Oxo anions of phosphorus

The separations of monomeric, dimeric and trimeric oxo acids of phosphorus, based on the steric exclusion effect, was achieved on Sephadex G-25 gel, regardless of the oxidation states of the phosphorus atoms [ref. 44]. This result was applied to the characterization of unknown oxo acids of phosphorus [ref. 94-96]. 

The values of monomeric oxo acids of phosphorus on Sephadex G-25 were almost independent of the pH of the eluent, while on more tightly crosslinked gels, i.e., Sephadex G-10 and G-15, the characteristic pH profiles of the values of the oxo acids were observed, which were similar to the pH titration curves of the corresponding oxo acids [ref. 57, 97]. Satisfactory separations of phosphinate, phosphonate and orthophosphate were effected by using the eluents of appropriate pH values [ref. 97]. 

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This review deals with the chemistry and coordination complexes of isoelectronic analogues of common oxo-anions of phosphorus such as PO3, POl", RPOl" and R2POy. The article begins with a discussion of homoleptic systems in which all of the 0x0 ligands are replaced by imido (NR) groups. This is followed by an account of heteroleptic phosphorus-centered anions, including [RN(E)P(/<-NR )2P(E)NR]2-, [EP(NR)3]3-, [RP(E)(NR)2] and [R2P(E)(NR )] (E=0,S, Se, Te). The emphasis is on the wide variety of coordination modes exhibited by these poly-dentate ligands, which have both hard (NR) and soft (S, Se or Te) centers. Possible applications of their metal complexes include new catalytic systems, coordination polymers with unique properties, and novel porous materials. 

The chemistry of homoleptic polyimido and heteroleptic imido-oxo- or -chalcogenido anions of phosphorus is described in chapter 6 (T. Chivers). Emphasis is placed on the versatile coordination behavior of these multident-date hgands, which have both hard (NR) and soft (S, Se, Te) centers. 

P-anions. A pH titration curve of this acid exhibits only one inflection point, like the known ring oxo acids of phosphorus, (-P-0-)rring,... 

Paper chromatography has been applied successfully to the separation and identification of oxo acid anions of phosphorus with various oxidation states by several investigators. Bonnin and Sue (69) have demon-... 

P-, P-, P-P-, P-, P-0-P-, (-P-0-)3-ring, (-P-0-)4-ring, and long chain metaphosphate anions, can be separated by two-dimensional paper chromatography. Blaser and Worms (19,41,44,47,50,56,65) employed Grunze and Thilo s solvents (72) for the identification of various lower 0X0 acids of phosphorus. Using Thilo and Heinz s basic solvent (73), Hamisch (4) demonstrated the separation of many lower oxo acids of phosphorus. 

Klement and Frieser (74) have reported that P-, P-, P-P-, and P-anions can be separated by paper electrochromatography. The liquid phase was a borate buffer of pH 8 and a potential of 220 v. was applied. The separation and identification of various oxo acids of phosphorus,... 

Thilo (25) classified oxo acids of various elements into three groups on the basis of the stability of the oxo acid in aqueous solutions, as shown in Table I. Although Thilo placed the elements in order of their ionic radii, covalent radii of the elements are used in Table I. The most stable phosphate in aqueous solutions is the monomer, orthophosphate. However, isopoly acid anions of phosphorus, i.e., condensed phosphates, are generally stable in an approximately neutral aqueous solution at room temperature. The rate of hydrolysis of the condensed phosphates is very low under these conditions. On the other hand, polysulfates and polyarsenates are very rapidly hydrolyzed into their monomers in aqueous solutions. In an alkaline solution, vanadate anions are present as monomer, i.e., orthovanadate. When the pH of the solution is de- creased, the orthovanadate anions are successively polymerized to form polymers with medium degrees of polymerization. Although silicate anions behave similarly, a highly polymerized form of silicate anions,... 

Chivers T (2003) Imido Analogues of Phosphorus Oxo and Chalcogenido Anions. 229 143-159 Chow H-F, Leung C-F, Wang G-X, Zhang J (2001) Dendritic Oligoethers. 217 1-50 Clarkson RB (2002) Blood-Pool MRI Contrast Agents Properties and Characterization. 221 201-235... 

Chivers T (2003) Imido Analogues of Phosphorus Oxo and Chalcogenido Anions. 229 143-159... 

The oxo acids and anions in both lower and higher states are a very important part of the chemistry of phosphorus and arsenic and comprise the only real aqueous chemistry of these elements. For the more metallic antimony and bismuth, oxo anion formation is less pronounced, and for bismuth only ill-defined bismuthates exist. 

All phosphorus oxo acids have POH groups in which the hydrogen atom is ionizable hydrogen atoms of the P—H type are not ionized. There is a vast number of oxo acids or ions, some of them of great technical importance, but we can deal only with some structural principles, and some of the more important individual compounds. The oxo anions are of main importance, since in many cases the free acid cannot be isolated, though its salts are stable. Both lower (Pra) and higher (Pv) acids are known. 

The relative amounts of molybdenum and phosphorus adsorbed onto y-alumina from molybdate and/or phosphate solutions by sequences of pulses are shown in Fig. 21 (59). When the solutions contain only molybdenum or phosphorus oxo-species, the amounts of molybdenum or phosphorus retained are high for the first pulses (—80 and —100%, respectively) and decrease in further pulses. On the other hand, the evolution during pulses with a Mo + P solution, which is equivalent to coimpregnation of molybdenum and phosphorus, is quite different. The molybdenum adsorption decreases significantly as a result of addition of phosphorus due to the strong competition between phosphorus- and molybdenum-containing anions. In addition, the molybdenum adsorption decrease in the presence of phosphorus can also be explained by the formation (Eqs. 15 and 16) of phosphomo-lybdate species that have lower affinities for alumina ... 

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