Coordination chemistry binuclear complexes

The coordination chemistry of the sulfido ligand is very varied. Scheme 4 illustrates the modes of coordination of to transition metal ions. The monosulfido ligand can act as a two-electron, terminal or /u-2-bridging donor, or up to a six-electron donor if it binds as /u.4-bridging or interstitial donor. It is, therefore, not surprising that a wide variety of binuclear and polynuclear sulfido clusters complexes can be prepared. 

Carbonate complexes are known since the beginning of coordination chemistry. Generally, they are rather stable and easily accessible. The reduction of COs to CO should be facilitated in mononuclear or binuclear carbonate complexes with metal centers that provide two excess electrons. The requested photoexcitation corresponds to an MLCT transition that terminates at the carbonate ligand as acceptor. However, MLCT absorptions of this type are unknown. They are expected to occm- at very short wavelength since the n acceptor orbital of COs is certainly located at rather high energies 29). 

During the last two decades, the supramolecular approach greatly contributed to the rapid evolution of standard coordination chemistry, usually limited to mono- and binuclear complexes, toward more complicated and sophisticated nanometric edifices bearing novel functionalities. 

The previous sections have documented the fact that binuclear complexes can be obtained with a variety of novel structural features and that these undergo, in some cases, unprecedented chemical reactions. We can expect that work along these lines will continue to point out new structural types and new classes of reactions. Progress so far can be said to have laid a foundation for the basic coordination chemistry of the most readily obtained binuclear systems. It remains to be seen whether these reaction types can be clearly utilized in the design of new catalysts or whether unusual forms of catalytic activity for binuclear complexes will be discovered serendipitously. 

Modulation of the physiological effects of histamine (Hm) (22) may also be an important biochemical role for Cu complexes. Walker, Siaw and Li [114], Walker, Reeves and Kay [115], and Walker and Reeves [116] considered the coordination chemistry of histamine in vivo and provided an abundance of evidence to support the suggestion that a binuclear, hydroxy-bridged Cu complex (23) was the active form of histamine. Intraperitoneal injections of... 

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