Preparation and spectroscopic characterization of two HoCl 3-galactitol complexes and one ErCl3-galactitol complex

Article abstract of DOI:10.1016/j.molstruc.2011.05.037

The interactions between metal ions and hydroxyl groups of carbohydrates are important for their possible biological activities. Here two HoCl ₃-galactitol complexes ([Ho(galac)(H₂O) ₃)]Cl₃·0.5galac) (HoG(I)) and ([Ho ₂(galac)(H₂O)₁₂)]Cl₆·2H ₂O) (HoG(II))) and one ErCl₃-galactitol complex ([Er(galac)(H₂O)₃)]Cl₃·0.5galac)(ErG)) were prepared and characterized. The possible structures of HoG(I) and ErG were deduced from FTIR, elemental analysis, ESI-MS, FIR, THz and TGA results. It is suggested that Ho³⁺ or Er³⁺ is 9-coordinated with six hydroxyl groups from two galactitol molecules and three water molecules, and another galactitol molecule is hydrogen-bonded in HoG(I) and ErG and the ratio of metal to ligand is 1:1.5. The structure of HoG(II) was determined by FTIR and X-ray diffraction analyses. The results demonstrate that lanthanide ions with galactitol may form two compounds in a system and different topological structures can be obtained.

Full text of DOI:10.1016/j.molstruc.2011.05.037

Journal of Molecular Structure 998 (2011) 225–232
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Preparation and spectroscopic characterization of two HoCl3–galactitol
complexes and one ErCl3–galactitol complex
a
c
Xiaohui Hua a, Qinghua Pan a, Lei Yu a, Junhui Xue a, Limin Yang b, , Yizhuang Xu , Guozhong Zhao ,
⇑
Weihong Li a, Zheming Wang a, Jinguang Wu a, Kexin Liu b, Jia’er Chen b
a The State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
b State Key Laboratory of Nuclear Physics and Technology, Institute of Heavy Ion Physics, School of Physics, Peking University, Beijing 100871, China
c Department of Physics, Capital Normal University, Beijing 100037, China
a r t i c l e i n f o
a b s t r a c t
Article history:
The interactions between metal ions and hydroxyl groups of carbohydrates are important for their pos-
sible biological activities. Here two HoCl3–galactitol complexes ([Ho(galac)(H2O)3)]Cl3Á0.5galac) (HoG(I))
and ([Ho2(galac)(H2O)12)]Cl6Á2H2O) (HoG(II))) and one ErCl3–galactitol complex ([Er(galac)(H2O)3)]
Cl3Á0.5galac)(ErG)) were prepared and characterized. The possible structures of HoG(I) and ErG were
deduced from FTIR, elemental analysis, ESI-MS, FIR, THz and TGA results. It is suggested that Ho3+ or
Er3+ is 9-coordinated with six hydroxyl groups from two galactitol molecules and three water molecules,
and another galactitol molecule is hydrogen-bonded in HoG(I) and ErG and the ratio of metal to ligand is
1:1.5. The structure of HoG(II) was determined by FTIR and X-ray diffraction analyses. The results dem-
onstrate that lanthanide ions with galactitol may form two compounds in a system and different topo-
logical structures can be obtained.
Received 8 March 2011
Received in revised form 20 May 2011
Accepted 20 May 2011
Available online 27 May 2011
Keywords:
Lanthanide ion
Holmium chloride
Complexation
Galactitol
Ó 2011 Elsevier B.V. All rights reserved.
FT-IR
1. Introduction
tions with sugar residues of biologically important compounds.
Here galactitol (C6H14O6, denoted as G or galac in formulas), one
The interactions between metal ions and carbohydrates are
involved in many biochemical processes, such as the transport of
metal ions, storage or the regulation of metalloenzymes, stabiliza-
tion of membrane structures, binding of glycoproteins to cell
surfaces, toxic metal metabolism, and the binding of proteins to
sugars [1–6]. There has been considerable interest in the develop-
ment of carbohydrate-based pharmaceuticals as therapeutics for
neurodegenerative diseases due to that they can easily pass the
blood brain barrier, or as potent radiopharmaca and cancerostatica
[7–10]. Metal-based glyconanoparticles (GNPs) are biofunctional
nanomaterials having potential application in antiadhesion
therapy and diagnosis [11]. Recently the investigation on the
binding site of the interaction between mucin and calcium ions
also show that when the concentration of Ca2+ is relatively low,
Ca2+ prefers to coordinate with the carbohydrate moiety of mucin
[12]. For a better understanding of the interactions involved in
these events, models need to be designed that identify the
coordination modes, the changes of conformations for sugars and
hydrogen bond networks after complexation, etc.
of the simplest representatives of carbohydrates, was chosen as a
model to study the coordination of hydroxyl groups to metal ions.
Lanthanide ions are often used as probe of calcium ion, and
have clinical pharmacology, for example, lanthanum carbonate is
used in medicine as a phosphate binder [13]. Since the first crystal
structure of galactitolÁ2PrCl3Á14H2O has been reported by Angyal in
1993, some alkaline earth ion, lanthanide chloride or nitrate–galac-
titol complexes have been reported [14–18]. In the structures of
these metal–galactitol complexes, galactitol has several coordina-
tion modes [14–18]: one is that three hydroxyl groups coordinated
to one metal ion and the other three hydroxyl groups coordinate to
another metal ion; or galactitol provides O-2, -3 to coordinate to
one metal ion, and O-4, -5 with another metal ion, to form a chain
structure; or galactitol provides O-1 to one metal ion, O-2, -3 to
coordinate to the second metal ion, and O-4, -5 with the third
metal ion, and O-6 to the fourth metal ion to form a network struc-
ture. And the coordination of chloride ions, water and nitrate ions
make the complexation complicated.
For different metal ions, especially lanthanide ions, they may
form complexes with similar structures, for example, here HoG(II)
has similar structure with 2PrCl3ÁC6H14O6Á14H2O [14]. But for one
metal ion and one ligand, several metal–ligand complexes can be
obtained, for example, two NdCl3, three CaCl2 and two CuCl2–
erythritol complexes have been reported [19–21]. In this paper,
The investigation on the interactions between metal ions and
simple sugars can improve the understanding of metal ion interac-
⇑
Corresponding author. Tel.: +86 10 62751889; fax: +86 10 62758849.
E-mail address: yanglm@pku.edu.cn (L. Yang).
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.05.037

226
X. Hua et al. / Journal of Molecular Structure 998 (2011) 225–232
Table 1
various topological structures can be obtained for metal–sugar
complexes.
Crystal data and structure refinement for [Ho2(galac)(H2O)12)]Cl6Á2H2O (HoG(II)).
Empirical formula
C6H42Cl6Ho2O20Á([Ho2(galac)(H2O)12)]Cl6Á2H2O)
Formula weight
Temperature
Crystal system, space
group
976.96
293(2) K
Triclinic, P 1
2. Experimental
ꢀ
2.1. Materials
Unit cell dimensions
a = 7.9469(2) Å, b = 9.6209(4) Å, c = 10.2728(5) Å;
ErCl3 was prepared and crystallized from corresponding rare
earth oxide of high purity (99.99%). HoCl3 was purchased from a
chemical company in Shanghai. Galactitol was purchased from a
chemical company in Beijing, and was used without further
purification.
a
= 88.5028(14)°, b = 72.1904(13)°, c = 87.363(3)°
Volume
746.93(5) Å3
14715
Refls. No. for cell
measurement
h range for cell
measurement
Z, calculated density
Absorption coefficient
F(0 0 0)
Crystal shape/crystal
color
Crystal size
h range for data
collection
Limiting indices
Reflections collected/
unique
Reflections with
I > 2r(I)
3.48–27.49°
4, 2.172 Mg/m3
5.866 mm–1
474
2.2. Preparation of two HoCl3–galactitol complexes and ErCl3–
galactitol complex
Block/pink
0.20 Â 0.30 Â 0.30 mm3
2.72–27.48°
Galactitol (3 mmol) and metal chlorides (6 mmol) were dis-
solved in H2O/ethanol (2:3) and heated to prepare a concentrated
solution and cooled down for crystallization. Small amount of EtOH
(0.5 ml for each time) was kept being added into the solution dur-
ing the heating process when the solution was about 4 ml to pro-
long the reaction time. For HoG(I), the elemental analysis results
are as follows: C, 18.11; H, 4.53, so the formula of HoG(I) may be
[Ho(galac)(H2O)3)]Cl3Á0.5galac (HoCl3Á1.5C6H14O6Á3H2O). and Anal.
Calcd. Data is C, 18.06; H, 4.55. Anal. Calcd. for HoG(II): [Ho2(gala-
c)(H2O)12)]Cl6Á2H2O (2HoCl3ÁC6H14O6Á14H2O): C, 7.38; H, 4.33.
Found: C, 7.78; H, 4.18. Anal. Calcd. for ErG: [Er(gala-
c)(H2O)3)]Cl3Á0.5galac (ErCl3Á1.5C6H14O6Á3H2O): C, 17.99; H, 4.53.
Found: C, 18.19; H, 4.54.
À10 ꢀ h ꢀ 10, À12 ꢀ k ꢀ 12, À13 ꢀ l ꢀ 13
14715/3421 [R(int) = 0.0689]
2382
Completeness to
h = 27.49
Absorption correction
Max. and min.
transmission
99.7%
Empirical
0.583 and 0.198
Data/restraints/
parameters
3421/27/206
Goodness-of-fit on F2
Final R indices
0.962
R1 = 0.0282, wR2 = 0.0511
[I > 2r(I)]
2.3. Physical measurements
R indices (all data)
Extinction coefficient
Largest diff. peak and
hole
R1 = 0.0434, wR2 = 0.0532
0.0498(10)
0.712 and À1.241 e ÅÀ3
The mid-IR spectra were measured on a Nicolet Magna iN10
spectrometer using micro-IR method, 64 scans at 4 cmÀ1 resolu-
tion. Element analyses were carried out on an Elementar Vario EL
spectrometer. The far-IR spectra of the molecules in the range of
650–50 cmÀ1 were measured using common used Nujol mull
method on a Nicolet Magna-IR 750 II spectrometer at room tem-
perature and at 8 cmÀ1 resolution, 128 scans. The THz absorption
spectra were recorded at room temperature and 10 K for HoG(I)
on the THz time-domain device of Capital Normal University of
China, based on photoconductive switches for generation and elec-
tro-optical crystal detection of the far-infrared light. The experi-
mental apparatus for terahertz transmission measurements has
been discussed in detail elsewhere [22]. The preparation of the
samples was by pressing mixed pellets with polyethylene powder,
the thick of the samples are about 0.8 mm. The detection of THz
the same phenomenon was observed. Two HoCl3–galactitol com-
plexes have been synthesized, one has the similar structure with
PrCl3–galactitol complex; and another has new structure. But
unfortunately, although ErCl3 and HoCl3 with galactitol can form
the same complexes having similar unknown structures, only pow-
der samples, no single crystals can’t be obtained for them. So we
deduce their possible structures from elemental analysis, ESI-MS,
IR, FIR, Terahertz (THz) and TGA measurements. Although the
ligand is a simple molecule, it has several coordination modes
[14–18] as shown in the references and may form different com-
plexes with the same metal ion. The results demonstrated that
HoG(I)
3323
ErG
HoG(II)
3500
3000
2500
1600
1400
1200
1000
800
Wavenumbers (cm-1)
Wavenumbers (cm-1)
Fig. 1. the mid-IR spectra of HoG(I), HoG(II) and ErG complexes in the 3700–2400 and 1700–650 cmÀ1 region.

X. Hua et al. / Journal of Molecular Structure 998 (2011) 225–232
227
493
505
510
Q600SDT TGA–DTA–DSC equipment at N2 environment and
10 °C/min from 27 to 600 °C. ESI-MS spectra of the samples were
determined on a Bruker APEX IV Fourier Transform ion cyclotron
resonance mass spectrometer.
The X-ray diffraction data of HoG(II) were collected on a NON-
IUS KappaCCD diffractometer equipped with graphite-monochro-
597
595
HoG(II)
116
PrG
595
595
219
208
505
502
NdG
179
107
131
SmG
210
155
109
112
133
583
mated Mo Ka radiation (k = 0.71073 Å) in the h range from 3.48
620
532
213
159
165
135
to 27.49° at 293 K. A pink crystal with approximate dimensions
of 0.20 Â 0.30 Â 0.30 mm3 was selected for data collection. The
structure was resolved by direct methods with SHELX-97 and re-
fined using the full-matrix least-squares on F2 method [23]. Empir-
ical absorption corrections were applied and anisotropic thermal
parameters were used for the non-hydrogen atoms and isotropic
parameters for the hydrogen atoms. Hydrogen atoms were added
geometrically and refined using a riding model. The crystallo-
graphic data and structure refinement are listed in Table 1. Param-
eters in CIF format are available as Electronic Supplementary
Publication from Cambridge Crystallographic Data Centre (CCDC
number 788084).
337
349
88
89
460
G
241
171
282
159
120
102
600
400
200
Wavenumbers (cm-1)
583
584
116
117
473
474
550
552
430
383
91
HoG(I)
287
516
3. Results and discussion
432
385
93
3.1. FTIR spectra of two HoCl3–galactitol complexes and ErCl3–
galactitol complex
ErG
289
The FT-IR spectra of two HoCl3–galactitol complexes and ErCl3–
galactitol complex were shown in Fig. 1. HoG(I) is [Ho(galac)
(H2O)3)]Cl3Á0.5galac (i.e., HoCl3Á1.5C6H14O6Á3H2O), ErG is [Er(galac)
(H2O)3)]Cl3Á0.5galac (ErCl3Á1.5C6H14O6Á3H2O) and HoG(II) corre-
sponds to [Ho2(galac)(H2O)12)]Cl6Á2H2O (2HoCl3ÁC6H14O6Á14H2O),
respectively. The FTIR spectrum of HoG(II) is similar to the spectra
of 2PrCl3ÁC6H14O6Á14H2O and 2NdCl3ÁC6H14O6Á14H2O, whose struc-
tures were determined [14,24]. Therefore, the structure of HoG(II)
should be similar to the structure of 2PrCl3ÁC6H14O6Á14H2O. And
the FTIR spectrum of HoG(I) is different from the spectrum of Ho-
600
400
200
Wavenumbers (cm-1)
Fig. 2. FIR spectra of HoG(I), HoG(II) and ErG.
absorption spectra was carried out at N2 atmosphere to avoid the
influence of water vapor. Effective spectrum range is 0.2–2.6 THz
(ꢁ7–87 cmÀ1). The thermo gravimetric curve was measured on a
45
130
HoG(I)-295k
HoG(I)-10k
HoG(II)
30
1.61
2.11
65
15
1.26
1.00
0.76
1.38
0
0
500.0G
1.0T
1.5T
2.0T
2.5T
500.0G
ErG
1.0T
1.5T
2.0T
Frequency (THz)
Frequency (THz)
50
40
30
20
10
0
2.12
1.43
500.0G
1.0T
1.5T
2.0T
2.5T
Frequency (THz)
Fig. 3. THz absorption spectra of HoG(I), HoG(II) and ErG.

228
X. Hua et al. / Journal of Molecular Structure 998 (2011) 225–232
G(II), which indicate that two HoCl3–galactitol complexes have
formed.
Comparing with the spectrum of free galactitol, the stretching
vibrations of the OH groups of HoG(I), HoG(II) and ErG were chan-
that the bands are shifted to lower wavenumbers compared to
HoG(II).
The bands in the 3000–2700 cmÀ1 region can be assigned to the
stretching vibrations of the CH group (mCH). The bands positions
ged upon salt formation. The
mOH bands in the salt spectra were
were changed in the two Ho3+ salts and ErG and the intensities be-
came weaker upon salt formation (Fig. 1). And the vibrations of OH
have masked the CH bands.
broadened. Mainly the bands at 3396, 3211 and 3134 cmÀ1 for
HoG(I), 3398, 3211 and 3126 cmÀ1 for ErG, 3323 and 3241 cmÀ1
for HoG(II) were observed. The OH stretching vibrations can be as-
signed to the H-bonds formed between the hydroxyl groups, water
molecules and ClÀ ions. The broad bands in the region indicate the
existence of complicated hydrogen bond networks in the com-
plexes, and stronger hydrogen bonds exist in HoG(I) and ErG for
The deformation vibrations of water molecules in the IR spectra
of three complexes are located at 1642 cmÀ1 for HoG(I) and ErG,
1631 cmÀ1 for HoG(II), absent from the free ligand, corresponding
to the water molecules in the structures. Usually dH2O is located at
ꢁ1644 cmÀ1 [25]. It has shifted to 1631 cmÀ1 corresponding to
Fig. 4. TGA results of HoG(I) (a), ErG (b) and HoG(II) (c).

X. Hua et al. / Journal of Molecular Structure 998 (2011) 225–232
229
coordinated water molecules in HoG(II), which indicate that more
coordinated water molecules exist in its structure.
vibrations [26]. Galactitol itself has six bands in this region at
1117, 1103, 1078, 1047, 1030 and 1001 cmÀ1; the bands are shifted
to 1071, 1053, 1019, 1009 and 981 cmÀ1 for HoG(I), 1099, 1068,
1029 and 983 cmÀ1 for HoG(II). The bands have different peak
positions and relative intensities, which indicate that HoG(I) and
HoG(II) have different structures and the IR spectra indicate the
coordination of hydroxyl groups to metal ions. For example,
1089 cmÀ1 band in the calculation results for galactitol
The dCH2 vibration (1459 cmÀ1 for galactitol) is shifted to 1469
or 1473 cmÀ1 in the three salt spectra. Other bands in the 1500–
650 cmÀ1 region are shifted after complexation, and different
changes occur for HoG(I) and HoG(II), which indicate the formation
of two HoCl3–galactitol complexes. The bands in the 1100–
1000 cmÀ1 region may be assigned mainly to CC, CO and OCH
(a) HoG (I)
(b) ErG
(c) HoG (II)
Fig. 5. ESI spectra of HoG(I) (a), ErGb) and HoG(II) (c).

230
X. Hua et al. / Journal of Molecular Structure 998 (2011) 225–232
determine the formation of metal–ligand complexes [27–29]. Ter-
ahertz spectroscopy was regarded as the renaissance of far infrared
spectroscopy [30]. HoG(I) and ErG have similar FIR spectra, which
confirm the formation of metal complexes and they have similar
structures. The FIR spectrum of HoG(II) is similar to PrG, NdG,
SmG and different with galactitol itself in peak position and rela-
tive intensities because of the similarity of their structures. In the
650–100 cm–1 region the peaks could be assigned to MÀO vibra-
tions: 209, 185, 175 cm–1 for HoG(I) and 210, 188, 179 cm–1 for
ErG, 219 cm–1 for HoG(II) according to the assignment in the refer-
ence [27,28]. Other bands in the region may be related to MÀO
vibration and dOMO, etc. [28]. This is an important evidence of
complex formation.
The changes of THz spectra also indicate the formation of me-
tal–sugar complexes. For HoG(II), a weak broad band at 1.61 THz
was observed. HoG(I) and ErG have similar THz bands. Relatively
broad bands at 1.38 and 2.11 THz for HoG(I); 1.43 and 2.12 THz
for ErG were observed and the two spectra are different with galac-
titol itself [29]. At low temperature, 0.76, 1.00, 1.26 THz band was
emphasized for HoG(I). These bands are related to crystal lattice
vibration and hydrogen bonds, etc. At low temperature the bands
have shift or some new bands appear. For these metal complexes,
the bands become broader, maybe because after complexation the
coordination structures are complicated, extensive hydrogen bond
networks formed and some of them may be similar, so the bands
become broader. The FIR and THz spectra confirm the formation
of metal complexes and the similarity of the spectra of ErG and
HoG(I) indicate that they should have similar structures.
3.3. TGA spectra of HoG(I), HoG(II) and ErG
The TGA spectrum of HoG(I), HoG(II) and ErG are shown in
Fig. 4. For HoG(I), the first broad peak may be related to water mol-
ecules, including absorbed and three coordinated water molecules.
Other weight losses (ꢁ35%) are related to galactitol molecules. Ele-
mental analyses were done for the residuals (ꢁ53%) after TGA
experiments, the results are C 26.82%, H 1.56%. And no obvious
weight loss can be observed in the region of 600–1000 °C. For
ErG, the weight losses are 12% (corresponding to the loss of water),
35% (the loss of galactitol), and C 27.16%, H 1.48% were observed
for 51% residuals. For HoG(II), the first two peaks are related to
the weight losses of water molecules, the third and fourth peak
maybe related to galactitol, respectively.
Fig. 6. Possible coordination structures of HoCl3–galactitol complexes (a) possible
coordination structure of HoG(I) (b) another possible coordination structure of
HoCl3–galactitol complex.
(1078 cmÀ1 in the experimental results) was assigned to C1O1,
O1C1H, C2O2, C3O3, O3C3H [26], the ꢁ10 cmÀ1 changes of peak
positions after compexation indicate that the coordination of hy-
droxyl groups (O1H, O2H and O3H). And the bands in the region
are similar for HoG(I) and ErG, which show that they should have
similar structures.
The subtraction spectra of HoG(I) or ErG minus galactitol indi-
cate the existence of uncoordinated galactitol molecule. When sub-
traction factor is ꢁ0.12 after normalization, the subtraction spectra
are nearly the same with the spectra of metal complexes, which
demonstrate that the uncoordinated galactitol molecule exists in
their structures.
The IR results indicate that the hydroxyl groups of galactitol
took part in the metal–oxygen interaction; the hydrogen-bond net-
work rearranged upon sugar metalation; the conformation of
galactitol skeleton changed as a result of salt formation; two
HoCl3–galactitol complexes have formed and ErCl3–galactiol can
form similar complex with HoG(I). And uncoordinated galactitol
molecule may exist in the structures of HoG(I) and ErG.
3.4. ESI-MS spectra of HoG(I), HoG(II) and ErG
The ESI-MS spectra of HoG(I), HoG(II) and ErG are shown in
Fig. 5. In fact, some peaks are similar in the ESI spectra of HoG(I)
and HoG(II) in some extent, for example, 391, 437 and 527 molec-
ular ion peaks are the same. There is no peaks corresponding to
molecular weight in HoG(II). For HoG(I), 943 is corresponding to
2HoCl3Á2C6H14O6Á2H2O, indicate that there is a chain structure
formed by Ho ions and galactitol ligands. Other molecular ion
peaks, are related to the loss of water, or fragment of galactitol
etc. compared to 2HoCl3Á2C6H14O6Á2H2O. For example, 391 may
be related to HoCl3ÁC4H8O4, 437 may be related to HoCl3ÁC6H14O5,
527 may be related to HoCl3ÁC6H14O6Á4H2O, and 563 may be re-
lated to HoCl3ÁC6H14O6Á6H2O. For ErG, the molecular ion peaks
are similar to HoG(I). For comparison, the ESI spectrum of galactitol
also has been measured. And 183.1 peak is corresponding to galac-
titol, but 205.1 peak is the strongest peak in the ESI spectrum of
galactitol, corresponding to fragment of galactitol molecules.
And according to above results, the possible structure of HoG(I)
may be as follows: Ho3+ ion is 9-coordinated with six hydroxyl
groups from two galactitol molecules and three water molecules,
and uncoordinated galactitol molecule is hydrogen-bonded. The
3.2. FIR and THz spectra of the metal complexes
The FIR and THz spectra of the metal complexes are shown in
Figs. 2 and 3, respectively. FIR and THz are effective methods to

X. Hua et al. / Journal of Molecular Structure 998 (2011) 225–232
231
Fig. 7. The crystal structure of HoG(II) (a) the crystal structure of HoG(II), with H-atoms omitted for clarity. Symmetry code: A 2 À x, Ày, Àz. (b) The projection of the crystal
cell in the structure of HoG(II) as viewed along a axis.
possible coordination structure was shown in Fig. 6a. Galactitol
provide three hydroxyl groups to one metal ion and another three
hydroxyl groups to another metal ion and links two Ho ions to-
gether. It is possible that the chloride ions exist in the structure
and do not coordinate to Ho ion in HoG(I) as in HoG(II). But this
is only a preliminary deduced possible structure. According to
the coordination mode of galactitol, there are still other possible
coordination structures, for example, Fig. 6b, Ho is 9-coordinated
with six hydroxyl groups of galactitol and three water molecules
to form metal to ligand 1:1 complex. It is also a resonable structure
according to the coordination modes of metal ion and ligand.
the structure of HoG(II) because of the existence of hydroxyl
groups, water molecules and chloride ions. The hydrogen bond
data indicate that most of the hydrogen bonds are formed by hy-
droxyl groups of galactitol and water molecules with chloride ions,
OÁ Á ÁCl hydrogen bonds.
For metal–sugar complexes, different metal ions, anion (for
example, chloride ion or nitrate ion), solvents (water or ethanol),
different ligands, and the environment (including pH or tempera-
ture), have influences on the coordination behavior of metal ions,
so the coordination between metal ions and carbohydrates are
complicated. Compared to the structure of galactitol, the coordina-
tion of metal ion would have influence on the conformation of
galactitol. Compared to Pr, Nd, Sm, Eu and Tb chloride–galactitol
complexes with the structure [Ln2(galac)(H2O)12)]Cl6Á2H2O, the
changes induced by metal ions are similar, for example, the angle
of C(3)–C(2)–C(1) and C(2)–C(1)–C(1)#1 after complexation are
close for these lanthanide–galactitol complexes, which show that
they have similar coordination structures.
3.5. X-ray crystal structure of [Ho2(galac)(H2O)12)]Cl6Á2H2O (HoG(II))
The crystal structure of [Ho2(galac)(H2O)12)]Cl6Á2H2O is shown
in Fig. 7. For HoG(II), the 9-coordinated Ho3+ binds to three hydro-
xyl groups of one galactitol molecule and six water molecules.
Galactitol links two Ho ions together. The chloride ions do not
coordinate to Ho ion and only participate to form hydrogen bonds.
Ho–O distances are from 2.356 to 2.459 Å. Some selected bond dis-
tances and bond angles are listed in Table 2 and hydrogen bond
data are listed in Table 3, respectively. Compared to other reported
lanthanide–galactitol complexes with similar structures, Pr–O dis-
tances from 2.473 to 2.571 Å; Nd–O distances from 2.461 to
2.552 Å; Sm–O distances from 2.417 to 2.520 Å; Eu–O distances
are from 2.412 to 2.515 Å; Tb–O distances are from 2.386 to
2.484 Å. These are consistent with the sequence of ion radius and
electrons of lanthanide ions, i.e., in a good agreement with lantha-
nide contraction. There is an extensive hydrogen bond network in
In conclusion, the FTIR, FIR, THz, TGA, ESI and X-ray single crys-
tal diffraction spectra results indicate that Ho ion with galactitol
can form two complexes in the same environment. The saccharide,
chloride ions and water molecules can competitively coordinate
with metal ions and form two different complexes, which indicate
the high reactivity of galactitol and complexity of the interactions
between metal ions and carbohydrates, i.e., solvent, anion ions and
other factors may have effect on the coordination of metal ions and
different topological structures can be obtained. But the coordina-
tion mode of galactitol to lanthanide ions as three hydroxyl group
donor may be the same because lanthanide ions have large coordi-

232
X. Hua et al. / Journal of Molecular Structure 998 (2011) 225–232
Table 2
nation numbers. Different lanthanide ions may have similar coor-
Selected bond lengths (Å) and angles (°) for HoG(II).
dination structures with ligands because of their similarities, here
ErG and HoG(I) having similar structures, HoG(II) having resemble
structure with NdG are new examples.
Bond lengths
Bond lengths
Ho(1)ÀO(6)
Ho(1)ÀO(8)
Ho(1)ÀO(7)
Ho(1)ÀO(1)
Ho(1)ÀO(9)
Ho(1)ÀO(5)
Ho(1)ÀO(4)
Ho(1)ÀO(2)
2.356(3)
2.363(3)
2.367(3)
2.377(3)
2.397(3)
2.403(3)
2.419(3)
2.459(3)
Ho(1)ÀO(3)
C(1)ÀO(1)
C(1)ÀC(2)
C(1)ÀC(1)#1
C(2)ÀO(2)
C(2)ÀC(3)
C(3)ÀO(3)
2.464(3)
1.437(5)
1.519(5)
1.522(8)
1.435(5)
1.509(6)
1.428(5)
Acknowledgements
We gratefully acknowledge the financial support by National
Natural Science Foundation of China for the Grants (21001009
and 50973003), the State Key Project for Fundamental Research
of MOST (2002CB713600) and National High-tech R&D Program
of China (863 Program) of MOST (2010AA03A406).
Bond angles
Bond angles
O(6)ÀHo(1)ÀO(8)
O(6)ÀHo(1)ÀO(7)
O(8)ÀHo(1)ÀO(7)
O(6)ÀHo(1)ÀO(1)
O(8)ÀHo(1)ÀO(1)
O(7)ÀHo(1)ÀO(1)
O(6)ÀHo(1)ÀO(9)
O(8)ÀHo(1)ÀO(9)
O(7)ÀHo(1)ÀO(9)
O(1)ÀHo(1)ÀO(9)
O(6)ÀHo(1)ÀO(5)
O(8)ÀHo(1)ÀO(5)
O(7)ÀHo(1)ÀO(5)
O(6)ÀHo(1)ÀO(3)
O(8)ÀHo(1)ÀO(3)
O(7)ÀHo(1)ÀO(3)
O(1)ÀHo(1)ÀO(3)
O(9)ÀHo(1)ÀO(3)
O(1)ÀC(1)ÀC(2)
83.51(12)
77.91(11)
70.69(10)
140.77(10)
84.81(11)
132.03(10)
70.97(11)
70.51(11)
132.19(11)
69.82(10)
69.63(11)
138.52(11)
73.11(11)
138.92(11)
134.23(10)
97.85(11)
70.42(10)
129.38(12)
106.0(3)
O(1)ÀHo(1)ÀO(5)
O(9)ÀHo(1)ÀO(5)
O(6)ÀHo(1)ÀO(4)
O(8)ÀHo(1)ÀO(4)
O(7)ÀHo(1)ÀO(4)
O(1)ÀHo(1)ÀO(4)
O(9)ÀHo(1)ÀO(4)
O(5)ÀHo(1)ÀO(4)
O(6)ÀHo(1)ÀO(2)
O(8)ÀHo(1)ÀO(2)
O(7)ÀHo(1)ÀO(2)
O(1)ÀHo(1)ÀO(2)
O(9)ÀHo(1)ÀO(2)
O(5)ÀHo(1)ÀO(2)
O(4)ÀHo(1)ÀO(2)
O(5)ÀHo(1)ÀO(3)
O(4)ÀHo(1)ÀO(3)
O(2)ÀHo(1)ÀO(3)
C(3)ÀC(2)ÀC(1)
135.60(11)
124.82(10)
87.38(12)
139.04(10)
145.35(11)
77.47(10)
68.75(11)
72.37(11)
143.23(12)
71.11(10)
68.93(10)
64.22(9)
121.45(10)
113.31(10)
129.16(11)
70.09(11)
73.11(11)
63.59(10)
114.3(4)
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O(1)ÀC(1)ÀC(1)#1
C(2)ÀC(1)ÀC(1)#1
O(2)ÀC(2)ÀC(3)
108.2(4)
113.0(4)
108.7(3)
104.5(3)
O(3)ÀC(3)ÀC(2)
C(1)ÀO(1)ÀHo(1)
C(2)ÀO(2)ÀHo(1)
C(3)ÀO(3)ÀHo(1)
108.3(3)
123.1(2)
110.2(2)
121.1(3)
O(2)ÀC(2)ÀC(1)
Symmetry transformations used to generate equivalent atoms: #1 À x + 2, Ày, Àz.
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Table 3
Hydrogen bonds with HÁ Á ÁA < r(A) + 2.000 Å and \DHA > 110° for HoG(II) (Å and °).
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D–HÁ Á ÁA
d(D–H)
d(HÁ Á ÁA)
d(DÁ Á ÁA)
\DHA
O1–H1Á Á ÁO10
0.931
0.931
0.926
0.916
0.916
0.928
0.944
0.943
0.918
0.925
0.936
0.921
0.942
0.937
0.926
0.931
0.943
0.937
1.745
2.146
2.268
2.391
2.540
2.146
2.249
2.269
2.268
2.416
2.167
2.261
2.254
2.266
2.189
2.184
2.248
2.483
2.664
3.034
3.177
3.001
3.445
3.039
3.159
3.155
3.139
3.302
3.101
3.118
3.153
3.167
3.101
3.109
3.123
3.284
169.14
159.19
167.04
124.06
169.75
161.23
161.59
156.33
158.06
160.27
175.77
154.48
159.46
161.31
168.08
172.40
153.91
143.62
O2–H2Á Á ÁCl1#1
O3–H3Á Á ÁCl(3)
O4–H41Á Á ÁO1
O4–H41Á Á ÁO10
O4–H42Á Á ÁO10#2
O5–H51Á Á ÁCl(2)
O5–H52Á Á ÁCl3
O6–H61Á Á ÁCl2#3
O6–H62Á Á ÁCl3#4
O7–H71Á Á ÁCl1
O7–H72Á Á ÁCl2#4
O8–H81Á Á ÁCl1#5
O8–H82Á Á ÁCl2#6
O9–H91Á Á ÁCl1#5
O9–H92Á Á ÁCl3
O10–H101Á Á ÁCl2#2
O10–H102Á Á ÁCl3#2
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Xu, X.Y. Lu, C.L. Zhang, J.G. Wu, J.E. Chen, Spectrochim. Acta A 69 (2008) 160.
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Symmetry transformations used to generate equivalent atoms: #1[Àx + 1, Ày,
Àz + 1] #2[Àx + 2, Ày + 1, Àz] #3[Àx + 2, Ày + 1, Àz + 1] #4[Àx + 1, Ày + 1, Àz + 1]
#5[Àx + 2, Ày, Àz + 1] #6[ x, y À 1, z ] #7[x + 1, y, z].