Rare phosphides

Phosphorus is the eleventh element in order of abundance in crustal rocks of the earth and it occurs there to the extent of 1120 ppm (cf. H 1520 ppm, Mn 1060 ppm). All its known terrestrial minerals are orthophosphates though the reduced phosphide mineral schrieber-site (Fe,Ni)3P occurs in most iron meteorites. Some 200 crystalline phosphate minerals have been described, but by far the major amount of P occurs in a single mineral family, the apatites, and these are the only ones of industrial importance, the others being rare curiosities. Apatites (p. 523) have the idealized general formula 3Ca3(P04)2.CaX2, that is Caio(P04)6X2, and common members are fluorapatite Ca5(P04)3p, chloroapatite Ca5(P04)3Cl, and hydroxyapatite Ca5(P04)3(0H). In addition, there are vast deposits of amorphous phosphate rock, phosphorite, which approximates in composition to fluoroapatite. " These deposits are widely... 

In comparison to alkali metal complexes of (di)organophosphide ligands, complexes of these metals with (di)organoarsenide ligands are relatively rare and few have been structurally characterized. This dearth of structural information is perhaps due in part to the relatively low importance of such complexes in inorganic and organic synthesis and to the lower stability (both thermal and photolytic) of arsenide complexes compared to their phosphide analogues. 

In the review by Kanatzidis et al. (2005), the preparation by the tin-flux method is mentioned also for several ternary phosphides and polyphosphides of rare-earth and transition metals. Typically the components (R metal, T metal, P and Sn in an atomic ratio of about 1 4 20 50) in sealed silica tubes were slowly heated, to avoid violent reactions, up to 800°C, annealed at that temperature for 1 week and slowly (2 K/h) cooled to ambient temperature. The tin-rich matrix was dissolved in diluted hydrochloric acid. The authors described the preparation of compounds corresponding for instance to the formula MeT4P12 (Me = heavy rare-earth metals and Th and U, T = Fe, Ru, etc.) and to the series of phases MeT2P2 (Me is a lanthanide or an actinide and T a late transition metal) having a structure related to the BaAl4 or ThCr2Si2 types. 

Likewise, irradiation of an n-Si electrode in an aqueous electrolyte efficiently forms an insulating SiOx interface [3]. Reductive decomposition of semiconductors is rarely observed, although it has been claimed that certain p-type III-V semiconductors in the phosphide family decompose to form PH3. 

IRON, Fe (Ar 55 85) - IRON(II) Chemically pure iron is a silver-white, tenacious, and ductile metal. It melts at 1535°C. The commercial metal is rarely pure and usually contains small quantities of carbide, silicide, phosphide, and sulphide of iron, and some graphite. These contaminants play an important role in the strength of iron structures. Iron can be magnetized. Dilute or concentrated hydrochloric acid and dilute sulphuric acid dissolve iron, when iron(II) salts and hydrogen gas are produced. 

The field of transition metal-rich phosphides in the ternary systems R T P (R = Zr, Hf, rare earth metal, actinoid metal) has intensively been investigated in the last 10 years by the groups of Franzen and Kleinke, Guerin, Jeitschko, Kuz ma, and Mewis. From a geometrical point of view, the main building motifs of these stmctures are mono-, di-, or tricapped... 

Figure 20 Crystal structures of various ternary and quaternary phosphide oxides of the alkaline earth, rare earth, and actinoid metals. Alkaline earth (rare earth, actinoid), transition metal, phosphorus, and oxygen atoms are drawn as large light grey, medium grey, filled, and open circles, respectively. Some relevant coordination polyhedra around the oxygen atoms and the transition metal-phosphorus bonds are emphasized...

With A = Rb and Cs, compounds of the type A2[PH] can be prepared containing an isolated hydrogenphosphide anion [PH] , which could also be named for example, as dicesiumphosphanide(l), when starting from phosphane(3). The orientation of the PH unit could not be determined by X-ray analysis, but its existence has been proven by solid-state H-NMR. The metal phosphide Ti3P forms hydrides or deuterides up to a maximum content of 2.6 H (D). The exact crystal structure depends on the H (D) content and the temperature. We note, that exact reliable studies of compounds M/P/H are very rare. 

Real information about the thermodynamic stability of solid phosphides is very rare. 

Phosphorus occurrence in the lithosphere is predominantly as phosphates, P04 , although a rare iron-nickel phosphide, schreibersite ((Fe, Ni)3P)g is also known in nature [1]. For this reason, phosphates are the primary source of elemental phosphorus for chemical process requirements. Only 0.20-0.27% phosphate (0.15-0.20% as P2O5 0.07-0.09% as P) is present in ordinary crustal rocks. 

Inhalation of gas (rare) or ingestion of solid phosphide reacts with gastric HC1 to form phosphine gas, which interferes with enzymes and protein synthesis, primarily in mitochondria of heart and lung cells, causing myofibril necrosis and secondary ionic changes in peripheral small vessels and lungs... 

Yu. Kuz maandS. ChykhriJ, Phosphides, in Handbook on the Physics and Chemistry of Rare Earths , eds, K. A. Gschneidner... 

The electrodes were mixtures of gallium phosphide (synthesized at the Institute of tbe Rare-Metal Industry) and red or black phosphors. These mixtures were prepared In an inert atmosphere. Gallium chloride (GaCy was prepared by the method described in [4]. 

Schreibesite, (Fe,Ni)3P, and Florenskyite, FeTiP, have been detected in meteorites and in lunar samples [35]. These constitute rare examples of naturally occurring reduced phosphate minerals, and phosphides of this type may be present in the earth s core. 

---