Synthesis, crystal structure and properties of three new holmium 2-fluorobenzoato complexes

Article abstract of DOI:10.1016/j.molstruc.2005.05.005

This paper reports three new holmium 2-fluorobenzoato (2-FBA) complexes with 1,10-phenanthroline (phen), 2,2′-bipydine (2,2′-bpy) and 4,4′-bipyridine, respectively. A rare and interesting structural feature of holmium 2-FBA complex containing phen is two non-equivalent binuclear molecules existed in an asymmetric unit, namely, [Ho(2-FBA)₃· phen·CH₃CH₂OH]₂ and [Ho(2-FBA) ₃·phen]₂. The dimeric complex [Ho(2-FBA) ₃·2,2′-bpy]₂ is a type of eight-coordinated lanthanide carboxylate complexes containing 2,2′-bpy. The {[Ho(2-FBA) ₃·2H₂O]·(4,4′-bpy)}_n is in one-dimensional polymeric structure, and the 3D supramolecular network structure is formed by the hydrogen bonds and π-π stacking interactions.

Full text of DOI:10.1016/j.molstruc.2005.05.005

Journal of Molecular Structure 751 (2005) 33–40
www.elsevier.com/locate/molstruc
Synthesis, crystal structure and properties of three new holmium
2-fluorobenzoato complexes
a,
a
Xia Li , Zhuo-Yong Zhang , Hai-Bin Song
b
*
aDepartment of Chemistry, Capital Normal University, Beijing 100037, People’s Republic of China
bState Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, People’s Republic of China
Received 18 April 2005; revised 5 May 2005; accepted 5 May 2005
Available online 15 June 2005
Abstract
This paper reports three new holmium 2-fluorobenzoato (2-FBA) complexes with 1,10-phenanthroline (phen), 2,20-bipydine (2,20-bpy)
and 4,40-bipyridine, respectively. A rare and interesting structural feature of holmium 2-FBA complex containing phen is two non-equivalent
binuclear molecules existed in an asymmetric unit, namely, [Ho(2-FBA)3$phen$CH3CH2OH]2 and [Ho(2-FBA)3$phen]2. The dimeric
complex [Ho(2-FBA)3$2,20-bpy]2 is a type of eight-coordinated lanthanide carboxylate complexes containing 2,20-bpy. The {[Ho(2-
FBA)3$2H2O]$(4,40-bpy)}n is in one-dimensional polymeric structure, and the 3D supramolecular network structure is formed by the
hydrogen bonds and p–p stacking interactions.
q 2005 Elsevier B.V. All rights reserved.
Keywords: Holmium complex; Structural study; 2-Fluorobenzoato; 1,10-Phenanthroline; 2,20-Bipydine; 4,40-Bipyridine
1. Introduction
2. Experimental
Lanthanide carboxylate complexes have variety of
crystal structures because of high coordination number
of the lanthanide ions and the various coordination modes
of carboxylate groups. This kind of complexes has
potential applications in calatysts, magnetic materials
and luminescent probes and many others. Dimeric and
polymeric forms are most frequently observed for these
compounds [1–10]. We have reported some mixed-ligands
lanthanide carboxylate complexes with aromatic diamines
such as 1,10-phenanthroline, 2,20-bipydine, and 4,40-
bipyridine [3,4,10]. In the present work, 2-fluorobenzoic
acid (2-HFBA), phen, 2,20-bpy, and 4,40-bpy, respectively,
were used as ligands to holmium ion and three new
complexes with different crystal structure, [Ho(2-
FBA)3$phen$CH3CH2OH]2 and [Ho(2-FBA)3$phen]2,
[Ho(2-FBA)3$2,20-bpy]2, and {[Ho(2-FBA)3$2H2O]$(4,40-
bpy)}n were obtained.
2.1. Materials and methods
HoCl3$6H2O was prepared by dissolving its oxide in
hydrochloric acid, and then drying the solution. Elemental
analysis was performed on an Elementar Vario EL analyzer.
The IR spectra were recorded with a Bruker EQUINOX-55
using the KBr pellet technique. Thermogravimetric analysis
was performed on a WCT-1A Thermal Analyzer at a
heating rate 10 8C/min in air. The UV–VIS spectra were
measured on a TU-1810 spectrophotometer in DMF.
2.2. Synthesis of complexes
About 1.5 mmol of 2-fluorobenzoic acid were dissolved
in appropriate amounts of ethanol. The pH of the solution
was controlled in a range of 5–6 with 2 mol dmK3 NaOH
solution. Then the ethanolic solutions of 1,10-phenanthro-
line (0.5 mmol) and HoCl3 (0.5 mmol) were dropped,
successively. The mixture was heated under reflux with
stirring for 2 h. Single crystal complex (1) was obtained
from the mother liquor after a week at room temperature.
Anal. calcd (%): C, 52.32; N, 3.78; H, 3.05. Found (%): C,
*
Corresponding author. Fax: C86 10 6890 2424.
E-mail address: gusto2008@vip.sina.com (X. Li).
0022-2860/$ - see front matter q 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2005.05.005

34
X. Li et al. / Journal of Molecular Structure 751 (2005) 33–40
Table 1
Crystal data and structure refinement for complexes (1), (2), and (3)
Empirical formula
Formula weight
Temperature (K)
C68H46F6Ho2N4O13
1570.95
C31H20F3HoN2O6
738.42
C31H24F3HoN2O8
774.45
293(2)
293(2)
293(2)
˚
Wavelength (A)
0.71073
0.71073
0.71073
Crystal system
Space group
Triclinic
P¯ı
Monoclinic
P2(1)/n
Monoclinic
P2(1)/c
Unit cell dimensions
˚
a (A)
˚
b (A)
11.241(4)
12.137(3)
17.709(5)
13.676(4)
90
9.762(3)
12.595(5)
26.132(8)
13.058(4)
90
˚
c (A)
22.717(8)
a (8)
b (8)
g (8)
81.226(6)
78.252(5)
111.411(4)
90
111.299(5)
90
80.620(6)
3
˚
V (A )
3083.3(19)
2
2736.7(13)
4
3103.7(16)
4
Z
Dc (mg/m3)
1.692
1.792
1.657
Absorption coefficient (mmK1
)
2.635
2.961
2.619
F(000)
1548
1448
1528
Crystal size (mm)
0.18!0.16!0.14
0.92–26.38
K14%h%11
K15%k%13
K28%l%28
17719/12406
[R(int)Z0.0263]
12406/0/859
1.128
0.20!0.20!0.18
1.97–25.01
K14%h%14
K19%k%21
K16%l%9
14135/4828
[R(int)Z0.0301]
4828/3/397
1.091
0.36!0.16!0.14
1.85–25.01
K11%h%10
K30%k%31
K15%l%12
16100/5471
[R(int)Z0.0338]
5471/288/448
1.056
Theta range for data collection (8)
Limiting indices
Reflections collected/unique
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [IO2s(I)]
R1Z0.0405
wR2Z0.0887
R1Z0.0653
wR2Z0.1005
1.276 and K0.943
R1Z0.0237
wR2Z0.0523
R1Z0.0397
wR2Z0.0587
0.871 and K0.527
R1Z0.0380
wR2Z0.0874
R1Z0.0613
wR2Z0.0981
0.672 and K0.655
R indices (all data)
K3
˚
Largest diff. peak and hole (e A
)
51.99; N, 3.56; H, 2.95. IR (KBr, cmK1): 3433(w), 1612(vs),
1462(s), 1409(vs), 845(m), 730(m), 453(w).
refinements are listed in Table 1 and the selected bond
distances and angles in Tables 2–4.
Synthesis of single crystal complex (2) is similar to that
of complex (1), whereas 2,20-bipydine was used instead of
1,10-phenanthroline. Anal. calcd (%): C, 50.20; N, 3.54; H,
2.68. Found (%): C, 50.44; N, 3.79; H, 2.73. IR (KBr, cmK1):
1612(vs), 1452(s), 1414(vs), 1015(m), 799(m), 454(w).
When 4,40-bipyridine was used instead of 1,10-phenan-
throline, complex (3) were obtained. Anal. calcd (%): C,
48.39; N, 3.65; H, 3.50. Found (%): C, 48.08; N, 3.62; H,
3.12. IR (KBr, cmK1): 3437(w), 1612(vs), 1462(s),
1411(vs), 460(w).
The crystallographic data have been deposited at
Cambridge Crystallographic Data Center, CCDC-268456,
268457, and 268458 for complexes (1), (2), and (3),
respectively, as the supplementary crystallographic data
for this paper. These data can be obtained free of charge
from CCDC, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: C44 1223 336033; email: deposit@ccdc.cam.ac.uk.
3. Results and discussion
2.3. Single-crystal X-ray diffraction
3.1. UV–VIS spectra
X-ray diffraction data of the single crystal were
collected by using a Bruker Smart 1000 CCD diffract-
ometer with monochromated Mo Ka radiation (lZ
UV–VIS absorption spectra of the three complexes were
measured in DMF solution with 1.0!10K4 and 1.0!10K3
mol/L, respectively. Results show that UV–VIS spectral
peak shapes and peak positions of the three complexes are
very similar. The broad absorption band at 294 nm
corresponds to the transition of the p–p* of the phen and
2-FBA group. The Hypersensitive transition of Ho3C ion
was observed at 450 nm, corresponding to the transition
5I6/5G6 of Ho3C ion.
˚
0.71073 A) at 293 K. Semi-empirical absorption correc-
tions were applied using the SADABS program. All
calculations were carried out on a computer with use of
SHELXS-97 and SHELXL-97 programs [11,12]. The structures
2
were solved by direct methods and refinement on jFj used
the full-matrix least-squares methods. A summary of
the crystallographic data and details of the structure

X. Li et al. / Journal of Molecular Structure 751 (2005) 33–40
35
Table 2
˚
Bond lengths (A) and angles (8) for complex (1)
Ho(1)–O(1)
2.277(4)
2.329(4)
2.346(4)
2.519(5)
2.275(4)
2.343(4)
2.408(4)
2.739(4)
2.631(5)
Ho(1)–O(3)
Ho(1)–O(4)#1
Ho(1)–O(7)
Ho(1)–N(1)
Ho(2)–O(8)
Ho(2)–O(12)
Ho(2)–O(13)
Ho(2)–N(3)
2.320(4)
2.343(4)
2.418(4)
2.575(5)
2.310(4)
2.392(4)
2.480(5)
2.530(6)
Ho(1)–O(2)#1
Ho(1)–O(5)
Ho(1)–N(2)
Ho(2)–O(10)#2
Ho(2)–O(9)#2
Ho(2)–O(11)
Ho(2)–O(10)
Ho(2)–N(4)
O(1)–Ho(1)–O(3)
74.85(15)
79.86(15)
122.70(14)
83.59(15)
144.91(14)
143.48(15)
72.59(14)
73.19(14)
77.96(16)
134.49(14)
75.87(14)
123.61(15)
80.31(16)
155.12(17)
89.39(15)
70.07(16)
65.84(13)
115.62(14)
118.50(15)
O(1)–Ho(1)–O(2)#1
O(1)–Ho(1)–O(4)#1
O(2)#1–Ho(1)–O(4)#1
O(3)–Ho(1)–O(5)
121.22(14)
78.05(14)
72.77(14)
84.14(15)
140.96(14)
75.07(15)
136.67(14)
64.14(16)
74.30(15)
143.49(14)
141.63(14)
86.04(16)
79.44(15)
126.01(16)
53.04(15)
74.91(15)
72.47(14)
49.44(14)
63.1(2)
O(3)–Ho(1)–O(2)#1
O(3)–Ho(1)–O(4)#1
O(1)–Ho(1)–O(5)
O(2)#1–Ho(1)–O(5)
O(1)–Ho(1)–O(7)
O(4)#1–Ho(1)–O(5)
O(3)–Ho(1)–O(7)
O(2)#1–Ho(1)–O(7)
O(5)–Ho(1)–O(7)
O(4)#1–Ho(1)–O(7)
N(2)–Ho(1)–N(1)
O(10)#2–Ho(2)–O(8)
O(8)–Ho(2)–O(9)#2
O(8)–Ho(2)–O(12)
O(10)#2–Ho(2)–O(11)
O(9)#2–Ho(2)–O(11)
O(10)#2–Ho(2)–O(13)
O(9)#2–Ho(2)–O(13)
O(11)–Ho(2)–O(13)
O(8)–Ho(2)–O(10)
O(12)–Ho(2)–O(10)
O(13)–Ho(2)–O(10)
O(10)#2–Ho(2)–O(9)#2
O(10)#2–Ho(2)–O(12)
O(9)#2–Ho(2)–O(12)
O(8)–Ho(2)–O(11)
O(12)–Ho(2)–O(11)
O(8)–Ho(2)–O(13)
O(12)–Ho(2)–O(13)
O(10)#2–Ho(2)–O(10)
O(9)#2–Ho(2)–O(10)
O(11)–Ho(2)–O(10)
N(3)–Ho(2)–N(4)
Symmetry transformations used to generate equivalent atoms: #1 KxC1, KyC1, KzC2; #2 Kx, KyC1, KzC1.
3.2. Thermal analysis
completely decomposed into Ho2O3 (calcd 75.95%). The
DTA-TG diagram of the complex (2) shows that the
complex begins to decompose at 222 8C and ends at
484.0 8C. The first, a mass loss of 21.91% corresponds to
the loss of 2,20-bpy molecule (calcd 21.14%). This is
understandable because the Ho–N(2,20-bpy) bond length is
The thermal behavior of complexes was studied in the
temperature ranged from 25 to 1000 8C. The DTA-TG
diagram shows that the thermal decomposition of the
complex (1) occurs in the range of 146.0–454.0 8C. The
total mass loss is 70.24%, which indicate the complex is
Table 4
˚
Bond lengths (A) and angles (8) for complex (3)
Table 3
˚
Bond lengths (A) and angles (8) for complex (2)
Ho(1)–O(3)
Ho(1)–O(1)
Ho(1)–O(7)
Ho(1)–O(6)
2.251(4) Ho(1)–O(2)#1
2.321(4) Ho(1)–O(4)#2
2.363(4) Ho(1)–O(8)
2.452(4) Ho(1)–O(5)
2.258(4)
2.340(4)
2.395(4)
2.468(4)
Ho(1)–O(1)
Ho(1)–O(2)#1
Ho(1)–O(6)
Ho(1)–N(1)
2.264(3)
2.324(3)
2.359(3)
2.534(3)
Ho(1)–O(3)
Ho(1)–O(4)#1
Ho(1)–O(5)
Ho(1)–N(2)
2.321(3)
2.327(3)
2.452(3)
2.568(3)
O(3)–Ho(1)–O(2)#1
O(2)#1–Ho(1)–O(1)
O(2)#1–Ho(1)–O(4)#2
O(3)–Ho(1)–O(7)
O(1)–Ho(1)–O(7)
O(3)–Ho(1)–O(8)
O(1)–Ho(1)–O(8)
O(7)–Ho(1)–O(8)
O(2)#1–Ho(1)–O(6)
O(4)#2–Ho(1)–O(6)
O(8)–Ho(1)–O(6)
O(2)#1–Ho(1)–O(5)
O(4)#2–Ho(1)–O(5)
O(8)–Ho(1)–O(5)
157.81(15) O(3)–Ho(1)–O(1)
96.22(15) O(3)–Ho(1)–O(4)#2
88.33(15) O(1)–Ho(1)–O(4)#2
83.74(14) O(2)#1–Ho(1)–O(7)
72.92(14) O(4)#2–Ho(1)–O(7)
79.50(16) O(2)#1–Ho(1)–O(8)
141.63(14) O(4)#2–Ho(1)–O(8)
69.61(14) O(3)–Ho(1)–O(6)
73.35(15) O(1)–Ho(1)–O(6)
73.26(14) O(7)–Ho(1)–O(6)
139.20(16) O(3)–Ho(1)–O(5)
126.17(14) O(1)–Ho(1)–O(5)
72.80(15) O(7)–Ho(1)–O(5)
133.23(14) O(6)–Ho(1)–O(5)
88.64(15)
99.95(15)
145.31(14)
77.09(14)
141.08(15)
83.37(15)
73.02(15)
128.71(15)
75.21(15)
133.26(13)
76.02(15)
76.92(14)
143.86(16)
53.11(14)
O(1)–Ho(1)–O(3)
77.82(10)
O(1)–Ho(1)–O(2)#1
O(1)–Ho(1)–O(4)#1
126.27(10)
79.87(10)
O(3)–Ho(1)–O(2)#1 80.22(10)
O(3)–Ho(1)–O(4)#1 128.45(10)
O(2)#1–Ho(1)–O(4)#1 76.74(9)
O(1)–Ho(1)–O(6)
O(2)#1–Ho(1)–O(6) 135.47(10)
O(1)–Ho(1)–O(5) 134.81(9)
O(2)#1–Ho(1)–O(5) 82.64(9)
86.78(10)
O(3)–Ho(1)–O(6)
O(4)#1–Ho(1)–O(6)
O(3)–Ho(1)–O(5)
O(4)#1–Ho(1)–O(5)
O(1)–Ho(1)–N(1)
O(2)#1–Ho(1)–N(1)
O(6)–Ho(1)–N(1)
O(1)–Ho(1)–N(2)
O(2)#1–Ho(1)–N(2)
O(6)–Ho(1)–N(2)
N(1)–Ho(1)–N(2)
79.13(11)
144.74(10)
74.01(10)
144.99(9)
142.35(10)
77.74(10)
93.20(11)
80.69(10)
134.02(10)
73.23(11)
63.47(11)
O(6)–Ho(1)–O(5)
O(3)–Ho(1)–N(1)
53.84(9)
139.13(10)
O(4)#1–Ho(1)–N(1) 78.71(10)
O(5)–Ho(1)–N(1)
O(3)–Ho(1)–N(2)
69.37(10)
145.70(11)
O(4)#1–Ho(1)–N(2) 72.47(10)
O(5)–Ho(1)–N(2) 104.19(10)
Symmetry transformations used to generate equivalent atoms: #1 KxC1,
Ky, Kz; #2 Kx, Ky, Kz.
Symmetry transformations used to generate equivalent atoms: #1 KxC1,
Ky, KzC1.

36
X. Li et al. / Journal of Molecular Structure 751 (2005) 33–40
the longest, and easy to be broken down. The mass of
the final product, 27.71%, indicates the remaining Ho2O3
(calcd 25.59%). Thermal decomposition of the complex (3)
occurs at 80.0–454.0 8C. The first weight loss of 26.06% in
the temperature ranged from 80.0 to 225.0 8C corresponds to
the 4,40-bpyC2H2O, calcd 24.80%. This decomposition
process can be explained by the bond length comparisons
obtained from the structural analysis. The 4,40-bpy
uncoordinated to metal exists in crystal only by hydrogen
bond, and the Ho–O (water) bond length is the longer than
(a)
(b)
Fig. 1. Molecular structures of the complex (1). (a) [Ho(2-FBA)3$phen$CH3CH2OH]2, (b) [Ho(2-FBA)3$phen]2.

X. Li et al. / Journal of Molecular Structure 751 (2005) 33–40
37
average distance Ho–O (carboxyl), which indicate 4,40-bpy
(a)
and H2O easy to be removed. A total mass loss is 73.83%,
which indicates the complex is completely changed into
Ho2O3 (calcd 75.60%).
3.3. Structural description of complex (1)
The crystal structure of the complex (1) is shown in
Fig. 1. Interestingly, the two kinds of binuclear molecules,
[Ho(2-FBA)3$phen$CH3CH2OH]2 and [Ho(2-FBA)3$
phen]2, exist in an asymmetric unit. Both binuclear
molecules are centrosymmetric, but their molecular formula
and structures are different. The complex (1) has two
molecules with different composition, unlike previously
reported complex Dy2(p-CH3C6H4COO)phen2 [3], in which
two different kinds of molecules exist owing to different
coordination mode of carboxyl groups. The complex
containing different molecules is very rare.
(b)
In binuclear molecule [Ho(2-FBA)3$phen$CH3CH2
OH]2, Ho13C ion is coordinated to eight atoms, five O
atoms from five 2-FBA groups, two N atoms from the phen
molecule and one O atom from ethanol molecule (Fig. 1a).
A coordinated polyhedron around Ho13C ion is a distorted
square-antiprism; atoms O1, O3, O2A, O4A and O5, O7,
N1, N2, O4A form upper and lower square planes,
respectively, with a dihedral angle between them of 2.78
(Fig. 2a). 2-FBA groups linked to Ho13C ion are in
monodentate and bridging coordination modes. O5–C15–
O6 group is in a monodentate mode, in which an oxygen
atom (O5) coordinates Ho3C ion. O1–C1–O2 group is in
bidentate bridging mode, in which two oxygen atoms
coordinate Ho3C ion to form a bidentate bridge. The phen
ligand coordinates to Ho3C ion in chelating mode, in which
two N atoms coordinate Ho3C ion forming a five-membered
ring. The bond distances of Ho1–Ocarboxyl (on average),
Ho1–Oethanol and Ho1–N (on average) are 2.323, 2.418 and
2.547 A, respectively. The distance of Ho13C/Ho1A3C is
Fig. 2. The coordination polyhedron of the Ho3C ion in the complex (1), (a)
and (b) show two different coordination environments.
˚
˚
4.416 A. Bond angles of O–Ho1–O range from 72.77(14) to
144.91(14)8, and that of N–Ho1–N is 64.14(16)8. The
hydrogen bond exists between the ethanol and uncoordi-
nated carboxyl oxygen atom, O7–H7/O6, in which the
O7–H7 distance is 0.930 A, H7/O6, 1.807 A and
:O7H7O6Z137.148.
a bidentate bridge. O10–C43–O11 group is in bridging-
chelating mode, in which two O atoms chelate one holmium
ion and one of them also simultaneously links another
holmium ion to form a tridentate bridge. This kind of crystal
structure is common in lanthanide carboxylate complexes.
Obviously, the two molecules of the complex (1) are
different in composition, coordination mode of carboxylate
groups, and coordination number of central ion. The average
˚
˚
In [Ho(2-FBA)3$phen]2, Ho23C ion is coordinated to
nine atoms, seven oxygen atoms from five 2-FBA groups
and two N atoms from the phen molecule (Fig. 1b). A
distorted monocapped square-antiprism is found. Atoms O8,
O11, O9A, O10A and O12, O13, N3, N4 form upper and
lower square planes, respectively, with a dihedral angle
between them of 7.38. O10 atom occupies the cap position
(Fig. 2b). 2-FBA ligands coordinate the Ho23C ion in three
different coordination modes. Carboxyl group O12–C50–
O13 adopts bidentate chelating mode, in which two oxygen
atoms coordinate the same Ho3C ion. The O8–C36–O9
group acts in a bidentate bridging fashion, in which two
oxygen atoms coordinate two different holmium ions to form
˚
distance of Ho2–O(carboxyl) is 2.421 A and that of Ho2/
Ho2A is 3.990 A. The phen ligand chelates Ho23C ion with
˚
˚
Ho2–N bond lengths of 2.530(6) and 2.631(5) A, respect-
ively. The bond angles of O–Ho2–O range from 49.44(14) to
155.12(17)8, and that of N–Ho2–N is 63.18.
The relationships of d(Ho2–O(carboxyl))Od(Ho1–
O(carboxyl)) and d(Ho2/Ho2A)!d(Ho1/Ho1A) in the
two molecules of complex (1) were observed. This is due to
carboxyl groups adopt different coordination modes linking

38
X. Li et al. / Journal of Molecular Structure 751 (2005) 33–40
Fig. 3. Molecular structure of the complex (2).
two Ho3C ions in the two molecules. The fact that Ln3C
ions are bridged by chelating–bridging carboxylate groups
results in a larger Ln–O distance and a smaller Ln–Ln
distance.
3.5. Structural description of complex (3)
A fragment of the structure of the complex {[Ho(2-
FBA)3$2H2O]$(4,40-bpy)}n (3) is shown in Fig. 4a, where it
can be seen that each Ho3C ion is bonded to eight atoms,
two oxygen atoms from the chelating carboxylate group,
two oxygen atoms from two water molecules, and four
oxygen atoms from bidentate bridging carboxyl groups. The
crystal structure [Ho(2-FBA)3$2H2O]$(4,40-bpy) is built as
coordination polymer that is typical for many lanthanide
carboxylate complexes such as {[Eu(m-MOBA)3$2H2O]$1/
2(4,40-bpy)}n (m-MOBA: m-methoxybenzoate) [7], {[Eu(p-
MOBA)3$2H2O]1/2 H2O$1/2 (4,40-bpy)}n (p-MOBA:
p-methoxybenzoate) [8], and {Eu(a-FURA)3$2H2-
O}]NO3(4,40-Hbpy)}n (a-FURA: a-furoate) [9]. These
complexes are an infinite polymeric structure by bridging
carboxyl groups, 4,40-bpy molecule is uncoordinated in the
polymer. Two neighbouring Ho3C ions are linked bidentate
bridging carboxyl groups to form a zigzag chain (Fig. 4a).
Ho3C ions are coplanar and the angle Ho1A–Ho1–Ho1B is
159.78. The distances between two neighbouring Ho3C ions
3.4. Structural description of complex (2)
The crystal structure of the complex (2) is shown in
Fig. 3. The complex is dimeric one with an inversion center.
The two Ho3C ions are linked together by four 2-FBA
ligands in bridging coordination mode. Each Ho3C ion
is eight-coordinated by six oxygen atoms of 2-FBA
ligands and two nitrogen atoms of a 2,20-bpy molecule.
The coordination sphere of Ho3C ion is in a square
antiprism with atoms O5, O6, N1, N2 and O1, O3, O2A,
O4A as the two square planes, respectively, with a dihedral
angle of 0.58 between them. Carboxyl groups act as
bidentate chelating and bidentate bridging coordination
modes. The 2,20-bpy ligand chelates Ho3C ion with two N
atoms forming a five-membered ring. The two pyridyl rings
are not coplanar with the dihedral angle of 6.68 in the
dimmer. The crystal structure of complex (2) is similar to
that of previously reported samarium (III) complex [4]. The
average distances of Ho–O (carboxyl), Ho–N, and Ho/Ho
˚
are 4.991 and 4.927 A, respectively. Viewed along a-axis
the p–p stacking interactions of aromatic rings and pyridine
ring are observed in the 1D chain (Fig. 4b). The complex (3)
is different from coordination polymer [La(2-FC6H4-
COO)3$(4,40-bpy)$H2O]n, in which 4,40-bpy coordinate
La3C ion in monodentate coordination mode, carboxyl
groups adopt bidentate bridging and chelating-bridging
coordination modes [10]. Coordination number of La3C ion,
nine, is larger than that of Ho3C ion in complex (3) because
the radius of La3C ion is larger than that of Ho3C ion as a
consequence of lanthanide contraction. The complex (3) is
also different from the eight-coordinated binuclear complex
˚
are 2.341, 2.551, and 4.133 A, respectively. These distances
are shorter than the corresponding distances in samarium
(III) complex [4] because the ionic radius of Sm3C ion is
longer than that of Ho3C ion. The bond angles O–Ho–O
vary considerably in the range of 53.84(9)–144.99(9)8. The
angle of N–Ho–N is 63.47(11)8. This is a common structure
of lanthanide carboxylate complexes containing phen or
2,20-bpy.

X. Li et al. / Journal of Molecular Structure 751 (2005) 33–40
39
(a)
(b)
(c)
Fig. 4. Polymeric structure of the complex (3). (a) A fragment of structure of the complex, (b) 1D chain viewed along the a-axis, and (c) 3D-network by p–p
stacking interaction and hydrogen bonding interaction viewed along the a-axis.
(2). In complex (2) 2,20-bpy molecule chelates the Ho3C ion
since 2,20-bpy is likely to form a chelated ring, however
4,40-bpy molecule is not involved in coordination for
complex (3). The Ho–O (carboxyl) bond lengths vary
˚
from 2.251(4) to 2.468(4) A with an average distance of
˚
2.348 A, which is in agreement with that in complex (1) due
to the same coordination modes of carboxyl groups in
the two complexes. There are two nitrogen atoms of
uncoordinated 4,40-bpy molecule at a distances of 4.541 and
3C
˚
6.418 A to the Ho
ion, respectively, and the dihedral
˚
angle between the two pyridyl rings is 7.7 A. The
neighbouring 1D chains are interlinked through 4,40-bpy
molecules by hydrogen bonds (Fig. 4c). The uncoordinated
4,40-bpy molecules form hydrogen bonds with coordinated

40
X. Li et al. / Journal of Molecular Structure 751 (2005) 33–40
water, O7–H7B/N1 [X, YK1, Z], with d(O7/N1)Z
References
˚
2.662 A and :O7H7BN1Z124.838, and O8–H8B/N1 [X,
˚
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KYC1/2, ZK1/2], with d(O8/N2)Z2.740 A and
:O8H8BN2Z135.288. The p–p stacking interactions
can be found, as shown in Fig. 4c. As a result, 3D
supramolecular structure is formed by the hydrogen bonds
and p–p stacking interactions (Fig. 4c). Furthermore, these
intermolecular interactions increase the stability of the
crystal packing.
[2] B. Barja, R. Baggio, M.T. Garland, P.F. Aramendia, O. Pena,
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(2000) 85.
Acknowledgements
[8] X. Li, L.P. Jin, Y.H. Wan, S.Z. Lu, J.H. Zhang, Chin. J. Chem. 20
(2002) 352.
We are grateful to the Natural Science Foundation of
Beijing (No. 2022007). This project is also sponsored by the
Science and Technology Program, Beijing Municipal
Education Commission (KM200510028007) and the Scien-
tific Research Foundation for Returned Overseas Chinese
Scholars, Beijing Municipal Government.
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[12] G.M. Sheldrick, SHELXL97, program for X-ray crystal structure
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