Homochiral porous lanthanide phosphonates with 1D triple-strand helical chains: Synthesis, photoluminescence, and adsorption properties

Article abstract of DOI:10.1021/ic060162h

Four homochiral porous lanthanide phosphonates, [Ln(H₂L) ₃]·2H₂O, (H₃L = (S)-HO ₃PCH₂-NHC₄H₇-CO₂H, Ln = Tb (1), Dy (2), Eu (3), Gd (4)), have been synthesized under hydrothermal conditions. These compounds are isostructural, and they possess a 3D supramolecular framework built up from 1D triple-strand helical chains. Each of the helical chain consists of phosphonate groups bridging adjacent Ln(III) ions. The helical chains are stacked through hydrogen bonds to form 1D tubular channels along the c axis. Moreover, helical water chains are located in the 1D channels, and after removal of these water chains, the compounds exhibit selective adsorption capacities for N₂, H₂O, and CH ₃OH molecules. Compounds 1 and 3 show strong green and red fluorescent emissions, respectively, in the solid state at room temperature. Crystal data for 1: TbP₃O₁₇N₃C ₁₈H₃₇, tetragonal (No.76), space group P4₁, a = 12.4643(3) A, b = 12.4643(3) A, c = 18.7577(5) A, V = 2914.17(13) A³, and Z = 4. For 2: DyP₃O ₁₇N₃C₁₈H₃₇, a = 12.4486(3) A, b = 12.4486(3) A, c = 18.7626(5) A, V = 2907.60(13) A³, and Z = 4. For 3, EuP₃O₁₇N ₃C₁₈H₃₇, a = 12.4799(3) A, b = 12.4799(3) A, c = 18.8239(5) A, V = 2931.78(13) A³, and Z = 4. For 4: GdP₃O₁₇N₃C₁₈H ₃₇, a = 12.4877(18) A, b = 12.4877(18) A, c = 18.824(4) A, V = 2935.5(8) A³, and Z = 4.

Full text of DOI:10.1021/ic060162h

Inorg. Chem. 2006, 45, 4431−4439
Homochiral Porous Lanthanide Phosphonates with 1D Triple-Strand
Helical Chains: Synthesis, Photoluminescence, and Adsorption
Properties
Qi Yue, Jin Yang, Guang-Hua Li, Guo-Dong Li, and Jie-Sheng Chen*
State Key Laboratory of Inorganic Synthesis and PreparatiVe Chemistry, College of Chemistry,
Jilin UniVersity, Changchun 130012, People’s Republic of China
Received January 29, 2006
Four homochiral porous lanthanide phosphonates, [Ln(H2L)3]‚2H2O, (H3L ) (S)-HO3PCH2-NHC4H7-CO2H, Ln )
Tb (1), Dy (2), Eu (3), Gd (4)), have been synthesized under hydrothermal conditions. These compounds are
isostructural, and they possess a 3D supramolecular framework built up from 1D triple-strand helical chains. Each
of the helical chain consists of phosphonate groups bridging adjacent Ln(III) ions. The helical chains are stacked
through hydrogen bonds to form 1D tubular channels along the c axis. Moreover, helical water chains are located
in the 1D channels, and after removal of these water chains, the compounds exhibit selective adsorption capacities
for N2, H2O, and CH3OH molecules. Compounds 1 and 3 show strong green and red fluorescent emissions,
respectively, in the solid state at room temperature. Crystal data for 1: TbP3O17N3C18H37, tetragonal (No.76), space
group P41, a
DyP3O17N3C18H37, a
3, EuP3O17N3C18H37, a
)
12.4643(3) Å, b
12.4486(3) Å, b
12.4799(3) Å, b
12.4877(18) Å, b
)
12.4643(3) Å, c
12.4486(3) Å, c
12.4799(3) Å, c
12.4877(18) Å, c
)
18.7577(5) Å, V
)
2914.17(13) Å3, and Z
2907.60(13) Å3, and Z
2931.78(13) Å3, and Z
18.824(4) Å, V
2935.5(8) Å3, and Z
)
4. For 2:
4. For
)
)
)
18.7626(5) Å, V
)
)
)
)
)
18.8239(5) Å, V
)
)
4.
For 4: GdP3O17N3C18H37, a
)
)
)
)
)
4.
Introduction
catalysis.5,6 In addition, attaching functional groups to the
phosphonic acid has led to the formation of metal phospho-
nates that possess functionalities within the micropores.6,7-9
Nevertheless, the previously reported open-framework metal
phosphonates mainly contain main-group metals or d-block
transition metals as the framework component,10-12 whereas
open-framework (or microporous) lanthanide phosphonates
are less common in the literature.13-18 As lanthanide ions
The synthesis of inorganic-organic hybrid materials has
attracted enormous attention because these extended systems
play a significant role in catalysis, chirality, luminescence,
magnetism, nonlinear optics, adsorption, and separation.1,2
Recently, there has been interest in metal phosphonates,
which are a special family of inorganic-organic hybrid
compounds, because of their versatile structural features and
potential applications.3,4 A variety of metal phosphonates with
an open-framework structure have been synthesized in the
past decade, and these phosphonate compounds may exhibit
microporosity for applications in adsorption and selective
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11563.
* To whom correspondence should be addressed. E-mail: chemcj@
jlu.edu.cn. Phone: +86-431-5168662. Fax: +86-431-5168624.
(1) Hagrman, P. J.; Hagrman, D.; Zubieta, J. Angew. Chem., Int. Ed. 1999,
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M., Kataoka, T., Suzuki, T., Eds.; Kodansha, Ltd.: Tokyo, 1991.
10.1021/ic060162h CCC: $33.50
Published on Web 04/28/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 11, 2006 4431

Yue et al.
exhibit variable high coordination numbers, it is believed
that the combination of lanthanide centers with phosphonate
groups will result in unusual architectures, and unique
properties resulting from f-f electronic transitions19 may be
found for the resulting materials.
of [Ln(H2L)3]‚2H2O, (H3L ) (S)-HO3PCH2-NHC4H7-CO2H;
Ln ) Tb (1), Dy (2), Eu (3), Gd (4)) and their adsorption
and photoluminescence properties will be described.
Experimental Section
Materials. EuCl3‚6H2O, GdCl3‚6H2O, TbCl3‚6H2O, and DyCl3‚
6H2O were prepared by dissolving Eu2O3, Gd2O3, Tb2O3, and Dy2O3
in hydrochloric acid followed by drying and crystallization. Other
reagents of analytical grade were obtained from a commercial source
(No. 4 Chemical Factory, Tianjin, China) and used without further
purification.
Chiral inorganic-organic hybrid materials with mi-
croporous architectures are potentially applicable in enan-
tioselective separation and asymmetric catalysis.20-29 There-
fore, it is of significance to incorporate enantiopure organic
species that exhibit high homogeneous catalytic activity for
asymmetric synthesis into the framework structures of
microporous hybrid compounds. (S)-proline and its deriva-
tives show high enantioselectivity in catalysis, and they are
able to produce good yields in many catalytical reactions.30-33
Although the past few years have witnessed significant
advances in the synthesis of chiral d-block transition metal
phosphonates with diverse structures using an enantiomeri-
cally pure derivative of (S)-proline, namely, N-(phospho-
nomethyl)proline, as the building unit,34-36 the acquisition
of functional chiral porous lanthanide phosphonates using
N-(phosphonomethyl)proline as a chiral reactant has not been
reported.
In this context, we chose the enantiomerically pure
derivative of (S)-proline, N-(phosphonomethyl)proline, as a
chiral building unit and successfully synthesized a series of
homochiral porous lanthanide phosphonates consisting of
one-dimensional triple-strand helical chains. These helical
chains interact with one another through hydrogen bonds to
form a 3D supramolecular framework with 1D tubular
channels. Interestingly, the structural characterization reveals
that there are one-dimensional helical water chains in the
1D channels. In addition, it is found that, after dehydration,
the obtained compounds exhibit selective adsorption capaci-
ties for N2 and other molecules. In this paper, the synthesis
Synthesis of (S)-HO3PCH2-NHC4H7-CO2H (H3L). This com-
pound was synthesized by following the procedure described in
the literature.37 Thus, 13 mmol (1.51 g) of L-proline, 26 mmol (2.13
g) of phosphorous acid, and 4 mL of hydrochloric acid (6.5 M in
water) were loaded into a round-bottom flask fitted with a reflux
condenser and heated for 5 min using a heating mantle. Formal-
dehyde (54 mmol, 1.5 mL, 36% aqueous solution) was added to
this mixture. The solution was further refluxed for 90 min. Water
was removed from the system by evacuation, and then 30 mL of
ethanol was added. Continuous refluxing led to the formation of a
white solid, which was subsequently recovered by filtration and
dried in vacuo to yield the target compound (2.12 g, 78%).
Synthesis of [Tb(H2L)3]‚2H2O, 1. A mixture of TbCl3‚6H2O
(0.112 g, 0.3 mmol) and H3L (0.251 g, 1.2 mmol) was dissolved
in 10 mL distilled water, followed by the addition of triethylamine
until the pH value of the system was adjusted to about 2.0. The
resulting solution was stirred for about 10 min at room temperature,
sealed in a 23 mL Teflon-lined stainless steel autoclave, and heated
at 100 °C for 2 days under autogenous pressure. Afterward, the
reaction system was slowly cooled to room temperature. Colorless
block crystals of 1 suitable for single-crystal X-ray diffraction
analysis were collected from the final reaction system by filtration,
washed several times with distilled water, and dried in air at ambient
temperature. Yield: 46.7% based on Tb. Anal. Calcd for 1: C,
26.36; H, 4.52; N, 5.13; Tb, 19.39. Found: C, 26.35; H, 4.51; N,
5.10; Tb, 19.35. Main IR bands (cm-1): 3507m, 3382v, 3291v,
3240v, 3052m, 3003vs, 2854m, 2699v, 1701m, 1411m, 1358m,
1329m, 1148s, 1081s, 1043s, 1008s, 823m, 763s, 686v, 608v, 538s,
436s.
Synthesis of [Dy(H2L)3]‚2H2O, 2. Compound 2 was prepared
in the same manner as compound 1, using DyCl3‚6H2O (0.113 g,
0.3 mmol) instead of TbCl3‚6H2O as the metal source. Colorless
block crystals were obtained in a 53% yield based on Dy. Anal.
Calcd for 2: C, 26.25; H, 4.50; N, 4.10; Dy, 19.75. Found: C,
26.24; H, 4.49; N, 4.08; Dy, 19.71. Main IR bands (cm-1): 3506m,
3286v, 3050m, 2853m, 2658v, 1700m, 1410m, 1358m, 1329m,
1149m, 1082,s 1044s, 1009s, 824m, 763s, 688v, 608v, 544s, 436s.
Synthesis of [Eu(H2L)3]‚2H2O, 3. Compound 3 was prepared
in a similar manner, and EuCl3‚6H2O (0.110 g, 0.3 mmol) was used
as the metal source. Colorless block crystals were obtained in a
43% yield based on Eu. Anal. Calcd for 3: C, 26.59; H, 4.55; N,
5.17; Eu, 18.71. Found: C, 26.56; H, 4.51; N, 5.15; Eu, 18.69.
Main IR bands (cm-1): 3508m, 3384v, 3052m, 2853m, 2698v,
1700m, 1410m, 1357m, 1328m, 1146s, 1080s, 1044s, 1007s, 824m,
763s, 687v, 609v, 539s, 436s.
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1736.
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340, 88.
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122, 5158.
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2003, 2002.
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O.; Yakhmi, J. V. Angew. Chem., Int. Ed. 2001, 40, 4242.
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Synthesis of [Gd(H2L)3]‚2H2O, 4. Compound 4 was successfully
crystallized with GdCl3‚6H2O (0.111 g, 0.3 mmol) as the metal
source using the procedure described above. Colorless block crystals
were obtained in a 40% yield based on Gd. Anal. Calcd for 4: C,
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4432 Inorganic Chemistry, Vol. 45, No. 11, 2006

Homochiral Porous Lanthanide Phosphonates
Table 1. Crystal Data and Structure Refinements for Compounds 1-4
1
2
3
4
empirical formula
fw
TbP3O17N3C18H37
819.34
DyP3O17N3C18H37
822.92
EuP3O17N3C18H37
812.38
GdP3O17N3C18H37
817.67
wavelength (Å)
temp (K)
cryst syst
space group
a (Å)
0.71073
293(2)
0.71073
293(2)
0.71073
293(2)
0.71073
293(2)
tetragonal
P41 (No. 76)
12.4643(3)
12.4643(3)
18.7577(5)
90
tetragonal
P41 (No. 76)
12.4486(3)
12.4486(3)
18.7626(5)
90
tetragonal
P41 (No. 76)
12.4799(3)
12.4799(3)
18.8239(5)
90
tetragonal
P41 (No. 76)
12.4877(18)
12.4877(18)
18.824(4)
90
90
90
2935.5(8)
4
1.850
b (Å)
c (Å)
R (deg)
â (deg)
90
90
90
90
90
90
γ (deg)
V (Å3)
2914.17(13)
4
1.867
2.673
1648
2907.60(13)
4
1.880
2.816
1652
2931.78(13)
4
1.840
2.384
1640
Z
F
calcd (Mg/m3)
µ (mm-1
F(000)
)
2.503
1644
reflns collected/unique
21 119/7231
R(int) ) 0.0815
0.31 × 0.29 × 0.27
7231/6/388
0.971
21 153/7202
R(int) ) 0.0597
0.32 × 0.25 × 0.19
7202/5/391
1.001
21 260/7013
R(int) ) 0.0477
0.30 × 0.25 × 0.18
7013/5/391
1.044
28 885/6562
R(int) ) 0.0610
0.33 × 0.24 × 0.25
6562/6/391
1.093
cryst size (mm)
data/restraints/ params
GOF on F2
Final R indices
[I > 2σ(I)]
R1 ) 0.0403
wR2 ) 0.0695
R1 ) 0.0521
wR2 ) 0.0731
1.116 and
-0.564
R1 ) 0.0302
wR2 ) 0.0558
R1 ) 0.0372
wR2 ) 0.0583
1.278 and
-0.573
R1 ) 0.0245
wR2 ) 0.0526
R1 ) 0.0294
wR2 ) 0.0550
1.184 and
-0.554
R1 ) 0.0326
wR2 ) 0.0586
R1 ) 0.0396
wR2 ) 0.0619
0.498 and
-0.808
R indices
(all data)
largest diff. peak
and hole (e A-3
)
26.42; H, 4.53; N, 5.14; Gd, 19.24. Found: C, 26.39; H, 4.51; N,
5.12; Gd, 19.21. Main IR bands (cm-1): 3508m, 3382v, 3052m,
2856m, 2700v, 1704m, 1410m, 1357m, 1329m, 1148s, 1081s,
1044s, 1007s, 823m, 762s, 685v, 608v, 538s, 434s.
tion, a slit width of 2.5 nm was selected for both excitation and
emission measurements.
Crystallographic Analyses. Crystallographic data of 1-4 were
collected at room temperature on a Bruker-AXS Smart CCD
diffractometer equipped with a normal-focus 2.4 kW X-ray source
(graphite-monochromated Mo KR radiation with λ ) 0.71073 Å)
operating at 50 kV and 40 mA with increasing ω (width of 0.3°
and exposure time 30 s per frame). The structures were solved by
direct methods using the program SHELXS-9738 and refined by
full-matrix least-squares against F2 using the SHELXTL-9739
crystallographic software package. All non-hydrogen atoms were
easily found from the difference Fourier maps and refined aniso-
tropically, whereas the hydrogen atoms of the organic molecules
were placed by geometrical considerations and were added to the
structure factor calculations. The H atoms on the water molecules
of the compounds were located initially from the difference Fourier
maps. However, the positions of these H atoms were adjusted by
taking into account of the O-H bond distance values. Pertinent
crystallographic data and structure refinement parameters for 1-4
are summarized in Table 1.
Physical Measurements. The infrared spectra were recorded
within the 400-4000 cm-1 region on a Bruker IFS 66V/S FTIR
spectrometer using KBr pellets. The C, H, N elemental analyses
were conducted on a Perkin-Elmer 240C element analyzer, whereas
the thermogravimetric (TG) and differential thermal analysis (DTA)
was performed on a Netzsch STA 449C thermogravimetric analyzer
under an atmospheric environment at a heating rate of 20 °C/min.
Inductively coupled plasma (ICP) analysis was conducted on a
Perkin-Elmer Optima 3300DV ICP spectrometer. The powder X-ray
diffraction (XRD) patterns were recorded on a Siemens D5005
diffractometer with Cu KR radiation (λ ) 1.5418 Å) over the 2θ
range of 4-40° at room temperature; the recording speed was 0.3°/
min. Nitrogen adsoption/desorption isotherms at the temperature
of liquid nitrogen were obtained with a Micromeritics ASAP 2020M
instrument after the samples were degassed at 200 °C and 1 ×
10-5 Torr for 10 h prior to the measurements. The specific surface
area was calculated using the BET equation, whereas the pore size
distribution was determined from the desorption branch of the
isotherm using the BJH method. The micropore surface area and
micropore volume values were determined by the t-plot method
from the volume adsorbed at a relative pressure of 0.4. The
adsorption isotherms of H2O and CH3OH were obtained at 298 K
by measuring the increase in weight at equilibrium as a function
of relative pressure. These measurements were performed using a
CAHN 2000 electrogravimetric balance. Prior to measurement, a
known weight (typically 20-40 mg) of the as-synthesized sample
was placed in a cylindrical Pt bucket and subjected to a programmed
heating (250 °C, 2 h) in a vacuum to remove the guest water
molecules. A point isotherm was recorded at the equilibrium state
(the stage when no further weight change was observed). The
photoluminescent properties of the samples were measured on a
Perkin-Elmer LS55 spectrometer. To obtain good spectral resolu-
Results and Discussion
Selected bond distances and angles for compounds 1, 2,
3, and 4 are listed in Tables 2-5. Compounds 2, 3, and 4
are isostructural with compound 1, and therefore only the
structure of 1 will be described in detail.
Crystal Structure. An ORTEP view of compound 1 is
shown in Figure 1. Each asymmetric unit of 1 consists of
one Tb(III) atom, three distinct H2L- anions, and two distinct
lattice water molecules. The Tb(III) center is six-coordinated
by phosphonate oxygen atoms from six H2L- anions in a
(38) G. M. Sheldrick, SHELXS-97, Programs for X-ray Crystal Structure
Solution; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(39) G. M. Sheldrick, SHELXTL-97, Programs for X-ray Crystal Structure
Refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
Inorganic Chemistry, Vol. 45, No. 11, 2006 4433

Yue et al.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 1a
Table 4. Selected Bond Lengths (Å) and Angles (deg) for 3a
Tb(1)-O(12)#1
Tb(1)-O(11)
Tb(1)-O(6)
Tb(1)-O(7)#1
Tb(1)-O(1)
Tb(1)-O(2)#2
P(1)-O(2)
2.239(4)
2.268(4)
2.274(4)
2.274(4)
2.274(4)
2.289(4)
1.493(4)
1.508(4)
1.555(4)
P(1)-C(5)
P(2)-O(6)
P(2)-O(7)
P(2)-O(8)
P(2)-C(11)
P(3)-O(11)
P(3)-O(12)
P(3)-O(13)
P(3)-C(17)
1.819(5)
1.492(4)
1.501(4)
1.534(4)
1.820(5)
1.495(4)
1.505(4)
1.536(4)
1.809(5)
Eu(1)-O(2)#1
Eu(1)-O(1)
Eu(1)-O(6)
Eu(1)-O(7)#1
Eu(1)-O(11)
Eu(1)-O(12)#2
P(1)-O(2)
2.279(3)
2.292(3)
2.294(3)
2.297(2)
2.309(3)
2.313(2)
1.491(3)
1.499(3)
1.544(3)
P(1)-C(5)
P(2)-O(6)
P(2)-O(7)
P(2)-O(8)
P(2)-C(11)
P(3)-O(12)
P(3)-O(11)
P(3)-O(13)
P(3)-C(17)
1.821(4)
1.496(3)
1.505(3)
1.538(3)
1.821(4)
1.498(3)
1.502(3)
1.550(3)
1.827(4)
P(1)-O(1)
P(1)-O(1)
P(1)-O(3)
P(1)-O(3)
O(12)#1-Tb(1)-O(11)
O(12)#1-Tb(1)-O(6)
O(11)-Tb(1)-O(6)
85.61(14) O(3)-P(1)-C(5)
155.34(14) O(6)-P(2)-O(7)
83.29(13) O(6)-P(2)-O(8)
106.1(2)
O(2)#1-Eu(1)-O(1)
O(2)#1-Eu(1)-O(6)
O(1)-Eu(1)-O(6)
O(2)#1-Eu(1)-O(7)#1
O(1)-Eu(1)-O(7)#1
O(6)-Eu(1)-O(7)#1
O(2)#1-Eu(1)-O(11)
O(1)-Eu(1)-O(11)
O(6)-Eu(1)-O(11)
O(7)#1-Eu(1)-O(11)
85.60(9) O(3)-P(1)-C(5)
154.90(10) O(6)-P(2)-O(7)
82.86(10) O(6)-P(2)-O(8)
81.09(9) O(7)-P(2)-O(8)
85.10(11) O(6)-P(2)-C(11)
119.83(10) O(7)-P(2)-C(11)
112.60(10) O(8)-P(2)-C(11)
155.92(10) O(12)-P(3)-O(11)
85.52(10) O(12)-P(3)-O(13)
82.51(9) O(11)-P(3)-O(13)
107.62(17)
115.75(16)
112.42(16)
107.24(15)
107.08(16)
106.68(16)
107.22(16)
115.83(16)
111.13(15)
108.89(15)
110.33(16)
103.72(16)
106.30(16)
163.35(18)
116.2(2)
112.4(2)
107.2(2)
106.5(2)
106.7(2)
107.4(2)
115.8(2)
112.2(2)
107.9(2)
109.3(2)
103.4(2)
107.5(2)
154.8(2)
O(12)#1-Tb(1)-O(7)#1 80.83(13) O(7)-P(2)-C(11)
O(11)-Tb(1)-O(7)#1
O(6)-Tb(1)-O(7)#1
O(12)#1-Tb(1)-O(1)
O(11)-Tb(1)-O(1)
O(6)-Tb(1)-O(1)
84.65(15) O(6)-P(2)-C(11)
119.77(13) O(7)-P(2)-C(11)
112.35(14) O(8)-P(2)-C(11)
155.92(13) O(11)-P(3)-O(12)
85.33(15) O(11)-P(3)-O(13)
82.70(13) O(12)-P(3)-O(13)
O(7)#1-Tb(1)-O(1)
O(12)#1-Tb(1)-O(2)#2 81.26(12) O(11)-P(3)-C(17)
O(2)#1-Eu(1)-O(12)#2 81.13(9) O(12)-P(3)-C(17)
O(11)-Tb(1)-O(2)#2
O(6)-Tb(1)-O(2)#2
111.53(14) O(12)-P(3)-C(17)
82.46(13) O(13)-P(3)-C(17)
O(1)-Eu(1)-O(12)#2
O(6)-Eu(1)-O(12)#2
111.73(10) O(11)-P(3)-C(17)
82.57(9) O(13)-P(3)-C(17)
O(7)#1-Tb(1)-O(2)#2 154.75(13) P(1)-O(1)-Tb(1)
O(7)#1-Eu(1)-O(12)#2 154.37(10) P(1)-O(1)-Eu(1)
O(1)-Tb(1)-O(2)#2
O(2)-P(1)-O(1)
O(2)-P(1)-O(3)
O(1)-P(1)-O(3)
O(2)-P(1)-C(5)
O(1)-P(1)-C(5)
87.82(13) P(1)-O(2)-Tb(1)#1 137.3(2)
O(11)-Eu(1)-O(12)#2
O(2)-P(1)-O(1)
O(2)-P(1)-O(3)
O(1)-P(1)-O(3)
O(2)-P(1)-C(5)
O(1)-P(1)-C(5)
87.46(9) P(1)-O(2)-Eu(1)#2 136.88(17)
115.91(17) P(2)-O(6)-Eu(1) 153.98(18)
107.87(16) P(2)-O(7)-Eu(1)#2 147.07(18)
155.06(16)
116.2(2)
111.2(2)
108.7(2)
110.6(2)
103.4(2)
P(2)-O(6)-Tb(1)
P(2)-O(7)-Tb(1)#2 147.1(2)
P(3)-O(11)-Tb(1) 161.9(3)
P(3)-O(12)-Tb(1)#2 138.4(2)
154.1(3)
112.13(18) P(3)-O(11)-Eu(1)
103.30(16) P(3)-O(12)-Eu(1)#1 136.23(15)
109.38(17)
a Symmetry transformations used to generate equivalent atoms: #1 -y
+ 1, x - 1, z + 1/4; #2 y + 1, -x + 1, z - 1/4.
a Symmetry transformations used to generate equivalent atoms: #1 -y
+ 2, x, z + 1/4; #2 y, -x + 2, z - 1/4.
Table 3. Selected Bond Lengths (Å) and Angles (deg) for 2a
Table 5. Selected Bond Lengths (Å) and Angles (deg) for 4a
Dy(1)-O(6)
Dy(1)-O(2)#1
Dy(1)-O(7)#1
Dy(1)-O(1)
Dy(1)-O(12)#2
Dy(1)-O(11)
P(1)-O(2)
2.234(3)
2.252(3)
2.255(3)
2.261(3)
2.270(3)
2.274(3)
1.502(3)
1.504(3)
1.534(3)
P(1)-C(5)
P(2)-O(6)
P(2)-O(7)
P(2)-O(8)
P(2)-C(11)
P(3)-O(11)
P(3)-O(12)
P(3)-O(13)
P(3)-C(17)
1.819(4)
1.494(3)
1.496(3)
1.534(3)
1.809(4)
1.495(3)
1.502(3)
1.550(3)
1.825(4)
Gd-O(6)
2.249(3)
2.282(4)
2.283(3)
2.287(3)
2.293(3)
2.293(3)
1.508(4)
1.509(3)
1.553(3)
P(1)-C(5)
P(2)-O(7)
P(2)-O(6)
P(2)-O(8)
P(2)-C(11)
P(3)-O(12)
P(3)-O(11)
P(3)-O(13)
P(3)-C(17)
1.827(5)
1.498(4)
1.505(4)
1.545(4)
1.818(5)
1.504(4)
1.509(4)
1.538(3)
1.826(5)
Gd-O(7)#1
Gd-O(12)#1
Gd-O(11)
Gd-O(1)
Gd-O(2)#2
P(1)-O(2)
P(1)-O(1)
P(1)-O(3)
P(1)-O(1)
P(1)-O(3)
O(6)-Dy(1)-O(2)#1
O(6)-Dy(1)-O(7)#1
O(2)#1-Dy(1)-O(7)#1
O(6)-Dy(1)-O(1)
O(2)#1-Dy(1)-O(1)
O(7)#1-Dy(1)-O(1)
O(6)-Dy(1)-O(12)#2
155.67(12) O(3)-P(1)-C(5)
85.80(11) O(6)-P(2)-O(7)
83.54(11) O(6)-P(2)-O(8)
80.80(11) O(7)-P(2)-O(8)
119.83(11) O(6)-P(2)-C(11)
85.14(12) O(7)-P(2)-C(11)
111.48(11) O(8)-P(2)-C(11)
106.85(19)
115.89(19)
107.81(18)
112.5(2)
103.39(18)
109.12(19)
107.5(2)
116.10(18)
111.00(17)
108.36(17)
110.58(18)
103.63(18)
106.54(18)
147.3(2)
O(6)-Gd-O(7)#1
O(6)-Gd-O(12)#1
O(7)#1-Gd-O(12)#1
O(6)-Gd-O(11)
O(7)#1-Gd-O(11)
O(12)#1-Gd-O(11)
O(6)-Gd-O(1)
O(7)#1-Gd-O(1)
O(12)#1-Gd-O(1)
O(11)-Gd-O(1)
O(6)-Gd-O(2)#2
O(7)#1-Gd-O(2)#2
O(12)#1-Gd-O(2)#2
O(11)-Gd-O(2)#2
O(1)-Gd-O(2)#2
O(2)-P(1)-O(1)
O(2)-P(1)-O(3)
O(1)-P(1)-O(3)
O(2)-P(1)-C(5)
O(1)-P(1)-C(5)
85.81(13) O(3)-P(1)-C(5)
155.52(13) O(7)-P(2)-O(6)
83.16(13) O(7)-P(2)-O(8)
80.96(13) O(6)-P(2)-O(8)
84.99(15) O(7)-P(2)-C(11)
119.56(12) O(6)-P(2)-C(11)
81.03(11) O(8)-P(2)-C(11)
111.62(14) O(12)-P(3)-O(11) 116.1(2)
82.85(12) O(12)-P(3)-O(13) 111.4(2)
154.40(13) O(11)-P(3)-O(13) 107.9(2)
106.2(2)
115.3(2)
111.4(2)
109.1(2)
109.5(2)
103.3(2)
107.7(2)
O(2)#1-Dy(1)-O(12)#2 85.60(12) O(11)-P(3)-O(12)
O(7)#1-Dy(1)-O(12)#2 156.66(11) O(11)-P(3)-O(13)
O(1)-Dy(1)-O(12)#2
O(6)-Dy(1)-O(11)
O(2)#1-Dy(1)-O(11)
O(7)#1-Dy(1)-O(11)
O(1)-Dy(1)-O(11)
O(12)#2-Dy(1)-O(11)
O(2)-P(1)-O(1)
82.46(11) O(12)-P(3)-O(13)
81.13(10) O(11)-P(3)-C(17)
82.39(11) O(12)-P(3)-C(17)
110.98(12) O(13)-P(3)-C(17)
154.72(11) P(1)-O(1)-Dy(1)
87.88(10) P(1)-O(2)-Dy(1)#2 154.4(2)
115.86(18) P(2)-O(6)-Dy(1) 139.17(19)
112.47(18) P(2)-O(7)-Dy(1)#2 161.3(2)
107.06(18) P(3)-O(11)-Dy(1) 137.81(17)
106.74(19) P(3)-O(12)-Dy(1)#1 154.34(19)
107.41(18)
112.22(13) O(12)-P(3)-C(17)
156.03(12) O(11)-P(3)-C(17)
85.26(14) O(13)-P(3)-C(17)
82.59(13) P(1)-O(1)-Gd
107.0(2)
106.6(2)
107.5(2)
136.6(2)
154.8(2)
138.4(2)
162.7(2)
147.1(2)
153.8(2)
87.57(12) P(1)-O(2)-Gd#1
116.1(2)
108.7(2)
111.1(2)
103.6(2)
110.5(2)
P(2)-O(6)-Gd
O(2)-P(1)-O(3)
P(2)-O(7)-Gd#2
P(3)-O(11)-Gd
P(3)-O(12)-Gd#2
O(1)-P(1)-O(3)
O(2)-P(1)-C(5)
O(1)-P(1)-C(5)
a Symmetry transformations used to generate equivalent atoms: #1 y,
-x + 1, z - 1/4; #2 -y + 1, x, z + 1/4.
a Symmetry transformations used to generate equivalent atoms: #1 -y
+ 1, x - 1, z + 1/4; #2 y + 1, -x + 1, z - 1/4.
severely distorted octahedral coordination sphere. The dis-
tances of the Tb-O bonds range from 2.239(4) to 2.289(4)
Å. There are three sets of O-Tb-O bond angles in the
ranges of 80.83(13)-87.82(13), 112.35(14)-119.77(13), and
154.75(13)-155.92(13)°. It is noteworthy that the three
distinct H2L- anions in the asymmetric unit of 1 adopt the
same coordination mode: only one phosphonate oxygen
atom is protonated, and another two of the three phosphonate
oxygen atoms coordinate to two adjacent Tb(III) centers in
a monodentate manner. The carboxylate group of the H2L-
4434 Inorganic Chemistry, Vol. 45, No. 11, 2006

Homochiral Porous Lanthanide Phosphonates
H atoms, and van der Waals radius of the H atoms is taken
into account) (Figure 2b and 2d). The protonated phosphonate
oxygen atoms (O(3), O(8), and O(13)) of three H2L- anions
act as the hydrogen donors and form O-H‚‚‚O hydrogen
bonds with the carboxylate oxygen atoms of the H2L- anions
(O(9)#3, O(14)#4, and O(4)#5) as the hydrogen acceptors
in neighboring helical chains (Table 6). Simultaneously, the
hydrogen atoms attached to the N atoms of the H2L- anions
(N(1), N(2), and N(3)) in the helical chain interact with the
carboxylate oxygen atoms of the H2L- anions (O(10)#3,
O(15)#4, and O(5)#5) in neighboring helical chains to form
N-H‚‚‚O hydrogen bonds, giving rise to a hydrogen-bonded
right-handed helical chain running along the c axis (Figure
3a). The hydrogen-bonding distances of O-H‚‚‚O (2.442-
(5), 2.449(5), and 2.543(6) Å) and N-H‚‚‚O (2.700(6),
2.782(6), and 2.865(6) Å) are slightly shorter than those
reported in the literature (mean O‚‚‚O and N‚‚‚O distances
are 2.765 and 2.946 Å, respectively). These strong hydrogen-
bonding interactions in compound 1 are favorable for
stabilization of the 3D supramolecular framework.
A notable feature for the compound is the presence of
helical water chains, and it is believed that the helical host
acts as a template for the formation of the helical chains of
water molecules. Among various types of water clusters, 1D
chain arrangements of water molecules are of interest because
of their occurrence in several biological processes related to
water and ion transport.41 Nevertheless, the knowledge of
structural constraints required in the stabilization of water
chains and the effect of chain structures on the host remains
incomplete. In 1, the one-dimensional helical water chain
with a pitch of 18.758 Å runs along the crystallographic 41
screw axis, and two types of lattice water molecule in the
water chain are arranged in an ABAB fashion (Figure 3a).
The water chains are stabilized by hydrogen bonds. The
interatomic distances and angles for the hydrogen-bonding
interactions in 1 are presented in Table 6. The O(2w)
molecule only acts as a donor, while the O(1w) molecule
only as an acceptor in the helical water chain, with the
O(2w)‚‚‚O(1w) and O(2w)‚‚‚O(1wA) distances being 2.903-
(9) and 2.782(9) Å, respectively. The angles O(2w)-O(1w)-
O(2wA) and O(1w)-O(2w)-O(1wA) in the water helix are
115.611 and 117.253°, respectively. Meanwhile, the helical
water chains are anchored onto the triple-strand helical host
chains, through hydrogen-bonding interactions (O1w‚‚‚O4
) 2.963(7) Å) between the noncoordinating carboxylate
oxygen atom (O4) and one of the water molecules (O1w)
(Figure S1 in the Supporting Information). Interestingly, such
weak interactions with the right-handed helical host chains
induce a left-handed helicity of water chains (Figure 3b and
c). In a sense, the formation of the helical water chains
depends on the chemical information and structure of the
helical host chains. Furthermore, the hydrogen-bonding
acceptors (carboxylate oxygen atoms) in 1 are in a favorable
position for anchoring different water molecules into an
extended array. In fact, the hydrogen bonds play an important
role not only in the formation of the water chains but also
in the stabilization of the supramolecular framework after
removal of the water chains. As demonstrated later, the
Figure 1. ORTEP view of compound 1 with 50% thermal ellipsoids. The
small green open circles represent the hydrogen atoms attached to the
phosphonate oxygen atoms, whereas the hydrogen atoms attached to nitrogen
atoms, carbon atoms, and lattice water molecules are omitted for clarity.
anions is deprotonated, but it does not coordinate to the Tb-
(III) center. The geometry about each phosphorus atom is
slightly distorted from tetrahedral with the O-P-O and
O-P-C angles being from 107.2(2) to 116.2(2)° and 103.4-
(2) to 110.6(2)°, respectively. The P-Obridging bond lengths
are in the range of 1.492(4)-1.508(4) Å, and the protonated
P-OH bond lengths are in the range of 1.534(4)-1.555(4)
Å, which are slightly longer than those of deprotonated P-O
groups. A strong absorption band in the range of 938-1149
cm-1, a weak one at 824 cm-1, and a medium one at around
763 cm-1 in the infrared spectrum of 1 can be attributed to
the stretching vibrations of P-O, P-OH, and P-C of the
phosphonate group, respectively.40
In compound 1, the Tb(III) centers are interconnected by
bridging phosphonate groups of the H2L- anions to form
infinite one-dimensional helical chains running along the c
axis with a Tb‚‚‚Tb separation of 4.8945 Å. Interestingly,
each helical chain is constructed by right-handed triple-
strands formed from three phosphonate groups of three H2L-
species which bridge two adjacent Tb(III) ions along the
crystallographic 41 screw axis (Figure 2a and 2c). An
individual strand of the triple helix has a repeat unit
consisting of Tb-O-P1-O-Tb-O-P2-O-Tb-O-P3-
O-Tb-O-P1-O with a period of 18.758 Å. The organic
moieties of the phosphonate groups appear to be leaves
pointing outward from the triple-strand helical chain, and
the pyrrolidinyl ring is approximately perpendicular to the
helical chain. The adjacent triple-strand helical chains are
further assembled through O-H‚‚‚O and N-H‚‚‚O hydrogen
bonds into a 3D supramolecular framework featuring 1D
tubular channels with a free diameter of about 4.32 × 3.81
Å (defined by the separation between the nearest diagonal
(40) Fu, R.; Xiang, S.; Zhang, H.; Zhang, J.; Wu, X. Cryst. Growth Des.
2005, 5, 1795.
Inorganic Chemistry, Vol. 45, No. 11, 2006 4435

Yue et al.
Figure 2. Helical chain structure in 1 running along the crystallographic 41 axis (the organic moieties of H3L are omitted for clarity) (a), the 3D supramolecular
framework of 1 viewed along the c (b) a axes (c), and the space filling structure of 1 viewed along the c axis (d). The arrows in panel a indicate the helicity
of the chain; the hydrogen atoms attached to carbon atoms are omitted for clarity, and the hydrogen bonds are indicated by the dotted lines: Tb, blue; P,
yellow; C, gray; N, green; O, red; H, white.
Table 6. Interatomic Distances and Angles for the Hydrogen Bonds in
synthesized compound. Porosity sustained by H-bonds has
1 (Å and deg)a
been occasionally observed42 for other metal-organic com-
D-H‚‚‚A
d(D-H) d(H‚‚‚A) d(D‚‚‚A)
(DHA)
pounds, but examples containing helical phosphonate chains
were not reported to the best of our knowledge. The infrared
spectrum of 1 shows two weak broad bands centered at
around 3506 and 3379 cm-1, as well as a very weak broad
band at around 3288 cm-1, attributable to the O-H stretching
vibrations of the water molecules. The O-H stretching
vibration in liquid water appears at 3490 and 3280 cm-1.
Hence, the O-H stretching vibration of water molecules in
the water chain of 1 are similar to those in liquid water,43
O(3)-H(3)‚‚‚O(9)#3
0.82
0.82
0.82
0.82
0.89(2)
0.91(2)
1.77
1.74
1.74
2.57
2.08(3)
2.11(6)
2.543(6) 156.0
O(8)-H(8)‚‚‚O(14)#4
O(13)-H(13)‚‚‚O(4)#5
O(13)-H(13)‚‚‚O(5)#5
O(1W)-H(1WA)‚‚‚O(4)
O(2W)-H(2WA)‚‚‚O(1W)
2.449(5) 144.2
2.442(5) 141.9
3.353(6) 159.0
2.963(7) 171(7)
2.903(9) 145(8)
O(2W)-H(2WB)‚‚‚O(1W)#5 0.866(6) 1.916(6) 2.782(9) 178.0(5)
N(1)-H(1)‚‚‚O(10)#3
N(2)-H(2)‚‚‚O(15)#4
N(3)-H(3A)‚‚‚O(5)#5
0.91
0.91
0.91
1.85
1.95
2.03
2.700(6) 153.6
2.782(6) 152.0
2.865(6) 152.6
a Symmetry transformations used to generate equivalent atoms: #1 -y
+ 1, x - 1, z + 1/4; #2 y + 1, -x + 1, z - 1/4; #3 -x + 2, -y + 1, z +
1/2; #4 -y + 1, x, z + 1/4; #5 y, -x + 1, z - 1/4.
(41) Lou, B.; Jiang, F.; Yuan, D.; Wu, B.; Hong, M. Eur. J. Inorg. Chem.
2005, 3214.
(42) (a) Sreenivasulu, B.; Vittal, J. J. Angew. Chem., Int. Ed. 2004, 43,
5769. (b) Mukherjee, A.; Saha, M. K.; Nethaji, M.; Chakravarty, A.
R. Chem. Commun. 2004, 716.
compound shows porosity upon heating which leads to the
removal of the water molecules occluded in the as-
4436 Inorganic Chemistry, Vol. 45, No. 11, 2006

Homochiral Porous Lanthanide Phosphonates
the electrogravimetric balance, the weight loss appeared to
be 4.43%, suggesting that the guest water molecules are
completely removed (ca. 4.37%). This phenomenon indicates
that the guest water molecules can be easily removed from
the host channels under vacuum. The powder XRD patterns
demonstrate the retention of the framework structure of 1
after the removal of both lattice water molecules at 250 °C
in a vacuum (Figure S3). The TG analysis results of 1, 2, 3,
and 4 are almost identical, indicating that the thermal
behaviors of the four compounds are very similar because
of isostructuralism.
Photoluminescent Properties. The photoluminescent
spectra of the as-synthesized samples of 1 and 3 are measured
at room temperature. As shown in Figure 4a, the free H3L
exhibits fluorescent emission bands at 371 and 425 nm (λex
) 235 nm), which are attributable to the π* f π and π* f
n transitions, respectively. Upon bonding of the H3L with
the lanthanide ions, the luminescent spectra of the compounds
formed display emission bands characteristic of the corre-
sponding lanthanide ions, whereas the emissions arising from
the free H3L are not observable. The absence of the free
H3L emissions in compounds 1 and 3 suggests energy
transfer from the phosphonate group to the central metal ions
during photoluminescence. When 1 is excited at 249 nm,
emissions appear in the range of 450-650 nm, and these
Figure 3. 1D hydrogen-bonded right-handed helical host chain (left) and
the 1D left-handed helical water chain (right) running along the c axis (a),
the anchoring of the water chain to the noncoordinating carboxylate oxygen
atoms of the helical host chain through hydrogen bonds (b), and a view of
the 1D helical water chain in the 1D channel formed from four adjacent
triple-stranded helical chains (c). The arrows in panel a indicate the helicity
of the host and the water chains; the hydrogen atoms attached to carbon
atoms are omitted for clarity, and the hydrogen bonds are represented by
the dotted lines: Tb, blue; P, yellow; C, gray; N, green; O, red; H, white.
5
7
emissions are attributed to the D4 f FJ (J ) 6, 5, 4, 3)
transitions of Tb(III) ion (Figure 4b). The 5D4 f 7F6, 5D4 f
7F5, and 5D4 f 7F4 emission bands each split into two peaks
(481 and 488, 540 and 548, and 582 and 595 nm, respec-
5
tively), corresponding to crystal field splitting. The D4 f
and the slight difference in vibrational frequency is attribut-
able to variation of the microenvironment for the water chain
and for liquid water.
Although compounds 2, 3, and 4 are isostructural with 1,
differences do exist for these four compounds. As shown in
Tables 2-5, the metal-oxygen bond distances and angles
for compounds 2, 3, and 4 vary from compound to compound
because the radii of the Ln(III) ions are different.
Thermal Properties. Thermogravimetric curves have been
obtained in air for crystalline samples of the four compounds
in the temperature range of 35-800 °C. The TG curve of 1
shows two main weight losses (Figure S2). The first weight
loss of 2.24% from 35 to 315 °C corresponds to removal of
one lattice water molecule in each formula unit (calcd
2.20%). It is presumable that the other water molecule in
the formula unit is lost during the sample preparation for
the TG analysis because the TG sample chamber is rather
dry. The second weight loss occurs in the temperature range
of 315-440 °C, attributable to the decomposition of the
organic groups. The final residual of the thermal process is
a mixture of TbPO4 and Tb2O3 on the basis of powder X-ray
diffraction. The observed total weight loss of 34.26% is less
than the theoretical value (37.81%) because the thermal
decomposition process is not complete at 800 °C, as shown
by the slope of the curve. When the as-synthesized sample
was subjected to heating at 250 °C for 2 h under vacuum in
5
7
7F6 and D4 f F5 emissions result from an electric dipole
transition and a magnetic dipole transition, respectively. The
spectrum is dominated by the 5D4 f 7F5 transition which is
more intense than the others, resulting in a strong green
luminescence output for the solid sample. When the Eu(III)
compound (3) is excited at 248 nm, characteristic luminescent
bands appear at 588, 596, 611, 652, and 700 nm via the
ligand-to-metal energy transfer mechanism, which correspond
5
7
to the transitions from the D0 state to the FJ (J ) 0-4)
levels, respectively (Figure 4c). Among these transitions, the
7
5D0 f F2 transition, which is an electric dipole transition
and is extremely sensitive to chemical bonds in the vicinity
of Eu(III) ion, is the strongest one, leading to bright red
5
luminescence. It is known that the intensity of the D0 f
7F2 transition increases as the site symmetry of Eu(III)
decreases, whereas the 5D0
f
7F0 transition is strictly
forbidden in a field of symmetry. Only one sharp, the second
5
7
most intense, band (588 nm) is observed for the D0 f F0
zero-phonon line in 3. The photoluminescence results reveal
not only the noncentrosymmetry of Eu(III) but also the
presence of only one type of Eu(III) site in the unit cell of
3. This is consistent with the result of the single-crystal X-ray
5
7
analysis. The D0 f F1 transition is a magnetic dipole
transition; its intensity varies with the crystal field strength
around the Eu(III) ion, and the intensity of this transition in
3 is weak. The intensity ratio of the 5D0 f 7F2 transition to
5
7
(43) Neogi, S.; Bharadwaj, P. K. Inorg. Chem. 2005, 44, 816.
the D0 f F1 one is widely used as a measure of the
Inorganic Chemistry, Vol. 45, No. 11, 2006 4437

Yue et al.
Figure 5. N2 adsorption isotherm for 2 at 77 K (a) (branches are
represented by the filled and open circles, respectively) and the H2O and
CH3OH sorption isotherms for 1 at 298 K (b).
adsorption isotherms. Here, only the adsorption properties
of 2 are described in detail because compounds 1-4 are
isostructural to one another and their adsorption behaviors
are similar. As shown in Figure 5, the N2 sorption of 2 at 77
K shows a reversible type-I isotherm, characteristic of a
microporous material and indicative of the permanent mi-
croporousity and architectural stability of the evacuated
framework. The N2 uptake of 29.14 cm3 (STP)/g (36.63 mg/
g) corresponds to 1.1 N2 molecules per formula unit of the
compound. With the BET model, the apparent surface area
of 2 is calculated to be 80.93 m2/g. By extrapolation of the
Dubinin-Radushkevich (DR) equation, the pore volume is
estimated to be 0.029 cm3/g. This smaller pore volume is
reasonable because the 3D supramolecular framework of 2
has only one-dimensional channels along the c axis. Com-
pound 2 also shows type-I isotherms upon exposure to H2O
and CH3OH vapors at 298 K (Figure 5). The H2O uptake of
38.41 mg/g amounts to 1.76 H2O molecules per formula unit,
which is in agreement with the theoretical value. The CH3-
OH uptake of 31.43 mg/g is equivalent to 0.8 CH3OH
molecules per formula unit. These results reveal that N2, H2O,
and CH3OH molecules can diffuse inside the micropores of
2. The powder XRD patterns indicate that 2 maintains its
structural integrity after dehydration-rehydration cycles.
Despite the stable framework structure, no CH3CH2OH
Figure 4. Emission spectrum of free H3L in the solid state at room
temperature, λexc ) 235 nm (a), the emission spectrum of 1 corresponding
to the 5D4 f 7FJ (J ) 6, 5, 4, 3) transitions in solid state at room temperature,
λexc ) 249 nm (b), and the emission spectrum of 3 corresponding to the
5D0 f 7FJ (J ) 0, 1, 2, 3, 4) transitions in solid state at room temperature,
λexc ) 248 nm (c).
coordination state and the site symmetry of the rare earth.44
For 3, the intensity ratio I(5D0 f 7F2)/I(5D0 f 7F1) is about
4.6, also indicating that the Eu(III) ions are not in an
inversion center in 3.
Adsorption Properties. To determine if these structures
have architectural rigidity and permanent porosity, we have
measured the N2, as well as H2O, CH3OH, and CH3CH2OH,
(44) Xu, Q. H.; Li, L. S.; Liu, X. S.; Xu, R. R. Chem. Mater. 2002, 14,
549.
4438 Inorganic Chemistry, Vol. 45, No. 11, 2006

Homochiral Porous Lanthanide Phosphonates
sorption capacity for 2 was observed at 298 K. The selective
sorption of N2, H2O, and CH3OH may be attributed to the
small aperture of the channels in 2, which discriminates these
molecules with small kinetic diameters. To the best our
knowledge, compounds 1-4 are the first homochiral porous
lanthanide phosphonates exhibiting permanent porosity for
selective sorption of molecules.
provides valuable information for further construction of
other homochiral porous lanthanide phosphonate frameworks.
Such chiral porous materials hold promise in applications
such as enantioselective separation and heterogeneous asym-
metric catalysis.
Acknowledgment. This work was supported by the
National Natural Science Foundation of China and the
Education Ministry of China.
Conclusions
Four isostructural homochiral porous lanthanide phospho-
nates with one-dimensional triple-strand helical chains have
been crystallized from a hydrothermal reaction system using
enantiomerical N-(phosphonomethyl)proline as the building
unit. These compounds show an interesting 3D supramo-
lecular framework structure with channels formed by helical
chains, and they exhibit selective adsorption capacities after
removal of the guest water molecules in the channels. The
successful preparation of the four solid compounds, 1-4,
Supporting Information Available: Four crystallographic
tables and X-ray crystallographic files (CIF), FTIR spectra and TG-
DTA curves for compounds 1, 2, 3, and 4, the powder XRD patterns
of the samples after removal of lattice water molecules at 250 °C
in a vacuum for 1, and the interatomic distances and angles for the
hydrogen bonding interactions for compounds 2, 3, and 4. This
material is available free of charge via the Internet at http://
pubs.acs.org.
IC060162H
Inorganic Chemistry, Vol. 45, No. 11, 2006 4439