Synthesis and Crystal Structure of (dmaaH^ CdmaH^ tPnSnN^ NH

Synthesis and Crystal Structure of (dmaaH^ CdmaH^ tPnSnN^ NH

Synthesis and Crystal Structure of (dmaaH^CdmaH^tPnSnN^NH^] •
4 dmaa, dmaa = N,N-Dimethylacetamide, dma = Dimethylamine,
an Anhydrous Example of the
Cage
Stephan Roth and Wolfgang Schnick
Department of Chemistry, University of Munich (LMU),
Butenandtstraße 5-13 (block D), D-81377 Munich (Germany)
Reprint requests to Prof. Dr. W. Schnick, Fax: +49-(0)89-2180-7440.
E-mail: wsc@cup.uni-muenchen.de
Z. Naturforsch. 56 b, 1020-1024 (2001); received July 18, 2001
Phosphorus, Cage Compounds
The title compound (dmaaH)2 (dmaH)2 [Pi2 Si2 Ni 2 (NH)2 ] • 4 dmaa (1) was obtained by crys­
tallization from a saturated solution of anhydrous Pi 2 Si 2 Ns(NH ) 6 in N,N-dimethylacetamide
(dmaa) as large single crystals. According to the X-ray structure determination (P2\/n, a =
1421.8(1), b = 1556.5(2), c = 1645.8(1) pm, ß = 112.207(6)°, Z = 2, 6388 observed reflections,
R 1 = 0.046, wR2 = 0.111) the anionic cage is built up from twelve P 3 N 3 rings in boat confor­
mation. N,N-dimethylammonium ions (dmaH+) are directly connected to the cage, and pairs
of N,N-dimethylacetamidonium ions (dmaaH+) and N,N-dimethylacetamide molecules (dmaa)
are interconnected by hydrogen-bonds.
Introduction
In the course of a systematic investigation of
nitridophosphates we also focus on phosphorusnitrogen cage compounds as possible molecular
precursors for the synthesis of solid-state P/N
materials [1]. Adamantoid-type structures derived
from the tetrahedral P4 molecule are very com­
mon in phosphorus chemistry (e.g. P4 O6 , P4 S 1 0 ,
[P4 N 1 0 ] 10-) [2, 3], For several decades the potas­
sium salt K<5[Pi 2 S i 2N i 4 ] • 8 H 2 O was the only
known compound containing the unusual and highly
symmetric [Pi2 S i 2 N i 4 ]6~ cage (idealized symmetry
2/m3). Unlike all other known cages [P 1 2 S 1 2 N 1 4 ]6“
is exclusively made up from six-membered rings
in boat conformation [4]. Analogous [G a ^ O ^ ]
cages in [Gai 2 fB ui2(/X3 - 0 )8 (^ - 0 )2 (^ - 0 H)4] and
[Gai2(CH3)i2 0 8(OH)6](C24F2oB)2 • 2 C 6 H 5 C1 •
2 H 2 O have been identified as further isoelectronic representatives of this uncommon cage topol­
ogy [5, 6]. More recently we have obtained
P i 2 S , 2 N 8 (NH ) 6 • 14 H2 O, the corresponding molec­
ular acid of the potassium salt K ^ P ^ S ^ N ^ ] , as
well as the new salts L iö tP ^ S ^ N u ] • 26 H 2 O and
(NH 4 )6[Pi 2 Si 2 N i4] • 10 H20 [7]. All these com ­
pounds are water soluble and have been obtained
with a remarkable high content of crystal water.
In order to explore the thermolytic decomposi­
tion leading to possible new solid-state materials
as well as for further reactions involving the acidic
protons of the acid P ^ S n N g tN H ^ the preparation
of completely anhydrous derivatives seemed to be
desirable.
In this paper we report the synthesis and
crystal structure of an anhydrous P 12N 14 cage
compound (dmaaH)2 (dmaH)2 [Pi 2 Si 2 N i 2 (NH)2 ] • 4
dmaa. Concerning the acid-base properties the ti­
tle compound represents an intermediate between
the fully deprotonated anion [P ^S ^N m ]6- and the
molecular acid P i 2 Si 2 Ns(NH) 6 .
Experimental
Synthesis and characterization
Pi 2 Si 2 Ng(NH) 6 • 14 H20 (1) was synthesized accord­
ing to the literature [4]. An anhydrous starting material
was obtained by the reaction of the hydrate 1 (1.89 g) with
SOCI2 (> 99%, Fluka, 5 ml, 25 °C, argon atmosphere,
30 min) under evolution of HC1 and SO2 . Subsequently
the product was dried in vacuo at room temperature. The
yield was 98.1% (1.47 g) of anhydrous Pi2 Si2 N 8 (NH)6 .
After dissolving 14.2 mg of this product in 1 ml of N,Ndimethylacetamide (> 98%, Fluka) transparent colourless
crystals of (dmaaH)2 (dmaH)2 [Pi2 Si2 Ni 2 (NH)2 ] • 4 dmaa
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1021
S. Roth and W. Schnick • P 1 2 N 1 4 Cage
Table 1. Crystallographic data for (dmaaH)->(dmaH)->[Pi2 S, 2 N i 2 (NH)2] • 4 dmaa (1).
Empirical formula
Molar mass [g mol-1]
Crystal system
Space group
a [pm]
b [pm]
c [pm]
ß n ,
v [pm ]
z
Calcd density [g mol-1]
Crystal size [mm3]
Transm. ratio (max/min)
Absorption coeff. // [mm- 1 ]
T [K]
6 Range [°]
Reflections collected
Independent reflections
Observed refls (/ > 2<r(/))
Number of parameters
R l, wR2 (F0 > 4cr(F0))
R \, wR2 (all data)
Goodness-of-fit on F 2
C 2 8H74N2 2 06Pl 2 Si2
1571.51
monoclinic
P2\!n (no. 14)
1421.8(1)
1556.5(2)
1645.8(1)
112.213(6)
3372.0(4) • 106
2
1.548
0.3 • 0.36 • 0.4
1.071
0.729
173(2)
1.6 to 27.5
29120 ( 2 octants)
7756 (Äim = 0.0344)
6388
372
0.0463,0.1018
0.0622, 0.1106
1.074
( 1 ) were obtained by careful evaporation of the solvent
dmaa (25 °C, 15 hPa) within 24 h.
IR (KBr), cm-1 : 3410w, 3110w,sh, 2926m, 2854m,
2814m, 2562m, 1616s, 1506m, 1450m, 1416m, 1400s,
1364m, 1259m, 1240m, 1173vs, 1060m, 973vs, 940vs,
828m, 745vs, 674m, 598m, 530vs, 472m. Elemental anal­
ysis (C2 8 H 7 4 N 2 2 O 6 P 1 2 S 1 2 ): calcd C 18.3, H 4.3, N 19.4, P
23.7, S 24.4; found C 21.4, H 4.8, N 19.6, P 23.7, S 24.5.
According to powder X-ray diffraction (Siemens
D5000, Cu-Kai) a single-phase product was obtained.
The powder pattern was unequivocally indexed and the
lattice parameters refined using GSAS [8 ] (a = 1430.2(2),
b = 1571.9(2), c = 1643.9(2) pm,/3 = 112.213(6)°) agree
well with the results of the single-crystal X-ray diffraction
analysis.
dimethylammonium ion were refined isotropically with­
out any restraints. Further informations on crystal data,
data collection, and structure refinement are summarized
in Table 1. Important interatomic distances and angles
are presented in Table 2. The atomic coordinates, the
displacement parameters, and all further crystallographic
details have been deposited with the Cambridge Crystal­
lographic Data Centre. The data are available on request
on quoting CCDC No. 167596.
Results
In the crystal structure of 1 cage-type anions
[Pi 2 S 12 N 12 (NH>2 ]4— were found (Fig. 1), which
are packed in a distorted body-centred arrange­
ment. The complex anion is made up from twelve
phosphorus atoms, which are tetrahedrally coor­
dinated by one sulfur and three nitrogen atoms.
Eight nitrogen atoms (denoted as N [3]) are ar­
ranged cube-like, and these are connecting three
neighbouring phosphorus atoms positioned above
the edges of the cube. The remaining six nitro­
gen atoms (denoted as N [2]) are located above the
faces of the cube, and they are bridging two neigh­
bouring phosphorus atoms. The cage anion is lo­
cated on a crystallographic inversion centre and
has the idealized symmetry 2/m3. Only two of the
N [2] bridges are protonated while the other four
carry a formally negative charge (Fig. 2). The bond
lengths P-N[2] ( « 160.5 pm) are significantly shorter
than the distances P-NH ( » 166 pm), and both
Crystal structure determination
Crystal data for 1 were collected on a Siemens P4
single-crystal X-ray diffractometer using Mo-Ka radia­
tion. The structure was solved using direct methods and
refined by means of full-matrix least squares calculations
on F 2 using SHELXL97 [9]. All non-H atoms were re­
fined anisotropically. The hydrogen atoms of the methyl
groups were located geometrically, those connected to
O and N were determined by difference-Fourier analysis
and all of them were refined isotropically using a rid­
ing model. The atoms H41 and H42 connected to the
Fig. 1. Structure of the cage-like anion [Pi2 Si 2 N]2(NH)2]4~ with surrounding dmaaH+ and dmaH+ ions.
1022
S. Roth and W. Schnick • P 1 2 N 1 4 Cage
Table 2. Selected bond lengths / pm and angles /° for (dmaaH)2 (dmaH)2 [Pi2 Si 2 N i 2 (NH)2 ] • 4 dmaa (1), standard
deviations are given in parantheses.
P l-S l
Pl-N 2(3]
P1-N4 131
P1-N3 121
P4-S4
P4-N2 ' 31
P4-N6[3]
P4-N5 121
N l-H l
N4[3 ]-Pl-N 2l3]
N3[2 ]-P1-N4[3]
N3[2 ]-P1-N2[3]
N4[3 ]-P1-S1
N2t3 ]-Pl-Sl
N3t2 ]-Pl-Sl
N6[3 ]-P4-N2[3]
N5[2 ]-P4-N2[3]
N5[2 ]-P4-N6[3]
N2[3 ]-P4-S4
N6[3 ]-P4-S4
N5[2 ]-P4-S4
P5-N1(H)-P3
P5-N1(H)-H1
P3-N1(H)-H1
P3-N6[3 ]-P4
P6-N6[3 ]-P4
P3-N6[3 ]-P6
O ll- C ll
191.8(1)
172.2(3)
171.4(2)
160.5(2)
192.5(1)
172.6(3)
172.0(2)
160.0(3)
91.3
1 0 1 . 1 (2 )
105.6(2)
104.6(2)
113.7(1)
115.0(1)
115.3(1)
101.7(2)
104.9(2)
105.1(2)
114.3(1)
114.6(1)
114.7(1)
125.0(2)
117.6
115.2
117.2(2)
119.9(2)
1 2 2 .0 (2 )
124.6(5)
N ll- C ll
N11-C13
N11-C14
C11-C12
C11-N11-C13
C l 1-N11-C14
C13-N11-C14
132.4(4)
145.7(5)
145.8(5)
151.1(6)
119.3(3)
124.3(4)
116.4(4)
0 1 1-C11-N11
011-C11-C12
NI 1-C11-C12
N41-C42
N41-C41
C42-N41-C41
C42-N41-H41
121.6(4)
120.4(4)
118.0(4)
145.7(7)
147.2(7)
114.1(5)
107(4)
P2-S2
P2-N7[3]
P2-N4[3]
P2-N5[2]
P5-S5
P5-N7t3]
P5-N2[3]
P5-N1(H)
191.9(1)
172.7(3)
172.2(2)
160.4(3)
192.0(1)
169.4(2)
169.3(2)
165.7(3)
P3-S3
P3-N6l3]
P3-N4l3]
P3-N1(H)
P 6 -S6
P6-N7[3]
P 6 -N 6 [3]
P6-N3[2]
191.6(1)
170.0(2)
168.9(2)
166.4(3)
192.5(1)
172.7(2)
171.7(2)
160.4(2)
N4[3 1 -P2-N7[3]
N5[2 ]-P2-N7[3]
N5[2 ]-P2-N4[3]
N4 131 -P2-S2
N7[3 i-P2-S2
N5[2 i-P2-S2
N1(H)-P5-N2|3]
N1(H)-P5-N7[3]
N2[3 ]-P5-N7[3]
N1(H)-P5-S5
N2 -P5-S5
N7[3 1 -P5-S5
P5-N2[3 1 -P4
Pl-N 2[3 ]-P4
P5-N2[3 ]-P1
P5-N7[3 1 -P2
P6-N7[3 1 -P2
P5-N7[3 ]-P6
021-C21
021-H221
N21-C21
N21-C23
N21-C24
C21-C22
C21-N21-C24
C21-N21-C23
C24-N21-C23
C21-021-H211
021-C21-N21
021-C21-C22
N21-C21-C22
N41-H41
N41-H42
C42-N41-H42
C41-N41-H41
1 0 1 .0 (2 )
104.1(2)
104.2(2)
113.6(1)
114.9(1)
117.1(1)
1 0 1 .8 ( 2 )
102.7(2)
104.3(2)
114.4(1)
115.5(1)
116.4(1)
116.9(2)
119.5(2)
1 2 2 .6 (2 )
117.6(2)
1 2 0 .0 ( 2 )
121.3(2)
128.3(4)
103(7)
129.6(4)
146.9(4)
146.6(5)
148.7(5)
121.6(3)
121.8(3)
116.6(3)
118(5)
118.7(4)
119.9(4)
121.4(4)
108(8)
86(7)
109(5)
102(4)
N1(H)-P3-N6[31
N1(H)-P3-N4[3]
N4[ ]-P3-N6[3]
N1(H)-P3-S3
N4 -P3-S3
N6[3 1 -P3-S3
N6[3 ]-P6-N7|3]
N3[2 ]-P6-N613]
N3[2 ]-P6-N7[3]
N 6 [3 1 -P6 -S6
N7[3 1 -P6-S6
N3[2 1 -P6-S6
P3-N4[3 ]-P2
Pl-N 4[3 ]-P2
P3-N4[3 ]-P1
P6-N3t2]-Pl
P4-N5l2 ]-P2
101.9(2)
1 0 2 .2 (2 )
103.0(2)
114.2(1)
116.2(1)
117.3(1)
1 0 2 . 1 (2 )
104.4(2)
104.6(2)
113.1(1)
114.1(1)
117.0(1)
117.9(2)
119.3(2)
122.3(2)
123.7(2)
124.2(2)
031-C31
125.8(5)
N31-C31
N31-C33
N31-C34
C31-C32
C31-N31-C34
C31-N31-C33
C34-N31-C33
132.0(5)
145.6(5)
145.9(6)
147.8(6)
121.3(4)
123.8(4)
114.9(4)
031-C31-N31
031-C31-C32
N31-C31-C32
118.3(4)
120.7(4)
121.0(4)
C41-N41-H42
H41-N41-H42
112(5)
113(6)
differ considerably from the P-N [31 bond lengths
(169 up to 173 pm). The shorter ones belong to
P(S)N[3]2 N(H) tetrahedra while the longer ones oc­
cur in the P(S)N[3]2 N [2] tetrahedra. All N [3] atoms
in 1 show a planar coordination whereas the angle
P -N ^ -P is about 124°. A slightly larger deviation
from the ideal angle (120°) occurs at the N(H) atoms
(125°). The entire P 12N 14 cage is formed by twelve
P 3 N 3 rings in boat conformation (Fig. 2). The ob­
served distances and angles are comparable to those
i n U t P n S u N u ] -2 6 H 20 , ( N H ^ P u S n N w ] • 1 0
H 2 O, and K^[P 12 S 12N 14 ] • 8 H 2 O [7].
S. Roth and W. Schnick • P 1 2 N 1 4 Cage
1023
Table 3. Hydrogen-bonds (pm) and angles (°) in (dmaaH)2 (dmaH)2 [Pi2 Si2 Ni 2 (NH)2 ] • 4 dmaa (1) (D = proton donator,
A = proton acceptor; standard deviations are given in parantheses; a) values after correction by PARST97).
D -H -A
D-H
D -A
H -A
D -H -A
D-H a)
H—A a)
D -H -A a)
N l-H l-O ll
021-H 211 - 0 3 1
N41-H41—N3
N 41-H 41-N 5
91.3(3)
103.4(3)
107(7)
8 6 (8 )
270.1(5)
243.9(4)
294.9(4)
304.3(5)
179.0(3)
141.6(3)
188(8)
245(7)
175.6(2)
169.0(3)
177(7)
127(6)
103
93.8
103
103
167.3
151.0
191.9
235.1
175.3
169.7
177.3
123.4
Fig. 3. Pair of dmaa and dmaaH+ in 1 connected by hydro­
gen-bond interactions.
Fig. 2. Two different variants of six-membered P3 N 3 rings
in boat conformation in 1 with thermal ellipsoids drawn
at 50% probability level. Top: P3 N 3 ring with protonated
N l. Bottom: P 3 N 3 ring with formally negatively charged
N3.
Besides the cage anions the unit cell of 1
contains two N,N-dimethylacetamidonium ions
(dmaaH+) and two N,N-dimethylammonium ions
(dmaH+) as well as four N,N-dimethylacetamide
molecules (dmaa) as solvate. These species are
interconnected by N-H - O, O-H - O and N -H —N
hydrogen-bonds. The distances and angles of possi­
ble hydrogen-bonds were determined using the pro­
gram PARST97 (Table 3) [10]. The hydrogen-bond
lengths (X-H - X with X = O, N) range from 142
to 245 pm. There is a remarkably short hydrogenbond between a pair of one solvent molecule dmaa
and its protonated cation dmaaH+, the proton being
located between two oxygen atoms (Fig. 3). Fur­
ther hydrogen-bonds connect a solvate molecule
dmaa with the protonated nitrogen atoms N l of
the cage (178.6 pm) and the two different deprotonated nitrogen atoms N3 and N5 of separate cage
anions with H41 (192.0 pm) and H42 (249.2 pm)
of dmaH+ respectively (Fig. 4). The latter weak FIbond is distorted with an angle of 125° because of
the tetrahedral surrounding of N41. In the crystal
there are layers of P 12N 14 cages and dmaH+ cations
connected through hydrogen-bonds parallel [0 1 0 ].
These layers are separated by the dmaa molecules
and the pairs dmaa/dmaaH+.
The formation of dmaH+ and dmaaH+ ions in the
reaction of dmaa with HCl have been described in
the literature [ 1 1 , 1 2 ].
S. Roth and W. Schnick • P 1 2 N 1 4 Cage
1024
responsible for the cleavage of acetamide and the
subsequent formation of Me 2 NH 2 + according to
eq. (1). Possibly both hydrogen chloride and the
acid P i 2 Si 2 N 8(NH )6 are involved in the cleavage
reaction. With the transfer of four protons the pro­
tonation capability of P ^S ^ N g (NH )6 appears to be
exhausted, and thus further dmaa molecules were
incorporated unprotonated in the crystal.
The IR-spectra are also indicative of a protonation
of dmaa: The band at 3410 cm - 1 is typical for O-H
groups and the absorption at 2854 cm - 1 could be
assigned to the dimethylammmonium ion.
Conclusion
of 1 .
MeC(0)NMe 2 + HCl — M eC(0)Cl + Me2NH
+H+
(1)
MeC(0)Cl + Me 2 NH2't
Presumably small amounts of HCl formed by the
drying procedure utilizing SOCI 2 remained on the
surface of the product. This contamination may be
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(1993).
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tallogr. C56, 1213 (2000).
With the new compound (dmaaH) 2 (dmaH )2
[Pi2 Si 2 N i 2 (NH)2 ] • 4 dmaa we obtained an anhy­
drous P 12N 14 cage compound. The anions represent
an intermediate between the fully protonated neutral
acid P 12 S 12N 8 (NH)ö and the six-fold deprotonated
anion that can be formed by classical acid-base re­
actions.
Acknowledgements
This work has been supported by the Deut­
sche Forschungsgemeinschaft (Gottfried-Wilhelm-Leibniz-Programm) and also by the Fonds der Chemischen
Industrie, Germany.
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