Nitrogen heterocyclic ligands

Magnetic Interaction in Metal Complexes with Bridging Nitrogen-Heterocyclic Ligands ... 

Coordination Compounds. A large number of iridium complexes with nitrogen ligands have been isolated, particularly where Ir is in the +3 oxidation state. Examples of ammine complexes include [Ir(NH3)6]3+ [24669-15-6], [IrCl(NH3)]2+ [295894)9-1], and trans-[Ir(03SCF3)2(en)2]+ [90065-94 4]. Compounds of IV-heterocyclic ligands include trans- [IrCl4(py)2] [24952-67-8], [Ir(bipy)3]3+ [16788-86-6], and an unusual C-metalated bipyridine complex, [Ir(bipy)2(C3,N-bipy)]2+ [87137-18-6]. Isolation of this latter complex produced some confusion regarding the chemical and physical properties of Pi(bipy)3]3+ (167). 

Heterocyclic ligands such as pyridine (py), V-methylimidazole (Meim), benzotriazole (btaH) and related molecules are good ligands due to the presence of at least one nitrogen ring atom with a localized pair of electrons. When this nitrogen bears a substituent, such as in pyrrole, the coordinating possibilities are reduced or absent. 

Reedijk and co-workers have prepared and studied a variety of Ru(ll) complexes of pyridyl- and pyrazinyl-substituted 1,2,4-triazoles of which 26 is an example. In ail cases the heterocyclic ligands were chelated to the metal center via one azole and one azine nitrogen atom and, in addition to various electrochemical and spectroscopic studies, pKa values for the pyrrole proton of the triazole ring were obtained. The Ru(bpy)2 + com-... 

Figure 10-2. Although they are relatively rare in biology, organometallic compounds with metal-carbon bonds are important. An typical example is coenzyme B12. The cobalt is co-ordinated to a tetraazamacrocyclic ligand, and has one axial nitrogen donor heterocyclic ligand and one axial alkyl group. The figure illustrates only the core of the macrocycle and the axial groups.

Emission from Complexes of Sulfur-Nitrogen Heterocyclic Ligands. 40... 

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