Fullerene complex with calixarene

The number of papers reporting the role of CH/ti interaction is rapidly increasing. Only recent key papers are cited here. Chloroform interacts favorably with an arene n-oloud of fullerene complexes of calixarenes " and cyclotriveratrylene. Evidence for the role of CH/ti interaction in self-assembly was presented.The significance in molecular capsules " " and lattice- and cavity-inclusion type clathrates is well documented. 

Fullerenes are also known to form the inclusion complexes with calixarenes. In the case of the water-soluble inclusion complex of Qo and calixarene (cationic homoox-acalix[3]arene), substantial interaction between fullerenes and the calixarene was observed in the ground state absorption spectrum [76]. Increase in the absorption intensity around 400-500 nm of C q in calixarene can be attributed to the charge-transfer complex formation due to the n -electron system of calixarene. Strong interaction between the calixarene and fullerenes was also observed in the excited states. The triplet absorption peak of 60 in the calixarene appeared at 545 nm, which is largely blueshifted compared to that of pristine Cgg- The triplet lifetime is as short as 50 ns. The substantial interaction between calixarene and included Qo was also observed in the singlet excited state as a large blueshift of the fluorescence peak. 

Low affinity to polar solvents and fullerenes aggregation in water limit their use in biologic systems. To increase water solubility of fullerenes, few ways are used solubilization with the use of some water-soluble polymers like PDT or polyvin-ilpyrrolidone, generation of complexes with cyclodextrines or calixarenes, and... 

It had been reported that fullerene Cgo forms a water-soluble complex with y-cyclodextrin by heating with an excess amount of y-cyclodextrin in water [10] or in a mixture of refluxing water and toluene for a long time, such as 30 h [ 11]. The isolated complex is considered to have the Cgo structure bicapped with y-cyclodextrin in a molar ratio of 1 2 [11], and the complex dissolved in water to give a solution of C o with a concentration of nearly 10 mol L 410,11 ]. Fullerene Qo was also solubilized in water by complexation with a sulfocalix[8] arene, i.e., calix-[8]aryloxy-49,50,51,52,53,54,55,56-octakis(propane-3-sulfonate). The concentration of this complex in water is estimated as 5x10 mol L [12]. Complex formation between fullerene and various calixarenes has also been reported [8]. 

Fullerene C70 does not form a complex with the same calixarene in toluene, but it does so in benzene, crystallizing as the 2 1 complex, (C7o)2(p-Bu -calix[8]arene) (structme unknown).The same fullerene also forms a 2 1 complex with / -Bu -calix[6]arene, and its precipitation from toluene solutions can be used to retrieve 87% purity C70 from Ceo-depleted fullerite. 

The cavity of these calixarenes is usually too small to accommodate fullerenes, and is confirmed by solution, unless they have extended cavity walls as in calix[4]-naphthalenes. Nevertheless, some calix[4]arenes were shown to form stable crystalline complexes with C60 with the fullerene eno- to the calixarene cavity, and they include p-Ph-calix[4]arene, which has a toluene molecule in the cavity, the overall structure dominated by fullerene-fullerene and eso-calixarene fullerene interactions p-Br-calix[4]arene propyl ether, the structure showing very close interfullerene contacts in a columnar structure (Fig. 2d), which most likely results in opposing induced dipoles from the unidirectionally aligned calix-arenes " and /7-I-calix[4]arene benzyl ether, where the fullerenes are ordered without appreciable interfullerene interactions. There is also a calix[4]resorcinarene, R = CH2CH2Ph, 3, which has a molecular capsule derived from head-to-head hydrogen bonding of two resorcinar-enes and propan-2-01 molecules, with the fullerenes also... 

In contrast to the larger calix[n]arenes (n > 4) the cavities of calix[4]arene (7) or p-ferf-butylcalix[4]arene (8), whether in the cone conformation or not, are generally too small to accommodate a Cgo fullerene molecule. Makha et al. [16] however showed that with Cgo, p-benzylcalix[4]arene (9) forms a 2 1 (Cgo)2 9 complex in which the fullerenes are packed into flat sheets with each calixarene nestled exo to the cavity of the calixarene but into a cavity created by a square array of fullerenes (Fig. 33.10) [16]. The X-ray structure determination of this complex which was formed by slow evaporation of an equimolar solution of both components, required synchrotron radiation to provide suitable stmctural data refinement. The authors compared the X-ray data from this (Cgo)2 9 complex with that from the corresponding 1 1 complex formed with the smaller van der Waals diameter ( 8.1 vs 10.0 A) o-carborane which resided endo within the cavity with the... 

Fullerenes C60 and C70 form supramolecular adducts with a variety of molecules, such as crown ethers, ferrocene, calixarene, and hydroquinone. In the solid state, the intermolecular interactions may involve ionic interaction, hydrogen bonding, and van der Waals forces. Figure 14.2.9 shows a part of the structure of [K(18C6)]3-C6o-(C6H5CH3)3, in which Cgg is surrounded by a pair of [K+(18C6)] complexed cations. 

The calix[8]arene depicted in Fig. 2.18 can bind fullerenes (see Chap. 3) the fullerene soccer ball is trapped in the calix. Fullerenes are usually prepared as mixture of Ceo, C70, 75, and so on, and separating them is not always easy. The calix[8]arene has a cavity with an inner diameter of 1 nm, which is therefore suitable for Ceo, since it has a diameter of 0.7nm. When the calixarene is added to a toluene solution of a mixture of fullerenes, a 1 1 complex of the calixarene and Ceo selectively precipitates. Isolation of the precipitates followed by dispersion of them in chloroform results in the precipitation of dissociated Ceo. Repeating these processes results in Ceo with high purity. 

The inclusion of buckminster fullerene Ceo into the cavity of a p-benzylcalix[5]-arene in toluene solution reported by Isaacs et al. [16], is associated with a dramatic partial molar volume change of AV = +195 cm mol which is consistent with the displacement of two toluene molecules from the cavity of the calixarene during complex formation (Fig. 11.5). 

Widening the opposite side of a calixarene upon complexation of small cations to the oxygen atoms of a calixarene lower riin leads to the positive heterotropic allosteric effectin the inclusion o/[60]fullerene in a cage molecule 14 (Fig. 4) derived from two calix[3]aryl esters by complexation of their pyridine groups with Pd(II). " ... 

The fullerene-rich calix[6]arene complexes. (C60 or C7o)2calix[6]arene, were structurally authenticated as isomorphous complexes,showing the calixarene in the double-cone conformation with a fullerene perched in each of the shallow cavities, resembling the jaws of a pincer acting on two adjacent cage molecules the... 

The four-fold symmetry of calixarenes and resorcinar-enes relates to complexation of the siloxane. 8, with 50 in toluene. " Here the fullerenes are arranged in double columnar arrays shrouded by edge on siloxanes (Fig. 2f), the siloxanes interlocking by one of the phenyl groups of one molecule residing in the cavity of another. 

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