Alkaline-earth metal cations

On the other hand, Bartsch et al. have studied cation transports using crown ether carboxylic acids, which are ascertained to be effective and selective extractants for alkali metal and alkaline earth metal cations 33-42>. In a proton-driven passive transport system (HC1) using a chloroform liquid membrane, ionophore 31 selectively transports Li+, whereas 32-36 and 37 are effective for selective transport of Na+ and K+, respectively, corresponding to the compatible sizes of the ring cavity and the cation. By increasing the lipophilicity from 33 to 36, the transport rate is gradually... 

Of course, the chemistry of zirconium cluster phases has been well described and reviewed in the literature [1-4]. Apart from a very few examples, mostly in the binary halides, almost all reduced zirconium halides contain octahedra of zirconium atoms centred on an interstitial atom Z. Several possible and experimentally realized Z include H, Be-N, K, Al-P, and the transition metals Mn-Ni. All these compounds have the general formula Ax"[(Zr6Z)Xi2X[J], with a " = alkali or alkaline earth metal cation, X=C1 Br or I, X =inner edge-bridging halide [5], X =outer exo-bonded halide, and 0[Pg.61]

Dabek-Zlotorzynska, E. and Dlouhy, J. F., Simultaneous determination of alkali, alkaline-earth metal cations and ammonium ion environmental samples by gradient ion chromatography, /. Chromatogr., 638, 35, 1993. 

LIGAND EXCHANGE PROCESSES ON THE SMALLEST SOLVATED ALKALI AND ALKALINE EARTH METAL CATIONS AN EXPERIMENTAL AND THEORETICAL APPROACH ... 

The mechanisms of regioselective and stereoselective 2 -E 2-photocycloadditions have been extensively reviewed. The intramolecular 2 -E 2-photocycloaddition of 2-allyl-2-(l//)-naphthalenone (13) on the surface of silica produces all four cycloadducts (14)-(17) (Scheme 4). ° Molecular mechanics have been used to study the regio- and stereo-selectivity of the 2 -E 2-photocycloadditions in complexes containing crown ether styryl dyes and alkaline earth metal cations."... 

Zeolites are crystalline aluminosilicates with porous, framework structures made up of linked [Si04] and [A104] tetrahedra that form channels and cages of discrete size [24]. The framework structures of zeolites bear a net negative charge, which must be balanced by positively charged species, typically alkali or alkaline earth metal cations these cations maybe exchanged for one another under appropriate experimental conditions. Zeolites are capable of... 

IV. Complexes of Alkali and Alkaline-Earth Metal Cations with Synthetic Organic Ligands... 

Table 7. Stability constants (log Ks) of alkali and alkaline-earth metal cation complexes with ligands of types A, B and C... 

These considerations go far to explain the selectivity behavior of a series of macroheterobicyclic ligands (Fig. 9). Table 4 shows that an increase in the number of coordination sites from 6 to 8 or 9 leads to an increased preference for large cations. Ligand VI, with 11 coordination sites is no longer suited for the complexation of even the largest alkali and alkaline earth metal cations. Furthermore, it is clear that a relatively large coordination number (5 6) is required to produce selectivity for divalent ions. 

Obviously, it is possible to produce bigger clusters at Aig = 4.76 by stabilizing them with suitably sized cations, available by electroequivalent substitution of alkali metal by alkaline earth metal cations. 

The formation of the merocyanine form 119 can be induced by addition of heavy metal cations (Pb, La, Eu, Tb ) to a solution of a spirooxazine 118 containing a crown ether group in the B-ring (Equation 1). The chelation occurs first to the crown ether and then to the negatively charged oxygen. In contrast, 118 does not react upon addition of alkaline earth metal cations (Mg, Ca, Ba ) <2005JP0504>. 

At almost the same time as other polymer-supported phase transfer catalysts were first reported, polymer-supported solvents and cosolvents were found to be effective catalysts for phase transfer reactions 155-156>. Dipolar aprotic solvents such as hexa-methylphosphoramide (HMPA)157, dimethylsulfoxide (DMSO)158), and tertiary amides159,1601 are well known to coordinate strongly with alkali and alkaline earth metal cations, and hence promote nucleophilic displacement reactions of the anions161). Catalysts 44 155-162>163> and 45163),... 

Whilst what has been termed the real scientific advancement in this area took place in 1967,5 complexes of alkali and alkaline earth metal cations (M"+) with simple monodentate ligands can be traced back, through the metal-ammonias , to Faraday.10 It was not until almost a century later, however, that precise determinations of the stoichiometries of the M"+—NH3 products were realized and the term coordination was introduced to describe the bonding mode of the ligand.11"13 The alkali metals themselves were first noted to dissolve in liquid ammonia in 186314 and since that time it has been found that the metals also dissolve in amines and ethers.15... 

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