skip to main content


This content will become publicly available on August 14, 2024

Title: Light- and Chemical-Doping-Induced Magnetic Behavior of Eu Molecular Systems
Variable temperature electron paramagnetic resonance (VT-EPR) was used to investigate the role of the environment and oxidation states of several coordinated Eu compounds. We find that while Eu(III) chelating complexes are diamagnetic, simple chemical reduction results in the formation of paramagnetic species. In agreement with the distorted D3h symmetry of Eu molecular complexes investigated in this study, the EPR spectrum of reduced complexes showed axially symmetric signals (g⊥ = 2.001 and g∥ = 1.994) that were successfully simulated with two Eu isotopes with nuclear spin 5/2 (151Eu and 153Eu with 48% and 52% natural abundance, respectively) and nuclear g-factors 151Eu/153Eu = 2.27. Illumination of water-soluble complex Eu(dipic)3 at 4 K led to the ligand-to-metal charge transfer (LMCT) that resulted in the formation of Eu(II) in a rhombic environment (gx = 2.006, gy = 1.995, gz = 1.988). The existence of LMCT affects the luminescence of Eu(dipic)3, and pre-reduction of the complex to Eu(II)(dipic)3 reversibly reduces red luminescence with the appearance of a weak CT blue luminescence. Furthermore, encapsulation of a large portion of the dipic ligand with Cucurbit[7]uril, a pumpkin-shaped macrocycle, inhibited ligand-to-metal charge transfer, preventing the formation of Eu(II) upon illumination.  more » « less
Award ID(s):
1905238
NSF-PAR ID:
10474790
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ;
Publisher / Repository:
ACS
Date Published:
Journal Name:
Inorganic Chemistry
Volume:
62
Issue:
32
ISSN:
0020-1669
Page Range / eLocation ID:
12721 to 12729
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. We report here the characterization in solution (NMR, luminescence, MS) and the solid-state (X-ray crystallography, IR) of complexes between phenacyldiphenylphosphine oxide and five Ln( iii ) ions (Sm, Eu, Gd, Tb, Dy). Four single crystal X-ray structures are described here showing a 1 : 2 ratio between the Ln 3+ ions Eu, Dy, Sm and Gd and the ligand, where the phosphine oxide ligands are bound in a monodentate manner to the metal center. A fifth structure is reported for the 1 : 2 Eu(NO 3 ) 3 -ligand complex showing bidentate binding between the two ligands and the metal center. The solution coordination chemistry of these metal complexes was probed by 1 H, 13 C and 31 P NMR, mass spectrometry, and luminescence experiments. The title ligand has the capability to sensitize Tb 3+ , Dy 3+ , Eu 3+ and Sm 3+ leading to metal-centered emission in solutions of acetonitrile and methanol and in the solid state. 
    more » « less
  2. [Cp*Rh] complexes (Cp* = pentamethylcyclopentadienyl) supported by bidentate chelating ligands are a useful class of compounds for studies of redox chemistry and catalysis. Here, we show that the bis(2-pyridyl)methane ligand, also known as dipyridylmethane or dpma, can support [Cp*Rh] complexes in the formally + iii and + ii rhodium oxidation states. Specifically, two new rhodium complexes ([Cp*Rh(dpma)(L)] n+ , L = Cl − , CH 3 CN) have been isolated and structurally characterized, and the properties of the complexes have been compared with those of [Cp*Rh] complexes bearing the related dimethyldipyridylmethane (Me 2 dpma) ligand. Complex [Cp*Rh(dpma)(NCCH 3 )] 2+ displays a quasireversible rhodium( iii / ii ) reduction by cyclic voltammetry; related electron paramagnetic resonance (EPR) spectroscopic studies confirm access to the unusual rhodium( ii ) oxidation state. Further reduction to the formally rhodium( i ) oxidation state, however, is followed by deprotonation of dpma, as observed in electrochemical studies and chemical reduction experiments. This reactivity can be understood to occur as a consequence of the presence of doubly benzylic protons in the dpma ligand, since use of the analogous Me 2 dpma enables reduction to rhodium( i ) without involvement of ligand deprotonation. These findings highlight the important role of the ligand backbone substitution pattern in influencing the stability of highly-reduced complexes, a key class of metal species for study of electron and proton management in catalysis. 
    more » « less
  3. null (Ed.)
    We report the solution structure of a europium-nicotianamine complex predicted from ab initio molecular dynamics simulations with density functional theory. Emission and excitation spectroscopy show that the Eu 3+ coordination environment changes in the presence of nicotianamine, suggesting complex formation, such as what is seen for the Eu 3+ –nicotianamine complex structure predicted from computation. We modeled Eu 3+ –ligand complexes with explicit water molecules in periodic boxes, effectively simulating the solution phase. Our simulations consider possible chemical events ( e.g. coordination bond formation, protonation state changes, charge transfers), as well as ligand flexibility and solvent rearrangements. Our computational approach correctly predicts the solution structure of a Eu 3+ –ethylenediaminetetraacetic acid complex within 0.05 Å of experimentally measured values, backing the fidelity of the predicted solution structure of the Eu 3+ –nicotianamine complex. Emission and excitation spectroscopy measurements were also performed on the well-known Eu 3+ –ethylenediaminetetraacetic acid complex to validate our experimental methods. The electronic structure of the Eu 3+ –nicotianamine complex is analyzed to describe the complexes in greater detail. Nicotianamine is a metabolic precursor of, and structurally very similar to, phytosiderophores, which are responsible for the uptake of metals in plants. Although knowledge that nicotianamine binds europium does not determine how plants uptake rare earths from the environment, it strongly supports that phytosiderophores bind lanthanides. 
    more » « less
  4. null (Ed.)
    Ligand-based mixed valent (MV) complexes of Al( iii ) incorporating electron donating (ED) and electron withdrawing (EW) substituents on bis(imino)pyridine ligands (I 2 P) have been prepared. The MV states containing EW groups are both assigned as Class II/III, and those with ED functional groups are Class III and Class II/III in the (I 2 P − )(I 2 P 2− )Al and [(I 2 P 2− )(I 2 P 3− )Al] 2− charge states, respectively. No abrupt changes in delocalization are observed with ED and EW groups and from this we infer that ligand and metal valence p-orbitals are well-matched in energy and the absence of LMCT and MLCT bands supports the delocalized electronic structures. The MV ligand charge states (I 2 P − )(I 2 P 2− )Al and [(I 2 P 2− )(I 2 P 3− )Al] 2− show intervalence charge transfer (IVCT) transitions in the regions 6850–7740 and 7410–9780 cm −1 , respectively. Alkali metal cations in solution had no effect on the IVCT bands of [(I 2 P 2− )(I 2 P 3− )Al] 2− complexes containing –PhNMe 2 or –PhF 5 substituents. Minor localization of charge in [(I 2 P 2− )(I 2 P 3− )Al] 2− was observed when –PhOMe substituents are included. 
    more » « less
  5. null (Ed.)
    The ligand-to-metal charge transfer (LMCT) transitions of [Re(dmpe)3]2+ (dmpe = bis-1,2-(dimethylphosphino)ethane) were interrogated using UV/Vis absorbance spectroscopy, photoluminescence spectroscopy, and time-dependent density functional theory. The solvent dependence of the lowest energy charge transfer transition was quantified; no solvatochromism was observed. TD-DFT calculations reveal the dominant LMCT transition is highly symmetric and delocalized involving all phopshine ligand donors in the charge transfer, providing an understanding for the absence of solvatochromism of [Re(dmpe)3]2+. 
    more » « less