Hosts cryptands

Laser flash photolysis has also been used to study the photophysics and photochemistry of metallocene-containing cryptands and their complexes with rare earth eations [69]. The metallocene moiety was shown to act as an efficient centre for the radiationless deactivation of the lanthanide excited state. Detailed time-resolved studies permitted the characterisation of the coordination chemistry about Dy " within the cryptate and showed, once again, that the functions within the host cryptand primarily responsible for coordination of the guest cation were the amide carbonyl groups. 

Fig. 3. Crown compounds/cryptands and analogous inclusion hosts. (1 4) Crown macro rings bicyclic cryptands (5) [37095-49-17, (6) [31250-06-3J, (7) [31364-42-8] (8) [23978-09-8]-, (9) spherical cryptand [56698-26-1]-, (10) cylindrical cryptand [42133-16-4]-, (11) apodand [57310-75-5]-, and (12) a spherand...

Facile syntheses of highly symmetric cage-type cryptands consisted of pyridine rings and their properties as host molecules 98YGK604. 

There are many examples of platinum(II) interacting with metals such as lead(II) or thallium(I) but few where the same metals interact with platinum(O). Catalano et al. have reported a series of metallocryptands such as the one shown in (11) that act as hosts for thallium(I)72 and lead(II).73 They have also reported an unsupported thallium(I) interaction with the platinum in [Pt(PR3)3] (R = Ph or R3 = Ph2py).74 The Pt Tl separations in the cryptands (2.791-2.795 A) are slightly shorter than those in the unsupported complexes (2.865-2.889 A).72,74... 

H. Plenio, R. Diodone, A fluorine-containing cryptand for the complexation of anions and the utility of F-19 Nmr-spectroscopy for the determination of host guest association, Z. Naturforsch. Section. B-. J. Chem. Sci. 50 (1995) 1075-1078. 

The X-ray crystal structures of the F", Cl , and Br" cryptates of 19-6H demonstrate the inclusion of one of the halide anions in an unsymmetrical fashion. In the case of the small fluoride ion complex a tetrahedral coordination environment is observed for the guest anion with a mean N(H) - P hydrogen-bonding distance of 2.72(8) A. The CP and Br" cryptates exhibit octahedrally coordinated halide ions situated more centrally within the host framework with N(H) - X" distances in the ranges 3.19-3.39 A (X = CP) and 3.33-3.47 A (X = Br ). It is noteworthy that the hydrogen-bonded distances for the anion within the cryptand host are longer by up to ca 0.15 A than those for the other anions in the lattice, suggesting a particularly... 

As stated by Pedersen [1] at the very beginning, systematic names of polyethers are too cumbersome for repeated use. Thus, he coined an efficient system of their trivial names that is in common use. The polyethers were dubbed crown ethers or crowns . The total number of atoms in the macrocycle preceded this term whilst the number ofoxygen atoms followed it. The presence ofaromatic 44 or saturated 60 rings in the systems is marked at the beginning. In Lehn s system for bicyclic molecules called cryptands the number of OCH2CH2 units in each branch ofthe bicyclic hosts 61-63 ([1.1.1]-, [2.1.1]- and [2.2.2]cryptands... 

As stated above, systematic names of macrocyclic host molecules were absurdly complicated for routine discussions [22]. Therefore Vogtle proposed the name coronand for crown ethers, and that of coronates for their complexes while cryptand complexes were called cryptates . The corresponding noncyclic analogues are podands such as 64 [23] and podates, respectively. The cumbersome name podando-coronands (and correspondingly podando-coronates ) was proposed for lariat ethers [24] having at least one sidearm like 65. Examples of hemispherands 66 [25], cavitands 25 [26] and those of some other hosts are discussed in Chapter 7 in some detail, whilst the exceptional stability of fragile guests 4 [2a] and 67 [27] in the hemicarcerand 5 cavity are discussed in Chapters 1 and Section 7.3. 

In addition to macrocyclic hosts discussed above, many other molecules capable of selective complexation have been synthesized. They belong to so-called macrocyclic chemistry [30] encompassing crown ethers discussed in this Chapter, cryptands 61-63 [21], spherands 70 [31], cyclic polyamines 71 [32], calixarenes 18 [5], and other cyclophane cages such as 72 [33] to name but a few. Hemicarcerand 5 [2b] discussed in Chapter 1 and Section 7.3 also belongs to this domain. Typical macrocyclic host molecules are presented in Chapter 7. 

Figure 7.1.4. The scheme of formation of [2.2.2]cryptand. marked the start of molecular recognition studies. As described in Chapters 2 and 3, the Pedersen analysis was later extended by Lehn s studies of the complementarity of sizes and shapes ofthe cryptand cavities and their guests, and by Cram s preorganization studies. In general, crown ethers and cryptands exhibit analogous complexation behaviour. Thus, similarly to the former host molecules, cryptands in the free, uncomplexed state elongate the vacant cavity by rotating a methylene group inward. Thus, the N...N distance in [2.2.2]-cryptand 54 across the cavity is extended to almost 70 pm [18] whilst, in the complexed...

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