Indian Journal of Chemistry
Vol. 49A, November 2010, pp. 1478-1482
Notes
Synthesis, crystal structure and
characterization of an organically templated
cobalt phosphate supramolecule
Xiaoyan You & Lixia Zhu∗
Department of Applied Chemistry, School of Science, Xidian
University, Xi’an, Shaanxi, PR China 710071
Email: [email protected] (XY)/ [email protected] (LZ)
Received 31 March 2010; revised and accepted 19 Oct 2010
A novel organically templated cobalt phosphate supramolecule,
[Co(H2O)6]2[HPO4]4·2(C2N2H10), has been synthesized hydrothermally and characterized by single crystal X-ray diffraction,
vibrational spectroscopy, elemental analysis and TGA-DSC. The
title compound crystallizes in monoclinic system, space group
P2(1)/c, a = 6.27(3) Å, b = 16.367(8) Å, c = 14.736(7) Å,
α = 90.00°, β = 91.405(7)°, γ = 90.00°, V = 1512.2(3) Å3, Z = 2. The
structure of the title compound consists of four isolated PO3(OH)
tetrahedrons, two cobalt complex cation [Co(H2O)6]2+ and two
diprotonated ethylenediamine molecules. The PO3(OH)
tetrahedrons and cobalt octahedras are linked together via hydrogen
bonding interaction, forming an open framework architecture.
Protonated ethylenediamine molecules reside in the spacing of the
framework and compensate the charge balance.
Keywords: Supramolecule, Crystal structure, X-ray diffraction,
Hydrothermal synthesis, Cobalt phosphate
Microporous materials have attracted considerable
interest because of their potential applications in
catalysts, ion-exchangers and sorbents1-3. Since the first
microporous aluminophosphate molecular sieve was
reported in 19824, open framework metal phosphates
have been extensively explored. Among these metal
phosphates, cobalt phosphates constitute an important
group for their potential applications and structural
diversities. Cobalt can exhibit tetrahedral, trigonal
bipyramidal and octahedronal structures resulting in
variation of structures types, such as two-dimensional
layer5 and three-dimensional open framework
structure6-9 linked by PO4 tetrahedrons. Most of these
cobalt phosphates contain vertex-sharing metalate and
phosphate polyhedrons. In the present work, we report
a novel cobalt phosphate supramolecular open
framework with one-dimensional channels based on
hydrogen bonding interactions, which are different
from those reported with M--O--P linkage6-9. The
compound has also been charaterised by vibrational
spectroscopy, elemental analysis and thermal analysis.
Experimental
All reagents were of analytical grade and
used without further purification. Single crystals
of the title compound were synthesized under
hydrothermal
conditions.
CoCl2·6H2O
(2.38 g, 10 mmol) and H3PO4(3.82 g, 40 mmol)
were mixed in 6 ml deionic water, and then
ethylenediamine(1.80 g, 30 mmol) was added
dropwise with vigorous stirring. The obtained
mixture (pH = 4) was transferred into a 20 ml
Teflon-lined autoclave at 170 oC for 2 days. After
the autoclave cooled to room temperature, pink
plane-like crystals were collected from the solution
and dried in air for further characterization. FT-IR
spectrum was recorded on a Bruker Vertex 70
FT-IR spectrometer with KBr pellet, while Raman
spectrum was recorded on a Nicolet Almega
dispersive Raman spectrometer. Elemental analyses
was recorded on a Vario EL III elemental analyzer
and TGA-DTA curves were recorded between 323K
and 873K on a SDT Q600 thermal analyzer in
nitrogen with a heating rate of 5 oC /min.
A pink crystal of suitable size (0.40×0.40×0.30 mm3)
was selected under microscope and glued to a thin
glass fiber with epoxy resin. Crystal structure was
determined on a Rigaku AFC10/Saturn 724+ CCD
diffractometer
with
graphite-monochromated
Mo-Kα (λ = 0.71073 Å) radiation in multiple scan
mode at 93(2) K. The structure was solved by direct
method and refined on F2 by full-matrix least
squares method using SHELXS-97 and SHELXL97 programs, respectively10. All non-hydrogen
atoms were refined anisotropically. Hydrogen
atoms were placed geometrically. Crystallographic
data are presented in Table 1, atom coordinates and
isotropic displacement are listed in Table 2 and
selected bonds and angles are listed in Table 3.
Results and discussion
Results of elemental analysis are in good
agreement with the calculated values based on the
formula given by X-ray single crystal diffraction
studies.
Elemental
analysis
(wt
%)
for
[Co(H2O)6]2[HPO4]4·2(C2N2H10):
Found
(%):
C, 5.70; H, 5.70; N, 6.65; Calc. (%): C, 5.62;
H, 5.69; N, 6.43.
1479
NOTES
Table 1  Crystal data and structure refinement for
[Co(H2O)6]2[HPO4]4·2(C2N2H10)
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system, space group
Unit cell dimensions
Volume
Z, Calculated density
Abs. coeff.
F(000)
Crystal size
θ range for data collection
Limiting indices
Reflections collected/unique
Completeness to θ = 27.44
Abs. corr.
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I>2σ(I)]
R indices (all data)
Extinction coefficient
Largest diff. peak and hole
[Co(H2O)6]2[HPO4]4·2(C2N2H10)
842.20
93(2) K
0.71073 (Å)
Monoclinic, P2(1)/c
a = 6.271(3) Å; α = 90°
b = 16.367(8) Å; β = 91.405(7)°
c = 14.736(7) Å; γ = 90°
1512.2(13) Å3
2, 1.850 mg/m3
1.418 mm-1
876
0.40 mm × 0.40 mm × 0.30 mm
3.03 − 27.44°
-7 ≤ h ≤ 8, -21 ≤ k ≤ 21, -18 ≤ l ≤ 18
11531/ 3396 [R(int) = 0.0291]
98.5%
Empirical
0.6756 and 0.6008
Full-matrix least-squares on F2
3396/3/274
0.999
R1 = 0.0307, wR2 = 0.0747
R1 = 0.0383, wR2 = 0.0789
0.0032(5)
0.753 and -0.430 e. Å-3
Table 3 Selected bond lengths and angles for
[Co(H2O)6]2[HPO4]4·2(C2N2H10)
Bond lengths (Å)
Co(1)-O(1)
Co(1)-O(1)#1
Co(1)-O(2)#1
Co(1)-O(2)
Co(1)-O(3)
Co(1)-O(3)#1
P(1)-O(10)
P(1)-O(9)
P(1)-O(8)
P(1)-O(7)
2.0592(18)
2.0593(18)
2.0755(19)
2.0755(19)
2.1122(19)
2.1123(19)
1.5240(16)
1.5314(17)
1.5344(16)
1.5924(17)
Co(2)-O(5)
Co(2)-O(5)#2
Co(2)-O(4)#2
Co(2)-O(4)
Co(2)-O(6)#2
Co(2)-O(6)
P(2)-O(13)
P(2)-O(11)
P(2)-O(14)
P(2)-O(12)
2.0645(18)
2.0645(18)
2.0717(18)
2.0717(18)
2.0976(19)
2.0976(19)
1.5270(16)
1.5327(16)
1.5329(17)
1.6062(17)
179.999(1)
179.999(1)
180.0
111.75(8)
111.73(9)
112.07(8)
109.38(9)
108.94(9)
102.52(8)
O(5)-Co(2)-O(5)#2
O(4)#2-Co(2)-O(4)
O(6)#2-Co(2)-O(6)
O(13)-P(2)-O(11)
O(13)-P(2)-O(14)
O(11)-P(2)-O(14)
O(13)-P(2)-O(12)
O(11)-P(2)-O(12)
O(14)-P(2)-O(12)
180.00(8)
180.0
180.0
111.62(9)
113.19(8)
112.04(8)
107.91(9)
104.25(8)
107.25(9)
Bond angles (°)
O(1)-Co(1)-O(1)#1
O(2)#1-Co(1)-O(2)
O(3)-Co(1)-O(3)#1
O(10)-P(1)-O(9)
O(10)-P(1)-O(8)
O(9)-P(1)-O(8)
O(10)-P(1)-O(7)
O(9)-P(1)-O(7)
O(8)-P(1)-O(7)
Symmetry transformations used to generate equivalent atoms:
#1 -x,-y+2,-z+1; #2 -x+2,-y+1,-z+1
Table 2  The atomic coordinates (×104) and equivalent
isotropic displacement parameters (Å2 × 103) for
[Co(H2O)6]2 [HPO4]4·2(C2N2H10). [U(eq) is defined as one third
of the trace of the orthogonalized Uij tensor]
Co(1)
Co(2)
P(1)
P(2)
O(1)
O(2)
O(3)
O(4)
O(5)
O(6)
O(7)
O(8)
O(9)
O(10)
O(11)
O(12)
O(13)
O(14)
N(1)
N(2)
C(1)
C(2)
x
y
z
U(eq)
0
10000
5888(1)
4167(1)
2965(2)
948(3)
836(3)
7029(3)
8881(3)
9072(3)
4951(2)
4999(2)
8328(2)
5054(2)
4916(2)
5380(2)
4879(2)
1767(2)
5924(3)
9017(3)
8304(4)
9539(4)
10000
5000
5812(1)
7475(1)
9634(1)
10021(1)
11239(1)
4705(1)
4813(1)
6226(1)
6612(1)
5871(1)
5854(1)
5059(1)
8305(1)
7379(1)
6775(1)
7466(1)
3499(1)
2116(1)
3581(1)
2818(1)
5000
5000
2476(1)
4913(1)
4587(1)
6359(1)
4825(1)
4449(1)
6289(1)
5115(1)
1999(1)
3435(1)
2484(1)
1973(1)
5283(1)
3972(1)
5535(1)
4689(1)
2600(1)
2173(1)
2528(2)
2783(2)
7(1)
8(1)
7(1)
7(1)
15(1)
18(1)
20(1)
15(1)
15(1)
17(1)
13(1)
9(1)
11(1)
10(1)
9(1)
11(1)
11(1)
11(1)
15(1)
13(1)
17(1)
17(1)
Fig. 1  The fundamental
[Co(H2O)6]2[HPO4]4·2(C2N2H10).
building
block
unit
of
The structure of the title compound contains two
isolated cobalt-centered octahedrons, two sets of
PO3(OH) phosphate groups and two diprotonated
ethylenediamine molecules (Fig. 1). The projection of
the crystal structure along a axis is shown in Fig. 2.
The structure contains 14-jointed windows built up of
hydrogen-bonded cobalt octahedrons and PO3(OH)
tetrahedrons. Both of the cobalt atoms are sixcoordinated with water molecules. The bond lengths
of Co--O are in the range of 2.0592(18)--2.1122(19)
(avg.: 2.0807 Å) and 2.0645(18) − 2.0976(19) Å
(avg.: 2.0779 Å) for Co1 and Co2 respectively. The
average Co−O distances are longer than the covalent-
1480
INDIAN J CHEM, SEC A, NOVEMBER 2010
Fig. 3  FT-IR spectrum of [Co(H2O)6]2[HPO4]4·2(C2N2H10).
Fig. 2  Projection of [Co(H2O)6]2[HPO4]4·2(C2N2H10) in the bc
plane. [Colour code: copper: light green; phosphorus: purple;
oxygen: red; hydrogen: light grey].
bonded cobalt phosphates reported in literature6, 7. The
P−O distances vary from 1.5240(16) − 1.5924(17)
and 1.5170(16) − 1.6062(17) Å for P1 and P2
tetrahedrons respectively, which lead to distorted
tetrahedrons. The average values of O−P−O are
109.40 and 109.25° for P1 and P2 tetrahedrons,
respectively.
The cobalt octahedrons connect with PO4
tetrahedrons via hydrogen bonds, forming an open
framework architecture. In the bc plane, each Co1
octahedron is surrounded by four Co2 octahedrons
linked together via hydrogen-bonded PO3(OH)
tetrahedrons with the two sets of P1 and P2
tetrahedrons in an alternating pattern of inward and
outward planes, while along the a axis, each Co1
polyhedra is linked by hydrogen-bonded P1O3(OH)
tetrahedrons (Co1−Co1 distance: 5.73 Å). The
configuration of Co2 is almost the same as that of
Co1 atoms except for the opposite orientation of each
P1 tetrahedron along the a axis. Moreover, the
interatomic O...O distance between two phosphate
tetrahedrons is in the range of 2.532(2)--2.602(2) Å,
indicating strong hydrogen bonding interaction. The
hydrogen-bonded linkage of metal octahedrons
and phosphate tetrahedrons indicates anionic
pseudo-open framework with alternatively deposited
Fig. 4  Raman spectrum of [Co(H2O)6]2[HPO4]4·2(C2N2H10).
one-dimensional channels with the aperture (P−P
distance) of about 8.2595×9.7921 Å in [100]
direction. The diprotonated ethylenediamine is held in
the channels through N−H...O interactions with O
atoms from phosphate units. The removal of the
ethylenediamine molecules creates 24.36% “solvent
accessible voids” (using platon software), which
indicates the potential application as adsorbents.
As
is
well
known,
hydrogen-bonded
supermolecules feature building blocks contain di- or
multiple tectons. In the title compound, each oxygen
atom (O1, O2, O3, O4, O5, O6), coordinated with
cobalt atoms, acts as hydrogen-bond donor and forms
two-fold hydrogen bonds. Also, the oxygens (O8, O9,
O10, O11, O13, O14) connected with phosphorus
atoms, act as hydrogen-bond acceptors, except O7 in
1481
NOTES
Table 4  Hydrogen bonds in [Co(H2O)6]2[HPO4]4·2(C2N2H10)
D-H...A
d(D-H)
(Å)
d(H...A)
(Å)
d(D...A)
(Å)
<(DHA)
(°)
O(1)-H(1A)...O(11)
O(4)-H(4B)...O(8)
O(6)-H(6B)...O(13)
O(12)-H(12O)...O(8)
N(1)-H(01A)...O(10)
N(1)-H(01C)...O(12)#3
N(1)-H(01B)...O(13)#4
N(2)-H(02A)...O(7)#3
N(2)-H(02C)...O(9)#5
N(2)-H(02B)...O(14)#3
O(1)-H(1B)...O(10)#6
O(2)-H(2B)...O(9)#7
O(2)-H(2A)...O(10)#8
O(3)-H(3B)...O(11)#9
O(3)-H(3A)...O(14)#1
O(4)-H(4A)...O(13)#4
O(6)-H(6A)...O(14)#10
O(7)-H(7O)...O(11)#11
O(5)-H(5A)...O(8)#4
O(5)-H(5B)...O(9)#2
0.87(3)
0.82(3)
0.816(10)
0.84(3)
1.04(4)
0.98(3)
1.01(3)
0.97(3)
0.96(4)
0.99(4)
0.819(10)
0.84(4)
0.89(4)
0.87(4)
0.91(4)
0.82(3)
0.88(3)
0.82(4)
0.83(3)
0.812(10)
1.82(3)
1.92(3)
2.051(11)
1.76(3)
1.76(4)
2.09(3)
1.87(3)
1.97(3)
1.74(4)
1.86(4)
1.925(12)
1.95(4)
1.83(4)
1.92(4)
1.88(4)
1.89(3)
1.85(3)
1.72(4)
1.88(3)
1.903(11)
2.687(2)
2.721(2)
2.861(2)
2.602(2)
2.765(3)
3.049(3)
2.842(3)
2.917(3)
2.693(3)
2.835(3)
2.731(2)
2.763(2)
2.711(3)
2.775(3)
2.780(2)
2.702(2)
2.725(2)
2.532(2)
2.717(2)
2.714(2)
175(3)
169(3)
172(3)
176(3)
160(3)
168(2)
162(3)
165(2)
174(3)
166(3)
168(3)
164(3)
171(4)
166(3)
173(3)
170(3)
176(3)
170(4)
176(3)
176(3)
Symmetry transformations used to generate equivalent atoms: #1 -x,-y+2,-z+1; #2 -x+2,-y+1,-z+1; #3 -x+1,y-1/2,-z+1/2; #4 -x+1,
-y+1,-z+1; #5 -x+2,y-1/2,-z+1/2; #6 -x+1,y+1/2,-z+1/2; #7 x-1,-y+3/2,z+1/2; #8 x,-y+3/2,z+1/2; #9 -x+1,-y+2,-z+1.
P1O3 (OH) and O12 in P2O3 (OH), which act as both
donors and acceptors linking the two phosphate
tetrahedrons. It is worth noting that in the second
sphere coordination, hydrogen bond interaction plays
an important role in maintaining the structure as
mentioned above. The details of hydrogen bonds are
listed in Table 4.
The IR and Raman vibrational spectra are
presented in Figs 3 and 4. The broad band at
3500 − 3000 cm-1 with a strong peak at 3446.90 cm-1
in the IR spectrum and in the range 3500−3000 cm-1
with a maximum at 3315.40 cm-1 in Raman
spectrum are due to the stretching vibration of
O−H, N−H, C−H. Bands at 2970.48, 2897.20 and
2820.06 cm-1 in the Raman spectrum are ascribed to
the asymmetric stretching mode of C−H. The band
at about 1600 cm-1 is attributed to the bending
mode of H−O−H. Bands at 1454.71 and
1354.43 cm-1 in the Raman spectrum correspond to
the bending mode of C−H. All the bands, as
mentioned above, confirm the presence of
ethylenediamine and water molecules in the
structure. Bands observed at 1040.95, 978.55 cm-1
in the IR spectrum and 951.38 cm-1 in the Raman
spectrum are assigned to the asymmetric stretching
vibration of P−O. The band at 851.51 cm-1 in the IR
spectrum is ascribed to the symmetric stretching
Fig. 5  TGA-DTA curves of [Co(H2O)6]2[HPO4]4·2(C2N2H10).
vibration of P−O. Bands at 551.69, 475.18 cm-1 in
the IR spectrum and at 552.18, 394.05 cm-1 in the
Raman spectrum are ascribed to the bending mode of
P−O.
TGA analysis shows a two-step weight loss process
(Fig. 5). The first weight loss of 30.12 %
(calc.: 29.92 %) corresponds to the decomposition of
fourteen water molecules with twelve water molecules
from cobalt octahedrons and the other two from
phosphates. Then, a second weight loss (found: 14.81 %,
calc.: 14.72 %) was observed, attributed to the release of
1482
INDIAN J CHEM, SEC A, NOVEMBER 2010
two ethylenediamine molecules in the channels. The
weight loss process can be ascribed as follows:
[Co(H2O)6]2[HPO4]4·2(C2N2H10)
−14 H O
2
→
Co(PO3)2(PO4)2·2(C2N2H10)
H-bonds, which compensate the charge balance and
make
the
crystal
structure
stable.
This
supermolecular architecture promises a new aspect
of microporous cobalt phosphate based on hydrogenbond linkage.
−2C N H
2 2 10 → Co(PO ) (PO )

3 2
4 2
The DTA curve presents an exothermal peak at
80 oC and a weak peak at about 380 oC, corresponds
to the two-step weight loss.
In the present study, the title compound was
synthesized under hydrothermal conditions and
characterized by single crystal X-ray diffraction,
elemental analysis, vibrational spectroscopy and
thermal analysis. The structure of the title compound
contains a pseudo-open framework architecture with
alternatively deposited one-dimensional channels
made of hydrogen-bonded metal octahedrons and
phosphate tetrahedrons, and the diprotonated
ethylenediamine occupying the channels through
References
1
2
3
4
5
6
7
8
9
10
Centi G, Catal Today, 16 (1993) 5.
Suib S L, Chem Rev, 93 (1993) 803.
Feng P, Bu X & Stucky G D, Nature, 388 (1997) 735.
Wilson S T, Lok B M & Flanigen E M, J Am Chem Soc, 104
(1982) 1146.
Guo H X & Liu S X , J Mol Struct, 74 (2005) 229.
Debord J R D, Haushalter R C & Zubieta J, J Solid State
Chem, 125 (1996) 270.
Yuan H M, Chen J S, Zhu G S , Li J Y, Yu J H, Yang G D &
Xu R R, Inorg Chem, 39 (2000) 1476.
Chiang R K, Inorg Chem, 2004 (39) 4985.
Huang T, B Vanchura A , Shan Y K & Huang S D , J Solid
State Chem, 180 (2007) 2110.
Sheldrick G M , SHELXS97 Program for Solution of Crystal
Structures; (University of Gottingen, Gottingen, Germany)
1997.