Interpenetrating networks hydrogen bonding

Pressure also affects water in an anomalous way. Even when still liquid, at high pressure (about 200 MPa), water undergoes a significant change in structure. Above 200 MPa, a number of the properties of water (viscosity, self-diffusion, compressibility and structure) change. The occurrence of the density maximum is also lost above this pressure. These effects are explained by an increase in the interpenetration of hydrogen-bonded networks at about 200 MPa (at 290 K). The... 

Wuest et al. have also prepared a related tetrahedral tecton 8.63, which also produces a diamondoid polymeric framework. In this case, the solid-state network is seven-fold interpenetrated, with one diamondoid lattice filling much of the large cavities in those adjacent. It is possible that the interpenetration in this instance is a result of the self-complementary nature of the host, which contains an equal number of hydrogen bond donor and acceptor sites. However, even in this case small cavities exist, which are filled by two molecules of butyric acid per host formula unit. The formation of these kinds of framework materials opens entirely new possibilities for tailor-made porous materials with very large cavities, although it is unlikely that purely organic frameworks will ever rival aluminosilicate-based materials for sheer mechanical strength. 

In the complex [Cu(L)4]PF6 (L = 3-cyano-6-methylpyrid-2(lH)-one), the hydrogen-bonded linkage involves the amido R2(8) supramolecular synthon [Fig. 20.4.15(a)]. Each Cu(I) center serves as a tetrahedral node in a fourfold interpenetrated cationic diamondoid network. The tetrahedral metal cluster [Mn(/z3-OH)(CO)3]4 can be used to construct a diamondoid network with the linear 4,4/-bipyridine spacers [Fig. 20.4.15(b)],... 

The hydrophilic groups on mucoadhesive polymers and the large amount of water associated with mucin present two possible adhesion mechanisms (i) hydrogen bonding and (ii) interpenetration of a swollen gel network with hydrated mucin. Many methods have been used for the assessment of bioadhesive properties, including fluorescent techniques and tensile tests. By using these methods, a number of natural and synthetic polymers have been discovered possessing mucoadhesive properties. 

Aakeroy et al. were also able to prepare building blocks based upon Ag(I) centres coordinated in a trigonal planar manner by three isonicotinamide ligands. The isostructural perchlorate and tetrafluoroborate salts of these cationic complexes involve amide-amide hydrogen-bonded links from each cation to six others, resulting in 3D interpenetrated networks that resemble the network found in a-ThSi [53]. 

The use of isonicotinic acid ligands leads to a threefold interpenetrated neutral square grid network in which [Pt(L)2(HL)2] building blocks (L = isonicotinate) (cf. IX), resulting from deprotonation of half of the acid groups, are linked by carboxyl-carboxylate hydrogen bonds (Figure 18) [27c,57]. A network of the same... 

Figure 20 Part of the four-fold interpenetrated 3D diamondoid network formed by [Cu(L)4]+ [L = 3-cyano-6-methylpyrid-2(l//)-one] as its PF6 salt [58], Hydrogen-bonded links are provided by R2(8) synthons involving all amide groups. Oxygen, nitrogen and key hydrogen atoms are shaded.

Tadokoro and Nakasuji used the monoanionic 2,2 -biimidazoleate (HBim ) ligand in conjunction with divalent octahedral metal centres, M(II), to prepare 2D honeycomb networks based upon M(Hbim) ( building blocks linked by N-H---N hydrogen bonds in an R IO) synthon (Figure 24) [64], The overall crystal structure depends on the counter-cation used, and can be a layer structure or an interpenetrated network. The interligand N-H N hydrogen bonds can... 

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