DFT models for copper(II) bispidine complexes: Structures, stabilities, isomerism, spin distribution, and spectroscopy

Abstract

Various DFT and ab initio methods, including B3LYP, HF, SORCI, and LF-density functional theory (DFT), are used to compute the structures, relative stabilities, spin density distributions, and spectroscopic properties (electronic and EPR) of the two possible isomers of the copper(II) complexes with derivatives of a rigid tetradentate bispidine ligand with two pyridine and two tertiary amine donors, and a chloride ion. The description of the bonding (covalency of the copper-ligand interactions) and the distribution of the unpaired electron strongly depend on the DFT functional used, specifically on the nonlocal DF correlation and the HF exchange. Various methods may be used to optimize the DFT method. Unfortunately, it appears that there is no general method for the accurate computation of copper(II) complexes, and the choice of method depends on the type of ligands and the structural type of the chromophore. Also, it appears that the choice of method strongly depends on the problem to be solved. LF-DFT and spectroscopically oriented CI methods (SORCI), provided a large enough reference space is chosen, yield accurate spectroscopic parameters; EDA may lead to a good understanding of relative stabilities; accurate spin density distributions are obtained by modification of the nuclear charge on copper; solvation models are needed for the accurate prediction of isomer distributions.

A DFT based ligand field study of the EPR spectra of Co(II) and Cu(II) porphyrins

“…For CuP there is an excellent agreement between calculated and experimental value for g x,y . However, the g z value is off by 30%, as previously reported for Cu(II) bispidine complexes [35]. A somewhat better agreement is obtained from LFDFT calculation (see Table 2) where 3d-metal electrons have been localized in a special treatment as discussed in the previous section.…”

Cyclic peptide marine metabolites and CuII

“…117 While the analysis of the ENDOR spectra of [Cu II (H 2 wa im )] + confirmed the bonding motif (N het -N amide -N het ), the three nitrogen nuclei are magnetically inequivalent. HYSCORE spectra revealed delocalization of the unpaired 91 together with the structural similarity of the cyclic pseudo-peptides to aza-crown ethers, suggested that the peptides are tailor-made for binding to metal ions, 43 although direct evidence for complex formation was originally not available.…”

DFT insight into o-semiquinone radicals and Ca2+ ion interaction: structure, g tensor, and stability

“…It is known that the DFT methods might misestimate the covalent character of metal-ligand bonds [81][82][83]. Although this is more frequently the case of transition metal coordination compounds, we decided to calculate the Dg tensors with a vast array of functionals (UBP86, UPBE, UOLYP, UB3LYP, UPBE0).…”