Alkali metals cation structure

Danil de Namor, A. E Al Rawi, N. Piro, O. E. Castellano, E. E. Gil, E. New Eower Rim Callx(4)arene Derivatives with Mixed Pendent Arms and Their Complexation Properties for Alkali-Metal Cations. Structural, Electrochemical, and Thermodynamic Characterization./. Phys. Chem. B 2002, 106, 779-787. 

Fig. 10. Unpolarized Raman spectra (T = 300 K) for solid Ceo, KaCeo, RbsCeo, NaeCeo, KaCco, RbeCeo and CseCeo [92, 93], The tangential and radial modes of Ag symmetry are identified, as are the features associated with the Si substrates. From the insensitivity of these spectra to crystal structure and specific alkali metal dopant, it is concluded that the interactions between the Cao molecules are weak, as are also the interactions between the Cao anions and the alkali metal cations.

The proportion of hydrochloric acid in the mobile phase was not to exceed 20%, so that complex formation did not occur and zone structure was not adversely affected. An excess of accompanying alkaline earth metal ions did not interfere with the separation but alkali metal cations did. The hthium cation fluoresced blue and lay at the same height as the magnesium cation, ammonium ions interfered with the calcium zone. 

Figure 4.11 Molecular structures of typical crown-ether complexes with alkali metal cations (a) sodium-water-benzo-I5-crown-5 showing pentagonal-pyramidal coordination of Na by 6 oxygen atoms (b) 18-crown-6-potassium-ethyl acetoacetate enolate showing unsymmelrical coordination of K by 8 oxygen atoms and (c) the RbNCS ion pair coordinated by dibenzo-I8-crown-6 to give seven-fold coordination about Rb.

In mimicking this type of function, noncyclic artificial carboxylic ionophores having two terminal groups of hydroxyl and carboxylic acid moieties were synthesized and the selective transport of alkali metal cations were examined by Yamazaki et al. 9 10). Noncyclic polyethers take on a pseudo-cyclic structure when coordinating cations and so it is possible to achieve the desired selectivity for specific cations by adjusting the length of the polyether chain 2). However, they were not able to observe any relationship between the selectivity and the structure of the host molecules in an active transport system using ionophores 1-3 10). (Table 1)... 

MiNbC F compounds have a NaC 1-type structure, and are stable only in the case of lithium due to the steric similarity between the lithium ion and Nb3. In the case of other alkali metal cations with larger ionic diameters, the M4Nb04F compounds decompose yielding orthoniobates and simple fluorides of alkali metals, as follows ... 

The variation that exists in the 0 F ratio of MMe6Oi5F-type compounds enables isomorphic replacement of alkali metal cations by other cations with appropriate radii. For instance, a copper-containing compound, Cuo.6Nb6Oi4 6F( 4, which crystallizes in a LiNbeOisF type structure, was obtained [255]. 

Summarizing all that has been said above concerning the structures of the octachloroditechnetates ( + 2.5), it may be concluded that their true composition is described by a formula with variable coefficients, namely M 6M"3-.,t(H30) [[Tc3Cl8] nH20, where x and n vary from 0 to 3. The substitution of some of the M ions by H30+ ions is possible by virtue of the similarity of the properties of the hydroxonium cation and the alkali metal cations both in solution and in the crystalline state [85,86],... 

Increasing the reducing agent/W ratio and using Na-naphthalenide led to the isolation of the two-electron-reduced, diamagnetic compound 19. The C2v symmetry of the h NMR spectrum and the X-ray analysis are in agreement with the cen-trosymmetric structure sketched in Scheme 2 for 19 [W = W, 2.614(1) A]. The six-coordination of the metal and the inclusion of the alkali metal cation removes the planarity ofthe 04 core and the cone conformation of the calix[4]arene. The sodium cation within the calix[4]arene cavity is r 3-bonded to two opposite arene rings. 

Mixed carbanion/alkoxide complexes were formed from combining n,sBu2Mg, TuOM (M = Na or K), and TMEDA to form the dimeric CIPs [(Bu)2(tBuO)MMg(TMEDA)]2 (M = Na and K) 437, 438.442 While the two structures are identical in their atom connectivity, they are not precisely isostructural in that K shows a bias toward C-coordination while Na is inclined toward N. The alkali metal cations are both formally five-coordinate bonding with two a-C(Bu) atoms, two N(TMEDA) atoms, and a single 0(cBu) atom. The dominant feature in both structures though is the [(Bu)2Mg(/x-tBuO)2MgBu2]2 dianion. 

Sulfur diimides react quantitatively with organolithium reagents at the sulfur centre to produce lithium sulfinimidinates of the type Li[RS(NR )2] A. The lithium derivatives may be hydrolysed by water to R NS(R)NHR which, upon treatment with MH (M=Na, K) or the metal (M=Rb, Cs) in THF, produces the heavier alkali-metal derivatives.132 The structures of these complexes are influenced by (a) the size and electronic properties of the R group, (b) the size of the alkali metal cation, and (c) solvation of the alkali-metal cation. 

Fig. 3.3).31 33 The observed crystal structures are similar to that reported18 for K4Sn2Se6 with, however, a small volatile hydrazinium species replacing the relatively nonvolatile alkali metal cation. Note that the sulfur-to-selenium ratio can be tuned in the final product by varying the amount of SnS2 and SnSe2 employed. 

Electrodes based on solutions of cyclic polyethers in hydrocarbons show a selective response to alkali metal cations. The cyclic structure and physical dimensions of these compounds enable them to surround and replace the hydration shell of the cations and carry them into the membrane phase. Conduction occurs by diffusion of these charged complexes, which constitute a space charge within the membrane. Electrodes with a high selectivity for potassium over sodium (> 1000 1) have been produced. 

The effect of remote substitutents on the complexing ability of crown ethers [256] towards t-butylammonium salts has been studied by Moore et al. (1977). The results (Table 52) show that electron-attracting substituents decrease the stability of the complex. The t-BuNHJ cation is even more sensitive to remote substituent effects than alkali-metal cations. This fact was attributed to the non-polar character of the alkyl group and to the different structure of the... 

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