A computational study of structural and magnetic properties of bi- and trinuclear Cu(II) complexes with extremely long Cu---Cu distances

TL;DR: Three recently synthesized copper(II) complexes with aroylhydrazones of trifluoroacetic and benzenecarboxylic acids have been computationally investigated by densit....

About: This article is published in Chemical Physics.The article was published on 2017-07-10 and is currently open access. It has received 11 citations till now. The article focuses on the topics: Copper.

Summary

3.1. QTAIM analysis for complexes 1-3.

• This fact is in a qualitative agreement with the thermal analysis (TGA) data [19] that indicate high thermal stability of the complexes up to 250 °C.
• The Py-Cu bonds are comparatively weaker than the other Cu-O and Cu-N bonds (Table 1 ), and therefore an increase of temperature before 250 °C leads to the removal of the pyridine molecules.

3.1. Magnetic properties of the dinucler complexes 1 and 2.

• As can be seen from Figure 2 both complexes 1 and 2 formally are isomeric except the additional axially-coordinated pyridine ligand in complex 2. The distance between the Cu(II) ions for complexes 1 and 2 equals 9.56 and 10.94 Å as determined by X-ray crystallography studies [19] .
• In order to explain the mechanism of exchange interactions for the studied dicuclear complexes the authors have constructed spin densities and magnetic SOMOs plots with a subsequent analysis of SOMOs decomposition coefficients.
• A detailed analysis of the decomposition coefficients clearly shows that both SOMOs for each complex have non-zero coefficients on the common atoms of the linker moiety.
• In the case of complex 1 the magnetic orbitals are mutually rotated about 120° relative to the inner linker moiety, that means they are side-to-side overlapping in contrast to complex 2 for which head-to-head overlapping occurs.
• The latter case is more spatially preferable and therefore J CuCu for complex 2 is two times higher than for complex 1 despite its longer Cu---Cu distance (10.94 Å vs. 9.56 for complex 1).

3.2. Magnetic properties of the trinuclear complex 3

• Actually, the more accurately the authors can account for the long-range exchange interactions the more reliable agreement with experiment is achieved.
• In their recent publication [24] the authors have shown that OSS and triplet states of weakly coupled dinuclear Cu(II) complexes become strictly degenerate if they exclude empirical dispersion corrections from their computational scheme.

Figures

Figure. 4. Spin density plots for the HS and BS states of the dinuclear complexes 1 and 2.

Figure. 5. Magnetic SOMOs plots for the dinuclear complexes 1 and 2 that are occupied by two “parallel” α-spins for the HS state and “opposite” α/β-spins for the BS state.

Table 1. Topological characteristics of the Cu–O and Cu–N coordination bonds calculated by the QTAIM method for the triplet state of complexes 1-3.

Figure 3. Structure of the complexes 1–3 in accordance with X-ray data and QTAIM analysis. In terms of the QTAIM formalism [46], all the coordination Cu–N and Cu–O bonds should be assigned to the intermediate type interactions that are characterized by positive values of the electron density Laplacian r2 and the negative electron energy density he(r) values. From one aspect, the positive r2 values indicate outflow of electron density from interatomic space into the

Figure 1. Schematic representation of magnetic exchange interactions for the dinuclear and triangular trinuclear Cu(II) complexes.

Figure. 6. Magnetic SOMOs plots for the trinuclear complex 3 that is occupied by three “parallel” α-spins for the HS quartet state and by 2α+β-spins for the BS doublet state. Assuming that the HS quartet and BS doublet states can be expressed by a single determinant

Figure. 6. Magnetic SOMOs plots for the trinuclear complex 3 that is occupied by three “parallel” α-spins for the HS quartet state and by 2α+β-spins for the BS doublet state. Assuming that the HS quartet and BS doublet states can be expressed by a single determinant

Table 2. Comparison between the calculated and experimentally estimated exchange coupling constants JCuCu for the complexes 1-3.

Figure 2. The structure of the Cu(II) complexes with aroylhydrazones of trifluoroacetic and isophthalic (1), terephthalic (2) and trimesic (3) acids.

Frequently asked questions

Q1. What are the contributions mentioned in the paper "A computational study of structural and magnetic properties of bi- and trinuclear cu(ii) complexes with extremely long cu---cu distances" ?

The calculated values of spinspin exchange for the studied dinuclear complexes indicate a very weak ferromagnetic coupling of the unpaired electrons in good agreement with experimental data. At the same time, the trinuclear copper ( II ) complex possesses a low-spin doublet ground state with one ferromagnetic and two antiferromagnetic spin projections between the triangular-positioned Cu ions.