Multi-bidentate ligands

The dynamic behavior of tris-chelates was of considerable interest due to the additional constraint of a third bidentate ligand, relative to the extensively studied bis-chelates, with two monodentate ligands (Section III.A.3). Also the question of whether N-Si dissociation takes place during multi-step ligand-site exchange processes was considered. 

Bridging ligands capable of binding more than two metal centers are less studied. Some examples were highlighted earlier. Polymetallic ruthenium complexes have been synthesized using the tetra-bidentate ligands (62) and (63) as multi-electron transfer agents.181,182... 

Unidentate ligands invariably add in a series of steps, as shown here. With multi-dentate ligands, the maximum coordination number of the cation may be satisfied with only one ligand or a few added ligands. For example, Cu(II), with a maximum coordination number of 4, can form complexes with ammonia that have the formulas Cu(NH3)2+, Cu(NH3)i+, Cu(NH3)i+, and Cu(NH3)i+.With the bidentate ligand glycine (gly), the only complexes that form are Cu(gly) and Cufgly) . ... 

Similar solutions have been worked out for bis- (bidentate) and multi-dentate systems, and the procedure has the merit of describing either the ligand conformations or the configuration of the complex, or both, for many systems. The octant method is rather cumbersome to use at the moment, but further examination may resolve this difficulty and lead to a general method for describing the stereochemical detail in these systems. In... 

The number and variety of coordination complexes of palladium(II) with sulfur-containing bidentate or multidentate ligands is legion, and it is possible here only to summarize the different kinds of complexes formed and to guide the reader into the literature. Table 2 contains a selection of typical palladium(II) complexes of bi- or multi-dentate sulfur or selenium donor ligands, and comments on pertinent aspects of particular complexes. Chelate... 

Two of the classical bis-nitrogen ligands to assemble porphyrins (predominantly zinc metallated) are the bidentate l,4-diazabicyclo[2.2.2]octane (DABCO) and 4,4 -bipyridine (bipy). Other di-topic nitrogen-ligands studied include hydrazine, 4,4 -bipyrimidine, diaza-pyrene, 5,5 -dicyano-2,2 -bipyri-dine, perylene-bisimide, extended bipyridine units and non-covalently linked di-pyridyl ligands via bipy-metal interactions. The formation of various bis-porphyrin and multiporphyrin assemblies using these versatile ligands were studied in detail by Sanders, Anderson, Hunter, Branda and many others. The structures of the supramolecular multi-porphyrin architectures are schematically represented in Fig. 9. 

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