Solute species, inorganic

G. L. Hug, Optical Spectra ofNonmetallic Inorganic Transient Species in Aqueous Solution, NSRDS-NBS 69, National Bureau of Standards, Washington,... 

It is very common for inorganic chemists to neglect or ignore the presence of solvent molecules coordinated to a metal centre. In some cases, this is just carelessness, or laziness, as in the description of an aqueous solution of cobalt(ii) nitrate as containing Co ions. Except in very concentrated solutions, the actual solution species is [Co(H20)6] . In other cases, it is not always certain exactly what ligands remain coordinated to the metal ion in solution, or how many solvent molecules become coordinated. Solutions of iron(iii) chloride in water contain a mixture of complex ions containing a variety of chloride, water, hydroxide and oxide ligands. 

This is only the beginning of a process which ultimately results in the formation of solid state hydroxides or oxides. Actually, the solution species present in neutral or alkaline solutions of transition-metal ions are relatively poorly characterized. The formation of numerous hydroxy- and oxy-bridged polynuclear species makes their investigation very difficult. However, it is clear that there is a near-continuous transition from mononuclear solution species, through polynuclear solution species to colloidal and solid state materials. By the way, the first example of a purely inorganic compound to exhibit chirality was the olated species 9.11. 

Both secondary active transport and positive cooperativity effects enhance carrier-mediated solute flux, in contrast to negative cooperativity and inhibition phenomena, which depress this flux. Most secondary active transport in intestinal epithelia is driven by transmembrane ion gradients in which an inorganic cation is cotransported with the solute (usually a nutrient or inorganic anion). Carriers which translocate more than one solute species in the same direction across the membrane are referred to as cotransporters. Carriers which translocate different solutes in opposite directions across the membrane are called countertransporters or exchangers (Figs. 10 and 11). 

The birth of a crystal and its growth provide an impressive example of nature s selectivity. In qualitative analytical chemistry inorganic solutes are distinguished from each other by a separation scheme based on the selectivity of precipitation reactions. In natural waters certain minerals are being dissolved, while others are being formed. Under suitable conditions a cluster of ions or molecules selects from a great variety of species the appropriate constituents required to form particular crystals. 

Despite the vast quantity of data on electropolymerization, relatively little is known about the processes involved in the deposition of oligomers (polymers) on the electrode, that is, the heterogeneous phase transition. Research - voltammetric, potential, and current step experiments - has concentrated largely on the induction stage of film formation of PPy [6, 51], PTh [21, 52], and PANI [53]. In all these studies, it has been overlooked that electropolymerization is not comparable with the electrocrystallization of inorganic metallic phases and oxide films [54]. Thus, two-or three-dimensional growth mechanisms have been postulated on the basis that the initial deposition steps involve one- or two-electron transfers of a soluted species and the subsequent formation of ad-molecules at the electrode surface, which may form clusters and nuclei through surface diffusion. These phenomena are still unresolved. 

Equations 11.171.1 to 11.171.3 are, however, of limited practical application because they demand precise knowledge of the state of speciation of carbonates in aqueous solution during solid phase condensation (or late exchanges). The fact that different carbonate solute species distinctly fractionate is masterfully outlined by the experiments of Romanek et al. (1992), which indicate a marked control by solution pH of the fractionation between total dissolved inorganic carbon (DIC) and gaseous CO2 (figure 11.38). 

It is found in this study that an adjustment of pH value of solution by acid (HF or HC1) to 10.5 is very important for the effective formation of uniform mesopores. However, the acid should be added into the mixture solution after the addition of surfactant otherwise, the formation of the ordered mesoporous structure would be affected. The explanation is that when acid is added to a mixture solution without surfactant, the pH value of system will reduce and subsequently influence the interaction between cationic surfactant and anionic silicate species in the mixture, leading to the poor polymerization of inorganic silicate species. In addition, when HF is used prior to the addition of surfactant, the formation of stable NajSiFg can deactivate the polymerization of silicate species, further terminating the growth of mesoporous framework. 

Other Inorganics. Inoiganic species in solution have been studied very effectively by Raman spectroscopy. Work in this area includes the investigation of coordination compounds (qv) of fluorine (qv) (40), the characterization of low dimensional materials (41) and coordinated ligands (42), and single-crystal studies (43). Several compilations of characteristic vibrational frequencies of main-group elements have been published to aid in the identification of these species (44,45). 

Raposo, J.C., Sanz, J., Zuloaga, O. et al. (2003) Thermodynamic model of inorganic arsenic species in aqueous solutions, potentiometric study of the hydrolytic equilibrium of arsenious acid. Journal of Solution Chemistry, 32(3), 253-64. 

Sorbent or ion-exchange material Type of water Temperature (°C) Initial pH Inorganic arsenic species Initial arsenic concentration (mg L-1) Batch sorbent dosage (sorbent/ batch solution) or column Initial surface area (m2g-1) of sorbent or ion-exchange material Maximum removal capacity (mg As g 1 sorbent or ion-exchange material) References... 

A detailed review of the stabilities of inorganic selenium species, i.e. Se and Se, in water has been published (Heninger et al., 1997). No loss of either species was detected in aqueous solutions stored at — 20°C for 1 year. The concentrations studied were 10 and SOngmF1 (Cobo et al., 1994). Losses of Se occurred at higher temperatures for solutions of pH 2 and 6 stored in polyethylene containers. The maximum time for preservation was 1-2 months. In another investigation (Heninger et al., 1997), aqueous samples stored in Teflon containers at 4°C lost 29% of Se by oxidation in less than 1 month. The authors stated that catalytic oxidation of Se had occurred as a result of chlorine produced by a reaction between dissolved chloride and oxygen. 

Hug, G. L. Optical Spectra of Nonmetallic Inorganic Transient Species in Aqueous Solutions NSRDS-NBS 69 U.S. Government Printing Office Washington, DC, 1981. 

For a classical SEI electrode such as lithium, the surface films formed on it in most of the commonly used polar aprotic systems conduct Li ions, with a transference number (t+) close to unity. As stated earlier the surface films on active metals are reduction products of atmospheric and solution species by the active metal. Hence, these layers comprise ionic species that are inorganic and/or organic salts of the active metal. Conducting mechanisms in solid state ionics have been dealt with thoroughly in the past [36-44], Conductance in solid ionics is based on defects in the medium s lattice. Figure 8 illustrates the two common defects in ionic lattices interstitial (Frenkel-type) defects [37] and hole (Schottky-type) defects [38],... 

As discussed in Ref. 84, Li/Hg amalgam cannot be a model system for solid Li surfaces, because reduction of solution species on the liquid Li/Hg interface does not produce stable surface films. Thus, a massive solvent reduction may occur on Li/Hg in which each solvent molecule reacts directly with the bare active surface. In such a situation, PC and EC are indeed reduced directly to Li2C03 [84,131], However, R0C02Li species are major reduction products of PC and EC on Li/Hg as well. It should be noted that when the Li is initially covered by native surface films (Li20, Li2C03), the situation is more complicated. Only part of the native surface films may be replaced upon storage in the solutions thus, in such a case the nature of the surface films remains more inorganic than in the case of fresh Li surfaces [101-105], In any event, upon Li deposition or dissolution, the replacement of the native surface films by solution reduction products is fast and pronounced, and the above-described surface chemistry is very relevant to practical Li anodes in batteries. 

Extensive work was devoted by Matsuda et al. to the study of additives for rechargeable Li battery systems [168-170], For instance, inorganic additives such as Mg2+, Fe2+, and Ga3+ ions were suggested [266], The idea behind these additives is that their reduction on the Li surface may lead to surface alloying that can modify the reactivity of the Li toward solution species. 

---