Theoretical Study of Ligand Superhyperfine Structure. Application to Cu(II) Complexes

Abstract

A theoretical and computational study of the nitrogen superhyperfine structure in Cu(II) complexes is reported. The determination of hybridization parameters for nitrogen donor orbitals from the data is examined. For most Cu(II) complexes the results deviate substantially from pure “sp2” or “sp3” hybridization. Semiempirical INDO/S calculations for five Cu(II) complexes were carried out at the UHF and ROHF level. The results suggest that the small anisotropy in the nitrogen hyperfine parameters is caused by spin polarization of the nitrogen valence shell orbitals. A simple, approximate way for the determination of the π-spin density from experimental data is outlined. A density functional study using various basis sets and functionals is reported for the same five complexes. Hybrid functionals, such as B3LYP and PWP1, give better predictions than functionals based on the generalized gradient approximation like BP or BLYP. Provided that at least a polarized triple-ζ basis is used, the hybrid functionals B3LYP and PWP1 give good predictions for the isotropic couplings but overestimate the anisotropic part by almost a factor of 2. The computational results are further analyzed in terms of local versus nonlocal contributions, influence of scalar relativistic and spin−orbit coupling effects and the transferability of quasi-atomic hyperfine couplings.

Interaction of CH2OH with silver cation in Ag–A/CH3OH zeolite: A DFT study

“…This leads to underestimating the spin density on the metal nucleus using the BP86 functional. The overestimated covalency leads also to a higher g-factor at the BP86 functional level [47].…”

Ligand spheres in asymmetric hetero Diels–Alder reactions catalyzed by Cu(ii) box complexes: experiment and modeling

“…10,37 The experimental and the DFT-calculated distances and angles for this reference agree rather well (Table 3) and are in line with X-ray structure data of related complexes. 37,70 Reaction stages S2 and S3: the EPR spectra taken for these two stages reveal almost matching 63,65 Cu coupling constants (S2: A k = 424, A ⊥ = 38 MHz: S3: A k = 460, A ⊥ = 38 MHz) indicating pseudo-axial symmetry. Moreover, the HYSCORE resonances obtained from S2 and S3 are basically identical.…”

“…The choice of this functional was based on previous computations which show that it is very successful in the prediction of hyperfine coupling (HFC) and g-tensor in nitrogen and Cu(II) complexes. 48,[64][65][66] Ligand atoms were treated by Huzinaga-Kutzelnigg type basis sets BII (denoted also as IGLO-II). 67,68 For the Cu center an accurate triply polarized basis set CP(PPP) was employed.…”

The Density Functional Theory

“…Since this property involves three contributions (Fermi contact, spin-dipolar, and spin-orbit coupling) which feature different physical mechanisms, it is difficult to calculate all of them simultaneously with quantitative accuracy. Ligand HFCs are easier to compute but, again, results are less accurate than for organic radicals, and errors of 30% must be tolerated (Neese 2001b). Kossmann et al (2007) investigated the performance of modern DFT functionals for the prediction of molecular hyperfine couplings in extended test calculations for a series of small radicals and transition metal complexes.…”