L i P N — A Lithium Phosphorus(v) Nitride
Containing the New Complex Anion Ρ Ν ™ * *
1 0
4
1 0
Θ
4
By Wolfgang Schnick* and Ute Berger
Dedicated to Professor Hans Georg von Schnering
on the occasion of his 60th birthday
Phosphorus(v) nitrides, like the nitrides of other light
main-group elements (boron, aluminum, silicon), are poten­
tial starting compounds for the development of new ceramic
materials with special properties. However, a systematic
entry to the class of compounds comprising binary phosphorus(v) nitrides and their ternary compounds with electropos­
itive elements has been hindered in the past, because the
methods used to prepare these compounds did not lead to
defined, pure or monocrystalline products. Recently, we em­
ployed a new method to prepare defined and finely crys­
talline P N P We obtained pure L i P N , as well as L i P N ,
by reaction of the binary nitrides P N and L i N . Exact
structural characterization of these ternary nitrides led to the
first detailed knowledge of the structure of phosphorus(v)
nitrides in the solid state.
"Isolated" Ρ Ν ^ ions were
found in L i P N , whereas, in L i P N , which has a P-N par­
tial structure analogous to /?-cristobalite, P N tetrahedra are
vertex-linked on all sides to produce the highest conceivable
degree of interconnection. Both compounds show a notice­
able cation mobility in the solid state and are therefore novel
lithium ion conductors.
We have now discovered L i P N , a new lithium phos­
phorus^) nitride whose composition lies between those of
L i P N and LiPN and which therefore represents the first
example of a phosphorus(v) nitride with an intermediate
degree of condensation of P N tetrahedra. L i P N can be
prepared by solid-state reaction of the binary nitrides L i N
and P N [Eq. (a)] as well as by reaction of LiPN with L i N
[Eq.(b)] or of L i P N with P N [Eq.(c)]. The title com­
pound is obtained as a colorless powder and as transparent
octahedral single crystals.
111
]
3
5
7
4
3
2
5
3
13,41
7
Θ
4
2
4
151
1 0
7
4
4
1 0
2
4
1 0
4
1 0
3
3
5
2
7
4
3
3
5
161
10Li N + 4 P N
3
3
7
5
2
a
C
S
d
°
>3Li
W crucible, N
1 0
P N
4
(a)
i 0
2
3
2Li N + 4LiPN
3
2
^ ° • Li
W crucible, N
1 0
P N
4
(b)
1 0
2
10U PN
7
4
+ 6P N
3
6
5
3
0
0
,
<
0
d
°
> 7Li
W crucible, Ν2
1 0
P N
4
1 0
(c)
[*] D r . W. Schnick, Dipl.-Chem. U . Berger
Institut fur Anorganische Chemie der Universität
Gerhard-Domagk-Strasse 1
W-5300 Bonn 1 ( F R G )
[**] This work was supported by the Minister fur Wissenschaft und Forschung
des Landes Nordrhein-Westfalen and by the Fonds der Chemischen Industrie.
830
©
VCH Verlagsgesellschaft mbH, W-6940 Weinheim, 1991
0570-0833/9110707-0830 $ 3.50 + .25/0
Angew. Chem. Int. Ed. Engl. 30 (1991) No. 7
171
Single-crystal X-ray structure analysis revealed that
L i P N has an ionic structure and contains the new com­
plex anion P N}{J , which is isoelectronic to molecular phosphorus(v) oxide, P O (Fig. 1). The anion shows ideal T
symmetry in the solid. As expected, the IR spectrum of
L i P N displays six vibrational bands for the complex
anion between 540 und 1070 c m " . The P-N bonds to the
terminal nitrogen atoms of the P N}£® ion are significantly
shorter than those to the bridging Ν atoms (P-N2 158.1(3),
P-Nl 167.6(3) pm). This is presumably due to a greater de­
gree of polar-bond character in the bonds between phospho­
rus and terminal nitrogen.
1 0
4
1 0
e
C A S Registry numbers:
L i N , 26134-62-3; P N ,12136-91-3; LiPN ,60883-1 ;-7;Li PN ,11118-04-0;
3
3
Li^N.o,
5
7
2
4
133670-95-8.
4
4
l 0
4
10
4
l o
l
181
4
[1] E . V . Borisov, E . E . Nifant'ev, Russ. Chem. Rev. 46 (1977) 842.
[2] W. Schnick, J. Lücke, unpublished.
[3] W. Schnick, J. Lücke, J. Solid State Chem. 87 (1990) 101.
(4] W. Schnick, J. Lücke, Ζ . Anorg. Allg. Ctiem. 588 (1990) 19.
[51 W. Schnick, J. Lücke, Solid State Ionics 38 (1990) 271.
[6] The composition of L i P N was determined by elemental analysis (lithium by flame photometry, phosphorus as molybdovanadatophosphate by
photometry, and nitrogen as indophenol by photometry). The absence of
hydrogen ( N - H ) was checked by I R spectroscopy.
[7] L i P N : Fdim, a = J230.9(l)pm, Ζ = 8, Enraf-Nonius C A D 4 diffractometer, M o radiation, graphite monochromator, scan width 2'\ ω scan,
958 measured reflections with 2° ^ Θ < 32°, 166 symmetry-independent
reflections with / ^ 3 σ ( / ) , R
= 0.047, anisotropic refinement. R =
0.074, / ? = 0.042 with w
10.8/(<7 (F )). Further details of the crystal
structure investigation may be obtained from the Fachinformations­
zentrum Karlsruhe, Gesellschaft für wissenschaftlich-technische Information m b H , W-7514 Eggenstein-Leopoldshafen 2 ( F R G ) , on quoting the
depository number CSD-55175, the names of the authors, and the journal
citation.
1 0
1 0
4
4
1 0
l 0
K i
Γ
Γ
0
0
iat
2
w
0
[8] In the I R spectrum ( K B r and P E discs, range 4000 to 150cm" ') the only
vibrational bands observed were those expected on the basis of the site
symmetry (7^) of the complex P N J J ® anion in the solid state: i> (P=N„ ),
1 0 6 7 c m ; <5(P=N„ ), 5 4 1 c m ; cage vibrations, 1000, 839, 778, and
660 c m .
4
- 1
a)(
0
- 1
0
- 1
[9] Κ. E . Almin, A . Westgren, Ark. Kemi Β15 (1942) 1.
[10] Temperature-dependent Guinier photographs revealed no phase transi­
tions between - 100 and + 120 °C for L i P N .
[11] M. Jansen, Μ . Mobs, Ζ . Kristallogr. 159 (1982) 283.
[12] Α . Rabenau, Solid State Ionics 6 (1982) 277.
[13] W. H . Baur, Crystallogr. Rev. 1 (1987) 59.
l 0
e
Fig. 1. Structure of the P N}JJ ion in the solid state (ellipsoids drawn at 50%
probability). Selected distances [pm] and angles [°] (standard deviations in
parentheses): P-N2 158.1(3), P - N l 167.6(3); N1-P-N2 112.7(1), N l - P - N l
105.9(1), P - N l - P 116.0(2).
4
4
1 0
Θ
Surprisingly, the packing of the Ρ Ν | 2 ions in the solid
corresponds to that of molecular A s O in the cubic hightemperature phase arsenolite, despite the differing composi­
tions.
Thus, the P N}JJ° ions in the solid are arranged
in a zinc blende fashion, resulting in an appreciably more
favorable packing of the complex anions compared with, for
example, molecular phosphorus(v) oxide, P O (distorted
body-centered arrangement).
I t is this ionic structure
formed by lithium cations and Ρ Ν } £ anions which renders
possible the space-saving packing, which cannot be achieved
for the topologically comparable and isoelectronic, but un­
charged, P O .
The arsenolite-like packing of the P 0 { £ ions in the solid
forces the Li® ions in L i P N to occupy markedly differ­
ent positions. In addition to trigonal-planar coordination of
Li® ions, tetrahedral and even near-octahedral coordination
by nitrogen are found. Finally, one-tenth of the Li® ions in
L i P N are distributed with disorder over positions with
a multiplicity higher than the actual number of atoms. The
L i - N contact distances (193-220 pm) correspond roughly to
the sum of the ionic r a d i i
and they increase, as expect­
ed, with the coordination number of the cations.
The close packing of the complex anions realized here is
apparently caused by the tendency toward coordinative sat­
uration of the Li® ions. Owing to the topology of the com­
plex Ρ Ν | ο ions, however, it is not possible to coordi­
nate the relatively large number of Li® ions (Li®:
p4N}o = 10:1) in the same way. For this reason the Li®
ions are distributed over positions that, from the viewpoint
of crystal chemistry, are surrounded by nitrogen in an un­
usual number of different ways. Analogously to L i P N and
L i P N , we expect L i P N to exhibit a significant lithium
ion conductivity.
4
4
e
19, 1 0 1
4
4
10
1111
Θ
4
4
10
θ
4
1 0
l 0
4
4
1 0
1 0
1 1 2 , 1 3 1
θ
4
e
7
2
1 0
4
4
1 0
Received: January 15, 1991 [Z4387 I E ]
Publication delayed at authors' request
German version: Angew. Chem. 103 (1991) 857
Angew. Chem. Int. Ed. Engl. 30 (1991) No. 7
© VCH Verlagsgesellschaft mbH, W-6940 Weinheim, 1991
0570-0833/91/0707-0831 S 3.50 + .25/0
831