PH-dependent syntheses, luminescence and magnetic properties of two-dimensional framework lanthanide 1,3-diarylphosphonate complexes

Article abstract of DOI:10.1039/c3nj01388j

A series of novel organic-inorganic complexes based on trivalent lanthanides and 1,3-C₆H₄[CH₂P(O)(OH) ₂]₂ (H₄L) formulated as Ln(HL)(H ₂O)₂ (Ln = La, 1; Pr, 2; Nd, 3;

Full text of DOI:10.1039/c3nj01388j

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ARTICLE TYPE
pH-Dependent Syntheses, Luminescence and Magnetic Properties of
Two-Dimensional Framework Lanthanide 1,3-Diarylphosphonate
Complexes
Yi-Fu Liu,a Guang-Feng Hou,a,b Ying-Hui Yu,a Peng-Fei Yan,*a Guang-Ming Lia and Jin-Sheng Gao*ab
5
Received (in XXX, XXX) Xth XXXXXXXXX 200X, Accepted Xth XXXXXXXXX 200X
DOI: 10.1039/b000000x
Abstract: A series of novel organic–inorganic complexes based on trivalent lanthanide and 1, 3-
C6H4[CH2P(O)(OH)2]2 (H4L) formulated as Ln(HL)(H2O)2 (Ln = La, 1; Pr, 2; Nd, 3; Sm, 4; Eu, 5; Gd,
6; and Tb, 7) have been obtained as single phases by regulating the pH under hydrothermal conditions.
10 Complexes are isostructural and feature a network in which the LnO7 polyhedra are interconnected by
bridging CPO3 tetrahedra into inorganic layers. Theses layers are further stacked with the benzyl groups
of ligands via C−H ··· π interaction into a laminar framework architecture. Luminescent measurements
indicate that complexes 4, 5 and 7 show strong metal-centered emission bands in yellow, red and
green light region, respectively. Magnetic properties of 2 and 7 have also been studied.
the difficulty in obtaining suitable single crystals for X-ray
structural determination, and some of their structures reported
were determined by X-ray powder diffraction.11 A series of
15 Introduction
Lanthanide ions possess fascinating optical properties and their
discovery, first industrial uses and high technological applications
are largely governed by their interaction with light.1 Lanthanide
complexes exhibit intense luminescence because of the long-lived
20 (milliseconds timescale) excited states of Ln3+ ions.
Luminescence has been instrumental and these lanthanide
elements have always played a prominent role in lighting and
light conversion technologies such as lasers, cathode-ray-tube
screens, plasma displays, and light-emitting diodes.2 This led to
25 some most interesting developments in the coordination
chemistry of lanthanide ions. Remarkably, the mostly studied
complexes of Eu3+ and Tb3+ could exhibit intensely visible
linelike emission.3 There has been tremendous recent interest
in the design and synthesis of functional materials based on
lanthanide
organodiphosphonates
with
3D
networks,
50 Ln[HO3P(CH2)nPO3] (n = 1−3; Ln = Pr, Nd, Eu, Gd) was
structurally determined from X-ray powder diffraction studies.12
Under 457.9 nm argon ion laser excitation at 77 K,
5
Eu[HO3P(CH2)3PO3] displayed five strong lines for the D0 →
7F2 transition in 610−622 nm.12c Rocha et al.13 afforded two new
55 Ln3+ phosphonates with 1,4-phenylenebis (methylene)
diphosphonic (H4pmd), [Ln(Hpmd)(H2O)] (Ln = Ce and Pr),
exhibiting an unprecedented trinodal topology with 3- and 8-
connected nodes. In summary, the lanthanide complexes with aryl
or alkyl substituted mono-phosphonic acids normally display a
60 layered structure whereas those of the corresponding di-
phosphonic acids prefer a pillared-layered structure.14,15 To gain a
deeper insight into the photoluminescence and magnetic
properties of lanthanide phenylphosphonates, we choose 1,3-
phenylenebis(methylene) diphosphonic acid (H4L) with rigid
65 phenyl group and flexible methylene group to investigate the
structures, luminescence, and magnetic properties of its
complexes with Ln3+ ions.
30 lanthanide arylphosphonates.4
A huge number of organic
moieties can be converted to phosphonic acids, allowing for a
vast array of metal phosphonates to be synthesized.5 So far, a
great number of metal phosphonates with intriguing structures
have been successfully constructed.6−9 In 1992, Clearfield and
35 coworkers10 first reported lanthanide benzylphosphonate,
La(O3PCH2C6H5)(HO3PCH2C6H5)(H2O)2. In this structure, six
oxygen atoms of the metal coordination sphere are provided by
the phosphonate ligands, the other two are from aqua ligands. The
deprotonated phosphonate group forms a La–O–P–O chelating
40 ring with a La3+ ion. The protonated phosphonate group bridges
two La3+ ions with two oxygen atoms. The third oxygen atom
with a longer P–O distance remains uncoordinated. Such
connectivity resulted in a layered structure with the benzyl ring
oriented toward the interlayer space. However, the low solubility
45 of lanthanide phosphonates in water and organic solvents led to
We synthesized the ligand from commercial 1,3-bis
(chloromethyl)benzene by Michaelis-Arbuzov reaction16 in three
70 steps according to the procedures outlined in Scheme 1.
Hydrothermal reactions of H4L with lanthanide (III) nitrates
through regulating the pH afforded seven novel lanthanide
diphosphonate complexes, namely, Ln(HL)(H2O)2 (Ln = La, 1;
Pr, 2; Nd, 3; Sm, 4; Eu, 5; Gd, 6; Tb, 7). Herein, we report their
75 syntheses, structures, thermal behaviors, luminescent, and
magnetic properties.
This journal is © The Royal Society of Chemistry [year]
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Page 2 of 7
Scheme 1. Synthesis of H4Lα
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DOI: 10.1039/C3NJ01388J
O
O
O
O
ii)
i)
EtO P
EtO
P OEt
OEt
HO P
HO
P OH
OH
ClH2C
CH2Cl
iii)
α(i) P(OEt)3, reflux, 6 h. (ii) 20 wt % NaOH/H2O, reflux, 6 h. (iii) 6 M HCl.
1
(MeOH): 208, 244 nm. H NMR (DMSO): δ 7.21–7.15 (m, J =
7.8Hz, 4H), 3.04−2.88 (m, J = 21.6 Hz, 4H). IR (KBr, cm−1):
55 3433(m), 2979(s), 1674(s), 1498(m), 1403(m), 1267(s), 1143(vs),
1064(vs), 982(vs), 830(s), 749(m), 590(s), 519(m).
5
Experimental Section
Materials and methods
All commercially available chemicals were of reagent grade and
used as received without further purification. Hydrated
lanthanides (III) nitrate were prepared in the usual way by
Synthesis of Ln(HL)(H2O)2 (Ln = La, 1; Pr, 2; Nd, 3; Sm, 4;
Eu, 5; Gd, 6; Tb, 7). A mixture of Ln(NO3)3·6H2O (0.10 mmol)
and H4L (0.027 g, 0.10 mmol) was added in 10 mL of distilled
10 evaporating the solution of the corresponding oxide (99.9%) in 60 water at room temperature. After the pH value of the solution was
HNO3. All hydrothermal syntheses were carried out in 15mL
poly(tetrafluoroethylene)-lined stainless steel containers under
autogenous pressure. The initial and final pH of the reaction were
adjusted to 2.66 (1), 2.58 (2), 2.53 (3), 2.49 (4), 2.43 (5), 2.39 (6),
and 2.34 (7) with 1.0 mol·L−1 HNO3, the suspension was sealed
in a 15 mL Teflon-lined autoclave and heated at 140 °C for 3
days. After slow cooling to room temperature, the final pH values
65 of 1.16 (1), 1.09 (2), 1.05 (3), 1.02 (4), 0.98 (5), 0.95 (6), and
0.93 (7) were recorded. The crystals were obtained after filtered
and washed with distilled water. Color, Yield (based on Ln),
Elemental Analysis and FT-IR are listed in Table 1.
measured using
a METTLER TOLEDO 320 pH meter.
15 Elemental analyses of C and H were performed on a Perkin-
Elmer 2400 elemental analyzer. The Fourier transform-
infrared (FT-IR) spectra were recorded on a Perkin Elmer
Spectrum 100 FT-IR spectrometer equipped with a DTGS
detector (32 scans) by using KBr pellets. Powder X-ray
20 diffraction (PXRD) data were collected with Cu Kα (λ =
Table 1. Color, Yield, Elemental Analysis and FT-IR for complex 1−7.
Elemental
Color
Com- and
1.542 Å) radiation on
a Rigaku D/Max-2500 X-ray
Analysis
FT-IR (KBr, cm−1)
diffractometer. Electronic absorption spectra in the UV-vis
region were recorded on a Perkin Elmer Lambda 35 UV-
visible spectrophotometer in CH3OH. Thermal analyses were
25 performed on a Perkin-Elmer STA 6000 with a heating rate of
10 °C min−1 in a temperature range from 30 to 800 °C in air
atmosphere. The proton nuclear magnetic resonance (1H NMR)
spectrum was recorded on a Bruker Avance III 400 MHz
spectrometer in DMSO solution. Excitation and emission spectra
30 were measured with an Edinburgh FLS 920 fluorescence
spectrophotometer. Luminescence lifetimes were recorded on a
single photon counting spectrometer from Edinburgh Instrument
(FLS 920) with microsecond pulse lamp as the excitation.
Magnetic susceptibility measurements were carried out on a
35 Quantum Design MPMS SQUID VSM magnetometer. The raw
data were corrected for the susceptibility of the container and the
diamagnetic contributions of the sample using Pascal constants.
Calc. Found:
C, H C, H
plex Yield
(%)
3294(m), 2975(s), 1486(w), 1442(m),
1203(m), 1268(m), 1127(s), 1091(vs),
2.99 3.02 1048(vs), 975(s), 880(m), 803(m), 773(w),
707(m), 549(m), 486(w)
3565(m), 2975(w), 1643(m), 1611(m),
1486(w), 1441(m), 1126(s), 1088(vs),
2.98 2.99 1068(vs), 1031(s), 980(s), 947(m), 802(w),
773(w), 704(w), 547(w), 476(m)
3565(m), 3382(m), 1643(w), 1612(w),
1486(w), 1441(m), 1126(s), 1088(vs),
2.96 2.99 1068(vs), 1031(s), 980(s), 947(m), 802(w),
773(w), 704(w), 547(w), 483(m)
3412(m), 2918(w), 1638(m), 1612(m),
21.38, 21.35, 1487(w), 1441(m), 1128(s), 1091(vs), 1070(s),
Color-
21.94, 21.98,
less
46.8
1
2
3
4
5
6
7
Light
green
37.6
21.84, 21.89,
Pale
pink
37.6
21.67, 21.71,
Pale
yellow
50.6
2.92 2.93
1036(s), 983(s), 948(m), 801(w), 704(w),
628(w), 547(w), 476(m)
3565(m), 2918(w), 1642(m), 1612(m),
1486(m), 1441(w), 1126(s), 1088(vs),
Color-
less
40.5
21.30, 21.39,
Synthesis
2.90 2.93 1068(vs), 1031(s), 980(s), 947(m), 802(w),
773(w), 704(w), 547(w), 483(m)
3554(m), 2916(w), 1638(s), 1617(vs),
21.05, 21.11, 1487(w), 1441(w), 1128(s), 1094(vs), 1068(s),
Synthesis of 1,3-Phenylenebis(methylene)diphosphonic acid
40 (H4L). Triethyl phosphite (49.8 g, 0.30 mol) was subsequently
added dropwise in 1,3-bis(chloromethyl)benzene (17.5 g, 0.10
mol) under stirring. After reacting for 6h at about 150 °C, the
mixture was cooled to room temperature and unreacted triethyl
phosphite was removed by distillation in vacuo (749 mmHg). An
45 aqueous solution of 20 % sodium hydroxide (80 mL, 0.40 mol)
was added in and refluxed for 6 h. The residual solution was then
acidified with 6 M hydrochloric acid solution until the pH value
reached 1.0. The resulting solution was vacuum-rotary
evaporated to give pale yellow solid H4L about 81.2 % yield
Color-
less
43.3
2.87 2.85
1038(s), 985(s), 947(m), 801(m), 773(w),
704(m), 627(s), 480(m)
3534(m), 2915(w), 1653(m), 1603(m),
1486(m), 1442(w), 1127(s), 1092(vs),
Color-
less
20.98, 21.07,
2.86 2.88 1068(vs), 1029(s), 980(s), 975(m), 803(w),
773(w), 707(m), 549(m), 487(m)
36.5
70 X-ray Crystallography.
Single-crystal X-ray diffraction data for complex
a Rigaku R-AXIS RAPID imaging plate
diffractometer with graphite-monochromated Mo Kα (λ
2 were
collected on
1
50 (21.6 g). H4L was characterized by elemental analyses, UV, H
=
NMR, and FT-IR (Fig. S1−3, ESI†). Elemental Anal. Calcd for
C8H12O6P2: C, 36.11; H, 4.54. Found: C, 36.35; H, 4.68. UV
0.71073 Å) at 291 K. Empirical absorption correction based on
75 equivalent reflections was applied. The structure was solved by
2
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Page 3 of 7
New Journal of Chemistry
direct methods and refined by full-matrix least-squares methods
positions occupied by phosphonate oxygen atoms (O1, O4, O3I,
45 O5II and O6III) from four ligands and the remaining sites (O7 and
O8) occupied by two water molecules (FiDg.O2I:c1)0..1I0ts39c/oCo3rNdJin0a1t3i8o8nJ
on F2 using the SHELXS-97 crystallographic software package.17
All non-hydrogen atoms were refined anisotropically. The crystal
parameters, data collection and refinement results for 2 are
summarized in Table 2. Selected bond lengths and angles are
listed in Table S1 (ESI†). Crystallography data have been
deposited to the Cambridge Crystallography Data Centre with
deposition number CCDC: 934429.
View Article Online
geometry may be described as a distorted single-capped trigonal
prism, in which O5II serves as a capping atom, {PrO7} (Fig. 2d).
The bond lengths of Pr−O are between 2.361(3) and 2.532(3) Ǻ,
50 and the angles around the Pr atom range from 70.22(10) ° to
153.97(9) ° (Table S1, ESI†). Four {PrO7} polyhedra and eight
{CPO3} tetrahedra are interconnected into a unit, and then these
units are in turn connected to form a inorganic layer along bc
plane. The distances between adjacent Pr3+ ions are 4.809(1) and
55 4.909(1) Ǻ (Fig. 2e). Overall, the structure can be described as
the stacking of layers, with a layer-to-layer separation of 11.43(1)
Ǻ (Fig. 2f). The interlayer distance is much shorter than that
before-reported La(O3PCH2C6H5)(HO3PCH2C6H5)(H2O)2 (16.6
Ǻ)10 due to the structure distortion caused by two phosphonate
5
Results and discussion
10 Syntheses
All complexes 1−7 were prepared under hydrothermal
conditions (140 °C, 72 h) by reactions of hydrated lanthanide
(III) nitrate and H4L at mole ratio of 1:1. The pH values of the
reaction mixtures were found to greatly affect the crystals growth
15 of 1−7. In order to obtain pure single-crystal, pH was controlled 60 group coordination. Connections between adjacent layers are
strictly through 1.0 mol·L−1 HNO3 (Table S2, ESI†). For complex
1, the reaction pH value in the range of 2.60−2.73 yields a pure
crystal phase of the resultant; however, a pH of less than 2.60
results in a solution and a pH above 2.73 leads to a powder. For
20 complex 2, a pure crystal phase can be obtained in the pH range
of 2.52−2.66. Similarly, the samples with good crystal quality
can be gained under the pH range of 2.49−2.58 for 3, 2.43−2.53
for 4, 2.38−2.46 for 5, 2.35−2.46 for 6 and 2.30−2.39 for 7,
respectively (Fig. 1). In accordance with the order of the
25 lanthanum contraction, a successive lower pH value is favorable
for the growth of crystal from La to Tb. The results of this study
provide further evidence that the pH value plays an important
role in the growth of single crystals.
ensured by the C−H ··· π interactions of ligands leading to an
alternation fragments along the b axis (Fig. 2g). The centroid-
centroid distance is 5.236(1) Å and dihedral angle between planes
is 146.8(1)°.
65 Table 2. Crystal data and structure refinements for complex 2.
2
empirical
C8H13O8P2Pr
Fw
440.03
formula
crystal system
a (Å)
monoclinic
12.198 (2)
8.3508 (17)
13.632 (3)
1300.6(4)
2.247
space group
α (deg)
β (deg)
P 21/c
90.00
110.50(3)
90.00
4
b (Å)
c (Å)
γ (deg)
V (Å3)
Z
Dcalc(g m−3)
µ (mm−1)
collected/
unique
4.023
F(000)
856
12188/2970
3.6
3.3
3.0
2.7
2.4
2.1
1.8
Solution
Crystal phase
Powder
R(int)
0.0315
0.0276
0.0576
GOF on F2
Rla (all)
wR2b (all)
1.075
0.0321
0.0592
Rla [I>2σ(I)]
b
wR2 [I> σ(I)]
a R1 = Σ||Fo| − |Fc||/Σ|Fo|.
bwR2 = {Σ[w(Fo2 − Fc2)2/Σw(Fo2)2]}1/2
.
Powder X-ray Diffraction
The crystal samples of complexes were gently ground in an agate
70 mortar in order to minimize the preferred orientation. High-
resolution X-ray diffraction (XRD) measurement was collected at
room temperature over the angular 2θ range from 5−50° with a
step of 0.013° and a counting time of 7 s. The PXRD patterns of
1−7 were compared with the calculated 2 (Fig. 3), indicating that
75 the products have been successfully obtained as isostructural pure
crystalline phases.
1
2
3
4
5
6
7
Complexes 1–7
30 Fig. 1 Influence of the initial pH of reaction on the crystal growth of 1−7.
Crystal Structure Description.
Complex 2 is a two-dimensional (2D) structure. The crystal
parameters, data collection and refinement results for 2 are
summarized in Table 2. It is found that complex 2 crystallizes in
35 the monoclinic system, space group P 21/c. The asymmetric unit
of 2 contains one Pr3+ ion, one ligand which adopts single type of
coordination mode and two coordinated water molecules (Fig.
2a). The coordination mode of the ligand is depicted in Fig. 2b.
The HL3− anion coordinates with four symmetry equivalent Pr3+
40 ions by its two phosphonates. Oxygen atoms (O1 and O4) are
bidentately chelating to one Pr3+ ion; the others (O3, O5 and O6)
bridge three Pr3+ ions in monodentate and bidentate mode
respectively. Each Pr3+ ion is seven-coordinated with five
Tb
Gd
Eu
Sm
Nd
Pr
La
Calculated
5
10 15 20 25 30 35 40 45 50
2θ (°)
Fig. 3 Powder XRD patterns of 1−7 and calculated 2.
Journal Name, [year], [vol], 00–00 |
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DOI: 10.1039/C3NJ01388J
Fig. 2 (a) Asymmetric unit of 2, where H atoms except those attached to O are omitted for clarity. Thermal ellipsoids are at the 50%
probability level. (b) Coordination mode of ligand [µ3 - (η1: η1: η1); µ3 - (η0: η1: η1)]. (c and d) Coordination environment of Pr3+. (e)
Perspective view of the inorganic layer along the a-axis. (f) The layer structure of 2 viewed along c axis. (g) C−H ··· π interactions
between layers. Symmetry code: (I) 1 − x, 1 − y, 1 − z ; (II) x, 1.5 − y, −0.5 + z ; (III) 1 − x, 2 − y, 1 − z.
5
black substance may be amorphous compound by Powder X-ray
35 diffraction (Fig. S4, ESI†). The very unusual feature observed in
FT-IR spectra
FT-IR spectra of ligand and complexes 1−7 are depicted in Fig.
the 400−475 ºC range, where mass loss is negative, may be
caused from the adsorption effect.
S3 (ESI†). The wide bands from 3600 cm−1 to 2000 cm−1, arising
10 from the O−H stretching vibrations of the protonated
phosphonate Oxygen O(5) and coordinated water molecules,
suggest that extensive hydrogen bonds are present in the
complexes because of the spectrum diffusion. The very strong
band at 1088 cm−1 may be due to P=O vibration frequency to
15 high frequency offset as a result of Ln3+ coordination effect. The
bands at 1068, 980 (strong) and 947 cm−1 (medium) are
characteristic of the stretching vibrations of the tetrahedral CPO3
group. Bands at 802 and 704 cm−1 are attributed to the C−H out-
of-plane vibrations for para-disubstituted phenylene ring. The
20 band at 773 cm−1 is characteristic of P−C stretching vibration.
Bands between 630 cm−1 and 476 cm−1 main correspond to the
bending modes of the CPO3 group. However, the band at 547
cm−1 may be assigned to Ln−O stretching vibration.18
100
95
90
La
Pr
85
80
75
Nd
Sm
Eu
Gd
Tb
100
200
300
400
500
600
700
800
Temperature (°C)
Fig. 4 TG curves of complexes 1−7.
40 Luminescent Properties
Thermal Properties
The solid-state luminescent spectra of free ligand and 4−7 were
investigated at room temperature. The free ligand H4L exhibits a
broad fluorescent emission band at 475 nm under excitation at
360 nm (Fig. S5a, ESI†). Complex 4 displays the characteristic
45 emission bands of Sm3+ ion (λex = 277 nm) (Fig. 5a). These bands
25 The thermal stability in the air of complexes 1−7 was
investigated. The TG curves of 1−7 are similar and exhibit two
main steps of weight loss (Fig. 4). Complex 1 was used as an
example. (i) Dehydration occurs only after ca. 180 °C. Up to 230
°C almost all the coordinated water molecules are removed and
30 weight lose 8.2 % (calculated value 8.22). (ii) From 475 °C to
800 °C the complex continue to decompose slowly. All the above
thermo gravimetric studies were performed up to 800 ºC. As the
decomposing process is not ended at 800 °C, we think the final
4
6
6
are attributed to G5/2 → H5/2 (563 nm), 4G5/2 → H7/2 (598 nm)
4
6
and G5/2 → H9/2 (645 nm) transitions.19 This strongest 598 nm
band emits the yellow luminescence and Sm3+ (4G5/2) two level
lifetimes are 3.3 and 14.37 µs because of ligand field interaction
50 (Fig. 5b). Complex 5 exhibits Eu3+ ion emission consisting of
4
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New Journal of Chemistry
5000
4000
3000
2000
1000
0
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DOI: 10.1039/C3NJ01388J
lifetime t1 = 3.3 µs
Ex. 277 nm
4G 6H7/2
(b)
1000
100
10
(a)
6
4G5/2 H5/2
563
t2 = 14.5 µs
5/2 598
6
4G5/2 H9/2
645
1
200
300
400
500
600
700
800
0
20
40
60
80
100
Time (µs)
Wavelength (nm)
1.0x105
1000
Ex. 375 nm
lifetime t1 = 293 µs
(c)
(d)
7F2
5D0
8.0x104 4000
615
3000
100
10
6.0x104
2000
7F3
5D0
1000
4.0x104
0
651
200 250 300 350 400 450
5D0 7F1
5D0 7F4
701
2.0x104
588
0.0
1
400 450 500 550 600 650 700 750 800
Wavelength (nm)
0
100
200
300
400
500
600
Time (µs)
1000
lifetime t1 = 1646 µs
Ex. 275 nm
(e)
4,000
3,000
2,000
1,000
0
(f)
5D4 7F5
542
100
10
1
7F4
5D4
583
5D4 7F6
487
5D4 7F3
622
200
300
400
500
600
700
800
0
1000
2000
3000
4000
Wavelength (nm)
Time (µs)
5 Fig. 5 Solid-state excitation (red) and emission (black) spectra of 4 (a), 5 (c), and 7 (e). Solid-state luminescence lifetimes and photos of 4 (b), 5 (d), and 7
(f) at room temperature.
four characteristic emission bands for the Eu3+ ion in the visible
region under excitation at 375 nm (Fig. 5c). These emission
electronic levels of the Gd3+ ion are known to be located at 31000
cm-1, which is typically well above electronic levels of the ligand
bands are 588, 592, 594 nm (weak, 5D0 → 7F1), 611, 615, 623 nm 25 (Fig. S5c, ESI†). Therefore, ligand-to-metal energy transfer and
5
7
5
7
10 (very strong, D0 → F2), 651 nm (very weak, D0 → F3), and
686, 698, 701 nm (weak, 5D0 → 7F4). The splitting of 5D0 → 7F1,
the consequent MC luminescence can not be observed.21
Complex 7 exhibits four characteristic emission bands for the
Tb3+ ion in the visible region under an excitation at 275 nm (Fig.
5e). These emission bands are 487 and 496 nm (weak, 5D4 → 7F6),
30 542 and 548 nm (very strong, 5D4 → 7F5), 583 and 591 nm (weak,
7
5
7
5D0 → F2, and D0 → F4 transition bands is due to the “crystal
field effect” of the Eu3+ ion in a Cs symmetry, which led to the
7
complete degeneracy of the F1 and the partial degeneracy of the
15 7Fj (j = 2 and 4) states. The D0 → F2 transition is very intense,
which is allowed by the electric dipole and hypersensitive to the
environment in the vicinity of Eu3+ ion, showing strong red
emission.20 The Eu3+ (5D0) lifetime (λex,em = 375 and 615 nm) is
5D4 → F4) and 619 and 622nm (weak, 5D4 → F3), respectively.
Among these emission bands, the strongest one is the green
luminescence of 5D4 → 7F5 transition. The Tb 3+ (5D4) lifetime for
λex, em = 275 and 542 nm is about 1.65 ms (Fig. 5f).22 Viewing 4,
5
7
7
7
measured to be 0.29 ms (Fig. 5d). The emission spectrum of 6 35 5, and 7 under a dark-field luminescence microscope, brilliant
20 only exhibits a broad blue fluorescent emission band at λmax = 493
nm (λex = 285 nm) (Fig. S5b, ESI†), which corresponds to a
ligand-centered (LC) fluorescence. The metal-centered (MC)
yellow, red, and green luminescence were revealed when they
were illuminated with UV light in Fig. 5b, 5d, and 5f,
respectively.
This journal is © The Royal Society of Chemistry [year]
Journal Name, [year], [vol], 00–00 | 5

New Journal of Chemistry
Page 6 of 7
View Article Online
DOI: 10.1039/C3NJ01388J
2.4
2.0
1.6
1.2
0.8
0.4
0.0
150
120
90
60
30
0
12
11
10
9
30
(a)
(c)
20
χMT
10
1/χM
8
χMT
1/χM
7
0
300
0
50
100
150
200
250
300
0
50
100
150
200
250
Temperature (K)
Temperature (K)
0.8
1.2
(b)
(d)
0.6
0.4
0.8
0.4
0.2
0.0
0.0
-0.2
-0.4
-0.6
-0.8
-0.4
-0.8
-1.2
-80 -60 -40 -20
0
20
40
60
80
-80 -60 -40 -20
0
20
40
60
80
H (kOe)
H (kOe)
Fig. 6 Plots of temperature dependence of χMT (red □) and 1/χM (blue ●) for the crystal sample of 2 (a) and 7 (c). Magnetization curves (measured at 1.8 K)
5 for the crystal sample of 2 (b) and 7 (d).
mol−1 at 65 K, and subsequently go down sharply to a minimum
Magnetic Property Measurements.
of 7.04 cm3 K mol−1 at 1.8 K (Fig. 6c). The decrease in χMT
The temperature dependent magnetic susceptibilities of 2 and 7
were measured in the range of 300−1.8 K at 1000 Oe. Plots of the
temperature dependence of χM for complexes 2 and 7 are shown
values with lowering the temperature can be attributed to the
depopulation of the Stark levels together with weak
35 antiferromagnetic interactions between the Tb3+ ions.25 At 300 K
10 in Fig. S6 (ESI†). For complex 2, the χMT versus T plots show
the effective magnetic moment (µeff = 9.55 µB) is slightly smaller
that χMT (2.21 cm3·K·mol−1, 300 K) decreases slowly upon
than the expected value of 9.72 µB for an isolated Tb3+ ion (7F6, S
cooling to 50K and drops rapidly to reach a value 0.36
= 3, L = 3, g = 3/2).23 The plots of 1/χM versus T obey the Curie–
cm3·K·mol−1 at 1.8 K (Fig. 6a). The room temperature effective
Weiss law. Fitting of the data above 30 K, it gets a CM of 11.61
magnetic moments (µeff) of 4.20 µB is less than the theoretical
40 cm3·K·mol−1 and a θ of -4.25 K, indicating antiferromagnetic
15 value of 5.06 µB for an isolated Pr3+ ion (3H4, S = 1, L = 5, g = 4/5)
interaction between magnetic centers. The field-dependent
calculated according to the van Vleck formula.23 The inverse of
isothermal magnetization measured at 1.8 K reveals that the
the χM data according to the Curie−Weiss law from 90K to 300K
magnetization displays an abrupt increase to 0.78 Nβ below 10
with a Curie constant (CM) of 2.60 cm3·K·mol−1 and a much more
kOe and then slowly reaches 0.95 Nβ at 70 kOe (Fig. 6d).
negative Weiss constant (θ) of -55.56 K, indicating an
20 antiferromagnetic interaction between magnetic centers. The
45 Conclusions
decrease of χMT and the negative value of θ are due primarily to
splitting of the ligand field of the Pr3+ ions as a result of strong
Seven new lanthanide diphosphonates with a 2D framework
structure have been synthesized under hydrothermal conditions
through adjusting pH. Complex 2 features a network in which the
PrO7 polyhedra are interconnected by bridging CPO3 tetrahedra
50 into inorganic layers. These layers are further stacked with the
benzyl groups of ligands via C−H ··· π interaction into laminar
spin−orbital coupling and is attributed partly to the possibly
antiferromagnetic intradimer coupling.24 The field dependence of
25 the magnetization of complex 2 is investigated at 1.8 K (Fig. 6b).
The magnetization increases continually to 0.64 Nβ at 70 kOe.
Magnetic behavior of complex 7 is similar to complex 2.
During the process of the temperature descend, the χMT remain
nearly unchanged from 11.40 cm3·K·mol−1 (300 K) to 11.39
30 cm3·K·mol−1 (150 K), and then gradually decrease to 10.86 cm3 K
framework architecture. These complexes are isomorphous and
have been obtained as a single phase and show higher thermal
stability, and their photoluminescence properties are also
6
| Journal Name, [year], [vol], 00–00
This journal is © The Royal Society of Chemistry [year]

Page 7 of 7
New Journal of Chemistry
10 R. C. Wang, Y. Zhang, H. Hu, R. R. Frausto and Clearfield, A. Chem.
Mater., 1992, 4, 864.
11 M. T. Wharmby, J. P. S. Mowat, S. P. Thompson andVPie.wAA.rWticrleigOhntl,inJe.
discussed. Complexes 4, 5, and 7 display metal-centered yellow,
red and green light emission, respectively. Magnetic properties
of 2 and 7 indicate that there are antiferromagnetic interactions
among Ln3+ ions in complexes. These complexes with intense
luminescence could be served as potential luminescence
materials.
DOI: 10.1039/C3NJ01388J
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This work is financially supported by the National Natural
Science Foundation of China (Nos. 21072049, 21272061 and
10 21371052) and Natural Science Foundation of Heilongjiang
Province (2010td03 and B201108).
Notes and references
a
Key Laboratory of Functional Inorganic Material Chemistry of
16 (a) N. A. Caplan, C. I. Pogson, D. J. Haynes and G. M. Blackburn,
Education Ministry, School of Chemistry and Materials Science,
15 Heilongjiang University, Harbin 150080, P. R. China. Tel: +86-451-
86608399; E-mail: yanpf@vip.sina.com
Engineering Research Center of Pesticide of Heilongjiang University,
Harbin 150080, P. R. China. Tel: +86-451-86609001; E-mail:
gaojins@hlju.edu.cn
20 † Electronic Supplementary Information (ESI) available: crystallographic
data in CIF, UV, 1H NMR, FT-IR, PXRD, luminescent and magnetic
patterns. See DOI: 10.1039/b000000x/
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