Sexadentate ligands

The preparation of the Ni(n) and Cu(n) complexes of the related 18-membered sexadentate ligand (283) has been performed (Hay, Jeragh, Lincoln Searle, 1978). The Ni(n) complex has a structure of type (284). Once again, both complexes are quite labile under acid conditions with the dissociation of the copper species being relatively... 

Tris-N-functionalization of 1,4,7-triazacyclononane has yielded a variety of sexadentate ligands, which form stable complexes with manganese(II). For example, the l,4,7-tris(2-pyridyl-methyl) derivative gives a complex of type [MnL](C104)2 in which the manganese ion has a... 

Ethylenediaminetetraacetate, a sexadentate ligand is assumed to form an octahedral complex with rare earth ions. Thus p was calculated for different electronic configurations using the equation... 

Mixed N—O donor atom quinque- and sexadentate ligands 96... 

The edta compound of Mn11 has played on important role in expanding the coordination chemist s vision of the occurrence of higher coordination numbers. Hoard et al.u5 demonstrated that the large size of the Mn11 ion pushed back the sexadentate ligand and allowed a water molecule to coordinate, thereby producing a seven-coordinate ion, [Mn(edta)H20)]. On the other hand, the tetramethyl-... 

Similar green or brown tris-chelated compounds are described283 for many of the usual range of available / -diketonates, the most stable compound being that formed with the sexadentate ligand (124).318... 

Tae-en, the amine analogue of edta, also called penten, originally synthesised and studied by Schwarzenbach et al. (130, 131) is able to form only a single geometric isomer when acting as a sexadentate ligand coordinated to the Co(III) ion. It exists as a pair of enantiomers. Its absolute configuration was determined by Muto et al. (132). The X-ray structure established that the (+>589-[Co(tae-en) complex is... 

Complexes of sexadentate ligands display a wide range of reduction potentials. The lowest reduction potentials reported for any cobalt(III) hexaamine are -0.61 V for the diamcyclam complex and -0.62 V for/be 063 [Co(diAmpnsar) Both of these complexes are expected to have unusually short Co-N bond lengths this has been confirmed for the diamcyclam complex 149). 

We noted in Chapter 10 two rather symmetrical arrangements of 7 nearest neighbours found in oxy- and fluoro-compounds of transition metals, namely, pentagonal bipyramidal (ZrF "), and monocapped trigonal prism (NbF ). The ions formed from ethylenediamine tetracetic acid and the closely related diamino cyclohexane acid are potentially sexadentate ligands, for there are 4 0 atoms and... 

This general method was then extended not only to complexes with other bidentate ligands but also to those with a terdentate or a sexadentate ligand, e.g. bidentates, (+)-hydroxymethylenecamphor (-+-)-3-acetylcamphor and (—)-cyclohexanediamine terdentates, 2,3-diaminopropionic add 2,4-diamino-butyric acid l,3-diamino-2-propanol and l-methyl-2,4,6-triaminocyclohexane... 

The sexadentate ligand, (L)-ethylenediamine-iV,Ar-diacetic-iV -n[ionosuccinic acid (Htcddams), can form two geometric isomers with cobalt(III) (Fig. 3.6), in which... 

---