Ethers, crown solid-state complexes

In the solid state. X-ray crystallography has provided (32, 62) valuable structural information on a wide variety of chiral crown ethers and their complexes with a range of substrates. These include... 

Salts of diazonium ions with certain arenesulfonate ions also have a relatively high stability in the solid state. They are also used for inhibiting the decomposition of diazonium ions in solution. The most recent experimental data (Roller and Zollinger, 1970 Kampar et al., 1977) point to the formation of molecular complexes of the diazonium ions with the arenesulfonates rather than to diazosulfonates (ArN2 —0S02Ar ) as previously thought. For a diazonium ion in acetic acid/water (4 1) solutions of naphthalene derivatives, the complex equilibrium constants are found to increase in the order naphthalene < 1-methylnaphthalene < naphthalene-1-sulfonic acid < 1-naphthylmethanesulfonic acid. The sequence reflects the combined effects of the electron donor properties of these compounds and the Coulomb attraction between the diazonium cation and the sulfonate anions (where present). Arenediazonium salt solutions are also stabilized by crown ethers (see Sec. 11.2). 

As indicated above in chiral mesophases, the introduction of a functional group in mesogenic stmctures offers the opportunity to achieve functional LCs. With this aim, mesomorphic crown-ether-isocyanide-gold(I) complexes (26) have been prepared recently [38]. The derivatives with one alkoxy chain show monotropic SmC mesophases at or close to room temperature. In contrast, the complexes with three alkoxy chains behave as monotropic (n = 4) or enantiotropic (n > 4) LCs. The structure of the mesophases could not be fully eluddated because X-ray diffraction studies in the mesophase were unsuccessful and mesophase characterization was made only on the basis of polarized optical microscopy. These complexes are luminescent not only in the solid state and in solution, but also in the mesophase and in the isotropic liquid state at moderate temperatures. The emission spectra of 26a with n=12 were... 

Arias, J., Bardaji, M. and Espinet, P. (2008) Luminescence and Mesogenic Properties in Crown-Ether-Isocyanide or Carbene Gold(I) Complexes Luminescence in Solution, in the Solid, in the Mesophase, and in the Isotropic Liquid State. Inorganic Chemistry, 47, 3559-3567. 

The Fe6 rings have also been extensively studied. [Fe6(p2-OMe)12(dbm)6] (32,33) is a neutral species but in the solid state it crystallizes with NaCl to give [Na c Fe6(p2-OMe)12(dbm)6]+. The Na+ ion is trapped in the center of the iron wheel, which acts like a crown ether complexing an alkaline ion. 

Some caution is required when comparing the association constants obtained from extraction experiments with those measured under anhydrous, homogeneous conditions. Iwachido et al. (1976, 1977) have shown that the extracted cation retains part of its aqueous solvation shell on complexation. In particular, the small univalent cations (Li+, Na+) and bivalent cations give high hydration numbers for their crown-ether complexes. Water molecules completing the co-ordination sphere of the cation have frequently been encountered in the solid state of crown-ether complexes (Bush and Truter, 1970, 1971). The effect of small amounts of water on the equilibria (1) has not been studied yet for crown ethers. However, it has been found that the presence... 

The proportion of the /rans-O-alkylated product [101] increases in the order no ligand < 18-crown-6 < [2.2.2]-cryptand. This difference was attributed to the fact that the enolate anion in a crown-ether complex is still capable of interacting with the cation, which stabilizes conformation [96]. For the cryptate, however, cation-anion interactions are less likely and electrostatic repulsion will force the anion to adopt conformation [99], which is the same as that of the free anion in DMSO. This explanation was substantiated by the fact that the anion was found to have structure [96] in the solid state of the potassium acetoacetate complex of 18-crown-6 (Cambillau et al., 1978). Using 23Na NMR, Cornelis et al. (1978) have recently concluded that the active nucleophilic species is the ion pair formed between 18-crown-6 and sodium ethyl acetoacetate, in which Na+ is co-ordinated to both the anion and the ligand. 

All alkali and ammonium DNM salts have been prepared and characterized. Solid state structures of the potassium, cesium, tetramethylammonium and a potassium crown-ether complex of DNM are available . 

The crown ethers and the related cryptates (cryptates were first reported by J-M Lehn (J ) of France in 1969 (Figure 3)), have been used in a variety of synthetic procedures primarily because of their ability to solvate ionic materials in organic solvents (1, 14). Recently, it has been shown that crown ethers in the solid state form "sandwich" like complexes with most metals and that the counterion is also tightly bound (1 ). It is this evidence that suggested their use as ion traps in silicone RTV formulations. 

Hz in complexes of [Hg Hg]2+ with crown ethers. In solid state minium, Pb304, the Pb4+-Pb2+ isotropic coupling, J(Pb, Pb), of 2.3 0.1 kHz is reported.457 The existence of this coupling is suggested to be a result of relativistically enhanced 6s- 6p promotion that seems to take place in heavy elements, which results in decreased hybridization efficiency and increased stability of lower oxidation states. It seems that such effects are to be expected for other relativistically bound molecular ions like [Hg2]2+. 

The bonding of an ion, such as Na+, with a polar molecule, such as water, is an example of an ion-dipole interaction, which range in strength from ca. 50 - 200 kj mol-1. This kind of bonding is seen both in the solid state and in solution. A supramolecular analogue is readily apparent in the structures of the complexes of alkali metal cations with macrocyclic (large ring) ethers termed crown ethers... 

The allyl lariat ether (Section 3.3) 3.132 forms complexes with both K+ and Ag+ (which are of similar ionic radius, Table 3.5). In the case of the K+ complex, as may be expected, the potassium ion is too large to fit snugly within the aza[15] crown-5 ring and lies somewhat above the donor atom plane. The exposed face of the metal atom is occupied by a PF6" anion. Similar coordination to the crown is exhibited by Ag+ but instead of an anion, the exposed face of the metal ion is coordinated to the allyl side chain of an adjacent molecule to give an infinite polymer in the solid state (Figure 3.91). 

KI and KSCN are dissolved by 5.12 but without complexation of the boron atom. The stabilisation of the K+ ion by the crown ether moiety is apparently sufficient in these cases.12 Similarly, the 18-membered phenolic crown ether analogue can be metalated (= exchange of a proton for a metal ion in this case the OH proton) with trimethylaluminium to give 5.13 which forms a ditopic complex with LiCl in solution and in the solid state. 

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