PHOSPHIDES

406

PHOSPHORUS : ARTHUR D. F. TOY

very high obscuring power. It is used also in incendiary bombs and shells as a self-igniting agent. Phosphorus-containing munition shells when exploded have the additional property of raining small particles of burning phosphorus which stick tenaciously to the clothing and skin of the enemy. The sensitivity of phosphorus to ignition is also utilized for amusement purposes, e.g. in caps for cap pistols. These caps have one section of potassium chlorate and the other of red phosphorus, sulfur and calcium carbonate. When the two sections are struck together in a cap pistol, a small explosion results. Other uses for elemental phosphorus are as poisons in baits for rodents and as ingredients for incendiaries.

2.

PHOSPHIDES

Phosphorus reacts with most of the metallic elements at elevated temperature to form phosphides. Each element forms one or more crystalline phosphides of a specific metal-tophosphorus ratio. Some ratios correspond to the classical valency rule and some do not. Literature references on phosphides are rather numerous. With the introduction of modern phase-analytical methods, many members of this class of compounds are well characterized. The properties of some metallic phosphides were summarized by Farr™ in 1950. Van 77 Wazer reviewed the subject in 1958 and more recently (1965) Aronsson, Lundström 78 and Rundqvist critically reviewed the preparation, properties and crystal chemistry of various phosphides. The structural chemistry of the phosphides was reviewed by 79 Corbridge . In Table 4 are listed the compositions of well-characterized phosphides 78 compiled by Aronsson, Lundström and Rundqvist . Readers are referred to the above references for detailed information and additional references.

2.1. M E T H O D S O F P R E P A R A T I O N

1. By the direct reaction of the elements heated in vacuum or in an inert atmosphere: For elements which form several stable phosphides of different metal-to-phosphorus ratio, the correct ratio of the elements must be used. For elements which form only one phosphide, an excess of phosphorus, either red or white, may be used and the excess phosphorus then removed by distillation. Other sources of phosphorus are the phosphorus-rich phosphides which when heated decompose to the lower phosphides with the liberation of phosphorus. 2. By the reduction of metal phosphate with carbon at high temperature : An example of this method is the preparation of calcium phosphide, Ca3P2, by the reduction of calcium phosphate with carbon. 3. By the heating of the metal or metal halide, or metal sulfide, with phosphorus 76 T. D. Farr, Phosphorus, Properties of the Element and Some of Its Compounds, Chemical Engineering Report No. 8, pp. 69-74, Tennessee Valley Authority, Wilson Dam, Alabama (1950). 77 J. R. van Wazer, Phosphorus and Its Compounds, Vol. I, pp. 123-75, Interscience Publishers Inc., New7 8 York (1958). B. Aronsson, T. Lundström and S. Rundqvist, Borides, Suicides and Phosphides, John Wiley & Sons Inc.,7 9 New York (1965). D. E. C. Corbridge, Topics in Phosphorus Chemistry, 3 (1966) 57-394.

CLASSES, PROPERTIES AND CRYSTAL STRUCTURES

halidc or phosphorus hydride: boron phosphide by the heating 4. By the high temperature oxide and an alkali phosphate: the preparation of W 3 P .

407

This method may be illustrated by the preparation of of B 2 S 3 with P H 3 at 1200° to 1400°. electrolysis of molten salt baths containing the metal This was reported to be the only successful method for

2.2. C L A S S E S , P R O P E R T I E S A N D C R Y S T A L S T R U C T U R E S

Phosphides may be divided into two general classes : (1) Those which are reactive and easily undergo hydrolysis. (2) Those which are metallic in nature and do not undergo hydrolysis easily. The alkali and alkaline earth phosphides, as well as the phosphides of the lanthanides 1600 r -

1370°C.

10

15

20

Weight percentage of phosphorus

10

I

I

20

30

40

Atomic percentage of phosphorus 77

FIG. 6. Phase diagram of the iron-phosphorus system . (Reprinted by permission of John Wiley & Sons Inc.)

Black needles with metallic luster

Hexagonal

Transparent, ruby needles, triclinic

Brown cubic a n t i - M n 20 3 type Cubic a n t i - M n 20 3 type Reddish-brown crystals tetragonal

Hexagonal

Ti 3P type

PbCl 2 type

Hexagonal cubic Hexagonal NiAs type

e

a, c

f

a, b, c

b

, c a, b, c

b, c

g

β

b, c

b, c

UP

N a 3P

KP15

Be 3P 2

M g 3P 2 C a 3P 2

ß-ZrV

Z r 3P

ZrP 2

HfP

VP

flat

Reddish-brown hexagonal

Li 3P

References

a, b, c

Phosphides

Color, crystal system, structure type

= 22.74 = 9.69 = 7.21 = 10.17

= 5.55 = 4.98 = 10.19 = 4.990 = 8.815

a c a b c a c a c

N a - P = 3.09 N a - N a = 2.93 P-P = 4.98 α = 116.7° β = 97.5° γ = 90.0° P-P = 3.59 Be-P = 2.20

Li-Li = 2.53 Li-P = 2.64 P-P = 4.26 β = 117.1°

= 10.7994 ±0.0003 = 5.3545 ±0.0003 = 6.4940±0.0005 = 8.7434±0.0005 = 3.5135±0.0003 = 3.651 = 12.37 = 3.18 = 6.22

c = 12.554

a = 3.684

a = 12.03 a = 5.44 c = 6.59

α b c a

b c a c

fl

a = 4.273 c = 7.595

Molecular data dimension in Â

TABLE 5

Odorless, stable in air, not attacked by water, slowly attacked by coned. oxidizing acids Density at 25° = 2.25 g/cm 3. Reacts with water to give phosphine

Density at 25° = 1.74 g/cm3. Reacts with water to give phosphine

Density at 25° = 1.43 g/cm3. Reacts with water to give phosphine

Physical and chemical properties

Electrolysis of metaphosphate melt containing V 2Os

Hf+P

P 4+ Z r

Z r P i . 2+ Z r

Hard metallic

Density at 15° = 2.51 g/cm 3 stable to 1250° under inert atm. Reacts with moist air to give phosphine, incandescent with 0 2 at 300° Hard metallic 2 Z r + P 4 -> 2ZrP 2 >1400° 4ZrP 2(s) -> 4ZrP(s)+P 4(g) ß-Zr0.99V " a - Z r 0. 9 3P + P 900°

Mg+red Ρ Ca+red Ρ C a 3( P 0 4) 2+ c a r b o n

Be+red Ρ

K + r e d Ρ at 300-20°

Na+P

L i 3P + r e d Ρ

Li+P

Methods of preparation

408 PHOSPHORUS: ARTHUR D. F. TOY

Orthorhombic MnP type

Orthorhombic

Grey-black FeS 2 type

C0AS3 type

Cubic system Grey-black

A, C> 1

c

a, b, c

a, b, c

b

A, b

A, b, c

W 3P

MnP

Fe 2P

FeP

FeP 2

OsP 2

C0P3

R h 2P Rh4P 3

Ir 2P

Orthorhombic

c

b

b

Grey-black α = V3S-type structure Tetragonal isostructural with Fe3P

a, b, c

Mo 3P

Lavender color cubic

Hexagonal

GeAs 2 type

SiAs type

h

h

Reterences

SiP 2

GeP

Phosphides

Color, crystal system, structure type = 15.14 ß = 101.1° = 3.638 Ζ = 12 = 9.19 = 13.97 Ζ = 8 = 10.08 = 3.436 = 9.794 = 4.827 = 9.890 = 4.808

a a b c a

a c a b c a b c a b c a

= = = = =

5.498 11.662 3.317 9.994 5.543

= 5.865 = 3.456 = 5.191 = 3.099 = 5.792 = 4.791 = 5.654 = 2.719 = 5.098 = 5.898 = 2.918 = 7.706

a = 5.258 b = 3.172 c = 5.918

a b c a b c a c a c

Molecular data dimension in  Methods of preparation

2CoP(s)+P 4(g) Very hard, chemically inert Very hard, chemically inert Very hard, chemically inert. Decomposed by alkali fusion

I r P 2+ h e a t

ΔΖ/AV = 71.6 kcal

2CoP 3(s)

Density at 25° = 4.26 g/cm3

Decomposes to metal and phosphorus above 1200°C

2FeP 2(s)->2FeP(s)+P 2(g) ΔΗ&ν = 67 kcal

ΔΖ/AV = 80.2 kcal

Density at 25° = 6.07 g/cm3 4FeP(s)-> 2Fe 2P(s)+P 2(g)

M.p. 1193°C, sp.gr. 5.0

Density at 25° = 9.07 g/cm* Chemically inert

Physical and chemical properties

Rh4P3+heat Rh+P

= - 5 2 kcal/mole

Co+3P Ped-»-CoP3

Os+P

2Pred+Fe-*FeP2 Δ//903 = - 3 4 kcal/mole

Crystallize from melt of MoP alloy Electrolysis of fused (NaP03> n containing W O 3 and NaCl Electrolysis in electrolyte compn. of NaCl, N a 4 P 2 0 7 , N a 2 B 4 0 7 , N a P 0 3 and M n 0 2 at 925° Pred+2Fe F e 2P Δ//903 = - 3 4 . 5 kcal/mole Pred+Fe->FeP Δ # 9 0 3 = - 2 5 kcal/mole

S i + P at 900°

G e + P at 900° AH = - 3 7 kcal

TABLE 5—Continued

CLASSES, PROPERTIES AND CRYSTAL STRUCTURES

409

Grey-black FeAsS type

Tetragonal

Black lustrous rod shape crystals pyrite-type CoAs 3 type

Metallic luster hexagonal Cu 3AS type

Iron-grey-metallic tetragonal

Red (tetragonal) Black (monoclinic)

Iron-grey metallic tetragonal Orange-red tetragonal B 4 C type

b, c

a, c

J

a, b

a, b, c

b, c, k, 1

c

b, c

b, c

c, m

Ni 3P

NiP 2

NiP 3

C u 3P

Z n 3P 2

ZnP 2

C d 3P 2

CdP 2

B i 3P 2

References

IrP 2

Phosphides

Color, crystal system, structure type = 5.746 = 5.791 = 5.850 = 8.954 = 4.386 β

= 111° 60'

a a b c a c a c a c

c = 7.15

= 5.08 c = 18.59 = 8.85 β = 102° 3 ' = 7.29 = 7.56 = 8.76 = 12.31 = 5.29 = 19.74 = 5.984 = 11.850

a = 8.11 c = 11.47

a = 6.95

a = 5.4706 ±0.0002 P-P = 2.12±0.03 Ni-P = 2.290±0.01 a = 7.819

a b c a c

Molecular data dimension in Â

TABLE 5—Continued

=

-39.5 ± 5

B + P at 1600° at 100 atm.

Cd+P

Cd s a l t + P H 3

Zn+P

kcal/mole

A/ÎWK

N i + Ρ or Ni-Sn alloy+P. S n 3P 4 removed by dissolution in HCl 3 C u + P r e d = C u 3P AH = - 3 2 kcal/mole at 888-903°K, heating C u P 2 ; electrolysis of sodium phosphate melt containing CuO Z n s a l t + P H 3: Z n P 2+ h e a t ; Z n + P r e d- + Z n 3P 2

N i + P 1200° at 65 kb

Δ / / 9 0 3 = - 4 8 . 4 kcal/mole

3 N i + P r e d - * N i 3P

Ir+exc. P 4

Methods of preparation

Does not react with water, reacts with acid to give P H 3

Good conductor of electricity

Conductor of electricity 620-820°K Z n 3P 2 > 3Zn(g)+l/2P 4(g) toxicity = 10-11 mg/kg to hens 8-10 mg/kg to ducks and geese 10-12 mg/kg to pigs

Density at 18° = 4 . 1 9 g/cm3 4NiP 3(s) -> 4NiP 2(s)+P 4(g) Δ / f a v = 43 kcal Conducts electricity, brittle and dense, feebly attacked by HCl, readily oxidized by air

Density = 4.70 g/cm^

Density at 25° = 7.7 g/cnP Decomposes at 960° to form N i 5 P 2

Physical and chemical properties

410 PHOSPHORUS : ARTHUR D. F. TOY

a,

b, c,

AIP

GaP

t, u

ρ

Cubic Greyish-black metallic cubic Greyish-black metallic cubic Cubic

Cubic ZnS type Cubic ZnS type

Cubic

Cubic

For refs. to table see p. 412.

c, w

PuP

ν

e,

b, c

UP

a,

b, c

LaP T h 3P 4

β,

b,

InP

r

b, q

b, c, η , ο,

References

BP

Phosphides

Color, crystal system, structure type

a = 5.644

T h - P = 2.98 P-P = 3.20 space group 143d a = 5.589

a = 6.02 a = 8.618

a = 5.8688

a = 5.451 Al-Al distance = 3.84 Al-P = 2.34 a = 5.4506

a = 4.538 cube edge 4.538 B-P distance 1.964

Molecular data dimension in  Methods of preparation

400-600°

P u H 3+ P H 3 ^ ^ , „ Tr PuP+3H2

U + P H 3; U 0 2+ C + P H 3

Ga+PCl3 2 G a P + 3 G a C l 2; G a + P In+P I n + P 4O i o In+ZnP2 La+P Th+P

P+Al

Z n P 2 + B B r 3 at 900°; B + P ; B 2 S 3 + P H 3 at 1200-1400°; B C 1 3 + H 2 over Pred at 500°

TABLE 5—Continued

disReacts with water to give P H 3 Decomposes in cold HCl soin, to liberate P H 3 density at 25° = 8.44 Decompd. to free metal below m.p. density at 25° = 10.16 g/cm*

Exhibits transistor properties, sociation temp. = 1015 ± 4 °

1000° B P + H 2 — - > B 5P 3 Pure AIP insol. in cold and boiling water, dissolves in dilute HCl to give P H 3, can act as ρ or Λ semiconductors

B+P vioietat22° = - 2 9 ± 2 kcal/mole Standard entropy = 6.4±0.1 cal/°K mole, stable to boiling water, decomposed by boiling cone, alkali

Physical and chemical properties

CLASSES, PROPERTIES AND CRYSTAL STRUCTURES

411

a T. D. Farr, Phosphorus, Properties of the Element and Some of Its Compounds, Chemical Engineering Report No. 8, pp. 69-74. Tennessee Valley Authority, Wilson Dam, Alabama (1950), b J. R. van Wazer, Phosphorus and Its Compounds, «Vol. I, pp. 123-75. Interscience Publishers Inc., New York (1958). 0 B. Aronsson, T. Lundström and S. Rundqvist, Borides, Silicides and Phosphides, John Wiley & Sons Inc., New York (1965). d D. E. C. Corbridge, Topics in Phosphorus Chemistry, 3 (1966) 57-394. e K. Langer and R. Juza, Naturwissenschaften, 54(9) (1967) 225 1 H. G. von Schnering and H. Schmidt, Angew. Chem. Intern. Ed. Eng. 6(4) (1967) 356. * T. Lundström, Acta Chem. Scand. 20(6) (1966) 1712-14. h T. Wadsten, Acta Chem. Scand. 21(2) (1967) 593-4. 1 D. H. Baker, Jr., Trans. Met. Soc. AIME 239(5) (1967) 755-6. J P. C. Donohue, T. Α. Bither and H. S. Young, Inorg. Chem. 7(5) (1968) 998-1001. k M. N. Mirianashvili, Sb. Tr., Gruz. Zootekh-Vet, Ucheb-Issled. Inst. 35 (1965) 415-17. 1 A. R. Venkitaraman and P. K. Lee, / . Phys. Chem. 71(8) (1967) 2676-83. m P. E. Grayson, J. T. Buford and A. F. Armington, Electrochem. Technol. 3(11-12) (1965) 338-9. n J. Cueilleron and F. Thevenot, Bull. Soc. Chim. Fr. (1966) (9) 2 7 6 3 ^ . ° W. Kischio, Z. anorg. u. allg. Chem. 349(3-4) (1967) 151-7. Ρ J. Cueilleron and F. Thevenot, Bull. Soc. Chim. Fr. (1965) (2) 402-4. W. E. White and A. H. Bushey, Inorganic Synthesis, Vol. IV, pp. 23-25. Ed. J. C. Bailar, Jr., McGraw-Hill Book Co., New York (1963). r G. Sanjiv Kamath and D. Bowman, / . Electrochem. Soc. 114(2) (1967) 192-5. » M. Kuisl, Angew. Chem. Intern. Ed. Engl 6(2) (1967) 177. 1 A. Addamiano, U.S. 3,379,502, April 23, 1968, to General Electric Co. u Y. A. Ugai and L. A. Bityutskaya, Simp. Protsessy Sin. Rosta Krist. Plenok Poluprov. Mater, Tezisy Dokl. Novosibirsk, (1965) 42-3. v M. Allbutt, A. R. Junkison and R. F. Carney, Proc. Brit. Ceram. Soc. No. 7 (1967) 111-26. w O. L. Kruger, J. B. Moser and B. Wrona, U.S. 3,282,656, Nov. 1, 1966, to U.S. Atomic Energy Commission.

412 PHOSPHORUS : ARTHUR D. F. TOY

APPLICATIONS

413

and other electropositive metals, are in general very reactive and hydrolyze in water to give phosphines. The phosphides of the transition metals constitute the largest and the most studied class of phosphides. These phosphides and the phosphides of the more noble metals are characterized by hardness, high melting point, high thermal and electric conductivity, 79 metallic luster and resistance to attack by dilute alkaline or acids . Some of this class of phosphides, however, will react with hot nitric acid. The properties of the phosphides are intimately associated with the electronic structure of the metal component. However, minute impurities also produce drastic changes in the properties, especially the electrical properties. Differences in homogeneity and porosity 78 (high melting materials are made by sintering) account for further discrepancies . Phosphides can also be classified as either "phosphorus rich" or "metal rich". The structure of the phosphorus-rich phosphides is that of polymerized phosphorus atoms around the metal atoms. The metal-rich phosphides may be described in terms of coordination polyhedra of metal atoms enclosing phosphorus atoms. The immediate 79 coordination sphere of the metal atoms contains both metal and phosphorus a t o m s . In Table 5 are listed some examples of phosphides; their method of preparation, crystal structure, molecular data and some physical and chemical properties. Of the metal-phosphorus systems studied, one of the more important ones is that of iron-phosphorus. Since the iron-phosphides "ferrophos" are produced as by-products in the commercial production of elemental phosphorus, they represent the largest volume 77 of metal phosphides produced. A phase diagram for this system is shown in Fig. 6.

2.3. A P P L I C A T I O N S

"Ferrophos" until recently was added to the iron smelting process used to manufacture high-grade steel. In this process, phosphorus in the "ferrophos", along with the phosphorus impurity present originally in the iron, is oxidized and reacted with the calcium and magnesium oxides in the lining of the furnace to form slag. Such phosphate-containing slag is useful as fertilizer. The phosphorus and iron values in ferrophos are thus recovered. Phosphorus in the concentration of 0.1 to 0.3% as an alloying element in iron greatly increases its strength and corrosion-resistance. Another interesting application for phosphorus in steel is the preventing of sticking of steel sheets together when several sheets 80 are pack rolled . Phosphorus has a marked effect in improving the hot and cold roll characteristics, softening, recrystallization, and grain growth of copper. Alloys of copper with 2-6% phosphorus can be hot-rolled at 450-650° down to 0.021 in. in thickness. This rolling is carried out with light passes which favors the breaking of the copper-copper phosphide 80 eutectic . One application for reactive phosphides depends on their property of releasing the highly toxic phosphines when reacted with moisture. Thus aluminum phosphide is used 81 in formulations for fumigants . Zinc phosphide has been used as the poison ingredient 80

J. R. van Wazer, Phosphorus and Its Compounds, Vol. II, pp. 1823-55, Interscience Publishers Inc., New York (1961). si L. Hüter, U.S. 2,826,486, March 11, 1958, to Deutsche Gold und Silber Scheideanstalt vormals Roessler.

414

P H O S P H O R U S I A R T H U R D . F. T O Y 82

in baits for rodents . Zinc phosphide was reported to have a toxicity (mg/kg) to hens 83 of 10-11, to ducks and geese of 8-10, and to pigs of 10-12 . For comparison, the toxicity (mg/kg) of H C N to birds is 0.1 and to rabbits 4. Calcium phosphide, when reacted with water, releases spontaneously flammable phosphines. This property makes it an important ingredient in certain types of navy sea flares. Phosphides of tantalum, tungsten, and niobium are resistant to oxidation at high temperature. It has been suggested that nose cones of space vehicles made of these metals be coated with layers of the respective phosphides to protect against too rapid oxidation 84 upon re-entry and passage through the atmosphere . Many phosphides are semiconductors. The energy gap Ε in eV for BP = 4.5, AIP = 2.5, 78 GaP = 2.25, InP = 1.25 . Thus some of these phosphides are proposed as ingredients for transistors.

3. P H O S P H O R U S H Y D R I D E S A N D P H O S P H O N I U M

COMPOUNDS

Investigations on phosphorus hydrides began in the latter part of the eighteenth century. The best known members of this class of compound are phosphine, PH3, and biphosphine, P2H4. The compound P H has been characterized only by spectroscopic means. Some of the higher phosphines have been isolated, but not fully characterized. 3.1. T H E P H M O L E C U L E

The P H molecule does not exist at room temperature. It is formed by the reaction of phosphorus vapor with hydrogen and detected by the prominent spectral band at 3 3 3 3400 Â. This corresponds to the Π -> Σ transition with a ground state of Σ ~ 85 86 The P H distance has been found to be 1.43 Â or a single b o n d . Peyton in his spectroscopic study of the green chemiluminescence from an atomic reaction between Η atom 3 and Ρ vapor, postulated that besides the Σ ~ ground state, there is also a new electronic ι + Σ state. Spectra of P H molecules are also observed in the shock wave decomposition 8 7

of argon-diluted P H 3 . 3.2.

PHOSPHINE

Preparation There are many methods for the preparation of phosphine. Convenient preparative methods for the laboratory are : 1. By the hydrolysis of a metal phosphide such as aluminum phosphide or calcium 88 phosphide. An example of this method is that described by Baudler, Ständeke and Dobbers for the preparation of several hundred grams quantity of phosphine at one time. It involves the hydrolysis of calcium phosphide, and the by-products P2H4 and higher phosphines 82 J. H. Krieger, Agr. Chemicals 7 (No. 4) (1952) 46-48, 135-43. 83 M. N. Mirianashrili, Sb. Tr.y Gruz. Zootekh-Vet, Ucheb-Issled. Inst. 35 (1965) 415-17. 84 H. A. Wilhelm and J. H. Witte, U.S. 3,318,246, May 9, 1967, to U.S. Atomic Energy Commission. 85 J. R. van Wazer, Phosphorus and Its Compounds, Vol. I, pp. 179-93, Interscience Publishers Inc., New York (1958). 86 M. Peyron, U.S. Dept. Com. Office Tech. Serv. (1961) A. D. 271740. 87 H. Guenebaut and B. Pascat, Compt. Rend. 255 (1962) 1741-3. »8 M. Baudler H. Ständeke and J. Dobbers, Z. anorg. u. allgem. Chem. 353 (1967) 122-6.