Synthesis, crystal structures, and luminescent properties of two types of lanthanide phosphonates

Article abstract of DOI:10.1016/j.jssc.2008.06.043

Hydrothermal reactions of different lanthanide(III) salts with an amino-diphosphonate ligand (H₄L= C₆H₅CH ₂N(CH₂PO₃H₂)₂) led to two series of lanthanide phosphonates, namely, Ln(H₂L)(H₃L) (Ln = La, 1; Pr, 2; Nd, 3; Sm, 4; Eu, 5; Gd, 6; Tb, 7). Compounds 1-5 feature a one-dimensional (1D) chain structure in which dimers of two edge-sharing LnO₈ polyhedra are interconnected by bridging phosphonate groups, such 1D arrays are further interlinked via strong hydrogen bonds between non-coordinated phosphonate oxygen atoms into a two-dimensional (2D) layer with the phenyl groups of the ligands orientated toward the interlayer space. Compounds 6 and 7 also show a different ID array in which the LnO₆ octahedra are bridged by phosphonate groups via corner-sharing, such chains are also further interlinked by hydrogen bonds into a 2D supramolecular layer. Compounds 5 and 7 emit red and green light with a lifetime of 2.1 and 3.7ms, respectively.

Full text of DOI:10.1016/j.jssc.2008.06.043

ARTICLE IN PRESS
Journal of Solid State Chemistry 181 (2008) 2713– 2718
Contents lists available at ScienceDirect
Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Synthesis, crystal structures, and luminescent properties of two types of
lanthanide phosphonates
Ã
Ya-Qin Guo a,b, Si-Fu Tang a, Bing-Ping Yang a, Jiang-Gao Mao a,
a State Key Laboratory of Structure Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, PR China
b Graduate School of the Chinese Academy of Sciences, Beijing 100039, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Hydrothermal reactions of different lanthanide(III) salts with an amino-diphosphonate ligand
(H4L ¼ C6H5CH2N(CH2PO3H2)2) led to two series of lanthanide phosphonates, namely, Ln(H2L)(H3L)
(Ln ¼ La, 1; Pr, 2; Nd, 3; Sm, 4; Eu, 5; Gd, 6; Tb, 7). Compounds 1–5 feature a one-dimensional (1D) chain
structure in which dimers of two edge-sharing LnO8 polyhedra are interconnected by bridging
phosphonate groups, such 1D arrays are further interlinked via strong hydrogen bonds between non-
coordinated phosphonate oxygen atoms into a two-dimensional (2D) layer with the phenyl groups of
the ligands orientated toward the interlayer space. Compounds 6 and 7 also show a different 1D array in
which the LnO6 octahedra are bridged by phosphonate groups via corner-sharing, such chains are also
further interlinked by hydrogen bonds into a 2D supramolecular layer. Compounds 5 and 7 emit red and
green light with a lifetime of 2.1 and 3.7 ms, respectively.
Received 25 April 2008
Received in revised form
7 June 2008
Accepted 14 June 2008
Available online 24 June 2008
Keywords:
Lanthanide phosphonates
Hydrothermal reactions
Crystal structures
Supramolecular assembly
Luminescent properties
& 2008 Elsevier Inc. All rights reserved.
1. Introduction
with functional groups with additional coordination atoms such
as the carboxylate acid or amino acid [24–27]. As an extension of
our previous work, in this work we used an amino-diphosphonate
ligand, N-benzyliminobis(methylenephosphonic acid), C6H5CH2
N(CH2PO3H2)2 (H4L), whose transition metal complexes have been
reported to exhibit two-dimensional (2D) layers or one-dimen-
sional (1D) arrays [28–31]. We hope to get better understandings
of the effects of different metal cations on the final structures and
the photoluminescence properties. Our research efforts afforded
two series of lanthanide phosphonates, namely, Ln(H2L)(H3L)
(Ln ¼ La, 1; Pr, 2; Nd, 3; Sm, 4; Eu, 5) and Ln(H2L)(H3L) (Ln ¼ Gd, 6;
Tb, 7). Both types of compounds feature 2D supramolecular
networks based on 1D arrays interconnected via hydrogen bonds.
Chemistry of metal phosphonates is expanding rapidly in
recent years due to these compounds’ versatile architectures and
topologies as well as their potential applications in catalysis, ion
exchange, magnetism, and materials chemistry [1–5]. The strategy
of modification of the phosphonic acid with various functional
groups such as crown ether, amine, hydroxyl, or/and carboxylate
groups has been proven to be an extremely effective route for the
construction of metal phosphonates with open framework
structures [6–15]. So far, a variety of intriguing networks have
been well documented in several reviews [4,16]. Lanthanide
phosphonates are important since they can exhibit intense
luminescence that has found applications in fluorescent probes
and electroluminescent devices [17–20]. However, lanthanide
phosphonates are still relatively unexplored, due to their low
solubility in water and other organic solvents as well as their poor
crystallinity; hence, it is still a difficult task to obtain single
crystals suitable for X-ray structural analysis. Results from our
previous studies indicate that phosphonic acid, in conjunction
with a suitable ancillary ligand such as 5-sulfoisophthalic acid
(H3BTS) or oxalate, is an effective route for the preparation of
crystalline lanthanide phosphonates [21–23]. Another useful
alternative method is the use of the phosphonic acid attached
2. Experimental section
2.1. Materials and methods
LnCl3 ꢀ nH2O (Ln ¼ La, Pr, Nd, Sm, Eu, Gd, Tb) were prepared by
dissolving lanthanide oxide in hydrochloric acid, and then the
mixture was heated at ꢁ100 1C in the air until a lot of powder
appeared. C6H5CH2N(CH2PO3H2)2 (H4L) were prepared by
a
Mannich-type reaction according to procedures described pre-
viously [32–34]. All other chemicals were obtained from com-
mercial sources and used without further purification. Elemental
analyses (C, H, and N) were carried out on a Vario EL III elemental
Ã
Corresponding author. Fax: +86 59183714946.
E-mail address: mjg@fjirsm.ac.cn (J.-G. Mao).
analyser. IR spectra were recorded on a Magna 750 FT-IR
0022-4596/$ - see front matter & 2008 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2008.06.043

ARTICLE IN PRESS
2714
Y.-Q. Guo et al. / Journal of Solid State Chemistry 181 (2008) 2713–2718
spectrophotometer using KBr pellets in the range 4000–400 cmꢂ1
Thermal gravimetric analyses (TGA) analysis was performed
on a NETZSCH STA 449C unit under oxygen flow at a heating
rate of 10 1C minꢂ1. Photoluminescence analyses were performed
.
(
l
¼ 0.71073 A). Intensity data were collected by the narrow frame
˚
method at 293 K and corrected for Lorentz and polarization effects
as well as for absorption by the SADABS programme [35,36]. Both
structures were solved by direct methods and refined by full-
matrix least-squares cycles in SHELX-97 [37]. All non-hydrogen
atoms were refined with anisotropic thermal parameters. Hydro-
gen atoms attached to the C and N atoms were located at
geometrically calculated positions and refined with isotropic
thermal parameters. Crystallographic data and structural refine-
ment parameters for compounds 4 and 7 are summarized in
Table 1. Important bond distances are listed in Table 2.
on
a Perkin-Elemer LS55 fluorescence spectrometer. XRD
powder patterns (CuKa) were collected on an XPERT-MPD 2y
diffractometer.
2.2. Syntheses of Ln(H2L)(H3L) (Ln ¼ La, 1; Pr, 2; Nd, 3; Sm, 4; Eu, 5)
A mixture of LnCl3 ꢀ nH2O (0.25 mmol), H4L (0.295 g, 1 mmol) in
10 mL of distilled water was sealed in an autoclave equipped with
a Teflon liner (23 mL) and its pH value is ꢁ1. Then the solution was
heated at 165 1C for 5 days. Crystals of 1 (colourless), 2 (green), 3
(purple), 4 (colourless), and 5 (yellow) were collected in ca. yields
of 78%, 81%, 82%, 73%, and 75% (based on lanthanide), respectively.
The measured XRD patterns are comparable with the simulated
ones (see Supporting Information). Anal. Calcd. for C18H27N2O12-
P4La: C, 29.77; H, 3.75; N, 3.86%. Found: C, 29.49; H, 3.98; N,
3.68%. IR data (KBr, cmꢂ1): 3005 (m), 2944 (m), 2815 (m), 2746
(m), 2601 (m), 1458 (m), 1249 (s), 1170 (s), 1118 (s), 920 (m), 852
(w), 811 (w), 738 (m), 588 (m), 565 (w), 531 (m). Anal. Calcd. for
CCDC-684385 (4) and CCDC-684386 (7) contain the supple-
mentary crystallographic materials for this paper. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Center via www.ccdc.cam.ac.uk/data_request/cif.
3. Results and discussion
The isolations of compounds 1–7 rely on the hydrothermal
techniques. Results indicate that the reaction conditions play an
important role in the formation of the title compounds. Pure
phases were obtained at the L/Ln ratio of 4:1, low pH values of the
reaction mixture favour the protonation of some phosphonate
groups and facilitate the formation of low-dimensional coordina-
tion polymers. When the L/Ln ratio is less than 1:1 at the same
conditions, we could not obtain the single crystals but only
unknown precipitates.
C18H27N2O12P4Pr: C, 29.69; H, 3.74; N, 3.85%. Found: C, 29.48; H,
3.96; N, 3.61%. IR data (KBr, cmꢂ1): 3007 (m), 2945 (m), 2813 (m),
2745 (m), 2565 (m), 1458 (m), 1249 (s), 1171 (s), 1134 (s), 920 (m),
740 (m), 589 (w), 567 (w), 531 (m). Anal. Calcd. C18H27N2O12P4Nd:
C, 29.55; H, 3.72; N, 3.83%. Found: C, 29.32; H, 3.89; N, 3.63%. IR
data (KBr, cmꢂ1): 3007 (m), 2944 (m), 2814 (m), 2745 (m), 2595
(m), 1458 (m), 1248 (s), 1171 (s), 1134 (s), 920 (m), 895 (m), 739
(m), 589 (w), 569 (w), 530 (m). Anal. Calcd. for C18H27N2O12P4Sm:
C, 29.31; H, 3.69; N, 3.80%. Found: C, 29.02; H, 3.91; N, 3.65%. IR
data (KBr, cmꢂ1): 3008 (m), 2956 (m), 2813 (m), 2746 (m), 2546
(m), 1459 (m), 1249 (s), 1173 (s), 1133 (s), 920 (m), 740 (m), 590
(w), 568 (w), 530 (m). Anal. Calcd. for C18H27N2O12P4Eu: C, 29.24;
H, 3.68; N, 3.79%. Found: H, 3.95; C, 28.06; N, 3.57%. IR data (KBr,
cmꢂ1): 3007 (m), 2946 (m), 2814 (m), 2746 (m), 2545 (m), 1458
(m), 1248 (s), 1172 (s), 1134 (s), 920 (m), 739 (m), 589 (w), 569 (w),
530 (m).
3.1. Structure description for Ln(H2L)(H3L) (Ln ¼ La, 1; Pr, 2; Nd, 3;
Sm, 4; Eu, 5)
Compounds 1–5 are isostructural, hence the structure of
compound 4 was described representatively. The asymmetric unit
of 4 consists of a Sm(III) ion, a {H2L}2ꢂ and a {H3L}ꢂ anion (Fig. 1).
The Sm(III) center is eight-coordinated by three oxygen atoms
from three {H3L}ꢂ anions and five oxygen atoms from three
{H2L}2ꢂ anions. The Sm–O distances are in the range of
˚
2.345(5)–2.725(6) A. The two phosphonate ligands adopt two
different types of coordination modes (Scheme 1). The {H3L}ꢂ
anion acts as a tridentate ligand, one phosphonate group is
monodnetate whereas the other one is bidentate bridging
(Scheme 1a), both phosphonate groups are singly protonated
(O7, O11) based on P–O distances (Table 2), so is the amine group.
2.3. Syntheses of Ln(H2L)(H3L) (Ln ¼ Gd, 6; Tb, 7)
A mixture of LnCl3 ꢀ 6H2O (0.25 mmol), H4L (0.295 g, 1 mmol) in
distilled water (10 mL) was sealed in an autoclave equipped with a
Teflon liner (23 mL) and its pH value is ꢁ1. Then the solution was
heated at 165 1C for 5 days. Needle-like crystals of 6 (colourless)
and 7 (colourless) were collected in ca. 64% and 82% yield (based
on lanthanide), respectively. The measured XRD powder patterns
are comparable with the simulated ones (see Supporting Informa-
tion). Anal. Calcd. for C13H27N2O12P4Gd: C, 29.04; H, 3.66; N,
3.76%. Found: C, 28.78; H, 3.82; N, 3.57%. IR data (KBr, cmꢂ1):
3007 (m), 2945 (m), 2850 (m), 2745 (m), 2545 (m), 1458 (m), 1247
(s), 1172 (s), 1133 (s), 920 (m), 739 (m), 589 (w), 568 (w), 529 (m).
Anal. Calcd. for C13H27N2O12P4Tb: C, 28.97; H, 3.65; N, 3.75%.
Found: C, 28.65; H, 3.78; N, 3.56%. IR data (KBr, cmꢂ1): 3007 (m),
2966 (m), 2756 (m), 2722 (m), 1430 (m), 1246 (s), 1164 (s), 1099
(s), 912 (m), 739 (m), 591 (m), 565 (m), 535 (m).
Table 1
Crystal data and structure refinements for 4 and 7
Compound
4
7
Formula
C18H27N2O12P4Sm
C18H27N2O12P4Tb
fw
737.65
746.22
Crystal system
Space group
Triclinic
Orthorhombic
Pꢂ1
P212121
˚
a (A)
8.056(3)
7.994(2)
˚
b (A)
12.755(5)
25.351(7)
˚
c (A)
13.498(7)
25.589(8)
a
b
g
(deg)
115.395(9)
90
92.49(2)
90
(deg)
(deg)
93.030(2)
90
2.4. Single-crystal structure determination
3
˚
V (A )
1247.8(9)
5186(3)
Z
2
8
Dc (g cmꢂ3
)
1.963
1.911
Based on the measured XRD powder patterns, compounds 1–5
are isostructural, so are compounds 6 and 7 (see Supporting
Information). Therefore, only compounds 4 and 7 were subject to
single-crystal structural analyses. Date collections for compounds
4 and 7 were performed on a Siemens Smart CCD diffracto-
m
(mmꢂ1
)
2.676
3.038
R1, wR2 [I42
R1, wR2 (all data)
GOFc
s
(I)]
R1 ¼ 0.0545, wR2 ¼ 0.1441
R1 ¼ 0.0576, wR2 ¼ 0.1460
1.087
R1 ¼ 0.0587, wR2 ¼ 0.1133
R1 ¼ 0.0780, wR2 ¼ 0.1267
1.093
R1
¼
S
JF0|ꢂ|FcJ/
S
|F0|, wR2
¼
S
[w(F20ꢂF2c)2]/
S
[w(F20)2]1/2
.
meter equipped with graphite-monochromated MoK
a radiation

ARTICLE IN PRESS
Y.-Q. Guo et al. / Journal of Solid State Chemistry 181 (2008) 2713–2718
2715
Table 2
˚
Selected bond lengths (A) for 4 and 7
Compound 4
Sm(1)–O(8)
Sm(1)–O(9)]2
Sm(1)–O(1)
Sm(1)–O(2)]3
P(1)–O(1)
2.345(5)
2.380(5)
2.428(5)
2.550(5)
1.504(5)
1.533(6)
1.493(5)
1.497(5)
1.489(5)
1.579(5)
Sm(1)–O(6)]1
2.360(5)
2.390(5)
2.542(6)
2.725(6)
1.525(5)
1.507(6)
1.581(5)
1.584(5)
1.485(6)
1.504(5)
Sm(1)–O(10)]3
Sm(1)–O(3)]3
Sm(1)–O(3)
P(1)–O(2)
P(1)–O(3)
P(2)–O(4)
P(2)–O(6)
P(2)–O(5)
P(3)–O(8)
P(3)–O(7)
P(3)–O(9)
P(4)–O(10)
P(4)–O(12)
P(4)–O(11)
Scheme 1. Coordination fashions of phosphonate ligands in compounds 4 and 7 as
Compound 7
Tb(1)–O(7)
Tb(1)–O(3)]1
Tb(1)–O(20)
Tb(2)–O(1)
Tb(2)–O(8)
Tb(2)–O(14)
P(1)–O(2)
well as its transition metal complexes.
2.211(6)
2.247(7)
2.292(6)
2.223(6)
2.279(6)
2.282(7)
1.512(7)
1.528(6)
1.502(6)
1.493(7)
1.537(7)
1.505(7)
1.497(7)
1.530(7)
1.499(7)
1.499(6)
1.544(7)
1.490(7)
Tb(1)–O(15)]1
Tb(1)–O(5)
Tb(1)–O(24)]1
Tb(2)–O(19)
Tb(2)–O(11)]2
Tb(2)–O(18)]1
P(1)–O(3)
2.241(6)
2.279(6)
2.297(6)
2.237(6)
2.279(6)
2.295(6)
1.522(7)
1.488(7)
1.568(7)
1.503(7)
1.498(7)
1.557(7)
1.519(6)
1.495(7)
1.565(7)
1.503(7)
1.573(7)
1.493(7)
P(1)–O(1)
P(2)–O(4)
P(2)–O(5)
P(2)–O(6)
P(3)–O(7)
P(3)–O(8)
P(3)–O(9)
P(4)–O(10)
P(4)–O(12)
P(5)–O(15)
P(6)–O(16)
P(6)–O(17)
P(7)–O(19)
P(8)–O(22)
P(8)–O(23)
P(4)–O(11)
P(5)–O(14)
P(5)–O(13)
P(6)–O(18)
P(7)–O(20)
P(7)–O(21)
P(8)–O(24)
Symmetry transformations used to generate equivalent atoms:
For 4: ]1 xꢂ1, y, z; ]2 ꢂxꢂ1, ꢂy, ꢂz+1; ]3 –x, ꢂy, ꢂz+1.
For 7: ]1 xꢂ1, y, z; ]2 x+1, y, z.
Fig. 2. A 2D supramolecular layer based on 1D chains of lanthanide(III)
phosphonates in 4. Hydrogen bonds are represented by the dashed lines.
pair of phosphonate groups from two {H3L}ꢂ anions into a 1D
chain along the a-axis (Fig. 2). Within the chain, intra-chain
hydrogen bonds are formed between protonated amine groups
and non-coordination phosphonate oxygen atoms. The corre-
sponding hydrogen bond lengths and angles are 2.635(8) and
˚
2.756(8) A, 156.21 and 154.11, respectively (Table 3). Adjacent
samarium(III) phosphonate chains are further interlinked via
hydrogen bonds between the non-coordinated phosphonate
oxygen atoms into a 2D sheet (Fig. 2). The hydrogen bond
˚
distances range from 2.579(7) to 2.648(8) A and bond angles from
160.691 to 172.641, respectively (Table 3). The phenyl rings of the
ligands are hanging on the interlayer space. These 2D sheets are
Fig. 1. ORTEP drawing of compound 4 with atom-labeling scheme. Hydrogen
atoms are omitted for clarity. Symmetry codes for the generated atoms: (a) xꢂ1, y,
z; (b) ꢂxꢂ1, ꢂy, ꢂz+1; (c) ꢂx, ꢂy, ꢂz+1.
further held together via
p–p stacking interactions between the
phenyl groups into a three-dimensional (3D) supramolecular
framework (Fig. 3). The close contact distance between adjacent
˚
aromatic rings is ca. 3.45 A.
Such coordination mode is also reported in M{H3L}2 (M ¼ Mn, Cd)
[28,31]. The {H2L}2ꢂ anion functions as a tetradentate ligand,
being chelating bidentately to two metal centres by using one
phosphonate group and also bridges to the third Sm(III) atom
(Scheme 1b) via the other phosphonate group, one phosphonate
oxygen atom (O5) is singly protonated based on P–O distance, so
is the amine group.
3.2. Structure description for Ln(H2L)(H3L) (Ln ¼ Gd, 6; Tb, 7)
Compounds 6 and 7 feature a different 1D lanthanide(III)
phosphonate chain from that of 1–5. As illustrated in Fig. 4, the
asymmetric unit of 7 contains two crystallographically indepen-
dent Tb(III) atoms, two {H2L}2ꢂ and two {H3L}ꢂ anions (Fig. 4).
Unlike the lanthanide(III) ions in 1–5, both Tb(III) ions in 7 are
octahedrally coordinated by six oxygen atoms from three {H2L}2ꢂ
and three {H3L}ꢂ anions. The smaller coordination numbers for
Each pair of Sm(III) ions is bridged by a pair of phosphonate
groups (Sm–O–Sm and Sm–O–P–O–Sm bridges) of two {H2L}2ꢂ
anions into
˚
a dimeric unit with a Sm?Sm separation of
4.390(1) A, neighbouring dimers are further interconnected by a

ARTICLE IN PRESS
2716
Y.-Q. Guo et al. / Journal of Solid State Chemistry 181 (2008) 2713–2718
Table 3
˚
Hydrogen bonding geometry (distances in A and angles in 1)
D–H?A
d(D–H)
d(H?A)
oDHA
d(D?A)
Compound 4
N1–H1A?O12i
N2–H2A?O4i
O5–H5A?O4ii
O7–H7C?O2iii
O11–H11A?O12iv
0.910
0.910
0.820
0.820
0.820
1.777
1.908
1.787
1.790
1.832
156.17
154.11
167.34
160.69
172.64
2.635(8)
2.756(8)
2.593(8)
2.579(7)
2.648(8)
Compound 7
N1–H1A?O23
N2–H2A?O16iii
N3–H3A?O10v
N4–H4A?O4
O6–H6A?O10vi
O9–H9C?O2iii
O12–H12A?O4vii
O17–H17C?O23viii
O21–H21A?O13
O22–H22A?O16ix
0.910
0.910
0.910
0.910
0.820
0.820
0.820
0.820
0.820
0.820
1.929
1.883
1.957
1.893
1.785
1.699
1.846
1.821
1.698
1.874
150.97
152.68
147.91
152.85
172.07
172.78
168.70
172.52
168.79
168.90
2.76(1)
2.72(1)
2.77(1)
2.73(1)
2.599(9)
2.51(1)
2.66(1)
2.636(9)
2.507(9)
2.68(1)
Symmetry transformations used to generate equivalent atoms:
(i) ꢂx, ꢂy, ꢂz+1; (ii) ꢂx+1, ꢂyꢂ1, ꢂz+1; (iii) xꢂ1, y, z; (iv) ꢂx, ꢂy+1, ꢂz+1; (v) x+1, y,
z; (vi) ꢂx, yꢂ1/2, ꢂz+1/2; (vii) ꢂx, y+1/2, ꢂz+1/2; (viii) ꢂx+2, y+1/2, ꢂz+1/2; (ix)
ꢂx+2, yꢂ1/2, ꢂz+1/2.
Fig. 4. ORTEP view of the asymmetric unit of compound 7. Hydrogen atoms as well
as the phenyl rings of the phosphonate ligands were omitted for clarity. Symmetry
codes for the generated atoms: (a) xꢂ1, y, z; (b) x+1, y, z.
Fig. 3. View of the structure of 4 down the a-axis. Hydrogen bonds are represented
by the dashed lines.
Gd(III) and Tb(III) ions compared to those for La–Eu is due to the
so-called ‘‘lanthanide contraction’’. The Tb–O bond lengths fall in
˚
the range 2.211(6)–2.297(6) A (Table 2), which are slightly shorter
than Sm–O bonds in 4. Both {H2L}2ꢂ and {H3L}ꢂ anions are
tridentate and bridge with three Tb(III) ions (Scheme 1a), one
{CPO3} group is monodentate, whereas the other one is bidentate.
Such coordination mode has also been observed in 4. The amine
groups of both {H2L}2ꢂ and {H3L}ꢂ anions are protonated, but the
protonation of phosphonate groups are different: both phospho-
nate groups are singly protonated in the {H3L}ꢂ anion whereas
only one phosphonate group is singly protonated in the {H2L}2ꢂ
anion.
The Tb3+ ions are bridge by the {CPO3} groups to form an
infinite chain running along the a-axis (Fig. 5a). Such chain is
racemic since it is composed of right-handed helical chain formed
by Tb(1) bridged by P(3)O3 and P(5)O3 groups, and left-handed
helical chain formed by Tb(1) bridged by P(1)O3 and P(7)O3
groups. Intra-chain hydrogen bonds are formed between amine
groups and non-coordination phosphonate oxygen atoms,
Fig. 5. (a) Wire representation of a racemic terbium phosphonate chain, (b) a 2D
supramolecular layer based on 1D chains of lanthanide(III) phosphonates in 7.
CPO3 tetrahedra are in purple; Tb octahedra, green; N, C and O atoms are drawn as
blue, grey and red, respectively. Hydrogen bonds are represented by the dashed
lines.
˚
the N–H?O bond lengths range from 2.72(1) to 2.77(1) A
(Table 3). These chains are further interconnected via extensive
interchain hydrogen bonds, resulting in a 2D supramolecular
assembly (Fig. 5b). The O–H?O bond lengths are in the range of

ARTICLE IN PRESS
Y.-Q. Guo et al. / Journal of Solid State Chemistry 181 (2008) 2713–2718
2717
˚
2.507(9)–2.683(10) A and the corresponding bond angles are in
the range of 168.70–172.781 (Table 3). Unlike those in compound
4, the phenyl rings are not parallel to each other, hence there
are no
p–p stacking interactions and these 2D layers are held
together via van der Waals interactions (Fig. 6). The structure
of 7 is in fact identical to those of the transition metal complexes,
M{H3L}2 (M ¼ Mn, Cd) [28,31], the only difference lie in that the
higher positive charge of Tb3+ ion compared to M2+ forces one
more proton to be removed from a {H3L}ꢂ anion to become a
{H2L}2ꢂ anion which lowers the symmetry of metal ion from
Ci to C1. The 1D chain of compound 7 is different from that
of 4 in that it lacks the Ln–O–Ln bridges and Tb3+ ion has a lower
coordination number, which is due to the different coordi-
nation modes adopted for the {H2L}2ꢂ anions as well as the so-
called lanthanide contraction. It should be also mentioned that
under higher pH value, Mn(H2L) with a layered structure is
formed in which the phosphonate anion adopts a different
coordination mode: tetradentate and bridging with four metal
centres (Scheme 1c) [31].
Fig. 7. TGA curves for compounds 4 and 7.
3.3. TGA and luminescence properties studies for compounds 4 and 7
The solid-state luminescent properties of compounds 5 and 7
are measured at room temperature (Fig. 8). The free H4L exhibits a
TGA were conducted to examine the stabilities of these
compounds. Compounds 1–7 show similar TGA curves and
compounds 4 and 7 were used as two representatives (Fig. 7,
see also Supporting Materials). The TGA curves of 4 displays two
major steps of weight losses. The first weight loss of 30.2%
between 310 and 552 1C can be attributed to the release of water
molecules formed by condensation of two protonated phospho-
nate groups and combustion of organic groups. The second step in
the temperature of 800–1000 1C corresponds to further decom-
position of the phosphonate ligands. The total weight loss at
1052 1C is 58.9% and the residuals were not characterized due
to its corrosion with the container (Al2O3 crucible). TGA curves of
compound 7 also show two major weight losses. The first weight
loss of 28.6% in the temperature of 294–575 1C corresponds to the
release of water molecules formed by condensation of two
protonated phosphonate groups and combustion of organic
groups. The second weight loss of 32.7% from 860 to 1060 1C is
due to the further decomposition of the organic groups. The total
weight loss at 1060 1C is 61.3% and the residuals were not
identified due to their reactions with the container (Al2O3
crucible).
broad fluorescent emission band at 417 nm under excitation at
Ã
370 nm, which can be assigned to the intra-ligand
p–p
transition
(see Supporting Materials). Upon complexion with lanthanide(III)
ion, only sharp emission bands associated with corresponding
lanthanide(III) ions were observed, indicating the complete
energy transfer from the phosphonate ligands to the central
lanthanide ions [21,22,24,26]. Upon excitation at 394 nm, com-
pound 5 displays characteristic emission bands in the 570–720 nm
region, corresponding to the 5Do-7Fn (n ¼ 0–4) transitions of
Eu3+ ion (Fig. 8a). The 5D0-7F2 transition, which is electric dipole
allowed and hypersensitive to chemical bonds in the vicinity of Eu
(III) ion, is very intense, emitting strong red luminescence. The
presence of only one sharp band for the 5D0-7F0 transition
confirms the existence of only one type of Eu(III) cation with a C1
symmetry. The Eu (5D0) lifetime of compound 5 for lex,em ¼ 394
and 616 nm is measured to be about 2.1 ms.
The luminescent spectrum of 7 (Fig. 8b) excited at 268 nm
exhibits the emissions bands associated with 5D4-7Fj (j ¼ 3,4,5,6)
of the Tb3+ ion. All of transition bands split into two sub-bands,
which is due to crystal field splitting as well as the presence of
two unique Tb(III) sites in the structure. The most-intense
emission appears at 550 nm in the green light region. The
Tb (5D4) lifetime of compound 7 for lex,em ¼ 368 and 616 nm
is 3.7 ms.
The non-centrosymmetric structures of compounds 6 and 7
(space group P212121) prompt us to measure their SHG properties.
Unfortunately, SHG measurements on the powder samples
indicated that their SHG signals are not observed, this is reason-
able since the 1D lanthanide phosphonate chains are racemic.
4. Conclusion
The systematic investigations of the reactions between
N-benzyliminobis(methylenephosphonic acid) and lanthanide
salts resulted in two types of 1D coordination polymers. The
structures of complexes 1–7 are completely different despite of
their similar structural formulae. Compounds 1–5 feature a chain
structure in which dimers of edge-sharing LnO8 polyhedra are
further interconnected by phosphonate ligands. For compounds 6
and 7, the 1D chain structure is formed by Ln(III) ions
interconnected via Ln–O–P–O–Ln bridges. The differences
between the two types of compounds stem from different
Fig. 6. View of the structure of 7 down the a-axis. CPO3 tetrahedra are in purple;
Tb octahedra, green; N,
C and O atoms are drawn as blue, black and red,
respectively. Hydrogen bonds are represented by the dashed lines.

ARTICLE IN PRESS
2718
Y.-Q. Guo et al. / Journal of Solid State Chemistry 181 (2008) 2713–2718
NSF of Fujian Province (no. E0610034), Key Project of Chinese
Academy of Sciences (no. KJCX2-YW-H01) and 973 Programme
(no. 2006CB932903).
Appendix A. Supplementary materials
Supplementary materials associated with this article can be
found in the online version at doi:10.1016/j.jssc.2008.06.043.
References
[1] A. Clearfield, Prog. Inorg. Chem. 37 (1998) 371–510.
[2] K. Maeda, Micro. Meso. Mater. 73 (2004) 47–55 and references therein.
[3] A. Inoue, H. Shinokubo, K. Oshima, J. Am. Chem. Soc. 125 (2003)
1484–1485.
´
[4] E. Matczak-Jon, V. Videnova-Adrabinska, Coord. Chem. Rev. 249 (2005)
2458–2488.
[5] M. Shanmugam, G. Chastanet, T. Mallah, R. Sessoli, S.J. Teat, G.A. Timco,
R.E.P. Winpenny, Chem. Eur. J. 12 (2006) 8777–8785.
[6] J.A. Groves, N.F. Stephens, P.A. Wright, W.P. Lightfoot, Solid State Sci. (2006)
397–403.
[7] Y. Qi, J. Yang, G.-H. Li, G.-D. Li, J.-S. Chen, Inorg. Chem. 45 (2006) 4431–4439.
[8] X.-M. Zhang, J.-J. Hou, W.-X. Zhang, X.-M. Chen, Inorg. Chem. 45 (2006)
8120–8125.
[9] J.A. Groves, P.A. Wright, W.P. Lightfoot, Inorg. Chem. 44 (2005) 1736–1739.
[10] J.A. Groves, S.R. Miller, S.J. Warrender, C. Mellot-Draznieks, P. Lighfoot,
P.A. Wright, Chem. Commun. (2006) 3305–3307.
[11] C.V.K. Sharma, A. Clearfield, J. Am. Chem. Soc. 122 (2000) 1558–1559.
[12] S. Bauer, N. Stock, Angew. Chem. Int. Ed. 46 (2007) 6857–6860.
[13] N. Stock, T. Bein, Angew. Chem. Int. Ed. 43 (2004) 749–752.
[14] R. Murugavel, S. Kuppuswamy, R. Boomishankar, A. Steiner, Angew. Chem. Int.
Ed. 45 (2006) 5536–5540.
[15] D.-K. Cao, J. Xiao, J.-W. Tong, Y.-Z. Li, L.-M. Zheng, Inorg. Chem. 46 (2007)
428–436.
[16] J.-G. Mao, Coord. Chem. Rev. 251 (2007) 1493–1520.
[17] J.M. Lehn, Angew. Chem. Int. Ed. English 29 (1990) 1304–1319.
[18] B. Zhao, X.-Y. Chen, P. Cheng, D.-Z. Liao, S.-P. Yan, Z.-H. Jiang, J. Am. Chem. Soc.
126 (2004) 15394–15395.
[19] S.-S. Bao, L.-F. Ma, Y. Wang, L. Fang, C.-J. Zhu, Y.-Z. Li, L.-M. Zheng, Chem.
Eur. J. 13 (2007) 2333–2343.
[20] Y.-J. Kim, M.-K. Suh, D.-Y. Jung, Inorg. Chem. 43 (2004) 245–250.
[21] J.L. Song, J.G. Mao, Chem. Eur. J. 11 (2005) 1417–1424.
[22] S.-M. Ying, J.-G. Mao, Cryst. Growth Des. 6 (2006) 964–968.
[23] J.L. Song, C. Lei, J.G. Mao, Inorg. Chem. 43 (2004) 5630–5634.
[24] S.-F. Tang, J.-L. Song, X.-L. Li, J.-G. Mao, Cryst. Growth Des.
360–366.
[25] S.-F. Tang, J.-L. Song, J.-G. Mao, Eur. J. Inorg. Chem. (2006) 2011–2019.
[26] S.-F. Tang, J.-L. Song, X.-L. Li, J.-G. Mao, Cryst. Growth Des.
2322–2326.
6
(2007)
(2006)
6
Fig. 8. Solid-state emission spectra of compounds 5 (a) and 7 (b).
´
[27] C. Serre, N. Stock, T. Bein, G. Ferey, Inorg. Chem. 43 (2004) 3159–3163.
[28] Z.-M. Sun, B.-P. Yang, Y.-Q. Sun, J.-G. Mao, A. Clearfield, J. Solid State Chem. 176
(2003) 62–68.
[29] Z.-M. Sun, J.-G. Mao, Y.-Q. Sun, H.-Y. Zeng, A. Clearfield, New J. Chem. 27
(2003) 1326–1330.
coordination modes of the phosphonate ligand as well as the
effect of lanthanide contraction. Strong intra- and inter-chain
hydrogen bonds are formed in both types of compounds. Future
research efforts will be devoted to the study of the effect of the
second ligand such as bipy or phen on the structures of lanthanide
phosphonates.
[30] Z.-M. Sun, J.-G. Mao, B.-P. Yang, S.-M. Ying, Solid State Sci.
295–300.
6 (2004)
[31] Z.-M. Sun, J.-G. Mao, Z.-C. Dong, Polyhedron 24 (2005) 571–577.
[32] J.-G. Mao, Z.-K. Wang, A. Clearfield, Inorg. Chem. 41 (2002) 2334–2340.
[33] J.-G. Mao, Z.-K. Wang, A. Clearfield, Inorg. Chem. 41 (2002) 6106–6111.
[34] J.-G. Mao, Z.-K. Wang, A. Clearfield, J. Chem. Soc. Dalton Trans. (2002)
4457–4463.
Acknowledgments
[35] G.M. Sheldrick, Program SADABS, Universita¨t Go¨ttingen, 1995.
[36] CrystalClear ver. 1.3.5. Rigaku Corporation, Woodlands, TX, 1999.
[37] G.M. Sheldrick, SHELXTL, Crystallographic Software Package, SHELXTL,
Version 5.1, Bruker-AXS, Madison, WI, 1998.
This work was financially supported by National Natural
Science Foundation of China (nos. 20371047 and 20521101), the