Coordination spheres monodentate

Substituted terpyridine, 4,4, 4"-tris(5-nonyl)-2,2 <5, 2"-terpyridine (tNtpy), is a planar tridentate ligand that was successfully used in homogeneous ATRP of methyl acrylate and styrene [79]. Polymerization of both monomers was controlled and the resulting polymers had relatively low polydispersities (MJMn < 1.2). Similarly to PMDETA, the typical ligand to copper halide ratio used in the polymerization was 1 1. Terpyridine and its derivatives are expected to form tetra-coordinated complexes with copper in which the fourth coordination sphere is occupied by a monodentate ligand (Br-, Cl , solvent, monomer, etc.). Although,... 

A monodentate ligand is one that binds to the central metal atom using only one donor atom (lone pair). A monodentate ligand only occupies one position in the coordination sphere. A polydentate ligand is one that binds to the central metal atom using two or more donor atoms and occupies two or more positions in the coordination sphere of the complex. 

The difference in behaviour has been attributed to the preferred formation, by cadmium(II) and mercury(II), of [MX2]oo chains in which pairs of chloride anions link metal centres to give a square planar MX/ arrangement, the octahedral coordination sphere then being completed by two monodentate bu molecules [MX2]oo chain formation does not occur for copper(II) and zinc(II) and so the anions only occupy two of the six available co-ordination sites allowing bu to act as a bidentate chelating ligand. 

There have been a number of other reports of the use of largely unsaturated, N4 donor macrocycles to generate 1 1 manganese(II) complexes." The majority of these have been assigned octahedral geometries in which two monodentate ligands occupy the remaining positions in the coordination sphere. 

ATR-FTIR data indicated that on goethite, glycophosphate adsorbs mainly as an inner-sphere, monodentate complex via the phosphonate group the carboxylate group does not appear to be involved in surface coordination in this case (Sheals et al 2002). 

In the available literature, only six PBP structures of Ni(II) have been reported so far (34,38,40,45,48,50) and four of them include acyclic pentadentates (XVII-XX). These pentadentates are equato-rially coordinated in their neutral form with weak conformational flexibility. Apical positions are always occupied by water molecules, while nitrate anions always represent counter ions in the structure. The change of any of the mentioned structural elements (polydentate, axial ligands, or counter ion) affords complexes of which the structure has not been determined (52,54,56,58). These are complexes with the same type of ligands XX-XXIII, containing Cl- ions and water molecules, but it is still unknown which of these two monodentate ligands occupies the apical positions. It is questioned whether both monodentates actually occur in the coordination sphere, and because of that it is impossible to discuss the geometry of these complexes in more detail. 

Many transition metal nitrates will form complexes which retain nitrate in the coordination sphere. Ni(N03)2 gives [Ni(02N0)2(pyN0)2] with both nitrate groups in bidentate coordinated form, but IR and electronic spectra suggest that the corresponding 2,6-lutNO complex is five-coordinate with one monodentate and one bidentate nitrate. 

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