redox noninnocent and their paramagneticfchars/pi.gif" BORDER=0 > radical monoanionic forms can exist in coordination complexes. Based on spectroscopic and structuralcharacterizations, the neutral complexes are best described as possessing a divalent metal center andtwo monoanionic fchars/pi.gif" BORDER=0 > radicals of the fchars/alpha.gif" BORDER=0>-iminopyridine. The neutral M(L
bull.gif">)2 compounds undergo ligand-centered,one-electron oxidations generating a second series, [(Lx)2M(THF)][B(ArF)4] [where Lx represents either theneutral fchars/alpha.gif" BORDER=0>-iminopyridine (L)0 and/or its reduced fchars/pi.gif" BORDER=0 > radical anion (Lbull.gif">)-]. The cationic series comprise mostlymixed-valent complexes, wherein the two ligands have formally different redox states, (L)0 and (Lbull.gif">)-, andthe two ligands may be electronically linked by the bridging metal atom. Experimentally, the cationic Feand Co complexes exhibit Robin-Day Class III behavior (fully delocalized), whereas the cationic Zn, Cr,and Mn complexes belong to Class I (localized) as shown by X-ray crystallography and UV-visspectroscopy. The delocalization versus localization of the ligand radical is determined only by the natureof the metal linker. The cationic nickel complex is exceptional in this series in that it does not exhibit anyligand mixed valency. Instead, its electronic structure is consistent with two neutral ligands (L)0 and amonovalent metal center or [(L)2Ni(THF)][B(ArF)4]. Finally, an unusual spin equilibrium for Fe(II), betweenhigh spin and intermediate spin (SFe = 2 
f"> SFe = 1), is described for the complex [(Lbull.gif">)(L)Fe(THF)][B(ArF)4],which consequently is characterized by the overall spin equilibrium (Stot = 3/2 f"> Stot = 1/2). The two differentspin states for Fe(II) have been characterized using variable temperature X-ray crystallography, EPRspectroscopy, zero-field and applied-field Mössbauer spectroscopy, and magnetic susceptibility measurements. Complementary DFT studies of all the complexes have been performed, and the calculations supportthe proposed electronic structures.
fchars/alpha.gif" BORDER=0>-iminopyridine)metal complexes featuring the first-row transition ions (Cr, Mn,Fe, Co, Ni, and Zn) is presented. It is shown that these ligands are redox noninnocent and their paramagneticfchars/pi.gif" BORDER=0 > radical monoanionic forms can exist in coordination complexes. Based on spectroscopic and structuralcharacterizations, the neutral complexes are best described as possessing a divalent metal center andtwo monoanionic fchars/pi.gif" BORDER=0 > radicals of the fchars/alpha.gif" BORDER=0>-iminopyridine. The neutral M(Lbull.gif">)2 compounds undergo ligand-centered,one-electron oxidations generating a second series, [(Lx)2M(THF)][B(ArF)4] [where Lx represents either theneutral fchars/alpha.gif" BORDER=0>-iminopyridine (L)0 and/or its reduced fchars/pi.gif" BORDER=0 > radical anion (Lbull.gif">)-]. The cationic series comprise mostlymixed-valent complexes, wherein the two ligands have formally different redox states, (L)0 and (Lbull.gif">)-, andthe two ligands may be electronically linked by the bridging metal atom. Experimentally, the cationic Feand Co complexes exhibit Robin-Day Class III behavior (fully delocalized), whereas the cationic Zn, Cr,and Mn complexes belong to Class I (localized) as shown by X-ray crystallography and UV-visspectroscopy. The delocalization versus localization of the ligand radical is determined only by the natureof the metal linker. The cationic nickel complex is exceptional in this series in that it does not exhibit anyligand mixed valency. Instead, its electronic structure is consistent with two neutral ligands (L)0 and amonovalent metal center or [(L)2Ni(THF)][B(ArF)4]. Finally, an unusual spin equilibrium for Fe(II), betweenhigh spin and intermediate spin (SFe = 2 f"> SFe = 1), is described for the complex [(Lbull.gif">)(L)Fe(THF)][B(ArF)4],which consequently is characterized by the overall spin equilibrium (Stot = 3/2 f"> Stot = 1/2). The two differentspin states for Fe(II) have been characterized using variable temperature X-ray crystallography, EPRspectroscopy, zero-field and applied-field Mössbauer spectroscopy, and magnetic susceptibility measurements. Complementary DFT studies of all the complexes have been performed, and the calculations supportthe proposed electronic structures.