Coordination compounds chelating ligands

In view of the presence of active functional groups at suitable sites in the above ligands and their substituted derivatives, these tend to form coordination compounds/chelates with a large number of metals. Excellent reviews have been published on the complex compounds of biguanides151152 and guanylureas, 51 and biuret.153,154... 

The peculiarities of classical localized coordination bonds (two-electron and two-center [1,4,5]) are displayed most clearly in MCC. Mostly, the elements of the first period of the Periodic Table (C, N, O) participate as electron donors in the formation of such bonds. In complexes of this type, the role of Ji-dative interactions is significant. These interactions are revealed in coordination compounds of ligands containing the elements of the next periods as donor centers (P, As, Sb S, Se, Te Cl, Br, I). We note that the examined complexes are the most successful objects to study the influence of ligand and metal nature on the character of the coordination bond, since, in this case, the factors which could distort this influence (chelate, macrocyclic, and other effects [117,135]) are absent. 

Coordination compounds formed by hard and charged donors with lanthanides, like those of d- and s-block metal ions, are usually thermodynamically stable — especially if coordinated by chelating ligands. Table 9.1 shows a comparison of thermodynamic constants for some key polydentate ligand systems in common with lanthanides. 

Heteroleptic complexes of uranium can be stabilized by the presence of the ancillary ligands however, the chemistry is dominated by methyl and benzyl ligands. Examples of these materials include UR4(dmpe) (R = alkyl, benzyl) and U(benzyl)4MgCl2. The former compounds coordinate "soft" chelating phosphine ligands, a rarity for the hard U(IV) atom. 

Transition metal polysulphides coordination compounds with purely inorganic chelate ligands. M. Draganjac andT. B. Rauchfuss, Angew. Chem., Int. Ed. Engl., 1985, 24, 742 (129). 

Draganjac M, Rauchfuss TB (1985) Transition metal polysulfides Coordination compounds with purely inorganic chelate ligands. Angew Chem Int Ed Engl 24 742-757 DuBois MR (1989) Catalytic applications of transition metal complexes. Chem Rev 89 1-9 Ansari MA, Ibers JA (1990) Soluble selenides and tellurides. Coord Chem Rev 100 223-266... 

TiCRjtftc) was prepared starting from Ti(NR2)4 4,5) or TiCl4 (6). The structure of the ethyl compound was elucidated by X-ray studies (7, S). The titanium atom is eight-coordinated by the sulfur atoms of the four chelating ligands and the coordination geometry closely approximates to that of a dodecahedron. 

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