Ligands, quadridentate atoms

Dockal etal. [57] used slow-scan CV to determine the 21 values for 17 Cu(II/I) complexes in 80% methanol —20% water (w/w) - including nine complexes with macrocyclic terdentate, quadridentate, quinquedentate, and sexaden-tate thioethers and eight complexes with acyclic quadridentate ligands containing thioether sulfur and/or amine nitrogen donor atoms. (In naming the denticity of multidentate ligands, Dwyer, Lions, and coworkers have pointed out that dentate is a Latin root and proper nomenclature requires that Latin prefixes be used. 

All of the complexes structurally characterized have either a square planar or a square pyramidal structure with a planar arrangement of the four donor atoms. Complexes having general formulas [NiL]Y2 and [NiXL]Y (L = quadridentate ligand X = coordinated anion Y = uncoordinated anion) are invariably low-spin as one can easily predict on the basis of the high nucleophilicity of the donor atoms.1389... 

A minor change in the nature of the ligands sometimes produces a great change in the nature of a complex. Thus, if R" is —(CH2)2— in the branched quadridentate ligand (6), the nickel complex is a dimer in which each half is planar and diamagnetic, but if R" is —(CH2)3— the complex is polymeric and paramagnetic each nickel atom is at the center of a tetrahedron.23... 

Fig. 8.6. The porphin molecule. The NH hydrogen atoms are readily removed as protons and the resulting dianion acts as a quadridentate ligand.

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