Trimetaphosphimates

Formation of water-soluble polymetaphosphimates by reaction of Ag3(P02NH)3 (93) with a halide under formation of silver halide. With the use of (NH4)2S, the ammonium trimetaphosphimate (NH4)3(P02 NH)3 H20 has been obtained (94). 

The crystal structure determinations of trimetaphosphimates showed that N-H 0 hydrogen bonds between the ring anions play an important role. In most of these salts the (P02NH)lj rings adopt approximately a chair conformation. In a few cases a conformation is found that is best described as a linear combination of the boat and the twist conformation. Examples of these conformations as well as some structural aspects of trimetaphosphimates are given in Fig. 2. 

In all trimetaphosphimates of monovalent cations, the formation of N-H- 0 hydrogen bonds leads to a connection of (P02NH)ij ions. 

Fig. 2. Examples of the chair (1) and the distorted boat (2) conformation as well as pairs of trimetaphosphimate ions connected by N-H O hydrogen bonds (3). 

Tri- and tetrametaphosphimates can act as polydentate ions. In principle, coordination by both nitrogen and oxygen is possible, but as seen in the salts of monovalent cations, almost exclusively coordination via oxygen is expected. Thus, the anions can act as polydentate and/or bridging ligands. The trimetaphosphimate ion can act in various ways ... 

In the following the compounds will be described, depending on the degree of condensation of the metal and trimetaphosphimate ions. Up to now phosphimatometallates with isolated and chainlike (single and double chains) units as well as a layered compound have been described. These structural possibilities are shown in Fig. 4. 

H. N. Stokes prepared diimidotriphosphoric add, PO(OH)2.NH.PO(OH). NH.PO(OH)2, by heating trimetaphosphimic acid for about seven minutes with nitric acid. The soln. was then treated with an excess of ammonia, and a magnesium salt, and filtered. The acid in question appeared in the filtrate. The silver salt was precipitated by the addition of silver nitrate. Diimidotriphosphoric acid forms two series of salts—an acid salt with three, and a normal salt with five atoms of hydrogen replaced by the metal. For example, trisodium diimidotriphosphate,... 

P3N203H4lprismatic crystals, neutral to litmus, while penta-sodium diimidotriphosphate has an alkaline reaction. The trisilver salt forms monoclinic crystals. Warming the pentasilver salt with ammonium nitrate destroys the yellow colour—yellow silver phosphate is not whitened by this treatment, while silver trimetaphosphimate becomes orange-yellow. The empirical composition of the acid corresponds with either ... 

H. N. Stokes prepared salts of triimidotetraphosphoric add, HN PO(OH).NH. PO(OH)2 2, by the hydrolysis of salts of pentametaphosphimic acid—e.g. a hot acetic acid soln. of sodium pentametaphosphate furnishes sodium triimidotetra-phosphate, NH PO(OH).NH.PO(ONa)2 2 and the addition of silver nitrate to the soln. furnishes the silver triimidotetraphosphate, HN PO(OH).NH.PO(OAg)2 2. The acid is so unstable that it cannot be made by heating tetrametaphosphimate as might have been anticipated by the formation of diimidotriphosphoric acid by the action of heat on trimetaphosphimic acid. 

When an aq. soln. of trimetaphosphimic acid, or of one of its salts, acidified with one of the stronger mineral acids, is heated or kept for a long time, decomposition occurs—slowly if cold, rapidly if heated. Orthophosphoric acid and ammonia (ammonium phosphate) are the ultimate products of the decomposition. Several intermediate products have been detected in addition to pyrophosphoric acid, what H. N. Stokes calls diimidotriphosphoric acid, and imidodiphosphoric acid have been found, and he represents the different stages of the decomposition ... 

While the hydrolysis of triphosphonitrilic chloride furnishes trimetaphosphimic acid, the hydrolysis of tetraphosphonitrilic chloride, P4N4018, furnishes tetrameta-phosphimic acid, P4N4H808, which, by analogy with trimetaphosphic acid, has the ring formula ... 

While the hydrolysis of triphosphonitrilic chloride with sodium acetate furnishes trimetaphosphimic acid and the hydrolysis of tetraphosphonitrilic chloride with water furnishes tetrametaphosphimic acid, the hydrolysis of pentaphosphonitrilic chloride, P5N5C1i0, with sodium hydroxide in ethereal soln. furnishes sodium pentametaphosphimic acid, PsNsHloO10, or rather the alkali pentameta-phosphimate—sufficient alkali must be present to maintain the alkalinity of the soln. The sodium salts are amorphous, and are precipitated in a gelatinous form by the addition of alcohol to the alkaline soln., or to the soln. neutralized with acetic... 

To an ice-cold solution of 35.1 g. (0.1 mol) of tripotassium trimetaphosphimate in 95 ml. of water is added, slowly, 62 ml. of 72% perchloric acid so that the temperature does not exceed 25°. The potassium perchlorate is filtered off and washed with 15 ml. of 5% perchloric acid. The combined filtrates are transferred to a 200-ml. round-bottomed flask and evaporated at reduced pressure. A Dry Ice trap and potassium hydroxide pellets are used before the oil pump. The solution is stirred with a magnetic stirring bar and is heated in a water bath at not over 31°. When nearly but not quite dry, the solids are slurried in ethyl acetate-methanol (80/20 by volume) to remove any crystallized potassium perchlorate, transferred to a Buchner funnel and rinsed, using a total of 125 ml. of the above solvent, then... 

Trimetaphosphimic acid, as the 2-hydrate, crystallizes as rectangular platelets which melt at 105 to 110° by a rapid determination. The solubility in water is approximately 111 g./lOO g. of water at 35°, and 48 g./lOO g. of water at 25°. The transition from 2-hydrate to anhydrous acid occurs at 33°. In the anhydrous form the acid crystallizes in characteristic rhombs which do not melt at 110° but decompose at higher temperatures. The crystals are not noticeably hygroscopic. Both forms are practically insoluble in alcohols, ethyl acetate, ether, or hexane. The x-ray diffraction patterns have been reported.1... 

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