Spin state, transition metal complexes

For transition metal complexes with several possible spin arrangements, a separate calculation within each spin multiplicity may be required to find the ground state of the complex. 

Electron configurations of transition metal complexes are governed by the principles described in Chapters. The Pauli exclusion principle states that no two electrons can have identical descriptions, and Hund s rule requires that all unpaired electrons have the same spin orientation. These concepts are used in Chapter 8 for atomic configurations and in Chapters 9 and 10 to describe the electron configurations of molecules. They also determine the electron configurations of transition metal complexes. 

Rates of Spin-State Transition for Solid Metal Complexes Based on the Line Shape... 

Most complexes showing spin-state transitions are in fact of low symmetry. In order to describe their electronic structure it is convenient to employ term symbols appropriate to cubic symmetry and this practice will be followed below. The most common transition-metal ions for which spin-state transitions have been observed are Fe " (3d ), Fe " (3d ) and Co (3d ), a minor role being played by Co " (3d ), Mn " (3d ), as well as Cr " and Mn " (3d ). The relevant ground states for an octahedral disposition of the ligands are LS Ui,(t ,) and HS r2,(t ,e ) for iron(II), LS and HS Ai,(t, e ) for... 

The interconversion between different spin states is closely related to the intersystem crossing process in excited states of transition-metal complexes. Hence, much of the interest in the rates of spin-state transitions arises from their relevance to a better understanding of intersystem crossing phenomena. The spin-state change can alternatively be described as an intramolecular electron transfer reaction [34], Therefore, rates of spin-state transitions may be employed to assess the effect of spin multiplicity changes on electron transfer rates. These aspects have been covered in some detail elsewhere [30]. 

Relaxation of Thermally Quenched or Optically Excited High-Spin States Resulting from the Spin-State Transition in Solid Metal Complexes... 

Alternatively, optical excitation of the LS state in a solid metal complex which is involved in a thermally driven spin-state transition may result in the formation of a trapped HS state, the study of the kinetics of the HS -> LS relaxation being then possible [134]. This process is initiated, e.g., in an iron(II) complex, by irradiation into the spin-allowed absorption band at... 

The Molecular Reorganization Associated with Spin-State Equilibria in Solution and the Structural Changes Accompanying Spin-State Transitions in Solid Metal Complexes... 

Table 19. Results of calorimetric and DSC measurements on spin-state transitions in solid transition-metal complexes... 

In the last example, a serious handicap is the extreme sensitivity of the calculations to the parameterization of the metal atoms. In a paper concerning the spin states of metal dimer complexes (38) as studied by EHT, heavy manipulation of the original theory was needed. In the field of transition metal coordination compounds self-consistent charge (SCC) calculations (of the type already mentioned for electronegative atoms) are essential to obtain the diagonal elements Hu. 

Sacconi (1971) Conformational and spin state interconversions in transition metal complexes [205]. 

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