Solution Structures of Europium Terpyridyl Complexes with Nitrate and Triflate Counterions in Acetonitrile

Abstract

Lanthanide−ligand complexes are key components of technological applications, and their properties depend on their structures in the solution phase, which are challenging to resolve experimentally or computationally. The coordination structure of the Eu 3+ ion in different coordination environments in acetonitrile is examined using ab initio molecular dynamics (AIMD) simulations and extended X-ray absorption fine structure (EXAFS) spectroscopy. AIMD simulations are conducted for the solvated Eu 3+ ion in acetonitrile, both with or without a terpyridyl ligand, and in the presence of either triflate or nitrate counterions. EXAFS spectra are calculated directly from AIMD simulations and then compared to experimentally measured EXAFS spectra. In acetonitrile solution, both nitrate and triflate anions are shown to coordinate directly to the Eu 3+ ion forming either ten-or eight-coordinate solvent complexes where the counterions are binding as bidentate or monodentate structures, respectively. Coordination of a terpyridyl ligand to the Eu 3+ ion limits the available binding sites for the solvent and anions. In certain cases, the terpyridyl ligand excludes any solvent binding and limits the number of coordinated anions. The solution structure of the Eu-terpyridyl complex with nitrate counterions is shown to have a similar arrangement of Eu 3+ coordinating molecules as the crystal structure. This study illustrates how a combination of AIMD and EXAFS can be used to determine how ligands, solvent, and counterions coordinate with the lanthanide ions in solution.

Structural Changes to the Gd‐DTPA Complex at Varying Ligand Protonation State

“…The χ(k) spectrum was computed for each frame using FEFF8.5 software, [65,66] as done recently by our group. [26,27,56,67] FEFF was used with the default Hedin-Lundqvist exchange correlation potential and a 6.0 Å cutoff for the self-consistent field calculation. The program was adjusted to include up to 15,000 single and multiple-scattering paths (increased from the 1,200 default), and multiple scattering paths with up to 8 legs were included.…”

“…The measured EXAFS spectra is directly compared, without fitting, to the EXAFS spectra predicted from MD simulations to determine the solution structures of Ln-ligand complexes in solution: we recently used this approach to determine the structure of Ln-ligand complexes in a nonaqueous solution. [27] In this work, the focus is to determine how the solution structure of a Ln-ligand complex, Gd-DTPA, varies with different ligand protonation states in aqueous solution.…”

Elucidating the Structure of the Eu‐EDTA Complex in Solution at Various Protonation States

“…The χ(k) spectrum was computed for each frame using FEFF8.5 software, [52][53][54] following previously reported procedures. [29,41,55,56] FEFF was used with the default Hedin-Lundqvist exchange correlation potential and a 6.0 Å cutoff for the selfconsistent field calculation. The program was adjusted to include up to 15,000 single and multiple-scattering paths (increased from the 1,200 default), and multiple scattering paths with up to 8 legs were included.…”

We Already Know Everything about Oxidative Addition to Pd(0): Do We?

“…The exploration of such systems should greatly benefit from ab initio molecular dynamic approaches. , This approach was recently used by the group of Ananikov to elucidate the R–NHC coupling mechanism with in a solvent cage . Experimentally, the dynamic structure of Pd complexes and/or particles in solution can be potentially explored by Extended X-ray Absorption Fine Spectroscopy (EXAFS) complemented by simulated EXAFS spectra from molecular dynamics simulations. − …”