Ligand-controlled hydrolysis

The most successful synthetic approach to structurally well defined lanthanide hydroxide complexes is the ligand-controlled hydrolysis approach [69-71]. The essence of this methodology is schematically shown in Figure 6.25. It makes use of the high propensity of lanthanide ions toward hydrolysis, but controlled and limited by certain supporting ligands. The scheme starts with a lanthanide complex whose coordination sphere constitutes both organic and aqua... 

Rationales of ligand-controlled hydrolysis approach to cluster synthesis... 

Controlled hydrolysis of Fe(III) complexes, using for example the [Fe20]4+ unit, in aqueous or non-aqueous solvents in the presence of appropriate ligands has been carried out to give a variety of products. These have been shown to contain di-, tri- and tetranuclear and even deca-, undeca-, dodeca-, heptadeca-, octadeca- and nonadecanuclear Fe(III) core structures (Gorin and Lippard, 1986 Micklitz etal, 1994 Heath et al., 1996 Lippard and Berg, 1994 Powell, 1998). 

Alkoxide gels, 23 60 Alkoxide gels, in optical fiber manufacturing, 11 145 Alkoxide initiators, 14 259 Alkoxide ligands, thorium, 24 770 Alkoxides, 12 190 25 72-86 controlled hydrolysis of, 23 56 iron, 14 533 mixed-metal, 25 100 titanium, 25 82 uranium complexation with,... 

A number of complexes of neutral -diketones are known, although such complexes are generally not very stable. They can be synthesized by addition of the /3-diketone to a simple metal salt or coordinatively unsaturated metal complex, by controlled hydrolysis of a metal /3-diketonate, or by displacement of a weakly bound neutral ligand by the /3-diketone. 

It should be noted that most structurally characterized dinuclear complexes are products of adventitious lanthanide hydrolysis, and are not reproducible. With the ligand-controlled hydrolytic approach, they can now be rationally synthesized starting from a mononuclear aqua complex. Shown in Figure 6.30 is the synthesis of [(EDTA)Er (ti-OH)2Er(EDTA)] (EDTA=ethylenediaminetetraacetate) the dinuclear core doubly bridged by the fi-OH groups is encapsulated by two hexadentate EDTA ligands, one on each metal atom [69],... 

V(Bu N)(SR) Cl3 J (n = 1,2). Controlled hydrolysis of the trithiolate complex with SR = SSiPha gave [ V(Bu N)(SSiPh3)2 20], and both this and the trithiolate complex were fully characterized by spectroscopic studies and X-ray structure determinations. It was confirmed that both complexes have distorted tetrahedral arrangements of the ligands around the metal. 

There are three significant types of iron(III) SMMs. The first two were made by controlled hydrolysis reactions, with the control provided by a polyden-tate ligand. In the Peg SMM the ligand used is 1,4,7-triazacyclononane ... 

The hydrothermal synthesis of the hexanuclear core-based hydroxido-lanthanide coordination polymers, [R3(BDC)3 5(0H)2(H20)2] H20 (R = Y, Yb, and Er BDC = 1,4-benzenedicarboxylate) further attests the rmiqueness of hydrothermal procedures (Weng et al., 2006). The controlled hydrolysis of lanthanide ions led to an open hexanuclear cluster core, drastically different from the commonly observed cubane or octahedral-shaped cluster cores. The hexanuclear core contains six /i3-OH-bridged R(III) ions from two asymmetric imits and adopts a chair-like configuration (R = Y, Figure 102). This hexanuclear building block is linked by the BDC ligands to form a 3D framework. 

The mechanism of Rh-catalysed decarboxylative conjugate addition (Scheme 2) has been investigated by DFT calculations, which indicate that the selectivity towards hydrolysis or jS-hydride elimination, affording (68) and (69), respectively, is a compromise between diffusion control and kinetic control. Ligand control can be adjusted by modifying the intermolecular interaction between the Rh(I) enolate intermediate and water. ... 

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