Lanthanide contraction and pH value controlled structural change in a series of rare earth complexes with p-aminobenzoic acid

Article abstract of DOI:10.1016/j.molstruc.2004.06.013

A series of rare earth complexes with p-aminobenzoic acid (HL) have been synthesized: [RE₂L₆(H₂O)₂] _n [RE=La (1), Ce(2), Pr(3), Sm(4), Eu(5), Tb(6), Dy(7), Er(9)] and [RE₂L₆(H₂O)₄]·2H ₂O [RE=Tb(6′), Ho(8), Yb(10), Lu(11), Y(12)]. The crystal structures of 1, 2, 6, 6′, 7, 9 and 12 have been determined and the isomorphous relationships of the others have been identified. Their structures change from two-dimensional (2D) array (the coordination number of the metal ions is nine for 1 and eight for 2-7 and 9) to double-nuclear structure (the metal ions are eight-coordinated) for 6′, 8 and 10-12, as controlled by lanthanide contraction. The structural type has been found influenced by the pH value of the reaction mixtures.

Full text of DOI:10.1016/j.molstruc.2004.06.013

Journal of Molecular Structure 702 (2004) 77–83
www.elsevier.com/locate/molstruc
Lanthanide contraction and pH value controlled structural change
in a series of rare earth complexes with p-aminobenzoic acid
a
Hao-Ling Sun , Chao-Hong Ye , Xin-Yi Wang , Jun-Ran Li , Song Gao , Kai-Bei Yu
a
a
a,
a,
b
*
*
a
State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering,
Peking University, Beijing 100871, China
b
Chengdu Center for Analysis and Measurement, Academia Sinica, Chengdu 610041, China
Received 2 May 2004; revised 6 June 2004; accepted 9 June 2004
Abstract
A series of rare earth complexes with p-aminobenzoic acid (HL) have been synthesized: [RE L (H O) ] [RE ¼ La (1), Ce(2), Pr(3),
2
6
2
2 n
0
Sm(4), Eu(5), Tb(6), Dy(7), Er(9)] and [RE
0
2
L
6
(H
2
O)
4
]·2H
, 7, 9 and 12 have been determined and the isomorphous relationships of the others have been identified. Their structures change from two-
2
O [RE ¼ Tb(6 ), Ho(8), Yb(10), Lu(11), Y(12)]. The crystal structures of 1, 2, 6,
6
dimensional (2D) array (the coordination number of the metal ions is nine for 1 and eight for 2–7 and 9) to double-nuclear structure (the
0
metal ions are eight-coordinated) for 6 , 8 and 10–12, as controlled by lanthanide contraction. The structural type has been found influenced
by the pH value of the reaction mixtures.
q 2004 Elsevier B.V. All rights reserved.
Keywords: Rare earth; Structure; p-aminobenzoic acid; Lanthanide contraction; pH value
1
. Introduction
X-ray powder diffraction patterns, Brzyska and Rzaczy n´ ska
suggested that the HL complexes of RE elements La–Tm, Y
and Yb–Lu are isostructural [8]. Nevertheless, a systematic
structural investigation on complexes of the lanthanide
series with this ligand has not existed to date. The
p-aminobenzoic acid complexes of some RE metals Nd,
Dy and Yb have been synthesized and their crystal
structures determined [9–11]. The results show that the
p-Aminobenzoic acid (HL), a biologically important
ligand, can form complexes with various metal ions. In
order to gain some understanding on the interaction between
biological ligands and metal ions, various complexes using
HL as ligand have been synthesized, and their crystal
þ
þ
structures studied. In complexes containing Na or K , the
2
ligand L is not directly coordinated to the metal ion, which
3
þ 3þ
crystal structures of the Dy and Yb complexes are
3
þ
alike, whereas the crystal structure of the Nd complex is
clearly different from the two complexes mentioned above.
The effect of lanthanide contraction on the structure of RE
complexes has been reported earlier [12–18] that, using 3,5-
is surrounded by coordination H O molecules [1]. In
2
2
complexes of Ba , Ag , Zn , Cd and Ni [1–5],
þ
þ
2þ
2þ
2þ
2
both the carboxylic group and the amino group of L are
2
þ
coordinated to the metal. However, in complexes of Sr
2
,
pyrazoldicarboxylic acid (H pdc) as the ligand, lanthanide
3
þ
2þ
2
Mg and Co with L [1,6,7], only the oxygen atoms of
the carboxylic groups are coordinated to the metal ion
complexes (Ln ¼ La, Ce, Eu, Er and Lu) of three different
structural types (two-dimensional single layer, two-dimen-
sional double layer and three dimensional array) can be
2
and the amino groups of the L ligands are not coordinated.
Therefore, the effect of metal ions on the structural type of
their HL complexes is apparent. Structural investigations
of HL rare earth (RE) complexes are sparse. Based on their
obtained [18]. Nitrilotriacetic acid (H NTA) is an important
3
derivative of glycine. A series of Ln–Cu–NTA complexes
have been synthesized in our laboratory. Crystal structures
of these complexes indicate that their dimensional diversity
is controlled by lanthanide contraction [17]. As an extension
of this work, we herein report the synthesis and structural
*
Corresponding author. Tel.: þ86-10-62753517; fax: þ86-10-
2751708.
E-mail addresses: lijunran@pku.edu.cn (J.-R. Li), gaosong@pku.edu.
cn (S. Gao).
6
2
diversity of a series of RE-L complexes.
0022-2860/$ - see front matter q 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2004.06.013

78
H.-L. Sun et al. / Journal of Molecular Structure 702 (2004) 77–83
Pan et al. [18] have suggested that the pH of the reactions
plays a crucial role in the formation of either single- or
Table 1
Results of C, H and N analyses for complexes (outside brackets, calculated
data; inside brackets, found data)
double-layered structures, because the tri-acid ligand
2
(
H pdc) could coordinate either in the form of H pdc or
3 2
Complexes Formula
N (%)
C (%)
H (%)
2
2
þ
Hpdc , which is controlled by the amount of H in a
reaction mixture. By adjusting the pH value, they success-
fully isolated a single-phase, double-layered erbium struc-
ture at pH 5, and a single-layered structure at pH 1,
respectively. Nonetheless, the effect of reaction pH on the
structure of the RE complex formed using a monoacid with
an amino group as the ligand, such as HL, has not been
reported before.
1
2
3
4
5
6
6
7
8
9
1
1
LaC21
CeC21
PrC21
SmC21
N
3
O
7
H
20
20
20
7.43 (6.67) 44.62 (44.57) 3.57 (3.19)
7.42 (7.28) 44.52 (44.55) 3.56 (3.46)
7.41 (7.02) 44.46 (44.50) 3.55 (3.14)
N
3
O
7
H
3 7
N O H
3 7
N O H20 7.29 (7.19) 43.73 (43.98) 3.50 (3.45)
EuC21
TbC21
TbC21
N
3
O
7
H
20
7.27 (7.15) 43.61 (43.62) 3.49 (3.57)
7.18 (6.93) 43.08 (42.56) 3.42 (3.37)
6.76 (7.11) 40.59 (40.86) 3.89 (3.51)
N
N
3
3
O
O
7
H
9
H
20
24
0
DyC21N
3
3
O
O
7
H
H
20 7.14 (7.40) 42.83 (43.31) 3.42 (3.41)
24 6.70 (6.66) 40.19 (40.43) 3.83 (3.82)
HoC21N
9
In order to further investigate the structure characteristics
of RE complexes with p-aminobenzoic acid, to gain better
knowledge on the different factors that may influence the
structure of these complexes, we have synthesized a series
ErC21N
3
O
7
H
20
7.08 (6.52) 42.50 (42.35) 3.37 (2.96)
0
1
YbC21N
3
O
9
H
24 6.61 (6.59) 39.69 (39.84) 3.81 (3.71)
LuC21
YC21
N
3
O
9
H
24
6.59 (6.53) 39.57 (39.69) 3.80 (3.65)
7.62 (7.61) 45.75 (46.58) 4.39 (4.26)
12
N
3
O
9
H
24
3
þ
of HL complexes of RE ions (RE ¼ La, Ce, Pr, Sm, Eu,
Tb, Dy, Ho, Er, Yb, Lu and Y). The structures of these
complexes have been determined. The effects of lanthanide
contraction and pH value on compound structure have been
studied.
˚
radiation (0.71073 A). For example, with TbC H N O
21 20
3
7
(6), intensity data was collected on a Nonius Kappa CCD
diffractometer in the v-scan mode. The structures were
solved by direct methods and refined by a full-matrix
2
least-squares technique based on F using the SHELXL 97
2
. Experimental section
program. All non-hydrogen atoms were refined aniso-
tropically, and the hydrogen atoms of water molecules
were located from difference electronic Fourier maps.
Other hydrogen atoms were placed by calculated
positions and refined isotropically. Crystal data, details
of data collection and refinement are listed in Table 2.
Crystal cell parameters of all the complexes are listed in
Table 3. Important bond lengths and angles are given in
Tables 4a–4d.
2
.1. Materials and apparatus
RE oxides of over 99.9% purity were obtained from the
Rare Earth Company in Beijing. Solutions of RECl were
3
prepared by dissolving RE oxides in hydrochloric acid.
Analytical grade hydrochloric acid and aqueous ammonia
were purchased from the Chemical Reagent Company in
Beijing.
Analyses of C, H, and N were performed on a German
Elementar Vario EL instrument. IR spectra were measured
using KBr pellets with a Nicolet Magna-IR 750
spectrometer at 295 K. Thermal analyses were performed
on a Du Pont 1090B thermal analyzer.
3
. Results and discussion
3.1. IR spectra
2
.2. Preparations of complexes
Since the IR spectra of isomorphous complexes are
0
generally alike, complex 7 and 6 are chosen as representa-
tives in the following discussion. The IR resonances of the
RE complexes were prepared with the following
2
carboxylate moiety, n (OCO) and n (OCO), in free L ion
procedure: Aqueous solution of HL (0.9 mmol), the pH
value of which was adjusted to ca. 4 with aqueous ammonia,
was mixed with RECl (0.3 mmol) under stirring. The pH
as
s
2
and coordinated L ligands, are compared. After coordi-
nation to the metal ion center, the nas (OCO) absorption is
3
2
1
found red-shifted from 1601 to 1589 and 1592 cm ; the
value of the solution was adjusted carefully to ca. 4.0 or 5.0.
After filtration, the solution was left to stand at room
temperature. Single crystals of the complexes were obtained
in ca. 40% yield after one week. The results of elemental
analysis are listed in Table 1.
2
1
n (OCO) absorption has also red-shifted from 1423 cm
s
2
1
0
down to 1398 and 1417 cm , in complexes 7 and 6 ,
respectively. These results indicate that the carboxyl groups
of the ligand are bound to the metal ions [19]. The value of
2
1
21
n (C–N) at 1326 cm in NH L shifted 30 cm down to
4
s
2
1296 cm in complex 7, whereas this shifting is not found
1
2
.3. X-ray crystallographic study
0
in complex 6 . These results suggest that the N atoms of the
ligands are coordinated to the metal ions in complex
[Dy L (H O) ] , and they are not coordinated in complex
All data collections were carried out on a Nonius
Kappa CCD diffractometer or a Siemens P4 four-circle
diffractometer with graphite-monochromated Mo Ka
2
6
2
2 n
[Tb L (H O) ]·2H O [19].
2 6 2 4 2

H.-L. Sun et al. / Journal of Molecular Structure 702 (2004) 77–83
79
Table 2
Crystallographic data for complexes 1, 6, 6 and 12
0
0
Empirical formula
Crystal size (mm)
T (K)
LaC21
H
20
N
3
O
7
(1)
TbC21
H
20
N
3
O
7
(6)
0.20 £ 0.18 £ 0.05
293 (2)
TbC21
H
24
N
3
O
9
(6 )
24 3 9
YC21H N O (12)
0.35 £ 0.15 £ 0.1
293 (2)
0.3 £ 0.2 £ 0.1
293 (2)
0.50 £ 0.46 £ 0.46
289 (2)
Crystal system
Space group
Monoclinic,
Monoclinic,
Triclinic
P¯ı
Triclinic
P¯ı
1
P2 /n
1
P2 /n
˚
a (A)
˚
b (A)
˚
c (A)
9.8404 (2)
22.7519 (5)
9.8811 (2)
90
9.7278 (2)
22.7462 (4)
9.8147 (2)
90.00
9.09640 (10)
11.01170 (10)
12.7430 (2)
89.3725 (5)
72.0360 (6)
75.0730 (7)
1169.97 (2)
2
9.0680 (10)
10.9943 (8)
12.716 (2)
88.740 (8)
71.990 (10)
74.447 (9)
1158.9 (2)
2
a (8)
b (8)
g (8)
100.043 (3)
90
99.9410 (10)
90.00
3
˚
V (A )
2178.36 (8)
4
2139.10 (7)
4
Z
M
565.31
585.32
621.35
551.34
2
3
D
c
(g cm
2
)
1.724
1.817
1.764
1.580
1
m (mm
F (000)
)
2.009
3.355
3.078
2.573
1120
1152
616
564
˚
l (A) (Mo K
Monochromator
a
)
0.71073
Graphite
3.41–27.47
212–12; 229–29;
0.71073
Graphite
3.41–27.50
212–12; 229–29;
212–12
32765
0.71073
0.71073
Graphite
1.69–25.01
0–10; 2 12–13;
214–15
4318
Graphite
3.45–27.47
u range for data collection (8)
Index range h; k; l
211–11; 214–14;
216–16
24082
212–12
32158
Reflections collected
Independent reflections
Observed reflections [I . 2s(I)]
Number of parameters refined
R [I . 2s(I)]
4963 (Rint ¼ 7.01%)
4909 (Rint ¼ 7.12%)
2954
5250 (Rint ¼ 4.4%)
4813
4038 (Rint ¼ 1.92%)
3215
2952
351
292
350
392
0.0286
0.0516
1.004
0.0311
0.0311
0.0288
wR [I . 2s(I)]
Goodness-of-fit on F
0.0682
0.0763
0.0553
2
0.993
1.066
0.926
0
3
.2. Thermal analysis
air. Complex 6 lost only one of its two coordination water
molecules in the temperature range 189.6–205.5 8C (loss of
weight found: 2.91%; loss of weight calculated based on the
Complex 6 lost its coordinated water molecule in the
temperature range 182.7–207.9 8C (loss of weight found:
.92%; loss of weight calculated based on the loss of one
water molecule for TbL ·H O: 3.08%); the complex loses
loss of one water molecule for TbL ·2H O: 2.99%). The
3 2
2
complex quickly decomposed in the temperature range
0
430.4–439.4 8C, that is, complex 6 lost the second
3
2
weight rapidly from thermal decomposition in the tempera-
0
coordination water molecule during thermal decomposition.
These results are consistent with the bond length compari-
sons from the structural analysis discussed below. The
˚
Tb–O(7) (water) bond length (2.499 A) is the longest
among all Tb-O bonds in complex 6 [see Table 4b].
ture range 372.6–456.6 8C. Complex 6 rapidly lost its
crystal water molecule when exposed to air at room
0
temperature; therefore, the thermal analysis of 6 was
performed when no more weight change was observed in
Table 3
Crystal cell parameters of complexes
Sample no.
Space group
að Aꢀ Þ
bð Aꢀ Þ
cð Aꢀ Þ
að8Þ
bð8Þ
gð8Þ
pH
1
2
3
4
5
6
P2
P2
P2
P2
P2
P2
P¯ı
1
1
1
1
1
1
/n
/n
/n
/n
/n
/n
9.8404 (2)
9.8257 (2)
9.823 (1)
22.7519 (5)
22.7462 (4)
22.732 (3)
9.8811 (2)
90
100.043 (3)
100.0091 (8)
100.05 (1)
90
4.0
5.0
4.0
5.0
5.0
5.0
4.0
5.0
4.0
5.0
5.0
5.0
4.0
9.8498 (2)
9.826 (1)
90
90
90
90
9.7761 (5)
9.7609 (4)
9.7278 (2)
9.09640 (10)
9.72190 (10)
9.0637 (11)
9.7214 (2)
8.8173 (4)
9.0317 (5)
9.068 (1)
22.7388 (5)
22.7802 (5)
22.7462 (4)
11.01170 (10)
22.7544 (5)
10.9934 (11)
22.7475 (5)
10.5753 (5)
10.9519 (4)
10.994 (1)
9.8366 (4)
9.8376 (3)
9.8147 (2)
12.7430 (2)
9.8065 (2)
12.7192 (17)
9.7812 (2)
12.2574 (4)
12.7067 (5)
12.716 (2)
90
99.9697 (5)
99.905 (2)
90
90
90
90
99.9410 (10)
72.0360 (6)
99.9360 (10)
72.0048 (104)
99.9280 (10)
71.627 (3)
90
0
6
89.3725 (5)
90
75.0730 (7)
90
7
8
9
P2
P¯ı
1
/n
/n
88.8481 (99)
90
74.5697 (93)
90
P2
P¯ı
1
1
1
1
0
1
2
89.840 (3)
88.3277 (4)
88.740 (8)
73.913 (2)
74.2445 (4)
74.447 (9)
P¯ı
71.9684 (6)
71.99 (1)
P¯ı

80
H.-L. Sun et al. / Journal of Molecular Structure 702 (2004) 77–83
Table 4a
˚
Selected bond lengths (A) and angles (8) for complex 1
Table 4c
˚
Selected bond lengths (A) and angles (8) for complex 6
0
˚
Bond lengths (A)
˚
Bond lengths (A)
La(1)–O(4)#1
La(1)–O(5)
La(1)–O(1)
La(1)–O(7)
La(1)–O(6)
2.451 (2) La(1)–O(3)
2.486 (2) La(1)–O(6)#2
2.550 (2) La(1)–O(2)
2.638 (2) La(1)–N(2)#3
2.982 (2)
2.467 (2)
2.488 (2)
2.580 (2)
2.777 (3)
Tb(1)–O(3)
Tb(1)–O(8)
Tb(1)–O(7)
Tb(1)–O(5)
2.277 (2)
2.351 (2)
2.419 (2)
2.504 (2)
Tb(1)–O(4)#1
Tb(1)–O(6)
Tb(1)–O(2)
Tb(1)–O(1)
2.264 (3)
2.367 (2)
2.422 (3)
2.514 (2)
Bond angles (8)
O(4)#1–Tb(1)–O(3) 109.25 (12) O(4)#1–Tb(1)–O(8)
Bond angles (8)
86.80 (12)
83.84 (11)
74.55 (9)
O(4)#1–La(1)–O(3)
O(3)–La(1)–O(5)
O(3)–La(1)–O(6)#2
O(4)#1–La(1)–O(1)
O(5)–La(1)–O(1)
O(4)#1–La(1)–O(2)
O(5)–La(1)–O(2)
O(1)–La(1)–O(2)
O(3)–La(1)–O(7)
O(6)#2–La(1)–O(7)
O(2)–La(1)–O(7)
O(3)–La(1)–N(2)#3
91.04 (7) O(4)#1–La(1)–O(5)
85.46 (8)
O(3)–Tb(1)–O(8)
O(3)–Tb(1)–O(6)
O(4)#1–Tb(1)–O(7)
O(8)–Tb(1)–O(7)
156.27 (11) O(4)#1–Tb(1)–O(6)
123.23 (10) O(8)–Tb(1)–O(6)
73.32 (10) O(3)–Tb(1)–O(7)
136.32 (8) O(4)#1–La(1)–O(6)#2 146.12 (7)
95.62 (7) O(5)–La(1)–O(6)#2
72.55 (7) O(3)–La(1)–O(1)
96.36 (8) O(6)#2–La(1)–O(1)
71.72 (7) O(3)–La(1)–O(2)
144.19 (8) O(6)#2–La(1)–O(2)
51.08 (6) O(4)#1–La(1)–O(7)
72.41 (7) O(5)–La(1)–O(7)
140.56 (7) O(1)–La(1)–O(7)
111.06 (7)
123.98 (7)
76.24 (7)
72.91 (7)
78.60 (7)
72.95 (7)
64.94 (8)
141.79 (7)
80.86 (10)
151.74 (10)
77.24 (11)
79.83 (9)
87.53 (9)
O(6)–Tb(1)–O(7)
O(4)#1–Tb(1)–O(2) 163.26 (11) O(3)–Tb(1)–O(2)
O(8)–Tb(1)–O(2)
O(7)–Tb(1)–O(2)
O(3)–Tb(1)–O(5)
O(6)–Tb(1)–O(5)
O(2)–Tb(1)–O(5)
O(3)–Tb(1)–O(1)
O(6)–Tb(1)–O(1)
O(2)–Tb(1)–O(1)
92.34 (11) O(6)–Tb(1)–O(2)
123.37 (8)
76.35 (9)
53.45 (8)
92.22 (9)
78.22 (9)
123.45 (8)
52.53 (8)
O(4)#1–Tb(1)–O(5)
O(8)–Tb(1)–O(5)
O(7)–Tb(1)–O(5)
74.95 (10)
125.90 (8)
131.69 (8)
O(4)#1–Tb(1)–O(1) 142.92 (10)
129.16 (6) O(4)#1–La(1)–N(2)#3 140.93 (8)
O(8)–Tb(1)–O(1)
O(7)–Tb(1)–O(1)
O(5)–Tb(1)–O(1)
78.54 (9)
72.20 (8)
140.38 (8)
79.61 (8) O(5)–La(1)–N(2)#3
76.32 (9)
142.86 (7)
68.05 (8)
O(6)#2–La(1)–N(2)#3 72.90 (8) O(1)–La(1)–N(2)#3
O(2)–La(1)–N(2)#3 137.85 (8) O(7)–La(1)–N(2)#3
Symmetry transformations used to generate equivalent atoms: #1 2
x þ 1; 2y þ 2; 2z þ 1:
Symmetry transformations used to generate equivalent atoms: #1
2
x þ 2; 2y; 2z; #2 2 x þ 1; 2y; 2z #3 2 x þ 2; 2y; 2z þ 1:
3
.3. Description of structures of complexes
0
In complex 6 [see Table 4c], the Tb–O(7) (water) bond
˚
length (2.419 A) is longer than the average value (2.391 A)
˚
Complex 1 is monoclinic and has space group P2 /n. As
1
3
þ
shown in Fig. 1, in this complex, each La ion is chelated
by two carboxyl groups, coordinated by three carboxylic
oxygen atoms from three ligands, one nitrogen atom
from another ligand and one water molecule. Therefore,
of Tb–O (COO) bond lengths, and Tb-O(8) (water) bond
˚
˚
length (2.351 A) is shorter than the average value (2.391 A).
Consequently, the temperature required for the loss of one
[
higher than that for the loss of the other [H O(7)]; and the
H O(8)] of the two coordinated water molecules is much
2
3
þ
2
each La
and one H O molecule. In complex 1, the ligand is
ion is nine-coordinated by six L ligands
2
loss of the second water molecule [H O(8)] is accompanied
2
2
by the loss of the L ligand from the compound.
2
3
coordinated to the La ion in three different coordination
þ
Table 4d
˚
Selected bond lengths (A) and angles (8) for complex 12
Table 4b
˚
Selected bond lengths (A) and angles (8) for complex 6
˚
Bond lengths (A)
˚
Bond lengths (A)
Y–O(1)
Y–O(7)
Y–O(8)
Y–O(3)
2.2347 (18)
2.310 (2)
Y–O(2)#1
Y–O(6)
Y–O(4)
Y–O(5)
2.236 (2)
Tb(1)–O(6)#1
Tb(1)–O(5)
2.287 (3)
2.319 (3)
2.327 (2)
2.335 (3)
Tb(1)–O(4)
Tb(1)–O(3)
Tb(1)–O(7)
Tb(1)–N(1)#3
2.446 (3)
2.452 (3)
2.499 (3)
2.688 (3)
2.3383 (18)
2.3928 (18)
2.4861 (18)
2.387 (2)
Tb(1)–O(1)
2.4822 (17)
Tb(1)–O(2)#2
Bond angles (8)
O(1)–Y–O(2)#1
O(2)–Y–O(7)#1
O(2)–Y–O(6)#1
O(1)–Y–O(8)
O(7)–Y–O(8)
O(1)–Y–O(4)
O(7)–Y–O(4)
O(8)–Y–O(4)
O(2)–Y–O(3)#1
O(6)–Y–O(3)
O(4)–Y–O(3)
O(2)–Y–O(5)#1
O(6)–Y–O(5)
O(4)–Y–O(5)
Bond angles (8)
108.23 (8)
85.42 (8)
83.00 (7)
78.95 (7)
87.62 (9)
79.22 (7)
93.26 (8)
123.79 (7)
142.74 (7)
123.46 (6)
53.26 (6)
75.58 (7)
53.78 (6)
91.30 (6)
O(1)–Y–O(7)
O(1)–Y–O(6)
O(7)–Y–O(6)
O(2)–Y–O(8)#1
O(6)–Y–O(8)
O(2)–Y–O(4)#1
O(6)–Y–O(4)
O(1)–Y–O(3)
O(7)–Y–O(3)
O(8)–Y–O(3)
O(1)–Y–O(5)
O(7)–Y–O(5)
O(8)–Y–O(5)
O(3)–Y–O(5)
157.00 (9)
124.05 (7)
74.91 (8)
73.86 (7)
152.06 (7)
162.27 (7)
79.60 (7)
79.84 (7)
78.29 (8)
72.19 (7)
75.67 (6)
126.60 (8)
131.21 (7)
140.22 (6)
O(6)#1–Tb(1)–O(5)
O(5)–Tb(1)–O(1)
O(5)–Tb(1)–O(2)#2
O(6)#1–Tb(1)–O(4)
O(1)–Tb(1)–O(4)
O(6)#1–Tb(1)–O(3)
O(1)–Tb(1)–O(3)
O(4)–Tb(1)–O(3)
O(5)–Tb(1)–O(7)
O(2)#2–Tb(1)–O(7)
O(3)–Tb(1)–O(7)
O(5)–Tb(1)–N(1)#3
103.29 (10) O(6)#1–Tb(1)–O(1)
92.77 (10)
143.97 (10) O(6)#1–Tb(1)–O(2)#2 148.42 (10)
89.09 (10) O(1)–Tb(1)–O(2)#2
77.07 (10) O(5)–Tb(1)–O(4)
127.78 (9) O(2)#2–Tb(1)–O(4)
79.65 (10) O(5)–Tb(1)–O(3)
74.41 (9) O(2)#2–Tb(1)–O(3)
53.42 (8) O(6)#1–Tb(1)–O(7)
71.10 (10) O(1)–Tb(1)–O(7)
73.33 (10) O(4)–Tb(1)–O(7)
93.78 (10)
87.57 (10)
74.53 (9)
139.71 (9)
72.49 (10)
138.09 (10)
75.39 (9)
141.35 (10)
132.06 (9) O(6)#1–Tb(1)–N(1)#3 69.29 (10)
74.71 (10) O(1)–Tb(1)–N(1)#3
81.44 (9)
136.57 (9)
69.24 (10)
O(2)#2–Tb(1)–N(1)#3 142.28 (10) O(4)–Tb(1)–N(1)#3
O(3)–Tb(1)–N(1)#3 139.38 (10) O(7)–Tb(1)–N(1)#3
Symmetry transformations used to generate equivalent atoms: #1 2 x þ 1;
y; 2z þ 1; #2 2 x þ 1; 2y; 2z; #3 2 x; 2y; 2z:
Symmetry transformations used to generate equivalent atoms: #1 2 x;
2y þ 1; 2z þ 1:
2

H.-L. Sun et al. / Journal of Molecular Structure 702 (2004) 77–83
81
Fig. 3. An ORTEP view of complex 6 showing the connection between
3þ
Fig. 1. An ORTEP view of complex 1 showing the connection between
Tb ions and ligands. Hydrogen atoms are omitted for clarity.
3
La ions and ligands. Hydrogen atoms are omitted for clarity.
þ
modes (mode 1, 2 and 3). In mode 1, the carboxyl group
with the bridging oxygen (m –O) connects two neighboring
linked together through hydrogen bonds forming a three-
dimensional structure.
2
3
þ
La ions in a tridentate-bridging mode. In mode 2, the
carboxyl group acts as a bidentate-bridge connecting two
As shown in Figs. 3 and 4, the structure of complex 6 is
similar to that of complex 1. There is also a two-dimensional
2
structure of complex 6 where the ligand L has
3
La ions that are coordinated by m –O, forming a one-
þ
2
dimensional chain. In other words, the carboxyl groups have
two types of bridging mode in the one-dimensional chain,
that is, either two tridentate-bridging carboxyl groups or two
bidentate-bridging carboxyl groups exist between the two
three different coordination modes (mode 1, 2 and 3),
and the links formed between the metal ions are similar
except for mode 1 between complexes 1 and 6. The two
2
tridentate-bridging carboxyl groups from the L ligands
(
by two bidentate-bridging carboxyl groups (mode 1)
3
mode 1) between two neighboring La ions are replaced
þ
3
þ
2
neighboring La ions. The amino group of the L ligand
that has a bidentate-bridging carboxyl group (mode 2) is
3
þ
3
þ
between two neighboring Tb ions, that is, there is no
bridging oxygen (m –O) in complex 6. As a result, each
coordinated to a La ion from the adjacent chain, forming a
two-dimensional plane (Fig. 2). In mode 3, the carboxyl
2
3
þ
2
Tb ion is eight-coordinated by six ligands (L ) and one
3
group chelates the La ion. The amino groups are not
þ
3
þ
H O molecule.
2
coordinated to any La ion in both mode 1 and 3. In
complex 1, the coordination water or carboxyl groups and
the uncoordinated amino groups from different layers are
0
Complex 6 is triclinic and has space group P ¯ı . It is a
binuclear complex that has two bidentate carboxyl groups
3
þ
3þ
bridging the two Tb ions (see Fig. 5). Each Tb ion is
also chelated by two carboxyl groups, and coordinated by
two H O molecules. The amino groups in the ligands are not
2
3
þ
3þ
connected to the Tb ions. Therefore, each Tb ion is
2
eight-coordinated by four ligands (L ) and two H O
2
molecules. Moreover, in the crystal structure of complex
0
6
, the coordination H O molecules in each binuclear
2
compound are linked to the amino groups or carboxyl
groups of adjacent binuclear molecules through hydrogen
bonds. Uncoordinated H O molecules in the crystal lattice
2
are linked to the amino groups or carboxyl groups of the
ligands through hydrogen bonds as well.
Based on the results of elemental analyses (see Table 1)
and crystal cell parameters (shown in Table 3) for complex
2
are isomorphous with 6, and complexes 8 and 10–12
–5, and 7–12, we have found that complexes 2–5, 7 and 9
0
are isomorphous with 6 . Details of data collection
and refinements are listed in Table 2. Selected bond lengths
0
and angles for complexes 1, 6, 6 and 12 are listed in
Table 4a–d.
Fig. 2. A two-dimensional structure of complex 1 showing the connection
between the chains. Hydrogen atoms are omitted for clarity.

82
H.-L. Sun et al. / Journal of Molecular Structure 702 (2004) 77–83
2
Fig. 4. A two-dimensional structure of complex 6 showing the connection between the chains. Hydrogen atoms and the L ligands in mode 3 are omitted
for clarity.
þ
3.4. Effect of lanthanide contraction and pH on the crystal
structure
than at low pH. This is because the concentration of H
ions, which can protonate amino groups and subsequently
affect their coordination ability with a metal ion, is lower in
a high pH solution than in a low pH solution. Furthermore,
sizes of the middle RE ions are suitable for formation of
In order to learn the effect of pH on structure, the solution
pH of the reaction mixture was carefully adjusted to ca. 4.0
or ca. 5.0, respectively, during the synthesis of the
complexes. However, single crystals suitable for X-ray
structure analysis were obtained only for complexes 1–12
2
2
complexes coordinated by either six L ligands or four L
ligands. Therefore, for the middle-RE ions, the complexes
0
and 6 . Corresponding solution pH values of the reaction
mixtures are listed in Table 3. These results indicate that
light-RE ions, which have relatively large ion radii, tend to
form two-dimensional (2D) array structures (monoclinic,
P2 /n) with a high metal ion coordination number (nine
1
coordination) (e.g. complex 1) or with a eight-coordinated
metal ion, such as complexes 2–5 and the NdL ·3H O [10]
complex, which is isostructural with complexs 2–5, each of
3
2
2
which has six L ligands surrounding a metal ion; in these
complexes, the N atoms of the amino groups are also able to
coordinate to the RE ions in existence of the carboxyl
groups and water molecules due to there is the adequate
space around the metal ions. The heavy-RE ions, which
have smaller ion radii, tend to form binuclear complexes
(
coordination), such as complexes 10 and 11, each of which
triclinic, P ¯ı ) with a lower metal coordination number (eight
2
has four L ligands surrounding a metal ion. A compound
identical to complex 10 has been reported in the literature
[
9]. The structures of the middle-RE ion complexes (e.g.
3
þ
3þ
3þ
3þ
Tb , and Dy , Ho ; Er may be included. The crystal
structure of complex DyL ·3H O obtained by Khiyalov et al.
3
2
[
11] is different from complex 7 but is identical to complex
0
0
6
.), they (6, 6 , 7, 8, 9) may be affected by the reaction pH.
0
Fig. 5. An ORTEP view of complex 6 showing the connection between
3þ
A possible explanation for this is that, coordination of the
amino group to the metal ion is more favorable at high pH
Tb ions and ligands. Hydrogen atoms and crystal water molecule are
omitted for clarity.

H.-L. Sun et al. / Journal of Molecular Structure 702 (2004) 77–83
83
obtained in the higher pH solutions (ca. 5.0) belong to two-
dimensional (2D) array structures in which the N atoms of
the amino groups can be coordinated to the metal ions, and
the complexes formed in the lower pH solutions (ca. 4.0)
possess binuclear structures in which the N atoms of the
amino groups are uncoordinated; however, for light-RE or
heavy-RE ions, the effect of solution pH on the crystal
structure of the complexes can be neglected in the range of
pH 4–5. The above observations indicate that various
free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html (or from the Cambridge Crystallographic
Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK;
fax: þ 44 1223 336033).
Acknowledgements
We acknowledge support from the National Science
Fund for Distinguished Young Scholars (20125104,
2
coordination modes of ligand L and the structural change
of the RE complexes are controlled by lanthanide contrac-
tion. As for the complexes of the middle-RE ions, the effect
of solution pH on the crystal structure should also be taken
into consideration.
2
0221101), National Key Project for Fundamental Research
(G1998061305).
According to the regularity, it may be suitable to divide
the RE elements into three groups according to the structure
of their corresponding RE-L complexes. La, the complex of
References
[
1] K.S. Mamedov, E.M. Movsumov, I.R. Amirasłanov, A.I. Shkurpieło,
Kristalochimia nieorganiczieskich i organiczieskich sojedinienij, AN
Moskowskoj SSR, Inst. Prikł. Fiziki, Kishiniev, 111, 1982.
which has a 2D layered structure (monoclinic, P2 /n) where
1
3þ
the La ion is nine-coordinated, belongs to group 1. Ce and
Pr, the complexes of which have 2D structures (monoclinic,
[2] I.R. Amirasłanov, F.N. Musaev, Kh.S. Mamedov, Zh. Strukt. Khim.
23 (1982) 118.
3
þ
P2 /n) where the RE
1
(RE ¼ Ce, Pr) ion is eight-
[
[
[
[
[
[
3] I.R. Amirasłanov, Kh.S. Mamedov, E.M. Movsumov, G.N. Nadzha-
fov, A.A. Mursaliev, Dokł. Akad. Nauk Az. SSR 35 (1979) 23.
4] I.R. Amirasłanov, Kh.S. Mamedov, E.M. Movsumov, F.I. Musaev,
A.I. Magerramov, G.N. Nadzhafov, Zh. Strukt. Khim. 20 (1979) 498.
5] I.R. Amirasłanov, Kh.S. Mamedov, E.M. Movsumov, F.I. Musaev,
A.N. Shnulin, G.N. Nadzhafov, Zh. Strukt. Khim. 19 (1978) 1129.
6] I.R. Amirasłanov, F.N. Musaev, Kh.S. Mamedov, Zh. Strukt. Khim.
coordinated, are in group 2. Nd–Eu may also belong to
group 2. Yb and Lu, the complexes of which have different
structural types (triclinic, P ¯ı ) where the coordination
3
þ
number of the RE ion (RE ¼ Yb, Lu) is eight, form
group 3. Tb–Er can be assigned to either group 2 or group 3,
because they have medium ion radii and consequently, their
complexes could have different structural types depending
on the reaction pH (4.0 or 5.0). Based on the results shown
in Table 3, the Y–L complex (complex 12) may have
2
3 (1982) 114.
7] I.R. Amirasłanov, Kh.S. Mamedov, E.M. Movsumov, F.I. Musaev,
G.N. Nadzhafov, Zh. Strukt. Khim. 20 (1979) 1075.
8] W. Brzyska, Z. Rzaczy n´ ska, Powder Diffr. File JCPDS. 41 1743, 1991
3
þ
˚
similar properties since the radius of the Y ion (1.019 A)
3
is close to that of the Ho ion (1.015 A).
[9] Z. Rzaczy n´ ska, V.K. belsky, Polish J. Chem. 68 (1994) 309.
[10] M.S. Khiyalov, I.R. Amirasłanov, Kh.S. Mamedov, E.M. Movsumov,
Zh. Strukt. Khim. 22 (3) (1981) 113.
þ
˚
[
11] M.S. Khiyalov, I.R. Amirasłanov, Kh.S. Mamedov, E.M. Movsumov,
Koord. Khim. 7 (3) (1981) 445.
4
. Conclusion
[
[
12] X.J. Zheng, L.P. Jin, Polyhedron 22 (18) (2003) 2617.
13] S.A. Cotton, V. Franckevicius, R.E. How, B. Ahrens, L.L. Ooi, M.F.
Mahon, P.R. Raithby, S.J. Teat, Polyhedron 22 (11) (2003) 1489.
14] Y.Z. Bian, D.Q. Wang, R.M. Wang, L.H. Weng, J.M. Dou, D.Y.
Zhao, D.K.P. Ng, J.Z. Jiang, New J. Chem. 27 (5) (2003) 844.
15] F. Benetollo, G. Bombieri, L. Calabi, S. Aime, M. Botta, Inorg. Chem.
A series of RE complexes with p-aminobenzoic acid
[
[
have been synthesized. The structural variation of these RE
complexes is controlled by lanthanide contraction. It may be
suitable to divide the RE elements into three groups
according to the structure of their corresponding RE-L
complexes. For complexes of middle-RE ions, effect of
solution pH on their structure should also be taken into
consideration.
4
2 (1) (2003) 148.
[16] Y.H. Wan, L.P. Jin, K.Z. Wang, L.P. Zhang, X.J. Zheng, S.Z. Lu, New
J. Chem. 26 (11) (2002) 1590.
[
[
[
17] Q.D. Liu, S. Gao, J.R. Li,, B.Q. Ma, Q.Z. Zhou, K.B. Yu, Polyhedren
1 (2002) 1097.
2
18] L. Pan, X.Y. Huang, J. Li, Y.G. Wu, N.W. Zheng, Angew. Chem. Int.
Ed. Commun. 39 (3) (2000) 527.
CCDC-228747, 228748, 230046, 230047, 230048,
30049, 230050 contains the supplementary crystallo-
2
graphic data for this paper. These data can be obtained
19] K. Nakamoto, Infrared Spectra of Inorganic and Coordination
Compound, fourth ed., Wiley, New York, 1986, p. 258.