Guest-free

Fig. 21 a and b. Stereoviews of a the 1 1 16 (R = Ph3C) toluene clathrate (the disordered guest methyl is not shown), and b the crystal structure of the uncomplexed host (it represents one of a very few examples of a guest-free lattice which could be obtained from this type of compounds) 21)... 

Guloy AM, Ramlau R, Tang ZJ et al (2006) A guest-free germanium clathrate. Nature 443 320-323... 

In clathrate solutions the bonds holding together the units of the host lattice are weaker, and the resistance to collapse, even of only partially guest-free host lattices, is much less. Thus it may not be possible to realize the whole isotherm as illustrated in Figure 1 (76) for Kr in the porous 0-phenol lattice at 195, 212, 222.2, and 228°K. A critical pressure pc of Kr and loading of 0-phenol by Kr are essential before 0-phenol forms from ordinary nonporous a-phenol. If pa and M/3 are the chemical potentials of phenol in these two forms, the critical condition can be expressed as ... 

Dianin s Compound. The unit cells of inclusion complexes in Dianin s compound and of the guest-free compound are almost the same, and there is no doubt that the guest-free lattice contains the same voids as those in which guests are present. 

Figure 7.32 Single crystal transformations between the 1 1 and 1 2 toluene inclusion complexes of p-f-butylcalix[4]arene. The transformation of the the toluene or benzene clathrates to the guest-free a-form causes crumbling of the crystal (reproduced by permission of The Royal Society of Chemistry).

Figure 7.44 X-ray crystal structure of the host portion of p I bulylcalix 4 arene (A) guest-free crystal showing a, b, c, d... repeating layers and (B) after exposure to vinyl bromide showing an a, b, a, b... repeat pattern arising from a shift of ca. 6A between layers b and c (reprinted with permission from AAAS from [55]).

Figure 7.4 5 Immersing sublimed crystals of the apparently guest-free po phase of p-t-butylca 1 ix [4] arene results in the immediate displacement of bubbles of air from the crystal lattice as the air molecules are replaced by nitrobenzene guest (reproduced by permission of The Society of Chemistry).

Related behaviour is exhibited by the dealkylated analogue, calix[4]arene (7.63). This material can also be sublimed to give a guest-free host but in this case the empty host forms an unusual trimer motif which is almost spherical and packs in a hexagonal close packed array with just a small interstitial void... 

Figure 2 Crystal structures of (a) DCA with acetone, (b) CA with y-valerolactone, (c) hexagonal crystal of CDCA, (d) guest-free crystal of LCA, (e) DCAM with 1-propanol, (f) CAM with m-cresol, (g) CDCAM with water, (h) LCAM with 2-hexanol, (i) DCAtriol with p-xylene, (j) guest-free crystal of CAtetraol, (k) CDCAtriol with ethanol, and (1) LCAdiol with dichloromethane.

CW = water-included crystal. GF = guest-free crystal. 

DCAM includes various types of organic compounds and does not give guest-free crystals at all (Table 3) [13]. There are several host frameworks which... 

It is interesting to note that the solvents which form complexes with rac-131 do not form complexes with optically active 131 and vice versa. For example, the powdered (+)-131 obtained by the evaporation of THF from the (+)-130-THF complex turns to guest-free crystals by recrystallization from solvents indicated in Table 8. The big difference of the role between the solvents shown in Tables 8 and 9 is interesting. X-ray crystal structural analysis of a 1 1 complex of (S)-(-)-131 and 1,2-dichloroethane showed that the latter is accommodated in the cavity of the inclusion complex as a form of nearly eclipsed chiral rotamer, but no any significant interaction between the host and guest molecules is present.59... 

The activity, a, of the guest is zero when the host is guest-free and has chemical potential y. Ay is thus the change in chemical potential of the host due to the inclusion of the guegt. 9 is the fractional saturation of the host by the guest, V = n /n and n i a he number of moles of guest at saturation of the Host, so that nQ 0 = n. = V/n is the molar volume of the host because... 

Table V gives values of -Ap /RTV for different values of K or of 0 at x = 1, according to Equation 8. For large K, Ay dominates this equation and the zeolite is therefore much stabilised relative to its guest-free state. Thus for faujasite at 100°C, Ay = V p = 0.005 kJ mol (Table II) and V = 1.25 (Table IV). The final two columns in Table V give Ay2 at 100°C for different K when V = 1.25...

Another class of inclusion complexes containing phosphorus in the host structure are cyclophosphazenes. Sozzani and co-workers have reported 31P CP/MAS studies of two organic derivatives tris(o-phenylene-dioxy)cyclotriphosphazene (TPP) and tris(2,3-naphtalene-dioxy)cyclotri-phosphazene (TNP). In the cited works, SS NMR technique was employed to recognise guest-free TNP matrix and of ICs with guests, for example benzene, tetrahydrofuran and p-xylene. The 31P NMR spectra were particularly informative regarding the symmetry of the phos-phazene ring. 

The luminescence decay in presence of DBA is fitted by a two-exponential model, with a long-lived component, which is present also on the guest free receptor, and... 

Fig. 10a-f Examples of the structural motifs of p-ferf-butylcalix[4] arene derivatives a guest-free structure b 1 1 complex c 2 1 host-guest complex d hydrogen-bonded structure with an amine guest e self-inclusion structure f 1 1 host-guest clay mimic structure. (Adopted from [44] with permission)... 

Solid state NMR was used to recognize guest-free TNP matrix and ICs with guests, e.g. benzene, tetrahydrofuran and p-xylene. Carbon relaxation times were used to study the motion mechanism of the guests. P CP/MAS spectra were particularly informative about the symmetry of the phosphazene ring. Figure 20 presents C MAS spectra of TNP ICs with benzene and THF guests in the matrix. 

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