Structural characterization of a series of cyclohexaphosphates: Ca2M2P6O18 · 6H2O (M = K, Tl, Rb)

Article abstract of DOI:10.1006/jssc.1996.0342

Three new cyclohexaphosphates with the general formula Ca₂M₂P₆O₁₈ · 6H₂O (M = K, Tl, Rb) are reported. They crystallize with monoclinic unit cells and are isotopic. As an example the paramters of Ca₂K₂P₆O₁₈ · 6H₂O are a = 7.266(1), b = 11.833(2), c = 12.300(2) A, β = 103.17(1)⁰, Z = 2, P2₁In, V = 1030(3) A³, and Dx = 2.387 g cm^-3. Crystal structure of this phase was determined using 6292 independent reflections with a final R = 0.025. The atomic arrangement can be described as puckered layers containing water bonded P₆O₁₈ anions and Ca²⁺ and K⁺ cations, alternating along the (1, 0, 1) direction. Synthesis and characterization by X-ray diffraction, IR absorption, and TA are described.

Full text of DOI:10.1006/jssc.1996.0342

JOURNAL OF SOLID STATE CHEMISTRY 126, 308–313 (1996)
ARTICLE NO. 0342
Structural Characterization of a Series of Cyclohexaphosphates:
Ca M P O ؒ 6H O (M ؍ K, Tl, Rb)
2
2
6
18
2
S. Abid and M. Rzaigui1
Laboratoire de Chimie des Mat e´ riaux, Facult e´ des Sciences, 7021 Zarzouna, Bizerte, Tunisia
Received July 15, 1996; accepted July 16, 1996
The cyclohexaphosphoric acid is added until pH 2 is
Three new cyclohexaphosphates with the general formula reached in the final solution. After some days of slow
Ca O (M ؍ K, Tl, Rb) are reported. They crystal- evaporation at room temperature, crystals appeared with
lize with monoclinic unit cells and are isotopic. As an example
the paramters of Ca O are a ؍ 7.266(1), b ؍
1.833(2), c ؍ 12.300(2) A, ␤ ؍ 103.17(1)؇, Z ؍ 2, P2 /n, V ؍
030(3) A , and Dx ؍ 2.387 g cm . Crystal structure of this
2
2 6 2
M P O18 ؒ 6H
a suitable dimension. They were sparingly soluble in water
and stable in air for months under normal conditions of
temperature and hygrometry.
2
2 6 2
K P O18 ؒ 6H
˚
1
1
1
˚
3
؊3
The cyclohexaphosphoric acid used in this reaction was
prepared from an aqueous solution of Li P O и 6H O (2)
phase was determined using 6292 independent reflections with
a final R ؍ 0.025. The atomic arrangement can be described
as puckered layers containing water bonded P O18 anions and
6
Ca and K cations, alternating along the (1, 0, 1) direction.
Synthesis and characterization by X-ray diffraction, IR absorp-
6
6
18
2
passed through an ion-exchange resin (Amberlite IR 120).
The compounds have been studied using different tech-
niques with the experimental conditions described below.
2
؉
؉
tion, and TA are described.
 1996 Academic Press, Inc.
B. Investigation
INTRODUCTION
X-ray diffraction. Powder diffraction patterns were re-
corded using a Philips PW 1729 diffractometer with the
CuK Ͱ¯ radiation (␭ ϭ 1.5418 A) and at low speed ( Ak Њ␪/
The study of the cyclohexaphosphates is of considerable
˚
6
Ϫ
importance as the P O anion in aqueous solution behaves
6
18
min). The symmetry space group has been determined
by Weissenberg technique on a single crystal. Unit cell
parameters have been refined by a least square method
using the powder data.
The intensity data collection was performed using a
CAD4 Enraf–Nonius diffractometer. The strategy used
for the structure determination and its final results are
gathered in Table 1.
as a polyelectrolyte, forming extraspherical complexes with
cations thanks to electrostatic interactions (1). In the pres-
ent investigation we report chemical preparation, char-
acterization, and crystal structure of three Ca M
2
2
P O и 6H O phases with M ϭ K, Tl, and Rb. This work
6
18
2
constitutes part of a more general investigation of diva-
lent–monovalent cation cyclohexaphosphates.
Thermal behavior. Thermal analysis was performed us-
ing a multimodule 92 Setaram Analyzer operating from
room temperature up to 873 K at an average heating rate
of 10Њ/min.
EXPERIMENTAL
A. Chemical Preparation
Crystalline samples of the title compounds were pre-
pared by slowly adding dilute cyclohexaphosphoric acid to
an aqueous solution of calcium carbonate and alkaline
carbonate with a stoichiometric ratio Ca/M ϭ 1. Schemati-
cally, they react according to equation
Infrared spectroscopy. Spectra were recorded in the
Ϫ
1
range 4000–200 cm with a Perkin–Elmer IR 983G spec-
trophotometer using samples dispersed in spectroscopi-
cally pure KBr pellets.
2
CaCO ϩ M CO ϩ H P O
3 2 3 6 6 18
RESULTS AND DISCUSSION
ϩ 3H O Ǟ Ca M P O и 6H O ϩ 3CO
2
2
2
2
6
18
2
A. Crystal Data
with M ϭ K, Tl, and Rb.
The Weissenberg and oscillation photographs show that
1
To whom correspondence should be addressed.
the title compounds crystallize in the monoclinic P2 /n
1
3
08
0
022-4596/96 $18.00
Copyright  1996 by Academic Press, Inc.
All rights of reproduction in any form reserved.

CYCLOHEXAPHOSPHATE STRUCTURE Ca
2
M
2
P
6
O18 и 6H
2
O
309
TABLE 1
space group with the refined unit cell dimensions men-
tioned in Table 2. Indexing of the X-ray diffraction pattern,
with the refined parameters, is reported for the three com-
pounds in Table 3. The Ca K P O и 6H O unit cell param-
Crystal Data and Experimental Parameters Used for the
Intensity Data Collection; Strategy and Final Results of the
Structure Determination
2
2
6
18
2
eters are close to those obtained with a four-circle diffracto-
meter (Table 1).
I. Crystal data
Formula: Ca
Crystal system: monoclinic
2
K
2
P
6
O
18 и 6H
2
O
Fw ϭ 740.28
Space group: P2
Z ϭ 2
1
/n
a ϭ 7.266 (1), b ϭ 11.833 (2),
˚
˚
3
c ϭ 12.300 (2) A, ͱ ϭ 103.17
V ϭ 1030(3) A
B. IR Absorption Spectroscopy
(1)Њ
Refinement of unit cell parame- 25 reflections (10.4Њ Ͻ ␪ Ͻ 11.6Њ)
The infrared absorption spectra exhibit:
ters with:
cal. ϭ 2.387 g cm
Ϫ
3
␳
F(000) ϭ 372
Ȑ(AgKͰ) ϭ 0.77 mm
—two broad bands at about 3600–3200 and another at
Ϫ
1
Linear absorption factor:
Ϫ
1
1
650 cm corresponding to the water molecules in the
crystal arrangement, and
various valency vibration bands the number and
Morphology: quadratic prism
Crystal size: 0.32 ϫ 0.19 ϫ 0.19 mm
II. Intensity measurements
—
˚
Temperature: 294 K
Diffractometer: Enraf–Nonius
CAD4
Wavelength: AgKͰ (0.5608 A)
Scan mode: Ͷ
Ϫ
1
positions of which, between 1300 and 600 cm , character-
ize a phosphoric ring anion (4). In this type of anions
the vibrations of the O–P–O groups appear at relatively
Monochromator: graphite plate
Max scan time: 65 s
Measurement area: Ϯh, k, l
Total background measuring
time:
Scan width: 1.20Њ
Theta range: 2–30
Ϫ
1
high frequencies, i.e., 1200 Ͻ ␯ Ͻ 1300 cm and
as
h
max. ϭ 12, kmax. ϭ 20, lmax. ϭ 21
Ϫ
1
1
050 Ͻ ␯ Ͻ 1200 cm . Those corresponding to the
s
sA scan time
P–O–P groups give rise to a broad band ␯ around 960
as
Ϫ
1
Ϫ
1
Total number of scanned reflec- 6573
tions:
Total number of independent re- 6292
flections:
cm and a doublet ␯ between 800 and 700 cm . Figure
s
1
a
shows, as an example, the IR spectrum of
Ca K P O и 6H O.
2
2
6
18
2
Two intensity and orientation
reference reflections:
2ළ 71, 2 ළ7 1ළ (no variation)
C. Thermal Analysis
III. Structure determination
Lorentz and polarization correc- No absorption correction
tions
At rising temperature the compounds show similar trans-
formations between 100 and 600ЊC (Table 4). We describe
here the thermal behavior on hand of that of
Ca K P O и 6H O.
Program used: MolEN (5)
Computer used: Micro-Vax 3100
Determination: Patterson and successive Fourier synthesis. H atoms
from difference Fourier map.
Thermal displacement parameters atoms: Isotropic for H atoms, aniso-
tropic for other
2
2
6
18
2
Two curves corresponding to DTA and TGA analyses
in open air are given in Fig. 2 for Ca K P O и 6H O. In
2
2
6
18
2
Unique reflections included:
Weighting scheme: unitary
Residual Fourier density:
3486 with I Ͼ 4 ␴(I)
Refined parameters: 178
Ϫ0.38 Ͻ ␳ Ͻ 0.71 e A
order to prepare an interpretation as correct as possible
of the two curves, we performed, in addition, an investiga-
tion by X-ray diffraction and IR absorption which we re-
port and discuss below.
˚
Ϫ
3
Unweighted agreement factor R: 0.025
Weighted agreement factor R
w
:
0.027
e.s.d.: 0.86
Largest shift/error: 0.32
The thermal analysis curves show that the cyclohexa-
phosphate Ca K P O и 6H O undertakes at about 125 and
2
2
6
18
2
170ЊC two endothermic dehydrations well confirmed by
TABLE 2
2 2 6 2
Main Crystal Data for Ca M P O18 ؒ 6H O Cyclohexaphosphates
Unit cell parameters
˚
a
Ͱ
b
ͱ
c(A)
Ͳ(Њ)
˚
Compounds
18 и 6H
18 и 6H
18 и 6H
S.G.
Z
2
V (A)
Ca
2
Ca
2
Ca
2
K
2
P
6
O
2
O
7.309(3)
7.233(3)
7.290(3)
11.862(3)
12.335(3)
12.193(4)
12.236(3)
P2
P2
P2
1
1
1
/n
/n
/n
1041
1006
1016
1
03.22(2)
Tl
2
P
6
O
2
O
11.582(5)
2
9
9.94(2)
Rb
2
P
6
O
2
O
11.593(3)
00.86(1)
2
1

310
ABID AND RZAIGUI
TABLE 4
2 2 6 2
Main Thermal Data for Ca M P O18 ؒ 6H O
Cyclohexaphosphates
Thermal analyses
Compounds
Pics temperature (ЊC)
Ca
2
Ca
2
Ca
2
K
Tl
Rb
2
P
6
O
18 и 6H
18 и 6H
18 и 6H
2
O
2
O
2
O
125
139
138
170
196
159
500
485
450
562
544
507
2
P
6
O
2
P
6
O
ray beam (Fig. 3b) and which no more exhibits the IR
absorption bands characteristic of a cyclic phosphate (Fig.
1
b). This amorphous phase itself dehydrates in turns in a
wide temperature range, 230–550ЊC, to crystallize at 562ЊC
exothermic peak, Fig. 2) into an anhydrous compound the
(
IR spectrum of which (Fig. 1c) characterizes a condensed
FIG. 1. IR spectra of the phosphates: (a) Ca
amorphous phase, and (c) anhydrous compound.
2
K
2
P
6
O18 и 6H
2
O, (b) phosphate with ring anions (4). The X-ray diffractogram
of the crystallized phase (Fig. 3c) corresponds to that of
the cyclotriphosphate CaKP O identified elsewhere (5).
3
9
In conclusion, from the global TGA weight loss curve,
the weight losses observed on the TGA curve. According we may deduce the presence of six water molecules per
to the latter, a slight weight loss corresponds to a first formula unit (% water: experimental 14.2, calculated 14.6),
dehydration. This partial dehydration leads to an interme- which the structural analysis by X-ray diffraction con-
diate amorphous phase which does not diffract the X- firms clearly.
TABLE 3
2 2 6 2
X-Ray Powder Diffraction Data for Ca M P O18 ؒ 6H O
Ca
2
K
2
P
6
O
18 и 6H
2
O
Ca
2
Tl
2
P
6
O18 и 6H
2
O
2 2 6 2
Ca Rb P O18 и 6H O
˚
˚
˚
˚
˚
˚
h
k
l
d
cal (A)
d
obs (A)
I(%)
h
k
l
d
cal (A)
d
obs (A)
I(%)
h
k
l
d
cal (A)
d
obs (A)
I(%)
0
1
0
1
0
0
1
0
0
1
2
0
1
0
0
1
1
0
1
2
1
1
1
3
1
1
3
3
0
4
2
1
4
2
2
2
2
4
4
1
0
2
1
0
2
1
3
1
3
0
2
2
4
0
2
4
1
3
4
3
4
2
2
8.44
6.10
6.00
8.44
6.10
6.00
100
4
6
0
1
0
1ළ
0
1
0
ළ1
2
1
ළ1
0
0
ළ1
1
0
0
ළ2
0
1ළ
0
ළ1
ළ2
1
1
1
2
1
2
2
1
0
1
3
3
2
3
2
1
0
1
1
3
3
2
2
2
1
1
0
1
2
2
1
3
3
0
0
1
3
2
3
3
4
4
3
3
3
4
4
3
4
8.34
6.07
5.22
4.62
4.17
4.07
3.78
3.78
3.40
3.39
3.34
3.29
3.25
3.17
3.14
3.00
2.907
2.835
2.779
2.701
2.666
2.632
2.610
2.547
8.34
6.07
5.21
4.62
4.17
4.06
100
10
16
9
14
11
0
ළ1
0
0
0
1
1
0
2
0
0
1
0
0
1ළ
1
0
1
ළ2
0
1
ළ1
ළ2
1
1
1
2
2
2
1
1
1
2
3
1
0
4
1
2
3
4
2
4
4
4
1
1
1
2
1
2
1
2
3
0
3
2
3
4
0
4
3
3
0
3
2
1
2
4
8.34
5.82
5.33
5.22
4.17
4.06
3.97
3.79
3.42
3.30
3.25
3.13
8.35
5.82
5.34
5.23
4.17
4.06
3.97
3.79
3.42
3.30
3.25
3.12
100
4
12
15
11
5
5.93
5.93
5.36
5.05
3.79
3.76
3.70
3.41
3.30
3.15
3.00
2.966
2.965
2.910
2.879
2.810
ͮ
5.93
8
5.36
5.05
3.79
3.76
3.70
3.41
3.30
3.15
3.00
10
3
12
12
3
18
18
9
3
ͮ
3.78
16
14
40
11
58
8
24
17
7
3.40
3.39
3.34
3.29
3.25
3.17
3.13
3.00
2.906
2.834
2.780
2.701
2.667
2.632
2.610
2.547
18
19
16
13
41
7
11
14
9
7
27
6
6
7
3.00
3.00
6
2.898
2.884
2.832
2.781
2.686
2.637
2.610
2.583
2.520
2.490
2.900
2.884
2.831
2.781
2.686
2.636
2.611
2.583
2.519
2.491
ͮ
2.966
7
2
0
0
1
6
2.911
2.879
2.810
8
4
9
20
17
10
9
3
8
1
2.695
2.695
2.679
2.659
2.578
ͮ
2.694
5
2
0
0
2.678
2.659
2.578
6
5
4
9
7
15
1

CYCLOHEXAPHOSPHATE STRUCTURE Ca
2
M
2
P
6
O18 и 6H
2
O
311
TABLE 5
Final Atomic Coordinates and Beq for the Nonhydrogen
Atoms, Biso , for H Atoms
Atoms
x(␴)
y(␴)
z(␴)
Beq(␴)
Ca
K
P1
P2
0.42112(4)
0.86954(6)
0.33202(6)
0.59319(6)
0.42217(6)
0.3130(2)
0.6561(2)
0.4616(2)
0.0778(2)
0.2277(2)
0.9187(2)
0.7707(2)
0.0845(2)
0.5310(2)
0.4973(2)
0.5954(2)
0.7459(3)
0.28955(3)
0.09537(4)
0.18064(4)
Ϫ0.01035(4)
0.21005(4)
0.2737(1)
0.3691(1)
0.0822(1)
0.5840(1)
0.9494(1)
0.4250(1)
0.7485(1)
0.2396(1)
0.7806(1)
0.4782(1)
0.7983(1)
0.5129(2)
0.29631(3)
0.09455(4)
0.01894(3)
Ϫ0.18662(3)
Ϫ0.19320(3)
0.0960(1)
0.4503(1)
0.0869(1)
0.2147(1)
0.1405(1)
0.2891(1)
0.2420(1)
0.2702(1)
0.0587(1)
0.2026(1)
0.5095(1)
0.0462(2)
0.961(4)
1.741(6)
0.853(5)
0.848(5)
0.858(5)
1.33(2)
1.21(2)
1.08(2)
1.37(2)
1.36(2)
1.27(2)
1.39(2)
1.41(2)
1.23(2)
2.24(3)
2.07(3)
2.78(3)
Biso
P3
O(E11)
O(E12)
O(L12)
O(E21)
O(E22)
O(L23)
O(E31)
O(E32)
O(L31)
O(W1)
O(W2)
O(W3)
2 2 6 2
FIG. 2. DTA and TGA curves of Ca K P O18 и 6H O at rising tem-
perature.
D. Structure Description
Final atomic coordinates of all atoms of Ca K
2
2
H(1W1)
0.075(6)
0.564(6)
0.484(6)
0.851(6)
0.830(6)
0.286(7)
0.029(4)
0.478(4)
0.812(4)
0.352(4)
0.545(4)
Ϫ0.977(4)
0.305(3)
0.155(3)
0.461(3)
Ϫ0.001(3)
0.093(3)
0.515(4)
3(1)
3(1)
4(1)
3(1)
4(1)
6(1)
2
P O и 6H O and their B are given in Table 5. Figure 4 H(2W1)
6
18
2
eq
H(1W2)
H(2W2)
H(1W3)
shows a perspective view of the corrugated layers in the
Ca K P O и 6H O structure (P2 /n).
2
2
6
18
2
1
The cyclohexaphosphate anions. The two P O ring H(2W3)
6
18
anions are located around the inversion centers at (0, 0,
Note. e.s.d. are given in parentheses. Beq ϭ dF
͚
i
j i j ij
͚ a b ͱ .
2
List of structure factors and anisotropic thermal parameters are avail-
able on request to the authors.
FIG. 3. X-ray powder diffractograms of the phosphates: (a) Ca
O, (b) amorphous phase, and (c) anhydrous compound.
2 2
K
P
6
O
18 и 6H
2
2 2 6 2
FIG. 4. Perspective view of the Ca K P O18 и 6H O structure.

312
ABID AND RZAIGUI
TABLE 6
˚
Main Interatomic Distances (A) and Bond Angles (؇) in
Ca
2
2 6 2
K P O18 ؒ 6H O
4
The P(1)O tetrahedron
P(1)
O(E11)
O(E12)
O(L12)
O(L13)
O(E11)
O(E12)
O(L12)
O(L13)
1.480(1)
117.72(8)
109.58(7)
109.35(8)
2.537(2)
1.484(1)
109.61(7)
110.34(7)
2.523(2)
2.526(1)
1.607(1)
98.54(7)
2.511(2)
2.529(2)
2.427(2)
1.596(1)
The P(2)O
4
tetrahedron
P(2)
O(E21)
O(E22)
O(L12)
O(L23)
O(E21)
O(E22)
O(L12)
O(L23)
1.477(1)
119.74(8)
109.14(7)
108.13(7)
2.560(2)
1.483(2)
108.19(7)
110.79(7)
2.521(2)
2.510(2)
1.615(1)
98.81(7)
2.488(2)
2.534(2)
2.437(2)
1.595(1)
The P(3)O
4
tetrahedron
P(3)
O(E31)
O(E32)
O(L32)
O(L13)
O(E31)
O(E32)
O(L23)
O(L13)
P(1)–P(2)
P(1)–P(3)
P(2)–P(3)
1.477(1)
119.42(8)
106.87(7)
110.61(7)
2.8457(6)
2.8527(6)
2.8819(6)
2.553(2)
1.480(1)
110.29(8)
106.61(7)
2.482(2)
2.538(2)
1.612(1)
2.543(2)
2.484(2)
2.450(2)
101.54(7)
1.615(1)
P(1)–O(L12)–P(2)
124.07(8)
125.36(7)
127.95(8)
P(1)–O(L13)–P(3)
P(2)–O(L23)–P(3)
132.14(2)
P(1)–P(2)–P(3)
P(1)–P(3)–P(2)
P(2)–P(1)–P(3)
92.94(2)
134.72(2)
The CaO
8
polyhedron
Ca–O(E13)
Ca–O(E11)
Ca–O(E21)
Ca–O(E12)
Ca–O(E22)
2.416(1)
2.436(1)
2.432(1)
2.395(1)
2.440(1)
2.465(1)
2.628(2)
2.632(2)
Ca–O(E23)
Ca–O(W1)
Ca–O(W2)
The KO11 polyhedron
K–O(E13)
K–O(L12)
K–O(E12)
K–O(E12)
K–O(E22)
K–O(E22)
K–O(L23)
2.949(1)
3.057(1)
2.732(1)
2.865(1)
3.066(1)
3.445(1)
3.049(1)
2.913(1)
3.418(1)
2.825(2)
2.760(2)
K–O(E23)
K–O(L31)
K–O(W1)
K–O(W2)
The hydrogen-bond
O(W)–H и и и O
O(W)–H
H и и и O
O(W)–H и и и O
O(W)–O
O(W1)–H(1W1) и и и O(E23)
O(W1)–H(2W1) и и и O(W3)
O(W2)–H(1W2) и и и O(E11)
O(W2)–H(2W2) и и и O(W3)
O(W3)–H(1W3) и и и O(E21)
O(W3)–H(2W3) и и и O(W2)
0.79(4)
0.84(4)
0.91(4)
0.77(4)
0.83(4)
0.68(5)
2.53(4)
2.12(4)
2.16(4)
2.17(4)
2.12(4)
2.32(5)
140(4)
168(4)
148(4)
169(3)
165(4)
150(5)
3.181(2)
2.952(3)
2.970(2)
2.934(2)
2.923(2)
2.934(2)
H(1W1)–O(W1)–H(2W1)
H(1W2)–O(W2)–H(2W2)
H(1W3)–O(W3)–H(2W3)
114(4)
99(4)
110(5)
Note. e.s.d. vlaues are given in parentheses.

CYCLOHEXAPHOSPHATE STRUCTURE Ca
2
M
2
P
6
O18 и 6H
2
O
313
0
) and ( As , As , As ). In these centrosymmetrical P O groups, part in the coordination polyhedra of the Ca and K atoms.
6
18
the three P–P–P angles vary from 92.94Њ to 134.72Њ. This The third water molecule O(W3) is connected by H bonds
range is wider than that observed in (EDA) P O и 2H O to O(E21) and O(W2). Figure 4 shows that the atomic
3
6
18
2
(
6) with the same space group P2 /n, in which the P–P–P arrangement can be considered as a succession of two types
1
angle varies from 91.76Њ to 111.90Њ. On the other hand, the of corrugated layers stacked perpendicuarly to the (1, 0,
local arrangement around one PO tetrahedron and the 1) direction. The first type of layer contains the centrosym-
4
P–O–P bond angles are quite similar to those normally metrical phosphoric groups, and the second the water mol-
observed in all other condensed phosphoric anions. Table ecules and the K and Ca atoms. A three-dimensional net-
6
reports the main interatomic distances and bond angles work of hydrogen bonds connecting these two types of
in this P O ring anion. layers is described in Table 6.
6
18
Cation environments. Within a coordination sphere of
.7 A, the Ca atom has an eightfold coordination, resulting
ACKNOWLEDGMENT
˚
2
from six external oxygen atoms belonging to three P O
The authors thank Dr. M. T. Averbuch-Pouchot (CNRS Grenoble,
rings and two water molecules. The CaO polyhedron is France) for the data collection.
6
18
8
slightly distorted with Ca–O distances ranging between
REFERENCES
˚
.395 and 2.632 A (Table 6). The shortest Ca–Ca distance
2
˚
is 6.42 A.
1
2
. J. Le Flem, Eur. J. Solid State Inorg. Chem. 28, 3 (1991).
. U. Sch u¨ lke and R. Kayser, Z. Anorg. Allg. Chem. 531, 167 (1985).
The potassium atom is coordinated, within a range of
˚
3
.5 A, with eleven oxygen neighbors including two water 3. ‘‘Structure Determination package Molen,’’ 1990 version, Enraf–
nonius, Delft.
molecules and nine external and internal oxygen atoms of
4
. A. N. Lazarev and A. Mitgoroski, Izv. Akad. Nauk SSSR, Neorg.
Mater. 10, 661 (1974).
. R. Andrieu and R. Masse, C. R. Acad. Sci. Paris, 259, 4708–4711 (1964).
. A. Durif and M. T. Averbuch-Pouchot, Acta Crystallogr. C 46, 2026
(1990).
the PO tetrahedra. Each KO11 polyhedron joins three
4
P O rings, while each anionic ring connects six K polyhe-
6
18
5
6
dra and six Ca octahedra. The shortest K–K distance is
˚
4.01 A. The water molecules, O(W1) and O(W2), take