A systematic approach to alkali biuretooxophosphates

Article abstract of DOI:10.1002/ejic.201101317

Biuretooxophosphates represent a link between carbon nitride and phosphorus (oxo)nitride precursor chemistry being closely related to cyanurates and trimetaphosphimates. The group of alkali biuretooxophosphates has been complemented by the synthesis of four salts M[PO₂(NH) ₃(CO)₂]·xH₂O in which M = Li, K, Rb, and Cs (x = 1, 0, 0.5, 0, respectively). The structures were solved by single-crystal X-ray diffraction and compared with the corresponding ammonium and sodium salts. For all of the salts, the 1-phospha-2,4,6-s-triazine ring exhibits a nearly planar conformation with the phosphorus atom being slightly deflected. In the sequence Li to Cs, the crystal structures show a significant change in orientation leading from a parallel to a perpendicular arrangement of the rings, the latter being bridged by N-H...O bonds. The thermal behavior of the biuretooxophosphates was examined by means of temperature-dependent powder X-ray diffraction measurements and combined thermogravimetric analysis (TGA) and differential thermal analysis (DTA). Moreover, the FTIR and photoluminescence spectra of the salts are discussed.

Full text of DOI:10.1002/ejic.201101317

FULL PAPER
DOI: 10.1002/ejic.201101317
A Systematic Approach to Alkali Biuretooxophosphates
[
a]
[a]
Eva Wirnhier and Wolfgang Schnick*
Keywords: Structure elucidation / Biuretooxophosphates / Photoluminescence spectroscopy / Alkali metals
Biuretooxophosphates represent a link between carbon ni-
tride and phosphorus (oxo)nitride precursor chemistry being
closely related to cyanurates and trimetaphosphimates. The
group of alkali biuretooxophosphates has been comple-
phosphorus atom being slightly deflected. In the sequence
Li to Cs, the crystal structures show a significant change in
orientation leading from a parallel to a perpendicular ar-
rangement of the rings, the latter being bridged by N–H···O
bonds. The thermal behavior of the biuretooxophosphates
mented by the synthesis of four salts M[PO
xH
2 3 2
(NH) (CO) ]·
2
O in which M = Li, K, Rb, and Cs (x = 1, 0, 0.5, 0, respec- was examined by means of temperature-dependent powder
tively). The structures were solved by single-crystal X-ray
diffraction and compared with the corresponding ammonium
and sodium salts. For all of the salts, the 1-phospha-2,4,6-s-
triazine ring exhibits a nearly planar conformation with the
X-ray diffraction measurements and combined thermogravi-
metric analysis (TGA) and differential thermal analysis
(DTA). Moreover, the FTIR and photoluminescence spectra
of the salts are discussed.
Introduction
With both s-triazine (1a) and tri-s-triazine (1b) cores (the
building units of carbon nitride networks) being very stable,
the targeted partial exchange of C by P during the conden-
sation process seems to be rather improbable. A different
approach to obtain well-defined phosphorus carbon nitride
compounds is the use of suitable precursors containing pre-
organized C-N-P motifs. Recently, Kroke et al. reported on
several s-heptazine-based iminophosphoranes C N -
Graphite-type carbon nitride networks have recently
gained significant interest regarding their exceptional chem-
ical stability and their manifold properties. Among others,
the ability to act as heterogeneous metal-free catalyst for
CO reduction and water splitting as well as the photovol-
2
taic effect have been shown for melon,[1–5] the most promi-
nent representative of this class of compounds. However,
with an optical band gap of approximately 2.7 eV, resulting
in absorption only of blue light up to 450 nm, pure melon
6
7
(
N=PR ) (R = methyl, ethyl, etc.), which can be seen as
3 3
[12]
exocyclic doped carbon nitride precursors.
Exchanging
one carbon ring atom in s-triazine-based compounds by
phosphorus may lead to precursor molecules with a defined
atomic ratio C/N/P = 2:3:1 (i.e., endocyclic doping). Such
compounds with this 1-phospha-2,4,6-s-triazine (1c) core
is not efficient enough for solar-energy conversion for appli-
cation in photovoltaic devices.[
3,5,6]
Several attempts have
been made to modify the electronic structure of graphite-
like carbon nitrides including chemical doping to alter the
[13]
were already synthesized in 1962 (Scheme 1).
[
5,7–11]
band gap.
In particular, the replacement of carbon
atoms by phosphorus, interpreted in the literature as n-dop-
ing, seems to be a promising strategy to lower the band
gap and shift the absorption more into the visible region,
therefore enhancing the performance of such organic semi-
conductors. Previous attempts based on the copolymeriza-
tion of dicyandiamide and 1-butyl-3-methylimidazolium
hexafluorophosphate indeed showed a shift in the band gap
to lower energies accompanied by a change in color from
[
5]
yellow to brown. However, no well-defined product was
obtained and the different possible doping sites led to a
UV/Vis absorption spectrum that was hard to interpret.
Scheme 1. The s-triazine (1a), tri-s-triazine (1b), and 1-phospha-
2,4,6-s-triazine core (1c).
[
a] Department Chemie, Lehrstuhl für Anorganische
Biuretooxophosphates establish a link between precursor
Festkörperchemie,
compounds of carbon nitride and phosphorus (oxo)nitride
chemistry or on a molecular level between cyanurates (2a)
and trimetaphosphimates (2c) (Scheme 2), the salts of the
latter compound being systematically investigated re-
Ludwig-Maximilians-Universität München
Butenandtstrasse 5–13 (D), 81377 München, Germany
Fax: +49-89-2180-77440
E-mail: wolfgang.schnick@uni-muenchen.de
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201101317.
[
14–19]
cently.
1840
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2012, 1840–1847

A Systematic Approach to Alkali Biuretooxophosphates
(
3c), NH [PO (NH) (CO) ] (3d), Rb[PO (NH) (CO) ]·
4 2 3 2 2 3 2
0
.5H O (3e), and Cs[PO (NH) (CO) ] (3f) could be iso-
2 2 3 2
lated.
Crystal Structures
Scheme 2. The cyanurate anion (2a), biuretooxophosphate anion
(2b), and trimetaphosphimate anion (2c).
All alkali biuretooxophosphates crystallize in space
group P2 /c except for the rubidium salt (3e), which crys-
1
tallizes in the monoclinic space group Cc forming an inver-
sion twin. Crystallographic data and details of the structure
refinements for 3a, 3c, 3e, and 3f are summarized in Table 6.
The first biuretooxophosphate, namely NH [PO (NH) -
4
2
3
[
20,21]
(
CO) ] (3d), was described in 1986 by Neels.
We are
2
now targeting a thorough characterization of biuretooxo-
phosphates as possible precursors for the synthesis of new
C/P/O/N-containing compounds.
For detailed investigation of the crystal structure of the re-
[22]
maining salts, single-crystal X-ray diffraction of 3b
and
[20]
3d
was reproduced. The comparison of simulated and
In this contribution we report on a new approach
towards the preparation of biuretooxophosphates in crys-
talline form. We have complemented the group of alkali bi-
uretooxophosphates and compare their structural and spec-
troscopic properties as well as the thermal behavior of these
air-stable and water-soluble salts.
experimental powder X-ray diffraction patterns of the bulk
phase is shown in Figure S1 (Supporting Information). Be-
sides phase purity, the diffractograms show that all reflec-
tions could be indexed with the known cell parameters and
their observed intensities were in very good agreement with
the calculated diffraction patterns based on single-crystal
diffraction data.
Whereas the potassium salt is isotypic with the ammo-
nium salt, the other alkali biuretooxophosphates exhibit
different crystal structures. In contrast to most trimeta-
phosphimates that adopt almost a regular chair, twist, or
Results and Discussion
+
NH -biuretooxophosphate (3d) was first synthesized by
4
+
oxidation of NH -biuretodithiophosphate (Scheme 3),
4
[
15,19,26–29]
boat conformation,
the biuretooxophosphates are
which was obtained as a byproduct of the synthesis of COS
[
30]
from P4S10 with urea.[
20,21]
nearly planar. Evaluation of the torsion angles (Table 1)
as well as the puckering parameters (amplitude and phase
coordinates that describe the geometry of the ring pucker-
The corresponding sodium salt
3b) was synthesized by ion exchange in aqueous solu-
(
[
22]
tion.
[
31]
ing relative to the plane)
(Table 2) suggest a weak pro-
nounced twist and chair or half-chair conformation for 3b
and 3f, respectively, while the other biuretooxophosphates
exhibit a half-chair conformation due to the fact that the
phosphorus atom maintains its preferred (distorted) tetra-
hedral coordination, whereas all C/N-ring atoms show
more or less the typical coplanar alignment for s-triazine
cores (Figure 1). For 3e, a second type of half-chair confor-
mation, with the nitrogen atom instead of the phosphorus
atom deflected, appears.
Scheme 3. Previous synthesis of 3d by oxidation of NH
4
+-biureto-
[
20]
dithiophosphate.
We have developed a novel approach to synthesize alkali
biuretooxophosphates [except the lithium salt (3a), which
was obtained by ion exchange] in crystalline form by the
controlled hydrolysis of 1,1,3,5-tetrachloro-1-phospha-
Table 1. Angles of torsion for the alkali biuretooxophosphates 3a–
3f.
3a[a]
3b[b]
3c[a]
3d[a]
3e [
3e
(Rb2)
3f[c]
[
23]
2
,4,6-s-triazine in the presence of the corresponding acet-
a]
[a]
(
Rb1)
ate (according to the synthesis of the alkali trimetaphosphi-
[
24,25]
5.87
6.18
13.90
26.16
26.50
13.58
–11.08
–1.34
7.65
–4.89
–3.81
–6.03 –6.28
8.33
–3.77
–14.89
22.28
–17.85
5.84
13.06
–11.62
0.55
5.85
–4.27
–3.55
–8.97
8.81
–5.69
2.82
–2.89
5.96
mates, Scheme 4).
After evaporation of the solvents,
–
4.53
13.98
4.69
9.73
large colorless blocklike crystals of Li[PO (NH) (CO) ]·
2
3
2
–
–
H O (3a), Na[PO (NH) (CO) ] (3b), K[PO (NH) (CO) ]
2
2
3
2
2
3
2
–23.51 –17.22
21.92 15.71
–10.57 –6.94
14.57
[a] Ideal sign sequence for half-chair conformation: x/–x/–x/x/–x/x.
[b] Ideal sign sequence for twist conformation: x/–x/–x/x/–x/–x.
[c] Ideal sign sequence for chair conformation x/–x/x/–x/x/–x.
The bond lengths P–O and P–N (148–150 and 166–
169 pm, respectively) and the angles O–P–O (115–118°) and
O–P–N (108–112°) are in the typical range of trimeta-
phosphimates, whereas the angles N–P–N (98–99°) are
smaller due to the biuretooxophosphate anion being more
Scheme 4. New synthesis route to alkali biuretooxophosphates by
the controlled hydrolysis of 1,1,3,5-tetrachloro-1-phospha-2,4,6-s-
triazine.
Eur. J. Inorg. Chem. 2012, 1840–1847
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1841

E. Wirnhier, W. Schnick
FULL PAPER
Table 2. Puckering parameters for the alkali biuretooxophosphates 3 pm shorter than the C–N(–C) bonds, but both in the
3
a–3f.
range of C–N single bonds. For the angles, the N–C–O
(118–124°) and N–C–N angles (115–119°) are also in typi-
cal ranges relative to cyanurates and cyamelurates, whereas
the distortion of the almost planar ring by the phosphorus
atom becomes more apparent by the appearance of larger
a[a]
3b[b]
3c[a]
3d[a]
3
q
q
2
0.239(2)
0.127(2)
0.7(4)
0.270(1)
61.9(4)
0.123(1)
–0.007(1)
–11.6(6)
0.123(1)
93.4(6)
0.208(1)
–0.111(1)
175.0(5)
0.236(1)
118.1(4)
0.159(1)
–0.074(1)
174.9(4)
0.175(1)
114.9(4)
3
Φ [°]
Q
θ [°]
[32–36]
T
C–N–C angles (127–129°).
A systematic change in the relative orientation of the an-
ionic rings is observed with increasing cation size. Whereas
the rings of 3a and 3b show a nearly parallel arrangement
without building a hydrogen-bonding network (Figure 2
and Figure 3), a slight zig-zag orientation for the rings ap-
pears for 3c and 3d (Figure 3). N–H···O (N···O 278–
3
e (Rb1)[a]
3e (Rb2)[a]
3f[a]
q
q
2
0.645(10)
–1.743(9)
–76.6(6)
1.858(8)
159.7(3)
1.169(22)
2.968(38)
–111.7(4)
3.190(42)
21.5(2)
0.032(2)
0.047(2)
178.5(47)
0.057(2)
33.9(18)
3
Φ [°]
Q
θ [°]
T
295 pm) bonds are bridging the rings, forming intercon-
[a] Ideal puckering parameters for the half-chair conformation: q
2
nected zig-zag strands. One half of the rings in 3e linked by
N–H···O bonds (N···O 281 pm) shows a more pronounced
zig-zag orientation, whereas the other half is aligned verti-
cally, also connected by N–H···O bonds (N···O 279–
2
2 1/2
=
Q
T
sinθ, q
3
= Q
T
cosθ, Q
T
= (q
2
+ q
2
3
)
. [b] Ideal puckering
3 T 2
parameters for twist conformation: q
0°.
϶ 0, q = 0, Q = q , θ =
9
288 pm) (Figure 3e). A 3D network is formed by the con-
nections of both types of rings by two further N–H···O
bonds (N···O 281–284 pm). For 3f, the vertically aligned
rings form a wire-mesh fencelike network by N–H···O
bonds (N···O 273–285 pm) (Figure 3).
Figure 1. View of the half-chair ring conformation of 3a showing
0% probability displacement ellipsoids. H atoms are drawn as
5
small circles of arbitrary size.
Figure 2. Crystal structure of 3a.
planar than the trimetaphosphimate anion.[26–28] The bond
The coordination number of the alkali ions increases
lengths C–O and C–N (120–124 and 133–139 pm, respec- with the ionic radii of the cations, thereby causing an in-
tively) are comparable to the distances observed in cyan- creasing connectivity of the coordination polyhedra. In 3a,
urates and cyamelurates with the C–N(–P) bonds being 2– the lithium ions exhibit a coordination number of four,
Figure 3. Crystal structures of 3b, 3c, 3e, and 3f.
1842
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Eur. J. Inorg. Chem. 2012, 1840–1847

A Systematic Approach to Alkali Biuretooxophosphates
which results in isolated, slightly distorted tetrahedrons visible for the symmetric and asymmetric PO stretching
2
–1
(
103–120°). The sixfold and (5+1)-fold coordination of the vibrations (1100–1070 and 1250–1200 cm ). In accordance
+
+
+
Na , K , and NH ions configuring edge-sharing dis- with trimetaphosphimates, the symmetric and asymmetric
4
torted octahedrons leads to 1D twisted strands along a (3b) P–N stretching vibrations appear between 1000 and
–1
and c (3c, 3d), respectively. The rubidium salt exhibits two 800 cm .
distinct Rb sites, once sevenfold coordinated (Rb1), show-
ing edge-shared strands along a and once sixfold coordi-
nated (Rb2), building corner-shared strands in the a,c
plane. For 3f, the only 2D motif arises by edge-sharing hep-
tagons in the b,c plane. In the case of 3a and 3e, a solvent
water molecule is incorporated to complete the coordina-
tion sphere, which is otherwise built up from both oxygen
species of the PO (NH) (CO) ring. The rings act as mono-
2
3
2
2
dentate and partially bridging (μ ) ligands for the corre-
sponding cations with an increasing number of ligand func-
tionalities with increasing cationic size (Table 3).
Table 3. Number and type of ligand functionalities of the PO
2
-
(
NH) (CO) ring.
3
2
3a
3b
3c/d
3e
3f
1
2
2
2
1
2
O1 (CO)
O2 (CO)
–
μ1
μ1
μ /μ
μ
1
1
1
2
1
2
2
μ
μ
μ
μ
μ
μ /μ
μ
1
2
1
1
O3 (PO
O4 (PO
2
)
)
μ
μ
μ /μ
μ
Figure 4. FTIR spectra of the alkali biuretooxophosphates 3a–f.
2
2
1
2
2
μ
μ
μ /μ
μ
Σ
3
6
6
5/7
7
–
1
Table 4. Vibrational frequencies [cm ] observed in the FTIR spec-
tra of the alkali biuretooxophosphates and their assignment.
The distances M–O are comparable with those of the al-
kali trimetaphosphimates and cyamelurates and are in ac-
cordance with the sums of the ionic radii [Li: 192–197 pm;
3a
3b
3c
3d
3e
3f
Assignment
Na: 230–252 pm; NH : 275–291(369) pm; K: 260–307 pm; 3515 s
3472 w
3410 w
ν(H O)
2
4
Rb: 283–315 pm; Cs: 308–336 pm].[
32–36]
3389 s
ν(H O)
2
3
3
254 s
171 s
3266 s
ν(NH)
3188 m
3175 m 3156 m ν(NH)
ν(NH
3044 vs 3068 vs 3045 m ν(NH)
ν(N–H···O)
2841 s 2814 vs 2826 s ν(N–H···O)
2745 s 2748 s ν(N–H···O)
3
143 vs
+)
4
3047 s
3053 m
2891 m
3054 m
2871 m
2813 m
2746 m
1696 vs
FTIR Spectroscopy
2810 m 2825 m
The FTIR spectra of the alkali biuretooxophosphates are 2735 w 2745 w
1
1
711 vs 1699 vs
643 s
1698 vs 1694 vs 1684 vs ν(C=O)
represented in Figure 4. They exhibit features of both alkali
trimetaphosphimates and alkali cyanurates. Accordingly,
2
δ(H O)
1491 s ν(C–N)
1496 m
the assignment of the bands (Table 4) was accomplished by
1
479 m 1477 m
428 m 1425 m
1470 m
1481 s 1476 vs 1452 s ν(C–N)
comparison with both compound classes.[
14,37]
For all bi-
ν(NH4+)
1456 s
1428 s 1445 vs 1417 m ν(C–N)
1401 s ν(NH
+)
1386 m δ(NH)
1323 vs 1319 vs 1330 vs δ(NH)
1
1429 m
uretooxophosphates, strong absorption in the N–H stretch-
–
1
4
ing region (3300–3000 cm ) occurs. The broadness of the
signals may be due to the participation of the NH groups
in hydrogen bonding, also resulting in weak (for the smaller
cations) and strong (for the bigger cations) bands between
1372 s
1
1
313 vs 1326 s
240 s
1326 s
1245 s
1216 s
1087 s
1224 vs 1194 vs 1211 vs
2
νas(PO )/
δ(NH)
–
1
1105 vs
ν (PO )
3
050 and 2730 cm . These effects are in accordance with
s
2
1079 s
1091 vs
1087 vs 1082 vs 1097 s
ν
ν
ν
s
(PO
2
)
)
the results from the crystal structure analysis, which show
intermolecular hydrogen bonds only between the rings of
1
069 vs 1076 vs
1004 m 1002 s 1007 m
907 s 916 s 914 s
814 m 814 m 815 m
s
(PO
2
1000 w 1001 w
1005 m
901 m
827 m
772 m
as(P–NH)
the salts of the heavier alkali elements. The bending and 918 m 899 m
δ(C–N)
(P–NH)
8
7
08 w
66 m
810 w
757 w
ν
s
wagging modes of the NH groups are also assigned in
Table 4. As for the cyanurates, strong absorption due to
C=O and C–N stretching vibrations occurs around
775 m 766 s
703 vw
642 vs 638 s
585 w 572 w 587 w ν(MO)
532 w 527 m 527 m δ(C=O)
758 m ω(NH)
ω(NH)
697 w
655 s
636 m
629 m
585 w
527 m
470 m
426 w
631 s
2
δ(PO )
–
1
–1
1700 cm and between 1500 and 1420 cm , respectively.
579 vw 577vw
The corresponding bending modes in the biuretooxophos- 529 vw 530 w
phates are observed around 900 (C–N) and 503 cm–1
481 s
16 w
467 w
417 vw
468 s
461 s
432 w 407 s
467 s
δ(NCO)
422 m δ(NCO)
4
(C=O), respectively. Very strong absorption bands are also
Eur. J. Inorg. Chem. 2012, 1840–1847
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1843

E. Wirnhier, W. Schnick
FULL PAPER
Table 5. Excitation and emission maxima of the alkali biuretooxophosphates in solution (solvent = H
2
O, c = 2ϫ10–3 molL–1).
4a
3
a
3b
3c
3d
3e
3f
4b
λ
λ
ex,max [nm]
em,max [nm]
264/344
390
269/333
374
260/329
371
253/290/ 327
369
267/ 354
403
252/ 324
365
253/ 288/ 326
379
289/ 334
366
Photoluminescence Spectroscopy
The excitation and emission spectra of the alkali biureto-
–
3
–1
oxophosphates in aqueous solution (c = 2ϫ10 molL )
are displayed in Figure S2 (Supporting Information). Exci-
tation and emission maxima are summarized in Table 5.
The excitation spectra of the alkali biuretooxophosphates –
recorded at the wavelength of the emission maximum –
show two maxima in the UV region (252–269 and 324–
3
54 nm, respectively) with the second signal being less in-
tense. Emission occurs close to the UV/Vis transition (365–
03 nm). For comparison, spectra of the sodium salts of the
cyanurates and trimetaphosphimates [NaH C N O ·H O
4
2
3
3
3
2
(
4a) and Na (PO NH) ·H O (4b)] were measured. Exci-
3 2 3 2
tation and emission maxima of these two compounds
(
Table 5) are in the same range as those for the alkali biureto- Figure 5. Decomposition temperatures of alkali cyanurates and al-
kali biuretooxophosphates (3a–f).[
37]
oxophosphates, with the maxima of the sodium biuretooxo-
phosphate being located in between. Further comparison
with the excitation and emission maxima of tri-s-triazine-
based compounds like melem (2,5,8-triamino-s-heptazine;
The decomposition of the alkali biuretooxophosphates is
accompanied by a continuous mass loss and endothermic
signals, which presumably indicate the release of gaseous
byproducts like CO , HNCO, and NH . The formation of
[38]
λex,max = 288 nm, λem,max = 366 nm),
2,5,8-triazido-s-
heptazine (λem,max = 430 nm),[ and 2,5,8-trichloro-s-hept-
azine (λex,max = 310 nm, λem,max = 468 nm)[ provides an
indication that the ring substituents have more influence on
the luminescent properties than the cations, thus changing
the electronic properties of the ring systems. Showing a sig-
nificant shift compared to the other tri-s-triazine based
compounds, the excitation and emission maxima of melem
are therefore closer to the biuretooxophosphates due to
39]
40]
2
3
the corresponding cyclic and linear metaphosphates
MPO ) as intermediates can be observed by temperature-
(
3
x
dependent powder X-ray diffraction patterns, accompanied
by an endothermic signal in the DTA curves of the less
heavier cations (3a: 354 °C; 3b: 357 °C; 3c: 329 °C; 3e:
296 °C).
similar electron-donating strengths of NH and OH.
2
Conclusion
In this contribution, we have presented a novel approach
to the alkali biuretooxophosphates M[PO (NH) (CO) ]·
2
3
2
Thermal Analysis
xH O (in which M = Li, Na, K, NH , Rb, Cs and x = 1,
2
4
0, 0, 0, 0.5, 0, respectively) with detailed investigation of
The thermal behavior of the alkali biuretooxophosphates crystal structures, FTIR and PL spectroscopic properties,
was examined by combined thermogravimetric analysis as well as the thermal behavior. From a structural point of
(TGA) and differential thermal analysis (DTA) measure- view, the biuretooxophosphates can be interpreted as inter-
ments (Figure S3 in the Supporting Information) and tem- mediates between precursor compounds in carbon nitride
perature-dependent powder X-ray diffraction analysis. For and phosphorus (oxo)nitride chemistry, the cyanurates and
the monohydrated lithium salt and the semihydrated rubid- the trimetaphosphimates. Temperature-dependent powder
ium salt the release of crystal water is visible at 190 °C X-ray diffraction analysis as well as combined DTA/TG
(
(
mass loss observed: 10.2%, calculated: 9.5%) and 170 °C measurements showed the stability of the 1-phospha-2,4,6-
mass loss observed: 5.0%, calculated: 3.5%), respectively. s-triazine ring up to temperatures of at least 200 °C. The
The resulting dehydrated lithium biuretooxophosphate is decomposition of the ring at higher temperatures is ac-
stable up to 320 °C; the thermal stability of the other salts companied by the formation of the corresponding meta-
decreases with increasing atomic mass of the alkali cation phosphates (MPO ) , therefore indicating a breakup of the
3
x
(
Figure 5); an analogous observation has been reported for ring next to the phosphorus atom and to a release of the
[
37]
the cyanurates.
remaining ring in the form of gaseous byproducts like CO2,
1844
www.eurjic.org
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2012, 1840–1847

A Systematic Approach to Alkali Biuretooxophosphates
HNCO, and NH . To use the biuretooxophosphates as pre- the corresponding acetate M(OOCCH
3
) [15.12 mmol; M = Na
3
(
Merck, 99%), NH
4
(Merck, 98%), K (Grüssing, 99%), Rb (Alfa
O (5 mL). A tempera-
cursors for the synthesis of crystalline C(O)NP networks it
is essential to keep the preorganized C-N-P motif intact or
at least to prevent the disappearance of the CN parts of the
ring. According to Le Chatelier’s principle, future work will
focus on pyrolysis of the biuretooxophosphates under ele-
vated pressure (for example, in an autoclave or by using a
high-pressure apparatus) to avoid the complete decomposi-
tion of the preorganized C-N-P motif and to enable the
synthesis of well-defined phosphorus-doped carbon nitride
networks.
Aesar, 99.8%), Cs (Alfa Aesar, 99.9%)] in H
2
ture of 55–60 °C was maintained, first by cooling with an ice bath,
later by heating in an oil bath. After cooling down to room tem-
perature and evaporation of the solvent, the product was obtained
as colorless blocklike crystals. The corresponding alkali chlorides
can be removed by stirring the precipitate in methanol (50 mL).
Lithium biuretooxophosphate monohydrate (3a) was obtained by
an ion-exchange reaction in aqueous solution at room temperature.
An aqueous solution of LiCl (75 mL; 9.7 g, 0.228 mol, Sigma–Ald-
rich, 99.9%) was poured onto a column (ion-exchange capacity:
76 mmol) containing a strongly acidic ion-exchange resin (15 mL;
Amberlyst 15, Fluka). After thoroughly washing the column with
+
deionized water (3 L), NH
4
-biuretooxophosphate (3d; 546.3 mg,
.5 mmol) in water (30 mL) was poured onto the column. The elu-
Experimental Section
2
Syntheses: 1,1,3,5-Tetrachloro-1-phospha-2,4,6-s-triazine was syn-
thesized according to the literature[ by reacting sodium dicyan-
amide (17.6 g, 0.20 mol, Fluka, 96%) with phosphorus pentachlor-
ide (41.6 g, 0.20 mol, Fluka, 98%) in dichloroethane (600 mL; re-
flux, 12–14 h). The byproduct NaCl was removed by filtration and
the filtrate was evaporated to a concentrated solution of 200 mL.
At 4 °C the product was obtained as large colorless crystals.
ate was collected and crystallized by evaporation of the solvent.
23]
Elemental analysis (wt.-%): 3a: calcd. C 12.71, H 2.67, Li 3.67, N
22.23, P 16.39; found C 12.45, H 2.75, Li 3.55, N 21.73, P 16.07;
3b: calcd. C 12.84, H 1.62, N 22.47, Na 12.3, P 16.56; found C
12.71, H 1.88, N 21.71, Na 12.7, P 14.70; 3c: calcd. C 11.83, H
1.49, K 19.3, N 20.69, P 15.25; found C 11.81, H 1.66, K 18.90, N
19.86, P 13.31; 3d: calcd. C 13.19, H 3.88, N 30.77, P 17.01; found
According to the synthesis of the trimetaphosphimates
C 11.39, H 4.04, N 29.08, P 13.60; 3e: calcd. C 9.29, H 1.56, N
(M+
=
Na , K ),
+
+ [24,25]
the alkali biuretooxo- 16.25, P 11.98, Rb 33.10; found C 9.44, H 1.45, N 16.33, P 11.85,
M
3
[PO
2
NH]
3
phosphates 3b–f were obtained by reaction of 1,1,3,5-tetrachloro-1-
Rb 31.28; 3f: calcd. C 8.09, H 1.02, N 14.15, P 10.43; found C 7.84,
phospha-2,4,6-triazine (300 mg, 1.26 mmol) in dioxane (5 mL) with
H 1.19, N 12.33, P 8.62.
Table 6. Crystallographic data and details of the structure refinement for 3a, 3c, 3e, and 3f.
3a
3c
3e
3f
Formula
Li[PO
189.00
monoclinic
P 2 /c (no. 14)
721.76(14)
683.90(14)
1551.5(4)
117.53(2)
679.1(3)
2
(NH)
3
(CO)
2
]·H
2
O
K[PO
2
(NH)
3
(CO)
2
]
Rb[PO
258.51
2
(NH)
3
(CO)
2
]·0.5H
2
O
2 3 2
Cs[PO (NH) (CO) ]
–1
Molar mass [gmol ]
Crystal system
Space group
a [pm]
b [pm]
c [pm]
203.14
monoclinic
P2 /c (no. 14)
296.95
monoclinic
P2 /c (no. 14)
monoclinic
Cc (no. 9)
926.55(19)
3255.3(7)
670.34(13)
132.07(3)
1500.9(9)
8
1
1
1
585.42(12)
1756.6(4)
691.70(14)
109.65(3)
669.9(2)
4
2.014
0.31ϫ0.16ϫ0.12
0.999
679.16(14)
1486.5(3)
745.37(15)
93.08(3)
751.4(3)
4
2.625
0.12ϫ0.10ϫ0.06
5.112
β [°] 6
3
V [10 pm ]
Z
4
–3
Calculated density [gcm ]
Crystal size [mm ]
Absorption coefficient [mm ] 0.389
1.849
0.12ϫ0.10ϫ0.09
2.279
0.15ϫ0.12ϫ0.11
6.791
3
–1
F(000)
384
none
408
none
992
552
Absorption correction
Min./max. transmission
Diffraction range [°]
Index range
multiscan
0.2704/0.3730
3.03 Յ θ Յ 27.49
–12 Յ h Յ 12
–42 Յ k Յ 42
–8 Յ l Յ 8
228/8
6178
3258
2820
multiscan
0.3820/0.6644
3.30 Յ θ Յ 27.49
–8 Յ h Յ 8
–19 Յ k Յ 19
–9 Յ l Յ 8
112/3
12375
1727
1573
3.13 Յ θ Յ 27.49
–9 Յ h Յ 9
3.34 Յ θ Յ 27.42
–7 Յ h Յ 7
–22 Յ k Յ 22
–8 Յ l Յ 8
112/3
5661
1531
–
–
8 Յ k Յ 8
20 Յ l Յ 20
Parameters/restraints
Total reflections
Independent reflections
Observed reflections
Min./max. resid. electron
density [e 10 pm ]
GooF
129/5
5357
1548
1364
1369
–
–6
–3
–0.395/0.260
1.045
–0.409/0.326
1.076
–1.159/1.161
1.035
–1.412/0.473
1.190
Final R indices [IϾ2σ(I)]
R1 = 0.0279, [
wR2 = 0.0745
R1 = 0.0333, [
wR2 = 0.0783
R1 = 0.0269,
wR2 = 0.0702
R1 = 0.0323,
wR2 = 0.0740
R1 = 0.0581,
wR2 = 0.1429
R1 = 0.0668,
wR2 = 0.1471
R1 = 0.0211,
wR2 = 0.0539
R1 = 0.0239,
wR2 = 0.0558
a]
a]
[b]
[c]
[d]
Final R indices (all data)
[b]
[c]
[d]
2
2
2
–1
2
2
2
–1
2
2
2
–1
[
[
a] w = [σ (F
0
) + (0.0385P) + 0.0388P] . [b] w = [σ (F
0
) + (0.0375P) + 0.3991P] . [c] w = [σ (F
0
) + (0.0997P) + 0.0000P] . [d] w =
2
2
2
–1
2
2
0 0 c
σ (F ) + (0.0286P) + 0.5402P] , for all with P = (F + 2 F )/3.
Eur. J. Inorg. Chem. 2012, 1840–1847
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1845

E. Wirnhier, W. Schnick
FULL PAPER
X-ray Structure Determination: Single-crystal X-ray diffraction
data were collected at 293 K (3a, 3e) and 173 K (3b, 3c, 3d, 3f) with
a Nonius Kappa CCD diffractometer (3a–d, 3f) and a STOE IPDS
[2] F. Goettmann, A. Thomas, M. Antonietti, Angew. Chem. 2007,
119, 2773–2776; Angew. Chem. Int. Ed. 2007, 46, 2717–2720.
[
3] X. Wang, K. Maeda, A. Thomas, K. Takanabe, G. Xin, J. M.
Carlsson, K. Domen, M. Antonietti, Nat. Mater. 2009, 8, 76–
I diffractometer (3e), both using monochromated Mo-K
α
radiation
80.
(
λ = 71.073 pm; Table 6). The diffraction intensities were scaled
[
[
4] Y. Zhang, M. Antonietti, Chem. Asian J. 2010, 5, 1307–1311.
[41]
using the SCALEPACK software package.
For 3a–d no ad-
5] Y. Zhang, T. Mori, J. Ye, M. Antonietti, J. Am. Chem. Soc.
ditional adsorption correction was applied, whereas for 3e and 3f
2
010, 132, 5294–5295.
an absorption correction was performed using the programs
[
6] J.-L. Brédas, J. E. Norton, J. Cornil, V. Coropceanu, Acc.
XPREP and SADABS, respectively.[
42,43]
The crystal structures
Chem. Res. 2009, 42, 1691–1699.
[7] B. Yue, Q. Li, H. Iwai, T. Kako, J. Ye, Sci. Technol. Adv. Mater.
2011, 12, 034401/1–034401/7.
[8] D. Portehault, C. Giordano, C. Gervais, I. Senkovska, S. Kas-
kel, C. Sanchez, M. Antonietti, Adv. Funct. Mater. 2010, 20,
were solved by direct methods using the software package
2
SHELXS-97 and refined against F by applying the full-matrix le-
ast-squares method (SHELXL-97).[
44–46]
Except for 3e, the hydro-
gen positions could be determined from difference Fourier synthe-
ses and were refined isotropically using restraints for oxygen–hy-
drogen and nitrogen–hydrogen distances. All non-hydrogen atoms
were refined anisotropically.
1
827–1833.
[
[
[
[
[
9] G. Liu, P. Niu, C. Sun, S. C. Smith, Z. Chen, G. Q. Lu, H.-M.
Cheng, J. Am. Chem. Soc. 2010, 132, 11642–11648.
10] Y. Wang, H. Li, J. Yao, X. Wang, M. Antonietti, Chem. Sci.
2011, 2, 446–450.
11] Y. Zhang, A. Thomas, M. Antonietti, X. Wang, J. Am. Chem.
Soc. 2009, 131, 50–51.
12] T. Saplinova, C. Lehnert, U. Böhme, J. Wagler, E. Kroke, New
J. Chem. 2010, 34, 1893–1908.
13] H. Beyer, T. Pyl, H. Lemke, J. Prakt. Chem. 1962, 16, 137–144.
[14] A. John, D. Philip, N. Stock, W. Schnick, S. Devanarayanan,
CCDC-854273 (for 3a), -854274 (for 3c), -854276 (for 3e), and
-854275 (for 3f) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Powder X-ray diffraction data were collected on a Stoe STADI
P diffractometer using Cu-Kα1 radiation (for 3a–e) and Mo-Kα1
radiation (for 3f).
Spectrochim. Acta Part A 2001, 57, 959–969.
[
[
15] N. Stock, E. Irran, W. Schnick, Z. Anorg. Allg. Chem. 1999,
625, 555–561.
General Techniques: FTIR measurements were carried out on a
Bruker IFS 66v/S spectrometer. Spectra of the samples were re-
corded in an evacuated cell at ambient conditions between 400 and
16] N. Stock, W. Herrendorf, J. Beck, W. Schnick, Eur. J. Inorg.
Chem. 1998, 469–476.
[17] N. Stock, W. Schnick, Z. Naturforsch. B 1997, 52, 251–255.
[18] S. Correll, N. Stock, W. Schnick, Solid State Sci. 2004, 6, 953–
4
3
000 cm–1 after diluting the samples in KBr pellets (2 mg sample,
00 mg of KBr, hand press with press capacity 10 kN).
9
65.
19] S. Correll, S. J. Sedlmaier, W. Schnick, Solid State Sci. 2005, 7,
261–1271.
[
[
PL measurements were performed on a Photon Technology Inter-
national (PTI) fluorescence system featuring a PTI 814 photomulti-
plier detector and a PTI A1010B xenon arc lamp driven by a PTI
LPS-220B lamp power supply.
1
20] J. Neels, K.-H. Jost, M. Meisel, Z. Anorg. Allg. Chem. 1986,
540/541, 307–318.
[21] J. Neels, M. Meisel, R. Moll, Z. Chem. 1984, 24, 389–390.
[
22] K. K. Palkina, S. I. Maksimova, N. T. Chibiskova, J. Neels, B.
Thermoanalytical measurements were carried out under an inert
atmosphere (He) with a Thermoanalyzer TG-DTA92 (Setaram).
The samples were heated in an alumina crucible from room tem-
Valis, Izv. Akad. Nauk SSSR 1991, 27, 340–346.
[
23] M. Becke-Goehring, D. Jung, Z. Anorg. Allg. Chem. 1970, 372,
233–247.
–1
perature to 600 °C with a heating rate of 5 Kmin .
[24]
M. L. Nielsen, T. J. Morrow, Inorg. Synth. 1960, 6, 99.
[
25] M. L. Nielsen, T. J. Morrow, Inorg. Synth. 1960, 6, 97–98.
26] H. Jacobs, R. Nymwegen, Z. Anorg. Allg. Chem. 1998, 624,
99–204.
Elemental analyses for C, H, and N were performed with the ele-
mental analyzer systems Vario EL and Vario Micro (Elementar
Analysensysteme GmbH). Alkali metal and phosphorus quantifi-
cation was performed by atomic emission spectrophotometry with
inductively coupled plasma (ICP-AES) on a Varian-Vista simulta-
neous spectrometer.
[
1
[
[
[
[
27] N. Stock, W. Schnick, Acta Crystallogr., Sect. C: Cryst. Struct.
Commun. 1996, 52, 2645–2647.
28] N. Stock, W. Schnick, Acta Crystallogr., Sect. C: Cryst. Struct.
Commun. 1997, 53, 532–534.
29] S. J. Sedlmaier, D. Johrendt, O. Oeckler, W. Schnick, Z. Anorg.
Allg. Chem. 2007, 633, 2217–2222.
30] R. Bucourt, Topics in Stereochemistry, vol. 8, John Wiley &
Sons, New York, 1974, pp. 159–224.
Supporting Information (see footnote on the first page of this arti-
cle): Figure S1 with the experimental and simulated powder X-ray
diffraction patterns for 3a–f, Figure S2 with the photoluminescence
spectra of 3a–f, and Figure S3 with the DTA/TG curves of 3a–f.
[
[
31] D. Cremer, J. A. Pople, J. Am. Chem. Soc. 1975, 97, 1354–1358.
32] A. Sattler, W. Schnick, Z. Anorg. Allg. Chem. 2006, 632, 531–
533.
Acknowledgments
[
33] E. Horvath-Bordon, E. Kroke, I. Svoboda, H. Fuess, R. Rie-
del, S. Neeraj, A. K. Cheetham, Dalton Trans. 2004, 3900–
3908.
We gratefully acknowledge financial support that was granted from
the Deutsche Forschungsgemeinschaft (DFG) (project SCHN377/
[34] F. Belaj, E. Nachbaur, Monatsh. Chem. 1987, 118, 1077–1085.
[35] K. Sivashankar, Proc. Indian Acad. Sci. Chem. Sci. 2000, 112,
607–614.
15-1) and from the Fonds der Chemischen Industrie (FCI) (schol-
arship for E. Wirnhier). We like to thank Dr. Peter Mayer and
Thomas Miller for single-crystal data collection as well as Christian
Argyo (all Department Chemie, LMU München) for help with the
photoluminescence measurements.
[
36] N. E. A. El-Gamel, J. Wagler, E. Kroke, J. Mol. Struct. 2008,
888, 204–213.
[
[
37] G. B. Seifer, Russ. J. Coord. Chem. 2002, 28, 301–324.
38] B. Jürgens, E. Irran, J. Senker, P. Kroll, H. Müller, W. Schnick,
J. Am. Chem. Soc. 2003, 125, 10288–10300.
[
1] B. V. Lotsch, M. Döblinger, J. Sehnert, L. Seyfarth, J. Senker,
[39] D. R. Miller, D. C. Swenson, E. G. Gillan, J. Am. Chem. Soc.
2004, 126, 5372–5373.
O. Oeckler, W. Schnick, Chem. Eur. J. 2007, 13, 4969–4980.
1846
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2012, 1840–1847

A Systematic Approach to Alkali Biuretooxophosphates
[
[
[
[
40] E. Kroke, M. Schwarz, E. Horvath-Bordon, P. Kroll, B. Noll,
[44] G. M. Sheldrick, SHELXS-97, Program for the Solution of
Crystal Structures, University of Göttingen, Germany, 1997.
A. Norman, New J. Chem. 2002, 26, 508–512.
41] Z. Otwinowski, W. Minor, Methods Enzymol. 1997, 276, 307–
[
45] G. M. Sheldrick, SHELXL-97, Program for the Refinement of
Crystal Structures, University of Göttingen, Germany, 1997.
46] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112–122.
Received: November 24, 2011
326.
42] G. M. Sheldrick, SADABS, version 2, University of Göttingen,
Germany, 2001.
43] Bruker-AXS, XPREP, Reciprocal Space Exploration, version
[
Published Online: February 27, 2012
6.12, 2001.
Eur. J. Inorg. Chem. 2012, 1840–1847
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1847