Synthesis and crystal structure of (p-CH3C6H4NH3)6P6O18·8H2O

Article abstract of DOI:10.1016/S0025-5408(99)00041-0

Preparation and complete structural characterization by X-ray diffraction (XRD), IR absorption, thermogravimetric and differential thermal analysis (TG-DTA), and mass angle spinning (MAS) NMR spectroscopy are given for a new cyclohexaphosphate, (p-CH₃C₆H₄NH₃)₆P₆O₁₈·8H₂O. This compound is monoclinic in space group P2₁/c, with Z = 2 and unit-cell parameters a = 10.695(6), b = 24.952(8), c = 11.163(4) angstrom, and β = 97.53(4)°. The crystal structure was solved and refined down to R = 0.036, using 4168 independent reflections. The atomic arrangement can be described as layer organization. Layers built by P₆O₁₈ ring anions and water molecules spread parallel to the plane (010). Between these layers are located the organic groups that form hydrogen bonds with P₆O₁₈ ring oxygens. Geometrical characteristics of the hydrogen bonds are described.

Full text of DOI:10.1016/S0025-5408(99)00041-0

Materials Research Bulletin, Vol. 34, No. 4, pp. 557–569, 1999
Copyright © 1999 Elsevier Science Ltd
Printed in the USA. All rights reserved
0025-5408/99/$–see front matter
PII S0025-5408(99)00041-0
SYNTHESIS AND CRYSTAL STRUCTURE OF (p-CH3C6H4NH3)6P6O18⅐8H2O
C. Ben Nasr* and M. Rzaigui
Laboratoire de Chimie des Mate´riaux, Faculte´ des Sciences, 7021 Zarzouna,
Bizerte, Tunisie
(Refereed)
(Received April 8, 1998; Accepted July 6, 1998)
ABSTRACT
Preparation and complete structural characterization by X-ray diffraction
(XRD), IR absorption, thermogravimetric and differential thermal analysis
(TG-DTA), and mass angle spinning (MAS) NMR spectroscopy are given for
a new cyclohexaphosphate, (p-CH3C6H4NH3)6P6O18⅐8H2O. This compound
is monoclinic in space group P21/c, with Z ϭ 2 and unit-cell parameters a ϭ
10.695(6), b ϭ 24.952(8), c ϭ 11.163(4) Å, and ␤ ϭ 97.53(4)°. The crystal
structure was solved and refined down to R ϭ 0.036, using 4168 independent
reflections. The atomic arrangement can be described as layer organization.
Layers built by P6O18 ring anions and water molecules spread parallel to the
plane (010). Between these layers are located the organic groups that form
hydrogen bonds with P6O18 ring oxygens. Geometrical characteristics of the
hydrogen bonds are described. © 1999 Elsevier Science Ltd
KEYWORDS: A. organometallic compounds, B. crystal growth, C. X-ray
diffraction, D. crystal structure
INTRODUCTION
Many physicists concerned with nonlinear optics are involved in research into very efficient
and highly transparent nonlinear optical crystals. Better performance of optical signal-
processing devices is linked to the discovery of new materials of this type [1]. The design of
organic–inorganic polar crystals for quadratic nonlinear optical applications is oriented and
supported by two main observations:
*To whom correspondence should be addressed.
557

558
C. BEN NASR and M. RZAIGUI
Vol. 34, No. 4
1. The organic molecules containing ⌸-electron systems asymmetrized by electron donor-
acceptor groups are highly polarizable entities in which transparency and problems of
crystal growth are related to molecular crystal packing.
2. The ionic inorganic host-matrices may increase the packing cohesion, shift the trans-
parency of the organic entities toward blue wavelengths, and induce the acentricity of the
symmetry.
Within a systematic investigation of new materials resulting from the association of organic
and inorganic species of interest in nonlinear optics [2], we report here the synthesis, crystal
structure, and some characteristic properties of a new organic cation-cyclohexaphosphate,
(p-CH3C6H4NH3)6P6O18⅐8H2O.
EXPERIMENTAL
Chemical Preparation. The title compound, (p-CH3C6H4NH3)6P6O18⅐8H2O, was prepared
in two steps. An aqueous solution of cyclohexaphosphoric acid was first obtained by passing
a solution of Li6P6O18 through an ion-exchange resin in its H-state (amberlite IR120). The
lithium salt was prepared according to the process described by Schu¨lke and Kayser [3],
using purum p.a. Fluka chemicals. Into this solution, we added, drop by drop, the distilled
p-toluidine (purum p.a. Fluka), with continuous stirring, until the solution exhibited a light
greenish aspect. Schematically the reaction can be written as
H2O
H6P6O18 ϩ 6 p-CH3C6H4NH2
O¡ ( p-CH3C6H4NH3)6P6O18⅐8H2O
In order to avoid the hydrolysis of the ring anion, the above reaction was performed at room
temperature. The thus-obtained solution was slowly evaporated until the formation of large
rectangular prisms of (p-CH3C6H4NH3)6P6O18⅐8H2O. The crystals were stable for months
under normal conditions of temperature and hygrometry.
Investigation Techniques. X-ray diffraction powder diagrams were recorded at low scan
speed (1/8 °␪/min) with a Philips 1729 diffractometer using Cu K␣ radiation. Symmetry and
space group were determined by the Weissenberg technique, using a single crystal. Unit-cell
parameters were refined by a least-squares method from the powder data. The intensity data
collection was performed with a CAD4 Enraf-Nonius diffractometer. The experimental
parameters used during these measurements, the strategy followed for the structure deter-
mination, and final results are gathered in Table 1.
Thermal analysis was performed using a multimodule 92 Setaram analyzer operating from
room temperature up to 550°C at an average heating rate of 10°/min. IR spectrum was
recorded in the 4000–200 cmϪ1 range with a Perkin-Elmer IR 983G spectrophotometer,
using sample dispersed in spectroscopically pure KBr pellets. Proton-decoupled 31P MAS
NMR spectra were recorded with a Bruker MSL-300 solid-state high-resolution spectrometer
operating at 121.495 MHz (magnetic field 7.05 T). The duration of the 90° pulse was 5 ␮s
and the pulse delay was 5 s. A cylindrical rotor with a spinning rate of 5 KHz was used in
the MAS experiments. Chemical shift values were obtained with respect to 85% H3PO4

Vol. 34, No. 4
ORGANIC PHOSPHATE
559
TABLE 1
Data Collection and Final Results of the Structure Determination
I. Crystal data
Formula:
(p-CH3C6H4NH3)6P6O18⅐8H2O
Formula weight:
System:
Space group:
1266.92
Monoclinic
P21/c
Unit-cell parameters:
a ϭ 10.695(6), b ϭ 24.952(8), c ϭ 11.163(4) Å,
␤ ϭ 97.53(4)°
2
Z:
V:
2953(2) Å3
Refinement of unit-cell parameters with:
25 reflections (9° Ͻ ␪ Ͻ 11°)
␳
:
1.425 g/cm3
calc
F(000):
1336
Linear absorption factor: ␮ (Mo K␣):
Crystal size:
Morphology:
0.274 mmϪ1
0.32 ϫ 0.64 ϫ 0.24 mm
Short stout prisms
II. Intensity measurements
Diffractometer:
Enraf-Nonius CAD4
Monochromator:
Graphite plate
Radiation:
Mo K␣ (␭ ϭ 0.7107 Å)
Temperature:
294 K
Scan mode, width:
␻, 1.20°
Theta range:
3–30°
Maximum scan time:
Total background measuring time:
Measurement area:
20 s
1/2 scan time
Ϯh, k, l; hmax ϭ 15, kmax ϭ 35, lmax ϭ 15
Number of scanned reflections:
Number of independent reflections:
Two intensity and orientation control
reflections:
9283
4168 (Rint ϭ 0.012)
3 7 3 and 3 7 3 (no variation)
៮ ៮ ៮
III. Structure determination
Lorentz and polarization corrections:
Program used:
No absorption correction
MOLEN [4]
Computer:
Micro-Vax 3100
Determination:
A direct method via MULTAN [5], Fourier and
difference Fourier maps
Thermal displacement parameters:
Unique reflections included:
Refined parameters:
Isotropic for H atoms, anisotropic for non-H atoms
4168 with I Ͼ 3 ␴(I)
513
Weighting scheme:
Unitary
Unweighted and weighted R factors:
ESD:
0.036 and 0.039, respectively
1.213
Largest shift/error:
Residual Fourier density:
Drawings made with:
0.11
Ϫ0.27 Ͻ ␳ Ͻ 0.28 ÅϪ3
MOLVIEW [6]

560
C. BEN NASR and M. RZAIGUI
TABLE 2
Vol. 34, No. 4
Powder X-ray Diffraction Data for (p-CH3C6H4–NH3)6P6O18⅐8H2O
h k l
dcalc (Å)
dobs (Å)
I/Imax
h k l
dcalc (Å)
dobs (Å)
3.72
I/Imax
17
0 2 0
12.52
10.64
12.53
10.64
100
19
2 5 2
3.72
3.61
៮
៮
1 0 0
1 1 3
3.61
3.55
10
25
}
2 0 2
3 0 0
3.61
3.55
0 1 1
10.14
10.15
41
}
0 2 3
3 1 0
2 2 2
0 6 2
3.55
3.51
3.47
3.33
3.26
3.23
3.15
3.13
3.09
3.01
2.96
2.93
1 2 0
1 3 0
1 2 1
8.11
6.57
6.25
5.87
5.45
4.97
4.67
4.62
4.49
4.33
4.15
8.11
6.57
6.25
5.87
5.45
4.97
4.67
4.62
4.49
4.33
4.15
19
68
68
18
31
10
19
17
11
11
16
3.51
3.47
3.33
3.26
3.23
3.15
3.13
3.09
3.01
2.96
28
10
14
19
17
16
17
12
12
9
៮
៮
1 3 1
1 6 2
0 4 1
3 1 1
3 2 1
0 8 0
៮
2 1 1
1 0 2
0 3 2
2 3 0
៮
3 2 2
0 7 2
1 4 3
៮
2 3 1
៮
0 4 2
1 8 1
2.93
7
}
2 5 2
2 4 3
2 1 3
2.93
2.881
2.844
៮
៮
2 1 2
4.07
4.00
4.07
4.01
3.91
25
29
42
2.882
2.844
10
7
៮
1 4 2
}
2 3 1
0 6 1
4.01
3.91
៮
2 8 2
2.493
2.494
16
(negative shifts were to high field). Proton-decoupled 31P NMR spectrum of an aqueous
cyclohexaphosphate (p-CH3C6H4NH3)6P6O18⅐8H2O solution was taken by a Bruker AM 400
instrument operating at 161.975 MHz. Phosphoric acid (85%) was used as a reference with
downfield positive shifts.
RESULTS AND DISCUSSION
Crystallographic Study
Crystal data. Weissenberg and oscillation photographs showed the title compound to be
monoclinic with the centrosymmetric space group P21/c. A least-squares refinement of the
powder diffraction angular data leads to the unit-cell parameters a ϭ 10.736(2), b ϭ
25.049(5), c ϭ 11.187(2) Å, ␤ ϭ 97.63(1)°. These parameters are comparable with those
obtained with the four-circle diffractometer data (Table 1). The indexing of the
(p-CH3C6H4NH3)6P6O18⅐8H2O powder diffractogram, with these unit-cell parameters, is
reported in Table 2.
Structure description. The final atomic coordinates of all nonhydrogen atoms of
(p-CH3C6H4NH3)6P6O18⅐8H2O and their Beq are given in Table 3. Those of hydrogen atoms

Vol. 34, No. 4
ORGANIC PHOSPHATE
561
TABLE 3
Final Atomic Coordinates and Beq for the Non-Hydrogen Atoms
Atoms
x (␴)
y (␴)
z (␴)
Beq (␴)
P(1)
P(2)
P(3)
0.43022(7)
0.67366(6)
0.27823(7)
0.4587(2)
0.4119(2)
0.5364(2)
0.7271(2)
0.7447(2)
0.3614(2)
0.3268(2)
0.1430(2)
0.3105(2)
0.2709(2)
0.2773(3)
0.2689(3)
0.2695(3)
0.2784(3)
0.2876(4)
0.2876(4)
0.2769(4)
0.5457(2)
0.5742(3)
0.6252(3)
0.6536(4)
0.6309(4)
0.5772(4)
0.5491(3)
0.6613(5)
0.9690(2)
0.9690(3)
0.0101(4)
0.0062(4)
0.9592(4)
0.9186(4)
0.9237(4)
0.9516(6)
0.9623(2)
0.0024(3)
0.6073(3)
0.8511(3)
0.47890(3)
0.47198(3)
0.44430(3)
0.53630(8)
0.44515(9)
0.45228(7)
0.43020(7)
0.48810(9)
0.47653(8)
0.38948(8)
0.45516(9)
0.4740(1)
0.0562(1)
0.1125(1)
0.1247(1)
0.3223(1)
0.2183(1)
0.2959(1)
0.3486(1)
0.2236(1)
0.38291(9)
0.1710(1)
0.3221(1)
0.2296(1)
0.2266(1)
0.2648(1)
0.2137(1)
0.1711(2)
0.0839(1)
0.1424(1)
0.3331(2)
0.2216(2)
0.2526(2)
0.2266(2)
0.3282(2)
0.1874(2)
0.4409(1)
0.4523(1)
0.0821(1)
0.0547(2)
0.74332(6)
0.89099(6)
0.93062(6)
0.7295(2)
0.6346(2)
0.8389(2)
0.9766(2)
0.7928(2)
1.0358(2)
0.9389(2)
0.9359(2)
0.8127(2)
0.9086(2)
0.8723(3)
0.7520(3)
0.2178(3)
0.8019(3)
0.4220(3)
0.4582(3)
0.2645(3)
0.0986(2)
0.6456(3)
0.2633(3)
0.8042(3)
0.2306(3)
0.6131(3)
0.5697(3)
0.2746(4)
0.5797(2)
0.5713(3)
0.9743(3)
0.4653(4)
0.5513(4)
0.6486(4)
0.1594(4)
0.0407(6)
0.7421(2)
0.3276(2)
Ϫ0.0047(2)
0.0024(3)
2.25(1)
2.00(1)
2.26(1)
3.39(4)
3.34(4)
2.38(4)
2.64(4)
3.29(4)
2.53(4)
3.36(4)
3.26(4)
3.44(4)
3.08(5)
2.75(6)
3.03(6)
3.27(6)
3.27(6)
4.14(7)
3.94(7)
4.62(9)
2.82(5)
2.67(5)
3.37(6)
3.97(7)
3.93(7)
4.06(8)
3.48(7)
6.3(1)
3.39(5)
3.48(7)
4.44(8)
5.3(1)
5.5(1)
6.0(1)
4.94(9)
8.3(2)
5.04(6)
4.88(6)
6.08(7)
6.68(8)
O(E11)
O(E21)
O(L12)
O(E12)
O(E22)
O(L23)
O(E13)
O(E23)
O(L31)
N(1)
C(11)
C(21)
C(31)
C(41)
C(51)
C(61)
C(1)
N(2)
C(12)
C(22)
C(32)
C(42)
C(52)
C(62)
C(2)
N(3)
C(13)
C(23)
C(33)
C(43)
C(53)
C(63)
C(3)
O(w1)
O(w2)
O(w3)
O(w4)
ESDs are given in parentheses. Beq ϭ 4/3 ⌺⌺ai⅐aj␤ij.

562
C. BEN NASR and M. RZAIGUI
TABLE 4
Vol. 34, No. 4
Main Interatomic Distances (Å) and Angles (°) in the the Phosphoric Ring Anion
P(1)O4 tetrahedron
P(1)
O(E11)
O(E21)
118.5(1)
1.469(2)
2.491(3)
2.492(3)
O(L12)
109.6(1)
108.6(1)
1.597(2)
2.455(3)
O(L31)
108.5(1)
109.3(1)
101.0(1)
1.585(2)
O(E11)
O(E21)
O(L12)
O(L31)
1.477(2)
2.531(3)
2.512(3)
2.486(3)
P(2)O4 tetrahedron
P(2)
O(L12)
O(E12)
106.2(1)
1.478(2)
2.537(3)
2.509(3)
O(E22)
110.8(1)
118.8(1)
1.469(2)
2.509(3)
O(L23)
99.7(1)
109.5(1)
110.0(1)
1.593(2)
O(L12)
O(E12)
O(E22)
O(L23)
1.585(2)
2.451(2)
2.515(3)
2.430(2)
P(3)O4 tetrahedron
P(3)
O(L23)
O(E13)
105.4(1)
1.462(2)
2.557(3)
2.530(3)
O(E23)
109.4(1)
120.7(1)
1.480(2)
2.444(3)
O(L31)
O(L23)
O(E13)
O(E23)
O(L31)
1.595(2)
102.4(1)
112.0(1)
105.5(1)
2.433(3)
2.510(3)
2.480(3)
1.588(2)
P(1)–P(2)
P(1)–P(3)
P(2)–P(3)
2.8983(9)
2.941(1)
2.885(1)
P(1)–O(L12)–P(2)
P(2)–O(L23)–P(3)
P(3)–O(L31)–P(1)
131.2(1)
129.6(1)
135.9(1)
P(2)–P(1)–P(3)
P(1)–P(2)–P(3)
P(1)–P(3)–P(2)
96.73(3)
114.52(3)
102.29(3)
were also determined, but are not given, in order to shorten the table. Main geometrical
features, bond distances, and angles are reported in Tables 4, 5, and 6, respectively.
The atomic arrangement of this compound is typical of a layer structure (Fig. 1). Layers
including the P6O18 ring anions and the water molecules develop around the y ϭ n/2 planes.
Between these layers we find the organic entities elongated in the b direction. These entities
establish hydrogen bonds to interconnect the different layers. Figure 2 shows how the basic
parts, P6O18, of one layer are linked by hydrogen bonds formed by water molecules and NH3
groups. Inside such a layer, the phosphoric ring is located around the inversion center
(1/2,0,0) and thus is built up of three independent PO4 tetrahedra. The main geometrical
features of this ring are reported in Table 4. This ring is significantly distorted: the P–P–P
angles vary between 96.73° and 114.52°. These angles, with an average of 104.51°, show
very large deviations from the ideal value of 120°, compared to the other types of well-
represented phosphoric rings such as cyclotri- and cyclotetraphosphates, in which the P–P–P

Vol. 34, No. 4
ORGANIC PHOSPHATE
563
TABLE 5
Main Interatomic Distances (Å) and Angles (°) in the
CH3–C6H4–NH3 Groups
N(1)–C(11)
C(11)–C(21)
C(21)–C(31)
C(31)–C(41)
C(41)–C(51)
C(51)–C(61)
C(61)–C(11)
C(41)–C(1)
1.465(4)
1.369(4)
1.376(4)
1.376(4)
1.377(5)
1.377(5)
1.359(4)
1.508(5)
N(1)–C(11)–C(21)
C(11)–C(21)–C(31)
C(21)–C(31)–C(41)
C(31)–C(41)–C(51)
C(41)–C(51)–C(61)
C(51)–C(61)–C(11)
C(61)–C(11)–C(21)
C(61)–C(11)–N(1)
C(31)–C(41)–C(1)
C(1)–C(41)–C(51)
119.1(3)
119.0(3)
121.3(3)
117.7(3)
121.9(3)
118.6(3)
121.4(3)
119.4(3)
121.4(3)
120.9(3)
N(2)–C(12)
C(12)–C(22)
C(22)–C(32)
C(32)–C(42)
C(42)–C(52)
C(52)–C(62)
C(62)–C(12)
C(42)–C(2)
1.461(4)
1.366(4)
1.387(5)
1.372(5)
1.377(5)
1.384(4)
1.365(4)
1.490(5)
N(2)–C(12)–C(22)
C(12)–C(22)–C(32)
C(22)–C(32)–C(42)
C(32)–C(42)–C(52)
C(42)–C(52)–C(62)
C(52)–C(62)–C(12)
C(62)–C(12)–C(22)
C(62)–C(12)–N(2)
C(32)–C(42)–C(2)
C(2)–C(42)–C(52)
120.0(2)
118.5(3)
122.0(3)
117.7(3)
121.4(3)
119.1(3)
121.2(3)
118.7(2)
122.0(3)
120.3(3)
N(3)–C(13)
C(13)–C(23)
C(23)–C(33)
C(33)–C(43)
C(43)–C(53)
C(53)–C(63)
C(63)–C(13)
C(43)–C(3)
1.464(4)
1.364(5)
1.369(6)
1.379(6)
1.383(7)
1.371(6)
1.366(5)
1.503(6)
N(3)–C(13)–C(23)
C(13)–C(23)–C(33)
C(23)–C(33)–C(43)
C(33)–C(43)–C(53)
C(43)–C(53)–C(63)
C(53)–C(63)–C(13)
C(63)–C(13)–C(23)
C(63)–C(13)–N(3)
C(33)–C(43)–C(3)
C(3)–C(43)–C(53)
120.0(3)
119.6(4)
121.3(4)
117.6(4)
121.5(4)
119.1(4)
120.8(3)
119.1(3)
121.7(4)
120.6(4)
ESDs are given in parentheses.
angles never depart significantly from their ideal values of 60 Ϯ 2° for cyclotriphosphates
and 90 Ϯ 4° for cylotetraphosphates. Nevertheless, this distortion is comparatively less
important than that observed in Cs6P6O18⅐6H2O, which shows the greatest distortion for the
same angles spreading between 93.2 and 145.5° [7].
The great flexibility of the P6O18 ring probably explains the strong stability of cyclo-
hexaphosphates. Examination of the main geometrical features (Table 4) of the three
independent PO4 tetrahedra shows clearly that, in spite of the P–P–P angles deformation, they
are in accordance with all that has been previously observed for PO4 tetrahedra involved in
other condensed phosphate anions. Indeed, three different types of O–P–O angles coexist in
PO4 tetrahedra. The O(L)–P–O(L) corresponding to the largest P–O bonds are always close
to 100°. The O(L)–P–O(E) angles have values expected for a regular tetrahedron, while the

564
C. BEN NASR and M. RZAIGUI
TABLE 6
Vol. 34, No. 4
Main Interatomic Distances (Å) and Angles (°) Involved in the Hydrogen Bonds
. . .
. . .
O(N)
O(N)–H . . . O(N)
O(N)–H
H
O(N)
O(N)–H
O(N)–O(N)
N(1)–H(1N1)–O(E21)
N(1)–H(2N1)–O(W2)
N(1)–H(3N1)–O(E22)
N(2)–H(1N2)–O(E13)
N(2)–H(2N2)–O(E11)
N(2)–H(3N2)–O(E12)
N(3)–H(1N3)–O(E23)
N(3)–H(2N3)–O(W2)
N(3)–H(3N3)–O(E12)
O(W1)–H(1W1)–O(E23)
O(W1)–H(2W1)–O(E22)
O(W2)–H(1W2)–O(W4)
O(W2)–H(2W2)–N(3)
O(W3)–H(1W3)–O(E21)
O(W3)–H(2W3)–O(E11)
O(W4)–H(1W4)–O(W1)
O(W4)–H(2W4)–O(W2)
0.94(3)
0.90(4)
0.95(4)
0.99(3)
0.92(4)
1.02(4)
0.91(4)
0.90(4)
1.01(4)
1.07(4)
0.82(4)
1.00(4)
0.87(4)
0.84(4)
0.89(4)
0.94(4)
0.87(5)
1.84(3)
2.11(4)
1.94(4)
1.77(3)
1.87(4)
1.76(4)
1.90(4)
2.00(4)
1.73(4)
1.66(4)
1.96(4)
1.72(4)
2.24(5)
2.06(4)
1.88(4)
1.88(4)
2.29(5)
171(3)
145(3)
150(3)
170(3)
173(3)
174(3)
168(3)
172(3)
164(4)
177(4)
157(4)
164(3)
131(4)
157(4)
172(4)
162(4)
109(4)
2.765(3)
2.903(4)
2.805(3)
2.755(3)
2.789(3)
2.775(3)
2.788(3)
2.888(4)
2.713(3)
2.728(3)
2.733(3)
2.699(4)
2.888(4)
2.846(4)
2.764(3)
2.785(4)
2.699(4)
ESDs are given in parentheses.
O(E)–P–O(E) angles corresponding to the shortest P–O distances always have large values,
close to 120°, probably induced by the mutual repulsion of the nonbridging oxygen atoms.
Nevertheless, the calculated average values of the distortion indices [8] corresponding to the
different angles and distances in the independent PO4 tetrahedra, DI(PO) ϭ 0.0386,
DI(OPO) ϭ 0.0510, and DI(OO) ϭ 0.0123 show a high distortion of the P–O distances
compared to the O–O distances. The PO4 tetrahedron is thus described by a regular oxygen
atoms arrangement with the phosphorus atom shifted from gravity center of PO4.
Lists of structure factors, anisotropic thermal displacements, and H-atom parameters can
be obtained on request to the authors.
Thermal Analysis. The two curves corresponding to DTA and TGA in open air are given
in Figure 3. The DTA curve shows that at about 95 and 127°C the cyclohexaphosphate
undertakes two endothermic dehydrations. This is well confirmed by the weight losses
observed from the TGA curve. From the latter, we deduced a departure of 8 water molecules
(% water: experimental 11.32; calculated 11.37). This total dehydration gives rise to an
intermediate amorphous material that does not diffract the X-rays and no longer exhibits the
IR absorption bands characteristic of a cyclic phosphate. This amorphous product undergoes
a decomposition of CH3C6H4NH3 group in a wide temperature range (167–550°C). This is
also confirmed by the significant weight loss observed from the TGA curve.
IR Absorption Spectroscopy. The infrared absorption spectrum is reported in Figure 4.
It exhibits:
1. Broad bands between 3600 and 2500 cmϪ1 and 1650 and 1400 cmϪ1 corresponding to the
valency vibration of the water molecules and 4-ammonium toluene cation of the compound.

Vol. 34, No. 4
ORGANIC PHOSPHATE
565
FIG. 1
The atomic arrangement of (p-CH3C6H4NH3)6P6O18⅐8H2O in projection along the c axis.
FIG. 2
The atomic arrangement of (p-CH3C6H4NH3)6P6O18⅐8H2O in projection along the b axis.

566
C. BEN NASR and M. RZAIGUI
Vol. 34, No. 4
FIG. 3
DTA and TGA curves of (p-CH3C6H4NH3)6P6O18⅐8H2O.
2. Various valency vibration bands whose positions, between 1300 and 600 cmϪ1, and
number are both characteristic of a phosphoric ring anion [9]. In these types of
anions, the vibrations of the O–P–O groups take place at relatively high frequencies,
1200 Ͻ ␯ Ͻ 1300 cmϪ1 and 1050 Ͻ ␯ Ͻ 1200 cmϪ1 and those corresponding to
as
s
the P–O–P groups constitute a broad band ␯ about 960 cmϪ1 and a doublet ␯
as
s
between 800 and 700 cmϪ1
.
FIG. 4
IR absorption spectra of the cyclohexaphosphate (p-CH3C6H4NH3)6P6O18⅐8H2O.

Vol. 34, No. 4
ORGANIC PHOSPHATE
567
FIG. 5
Proton-decoupled 31P MAS NMR spectrum of crystalline cyclohexaphosphate (p-CH3
C6H4NH3)6P6O18⅐8H2O. Signal is marked by arrow; sidebands are left unsuppressed.
NMR Spectroscopy. Proton-decoupled 31P MAS NMR spectrum of crystalline cyclo-
hexaphosphate (p-CH3C6H4NH3)6P6O18⅐8H2O is presented in Figure 5. It exhibits three
resonance peaks with comparable relative intensity. The respective chemical shifts Ϫ18.7,
Ϫ21.5, and Ϫ23.3 ppm were recorded with respect to 31P MAS NMR of 85% H3PO4. The
number of signals observed are related to the number of crystallographically distinguishable
phosphorus sites.
To search for a correlation between NMR and X-ray results, we have studied the local
geometry deformation of the three PO4 tetrahedra of the asymmetrical unity of P6O18 ring.
TABLE 7
31P MAS NMR and X-ray Data of Two Crystalline
Cyclohexaphosphates
Samples
Phosphorus
⌬ (Å)
␦ (ppm)
(p-CH3C6H4NH3)6P6O18⅐8H2O
P(1)
P(2)
P(3)
P(1)
P(2)
P(3)
0.129
0.139
0.136
0.109
0.168
0.151
Ϫ23.3
Ϫ18.7
Ϫ21.5
Ϫ25.1
Ϫ21.9
Ϫ23.1
(1-C10H7NH3)6P6O18⅐2H2O

568
C. BEN NASR and M. RZAIGUI
Vol. 34, No. 4
FIG. 6
Plot of 31P chemical shift (␦) as a function of the distance ⌬ for two cyclohexaphosphates:
(p-CH3C6H4NH3)6P6O18⅐8H2O (ϩ) and (1-C10H7NH3)6P6O18⅐2H2O (o).
FIG. 7
Proton-decoupled 31P NMR spectrum of an aqueous solution of cyclohexaphosphate
(p-CH3C6H4NH3)6P6O18⅐8H2O.

Vol. 34, No. 4
ORGANIC PHOSPHATE
569
We have determined the distance ⌬ (Å) between the gravity center of PiO4 (i ϭ 1, 2, 3)
tetrahedra and the phosphorus position P(i) in two different cyclohexaphosphates. The results
(Table 7) show different ⌬, consequently, a different deformation of PO4 tetrahedra. Thus,
the phosphorus sites have not the same electronic density, which justifies the observed
difference of the corresponding chemical shifts (␦). In fact, if ␦ decreases, the electronic
density increases and the chemical shift (␦) is weaker. This correlation between the distance
⌬ and the chemical shift (␦) is represented in Figure 6. The latter shows that, for two
cyclohexaphosphates, the chemical shifts (␦) increase with the distance ⌬, thus with the PO4
tetrahedra deformation. Therefore, the observed NMR peaks could be assigned to phosphorus
P(i) according to ␦ and ⌬ values (Table 7).
The proton-decoupled 31P NMR spectrum of an aqueous (p-CH3C6H4NH3)6P6O18⅐8H2O
solution (Fig. 7) exhibited only one peak due to a middle PO4 group at Ϫ23.2 ppm. In
solution, the phosphorus of P6O18 ring are not stuck on sites as in crystalline state. Liberated
from the solid constraints, the P6O18 ring obtains a symmetrical conformation where all
phosphorus atoms are equivalent.
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