Synthesis, Structure, and Properties of Bipy Complexes

The details for the preparations of complexes with specific metals are found at the appropriate point in the text. This section discusses the general strategies for the syntheses. 

2 -Bipyridine is a strong field ligand that forms relatively stable complexes, with the inherent M—N bond strength enhanced by the chelate effect. These factors favor the formation of 4-coordinate bis and 6-coordinate tris complexes. The tris complexes of the first row transition metals in normal oxidation states (+2 or +3) are best prepared by the reaction of a suitable metal salt with an excess of bpy in water, methanol, or other organic solvent. The solid complexes can be obtained by crystallization or by the precipitation of the perchlorate, hexafluorophosphate, tetrafluoroborate, or other salts. Because bpy is a strong field ligand, the lower oxidation states tend to be favored, and reduction of M(III) complexes can occur in these preparations. The M(III) complexes are usually readily obtained by the chemical, aerobic, or electrochemical oxidation of the M(II) species. 

Complexes with main group metal ions, and with lanthanides and actinides, can be prepared in water or organic solvents. The complexes are probably (but see later) less robust than those of the transition 

Numerous examples of homoleptic complexes in high or low formal oxidation states are known. In general, the high oxidation state complexes are best prepared by chemical or electrochemical oxidation of the normal oxidation state compounds, followed by further reaction in situ or precipitation with a suitable inert anion. In this respect, perchlorate is ideal as both oxidant and precipitant, but the complexes obtained are frequently violently explosive. Similarly, the low oxidation state complexes are best obtained by chemical or electrochemical reduction of available compounds (or normal oxidation salts in the presence of an excess of bpy). Commonly used reductants have included dissolving metals (zinc, sodium, lithium, magnesium) and the complexes Li(bpy) and Li2(bpy). Isolated examples are known of the synthesis of low oxidation state complexes by reaction of M(0) complexes with bpy or by metal vapor synthesis. 

The bis complexes are known for a range of metals and oxidation states though they tend to be more common for lower formal oxidation states. The precise geometry depends on the electronic configuration of 

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