Polynucleating ligands

One of the most popular methods for the preparation of low-molecular weight polynuclear metallochelate is the interaction of MXn with polynucleating ligands... 

The synthesis of low-dimensional solids has become more important than ever before, both to chemists and physicists. In the catenation of metal ions, the catenating blocks are usually polynucleating ligands. The 1,2,4-triazole ligand acts in most of its metal complexes as a 1,2-bicoordinating ligand. In this type of coordination, linear polynuclear complexes are formed. 

Virtually all types of metal ions have been complexed with macrocyclic ligands.2-7 Complexes of transition metal ions have been studied extensively with tetraaza macrocycles (Chapter 21.2). Porphyrin and porphyrin-related complexes are of course notoriously present in biological systems and have been receiving considerable investigative attention (Chapter 22).8 Macrocyclic ligands derived from the Schiffbase and template-assisted condensation reactions of Curtis and Busch also figure prominantly with transition metal ions.6,7 The chemistry of these ions has been more recently expanded into the realm of polyaza, polynucleating and polycyclic systems.9 Transition metal complexes with thioether and phosphorus donor macrocycles are also known.2... 

Polynuclear PCMU can be synthesized by means of all the above described methods for the preparation of mononuclear PCMU, such as binding a few metals with polynucleating macromolecular ligands, immobilization of the ready-made and well characterized polynuclear complexes or clusters on polymers and assemblage of polymetallic sites on polymer supports. 

Only a handful of pseudotetrahedral or octahedral oxosulfido-Mo(VI) and -Mo(V) complexes are known, and their chemistry is described in Section 11. Mononuclear sulfido-Mo(V) complexes are unstable due to their susceptibility to redox, polynucleation, and hydrolysis reactions. Trispyrazolylborate derivatives such as sfructuraUy characterized Tp Mo SX2 (X = Cl, OPh derivative X2 = bdt, catecholate) are most commonly encountered. The Tp complexes exhibit short Mo=S bonds (ca. 2.13 A), intense S(ls)- - n (Mo=S) XAS transitions characteristic of terminal thio ligands, and EPR iso see g-Factor) values substantially lower than their 0x0 analogues. ... 

These polynucleating macrocyclic ligands sometimes have a mind of their own and do not form the desired tetranuclear species. Thus, under certain conditions, ligands of type L H4 or L H4, which contain short-chain alcohol backbones, do not deprotonate at the secondary alcohol moiety. They form polymeric species with Cu(II) halides or azides, probably because of the small macrocyclic ring size (304). Somewhat similar effects were alluded to earlier in regard to the tetraphenolic Schiff-base macrocycles (263), and we have had related experiences with open-chain analogues (305). 

The polynucleating Schiff base ligand, P-dhtenH2 was prepared by refluxing ethylenediamine and 2,5-dihydroxyterephthalaldehyde in methanol. The formation of Schiff base was monitored by IR spectroscopy. At the end of this Schiff base formation the carbonyl stretching frequency at 1668 cm was almost disappeared. The C=N... 

Polynucleating macrocycUc systems able to bind up to nine metal ions have been obtained. However, the techniques developed for their synthesis could be extended to facilitate the production of yet more complex ligands able to coordinate even more cations. In addition, the strategy used for successive increases in the number of known polynucleating Ugands probably has the potential for assembling new and highly polynuclear mixed-metal macrocycUc complexes. 

A hexaamide covalent capsule 148 with an extended macrobicyclic framework has been described in [111] as a first polynucleating amide caging ligand with two of three pyridine-containing ribbed fragments having the same orientation and the third one looking at the... 

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