Tripod molecule

The Anslyn group has pioneered supramolecular displacement assays as a distinctive method of analysis. A typical example used a tripodal molecule, or podand, to determine the amount of citrate in drinks and the quality of wine made from Pinot Noir grapes [7], The initial work on citrate utilized a complex between a tris(guanidinium) derivative of 1,3,5-triethylbenzene with a fluorescent dye, car-boxyfluorescein. In the presence of citrate the dye is ejected and replaced with the... 

Figure 34. Two possible ways a tripodal molecule can crystallize trigonal noncentrosymmetry (a) and hexagonal centrosymmetry (b).

The interesting tripod molecule MeSi(PBu2)3 was prepared in 70% yield by treating MeSiCls with LiPBu2 in diethyl ether at -80 C. 

Figures 62 and 63 show other systems combining hydrogen and coordination bonds. Whitesides and co-workers assembled poiphyrins on hydrogen-bonded aggregates based on the complementary interaction between isocyanuric acid and melamine. Using the trismelamine tripod molecule 109 bearing pendant imidazole ligands.

Stearic acid is a saturated fatty acid. This means it has only single bonds between its carbon atoms. This means it can coil up and form into random shapes. Double bonds between carbon atoms restrict the bending of the molecule at the point of the bond, like a hinge that lets a door swing back and forth but not up and down. Triple bonds are even more restrictive, locking the joint in place three-dimensionally, like the legs of a tripod. 

Iron(II) complex of tris(N -tert-butylurea-ylato)-N-ethylene]aminato activates dioxygen at room temperature to afford an iron(III) complex containing a single terminal oxo ligand. X-ray structures show that the three urea molecules act as a tridentate N,N,N-hgand [52]. The tripodal ligand was also used to synthesise complexes of cobalt, iron or zinc with terminal hydroxo ligands (Scheme 8) [53]. 

In order to construct new types of binding and activating models of dioxygen molecules, Jitsukawa, Masuda and their co-workers have synthesized a novel group of tripodal tetradentate ligands and successfully utilized them in the formation of mononuclear copper(II) complexes with novel structural features (complexes (473)-(488)).395-403 This group of ligands has four... 

The effect of molecular geometry can often be evaluated in a straightforward manner. Consider the tetrahedral CH4 molecule, which will be shown as having one C-H bond pointing "up" and the other three forming a tripod-like base ... 

The effect of the amino acid spacer on iron(III) affinity was investigated using a series of enterobactin-mimic TRENCAM-based siderophores (82). While TRENCAM (17) has structural similarities to enterobactin, in that it is a tripodal tris-catechol iron-binding molecule, the addition of amino acid spacers to the TRENCAM frame (Fig. 10) increases the stability of the iron(III) complexes of the analogs in the order ofbAla (19)complex stability is attributed to the intramolecular interactions of the additional amino acid side chains that stabilize the iron-siderophore complex slightly. 

Metalated container molecules can be viewed as a class of compounds that have one or more active metal coordination sites anchored within or next to a molecular cavity (Fig. 2). A range of host systems is capable of forming such structures. The majority of these compounds represent macrocyclic molecules and steri-cally demanding tripod ligands, as for instance calixarenes (42), cyclodextrins (43,44), and trispyrazolylborates (45-48), respectively. In the following, selected types of metalated container molecules and their properties are briefly discussed and where appropriate the foundation papers from relevant earlier work are included. Porphyrin-based hosts and coordination cages with encapsulated metal complexes have been reviewed previously (49-53) and, therefore, only the most recent examples will be described. Thereafter, our work in this field is reported. 

The activation and transformation of small molecules by metal complexes with sterically demanding tripod ligands, whose... 

Tripodal Carbene and Aryloxide Ligands for Small-Molecule Activation at Electron-Rich Uranium and Transition Metal Centers Karsten Meyer and Suzanne C. Bart... 

The majority of the titanium ions in titanosilicate molecular sieves in the dehydrated state are present in two types of structures, the framework tetrapodal and tripodal structures. The tetrapodal species dominate in TS-1 and Ti-beta, and the tripodals are more prevalent in Ti-MCM-41 and other mesoporous materials. The coordinatively unsaturated Ti ions in these structures exhibit Lewis acidity and strongly adsorb molecules such as H2O, NH3, H2O2, alkenes, etc. On interaction with H2O2, H2 + O2, or alkyl hydroperoxides, the Ti ions expand their coordination number to 5 or 6 and form side-on Ti-peroxo and superoxo complexes which catalyze the many oxidation reactions of NH3 and organic molecules. 

Significant progress has been achieved in the preceding few years in the study of titanosilicate molecular sieves, especially TS-1, TS-2, Ti-beta, and Ti-MCM-41. In the dehydrated, pristine state most of the Ti4+ ions on the surfaces of these materials are tetrahedrally coordinated, being present in either one of two structures a tetrapodal (Ti(OSi)4) or a tripodal (Ti(OSi)3OH) structure. The former predominates in TS-1, TS-2, and Ti-beta, and the latter is prominent in Ti-MCM-41. The Ti ions are coordinatively unsaturated and act as Lewis acid sites that coordinatively bind molecules such as H20, NH3, CH3CN, and H202. Upon interaction with H202 or H2 + 02, the Ti ions form titanium oxo species. Spectroscopic techniques have been used to identify side-bound hydroperoxo species such as Ti(02H) and superoxo structures such as Ti(02 ) on these catalysts. 

We have performed Spin-Coupled calculations on a series of selected carbonium ions (55). The Spin-Coupled calculations allow the study of chemical structure of die molecule, since chemical structure and connectivity are central features of VB theory. Spin-Coupled calculations for CHS+ in CSI show the system as bonded by the intuitively proposed 3c2e bond, which connects the carbon atom to two hydrogens, and three ordinary 2c2e bonds between the carbon and the other hydrogens, commonly called the tripod (Figure 3). 

TRIPODAL CARBENE AND ARYLOXIDE LIGANDS FOR SMALL-MOLECULE ACTIVATION AT ELECTRON-RICH URANIUM AND TRANSITION METAL CENTERS... 

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