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
