Alkaline-earth strontium complex

The calcium, strontium, barium, and lead 80) complexes of 160 and 161 have also been reported. In these two ligands the six donor atoms are essentially confined in a plane these complexes thus permit study of unusual coordination geometries in species of high coordination number. Attempts to form alkali metal complexes with 160 and 161 under the same conditions as employed for the alkaline earth metal complexes have failed. The successful syntheses of complexes of the latter type indicate that the higher charge to radius ratio is of consequence when spherically charged cations are employed. Such metal ions have no apparent coordinative discrimination as the template ion 87). 

A question prior to the one written above is can a species featuring an alkaline earth (AE) metal-carbon formal double bond be synthesized In fact, this is no trivial matter and AE=CH2 species are likely polymeric. The first synthesis of such a molecular complex was only realized in 2006. Therefore, examples of structurally characterized alkaline earth metal complexes featuring a hypervalent phosphorus-stabilized geminal dianion as a ligand are scarce enough to be thoroughly reviewed here. Wlule a few examples are found for magnesium [24, 37, 38], calcium [39-41], and even barium [30], there is to date no example of such complexes with strontium or beryllium. The full set of complexes is represented in Chart 3. 

Alkaline-earth metals are often deterruined volumetricaHy by complexometric titration at pH 10, using Eriochrome Black T as indicator. The most suitable complexing titrant for barium ion is a solution of diethylenetriaminepentaacetic acid (DTPA). Other alkaline earths, if present, are simultaneously titrated, and in the favored analytical procedure calcium and strontium are deterruined separately by atomic absorption spectrophotometry, and their values subtracted from the total to obtain the barium value. 

It is also possible to isolate bis(carbene) complexes involving the heavier alkaline earth metals. Thus, the reaction of two equivalents of 4 (R = Me or (Bu, R = H) with calcium, strontium and barium bis(trimethylsilyl)amides [M N(SiMe3)2 2(thf)2] (M = Ca, Sr, Ba) resulted in the displacement of two thf molecules to afford the corresponding biscarbene species, 19 (19). The solubilities and stabilities of these complexes were found to decrease from calcium to barium. 

This chapter discusses the coordination chemistry of selected main group and transition metal complexes with dipicolinic acid, its analogues, and derivatives as ligands. Selected elements will be presented in terms of increasing atomic number. Out of all of the alkali metals, there has been a report of the crystal structure of sodium coordinated to dipicolinic acid. Calcium, magnesium, and strontium, three alkaline earth metals, are popular metal centers, which have been reported in the literature to be coordinated to dipicolinic acid or its analogues. ... 

Relatively few ammines occur in this group. The alkaline earth metals, namely, Subgroup A, show little tendency to form complex salts. A few have been prepared, such as strontium lluorocliloride,... 

Even a cursory reading of Chapter 3 of the previous volume/ dealing with alkaline earth diorgano amides, shows that detailed information on their preparation, structure and reactivity was quite sparse. For example, there were no data available for strontium or barium amide derivatives and there was just one structure of a complex related to a calcium amide - that of [(thf)3Ca( AIH j(. - in which calcium was incorporated as part of an... 

Complexes of alkali metals and alkaline-earth metals with carbohydrates have been reviewed in this Series,134 and the interaction of alkaline-earth metals with maltose has been described.135 Standard procedures for the preparation of adducts of D-glucose and maltose with the hydroxides of barium, calcium, and strontium have been established. The medium most suitable for the preparation of the adduct was found to be 80% methanol. It is of interest that the composition of the adducts, from D-glucose, maltose, sucrose, and a,a-trehalose was the same, namely, 1 1, in all cases. The value of such complex-forming reactions in the recovery of metals from industrial wastes has been recognized. Metal hydroxide-sugar complexes may also play an important biological role in the transport of metal hydroxides across cell membranes. 

Amide. — It has been pointed out before that europium behaves more or less like the alkaline earths and is closely related to strontium and barium. It is found to react with liquid ammonia at —78° C in much the same way as the alkali metals forming a characteristic deep blue solution. Eu(NH2)2 can be isolated [260] from the blue solution. Recent electron paramagnetic studies [261] of solutions of europium in liquid ammonia showed the presence of complex hyperfine lines arising from Eu2+ (8 7/2, g — 1.990 0.002) besides the characteristic single line of the solvated electron (g = 2.0014 0.0002) K The departure of the Eu2+ <7-value from the free electron value is explained as being due to spin-orbit coupling and a slight admixture (3.5%) of the 6P7/2 state. 

In the early 1990s, there existed several classes of extractants for actinides (CMPO), for cesium and more generally alkali cations, and for strontium and alkaline earth cations (crown ethers and cosan). The combination of these extractants and the grafting of these functions on calixarene platforms have led to new classes of extremely efficient and selective extractants, in particular calixarene-crown, which are presently applied in the United States to treat the huge amounts of waste at the SRS. Calixarenes/ CMPO, crown ethers/cosan, CMPO/cosan, and more recently calixarenes/CMPO/ cosan are promising compounds. It is desirable that these studies, conducted at the international level, continue in particular to obtain a better understanding of the complex mechanisms of extraction of these compounds.127187... 

Other examples of this series include a selection of ate complexes prepared by the treatment of alkylzinc reagents with freshly distilled alkaline earth metals under extrusion of elemental zinc. This route was employed to prepare a strontium zincate in which the alkaline earth metal center adopts a distorted octahedral geometry completed by two THF solvent donors. Similar reactions with barium metal lead to structurally closely related compounds. Flexibility in solvent choice is noted by the preparation of related complexes in toluene, displaying metal-toluene itt-interactions. 

As noted above, the ability of ligands with multiple phenyl rings positioned to allow resonance stabilization in an anion makes them ideal candidates for DAIP. Recent reports have demonstrated this with the presentation of a family of heavy alkaline earth triphenyhnethanides, all of which occur as charge-separated complexes in the solid state. Reaction of dibenzylbarium or strontium with triphenylmethane in the presence of 18-crown-6 and HMPA leads to the isolation of the DAIP triphenylmethanide, the barium compound of which is shown in Figure 35. 

Carbene complexes of alkaline earth metal amides and metallocenes have also been reported. Reaction of calcium, strontium, and barium bis(trimethylsilyl)amides [M(N(SiMe3)2 2(thf)2] (M = Ca, Sr, Ba) with two equivalents... 

Reaction of the sterically encumbered silylselanol HSeSi(SiMe3)3 with either Bu2Mg or the bis(trimethylsilyl)amides of Ca, Sr, and Ba in the presence of Lewis bases yields crystalline alkaline-earth selenolates. The Mg selenolate has been crystallized as a tris((dimethylphosphino)-methyl)-t-butylsilane complex, whereas the Ca, Sr, and Ba complexes have been isolated as TMEDA adducts. The magnesium complex is constructed around a six-membered P—Mg— P— C—S—C-ring that is puckered in a chair conformation. The strontium complex has Sr— Se = 2.94A with a linear Se—Sr—Se core. ... 

Studies have continued on the intercalation of the alkaline-earth metals into lattices of the transition-metal sulphides. Calcium and strontium are intercalated into M0S2 from liquid ammonia solution. X-Ray data reveal a lowering of the crystal symmetry of the sulphide and an increase in the complexity of the structure on intercalation. The intercalation compounds begin to superconduct at ca 4 K (for Ca) and 5.6 K (for Sr), and they show considerable anisotropy with respect to the critical magnetic field. Calcium in liquid ammonia also intercalates with TiS2- Two Ca,TiS2 phases have been identified. The limits of the first are 0.03 0.50, for which a relationship between x and cell parameters a and c... 

The alcoholates of calcium, strontium, and barium dissolve on warming in triethylalane in a manner analogous to that of the alcoholates of the alkalis, and compounds of the composition M[A1(C2HB)30R]2 are obtained. When these viscous liquids are treated further with two moles of triethylalane per mole of the complex salt, diethylaluminum alcoholate is set free. The pure alkaline earth bis(tetraethylalanates) may thus be prepared according to the equation ... 

---