High-pressure synthesis and X-ray powder structure determination of the nitridophosphate BaP2N4

Article abstract of DOI:10.1016/j.jssc.2004.10.034

The novel nitridophosphate BaP₂N₄ was obtained by means of high-pressure high-temperature synthesis utilizing the multianvil technique (8 GPa, 1400°C). The [PN₂]^- network is isoelectronic with silica. The structure was solved from synchrotron powder data by a combination of direct methods and difference FOURIER synthesis and refined using the RIETVELD method (BaP₂N₄, Pa3, Z = 12, a = 10.22992(2)A). BaP₂N₄ is isotypic with BaGa ₂S₄, BaAl₂S₄ and the high-pressure phase of CaB₂O₄. The ³¹P solid-state NMR yielded a single sharp resonance at 0.4 ppm.

Full text of DOI:10.1016/j.jssc.2004.10.034

ARTICLE IN PRESS
Journal of Solid State Chemistry 178 (2005) 135–141
www.elsevier.com/locate/jssc
High-pressure synthesis and X-ray powder structure determination of
the nitridophosphate BaP N4
2
Ã
Friedrich W. Karau, Wolfgang Schnick
Department Chemie und Biochemie, Ludwig-Maximilians-Universit a¨ t M u¨ nchen, Lehrstuhl f u¨ r Anorganische Festk o¨ rperchemier,
ButenandtstraXe 5-13 (Haus D), D-81377 M u¨ nchen, Germany
Received 7 September 2004; received in revised form 27 October 2004; accepted 28 October 2004
Abstract
The novel nitridophosphate BaP2N4 was obtained by means of high-pressure high-temperature synthesis utilizing the multianvil
À
ꢀ
technique (8 GPa, 1400 C). The ½PN2Š network is isoelectronic with silica. The structure was solved from synchrotron powder data
by a combination of direct methods and difference FOURIER synthesis and refined using the RIETVELD method ðBaP2N4; Pa3; Z ¼
(
31
1
yielded a single sharp resonance at 0.4 ppm.
2; a ¼ 10:22992ð2Þ AÞ: BaP2N4 is isotypic with BaGa2S4; BaAl2S4 and the high-pressure phase of CaB2O4: The P solid-state NMR
r 2004 Elsevier Inc. All rights reserved.
Keywords: High-pressure synthesis; Phosphorus nitrides; Crystal structure; Powder diffraction; Solid-state NMR
1
. Introduction
reconstructive crystallization of highly condensed PN
network structures is not achieved at temperatures
ꢀ
In the past decade, we have performed a detailed
investigation of several nitridophosphates [1–5]. We
have also been able to fully characterize the nitride P3N5
below 1000 C: On the other hand, phosphorus nitride
P3N5 and most of the nitridophosphates decompose
ꢀ
above 850 C: Therefore, specific synthetic approaches
[
6–8] which is the binary parent compound of all
have been developed for the synthesis of highly
condensed PN compounds like P3N5 [6] or HP4N7
ð¼ P N ðNHÞÞ [10], which have been obtained by
nitridophosphates. Less condensed nitridophosphates
with molar ratio P : Np1 : 2 usually exhibit PN
substructures in analogy with conventional (oxo)sili-
4
6
pyrolysis of particular molecular precursor compounds
cates or (oxo)phosphates (e.g. HPN ð¼ PNðNHÞÞ;
like PðNH Þ I or ðNH Þ PðSÞNPðNH Þ ; respectively.
2
2 4
2 2
2 3
Li10P4N10; Ca2PN3) [9]. These are obtained by conven-
tional solid-state reactions of the respective binaries.
Only a very few nitridophosphates with molar ratio P :
N ¼ 1 : 2 have been obtained analogously, e.g.
LiPN2; Zn7P12N24Cl2 [9].
Nevertheless, this approach cannot be easily extended to
other highly condensed metal nitridophosphates with
molar ratio P : N41 : 2:
Recently, we achieved the synthesis of novel, highly
condensed ternary nitridophosphates by the reaction of
the respective metal azides with P N utilizing high-
According to our experience, nitridophosphates with
molar ratio P : N41 : 2 cannot be synthesized by simple
reactions of the respective binary starting materials,
because the resulting highly condensed PN network
structures do not easily crystallize. On the one hand, the
3
5
pressure reactions (around 3.5 GPa) [1,2]. Typically,
þI
þI
these nitridophosphates (e.g. M P N with M
4
¼
7
þI
þI
Na; K; Rb; Cs; M3 P6N11 with
M
¼ Rb; Cs) have
crystal structures deriving from those of isoelectronic
alkaline earth (oxo)gallates and (oxo)aluminates.
Now, we are targeting novel metal nitridophosphates
with molar ratio P : N ¼ 1 : 2: These compounds are
Ã
Corresponding author. Fax: +49 89 2180 77440.
E-mail address: wolfgang.schnick@uni-muenchen.de (W. Schnick).
0022-4596/$ - see front matter r 2004 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2004.10.034

ARTICLE IN PRESS
F.W. Karau, W. Schnick / Journal of Solid State Chemistry 178 (2005) 135–141
136
made up of PN network structures which are isoelec-
tronic with SiO2: LiPN2 and Zn7P12N24Cl2 [9], which
are obtained by conventional solid-state reactions (see
2.2. Synthesis of barium azide
Barium azide was obtained by the reaction of barium
hydroxide with an aqueous solution of HN3; synthesized
from NaN (Merck, p.a.) and H SO by destillation, in
À
above), already contain SiO2 analogous ½PN2Š network
structures. Now, we utilized the azide route (see Section
) for the synthesis of novel nitridophosphates with
3
2
4
2
accordance with [12]. BaðN Þ was dried over P O
3
2
4
10
molar ratio P : N ¼ 1 : 2: The first example is BaP2N4;
using a vacuum desiccator.
which is described in this contribution.
2.3. Synthesis of BaP N
2
4
The high-pressure synthesis of BaP2N4 was carried
out using the multianvil technique and a hydraulic press
13,14] according to Eq. (2). Cr O -doped MgO
octahedra (Ceramic Substrates & Components Ltd, Isle
of Wight) with an edge length of 18 mm were used. Eight
truncated tungsten carbide cubes separated by pyro-
phyllite gaskets served as anvils for the compression of
the octahedra. The truncation edge length was 11 mm.
A mixture of barium azide and partially crystalline
phosphorus(V) nitride, prepared as described in section
2
. Experimental procedure
[
2
3
As outlined before, increasing the temperature above
ꢀ
8
50 C does not activate the desired reconstructive
crystallization of nitridophosphates to a long-range
ordered and crystalline structure, but it causes an
irreversible thermal decomposition under evolution of
N : Therefore, crystalline and highly condensed phos-
2
phorus nitrides were synthesized at both high tempera-
ꢀ
tures ð41000 CÞ and high pressures ð45 GPaÞ: To
2.1, was ground thoroughly and loaded into a cylind-
rical capsule of hexagonal boron nitride (Henze,
additionally prevent thermal decomposition of the
phosphorus nitrides, the nitrogen partial pressure was
increased by in situ decomposition of a metal azide
according to Eq. (1). During this reaction the metal
azide is transformed into the respective metal nitride
which immediately reacts with the phosphorus nitride
under formation of the desired product according to Eq.
2
Kempten) with a capacity of 35 mm and sealed with a
BN cap. The capsule was centered within two nested
graphite tubes, which acted as an electrical resistance
furnace. The remaining volume and both ends of the
sample capsule were filled out with two cylindrical pieces
of magnesium oxide. The arrangement was placed into a
zirconium dioxide tube and then transferred into a
pierced MgO octahedron. The electrical contact of the
graphite tubes was arranged by two plates of molybde-
num.
(
2) (the so-called azide route).
ꢀ
41000
C
3
BaðN3Þ2 À! Ba3N2 þ 8N2;
(1)
(2)
43:5 GPa
ꢀ
1400
C
The assembly was compressed up to 8 GPa at room
ꢀ
2
P N þ 3 BaðN Þ À! 3 BaP N þ 8 N :
3
5
3 2
2
4
2
8
GPa
temperature within 3.5 h and then heated up to 1400 C
within 25 min. Under these conditions the sample was
treated for 40 min and finally cooled down to room
temperature during 1 h. Subsequently, the pressure was
released within a period of 8 h. After the reaction was
completed, about 95 mg BaP N were obtained as a
The high-pressure reactions were performed utilizing the
multianvil technique and a WALKER-type module. Under
these conditions the reaction temperature could be
increased up to 1500 C without decomposition of the
phosphorus nitrides. Details of the experimental setup
are given in [7].
ꢀ
2
4
colorless and crystalline powder.
The temperature was calculated from the electrical
power applied to the furnace which was determined on
the basis of calibration curves from measurements
with W97Re3–W75Re25 thermocouples, as described in
As starting materials for the high-pressure high-
temperature synthesis of BaP2N4 we used P3N5 and
BaðN3Þ : These compounds were synthesized starting
2
from
commercial
Merck, p.a.) and gaseous ammonia (Messer Gries-
hexachlorocyclotriphosphazene
[
14,15].
(
sheim, 3.8) as well as barium hydroxide (Merck, p.a.).
2.4. Solid-state NMR investigation
3
1
2
.1. Synthesis of phosphorus(V) nitride
The P MAS NMR spectrum (Fig. 1) was acquired
with a rotation frequency of nrot ¼ 15 kHz using a
conventional FOURIER-transform NMR spectrometer
DSX Avance (Bruker, Germany) working with a
Phosphorus(V) nitride was obtained by the reaction
of gaseous ammonia with hexachlorocyclotriphospha-
zene in accordance with [11]. The reaction was carried
3
1
resonance frequency n ¼ 202:5 MHz for the P nuclei.
0
ꢀ
out at 950 C in a gas flow of dried ammonia (dried by
flowing through a column ðl ¼ 1000 mm; + ¼ 50 mmÞ
The data collection was carried out with a single pulse
sequence and a repetition delay of 200 s to guarantee
ꢀ
filled with KOH pellets).
complete relaxation. The 90 pulse length was adjusted

ARTICLE IN PRESS
F.W. Karau, W. Schnick / Journal of Solid State Chemistry 178 (2005) 135–141
137
6
5
4
3
2
1
000
000
000
000
000
000
0
obtained using the routine refcalc implemented into
GSAS and converted into a h k l f 4 file readable by
SHELX-97 [20] using a data conversion routine written
in FORTRAN. The Ba and P atoms were found using
SHELXS by direct methods. The nitrogen atoms were
located from the difference FOURIER map and added
step-by-step during the refinement procedure. The
crystallographic data are summarized in Table 1.
The profile fit was performed utilizing a pseudoVOIGT
function [21] with asymmetry correction [22]. The
anisotropic displacement factor has the form
2
%
2
%
2
%
%
expðÀ2p ½ðha Þ U11 þ Á Á Á þ ðlc Þ U33 þ 2U23klb c þ
-
1000
%
%
%
%
-100
-50
0
50
100
2U hla c þ 2U hka b ފÞ: U is defined as one-third
1
3
12
eq
δ [ppm]
of the trace of the U tensor.
ij
Later on the preparation of phase-pure BaP2N4 was
successful. Further details of the crystal structure
analysis may be obtained from the Fachinformations-
zentrum Karlsruhe, D-76344 Eggenstein-Leopoldsha-
fen, Germany, by quoting the depository number CSD-
414350.
3
1
Fig. 1. P MAS NMR spectrum of BaP2N4:
to 2:1 ms: The spectrum is referenced according to
phosphoric acid (85%).
The crystallographic results are consistent with the
P-NMR spectrum (Fig. 1). The spectrum shows
one P signal at 0.4 ppm corresponding with one
crystallographic phosphorus site (see Table 2). The
observed chemical shift is in the same region
3
1
2
.5. X-Ray powder diffraction
3
1
Initially the powder diffraction pattern collected on a
Stoe StadiP diffractometer (Stoe &Cie, Darmstadt)
using MoKa1 radiation could not be indexed unam-
biguously. This shortcoming resulted from the presence
of an unknown and uncharacterized minor phase, which
could only be discovered using synchrotron radiation
(
À23:5 ppm ðNaP4N7Þ to 54:6 ppm ðLi7PN4Þ) as those
of other ternary nitridophosphates. An overview is given
in [25]. Likewise it agrees with the shift of other
nitridophosphates with a molar ratio P : N ¼ 1 : 2; e.g.
LiPN [23] with a shift of 0 ppm.
2
(
Swiss Norwegian Beamline, Grenoble, histogram see
The thermal stability of BaP2N4 at ambient pressure
was investigated by temperature programmed powder
diffraction on a Stoe StadiP diffractometer with
mounted electrical furnace using MoKa1 radiation.
Surprisingly, neither a phase transition nor decomposi-
Fig. 2). The title compound and the minor phase show
significant differences in the half-widths of the neighbor-
ꢀ
ing main diffraction peaks (BaP N : 0:0237ð3Þ at
2
4
ꢀ
ꢀ
1
1
4:88174ð8Þ (see Fig. 3(a)), minor phase 0:045ð2Þ at
ꢀ
4:4056ð5Þ see Fig. 3(b)). Selecting only the reflections
ꢀ
tion occurred up to 1050 C in air. After about 10 min at
ꢀ
of BaP2N4; an indexation was successful with the
program WERNER [16] (DE-WOLFF figure of merite
Mð20Þ ¼ 90; Mð30Þ ¼ 83; Mð62Þ ¼ 43), implemented
into the program package CMPR [17]. The lattice is
1100 C; amorphization was observed. Accordingly,
cubic BaP N does not seem to be a classical high-
2
4
pressure phase, which would show a thermally induced
first order, irreversible phase transition. Furthermore,
the chemical stability of BaP2N4 against air at high
temperatures significantly exceeds that of the binary
parent compound P3N5; which decomposes above
(
cubic primitive with a lattice parameter of 10:23 A: Fig.
2
(b) shows the resolved diffraction peaks of both the
minor phase and BaP2N4: According to the observed
extinction conditions 0 k l; h 0 l; h k 0 and 0 0 l; the space
group Pa3 unequivocally was derived. The space group
ꢀ
1
850 C in argon atmosphere.
Pn3 could be excluded because of the presence of the
unambiguous indexed reflection (210). The structure
solution and refinement was only possible using space
group Pa3:
3. Description of the structure
The structure was solved on the basis of the integrated
intensities from a LE BAIL fit performed in the space
group Pa3 with the program GSAS [18] implemented
into the program package EXPGUI [19]. A file contain-
ing the MILLER indices and integrated intensities was
The result of the crystal structure refinement with the
RIETVELD method based on the synchrotron data is
shown in Table 2. Within the accuracy of the measure-
ment these data agree well with those obtained from
phase pure material utilizing MoKa1 radiation
(Table 3). Selected interatomic bond distances and bond
angles are given in Tables 4 and 5.
1
For the extinction condition 0 k l; h 0 l and h k 0 only cyclic
permutations are permitted.

ARTICLE IN PRESS
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138
Fig. 2. The synchrotron measurement resolves the diffraction pattern of BaP2N4 and the unknown minor phase completely. The inset shows the
good signal-to-noise ratio at high angles. (a) Whole diffraction pattern of BaP2N4 and (b) Histogram of BaP2N4 and minor phase (marked with an
arrow).
1
1
1
1
6000
4000
2000
0000
fit for the main diffraction peak of
cubic BaP N :
FWHM = 0.0237(3) at 14.88174(8)°
calculated
measured
4
4
3
3
2
2
1
50
2
4
fit for the main diffraction peak of
00 the minor phase:
FWHM = 0.045(2) at 14.4056(5)°
calculated
measured
4
area = 9.7(6)·10
50 area = 4.7(2)·104
00
50
00
50
8
6
4
2
000
000
000
000
0
100
50
14.6 14.7 14.8 14.9 15
15.1 15.2 15.3
14.2 14.25 14.3 14.35 14.4 14.45 14.5 14.55 14.6
(a)
2θ [°]
(b)
2θ [°]
Fig. 3. Fitted main diffraction peaks and calculated half-width of cubic BaP2N4 (a) and the unknown minor phase (b) taken from the synchrotron
measurement.
(
The crystal structure of BaP2N4 (see Fig. 4) is isotypic
with that of BaGa2S4; BaAl2S4 [27] and HP-CaB2O4
[29] and LiPN2 [24] (1.599(4) and 1:645ð7Þ AÞ: Accord-
ingly, each 3-ring unit is connected to six other
neighboring units. The resulting framework thus con-
tains 6-and 7 -r ings (see Fig. 6). The N–P–N angles are
between 105.1(3) and 112.5(4) varying around the
respective angles in HPN2 [29] and LiPN2 [24]
2þ
[
framework structure of corner sharing PN tetrahedra
28]. In the crystal there are Ba ions embedded into a
4
2À
(
see Fig. 5). From a formula point of view, the ½P N Š
2
4
substructure is isoelectronic with SiO2: Nevertheless, its
topology is rather different to any known SiO2
polymorph. ½P3N3Š 3-rings (see Fig. 6(a)) occur as
fundamental building units. These 3-rings are exclu-
sively made up of P(1) and N(1). The distances
ꢀ
(107.5(5)–113.4(5), 107.0(5)–114:5ð2Þ ). The P(1)–N(1)–
P(1) angle of BaP2N4 is 121.7(4) and the P(1)–N(2)–P(1)
ꢀ
angle is 125:3ð4Þ according to the respective P–N–P
ꢀ
angles in HPN2 [29] ð130:1ð4Þ Þ and LiPN2 [24]
(
ꢀ
P(1)–N(1) amounts to 1.630(6) and 1:658ð6Þ A; respec-
ð123:6ð8Þ Þ: The cycle class sequence (i.e. the relative
tively (Tables 4 and 5). N(2) connects the 3-ring units
with other 3-ring units. The distance P(1)–N(2) is
frequency of the P N ring sizes occurring in the
n
n
network for n ¼ 1; 2; 3; . . .) has been calculated with
the program TOPOLAN [30] and it amounts to
fÀ; 0; 8; 0; 0; 4; 24; 72; . . .g:
(
(
1:661ð7Þ A and 1:633ð6Þ A; respectively. These values
are similar to the P–N distances determined for HPN2

ARTICLE IN PRESS
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139
Table 1
Crystallographic data for BaP2N4; for the synchrotron and the diffractometer (Stoe StadiP) measurement
Synchrotron
Stoe StadiP
Crystal data
Formula units
12
BaP2N4
Chemical formula
Crystal system, space group
˚
Unit cell dimensions (A)
Cubic, Pa3 (No. 205)
a ¼ 10:22992ð2Þ
1070.575(3)
a ¼ 10:2200ð2Þ
3
(
1067.46(2)
Cell volume ðA Þ
X-ray density, r ðg cmÀ3Þ
4.752
4.766
Data collection
Radiation
Synchrotron
0.7996002
Nobs ¼ 465
12 292
MoKa1
0.70930
˚
Wavelength l (A)
Observed reflections
Measured data points
Nobs ¼ 546
5242
2
Y-range
4:03p2Yp65:485
0.005
7:0p2Yp59:98
0.01
ꢀ
Step size ( )
Refinement with GSAS
Background function
Background points
Profile function
CHEBYSHEV-function
44
PseudoVOIGT funct. with asym. corr.
[9.1450, 9.7950]
32
ꢀ
Excluded regions2Y( )
No excluded regions
[
[
[
[
[
[
[
[
[
11.330, 12.350]
12.790, 13.170]
14.290, 14.630]
16.310, 16.590]
20.770, 20.975]
21.310, 21.955]
23.685, 24.045]
32.165, 32.300]
33.490, 33.785]
2
2
R-values
RðF Þ ¼ 0:053
fit
RðF Þ ¼ 0:063
fit
wRp ¼ 0:117
wRp ¼ 0:080
Rpfit ¼ 0:093
back
Rpfit ¼ 0:061
back
wRp
Rpback ¼ 0:074
¼ 0:082
wRp
Rpback ¼ 0:063
¼ 0:080
Table 2
Atomic coordinates anisotropic and isotropic displacement parameters (multiplied by 100) of BaP2N4 (synchrotron measurement)
Atom
x
y
z
Uiso=eq
U11
U22
U33
U12
U13
U23
Ba(1)
Ba(2)
P(1)
0
0
0
1.09(2)
0.35(1)
0.30(4)
0.08(9)
0.08(9)
1.09(2)
0.35(1)
0.30(4)
0.08(9)
0.08(9)
U11
U11
U11
U11
U11
U11
U11
U11
U11
U11
À0.27(4)
U12
U12
0
U12
U12
0
0.36863(5)
0.1861(2)
0.3225(6)
0.2205(6)
x
x
0.00(2)
0.3342(2)
0.2520(6)
0.4920(7)
0.1088(2)
0.1112(6)
0.0920(6)
0
0
0
N(1)
N(2)
0
0
0
0
The displacement parameters of N(1) and N(2) are set to be equal.
Table 3
Atomic coordinates anisotropic and isotropic displacement parameters (multiplied by 100) of BaP2N4 (MoKa1-diffractometer)
Atom
x
y
z
Uiso=eq
U11
U22
U33
U12
U13
U23
Ba(1)
Ba(2)
P(1)
0
0
0
1.85(3)
1.17(2)
1.25(8)
0.5(2)
1.85(3)
1.17(2)
1.25(8)
0.5(2)
U11
U11
U11
U11
U11
U11
U11
U11
U11
U11
À0.46(6)
U12
U12
0
U12
U12
0
0.36858(9)
0.1850(4)
0.3216(7)
0.2181(8)
x
x
À0.14(4)
0.3341(4)
0.2508(8)
0.490(1)
0.1083(3)
0.1062(9)
0.0979(9)
0
0
0
N(1)
N(2)
0
0
0.5(2)
0.5(2)
0
0
The displacement parameters of N(1) and N(2) are set to be equal.

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140
Table 4
Selected bond distances in A and bond angles in
˚
ꢀ
Atom
Synchrotron
1.630(6)
MoKa1-Diffrac.
P(1)–N(1)
1.635(8)
1.669(8)
1.63(1)
1
.658(6)
1.661(7)
.633(6)
P(1)–N(2)
1
1.60(1)
120.9(6)
129.4(5)
P(1)–N(1)–P(1)
P(1)–N(2)–P(1)
121.7(4)
125.3(4)
Fig. 5. Ba(1) is connected to six N(1) (gray) and N(2) (black) with
(
distances 3.320(6) and 3:011ð6Þ A: The coordination of Ba(1) with N(2)
Table 5
N–P–N angles in
is a significant distorted octahedron. Ba(2) is also connected to six N(1)
(
ꢀ
and six N(2) with distances between 2.811(6) and 3:449ð6Þ A: Therefore
both Ba atoms have a 6 þ 6 coordination sphere. (a) Coordination
Atom
Synchrotron
MoKa1-Diffrac.
sphere of Ba(1) and (b) coordination sphere of Ba(2).
N(1)–P(1)–N(1)
N(1)–P(1)–N(2)
N(1)–P(1)–N(2)
N(1)–P(1)–N(2)
N(1)–P(1)–N(2)
N(2)–P(1)–N(2)
110.2(4)
108.7(4)
109.8(3)
105.1(3)
110.5(3)
112.5(4)
112.5(6)
109.3(5)
107.0(5)
103.4(4)
111.5(5)
113.2(6)
2
þ
the sum of the ionic radii [31]. Both Ba ions are 12-
fold coordinated.
4. Conclusion
In this contribution the first alkaline earth nitridopho-
sphate with molar ratio P : N ¼ 1 : 2; namely BaP2N4; is
described. It was synthesized by means of high-pressure
high-temperature synthesis and characterized by syn-
chrotron powder diffraction and MAS solid state NMR.
Whereas the parent compound P3N5 decomposes above
ꢀ
ꢀ
8
50 C; BaP2N4 is stable up to 1050 C in air.
While other nitridophosphates with molar ratio P :
N ¼ 1 : 2 (e.g. HPN2 [29], LiPN2 [24] and NaPN2 [26])
show structural similarities to silica analogous networks
BaP N forms a PN tetrahedral network, that shows
2
4
4
similarities to thiogallates and thioaluminates. Cur-
þII
rently, we are expanding our focus on M P2N4
compounds of alkaline earth elements or other bivalent
À
metals, which have SiO2 isoelectronic ½PN2Š networks.
Especially we are investigating the compounds
þII
M
expect the transition from an alkaline earth cation
P2N4; with M ¼ Be; Mg; Ca; Sr: For BeP2N4 we
À
containing ½PN Š network (nitridophosphate) to a
2
þII
double nitride, that is completely built up of M
þV
Fig. 4. Crystal structure of BaP2N4; view along [001].
tetrahedra and P tetrahedra. These investigations will
be presented in forthcoming papers.
This arrangement of PN4 tetrahedra forms large
þ
Acknowledgements
2
empty cages in which the Ba ions are situated. The
Ba(1)–N distances are 3.320(6) (Ba(1)–N(1)) and
3
The research of W. Schnick was generously supported
by the Deutsche Forschungsgemeinschaft and the Fonds
der Chemischen Industrie. The authors thank Dr. J.
Senker for the NMR investigation.
(
:011ð6Þ A (Ba(1)–N(2)). The Ba(2)–N distances are
(
between 2.811(6) (Ba(2)–N(1)) and 3:449ð6Þ A
Ba(2)–N(2)). These distances roughly correspond with
(

ARTICLE IN PRESS
F.W. Karau, W. Schnick / Journal of Solid State Chemistry 178 (2005) 135–141
141
Fig. 6. The left figure is a section of the BaP2N4 structure. It shows characteristic 3-rings connected by corner sharing tetrahedra forming 7-rings
view along [001], Ba atoms are left out). The right figure shows the 6-rings (view along [010]). For reasons of clarity only the P-atoms are shown. One
-ring is marked light gray. (a) 3-rings and 7-rings and (b) 6-rings.
(
6
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