Organic-inorganic hybrid materials constructed from inorganic lanthanide sulfate skeletons and organic 4,5-imidazoledicarboxylic acid

Article abstract of DOI:10.1039/b706072f

Five different types of the lanthanide sulfate-carboxylates family, [La₂(SO₄)(Himdc)₂(H₂O)₂] 1, [Gd₂(SO₄)₂(Himdc)(H₂O) ₃]·H₂O 2, [Ln₂(SO₄) ₂(Himdc)(H₂O)₃]·H₂O (Ln = Gd 3a, Eu 3b), [Eu₆Cu(SO₄)₆(Himdc) ₄(H₂O)₁₄] 4, and [Ln(Himc)(SO ₄)(H₂O)] (Ln = Eu 5a, Gd 5b, Tb 5c, Dy 5d, Er 5e); H ₂imc = 4-imidazolecarboxylic acid, H₃imdc = 4,5-imidazoledicarboxylic acid) have been obtained by hydrothermal reactions of Ln₂O₃, transition metal sulfates and H₃imdc at 170 °C and characterized by means of elemental analyses, IR, TG analysis, luminescence spectroscopy and single crystal X-ray diffraction. The 3D structure of 1 is constructed from alternately linkages of organic {La(Himdc)} layers and inorganic {La₂O₂(SO₄)} layers, with the La atoms as hinges. 2 and 3a/3b both contain alternately arranged 1D left- and right-handed helical {Ln(imdc)} chains bridged by SO₄^2- anions to form a 3D framework with 1D rectangle-like channels along the b axis. The structural differences of 2 and 3a/3b lie in the linkages of the SO ₄^2- anions. Complex 4 consists of 2D tubular Eu-sulfate layers pillared by {Cu(Himdc)₂} units to generate a 3D network. Complexes 5a-5e possess 2D bamboo-raft-like layer structures based on helical tubes. Interestingly, H₂imc comes from the in-situ decarboxylation of H₃imdc in the hydrothermal reactions. The luminescence properties of the complexes 3a, 4, 5a 5c, 5d were investigated in solid state at room temperature. The Royal Society of Chemistry.

Full text of DOI:10.1039/b706072f

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PAPER
www.rsc.org/dalton | Dalton Transactions
Organic–inorganic hybrid materials constructed from inorganic lanthanide
sulfate skeletons and organic 4,5-imidazoledicarboxylic acid†‡
Yan-Qiong Suna and Guo-Yu Yang*a,b
Received 23rd April 2007, Accepted 6th July 2007
First published as an Advance Article on the web 1st August 2007
DOI: 10.1039/b706072f
Five different types of the lanthanide sulfate–carboxylates family, [La2(SO4)(Himdc)2(H2O)2] 1,
[Gd2(SO4)2(Himdc)(H2O)3]·H2O 2, [Ln2(SO4)2(Himdc)(H2O)3]·H2O (Ln = Gd 3a, Eu 3b),
[Eu6Cu(SO4)6(Himdc)4(H2O)14] 4, and [Ln(Himc)(SO4)(H2O)] (Ln = Eu 5a, Gd 5b, Tb 5c, Dy 5d, Er
5e); H2imc = 4-imidazolecarboxylic acid, H3imdc = 4,5-imidazoledicarboxylic acid) have been
obtained by hydrothermal reactions of Ln2O3, transition metal sulfates and H3imdc at 170 ◦C and
characterized by means of elemental analyses, IR, TG analysis, luminescence spectroscopy and single
crystal X-ray diffraction. The 3D structure of 1 is constructed from alternately linkages of organic
{La(Himdc)} layers and inorganic {La2O2(SO4)} layers, with the La atoms as hinges. 2 and 3a/3b both
2−
contain alternately arranged 1D left- and right-handed helical {Ln(imdc)} chains bridged by SO4
anions to form a 3D framework with 1D rectangle-like channels along the b axis. The structural
2−
differences of 2 and 3a/3b lie in the linkages of the SO4 anions. Complex 4 consists of 2D tubular
Eu–sulfate layers pillared by {Cu(Himdc)2} units to generate a 3D network. Complexes 5a–5e possess
2D bamboo-raft-like layer structures based on helical tubes. Interestingly, H2imc comes from the in-situ
decarboxylation of H3imdc in the hydrothermal reactions. The luminescence properties of the
complexes 3a, 4, 5a 5c, 5d were investigated in solid state at room temperature.
diversities of the final networks. The reported lanthanide sulfate
structures are mainly restricted to inorganic hydrates, or species
Introduction
containing alkali metal or ammonium ions, or organic amines.20–24
However, organic–inorganic hybrids by incorporating carboxylic
acid ligands in the structure of lanthanide sulfates are rare.25–27
The organic component of hybrid materials is most commonly
incorporated as a charge compensating reagent or as a ligand
coordinated to the metal ions of the inorganic framework.
Carboxylic acids with O-donors tend to bond to the lanthanide
moieties, so the introduction of carboxylic acid into the lanthanide
sulfate frameworks could open a route to preparing new organic–
inorganic hybrid materials, in which the carboxylic acids not only
serve as charge-compensating units but also as bridging ligands
linking to the lanthanide moieties.
4,5-Imidazoledicarboxylic acid(H3imdc), as a multidentate lig-
and, has been extensively used by us and other groups in
the construction of metal–organic frameworks with both single
transition metal (TM) and lanthanide (Ln) ions as nodes.28–37
However, the incorporation of H3imdc into Ln–sulfate frame-
works remains unexplored. We chose H3imdc as the organic
bridging linker, based on the following considerations: (a) It
has three protonated hydrogens and can be successively depro-
tonated to generate H2imdc−, Himdc2− and imdc3− dependant
on the pH level, and hence may supply three different valence
anions as compensating charge and various, acidity-dependant
coordination modes and; (b) The steric effect between the two
adjacent carboxyls will cause the carboxyls to connect metal
ions in different directions.38 Such skew coordination orientation
of the carboxyls is favorable for the construction of the helical
structure.39 On the basis of the aforementioned points, our aim
is to synthesize novel Ln–sulfate–carboxylates frameworks with
In recent years, the design and synthesis of novel organic–
inorganic hybrid materials have provoked significant interest
owing to their enormous variety of intriguing structural topologies
and their fascinating properties as well as great potential applica-
tions as microporous, magnetic, non-linear optical and fluorescent
materials.1–5 In such materials, there is a synergistic interaction
between organic and inorganic components,6 so synthetic and
structural investigations of the hybrid materials will contribute
to the understanding of the synergistic interaction and structure–
function relationships for these hybrid materials.
A variety of families of inorganic frameworks involving
tetrahedral anionic moieties such as silicates,7–8 phosphate,9–10
germanates11–15 and arsenates16 have been reported. The architec-
tures formed by sulfates, on the other hand, have been less
investigated.17–19 So far few lanthanide sulfates have been struc-
turally characterized. The sulfate ion, as a simple tetrahedral
oxo-anion, can adopt a number of coordination modes, such as
monodentate, bidentate bridging, bidentate chelating, tridentate,
and even tetradentate bridging, etc., contributing to the structural
aState Key Laboratory of Structural Chemistry, Fujian Institute of Research
on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian
350002, P. R. China. E-mail: ygy@fjirsm.ac.cn; Fax: +86-591-83710051
bState Key Lab of Rare Earth Materials Chemistry and Applications, Peking
University, Beijing 100871, P. R. China
† CCDC reference numbers 604058 (1), 604059 (2), 604060 (3a), 604061
(3b), 604062 (4), 293650 (5a), 601352 (5b), 601351 (5c), 293649 (5d) and
601353 (5e). For crystallographic data in CIF or other electronic format
see DOI: 10.1039/b706072f
‡ Electronic supplementary information (ESI) available: Fig. S1–S23 and
Tables S1–S2. See DOI: 10.1039/b706072f
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significant properties by using H3imdc ligand, Ln2O3 and TM
sulfates. In this report, we present the systematic syntheses,
structures, thermogravimetric analysis and luminescent properties
of five types of Ln–sulfate–carboxylates coordination polymers,
[La2(SO4)(Himdc)2(H2O)2] 1, [Gd2(SO4)2(Himdc)(H2O)3]·H2O
2, [Ln2(SO4)2(Himdc)(H2O)3]·H2O (Ln = Gd 3a, Eu 3b),
[Eu6Cu(SO4)6(Himdc)4(H2O)14] 4, and [Ln(Himc)(SO4)(H2O)]
(Ln = Eu 5a, Gd 5b, Tb 5c, Dy 5d, Er 5e); H2imc = 4-
imidazolecarboxylic acid). These organic–inorganic hybrid ma-
terials are built from organic carboxylic acid and inorganic sulfate
bridging units.
in a molar ratio of 1 : 2 : 2 : 1111 was sealed in a 30 mL stainless
steel reactor with Teflon liner and heated at 170 C for 10 days,
◦
then cooled to room temperature. Pink crystals of 3a and 3b were
obtained. Yield: 22 and 21% for 3a and 3b (based on Ln2O3). Anal.
Calcd for C5H10Gd2N2O16 S2 3a: C, 8.20; H, 1.38; N, 3.82%. Found:
C, 8.08; H, 1.47; N, 3.68%; and Calcd for C5H10Eu2N2O16S2 3b: C,
8.32; H, 1.40; N, 3.88%. Found: C, 8.16; H, 1.63; N, 3.67%. Main
IR absorption bands (cm−1) for 3a: 3406 m, 1573 s, 1384 s, 1109 m,
1109 m, 830 m, 664 w, 539 w; and for 3b 3395 m, 1598 s, 1384 m,
1112 m, 823 m, 656 w, 521 w (Fig. S1a‡).
[Eu6Cu(SO4)6(Himdc)4(H2O)14] 4
Experimental
A mixture of Eu2O3 (0.083 g, 0.25 mmol), H3imdc (0.156 g,
1 mmol), CuSO4·5H2O (0.125 g, 0.5 mmol) and H2O (10.00 g,
556 mmol) in a molar ratio of about 1 : 4 : 2 : 2222 (pH = 3) was
sealed in a 30 ◦mL stainless steel reactor with a Teflon liner and
heated at 170 C for 10 days, then cooled to room temperature.
Light blue needle-like crystals of 4 were recovered by filtration,
washed with distilled water and dried in air, respectively. Yield:
3% (based on Eu2O3). Anal. Calcd. for C20H36CuEu6N8O54S6 4:
C, 9.93; H, 1.50; N, 4.63%. Found: C, 9.86; H, 1.62; N, 4.56%.
Main IR absorption bands (cm−1): 3400 s, 1595 s, 1414 m, 1092 m,
856 m, 609 w (Fig. S1a‡).
General remarks
Commercially available solvents and chemicals were used without
further purification. IR spectra were measured as KBr pellets on a
Bomem MB102 FT-IR in the range 400–4000 cm−1. The elemental
analyses were determined on a Vario EL III CHNOS elemental
analyzer. Thermal gravimetric data were collected on a Mettler
Toledo TGA/SDTA 851e analyzer in flowing air at a heating
◦
rate of 10 C min−1. Fluorescence measurements were made
with an Edingbergh Instrument FL-FS920 TCSPC luminescence
spectrometer in the solid state at room temperature.
[Ln(Himc)(SO4)(H2O)] (Ln = Eu 5a, Gd 5b, Tb 5c, Dy 5d, Er 5e)
Synthesis
A mixture of Ln2O3 (0.25 mmol), H3imdc (0.156 g, 1 mmol),
CuSO4·5H2O (0.125 g, 0.5 mmol) and H2O (10.00 g, 556 mmol)
in a molar ratio of about 1 : 4 : 2 : 1111 (pH = 3) was sealed in
a 30 mL stainless steel reactor with a Teflon liner and heated at
170 ◦C for 10 days and then cooled to room temperature. Prismatic
crystals of 5a–5e were obtained, respectively. Yield: 6, 11, 9, 8 and
7% for 5a, 5b, 5c, 5d and 5e (based on Ln2O3). Anal. Calcd. for
C4H5EuN2O7S 5a: C, 12.73; H, 1.34; N, 7.43%. Found: C, 12.64;
H, 1.41; N, 7.41%. Anal. Calcd. for C4H5GdN2O7S 5b: C, 12.56;
H, 1.32; N, 7.33%. Found: C, 12.38; H, 1.58; N, 7.29%. Anal.
Calcd. for C4H5N2O7STb 5c: C, 12.51; H, 1.31; N, 7.29%. Found:
C, 12.33; H, 1.48; N, 7.21%. Anal. Calcd. for C4H5DyN2O7S 5d: C,
12.39; H, 1.30; N, 7.23%. Found: C, 12.22; H, 1.36; N, 6.98%. Anal.
Calcd. for C4H5ErN2O7S 5e: C, 12.28; H, 1.68; N, 7.14%. Found:
C, 12.28; H, 1.41; N, 7.06%. IR spectra (KBr pellet, m/cm−1) for 5a:
3400 s, 1640 m, 1582 s, 1394 m, 1208 m, 1132 s, 1061 s, 818 m, 654
m; for 5b: 3399 s, 1634 m, 1581 s, 1393 m, 1208 m, 1093 s, 1058 s,
740 m, 654 m; 5c: 3401 s, 1638 m, 1581 s, 1393 m, 1110 m, 1058 s,
741 m, 654 m; 5d: 3400 s, 1637 m, 1583 s, 1425 m, 1209 m, 1132 s,
1052 s, 996 m, 741 m, 653 s, 608 m; and for 5e: 3403 s, 1640 m,
1584 s, 1393 m, 1095 m, 1062 m, 742 m, 654 m (Fig. S1b‡).
Syntheses of the compounds were achieved by a hydrothermal
technique in a teflon-lined autoclave under synthetic reaction
conditions determined empirically.
[La2(SO4)(Himdc)2(H2O)2] 1
In a typical synthesis for 1, a mixture of LaCl3·7H2O (0.371 g,
1 mmol), H3imdc (0.156 g, 1 mmol), and water (8.00 g, 444 mmol)
in the presence of H2SO4 (0.33 g, 0.38 mmol, 20 wt%) in a molar
ratio of 1 : 1 : 444 : 0.38 (pH = 2) was sealed in a 30 mL
stainless steel reactor with a Teflon-liner and heated at 170 ◦C
for 10 days, then cooled to room temperature. White needle-like
crystals were obtained in 23% yield (based on LaCl3). Anal. Calcd
for C10H8La2N4O14S: C, 16.73; H, 1.12; N, 7.80. Found: C, 16.97;
H, 1.25; N, 7.54. Selected IR (cm−1): 3489 w, 3415 m, 1618 vs, 1376
vs, 1112 m, 1079 m, 799 vs, 634 s, 621 m, 527 m (Fig. S1a‡).
[Gd2(SO4)2(Himdc)(H2O)3]·H2O 2
The lanthanide oxide, Gd2O3 (0.181 g, 0.5 mmol), H3imdc (0.156 g,
1 mmol), and H2O (10.00 g, 556 mmol) in the presence of H2SO4
(0.33 g, 0.38 mmol, 20 wt%) in a molar ratio of 1 : 2 : 1111 : 0.76
reacted in a 30 mL stainless steel reactor with a Teflon liner at
170 ◦C for 10 days, then cooled to room temperature. Pink single
crystals suitable for X-ray diffraction were obtained in 21% yield
(based on Gd2O3). Anal. Calcd for C5H10Gd2N2O16S2: C, 8.20; H,
1.38; N, 3.82%. Found: C, 8.47; H, 1.52; N, 3.90%. Selected IR
(cm−1): 3443 m, 1621 s, 1590 s, 1393 vs, 1128 m, 1096 m, 820 w,
641 w, 479 w (Fig. S1a‡).
X-Ray crystallography
Suitable single crystals were selected and mounted on a glass
fiber. All data were collected at room temperature on a Siemens
SMART CCD diffractometer with graphite-monochromated Mo-
˚
Ka (k = 0.71073A) radiation in the x scanning mode. An
empirical absorption correction was applied using the SADABS
program. The structures were solved by direct methods and refined
by full-matrix least squares on F2 using the SHELXS-97 and
SHELXL-97 program packages.40–41 All hydrogen atoms bond N
and C in compounds 4 and 5a–5e were generated geometrically
[Ln2(SO4)2(Himdc)(H2O)3]·H2O (Ln = Gd 3a, Eu 3b)
A mixture of Ln2O3 (0.5 mmol), H3imdc (0.156 g, 1 mmol),
MnSO4·H2O (0.17 g, 0.1 mmol) and water (10.00 g, 556 mmol)
3772 | Dalton Trans., 2007, 3771–3781
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˚
˚
prism (Fig. S2‡): one imidazole nitrogen (Nim) and five carboxyl
oxygen (OCOO) atoms from four Himdc ligands, one oxygen atom
from one SO4 anion (OS) as well as two coordinated water
(C–H = 0.93 A, N–H = 0.86 A). H atoms associated with
water molecules were located in a difference Fourier map and
refined with fixed isotropic displacement parameters. Detailed
information about the crystal data and structure determination
is summarized in Tables 1 and S1‡. Selected bond distances and
bond angles are given in Tables 2 and 3.
2−
molecules. The La(2) ion is also nine-coordinated by one Nim
and six OCOO atoms from four Himdc moieties as well as two
2−
OS atoms of two SO4 anions (Fig. 1), but it is not possible to
assign the coordination environment of La(2) to either tricapped
trigonal prismatic or monocapped square antiprismatic geometry
CCDC reference numbers 604058 (1), 604059 (2), 604060 (3a),
604061 (3b), 604062 (4), 293650 (5a), 601352 (5b), 601351 (5c),
293649 (5d) and 601353 (5e).
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b706072f
˚
(Fig. S2‡). The La–O distances range from 2.434(2) to 2.763(2) A,
˚
and those of the La–N bond are 2.670(3) and 2.681(3) A. The
Himdc2− exhibits two kinds of distinctly different bridging modes:
one behaves as a l7-Himdc mode linking four La atoms in a tri(bi-
dentate) and a monodentate mode (Scheme 1a); the other acts as a
l6-Himdc mode connecting four La centers in two bis(bidentate)
and two monodentate modes (Scheme 1b). The l-O atoms in mode
1a and in mode 1b coordinated to two La3+ ions play a key role
Results and discussion
Syntheses
2−
in the formation of 1 with a 3D network. The SO4 anions in the
The series of Ln–sulfate–carboxylates were prepared by the
hydrothermal reaction of Ln2O3 (or Ln3+), TM sulfate (or H2SO4),
and H3imdc in water solvent. The overall topology of the
final Ln–sulfate–carboxylates mainly depends on the different
structure are coordinated to three La3+ centers in a monodentate
mode (Scheme 2a).
2−
coordination modes of the organic ligands and inorganic SO4
anions. In our efforts to investigate the effect of lanthanide ions
and sulfate salts on the structure of lanthanide complexes of
H3imdc, various reactions were carried out, by using different
lanthanide compound and sulfates. The reactions of LaCl3 with
H3imdc in the presence of H2SO4 acid give complex 1, whereas
treatment of Gd2O3 with H3imdc under the same conditions
produces another compound 2. The structure difference of 1 and
2 may be due to the sizes of lanthanide ion and the solubility
of the starting materials. The reaction of H3imdc, Ln2O3, and
MnSO4·H2O resulted in the formation of crystalline 3a/3b. But
unfortunately, it did not form a heterometallic framework. This
finding shows that there is a greater affinity for Ln3+ to coordinate
to H3imdc ligand than the Mn2+. Then we changed the TM
salts and used cupric sulfate instead of manganese sulfate in the
reactions, 4 and 5a were both obtained in the same reaction.
It is interesting to note that decarboxylation occurred and a
part of the H3imdc ligands were transformed into H2imc under
hydrothermal conditions in the presence of Cu2+ ions. Various
parallel reactions have been carried out to illustrate the role of
Cu2+. It was observed that H3imdc did not lose a carboxyl in
the absence of Cu2+ and a series of [Ln2(imdc)2(H2O)3]·nH2O
complexes were obtained by directly using Ln2O3 and H3imdc
under hydrothermal conditions.28 Only crystals of transitional
complexes were isolated using CoSO4·7H2O or NiSO4·6H2O
instead of CuSO4·5H2O. These results indicate that Cu2+ plays
a promotional role in the decarboxylation procedure. Other
decarboxylations in the presence of Cu2+ ions have also been
reported.42
Fig. 1 ORTEP view of coordination environments of La3+ with thermal
ellipsoid at 50% probability in 1 (Symmetry code: A: −x, y + 1/2, −z +
1/2; B: −x + 1, −y + 2, −z; C: −x + 1/2, y + 1/2, z; D: x + 1/2, y, −z +
1/2; E: x−1, y, z).
Scheme 1 Coordination modes of the Himdc and imc ligands.
Structural description of [La2(SO4)(Himdc)2(H2O)2] 1
The single-crystal X-ray analysis reveals that the structure of 1 is
an extended 3D framework constructed from alternately arranged
organic {Ln(Himdc)} layers and inorganic {La2O2(SO4)} layers.
In the asymmetrical units of 1, there are two crystallographically
independent La3+ ions, one SO4 anion and two unique Himdc
2−
with two different coordination modes. The coordination geome-
try for nine-coordinated La(1) ion is close to a tricapped trigonal
2−
Scheme 2 Coordination modes of the SO4 anions.
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Each pair of adjacent La(1) ions are connected by Himdc
with mode 1a to form a chiral helical chain running along
a crystallographic 21 axis in the [100] direction with a pitch
(Fig. 3b). The La(2) centers and ligands with mode 1b serve as 3-
connected nodes in the layer and the shortest closed loop around
the nodes are three 6-circuits, thereby the infinite 2D layer is a (6,3)
network containing large edge-sharing hexagons (Fig. S4‡). The
whole 2D network extends parallel to the ab plane in a wavelike
˚
of 6.879(2) A (Fig. 2a). The adjacent helical chains with left-
/right-handedness are bridged by common OCOO atoms which
are alternatively offered by two helical chains to generate a 2D
{La(1)(Himdcmode 1a)} layer in the ab plane (Fig. 2b). We define
each chelate ring as a single point of connection to Ln, then
the ligands with mode 1a and La(1) atoms can be considered
as 3-connected nodes in the 2D layer. From the topological point
of view, the {La(1)(Himdcmode 1a)} layer is a unique 3-connected
2D 4.82 net in which the shortest circuits formed around each 3-
connected node are 4-circuits and 8-circuits. One 4-circuit and two
8-circuits are surrounded each by 3-connected nodes (Fig. S3‡).
Each ligand with mode 1b bridges two La(2) ions to generate an
infinite single helix running along a crystallographic 21 axis in
˚
fashion with a layer thickness of ca.6.35 A. These two types of 2D
organic layers are further linked together by l-O atoms to form
a 3D cationic metal–organic framework with hexagonal channels
along the b axis. SO42− anions lie in the channels and are bonded to
three La3+ ions. There are strong H-bonding interactions among
coordinated water molecules, nitrogen atoms of Himdc ligands,
2−
oxygen atoms of Himdc and SO4 anions with an O · · · O(N)
˚
distance in the range of 2.659–2.952 A; (Fig. 4 and S5‡).
˚
the [010] direction with a long pitch of 14.067 (5) A (Fig. 3a).
The helices are further organized into a 2D wavelike layer of
{La(2)(Himdcmode 1b)} through interhelix bridging of the carboxyls
Fig. 4 3-D framework of 1 viewed along the a-axis, showing alter-nately
arrangement of La(1)(imdc) and La(2)(imdc) layers. Key: cyan, La(1);
green, La(2); black, C; blue, N; red, O.
Fig. 2 (a) Stick view of the left/right-handed La(1)(Himdc) chain in 1,
L/R, running along the a axis; (b) View of the 2D La(1)(imdc) layer with
4.82 net, parallel to the ab plane showing two kinds of helical chains L and
R in 1. Key: cyan, La(1); green, La(2); black, C; blue, N; red, O. La(1) ions
and Himdc ligands function as 3-connected nodes in the net.
Remarkably, there is a 2D inorganic {La2O3(SO4)} layer
between two organic {La(imdc)} layers in 1. La(1) and La(2)
ions are simultaneously bridged by l-O(4) and l-O(8) atoms
to form a [La2O2] dinuclear clusters. These cluster units are
connected through bridging l-O(3) to form an interesting 1-D
zig-zag inorganic lanthanide cluster chain running along the
b axis, in which l-O(3) atom coordinates to La(1) and La(2)
(Fig. S6‡). The parallel inorganic chains along the [100] direction
2−
are interlinked by the SO4 anions into a 2D grid-like layer
containing rectangular sheets (Fig. 4 and 5). In the 2D network,
2−
each [La2O2] unit is bridged by two l-O(3) and two SO4 anions
to four adjacent [La2O2] units, thus the inorganic layer has a
(4,4) topology. The [La2O2] units function as 4-connected nodes
2−
while the l-O(3) and SO4 anions serve as linkers. (Fig. S7‡).
Compound 1 is a unique organic and inorganic hybrid compound
constructed from alternately arranged organic layers and inor-
ganic layers. We presume that there may be a synergistic interaction
between them.
Structural description of [Gd2(SO4)2(Himdc)(H2O)3]·H2O 2
The structure of 2 can be described as a 3D open-framework with
1D rectangular channels. The asymmetric unit comprises two Gd2+
2−
cations, one Himdc, two SO4 anions and four water molecules.
Both Gd(1) and Gd(2) ions are nine-coordinated in a tricapped
trigonal prism (Fig. S8‡). The Gd(1) ion are coordinated by one
Nim and three OCOO atoms from two Himdc ligands, and five OS
atoms of three SO4 anions; while the Gd(2) ion are bonded
to three OCOO atoms from two Himdc ligands, three OS atoms
Fig. 3 (a) Stick view of the left- and right-handed La(2)(imdc) chain in
1, L and R, running along the b axis; (b) View of the 2D La(2)(imdc) layer
with (6.3) topology, parallel to the ab plane showing two kinds of helical
chains L and R in 1. Key: cyan, La(1); black, C; blue, N; red, O. The La(2)
centers and ligands serve as 3-connected nodes in the layer.
2−
3774 | Dalton Trans., 2007, 3771–3781
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Fig. 7 (a) Polyhedral view of the left- and right-handed chain (L and R)
in 2. (b) View of the 2D (4,4) grid layer in 2 along the a axis constructed
2−
from the alternately connection of left- and right-handed chains by SO4
anions. Key: cyan, Gd; black, C; blue, N; red, O; yellow, SO4.
Fig. 5 (a) Polyhedral view of the inorganic layer made of the {La2O2}n
chains and SO42− tetrahedra in 1; Key: Cyan, La(1); Green, La(2); Yellow,
2−
SO4
.
2−
of three distinct SO4 anions as well as three water molecules
(Fig. 6). The Gd–O bond distances are in the range of 2.329(2) to
˚
˚
2.704(2) A, and that of the Gd–N bond is 2.482 (3) A. The Himdc
adopts l7-mode linking four Gd atoms in a tri(bidentate) and a
2−
monodentate modes (Scheme 1c). The two SO4 anions in the
structure adopt the same coordination mode bonding three Gd3+
ions in one bidentate and two monodentate modes (Scheme 2b).
Fig. 8 Polyhedral view of 3-D framework of 2 viewed along the a axis
showing the hexagon channels. Key: cyan, Gd; black, C; blue, N; red, O;
yellow, S.
Fig. 6 ORTEP view of coordination environments of Gd2+ in 2 with
thermal ellipsoid at 50% probability. Atoms having “A”, “B” and “C” in
their labels are symmetry-generated. Symmetry code: A: −x + 2, y − 1/2,
−z + 1/2; B: x, −y + 1/2, z − 1/2; C: −x + 1, −y, −z; D: −x + 1, −y +
1, −z; E: x − 1; −y + 1/2; z − 1/2.
the adjacent layers to generate the 3D open framework exhibiting
different channels, which propagate infinitely along the [100] and
[010] directions (Fig. 8 and 9), respectively. The approximate size
˚
of channels along the b axis is 7.41 × 10.46 A; (Fig. 9). The
The Gd(1) and Gd(2) ions are simultaneously bridged by l-O(2)
and l-O(4) atoms to form a [Gd2O2] rhombic unit. Interestingly,
these [Gd2O2] units are connected by Himdc ligands to produce
left- and right-helical chains {GdHimdc} running along the b
water molecules reside in the channels and there are strong H-
bonding interactions between water molecules, water molecules
2−
and SO4 anions as well as between water molecules and Nim
atoms of Himdc with the O · · · O(N) distance in the range of 2.737–
˚
aixs with a long pitch of 13.4407(7) A (Fig. 7a). The central-
˚
2.947 A; (Fig. S11‡).
symmetry left-/right-helical chains are further alternately linked
2−
by S(1)O4 units in the c axis to result in an infinite 2D step-like
Structural description of [Ln2(SO4)2(Himdc)2 (H2O)3]·H2O (Ln =
(4,4) {Gd(Himdc)(SO4)} layer in the bc plane with rectangular
Gd 3a, Eu 3b)
grids (Fig. 7b and S9‡) in which the [Gd2O2] units as 4-connected
2−
nodes are bridged by S(1)O4 and Himdc linkers. Each grid
3a and 3b are isomorphous. The structure of 3a/3b, represented
by 3a, is very similar to that of 2. Complex 3a contains the same
asymmetric unit as 2. Interestingly, the coordination environment
contains four [Gd2O2] units. The layers are stacked along the a
−→
axis in an –AAAA– sequence and each layer is shifted by a with
respect to the next one (Fig. 8, S10‡). The S(2)O4 units support
2−
2−
of Gd3+ ions, and the coordination modes of Himdc and SO4
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Fig. 9 3-D network of 2 viewed along the b axis showing the rectangular
channels. Key: cyan, Gd; black, C; blue, N; red, O; yellow, S.
Fig. 11 3-D framework of 3a viewed along the a axis showing alternative
arrangement of left-handed (L) layers and right-handed (R) layers. Key:
cyan, Gd; black, C; blue, N; red, O; yellow, S.
anions in 3a are identical with those in 2. The left-/right-handed
helical chains {GdHimdc} are also observed in 3a. The pitch
˚
is 13.3235 (9) A; running along the b axis (Fig. 10a). Different
from the {Gd(Himdc)(SO4)} layer of 2, only single-helical chains
so every layer has a chirality (Fig. 10b, S12). It is also noteworthy
that the arrangement of the layers in 3a is different from that of
2. That is, all the layers adopt an AAAA arrangement along the
a axis in 2, while in 3a they adopt an ABAB arrangement in the
c axis. The chiral layers of opposite handedness in 3a coexist in
the crystal structure, so the whole crystal does not show chirality
(Fig. 12).
2−
are bridged by S(1)O4 anions in the a axis to result in a 2D
homochiral (4,4) {Gd(Himdc)(SO4)} layer in the ab plane in 3a
(Fig. 10b, S12‡). The left-/right-handed layers in 3a are alternately
2−
connected by S(2)O4 anions to produce a 3D framework,
exhibiting different channels, which propagate infinitely along the
a and b axis, respectively (Fig. 11, S13‡). The water molecules
reside in the channels and there are strong H-bonding interactions
2−
between water molecules and SO4 anions as well as between
water molecules and Nim atoms of Himdc with O · · · O (N) distance
˚
in the range of 2.722–2.965 A; (Fig. S14‡).
Fig. 12 Representation showing the different topologies of the 3D
framework for 2 (a) and 3a (b). Key: cyan, Gd; yellow: SO42−. The
[Gd2O2] units as 4-connected nodes are denoted by cyan spheres, and
2−
the yellow and green lines represent S(1)O4 anions and Himdc ligands.
Structural description of [Eu6Cu(SO4)6(Himdc)4(H2O)14] 4
Fig. 10 (a) Polyhedral view of the left- and right-handed chain (L and
R) in 3a. (b) View of the 2D chiral (4,4) grid layer in 3a along the c axis
constructed from only left-handed chains bridged by SO4 anions. Key:
The 3D framework of 4 consists of inorganic {Eu(SO4)} layers of
pillared by [Eu4Cu(Himdc)4] units. The asymmetric unit contains
three unique Eu3+ ions, a half Cu2+ centers, two Himdc ligands,
2−
cyan, Gd; black, C; blue, N; red, O; yellow, S.
2−
three SO4 anions and seven coordinated water molecules. As
The {Gd(Himdc)(SO4)} layer in 2 and 3a present an interesting
shown Fig. 13, the Cu2+ ions lie in the inversion centers and are
each coordinated by two water molecules at the trans positions and
two Nim as well as two OCOO atoms from two Himdc to complete
a slightly distorted octahedral. The Cu–O bond distances are
comparison. In 2, the S(1)O4 anions are bonded to two Gd3+
2−
centers symmetry-related by the c glide plane, forming a 1D zig-
zag inorganic {Gd(SO4)} chain running along the c axis. Because
left-/right-handed helical chains coexist in each layer, every layer
is mesomeric and dose not exhibit chirality (Fig. 7b, S9). On the
other hand, two equivalent Gd3+ ions in 3a are connected by
˚
˚
2.012(4) and2.170(5)A, andthe Cu–Nbonddistance is 2.075(4) A.
Eu3+ ions exhibit three types of coordination environment. Eu(1)
ion is nine-coordinated in a tricapped trigonal prism by four OCOO
2−
2−
S(1)O4 ions in the a axis to generate a 1D linear {Gd(SO4)}
atoms from two Himdc, three OS atoms of three SO4 anions
inorganic chains. There are only homochiral helices in each layer,
and two water molecules. Eu(2) ion exhibits mono-capped square
3776 | Dalton Trans., 2007, 3771–3781
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Fig. 13 ORTEP view of coordination environments of Eu3+ and Cu2+
with thermal ellipsoid at 30% probability in 4 (Symmetry code: A: x − 1,
y, z; B: x − 1, y − 1, z; C: −x + 2, −y, −z + 1; D: x + 1, y, z; E: −x + 2,
−y + 1, −z).
antiprismatic geometry coordinated by one OCOO atoms and one
Nim from one Himdc, five OS atoms of three SO4 anions and
Fig. 15 (a) Tubular structure in 4 made up of 8-MR. (b) 2-D tubular
layer made of 8-MR channels in 4. Key: cyan, Eu(1)/Eu(2); green, Eu(3);
yellow, S; red, O.
2−
two water molecules. Eu(3) ion is eight-coordinate and described
as a dodecahedron: four one OCOO atoms from two Himdc, two
2−
OS atoms of two SO4 as well as two terminal water molecules
4-/8-MR channels (Fig. 15b). The Eu(3) atoms are bridged by
(Fig. S15‡). The Eu–O bond lengths fall in the regions 2.288 (4)–
2−
S(1)O4 anions into a 1D linear inorganic chain running along
˚
˚
2.694(4) A, and the Eu–N bond length is 2.514(4) A. Two types of
Himdc both adopt the l6-Himdc mode in a tri(bidentate) fashion,
but they are coordinated to different metal atoms, one is chelated
by three Eu atoms (Scheme 1d), while the other is bonded to one
Cu and two Eu atoms (Scheme 1e). The coordination modes of
the a axis (Fig. S17‡). These linear chains are attached above or
2−
below the 2D tubular layer through the oxygen donors of S(1)O4
anions bonding to Eu(1) atoms.
There are two types of Himdc ligands in 4. One behaves as
an ancillary ligand chelated with Eu atoms to decorate the 2D
tubular layer. The other one coordinates to Cu atoms to form the
{Cu(Himdc)2} complex (Fig. S18‡), which supports the adjacent
tubular layers to generate a 3D framework exhibiting different
channels, which propagate infinitely along the a and b axis,
respectively (Fig. 16, S19‡). The approximate size of channels
2−
SO4 of 4 are also observed in 1 and 2 (Scheme 2a and b).
The inorganic {Eu{SO4}} layer can be viewed as consisting of
open-ended, hollow tubes in a side by side arrangement along the
b axis with crystallographically inversions through the center of
each tube. As shown in Fig. 14b and S16‡, each tube consists
2−
of 8-membered rings (MRs) made up of four SO4 units and
four Eu3+ ions. Within 8-MRs, there are two different types of
SO42− units and Eu3+ ions: S(2)O42− and S(3)O42−, Eu(1) and Eu(2).
Each S(2)O42− anion utilizes its three OS donors to link Eu(1) and
2−
Eu(2) atoms, while each S(3)O4 anion uses its two OS donors
bridging the Eu(1) and Eu(2) atoms, thus forming the fused 8-
2−
MRs. In addition, the third OS donor of each S(3)O4 unit is
bound to one of the Eu(2) atoms belonging to adjacent 8-MRs.
Stacking of such 8-MRs results in 1D nanosize tubes extending
along the a axis (Fig. 15a). Such 1D tubes are connected along the
2−
b axis via the remaining OS atoms of S(2)O4 which are offered
by two adjacent tubes to generate the 2D tubular layer with 1D
2−
Fig. 14 (a) The 4-MR in 4 composed of two Eu2+ ions and two SO4
anions. (b) The 8-MR composed of four Eu2+ ions and four SO4 anions
Fig. 16 3-D framework of 4 viewed along the approximate the a axis.
2−
in 4. Key: cyan, Eu; yellow: S; red, O.
Key: cyan, Eu; green, Cu; white, C; blue, N; red, O; yellow, S.
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˚
along the a axis is 6.29 × 9.47 A; and are located by coordinated
water molecules. There are strong H-bonding interactions between
2−
water molecules, water molecules and SO4 anions as well as
between water molecules and Nim atoms of Himdc with an
˚
O · · · O(N) distance in the range of 2.656–2.971 A.
Structural description of [Ln(Himc)(SO4)(H2O)] (Ln = Eu 5a, Gd
5b, Tb 5c, Dy 5d, Er 5e)
Complex 5a43 was synthesized under the same hydrothermal
reaction as that used for complex 4, but the decarboxylation
occurred in 5a. H2imc comes from the in-situ decarboxylation of
H3imdc in the hydrothermal reactions (Scheme 3). This indicates
that only a part of H3imdc was transformed into H2imc under
hydrothermal conditions. Complexes 5b–5e are isomorphous to
the recently reported 5a and also display 2D bamboo-raft like
layer structures. Therefore, only the structure of 5c is described
in detail. The novel 2D bamboo-raft-like layered network is built
from alternately arranged left- and right-handed helical tubes.
Fig. 18 (a) View of the left- and right-handed helical chains along
the b axis in 5a. Color code: Dy, yellow; O, red; C, white; N, blue; S,
purple. (b) The helical tubes constructed from the helical chains weaved by
SO4 anions. The helical chain is marked yellow for identification. L/R:
left/right.
2−
the tubular layers (Fig. 19). The H-bondings between N and OS
atoms link the adjacent layers into a 3D framework (N · · · O 2.94)
(Fig. 20) (Tables 1–3).
Scheme 3 H2imc formed via the decarboxylation of H3imdc.
The Tb3+ ion is eight-coordinate and described as a dodec-
ahedron (Fig. 17). Each Himc connects two Tb3+ ions in one
monodentate and one bidentate mode (Scheme 1f); while each
2−
SO4 ion adopts a l3-tetradentate mode (Scheme 2c) bridging
three Tb3+ ions. A pair of Tb3+ ions are bridged by two l-O atoms
of two SO42− units to form a [Tb2O2] rhombic unit. These units are
linked up via carboxyls of Himc to give rise to two types of helical
˚
chains with opposite chirality with a pitch of 6.4982(5) A running
along the 21 axis (Fig. 18a). The left-/right-handed helical chains
Fig. 19 View of 2-D bamboo-raft-like structure formed by the alternating
assembly of the helical tubes with opposite chirality in 5a. The helical chain
is marked yellow for identification and the coordinated water molecules
are omitted for clarity. L/R: left/right-handed helical tube, respectively.
2−
are further weaved by SO4 anions through their remaining l-O
atoms to chelate two Tb3+ ions of adjacent [Tb2O2] units to make
helical tubes with opposite chirality. The dimension of the helical
˚
tube is about 4.66 × 5.73 A (Fig. 18b). These two types of helical
tubes are alternately connected, with [Tb2O2] units functioning as
hinges. As a result, a novel 2D bamboo-raft-like layered network
forms in the bc plane. The imidazole rings are above or below
Fig. 17 The coordination environments of Tb3+ in 5a. Thermal ellipsoids
are at 50% probability. Atoms having “A”, “B” or “C” in their labels are
symmetry-generated [A = (x,1/2 − y, 1/2 + z), B = (−x, 1 − y, 1 − z),
C = (−x, −y, 1 − z)]. Hydrogen atoms were omitted for clarity.
Fig. 20 View of 3-D supramolecular network for 5a.
3778 | Dalton Trans., 2007, 3771–3781
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Table 1 Crystal data and structure refinements for compounds 1–5a
1
2
3a
4
5a
Formula
Fw
C10H8La2N4O14S
718.08
Orthorhombic
Pbca
6.879(2)
14.067(5)
33.802(1)
90
90
90
3270.7(2)
8
2.917
C5H10Gd2N2O16S2
732.79
Monoclinic
P21/c
9.469(1)
13.441(1)
12.775(1)
90
105.15(1)
90
1569.3 (2)
4
C5H10Gd2N2O16S2
732.79
Monoclinic
P21/c
6.586(1)
13.276(1)
18.874(1)
90
106.61 (1)
90
1581.5(1)
4
C20H36CuEu6N8O54S6
2420.23
Triclinic
P-1
6.628(1)
9.465(1)
21.503(2)
96.78(1)
94.31(1)
97.89(1)
1321.1(2)
1
C4H5EuN2O7S
377.12
Monoclinic
P21/c
11.209(2)
6.541(1)
12.203 (2)
90
107.92(1)
90
851.2(3)
4
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
˚
V/A
Z
Dc/g cm−3
3.101
8.739
3.078
8.672
3.042
7.791
2.943
7.635
l/mm−1
5.377
F(000)
2704
1.188
0.0260
0.0466
1368
1.032
0.0191
0.0426
1368
1.141
0.0296
0.0661
1147
1.065
0.0308
0.0746
712
1.351
0.0174
0.0639
S(F2)
R1, (I > 2r (I))
wR2 (I > 2r (I))
˚
Table 2 Selected bond distances (A) for 1–4
1
La(1)–O(2)
La(1)–O(2W)
La(1)–O(12)
La(1)–O(8A)
La(1)–O(1B)
2
2.434(2)
2.531(3)
2.550(2)
2.556(2)
2.567(2)
La(1)–O(4)
2.590(2)
2.605(2)
2.640(3)
2.670(3)
2.448(2)
La(2)–O(5)
2.454(2)
La(2)–N(3A)
La(2)–O(3)
La(2)–O(4)
2.681(3)
2.750(2)
2.763(2)
La(1)–O(3C)
La(1)–O(1W)
La(1)–N(2C)
La(2)–O(11)
La(2)–O(6D)
La(2)–O(7D)
La(2)–O(9E)
La(2)–O(8A)
2.477(2)
2.514(2)
2.526(3)
2.628(2)
Gd(1)–O(4A)
Gd(1)–O(7)
Gd(1)–O(1A)
Gd(1)–O(11)
Gd(1)–O(2)
3a
Gd(1)–O(4)
Gd(1)–O(7A)
Gd(1)–O(1)
Gd(1)–O(11)
Gd(1)–O(2)
3b
2.340(2)
2.329(2)
2.356(2)
2.412(2)
2.572(2)
Gd(1)–O(10)
Gd(1)–O(8B)
Gd(1)–N(1)
Gd(1)–O(5B)
Gd(2)–O(12)
2.704(2)
2.573(2)
2.482(3)
2.429(2)
2.418(2)
Gd(2)–O(9C)
Gd(2)–O(6E)
Gd(2)–O(2W)
Gd(2)–O(2E)
Gd(2)–O(3W)
2.352(2)
2.485(2)
2.496(3)
2.470(2)
2.417(3)
Gd(2)–O(4W)
Gd(2)–O(3D)
Gd(2)–O(4D)
2.443(3)
2.430(2)
2.669(2)
2.359(4)
2.358(5)
2.359(4)
2.448(4)
2.474(4)
Gd(1)–O(10)
Gd(1)–O(8)
Gd(1)–N(1)
Gd(1)–O(5)
Gd(2)–O(12B)
2.514(4)
2.516(6)
2.520(6)
2.670(7)
2.356(5)
Gd(2)–O(9C)
Gd(2)–O(6)
Gd(2)–O(2W)
Gd(2)–O(2D)
Gd(2)–O(3W)
2.403(4)
2.400(5)
2.428(5)
2.460(4)
2.462(5)
Gd(2)–O(4W)
Gd(2)–O(3D)
Gd(2)–O(4D)
2.499(5)
2.505(5)
2.519(5)
Eu(1)–O(4)
Eu(1)–O(7A)
Eu(1)–O(1)
Eu(1)–O(11)
Eu(1)–O(2)
4
Eu(1)–O(18)
Eu(1)–O(9)
Eu(1)–O(15)
Eu(1)–O(7W)
Eu(1)–O(2W)
Eu(1)–O(7)
Eu(1)–O(1)
Eu(1)–O(8)
2.368(3)
2.376(4)
2.366(3)
2.453(3)
2.481(3)
Eu(1)–O(10)
Eu(1)–O(8)
Eu(1)–N(1)
Eu(1)–O(5)
Eu(2)–O(12B)
2.526(3)
2.537(5)
2.539(4)
2.634(5)
2.363(3)
Eu(2)–O(9C)
Eu(2)–O(6)
Eu(2)–O(2W)
Eu(2)–O(3W)
Eu(2)–O(2D)
2.412(3)
2.415(4)
2.443(4)
2.469(4)
2.470(3)
Eu(2)–O(3D)
Eu(2)–O(4W)
Eu(2)–O(4D)
2.513(4)
2.516(4)
2.535(3)
2.340(4)
2.382(4)
2.399(4)
2.449(4)
2.449(4)
2.496(3)
2.528(4)
2.620(3)
Eu(1)–O(2)
2.630(4)
2.320(4)
2.364(4)
2.385(4)
2.436(4)
2.479(4)
2.498(4)
2.514(4)
Eu(2)–O(8)
2.537(3)
2.694(4)
2.288(4)
2.289(4)
2.397(3)
2.402(5)
2.410(4)
2.445(4)
Eu(3)–O(7D)
Eu(3)–O(6W)
Eu(3)–O(10)
Cu(1)–O(4)
Cu(1)–N(1)
Cu(1)–O(4W)
2.477(3)
2.612(5)
3.093(7)
2.012(4)
2.075(4)
2.170(5)
Eu(2)–O(19A)
Eu(2)–O(14B)
Eu(2)–O(17)
Eu(2)–O(5W)
Eu(2)–O(16C)
Eu(2)–O(1W)
Eu(2)–N(4)
Eu(2)–O(13C)
Eu(3)–O(3D)
Eu(3)–O(6D)
Eu(3)–O(2D)
Eu(3)–O(11)
Eu(3)–O(12D)
Eu(3)–O(3W)
˚
Table 3 Selected bond distances (A) for 5a–5e
Lanthanide contraction
5a (Eu)
5b (Gd)
5c (Tb)
5d (Dy)
5e (Er)
5a–5e are isomorphous. The various crystal lattice constants
of these isomorphous complexes clearly exhibit the lanthanide
contraction effect. The same effect is observed in 5a–5e and
3a–3b for lattice constants. As shown in Table 4, the average
Ln–O and Ln–N bond distances of 5a–5e decrease along the
series of Eu, Gd, Tb, Dy to Er, where it was ascribed to crystal
field contractions of those rare earth ions lacking spherical
symmetry.44
Ln–O(1A)
Ln–O(3B)
2.344(3)
2.351(3)
Ln–O(1W) 2.386(3)
2.331(5)
2.347(5)
2.380(5)
2.391(5)
2.421(5)
2.440(6)
2.479(6)
2.531(5)
2.322(3)
2.323(3)
2.363(3)
2.367(3)
2.403(3)
2.423(3)
2.472(4)
2.521(3)
2.313(2)
2.318(3)
2.342(3)
2.355(2)
2.390(3)
2.405(3)
2.455(3)
2.514(2)
2.300(5)
2.291(6)
2.315(6)
2.336(5)
2.366(5)
2.382(6)
2.440(7)
2.500(5)
Ln–O(6)
Ln–O(2)
Ln–O(5C)
Ln–N(2)
Ln–O(6C)
2.387(3)
2.431(3)
2.453(3)
2.499(3)
2.543(3)
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˚
Table 4 The average bond lengths (A) of complexes 3a–3b and 5a–5e based on H3imdc and H2imc, respectively
3b(Eu)
3a(Gd)
5a(Eu)
5b(Gd)
5c(Tb)
5d(Dy)
5e(Er)
Ln–OC
Ln–OS
Ln–OW
Ln–N
2.456
2.465
2.481
2.539
2.446
2.464
2.463
2.520
2.388
2.434
2.386
2.499
2.376
2.427
2.380
2.479
2.363
2.409
2.363
2.472
2.352
2.398
2.342
2.455
2.333
2.377
2.315
2.440
OC: oxygen atom of carboxylate group; OS: oxygen atom of sulfate group; OW: oxygen atom of coordination water.
Discussion on structure evolution
may make them excellent candidates for potential photoactive
materials (Fig. S20–22‡).
The present study reports a series of Ln–sulfate–carboxylates
with H3imdc. As a simple tetrahedral oxoanion, the SO4 has
2−
Acknowledgements
been found to be a versatile building block and to exhibit
diverse coordination modes, which may ligate and bridge metal
centers of the coordination polymer chain and hence dictate the
interchain geometry and even the dimensionality of the structure.
There is a synergistic interaction between organic and inorganic
components. The H3imdc also exhibits coordination variety: two
carboxyls can be chelating or bridging in the flexible orientations,
and the imidazole ring can coordinate lanthanide atoms, which
their variable coordination modes and linkages have profound
influences on the dimensionality and the topology of the final
framework. In the structure of 1, the l7-Himdc and l6-Himdc
connect La ions to generate 2D 4.82 and (6,3) layers, respectively.
These two types of 2D organic layers are further linked together
by bridging O(3), O(4) and O(8) atoms to form a 3D cationic
metal-organic framework with hexagonal channels along the b
axis. SO42− anions lie in the channels and bond to three La3+ ions.
In 2 and 3a/3b, Himdc adopts the l7-mode and connects Ln ions
to generate a 1D helical chain interlinked through bridging sulfate
into a open-framework. The SO42− binds to three Ln ions through
all oxygen atoms with one chelating and two monodentate sites. In
This work was supported by 973 Program (no. 2006CB932900),
the National Natural Science Foundation of China (no.
20473093/20271050), the Natural Science Foundation of Fujian
Province (no. E0510030), and the Project from CAS (KJCX2-YW-
H01).
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