Magnetic block metal complexes

Crystal field theory can bring together structures, magnetic properties and electronic properties, and we shall expand upon the last two topics later in the chapter. Trends in CFSEs provide some understanding of thermodynamic and kinetic aspects of J-block metal complexes (see Sections... 

In this chapter, we discuss complexes of the -block metals and we consider bonding theories that rationalize experimental facts such as electronic spectra and magnetic properties. Most of our discussion centres on first row J-block metals, for which theories of bonding are most successful. The bonding in fif-block metal complexes is not fundamentally different from that in other compounds, and we shall show applications of valence bond theory, the electrostatic model and molecular orbital theory. 

Ligand-field theory is concerned only with the low-lying electronic states of a d- or y block metal complex which can be described by the rearrangements of electrons within the d- or y shell. These states describe the magnetic properties (paramagnetism, g-values) and the ""d-d (or ""f-f ) electronic spectra (color, linear, and circular dichroism). 

The broadly successful application of these formulas to the paramagnetism of lanthanide complexes was due to the wide multiplet widths in the/block metals (large spin—orbit coupling coefficients X) and to the small effect of the ligand field on the deep-lying / orbitals. No comparably useful formula for the magnetic moments of d block complexes exists, except perhaps for the spin-only formula ... 

The magnetic properties of d- or f-bloek metal ion complexes can usually be predicted from ionic bonding models. Orbital contributions to magnetism can often be neglected for first row d-block metal ions but must be included when considering f-block metal ions. 

Biomimetic oxidation catalysis has largely focused on complexes with planar tetradentate ligands such as manganese or iron porphyrins and related macrocyclic trans-chelates[5]. There is considerable interest in the synthesis of multinuclear metal complexes since these molecules might be useful as building block for magnetic molecular materials[6] and model compounds for understanding the properties of metalloproteins[7]. 

Paramagnetism arises from unpaired electrons. Each electron has a magnetic moment with one component associated with the spin angular momentum of the electron and (except when the quantum number / = 0) a second component associated with the orbital angular momentum. For many complexes of first row J-block metal ions we can... 

Table 20.8 Calculated magnetic moments for first row

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