Ligands hexa-dentate

Table 52 Selected Nickel(II) Complexes with Tetra-, Penta-, and Hexa-dentate Schiff Base Ligands... 

Selected examples of tetra-, penta- and hexa-dentate Schiff base ligands and of the corresponding nickel(II) complexes are reported in Table 52. 

In Table 108 significant examples of nickel(II) complexes with mixed-donor macrocycles of various denticity are reported. Apart from the nitrogen atoms, the heteroatoms in the macrocyclic rings are usually either O or S, or in a few cases P. Few examples of nickel complexes with macrocycles containing all-sulfur or all-phosphorus donor atoms have been reported to date they are also included in Table 108. In nickel(II) complexes formed by mixed-donor penta- and hexa-dentate ligands the oxygen atoms of the macrocycle are often only weakly coordinated or are not coordinated at all. 

Table 7 Products from the Reactions of Re3CL, with Tri-, Tetra- and Hexa-dentate Phosphine and Arsine Ligands...

Penta- and Hexa-dentate Ligands. Perhaps the best known hexadentate ligand is ethylenediaminetetraacetate, EDTA4-, which can also be penta-dentate as EDTAH3-. 

Intorre and Martell (237) have also studied the formation of mixed chelate species in which the zirconium 1 1 complex with the hexa-dentate chelating ligands, ethylenediaminetetraacetic acid, iV-hydroxy-ethylethylenediaminetriacetic acid, and m7 s-cyclohexanediaminetetra-acetic acid, are shown to take up one mole of the bidentate ligands, l,2-dihydroxybenzene-3,5-disulfonate l,8-dihydroxynaphthalene-3,6-disulfonate 8-hydroxyquinoline-5-sulfonate, and acetylacetone (except ZrHEDTA), to form 8-coordinate 1 1 1 species. At least for the zir-conium-EDTA-l,2-dihydroxybenzene-3,5-disulfonate species, there is evidence for dimerization (230). Additionally, the Zr EDTA complex reacts with one mole of the bidentate ligands, 5-sulfosalicyclic acid, alizarin sulfonate, citric acid, and lactic acid to form 1 1 1 complexes tartaric acid and pyrophosphate ions form complexes which could not be identified. The zirconium-nitriloacetic acid complex in the presence of two moles of oxalic acid or l,2-dihydroxybenzene-3,5-sulfonate also forms 1 1 1 complexes in solution. 

The template synthesis has also been successfully employed for the preparation of macrocycles containing mixed donor atoms. Examples which refer to tetra- and hexa-dentate ligands are given in Schemes 42, 47 and 50.2649.2653,2654,2658 Apart from the template synthesis a number of nickel macrocycles have been prepared by direct combination of the appropriate nickel(II) salt with the preformed macrocyclic ligand in alcoholic medium, often MeOH (see also Tables 103, 106-108). 

Considering the denticity of ligand products typically assembled, the most often encountered are tetradentate macrocycles, followed by hexadentate species. Potentially tridentate macrocyclic products are described for nickel(II), copper(II), bor-on(III) and molybdenum(O) silver(I) and mercury(II) promote assembling penta-dentate and hexadentate macrocycles thallium(I), strontium(II), lanthanum(III) and the lanthanides(IIl) from Ce to Gd (Pm was not studied bccau.sc of its radioactivity) hexadentate products and the metal ions from Tb to Lu promote the formation of tetra- and hexa-dentate macrocyclic ligand products. Variable denticity of synthesised systems is conunon to most first-row transition elements as well as to alkaline metal ions which serve mainly to form crown ethers and related compounds. 

Osmium(VI) forms irons-0s02(malt)2 (98), while dioxouranium(VI) forms irons-U02(malt)2 (98) and many hydroxypyridinonate complexes, with bidentate and with tetradentate (177) ligands - trans-UO2L2 and UO2L, respectively. Several actinide elements form complexes with hexa- and octa-dentate hydrox5rpyridinonates (see Section IV.C.7 later). 

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