Intermolecular bridges

Compound 200e provides one example in which a pair of calixarenes are intermolecularly joined by a pair of upper rim to lower rim bridges. Other examples of upper rim to upper rim bridging are illustrated by (a) 215a, obtained in 48% yield by treating p-A,C-bis(hydroxymethyl)calix[4]arene with p-A,C-bis(chloromethyl)calix[4]arene in the presence of (b) 215b and 

Also obtained in 5% yield from a ruthenium-catalyzed reaction of A,C-p-diallylcalix[4]arene.  

A strategy used by Reinhoudt, and others for constructing artificial receptor molecules as biochemical mimics makes use of medium-sized molecules as platforms to which functional groups can be attached. Included among such platforms are calix[4]arenes, calix[4]resorcarenes, cyclodextrins, and porphyrins (see Section 5.1.3.1), which have been combined in various ways. Several striking examples involve the intermolecular linking of calix[4]resorcarenes with 

Sisido, K. Hisaichi, K. Shinkai, S. Tetrahedron Lett. 1993, 34,8297. 

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The reactions of the six-membered chlorocyclophosphazene were studied with a number of aliphatic diamines (169 175), aromatic diamines (176), aliphatic diols (177-179), aromatic diols (180,181) and compounds containing amino and hydroxyl functional groups (169,170,182). This subject has been reviewed (11,16,20). There are at least five different reaction products that are possible (Fig. 19). Replacement of two chlorine atoms from the same phosphorus atom produces a spirocyclic product. Replacement of two chlorine atoms from two different phosphorus atoms in the same molecule produces an ansa product. Reaction of only one end of the difunctional reagent, resulting in the substitution of only one chlorine atom, leads to an open-chain compound. Intermolecular bridged compounds are formed when the difunc-... 

We can then deduce that gelation requires well defined conditions corresponding to suitable respective probabilities of intra and intermolecular bridges ... 

Spirocyclic product is formed as a result of replacement of both the chlorines on the same phosphorus atom, while the ansa product is formed as a result of the replacement of chlorines from two distinct phosphorus atoms within the same molecule. In open chain product only one end of the difunctional reagent is involved in reaction with the chlorocyclophosphazene. Finally, intermolecular bridged products result from the reaction of two chlorocyclophosphazene molecules with a difunctional reagent. This last reaction also is a model reaction for condensation polymerization involving phosphazenes. 

All polymer chemists know this technique as cross-linking. It is the process of building intermolecular bridges. If two adjacent polymer molecules of equal size are connected by a cross-link, the molecular weight effectively doubles. From a... 

The transport of charge carriers is evidently also facilitated by the lowering of the barrier potentials between molecules due to the intermolecular bridges in n complexes of copper with acetylenic bonds. 

Binding of cation to fragment 1 also induces dimerization probably by intermolecular bridging of gla residues.397 Ca2+ is the most effective cation in inducing dimerization and Mg2+ inhibits. This is in accord with earlier comments on the ability of these two cations to play bridging roles. 

Since the conformation of a particular LPS molecule depends on the phase state of its hydrocarbon moiety, it is variable and, thus, may exist in a highly ordered gel state or in a less ordered liquid-crystalline state. These states and the changes from one to the other are dependent on the phase-transition temperature and other parameters, like water and ion concentration [79]. The state of order of LPS with a longer saccharide moiety shows a stronger dependence on water and ions than that of LPS with shorter saccharide chains. The addition of cations, e. g., Mg " ", results in the aggregation of LPS due to intermolecular bridging. 

Bis(trimethyltin) oxide in the gas phase has rSnO 194 pm, SnOSn 140.8°. It reacts with trimethyltin chloride or bromide to give the compounds 12-5 with a trigonal planar cation.30 In the crystal, the chloride (X = Cl-) has rSnO 209.99(4) pm, and SnOSn 120.0(0)°, and the chloride ion intermolecularly bridges two tin atoms to give a graphitelike layer lattice.30... 

Bu2)2Sn(2,5-PDC) 3] (2,5-PDC = 2,5-pyridinedicarboxylate, D = Lewis base, such as DMSO, H2O) and [ (n-Bu2)2Sn(l,3-BDC)(D) 3] (1,3-BDC = 1,3-benzenedicarboxylate) (Table 2.4.2, entries 4 and 6) deserve special mention. Both of these are macrocyclic compounds formed as a result of intermolecular bridging by the dicarboxylate ligands. Among these, [ (n-Bu2)2Sn(2,5-PDC) 3] forms a three-dimensional hybrid supramolecular network which traps hydrophobic molecules in its microporous channels. ... 

The bulky neopentyl groups prevent intermolecular bridging (trineopentylaluminum is monomeric), but promote intramolecular C-C bond interaction... 

Steric and electronic factors often force the stabilization of monometallic species via agglomerization. As a rule, the formation of di- and multinuclear species is achieved by intermolecular bridging of the smallest, most reactive and labile Ln-X bond and, hence, leads to decreased reactivity. 

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