Broken symmetry density functional study of a mixed‐valence unsymmetrical dinuclear iron complex

Abstract

Density functional theory (DFT) calculations with different exchangecorrelation functionals were performed for a mixed valence Fe(II)/Fe(III) binuclear complex with -methoxo and two -carboxylate bridging ligands, (1) with geometry optimizations being performed for all possible spin multiplicities (M S ϭ 2, 4, 6, 8, and 10). Within the exchange-correlation functionals studied, only the hybrid GGA functionals B3P and B3LYP and also the pure GGA functional RPBE, predicts the geometry with high spin (S ϭ 9/2) to be more stable than the geometry with low spin state (S ϭ 1/2) by 20 kcal/mol, in agreement with the experimental findings. These functionals also predict the same stability order for the different spin states, being M S ϭ 10Ͼ8Ͼ6Ͼ2Ͼ4. The meta-GGA functionals TPSS and TPSSh and also the pure GGA functionals BLYP and BP86 predict different stability orders. The computed average EPR g-tensor, g av , of 2.03, at the B3LYP level, is in good agreement with the experimental findings. Heisenberg exchange coupling constants, J, were calculated within the broken-symmetry formalism, at the B3LYP level, showing that the two iron centers are antiferromagnetic coupling, with a very weak coupling constant of about Ϫ7 cm Ϫ1 , in good agreement with the experimental value. Additionally, the effect of using different multiplicities of the reference geometries on the computed J value is discussed. were obtained using Eqs. 2, 3, and 4, respectively. Values are given in units of cm -1 . a HS and LS mean that the J values were obtained using the geometry of complex (1) in its high (S ϭ 9/2) and low (S ϭ 1/2) spin states, respectively.

Synthesis, Magnetostructural Correlation, and Catalytic Promiscuity of Unsymmetric Dinuclear Copper(II) Complexes: Models for Catechol Oxidases and Hydrolases

“…Third, we considered the full system and optimized the structure with no geometry or symmetry constraints. In the latter case, the geometry was optimized considering only the low-spin (LS) state because a previous study 80 showed that a better agreement between the magnetic susceptibility measurements and the computed magnetic coupling constant is obtained when the LS geometry is used. Neese and co-workers 79 also noted that the use of the LS geometry to compute J seems to be more appropriate because the electron density of the LS state corresponds to the electron density of the real antiferromagnetic state.…”

“…DFT, combined with the broken-symmetry (BS) approach, was adopted in our calculations of the magnetic interaction between the Cu II centers in complexes 1 and 2 . In fact, the BS formalism has been proven to be an efficient and practical alternative to elucidate the magnetic exchange couplings of dinuclear transition-metal systems. − …”

Antiferromagnetic coupling across a tetrametallic unit through noncovalent interactions

“…Calculations were also performed with ADF2010 42,43 on highspin C 2 [PtM(tba) 4 (OH 2 )] (M ¼ Fe, Co, Ni) geometries to detail the electronic structure in the absence of any close contacts between these units and optimized with all electron triple-z singly polarized basis sets (AE-TZP) for all elements and relativistic (ZORA) corrections. The native PBE functional is effective in the determination of paramagnetic electronic structures, 44,45 and all cases here were treated with the dispersion corrected PBE-D3 46 functional that has proven suitable for the treatment of transition-metal complexes. 47,48 An MO energy level diagram for C 2 symmetry [PtNi(tba) 4 (OH 2 )] analogous to Fig.…”