Influence of axial ligation on the spin state and exchange coupling in heterotrimetallic bis[iron(III) porphyrin]-copper (II) maleonitrile triple-decker complexes

1987 ◽  
Vol 26 (12) ◽  
pp. 1930-1933 ◽  
Author(s):  
William E. Hatfield ◽  
C. Michael Elliot ◽  
Juergen Ensling ◽  
Kozo Akabori
Keyword(s):  
Spin State ◽  
Exchange Coupling ◽  
Axial Ligation

scholarly journals Magnetic exchange coupling in Cu dimers studied with modern multireference methods and broken-symmetry coupled cluster theory

2021 ◽  
Vol 140 (10) ◽  
Author(s):  
Gurjot Singh ◽  
Stefani Gamboa ◽  
Maylis Orio ◽  
Dimitrios A. Pantazis ◽  
Michael Roemelt
Keyword(s):  
Spin State ◽  
Electron Correlation ◽  
Exchange Coupling ◽  
Broken Symmetry ◽  
Coupled Cluster ◽  
Coupled Cluster Theory ◽  
Cluster Theory ◽  
Advantages And Disadvantages ◽  
Theoretical Approaches ◽  
Multireference Methods

AbstractSpin-state energetics of exchange-coupled copper complexes pose a persistent challenge for applied quantum chemistry. Here, we provide a comprehensive comparison of all available theoretical approaches to the problem of exchange coupling in two antiferromagnetically coupled bis-μ-hydroxo Cu(II) dimers. The evaluated methods include multireference methods based on the density matrix renormalization group (DMRG), multireference methods that incorporate dynamic electron correlation either perturbatively, such as the N-electron valence state perturbation theory, or variationally, such as the difference-dedicated configuration interaction. In addition, we contrast the multireference results with those obtained using broken-symmetry approaches that utilize either density functional theory or, as demonstrated here for the first time in such systems, a local implementation of coupled cluster theory. The results show that the spin-state energetics of these copper dimers are dominated by dynamic electron correlation and represent an impossible challenge for multireference methods that rely on brute-force expansion of the active space to recover correlation energy. Therefore, DMRG-based methods even at the limit of their applicability cannot describe quantitatively the antiferromagnetic exchange coupling in these dimers, in contrast to dinuclear complexes of earlier transition metal ions. The convergence of the broken-symmetry coupled cluster approach is studied and shown to be a limiting factor for the practical application of the method. The advantages and disadvantages of all approaches are discussed, and recommendations are made for future developments.

scholarly journals Two structurally and kinetically distinct forms of Wolinella succinogenes nitrite reductase

1990 ◽  
Vol 271 (1) ◽  
pp. 259-264 ◽  
Author(s):  
R S Blackmore ◽  
T Brittain ◽  
P M A Gadsby ◽  
C Greenwood ◽  
A J Thomson
Keyword(s):  
Electron Transfer ◽  
High Spin ◽  
Spin State ◽  
Nitrite Reductase ◽  
Exchange Coupling ◽  
Methyl Viologen ◽  
Rapid Rate ◽  
Wolinella Succinogenes

It is shown that the oxidized form of the hexa-haem nitrite reductase of Wolinella succinogenes exists in two structurally and functionally distinct forms, termed ‘resting’ and ‘redox-cycled’. The nitrite reductase as initially isolated, termed ‘resting’, has five low-spin ferrihaem groups and one high-spin ferrihaem group. The reduction of these haem groups by Na2S2O4 occurs in two kinetically and spectrally distinct phases. In the slower phase the haem groups are reduced by dithionite with a limiting rate of 4 s-1. If the enzyme is re-oxidized after reduction with dithionite or with methyl viologen, the resulting ferric form, termed ‘redox-cycled’, possesses only low-spin haem centres and a rate of reduction in the slower phase that is no longer limited. In the resting form of the enzyme the high-spin ferrihaem group is weakly exchange-coupled to a low-spin haem group. It is proposed that in the redox-cycled form the exchange coupling occurs between two low-spin ferric haem groups. This change in spin state allows a more rapid rate of electron transfer to the coupled pair.

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