Cucurbituril structure

Cubed compound, in PVC siding manufacture, 25 685 Cube lattice, 8 114t Cubic boron nitride, 1 8 4 654 grinding wheels, 1 21 hardness in various scales, l 3t physical properties of, 4 653t Cubic close-packed (CCP) structure, of spinel ferrites, 11 60 Cubic ferrites, 11 55-57 Cubic geometry, for metal coordination numbers, 7 574, 575t. See also Cubic structure Cubic symmetry Cubic silsesquioxanes (CSS), 13 539 Cubic structure, of ferroelectric crystals, 11 94-95, 96 Cubic symmetry, 8 114t Cubitron sol-gel abrasives, 1 7 Cucurbituril inclusion compounds,... 

The network structures to be discussed will all involved hydrogen bonding as the supramolecular synthon. It should be noted however that other interactions such as coordinate bonds and host-guest interactions may also organise host molecules into network structures. Coordination polymers constructed from molecular hosts may involve functionalised calixarenes [8-11], cyclotriveratrylene [12], or cucurbituril [13]. Calixarenes have also been used to build up network structures via host-guest interactions [14,15]. It is also notable that volatile species may be trapped within the solid state lattice of calix[4] arene with a structure entirely composed of van der Waals interactions [16]. 

Fig. 1. Perspective representation of the structure of cucurbituril from [15] with permission...

The availability of formation constants for a large number of structurally diverse alkylammonium ions also encourages attempts to identify quantitatively those chemical features of a resident ligand species that are responsible for stability and selectivity within complexes of cucurbituril. In order to secure interpretable results, a subset of data was compiled, restricted to mono-substituted ammonium ions carrying exclusively alkyl or thioether residues [9]. Only included were moieties for which internal complexation with cucurbituril was established (NMR evidence) and for which substrate-specific overcrowding (such as with the arenes) was unlikely. A short list consisting of the first 24 guests in Table 1 was... 

Initial attempts to correlate the affinity of ligands toward cucurbituril using independently estimable parameters such as van der Waals molecular surface area or molecular volume of the guests were relatively unsua sful. The difficulty apparently is that the interior of the receptor has a definite shape and distribution of polarity, so that complementarity between cucurbituril and its ligand depends more subtly upon structure of the bound entity. Consequently we opted for an empirical treatment of our data, which would yield an indication of how particular regions of the interior of cucurbituril interact with ligands. 

A related example involving (6,3) rather than (4,4) nets, in which any 6-gon has components of two independent inclined sheets passing through it is noteworthy in the context of this book in that the connecting rods themselves are encircled in rotaxane fashion by bead-like cucurbituril components, as in structure 5. The 3-connecting nodes of the (6,3) nets are provided by Ag1 each of which is linked to three others by bridging ligands of type 5 [22]. 

Fig. 9. Cucurbituril inclusion chemistry (a) tridimensional structure of cucurbit[6]uril (b) conjectured cross-sectional representation of a host—guest...

Kim, Kimoon, Self-Assembly of Interlocked Structures with Cucurbituril Metal Ions and Metal Complexes, 5, 371. 

Cucurbituril (cucrbit[6]uril or CB[6]), a hexameric macrocycle 141 (R = H, = 6) with a 1,3,5,6-tetraazocane core unit, is self-assembled from an acid-catalyzed condensation reaction of glycouril and formaldehyde (see Section 14.09.9.1.1 and 1996CHEC-II(9)705). Although its synthesis first appeared in 1905, its chemical nature and structure remained unknown until 1981, when full characterization was reported by Mock and co-workers <1981JA7367>. 

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