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17 Mass Spectrometry of Molecules of the Nitrogen Family K. DOUGLAS CARLSON, FRED J. KOHL, and O. MANUEL UY

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Case Institute of Technology, University Circle, Cleveland, O h i o

Mass spectrometric

studies

of the gaseous

duced from solid compounds ments are briefly

molecules

of the nitrogen

summarized.

The

family

variety

and nature

the solids are examined first to demonstrate for observing

complex

temperatures.

Then

these molecules shown

variety

are observed.

between

parent

and fragmented

absolute

partial

pressures

various

homonuclear

correlated comparable

examples.

and heteronuclear

with the polymeric binding

species

of the parent

with some specific

energies

elevated

are described.

of both parent

nature of the

and of

of

possibilities

and characterization

The problems

scribed

the

in these systems at

by mass spectrometry

that a wide

ion species

molecules

the detection

pro­ of ele­

of It is

fragmented differentiating

and of

estimating

molecules

The existence molecules

are

de­

of

the

can

of the solids and

be the

molecules.

A toms of the Group VA family of elements Ν, P, As, Sb, and Bi combine among themselves to form an interesting class of diatomic and tetratomic molecules and perhaps molecules of a more complex nature. The homonuclear species, such as P , As , P 4 , and As , are well known from early vapor density and more recent mass spectrometric investigations of the vaporization properties of the solid elements. The heteronuclear species, such as AS2P2, have been observed only recently in studies of the vaporization of mixtures and binary compounds of the elements. This paper presents a brief introduction and summary of current systematic studies of these molecules by mass spectrometry. Because the solid-vapor systems of the pnictides are complex, and for various reasons are intrinsically difficult to study quantitatively, there 2

2

4

245

Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

246

MASS S P E C T R O M E T R Y

IN INORGANIC C H E M I S T R Y

are m a n y details that c a n n o t b e c o v e r e d i n this p a p e r .

Instead, our i n ­

t e n t i o n is to present here a b r o a d b u t b r i e f s u r v e y o f these systems, d r a w ­ i n g u p o n b o t h o u r w o r k a n d t h a t of others a n d e m p h a s i z i n g the a p p l i c a ­ tions of mass spectrometry. T h e i n t e r - p n i c t i d e m o l e c u l e s are of g e n e r a l interest as a d d i t i o n a l examples of the c o m p l e x i t y of the v a p o r phase a b o v e s o l i d i n o r g a n i c m a t e r i a l s at e l e v a t e d temperatures. S p e c i f i c a l l y , t h e y are o f interest h e r e as examples of systems that r e q u i r e the f u l l a p p l i c a t i o n of mass spec­ t r o m e t r i c t e c h n i q u e s c o m b i n e d w i t h s u b s i d i a r y experiments.

Most im­

portant, these m o l e c u l e s p r o v i d e a u s e f u l class of r e l a t e d m o l e c u l e s for

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a systematic s t u d y of the c h e m i c a l b o n d i n g effects i n a series of i n o r g a n i c species h a v i n g s i m i l a r c h e m i c a l b o n d s a n d r e l a t e d s y m m e t r y p r o p e r t i e s . Solid

Phases C h a r a c t e r i s t i c s of the solids of the G r o u p V A elements are f a i r l y w e l l

k n o w n . T h e r e are s e v e r a l a l l o t r o p i e forms a n d b o t h stable a n d metastable phases. A n i n t e r e s t i n g feature of m a n y of these solids is t h e i r p o l y m e r i c c o m p o s i t i o n i n v o l v i n g chains of t e t r a h e d r a l units. B e c a u s e of this k i n d of a t o m i c a r r a n g e m e n t , t h e i r v a p o r i z a t i o n at e l e v a t e d t e m p e r a t u r e s p r o d u c e s t e t r a m e r i c a n d d i m e r i c v a p o r molecules. T h e r e is m u c h less k n o w n a b o u t the b i n a r y a n d h i g h e r c o m p o u n d s of these elements.

T h e best k n o w n

s o l i d i n t e r - p n i c t i d e c o m p o u n d is P3N5, b u t the other s o l i d n i t r i d e s A s N , S b N , a n d B i N h a v e b e e n r e p o r t e d i n the o l d e r l i t e r a t u r e . C o m b i n a t i o n s of A s a n d P , S b a n d A s , B i a n d A s , a n d B i a n d S b f o r m v a r i o u s s o l i d s o l u t i o n phases. N o s o l i d p h o s p h i d e s of S b or B i h a v e b e e n r e p o r t e d . A l t h o u g h the first h o m o g e n e o u s s o l i d p h o s p h o r u s n i t r i d e , P N 5, w a s 3

p r e p a r e d i n 1903 f r o m a r e a c t i o n of P S 2

5

and N H

3

( 5 3 ) , chemists h a v e

l o n g b e e n s y n t h e s i z i n g v a r i o u s solids c o n t a i n i n g b o t h n i t r o g e n a n d p h o s ­ p h o r u s , s u c h as p h o s p h o n i t r i l i c c o m p o u n d s , m e t a p h o s p h i m i c acids a n d phosphorus amides.

A m o r p h o u s solids w i t h N / P ratios r a n g i n g f r o m

u n i t y to 1.7 h a v e b e e n r e p o r t e d (34, 35, 36, 38, 39,44).

T h e inconsistency

of n o m e n c l a t u r e a n d analysis i n p u b l i s h e d r e s e a r c h makes i t difficult to ascertain " w h e t h e r or not the m a t e r i a l d e s c r i b e d as p h o s p h a m b y one is t h e same as the m a t e r i a l d e s c r i b e d as p h o s p h o r u s n i t r i d e b y (34, 5 5 ) , or w h e t h e r t h e y w e r e not ( P N C 1 ) 2

(37),

P3N5

W

(43,

44)

another"

and P ( N H ) 2

2

3

w h i c h are p r o d u c t s f o r m e d f r o m t h e r e a c t i o n u s e d to p r e p a r e from N H

3

and ΡΟ . Γ )

It seems r a t h e r c e r t a i n at this t i m e that

P3N5 is the o n l y c r y s t a l l i n e b i n a r y s o l i d phase i n the P - N system. C r y s t a l ­ l i n e P3N5 has a f a i n t orange color, is i n e r t at r o o m t e m p e r a t u r e , n o n hygroscopic, a n d exhibits no appreciable decomposition i n v a c u u m u p to ~

700°C.

A l t h o u g h i t exhibits sharp x-ray diffraction p o w d e r

pat­

terns, i t is c o m p l e x , a n d a c r y s t a l l o g r a p h i c analysis has n o t b e e n c a r r i e d

Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

17.

CARLSON E T AL.

Nitrogen

247

Family

out. It is p r e s u m e d to b e a h i g h p o l y m e r n e t w o r k w h i c h is either p l a n a r or t h r e e - d i m e n s i o n a l ( 5 5 ) .

T h e r m o d y n a m i c d a t a for s o l i d P N 3

5

is sparse

and apparently unreliable. T h e f o r m a t i o n of A s N w a s first r e p o r t e d i n 1904 ( 2 5 ) .

It is a r e d -

orange s o l i d o b t a i n e d u p o n gentle h e a t i n g of the p r o d u c t s of the r e a c t i o n between A s C l

3

a n d N H . A n o t h e r m e t h o d of p r e p a r i n g a 3

somewhat

i m p u r e s o l i d arsenic n i t r i d e i n v o l v e s the d i s c h a r g e of a n a r c i n a n a t m o s p h e r e of n i t r o g e n , or i n a m i x t u r e of 9 0 % l i q u i d N of m e t a l l i c A s ( 1 2 ) . 250°C.

2

i n the presence

T h e s o l i d decomposes r a p i d l y w h e n h e a t e d a b o v e

N o c r y s t a l l o g r a p h i c or t h e r m o d y n a m i c d a t a exist for s o l i d A s N .

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A n t i m o n y n i t r i d e , S b N , has b e e n p r e p a r e d b y m e t h o d s s i m i l a r to t h a t for the p r e p a r a t i o n of A s N , b y arc d i s c h a r g e i n m i x t u r e s of N S b m e t a l ( 1 2 ) , a n d f r o m t h e reactions of S b C l , S b B r , a n d S b l 3

liquid N

2

(16, 42, 47).

3

3

2

and with

T h e orange n i t r i d e is e x t r e m e l y sensitive to m o i s ­

ture, a n d i t decomposes u p o n h e a t i n g at 5 5 0 ° C . f o r m e d s i m i l a r l y (15, 27, 42)

B i s m u t h n i t r i d e is

a n d is r e p o r t e d to b e e x t r e m e l y u n s t a b l e ,

d e c o m p o s i n g e x p l o s i v e l y to the elements w h e n h e a t e d (12).

A g a i n , no

c r y s t a l l o g r a p h i c or t h e r m o d y n a m i c d a t a exist for s o l i d S b N or B i N . S e v e r a l investigations (30, 32)

o f the a r s e n i c - p h o s p h o r u s system b y

x - r a y p o w d e r d i f f r a c t i o n a n d t h e r m a l analysis h a v e s h o w n the presence of three d i s t i n c t h o m o g e n e o u s phases: the Ρ phase f r o m 0 to 43 a t o m i c % A s , the A s phase f r o m 87 to 100 a t o m i c % A s , a n d the A s P phase f r o m 53 to 74 a t o m i c %

A s . T h e Ρ p h a s e is a d a r k r e d s o l i d a n d gives a n

x - r a y p a t t e r n s i m i l a r to that of a m o r p h o u s r e d P . T h e A s phase is s i m i l a r i n a p p e a r a n c e to m e t a l l i c A s a n d possesses lattice constants close to those of h e x a g o n a l A s . T h e A s P phase consists of b l a c k leaflets s i m i l a r to g r a p h i t e . T h i s phase is i s o m o r p h i c to b l a c k p h o s p h o r u s a n d exists as a side-centered orthorhomic cell (30).

T h e v a r i o u s phases are p r e p a r e d

b y h e a t i n g m i x t u r e s of the elements i n sealed q u a r t z tubes at 600° to 700°C.

N o t h e r m o d y n a m i c d a t a exist for s o l i d A s P .

A l t h o u g h p h o s p h o r u s is s l i g h t l y s o l u b l e i n l i q u i d a n t i m o n y (30)

and

b i s m u t h ( 5 2 ) , n o i n f o r m a t i o n is a v a i l a b l e o n the existence of s o l i d phases or c o m p o u n d s of these elements. I n t e r - m e t a l l i c alloys of a n t i m o n y - a r s e n i c a n d b i s m u t h - a n t i m o n y exist i n the r h o m b o h e d r a l c r y s t a l s t r u c t u r e

(46).

T h e S b - A s system, w h i c h is f o u n d i n n a t u r e as the m i n e r a l a l l e m o n t i t e , exhibits a c o m p l e t e range of s o l i d solutions w i t h a eutectic p o i n t b e ­ t w e e n 22 a n d 29 a t o m i c % A s (48).

W h e r e a s the S b - A s alloys possess

a h i g h e l e c t r i c a l c o n d u c t i v i t y , the B i - S b alloys (46)

are w e l l - d o c u m e n t e d

s e m i c o n d u c t o r s f r e q u e n t l y s t u d i e d w i t h respect to t h e i r t h e r m o e l e c t r i c a n d m a g n e t i c effects.

T h e B i - S b phase ( J O ) forms a c o n t i n u o u s series

of l o w m e l t i n g s o l i d solutions w i t h no eutectic.

I n the B i - A s system,

there is a eutectic at