Polydentate ligands coordination modes

Repetition and modification of his procedures have both confirmed this work and led to the possibility that the technique may be utilized to determine the mode of coordination of polydentate ligands containing amino groups (10). 

The crystallochemical analysis of complexonates has been carried out and the crystallostructural role of various ligands, on the formation of different coordination modes by metal atoms, is extensively reviewed [761-763], It is established that com-plexonate ions of the diamine type are capable of forming 14 different types of coordination [761], Depending on the coordination mode present, one polydentate diaminocarboxylate ligand has the capability to bind from one to four metal atoms, producing from two to 10 coordination bonds. 

The reaction control should be emphasized amongst the conditions of reactions of competitive complex formation [19,23], It is necessary to take into account that it is possible to determine, and frequently predict, the direction of the electrophilic attack to the donor center of di- and polyfunctional donors (ligands) only in the case when the thermodynamically stable products are formed under conditions of kinetic control. Thus, the thermodynamic stability of complexes is discussed, when the bond between the metal and di- and polydentate ligands is localized in the place of primary attack on one of any of the donor centers by the electrophilic reagent, without further change of coordination mode in the reaction of complex formation. 

A large number of lanthanide-based frameworks have been synthesized utilizing polydentate ligands such as sulfoxides, carboxylates, nitriles, pyridones, and lactams." In spite of the difficulty in controlling coordination mode, the high numbers (e.g., 7-10) encountered with... 

Zirconium and hafnium tetrahalides form six-, seven- and eight-coordinate adducts with polydentate phosphine and arsine ligands. The 1 1 adducts [MXt(dppe)] and [MX dpae)] (M = Zr, X = C1 or Br M = Hf, X = C1 dppe = Ph2PCH2CH2PPh2, dpae = Ph2AsCH2CH2AsPh2) have been prepared in benzene media. IR spectra of the [MCLt(dppe)] complexes exhibit four v(M—Cl) modes in the 353-278 cm-1 region, consistent with a six-coordinate octahedral structure.45... 

The coordination chemistry of these and other polydentate tertiary phosphines has been documented with a variety of ligating modes observed for these ligands.214"216 Aspects of coordination behavior of the above polydentate phosphines with Fe,22, 225,231,232 Ru,233 Co,221... 

---