Synthesis, structure, and photoluminescence property of a new layered zirconium phosphate |Co(dien)2|[Zr4H8P 5O26]·3H2O

Article abstract of DOI:10.1021/ic061873i

A new layered zirconium phosphate |Co(dien)₂|[Zr ₄H₈P₅O₂₆]·3H₂O (denoted ZrPO-CJ37) has been synthesized hydrothermally by using a racemic mixture of a chiral cobaltammine complex Co(dien)₂Cl₃ as the template. Its structure is determined by single-crystal X-ray diffraction analysis and further characterized by X-ray powder diffraction, inductively coupled plasma, thermogravimetric, UV-vis, and photoluminescence analyses. The inorganic layer of ZrPO-CJ37 is built up from the linkage of Zr-centered octahedra and P-centered tetrahedra via vertex oxygen atoms forming a 4.6-net sheet. Its structure features the edge-sharing chains of Zr(OM)₆ (M = P, H) octahedra. The cobaltammine complex cations are located in the interlayer region and interact with the host network through H bonds. ZrPO-CJ37 exhibits interesting photoluminescence in the UV-vis spectral region. The edge-sharing chains of Zr(OM)₆ octahedra in the inorganic layer might be responsible for this unusual photoluminescence.

Full text of DOI:10.1021/ic061873i

Inorg. Chem. 2007, 46, 5847−5851
Synthesis, Structure, and Photoluminescence Property of a New
Layered Zirconium Phosphate Co(dien)2 [Zr4H8P5O26] 3H2O
|
|
‚
Yu Du, Qinhe Pan, Jiyang Li, Jihong Yu,* and Ruren Xu
State Key Laboratory of Inorganic Synthesis and PreparatiVe Chemistry, Jilin UniVersity,
Changchun 130012, People’s Republic of China
Received September 29, 2006
A new layered zirconium phosphate
hydrothermally by using a racemic mixture of a chiral cobaltammine complex Co(dien)2Cl3 as the template. Its
|
Co(dien)2 [Zr4H8P5O26]‚3H2O (denoted ZrPO-CJ37) has been synthesized
|
structure is determined by single-crystal X-ray diffraction analysis and further characterized by X-ray powder diffraction,
inductively coupled plasma, thermogravimetric, UV
ZrPO-CJ37 is built up from the linkage of Zr-centered octahedra and P-centered tetrahedra via vertex oxygen
atoms forming a 4.6-net sheet. Its structure features the edge-sharing chains of Zr(OM)6 (M P, H) octahedra.
The cobaltammine complex cations are located in the interlayer region and interact with the host network through
H bonds. ZrPO-CJ37 exhibits interesting photoluminescence in the UV vis spectral region. The edge-sharing chains
of Zr(OM)6 octahedra in the inorganic layer might be responsible for this unusual photoluminescence.
−vis, and photoluminescence analyses. The inorganic layer of
)
−
Introduction
and iron phosphates,15,16 etc. Compared with the large number
of metal phosphates mentioned above, there are a few reports
on zirconium phosphates with new structures differing
from the R and γ types. Such compounds are known as one-
dimensional [enH2][Zr(HPO4)3], two-dimensional (2-D)
[enH2]0.5[Zr(PO4)(HPO4)],17 [C6H18N2]0.5[Zr2(PO4)(HPO4)2F2]‚-
0.5H2O, and [C6H18N2]1.5[Zr3(PO4)3F6]‚1.5H2O,18 and three-
dimensional [(enH2)0.5][Zr2(PO4)2(HPO4)F]‚H2O,19 [C5H18N2]0.5-
[Zr3(PO4)3(HPO4)F2]‚1.5H2O,18 and [C6H16N2]0.5[Zr2(PO4)-
(HPO4)2F2]‚0.5 H2O,20 etc.
Recently, by using optically pure or racemic mixtures of
chiral cobaltammine complexes such as Co(en)3Cl3, Co(dien)2-
Cl3, and Co(1, 2-diaminocyclohexane) as the templates, our
group has prepared a series of open-framework metal
phosphates,21-24 metal oxides |Co(en)3|[V3O9]‚H2O and |Co-
Over the past few decades, by employing various alkali-
metal ions or organic amines as structure-directing agents,
a large number of open-framework metal phosphates have
been synthesized under hydrothermal/solvothermal condi-
tions. These open-framework metal phosphates include
aluminophosphates,1-3 gallium phosphates,4-6 indium
phosphates,7-9 zinc phosphates,10-12 titanium phosphates,13,14
* To whom correspondence should be addressed. E-mail: jihong@
mail.jlu.edu.cn.
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10.1021/ic061873i CCC: $37.00
Published on Web 06/26/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 15, 2007 5847

Du et al.
(dien)2|[V3O9]‚H2O,25 and metal fluorides |Co(en)3|2(Zr2F12)-
(SiF6)‚4H2O and |Co(chxn)3|(ZrF6)Cl‚3.5H2O with chiral
characters.26 Interestingly, the latter two metal fluorides
containing H-bonded assemblies of each component species
show unusual photoelectronic effect. In our continued
research for new materials, by using a racemic mixture of a
chiral cobaltammine complex Co(dien)2Cl3 as the template,
we have successfully prepared a new layered zirconium
phosphate |Co(dien)2|[Zr4H8P5O26]‚3H2O (denoted ZrPO-
CJ37). Interestingly, it exhibits unusual photoluminescence
in the UV-vis spectral region.
More recently, the synthesis of inorganic materials with
luminescent property has received considerable attention.27-29
In particular, an unprecedented finding on the luminescent
properties of open-framework metal phosphates has been
reported, which provides insight into the influences of the
structure of active sites on the luminescence of microporous
materials.30 Developing an understanding of the relationship
between structure and photoluminescence is of practical and
theoretical importance in the design and synthesis of new
phosphor compounds.
In this work, a new layered zirconium phosphate |Co-
(dien)2|[Zr4H8P5O26]‚3H2O has been synthesized hydrother-
mally. Interestingly, it exhibits unusual photoluminescence
in the UV-vis spectral region. The study suggests that the
edge-sharing chains of Zr(OM)6 octahedra in the inorganic
layer might be responsible for this intriguing photolumines-
cence.
Figure 1. Experimental and simulated X-ray power diffraction patterns
for ZrPO-CJ37.
coupled plasma (ICP) analysis indicated a Zr/Co/P molar ratio of
1/0.25/1.25, in agreement with the empirical formula of |Co(dien)2|-
[Zr4H8P5O26]‚3H2O given by single-crystal structure analysis.
2. Characterization. X-ray powder diffraction (XRD) data were
collected on a Siemens D5005 diffractometer with Cu KR radiation
(λ ) 1.5418 Å). ICP analysis was performed on a Perkin-Elmer
Optima 3300DV spectrometer. A Perkin-Elmer TGA 7 unit was
used to carry out the thermogravimetric analysis (TGA) in air with
a heating rate of 10 °C /min. The UV-vis absorption spectrum
was recorded on a Perkin-Elmer Lambde 20 UV-vis spectrometer
using BaSO4 pellet and measured in a scattering geometry. The
luminescent property was measured on a Perkin-Elmer LS55
spectrometer. The slit width for both excitation and emission
measurements was 5 nm. The powdered sample was placed in the
quartz cell for the photoluminescence spectrum measurement. The
magic-angle-spinning NMR spectra were recorded on a Varian
Infinity Plus-400 spectrometer. The 31P NMR spectrum was taken
at 161.9 MHz with a spinning rate of 11 kHz. Chemical shifts were
referenced to 85% H3PO4. The recycle delay time was 60 s.
Experimental Section
1. Synthesis. In a typical synthesis, zirconium tetrachloride
(ZrCl4, 0.233 g, 1.00 mmol) was dissolved in distilled water (10
mL), followed by the addition of bis(diethylenetriamine)cobalt(III)
chloride (Co(dien)2Cl3, 0.118 g, 0.25 mmol) and phosphoric acid
(H3PO4, 0.159 mL, 85 wt %, 2.34 mmol) with stirring. Hydrofluoric
acid (HF, 0.3 mL, 40 wt % aq, 6.00 mmol) and tetraethylortho-
silicate (Si(OEt)4, 0.20 mL, 97 wt % aq, 0.87 mmol) were then
added to the above reaction mixture. After stirring for 30 min, the
final reaction mixture with a pH value of ca. 1.0 was transferred
into a Teflon-lined stainless steel autoclave (20 mL), heated at 140
°C for 6 days, and cooled at room temperature. The resulting
product, containing orange plate-shaped crystals, was isolated by
filtration, washed with deionized water, and dried in air. The phase
purity of ZrPO-CJ37 was checked by recording its X-ray powder
diffraction pattern, which was consistent with that simulated on
the basis of the single-crystal structure data (Figure 1). Inductively
3. Structural Determination. A suitable single crystal with
dimensions of 0.2 × 0.2 × 0.08 mm3 was selected for single-crystal
X-ray diffraction analysis. The intensity data were collected on a
Rigaku R-AXIS RAPID IP diffractometer by oscillation scans using
graphite-monochromated Mo KR radiation (λ ) 0.71073 Å). Cell
refinement and data reduction were accomplished with the RAPID
AUTO program. The structure was solved in the space group P2/c
by direct methods and refined on F2 by full-matrix least squares
using SHELXTL97.31 No absorption correction was applied. The
heaviest atoms of Zr, Co, and P were easily located, and O, C, and
N atoms were subsequently located in the difference Fourier maps.
H atoms attached to the terminal Zr-O and P-O groups, and parts
of the cobaltammine complex cations were placed geometrically
and refined using a riding model. H atoms associated with water
molecules were not added. It was noted that the C(2) atom of the
Co(dien)23+ cation was positionally disordered. The low-temperature
X-ray study has been made at 80 K, but there was no improvement
for the disorder of C(2) atom in the structure. All non-hydrogen
atoms were refined anisotropically. Crystal data and refinement
parameters for the structure determination are presented in Table
1. The selected bond distances and bond angles are presented in
the Supporting Information Table 2s. CCDC publication no. 622251
contains the supplementary crystallographic data for this paper.
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5848 Inorganic Chemistry, Vol. 46, No. 15, 2007

New Layered Zirconium Phosphate
Figure 2. ORTEP view (50%) for ZrPO-CJ37.
Table 1. Crystal Data and Structure Refinement for
[Co(dien)2][Zr4H8P5O26]‚3H2O
empirical formula
fw
C8H40CoN6O29P5Zr4
1263.12
T (K)
273(2)
wavelength (Å)
cryst syst, space group
unit cell dimens
0.71073
monoclinic, P2/c
a ) 12.1149(11) Å
b ) 8.8183(8) Å
c ) 17.3298(16) Å
1760.8(3)
R ) 90°
â ) 107. 997(2)°
γ ) 90°
V (Å3)
Z, calculated density
2, 2.382
(Mg/m3)
abs coeff (mm-1
F(000)
)
1.944
1248
cryst size (mm)
θ range for data
collection (deg)
limiting indices
0.2 × 0.2 × 0.08
1.77-27.81
-15 e h e 15,
-11 e k e 7,
-22 e l e 22
10204/3747
[R(int) ) 0.0586]
89.8
Figure 3. (a) View of 4.6-net sheet structure parallel to the *bc* plane in
ZrPO-CJ37. (b) Packing of the inorganic sheets in an AAAA sequence along
the [100] direction.
reflns collected/unique
distance of 1.553(5) Å. A P(3) atom lying on the 2-fold axis
is in the tetrahedral environment to make four P-O-Zr
linkages, and the P-O distances are in the range of 1.520-
(5)-1.536(5) Å. The asymmetric unit also contains two water
molecules and one unique Co atom on the 2-fold axis. The
C(2) atom of the Co(dien)3+ cation is disordered over two
sites, with 50% occupancy.
completeness to θ )
27.48° (%)
refinement method
full-matrix least
squares on F2
3747/12/255
0.992
data/restraints/params
GOF on F2
final R indices
[I > 2σ(I)]
R indices (all data)
R1 ) 0.0514,
R2 ) 0.0991
R1 ) 0.0838,
R2 ) 0.1097
0.991 and
As seen in Figure 3a, the linkage of Zr-centered octahedra
and P-centered tetrahedra via vertex oxygen atoms forms a
2-D sheet containing four and six rings (denoted 4.6-net).
The inorganic sheets stack in an AAAA sequence along the
[100] direction, with the cobaltammine complex cations and
H2O molecules residing in the interlayer regions (Figure 3b).
The cobaltammine complex cations interact with the terminal
OH groups in the inorganic framework and H2O molecules
through H bonds, with the N(O)‚‚‚O separations of 2.786-
(7)-3.124(13) Å. It is worth noting that the inoganic layer
can be viewed as being composed of the edge-sharing chains
of Zr(OM)6 (M ) P, H) octahedra along the [010] direction;
as seen in Figure 4, the zirconium atom acts as the octahedra
center and the M atom acts as the octahedra vertex.
largest diff peak and
hole
-0.677 e‚Å-3
Results and Discussion
1. Structure and Characterization. Single-crystal X-ray
diffraction analysis indicates that ZrPO-CJ37 crystallizes in
the monoclinic space group of P2/c (No. 13) with the formula
|Co(dien)2|[Zr4H8P5O26]‚3H2O. Each asymmetric unit (Figure
2) contains two crystallographically distinct Zr atoms and
three distinct P atoms. Both Zr atoms are coordinated by
six oxygen atoms to form distinct Zr(1)O5(OH) and Zr(2)-
O4(OH)2 octahedra, with the Zr-Obridging and the terminal
Zr-OH distances in the range of 2.029(5)-2.092(4) Å and
1.981(4)-1.987(5) Å, respectively. The O-Zr-O angles are
in the range of 84.4(2)-178.8(2)°. Both P(1) and P(2) atoms
are tetrahedrally coordinated by oxygen atoms, forming P(1)-
O3(OH) and P(2)O4 tetrahedra, with the P-Obridging distances
in the range of 1.513(5)-1.529(4) Å and the terminal P-OH
TGA shows three weight loss steps between 50 and
1200 °C (Supporting Information, Figure 1s). The first weight
loss of 4.32 wt % from 50 to 250 °C corresponds to the loss
of three water molecules (calcd 4.28 wt %). The second
Inorganic Chemistry, Vol. 46, No. 15, 2007 5849

Du et al.
Figure 4. Inoganic layer composed of the edge-sharing chains of Zr(OM)6 (M ) P, H) octahedra along the [010] direction (octahedra center, Zr atoms;
vertex, M atom).
Figure 6. UV-vis absorption spectrum of ZrPO-CJ37.
Figure 5. 31P MAS NMR spectroscopy of ZrPO-CJ37.
The UV-vis absorption spectrum of ZrPO-CJ37 shows
three bands with maxima at approximately 243, 345, and
weight loss of 10.7 wt % between 250 and 500 °C is
attributed to the loss of hydroxyl groups in the framework
(calcd 10.8 wt %), which can be confirmed by the fact that
the -OH absorption bands around 3520 and 1612 cm-1 32
466 nm (Figure 6). The two bands at 345 and 466 nm are
3+
d-d transitions characteristic of Co(dien)2 cations.35 The
band at 243 nm is assigned as a ligand-to-metal charge
transfer from the oxygen to the zirconium center.36
are absent in the IR spectrum when ZrPO-CJ37 is calcined
2. Luminescent Property. The photoluminescence (PL)
at 500 °C (Supporting Information, Figure 2s). The third
spectrum for ZrPO-CJ37 excited at 243 nm shows wide and
weight loss of 14.6 wt % from 500 to 1200 °C corresponds
to the decomposition of the cobaltammine complex (calcd
14.7 wt %) in the product. XRD studies indicated that the
final product upon calcination above 1200 °C is a mixture
of ZrO2, CoO, and Zr2O(PO4)2.33
distinct emission bands at 300, 380-430, and 450-600 nm
(Figure 7a). This is scarcely observed in the known zirconium
phosphates.37 A previous study shows that the photolumi-
38
nescence of K2Hf1-xZrx(PO4)2 and KHf2(1-x)Zr2x(PO4)3 is
ascribed to oxygen-to-zirconium charge transfer within the
As seen in Figure 5, 31P MAS NMR spectroscopy shows
Zr(PO4)6 subunits. This octahedral Zr(PO4)6 moiety appears
two sharp resonance lines at -19.29 and -24.09 ppm,
to be an important structural element for efficient lumines-
respectively. The signal at -24.09 ppm with one shoulder
cence. It is believed that the luminescence for ZrPO-CJ37
at -26.00 ppm indicates that it is the superposition of two
might be due to the charge transfer from oxygen to zirconium
lines with close chemical shifts. The three 31P signals are in
in the octahedral Zr(OM)6 moiety of the edge-sharing chains.
agreement with the three crystallographically distinct P sites
Because its luminescence is described as a self-activated
in the structure and are characteristic of the tetrahedral
charge-transfer mechanism, it is possible that a shorter
phosphate sites.34
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5850 Inorganic Chemistry, Vol. 46, No. 15, 2007

New Layered Zirconium Phosphate
380-600 nm might be due to the charge transfer from
oxygen to zirconium in Zr-O-H and Zr-O-P linkages,
respectively. Figure 7 shows the photoluminescence spectra
of the as-prepared sample of ZrPO-CJ37 and the sample
calcined at 500 and 1200 °C. The wavelengths of the
excitation light are all 243 nm. It is worth noting that, in
contrast to Figure 7a, the intensities of the emission bands
around 300 nm and in the region of 450-600 nm decrease
remarkably in Figure 7b. It might be caused by the change
of luminescence environment for Zr-O-H and part of the
Zr-O-P linkages with the loss of hydroxyls at 500 °C. As
seen in Figure 7c, the fact that all the emission bands almost
vanish might be explained by the structure transformation
of ZrPO-CJ37 with Zr(OM)6 octahedra to Zr2O(PO4)2, with
ZrO7 pentagonal bipyramids in geometry,33 when ZrPO-CJ37
is calcined at 1200 °C. These results in Figure 7 not only
present the influences of crystal structure on the photolu-
minescence but also further confirm the analyses of the
emission bands in Figure 7a.
Conclusions
|Co(dien)2|[Zr4H8P5O26]‚3H2O is the first zirconium phos-
phate templated by a metal complex. The linkage of
Zr-centered octahedra and P-centered tetrahedra forms the
2-D layered structure. The cobaltammine complex cations
are accommodated in the interlayer region. It exhibits
interesting photoluminescence in the UV-vis spectral region,
which is ascribed to an oxygen-to-zirconium charge transfer
within the octahedral Zr(OM)6 moiety of the edge-sharing
chains, and may be influenced by the complicated coordina-
tion environments of the luminescent center of zirconium.
The successful synthesis of ZrPO-CJ37 and the discovery
of its unusual optical property will be helpful for the search
of new materials with useful luminescent properties.
Figure 7. Photoluminescence spectra of the as-prepared sample of
ZrPO-CJ37 (a) and the sample calcined at 500 °C (b) and 1200 °C in air
(c) (λex ) 243 nm, slit (Ex), 5.0 mm; and slit (Em), 5.0 mm).
distance between the luminescent Zr4+ cations facilitates
energy transfer from the oxygen ligands and encourages
significant electronic reorganization.39 Moreover, we found
that the known zirconium phosphates, which are not com-
posed of the edge-sharing chains of the Zr(OM)6 octahedra,
did not exhibit luminescence.
Acknowledgment. This work is supported by the Na-
tional Natural Science Foundation of China and the State
Basic Research Project of China (2006CB806103).
The complicated coordination environment of the lumi-
nescent center for zirconium in ZrPO-CJ37 might lead to
different Stokes shifts and consequently result in the wide
and distinct luminescence emission in the UV-vis spectral
region. As is known, the Stokes shifts increase with the
decrease of the electronegativity of adjacent or subadjacent
coordinated atoms to the luminescent center atom.40 There-
fore, the emission bands at 300 nm and in the regions of
Supporting Information Available: One PDF and one CIF
file. This material is available free of charge via the Internet at
http://pubs.acs.org.
IC061873I
(40) Tamatani, M. Luminescence centers of transition metal ions. In
Phosphor Handbook; Shionoya, S., Ed.; CRC Press: Boca Raton, FL,
1999; p 153.
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Inorganic Chemistry, Vol. 46, No. 15, 2007 5851