Alkaline-earth calcium 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). 

It will be noted that this type of complex-formation is entirely different from that in which complexes are formed between amylose and certain polar, organic compounds. In contrast to the precipitates of the latter complexes (which are of a distinct, crystalline appearance), the starch-alkaline-earth hydroxide complexes are amorphous, curdlike flocculates. These complexes di,s.sociate on diluting them with water, and the starch redissolves. According to the patent description, the amylose complexes dissolve much more easily than the amylopectin complexes hence, fractionation must occur if water is added stepwise. Likewise, fractionation will take place if the starch complexes are partially neutralized, by the gradual addition of an acid. For obvious reasons, such acids as carbonic acid and sulfuric acid (which give insoluble calcium salts) are preferred. Furthermore, it is claimed that gradual addition of caustic alkali to a starch solu-... 

The stability of the alkaline-earth EDTA complexes decreases down the group as expected from the increased ionic radius. However, Ca ions are exceptional in forming the most stable EDTA complex. For this reason, calcium cannot be titrated using the Erio T indicator, since no colour change to steel blue is observed. However, when a suspension of magnesium complexone is added, the calcium replaces magnesium in the complexone releasing Mg ions which can be titrated. This replacement titration may be used to standardise EDTA solution. 

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. 

Alkali metal haHdes can be volatile at incineration temperatures. Rapid quenching of volatile salts results in the formation of a submicrometer aerosol which must be removed or else exhaust stack opacity is likely to exceed allowed limits. Sulfates have low volatiHty and should end up in the ash. Alkaline earths also form basic oxides. Calcium is the most common and sulfates are formed ahead of haHdes. Calcium carbonate is not stable at incineration temperatures (see Calcium compounds). Transition metals are more likely to form an oxide ash. Iron (qv), for example, forms ferric oxide in preference to haHdes, sulfates, or carbonates. SiHca and alumina form complexes with the basic oxides, eg, alkaH metals, alkaline earths, and some transition-metal oxidation states, in the ash. 

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. 

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. 

Acid resistance This property is best appreciated when the glass structure is understood. Most enamel frits are complex alkali metal borosilicates and can be visualised as a network of Si04 tetrahedra and BO, triangular configurations containing alkali metals such as lithium, sodium and potassium or alkaline earth metals, especially calcium and barium, in the network interstices. 

The chapter on kinetics and mechanisms of complex formation and ligand substitution at alkali metal and alkaline earth cations elsewhere in this volume provides context and complementary discussion of these processes in relation to calcium. 

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. 

The use of alkali and alkaline earth group metal ions, especially those of sodium, potassium, magnesium, and calcium, for maintenance of electrolyte balance and for signaling and promotion of enzyme activity and protein function are not discussed in this text. Many of these ions, used for signaling purposes in the exciting area of neuroscience, are of great interest. In ribozymes, RNAs with catalytic activity, solvated magnesium ions stabilize complex secondary and tertiary molecular structure. Telomeres, sequences of DNA at the ends of chromosomes that are implicated in cell death or immortalization, require potassium ions for structural stabilization. 

Cyanide occurs most commonly as hydrogen cyanide in water, although it can also occur as the cyanide ion, alkali and alkaline earth metal cyanides (potassium cyanide, sodium cyanide, calcium cyanide), relatively stable metallocyanide complexes (ferricyanide complex [Fe(CN)6]-3), moderately stable metallocyanide complexes (complex nickel and copper cyanide), or easily decomposable metallocyanide complexes (zinc cyanide [Zn(CN)2], cadmium cyanide [Cd(CN)2]). Hydrogen cyanide and cyanide ion combined are commonly termed free cyanide. The environmental fate of these cyanide compounds varies widely (Callahan et al. 1979). 

Apatites are complexes of cationic Ca " matched by HP04, COa ", OH , or F as anions. Depending on the counter-ion, apatite can occur in the forms carbonate apatite Caio(P04)6C03, as hydroxyapatite Caio(P04)e (0H)2, or fluoroapatite Caio(P04)6F2. In addition, alkaline earth carbonates also occur in bone. In adults, more than 1 kg calcium is stored in bone. 

These titrations arc used in the estimation of metal salts. Ethylenediamine tetracetic acid (EDTA) shown in Figure 3.10 is the usual titrant used. It forms stable 1 1 complexes with all metals except alkali metals such as sodium and potassium. The alkaline earth metals such as calcium and magnesium form complexes which are unstable at low pH values and are titrated in ammonium chloride buffer at pH 10. The general equation for the titration is ... 

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. ... 

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