Spacer ligand

Biospecific Chromatography Advantages of Polymer-Spacered Ligands 169... 

Two-dimensional planar interpenetrating networks have been formed using the spacer ligand 2,2 -bis-l,6-naphthyridine with a zinc salt.274 Helicate structures have been synthesized which rely heavily on non-covalent interactions in the metal-assisted self-assembly process in solution.275... 

Gold nanoparticles (or other metallic or semiconductor particles) are functionalized with azide groups by suspending a 2.8 nM concentration of particles in 20 ml of water and adding a 20 pm ole amount of a thiol-PEG-azide spacer ligand to the suspension with stirring. 

Lindner et al. carried out detailed studies on the use of the sol-gel procedure to obtain new materials as suitable matrices [45]. A co-condensation of Si(OR)4, Si(OR)3-spacer-Si(OR)3 and Si(OR)3-spacer-ligand resulted in new hybrid materials, the properties of which strongly depended upon the spacer and the ratio of the different components used. Most of these materials were characterised with IR, EXAFS, and EDX spectroscopy, scanning electron microscopy and solid state NMR spectroscopy. Solid state 31P NMR was used to quantify the mobility of the interphases the changes in line-... 

Targeting Hgands can be attached to the microbubble directly (Fig. 12 A) or via a flexible polymer spacer arm (e.g., polyoxyethylene. Fig. 12 C). Use of the spacer arm may allow for tighter binding in some situations. When the detachment force of the targeted microbubble removal from the receptor-coated surface was measured, microbubbles with spacer-ligand construct demonstrated superior retention as compared with the bubbles where the ligand was connected directly to the lipid anchor, without a spacer [92]. 

The two main immobilisation techniques on a mesoporous material are direct grafting and indirect grafting (tethering), as shown in Scheme 1. In the former case, the complex interacts directly with the matrix. In the latter case, the complex is tethered to the supporting material via a spacer ligand, which is either introduced first on the support (as shown on the upper part of Scheme 1) or integrated into the complex before being anchored onto the support (lower part of Scheme 1). 

Another useful strategy for the confinement of metal centres in molecular sieves is the covalent attachment of coordination complexes via a spacer ligand (tethering). The use of surface-fixed N-donor ligands (Lewis base Hg-ands) coordinating dioxomolybdenum M0O2 moieties has been described mainly by Thiel et al. [22,23,28,29] and Gonsalves et al. [15,24,40]. 

Table4 Cyclooctene epoxidation with TBHP/MCM-spacer ligand-tethered Cp Mo(CO)3R complexes... 

Scheme 7 Functionalisation of the mesoporous material prior to the grafting of the complex via an alkyl-siloxane spacer ligand...

Transition-metal ions are employed as nodes and bifunctional ligands as spacers. Commonly used spacer ligands are pseudohalides such as cyanide, thiocyanate, and azide, and N-donor ligands such as pyrazine, 4,4 -bipyridine, and 2,2/-bipyrimidine. Besides discrete supermolecules, some one-, two-, and three-dimensional architectural motifs generated from this strategy are shown in Fig. 20.3.9. 

Schematic representation of the motifs generated from the connection of transition metals by bifunctional spacer ligands. One-dimensional ...

Recently, two pyrazine (pz)-linked hetero-triads of cobalt phthalocyanine (CoPc) and ZnTPP, namely (CoPc)-pz-(ZnTPP)-pz-(CoPc) (15) and (ZnTPP)-pz-(CoPc)-pz-(ZnTPP) (16), have been prepared [30], The thermal properties of these triads and related macrocyclic components have been studied by thermal gravimetric analysis and differential scanning calorimetry. It has been found that the thermal stability of axial coordination increases in the order ZnPc(pz)2 < ZnTPP(pz)2 sa CoPc(pz)2, and the thermal decomposition of the triads 15 and 16 proceeds firstly via the degradation of the spacer ligand. 

Scheme 4 illustrates the possible structures that can result from self-assembly of a m-octahedral or c/s-square-planar metal and a linear spacer ligand. There are... 

Scheme 4. Possible supramolecular isomers for compounds formed from a cis-octahedral or square-planar metal and a "spacer" ligand.

Flexibility in ligands can lead to subtle or dramatic changes in architecture. For example, l,2-bis(pyridyl)ethane, dipy-Et, can readily adapt gauche or anti conformations. In the case of [Co(dipy-Et), 5(N03)2]n, which contains a T-shape node, infinite molecular ladders which contain six molecules of chloroform per cavity exist as the most commonly encountered architecture (Figure 3A).45b In such a situation all spacer ligands are necessarily anti. However, under certain crystal-... 

Square grid networks generated with bipy spacer ligands were first reported by Fujita et al.46 Fujita s structures are based on Cd(II) and numerous other examples have subsequently been reported based on a number of other transition metals, including Ni(II) and Co(II). Although these 2D coordination networks are essentially identical within the coordination grid (square dimensions ca. 11.5 x 11.5 A), the crystal structures of compounds differ in the mode that networks stack with each other (interlayer separations range from 6-8 A). 

Another metal geometry or node that is of particular interest because of its potential range of supramolecular isomers is the T-shaped geometry, i.e. a mer-substituted metal moiety with 1 1.5 metal spacer ligand ratio. This node has thus far produced three distinct 2D supramolecular isomers brick wall,46 herringbone,49... 

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