Spectroscopic studies of the non-heme ferric active site in soybean lipoxygenase: magnetic circular dichroism as a probe of electronic and geometric structure. Ligand-field origin of zero-field splitting

1991 ◽  
Vol 113 (14) ◽  
pp. 5162-5175 ◽  
Author(s):  
Yan Zhang ◽  
Matthew S. Gebhard ◽  
Edward I. Solomon
Keyword(s):  
Geometric Structure ◽  
Active Site ◽  
Magnetic Circular Dichroism ◽  
Spectroscopic Studies ◽  
Ligand Field ◽  
Soybean Lipoxygenase ◽  
Zero Field ◽  
Zero Field Splitting ◽  
Field Splitting ◽  
Circular Dichroïsm

scholarly journals Design, Isolation, and Spectroscopic Analysis of a Tetravalent Terbium Complex

2019 ◽  
Author(s):  
Natalie Rice ◽  
Ivan Popov ◽  
Dominic Russo ◽  
John Bacsa ◽  
Enrique Batista ◽  
...  
Keyword(s):  
Ground State ◽  
Molecular Complexes ◽  
Lanthanide Ions ◽  
Ligand Field ◽  
Zero Field ◽  
High Symmetry ◽  
Zero Field Splitting ◽  
Terbium Complex ◽  
Field Splitting ◽  
Metal Ligand

Synthetic strategies to yield molecular complexes of high-valent lanthanides, other than the ubiquitous Ce<sup>4+</sup> ion, are exceptionally rare, and thorough, detailed characterization in these systems is limited by complex lifetime and reaction and isolation conditions. The synthesis of high-symmetry complexes in high purity with significant lifetimes in solution and solid-state are essential for determining the role of ligand-field splitting, multiconfigurational behavior, and covalency in governing the reactivity and physical properties of these potentially technologically transformative tetravalent ions. We report the synthesis and physical characterization of an <i>S</i><sub>4</sub> symmetric, four-coordinate tetravalent terbium complex, [Tb(NP(1,2-bis-<i><sup>t</sup></i>Bu-diamidoethane)(NEt<sub>2</sub>))<sub>4</sub>] (where Et is ethyl and <i>t</i>Bu is <i>tert</i>-butyl). The ligand field in this complex is weak and the metal-ligand bonds sufficiently covalent so that the tetravalent terbium ion is stable and accessible via a mild oxidant from the anionic, trivalent, terbium precursor, [(Et<sub>2</sub>O)K][Tb(NP(1,2-bis-<i><sup>t</sup></i>Bu-diamidoethane)(NEt<sub>2</sub>))<sub>4</sub>]. The significant stability of the tetravalent complex enables its thorough characterization. The step-wise development of the supporting ligand points to key ligand control elements for further extending the known tetravalent lanthanide ions in molecular complexes. Magnetic susceptibility, electron paramagnetic resonance (EPR) spectroscopy, X-ray absorption near-edge spectroscopy (XAS), and density functional theory studies indicate a <i>4f<sup>7</sup></i> ground state for [Tb(NP(1,2-bis-<i><sup>t</sup></i>Bu-diamidoethane)(NEt<sub>2</sub>))<sub>4</sub>] with considerable zero-field splitting: demonstrating that magnetic, tetravalent lanthanide ions engage in covalent metal-ligand bonds. This result has significant implications for the use of tetravalent lanthanide ions in magnetic applications since the observed zero-field splitting is intermediate between that observed for the trivalent lanthanides and for the transition metals. The similarity of the multiconfigurational behavior in the ground state of [Tb(NP(1,2-bis-<i><sup>t</sup></i>Bu-diamidoethane)(NEt<sub>2</sub>))<sub>4</sub>] (measured by Tb L<sub>3</sub>-edge XAS) to that observed in TbO<sub>2</sub> implicates ligand control of multiconfigurational behavior as a key component of the stability of the complex.

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