Rotaxanes crystal structure

When diphenyhnagnesium is crystallized from a solution containing l,3-xylyl-18-crown-5, an X-ray crystal-structure determination showed the formation of rotaxane 116 (Figure 56) . Only four of the five oxygen atoms of the crown are involved in coordination to magnesium, two with a relatively short bond distance [2.204(3) and 2.222(4) A] and two with a longer bond distance [2.516(4) and 2.520(4) A]. The C(l)-Mg-C(2)... 

Since caroviologens are rather fragile compounds, they can be protected from the environment by inclusion into polyanionic derivatives of (J-cyclodextrin in a rotaxane fashion 102 [8.156]. Also, in the design of molecular devices, it may be desirable to introduce some extent of redundancy in order to reduce the risk of device failure. This is the case in the tris-carotenoid macrobicycle 103 that represents a sort of triple-threated molecular cable whose crystal structure 104 has been determined. It forms a dinuclear Cu(i) complex 105 in which the bound ions introduce a positive charge at each of the species, a feature of potential interest for transmembrane inclusion [8.157]. 

A successful synthesis of a rotaxane of this type is shown in Figure 5. First, one tiityl aniline stopper is reacted with the terephthaloyl chloride to from semiaxle 9. This semiaxle threads into the tetralactam macrocycle 3 and is held by the amide template. Then, the preorganized complex is reacted with the second stopper 11 to yield rotaxane 12. Figure 5 shows three hydrogen bonds to form, which is in accord with AMI calculations on this system [19] and X-Ray crystal structure analysis [22],... 

On a simpler scale the Rybak-Akimova group found that when 4/-(amino-methylene)benzo[18]crown-6 was treated with an acid salt, mass spectrometric evidence indicated that dimers were the most stable species [13]. This was backed up by an X-ray crystal structure of the compound crystallized from methanol which revealed pairs of mutually interlocked crowns. The amine termini had become pro-tonated and the resultant ammonium group, illustrated in Fig. 8.4, formed a complex with a second crown. Although yet to be attempted, it would be intriguing to react the complex with a linear component containing a second amine and a bulky stopper group to generate a metal-free, interlocked pair of rotaxanes with two amine stations . The contraction and extension of the complex could then be controlled as a function of pH. 

The binding of ammonium ion, NH4+, by 18-crown-6 was demonstrated early in the history of macrocycle chemistry. The O-H-N in crowns or N-H-N interaction in azacrowns has been characterized by a variety of techniques, including NMR, calorimetry, and X-ray crystal structure analysis. Recent studies in this area have shown that both quaternary and secondary ammonium salts can form complexes with crowns. In the latter case, a rotaxane molecule was prepared by treatment of a dibenzylammonium salt with dibenzo-24-crown-8 and other macrocycles, including pyrido-24-crown-8. The solid-state structure of the pseudo-rotaxane structure obtained with pyrido-24-crown-8 is shown in the left panel of Figure 23. 

The studies described in this section were started shortly after the X-ray crystal structure of the RC of Rh. viridis was disclosed [73]. During these years, the role of the so-called accessory bacteriochlorophyll BCh was under debate [79]. In particular, the possibility was considered that it could play the role of a superexchange relay between SP and BPh (see Figure 22). In this respect, the copper(I)-complexed [2]rotaxane Cu.20+ represented a functional artificial model of the SP/BPh/BCh triad, the central Cu complex fragment between the Zn porphyrin donor and the Au porphyrin acceptor mimicking the function of BCh between SP and BCh. However, the kinetic scheme shown in Figure 22a has been revised, being now quite firmly established that (at least at room temperature) BCh is directly involved in the electron transfer reaction the transfer from the electronically excited special pair SP to BCh takes about 3 ps, and the next transfer step to the BPh, 0.65 ps [80]. In the earlier experiments, detection of the intermediate state SP+BCh was prevented by its relatively slow population and fast decay. 

Since the publication of 26, we have determined the crystal structures of three additional diarylmagnesium-polyether complexes. Instead of diphenylmagnesium, its 4,4 -bis(tm-butyl) derivative was used in the com-plexation experiments since this species as a rule gives higher quality crystals. Complexation with 1,3-xylyl-18 crown-5 resulted in the formation of a rotaxane complex (27), too. Bond angles and distances, and even the... 

Bickelhaupt and coworicers have determined the crystal structures of a series of crown ether solvated magnesium compounds. A sequence of these compounds is illustrated as the internally coordinated 13-crown-4-xylylmagnesium chloride (134) and bromide (135), as well as the organometallic, rotaxane (136). Note the similarity between these structures and the corresponding aliphatic dialkylmagnesium rotaxane (83). 

Figure 11 X-ray crystal structure of rotaxane 11. Counter anions are omitted for clarity.

Jeon. Y.-M. Whang. D. Kim, J. Kim. K. A simple construction of a rotaxane and pseudorotaxane Syntheses and X-ray crystal structures of cucurbituril threaded on substituted spermine. Chem. Lett. 1996. (7), 503-504. 

Figure 3.27 (a) The synthesis and (b) the X-ray crystal structure of an ammonium/crown ether-based (2]-rotaxane (3.12). (c) A simple [2]-rotaxane in which the — O interactions are supported by ir ir interactions (counter anions are omitted for clarity). 

The knotted structure was patent in the crystal structure (Figure 12), which showed a pattern of hydrogen bonds between amide groups. A similar pattern is also found in the structure of [2]catenanes and rotaxanes synthesized using the same basic template. ... 

FIGURE 13.8 Molecular structures of some common organic host species, (a) Encapsulation of a Ba ion in a 30-crown-10-ether, (b) Crystal structure of a p-cyclodextrin. (c) Crystal structure of a rotaxane. (d) Encapsulation of a K ion in a cryptand. (e) Crystal structure of a catenane. (f) Crystal structure of a thiacalix[4]arene. (Part a Adopted from Ref. [90], CCDC 638697. Part b Adr jtedfrom Ref. [91J, CCDC 762697. Part c Attested from Ref. [92], CCDC 213301. Part d Aelerpted from Rrf. [93], CCDC 241667. Part e Adapted from Ref. [94], CCDC 917010. Part f Adapted from Ref [95], CCDC 193202)... 

Figure 8.10 (a) Synthesis of the hetero[4] rotaxanes consisting of one pillar[5]arene and two cucurbit[6]uril wheels by copper-free AAC reaction and (b) X-ray crystal structure of 8.60. 

Fig. 14.15 X-ray crystal structures of organosilver cluster-centered pseudo-rotaxane. All hydrogen atoms are omitted for clarity [74]...

Fig. 18.8 (a) Chemical stractures of guests 28a-g (b) Crystal stmcture of complex 13a 28f (c) Crystal structure of [2]rotaxane formed by 13a and 28d. Solvent molecules, PFg" counterions, and hydrogen atoms are omitted for clarity... 

Originally, Stoddart s group used azide-bearing thread-like fragments as a way to build the stoppers by the thermally allowed 1,3-dipolar cycloadditions between azides and bulky electron-deficient alkynes. By this threading-followed-by-stoppering approach, the synthesis of the [2]rotaxane 17 (Scheme 14.7) was achieved with 31% yield, after reflux for seven days. NMR spectroscopy, FAB mass spectrometry and X-ray crystal structure confirmed the interlocked nature of this molecule. 

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