Inorganic-organic hybrid compounds: Synthesis and characterization of three new metal phosphonates with similar characteristic structural features

Article abstract of DOI:10.1016/j.jssc.2005.10.008

The phosphonocarboxylic acid H(HO₃PCH₂) ₂NH-CH₂C₆H₄-COOH (H₅L) was synthesized and characterized by NMR- and IR-spectroscopy, thermogravimetric (TG) analysis and single-crystal X-ray diffraction. Reactions of H₅L with samarium(III) chloride and calcium(II) chloride resulted in three new compounds, Sm[(O₃PCH₂)₂NH-CH₂C ₆H₄-COOH]·H₂O (1), Ca[H(O ₃PCH₂)₂NH-CH₂C₆H ₄-COOH]·H₂O (2), and Ca[(HO₃PCH ₂)₂NH-CH₂C₆H₄-COOH] ₂·4H₂O (3). The single-crystal structure determination of the title compounds reveals that in H₅L as well as in compounds 1, 2, and 3 zwitterions are present. Within the M-O building units of the metal phosphonates we observed a different degree of dimensionality, depending on the oxidation state of the metal ion and the synthesis conditions. In 1, one-dimensional chains of edge-sharing SmO₈ polyhedra are observed while in 2, isolated units of edge-sharing CaO₆ octahedra and in 3 isolated CaO₆ octahedra are observed. However, looking at the organic part, the rigid phenyl carboxylic acid moieties arrange in a zipper-like fashion and hydrogen bonding plays an important role in the stabilization of the crystal structure. The title compounds were further characterized by IR spectroscopy and TG analysis. Additionally, the thermal stability of 1 was investigated by temperature-dependent X-ray diffraction.

Full text of DOI:10.1016/j.jssc.2005.10.008

ARTICLE IN PRESS
Journal of Solid State Chemistry 179 (2006) 145–155
www.elsevier.com/locate/jssc
Inorganic–organic hybrid compounds: Synthesis and characterization
of three new metal phosphonates with similar characteristic
structural features
Ã
Sebastian Bauera, Thomas Beinb, Norbert Stocka,
aInstitute of Inorganic Chemistry, Christian-Albrechts-University, Otto-Hahn-Platz 6/7, D 24118 Kiel, Germany
bDepartment of Chemistry and Biochemistry, Ludwig-Maximilians-University, Butenandtstr. 5-13 (E), D 81377 Munich, Germany
Received 11 August 2005; received in revised form 7 October 2005; accepted 9 October 2005
Available online 15 November 2005
Abstract
The phosphonocarboxylic acid H(HO3PCH2)2NH-CH2C6H4-COOH (H5L) was synthesized and characterized by NMR- and IR-
spectroscopy, thermogravimetric (TG) analysis and single-crystal X-ray diffraction. Reactions of H5L with samarium(III) chloride and
calcium(II) chloride resulted in three new compounds, Sm[(O3PCH2)2NH-CH2C6H4-COOH] ꢀ H2O (1), Ca[H(O3PCH2)2NH-CH2C6H4-
COOH] ꢀ H2O (2), and Ca[(HO3PCH2)2NH-CH2C6H4-COOH]2 ꢀ 4H2O (3). The single-crystal structure determination of the title
compounds reveals that in H5L as well as in compounds 1, 2, and 3 zwitterions are present. Within the M–O building units of the metal
phosphonates we observed a different degree of dimensionality, depending on the oxidation state of the metal ion and the synthesis
conditions. In 1, one-dimensional chains of edge-sharing SmO8 polyhedra are observed while in 2, isolated units of edge-sharing CaO6
octahedra and in 3 isolated CaO6 octahedra are observed. However, looking at the organic part, the rigid phenyl carboxylic acid moieties
arrange in a ‘‘zipper-like’’ fashion and hydrogen bonding plays an important role in the stabilization of the crystal structure. The title
compounds were further characterized by IR spectroscopy and TG analysis. Additionally, the thermal stability of 1 was investigated by
temperature-dependent X-ray diffraction.
r 2005 Elsevier Inc. All rights reserved.
Keywords: Metal phosphonates; Phosphonocarboxylic acid; Inorganic–organic hybrid compounds; Crystal structure; Samarium; Calcium
1. Introduction
the high coordination flexibility of the phosphonate group.
Nevertheless, metal phosphonates are promising candi-
dates for the synthesis of inorganic–organic hybrid
open-framework materials [3]. We are interested in the
systematic investigation of polyphosphonic and phospho-
nocarboxylic acids as starting materials for the synthesis of
new metal phosphonates. The goal is to establish structural
and synthetic trends in these systems for a better under-
standing of metal phosphonate chemistry. Thus, we have
established high-throughput methods in our group, which
allow us the systematic and rapid investigation of reac-
tions under hydrothermal conditions [4–7]. Recently, we
have started an investigation in the application of
functionalized iminobis (methylphosphonic acid)-deriva-
tives, (H2O3PCH2)2N-R, for the synthesis of metal
phosphonates [8,9]. Thus, by reacting (H2O3PCH2)2
Hybrid materials with organic and inorganic moieties are
an attractive field of research due to their composite
properties and the possibility of tuning their chemistry [1].
The potential of these inorganic–organic hybrid materials
lies in their use as sorbents, ion exchangers, catalysts, or
charge storage materials. In the field of metal carboxylates
a concept for the rational design of porous compounds has
been developed that allows in some cases the systematical
variation of the pore size and functionality [2]. In contrast,
in metal phosphonate chemistry there seem to be left too
many unknown factors for controlling the structure such as
Ã
Corresponding author. Fax: +49 431 880 1775.
E-mail address: stock@ac.uni-kiel.de (N. Stock).
0022-4596/$ - see front matter r 2005 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2005.10.008

ARTICLE IN PRESS
S. Bauer et al. / Journal of Solid State Chemistry 179 (2006) 145–155
146
N-(CH2)4-N(CH2PO3H)2 [6,10], and (H2O3PCH2)2N-CH2
C6H4CH2-N(CH2PO3H)2 [11] with different metal ions we
obtained a number of new compounds, some containing
three-dimensional framework structures and one showing
reversible dehydration/hydration properties. For current
studies, we chose the ligand H(HO3PCH2)2NH-CH2C6H4
-COOH (H5L) were the carboxylic acid group is separated
from the bisphosphonic acid group by means of the phenyl
group. This rigid moiety in combination with the flexible
coordination properties of the iminobis (methylphosphonic
acid) and carboxylic acid functionality makes H5L a
promising candidate for the synthesis of new metal
phosphonates with interesting structural features. Since
limited information on the chemistry of the ligand H5L is
available [9,12,13] high-throughput methodology is the
method of choice to systematically study its coordination
behavior in the presence of different metal ions. In one
detailed study, we recently obtained four new cobalt
compounds, Co2[(O3PCH2)2N-CH2C6H4-COOH] ꢀ H2O,
influence of the molar ratio Sm:H5L and the influence of
the pH of the starting mixture, reactions with different
molar ratios xSm:yH5L:zNaOH (see Supplementary
Material) were performed in a 48-reactor multiclave
[6,15]. After the work-up and characterization by auto-
mated X-ray powder diffraction all products were identi-
fied as microcrystalline Sm[(O3PCH2)2NH-CH2C6H4-
COOH] ꢀ H2O. No additional phase was observed.
2.3. Synthesis of Ca[H(O3PCH2)2NH-CH2C6H4-
COOH] ꢀ H2O (2)
In a reaction of 19 mg (56 mmol) H5L with 28 mL 2M
aqueous CaCl2 ꢀ 2H2O solution (56mmol), 66 mL 2.5M
aqueous NaOH solution (165 mmol), and 156 mL ꢀ H2O in a
Teflon microreactor at 150 1C for four days, single crystals of
Ca[H(O3PCH2)2NH-CH2C6H4-COOH] ꢀ H2O (2) among
pure phase microcrystalline product were obtained. This
was confirmed by X-ray powder diffraction measurements.
Co[(O3PCH2)(OCH)N-CH2C6H4-COOH] ꢀ H2O,
Co[H
2
(O PCH ) N-CH C H -COOH], and [Co (O PCH ) N-CH
C H -COOH] ꢀ 3.5H O [9].
2.4. Synthesis of Ca[(HO3PCH2)2NH-CH2C6H4-
COOH]2 ꢀ 4H2O (3)
3
2
2
2
6
4
2
3
2 2
2
6
4
2
Since only structures of H5L with Zn2+, Co2+, and
Pb2+ are known [9,12,13], we were further interested in the
chemistry of other two-valent cations and those with higher
oxidation states. Herein, we report on the synthesis and
characterization of three new metal phosphonates,
Sm[(O3PCH2)2NH-CH2C6H4-COOH] ꢀ H2O (1), Ca[H(O3
PCH2)2NH-CH2C6H4-COOH] ꢀ H2O (2), and Ca[(HO3
PCH2)2NH-CH2C6H4-COOH]2 ꢀ 4H2O (3). Furthermore,
we were able to additionally characterize H5L by single-
crystal structure determination and compare the thermal
behavior as well as the IR-spectroscopic properties of all
four compounds.
To investigate the influence of the temperature on the
product formation in the system Ca2+:H5L:NaOH:H2O
the following reaction was performed. 75.0 mg
(0.221 mmol) H5L were dispersed in 3 mL ꢀ H2O in a
supersonic bath. The dispersion was heated to 100 1C.
After the addition of a solution of 21.7 mg (0.148 mmol)
CaCl2 ꢀ 2H2O in 2 mL ꢀ H2O a colorless solid precipitates.
The suspension is again heated to 100 1C and treated in the
supersonic bath. The sample was allowed to cool to room
temperature. Over night needles of colorless single-crystals
of Ca[(HO3PCH2)2NH-CH2C6H4-COOH]2 ꢀ 4H2O formed
over microcrystalline product. Both products were
shown to be identical by X-ray powder diffraction
measurement.
2. Experimental section
2.1. Synthesis of H(HO3PCH2)2NH-CH2C6H4-COOH
2.5. Physical characterization
The carboxyaryl-iminobis (methylphosphonic acid), was
synthesized by a Mannich-type reaction starting from 4-
(aminomethyl)benzoic acid, phosphoric acid, and formal-
dehyde [9,14].
High-throughput X-ray analysis was carried out using a
STOE high-throughput powder diffractometer equipped
with an image-plate detector system [6]. The data collection
time was 6 min per sample. High-precision X-ray powder
diffraction patterns were recorded with a STOE STADI P
diffractometer using monochromated CuKa1 radiation. IR
spectra were recorded on a Bruker IFS 66v/S FTIR
spectrometer in the spectral range 4000–400 cmꢁ1 using
the KBr disk method. Thermogravimetric (TG) analyses
were carried out in air (25 mL/min, 30-900 1C, 10 1C/min)
using a NETZSCH STA 449C Analyzer (compounds 1 and
2) or a NETZSCH STA 429 Analyzer (compound 3).
2.2. Synthesis of Sm[(O3PCH2)2NH-CH2C6H4-
COOH] ꢀ H2O (1)
Sm[(O3PCH2)2NH-CH2C6H4-COOH] ꢀ H2O (1) was pre-
pared by reacting 53.8 mg (159 mmol) H5L, 120 mL
(120 mmol) of a 1 M aqueous solution of SmCl3 ꢀ 6H2O,
and 130 mL deionized water in a sealed 500 mL Teflon
microreactor. The reaction was carried out at 150 1C for 4
days. The resulting single-phase yellow product was
filtered and washed with deionized water and acetone.
X-ray powder diffraction experiments confirmed the
presence of only one phase, Sm[(O3PCH2)2NH-
CH2C6H4COOH] ꢀ H2O (1). In order to investigate the
3. Crystallography
The single-crystal structure determination by X-ray
diffraction for H(HO3PCH2)2NH-CH2C6H4-COOH (H5L),

ARTICLE IN PRESS
S. Bauer et al. / Journal of Solid State Chemistry 179 (2006) 145–155
147
compounds 1, and 2 was performed on a STOE IPDS
diffractometer equipped with a fine-focus sealed-tube X-
bonds are given in Tables 2–5 and Tables S2–S5 in the
Supplementary Material, respectively.
˚
ray source (MoKa radiation, l ¼ 0:71073 A) operating at
55 kV and 50 mA. For data reduction and the absorption
correction the program Xred was used [16]. For compound
3, the data collection was performed on a STOE Imaging
Plate Diffraction System (IPDS-1). All single-crystal
structures were solved by direct methods and refined using
the program package SHELXTL [17]. All H-atoms bound
to carbon atoms were placed onto calculated positions.
These H-atoms were refined using a riding model and fixing
the temperature factor to be 1.2 times the value of the atom
they are bonded to. Additionally, for H-atoms bound to O-
atoms that could be located from the difference Fourier
4. Results and discussion
4.1. Crystal structures
4.1.1. Crystal structure of H(HO3PCH2)2NH-CH2C6H4-
COOH
The asymmetric unit of the phosphonocarboxylic acid is
shown in Fig. S1 in the Supplementary Material and
selected bond lengths are given in Table 2. The three-
dimensional structure is composed of H(HO3PCH2)2NH-
CH2C6H4-COOH zwitterions, in which one phosphonic
acid group is monodeprotonated and the N-atom is
protonated (Fig. S1). The positions of the hydrogen atoms
were unambiguously derived from the single-crystal struc-
ture determination. The N-atom and all O-atoms except
the carbonyl oxygen O8 are involved in a hydrogen
bonding scheme in such way as to stabilize the structure
(Table S2 in the Supplementary Material). In Fig. 1, the H-
bonding modes of the dihydrogen-phosphonate group (P1)
are given. Oxygen atoms O2 and O3 interact as H-donor
˚
maps the O–H bond distance was set to 0.82 A H-atoms
bound to N-atoms that could be located from the
difference Fourier maps the N–H bond distance was set
˚
to 0.86 A. These atoms were refined using a riding model
and fixing the temperature factor to be 1.5 (in case of
oxygen) or 1.2 (in case of nitrogen) times the value of the
atom they are bonded to. The crystal data for
H(HO3PCH2)2NH-CH2C6H4-COOH and compounds 1–3
is listed in Table 1. Selected bond distances and hydrogen
Table 1
Summary of crystal data, intensity measurement, and structure refinement parameters for H(HO3PCH2)2NH-CH2C6H4-COOH (H5L),
Sm((O3PCH2)2NH-CH2C6H4-COOH) ꢀ H2O (1), Ca(H(O3PCH2)2NH-CH2C6H4-COOH) ꢀ H2O (2), and Ca((HO3PCH2)2NH-CH2C6H4-COOH)2 ꢀ 4H2O
(3)
Compound
H5L
1
2
3
Crystal system
Space group
a (pm)
Monoclinic
P21/c
Orthorhombic
Pbca
Monoclinic
P21/n
Monoclinic
P21/c
5.5953(1)
34.0036(6)
7.0121(1)
90
6.9890(3)
32.925(2)
12.9079(7)
90
5.7132(3)
7.9600(4)
31.729(2)
90
17.056(1)
7.4224(4)
14.018(1)
90
b (pm)
c (pm)
a (deg)
b (deg)
94.8644(7)
90
90
90
94.396(7)
90
114.164(8)
90
g (deg)
Volume (106 pm3)
Z
1329.32(4)
4
339.17
2970.3(3)
8
504.51
1438.7(1)
4
395.25
1619.2(2)
2
788.47
Formula mass (g/mol)
r (g/cm3)
F (000)
Crystal size (mm3)
m (mmꢁ1
1.69
704
2.256
1960
1.825
816
1.617
820
0.11 ꢂ 0.08 ꢂ 0.06
0.368
0.15 ꢂ 0.07 ꢂ 0.03
4.217
0.43 ꢂ 0.05 ꢂ 0.03
0.708
0.1 ꢂ 0.02 ꢂ 0.02
0.478
)
Absorption correction
Tmin/Tmax
Numerical
0.9595/0.9796
3.134–27.485
ꢁ7php7,
ꢁ43pkp43,
ꢁ9plp9
18207
Numerical
0.6930/0.880
2.0–28.0
ꢁ8php9,
ꢁ43pkp21,
ꢁ16plp17
13224
Numerical
0.9505/0.9866
2.58–27.97
ꢁ7php6
ꢁ10pkp10
ꢁ41plp41
12109
Numerical
0.9595/0.9796
2.62–25.08
ꢁ18php18
ꢁ7pkp8,
ꢁ16plp16
7174
y range (deg)
Range in hkl
Total data collect.
Unique/obs. data (I42sðIÞ)
Extinction coeff.
R(int)
3029/2192
None
0.0863
3471/2090
None
0.0790
3369/2433
None
0.0645
2475/2192
0.013(2)
0.0572
R1, wR2 (I42sðIÞ)
R1, wR2 (all data)
Goodness of fit
0.0412, 0.0984
0.0708, 0.1121
1.025
0.0342, 0.0557
0.0740, 0.0621
0.824
0.0331, 0.0694
0.0525, 0.0734
0.895
0.0364/0.0804
0.0572/0.0874
0.965
No. of variablesꢁ3
250
ꢁ0.516/0.511
209
ꢁ0.969/0.882
209
ꢁ0.393/0.460
216
ꢁ0.319/0.310
˚
De min/max (eA
)

ARTICLE IN PRESS
S. Bauer et al. / Journal of Solid State Chemistry 179 (2006) 145–155
148
Table 2
Selected bond distances (A) for H(HO3PCH2)2NH-CH2C6H4-COOH
˚
O4
P1–O1
P1–O2
P1–O3
P1–C1
C–N
1.482 (2)
1.533(2)
P2–O4
P2–O5
P2–O6
P2–C2
C3–C4
C7–C10
C10–O7
1.497 (2)
1.509 (2)
1.564(2)
1.819(3)
1.501(3)
1.483(3)
1.336(3)
O6
1.563(2)
1.813(2)
O3
P1
1.502(3)–1.524(3)
1.379(4)–1.397(4)
1.215(3)
C–Cphenyl
C10–O8
O2
N1
O1
O7
Table 3
˚
Selected bond distances (A) for Sm[(O3PCH2)2NH-CH2C6H4-COOH] ꢀ
H2O (1)
Sm–O
2.319(4)–2.649(4)
1.521(4)
1.523(5)
P–C
1.845(6)–1.828(7)
1.519(4)
1.539(4)
P1–O1
P1–O2
P1–O3
C–N
P2–O4
P2–O5
P2–O6
C3–C4
C7–C10
C10–O8
1.539(4)
1.501(3)
1.497(9)
P
O
N
C
1.512(7)–1.517(7)
1.37 (1)–1.408(9)
1.329(8)
C–Cphenyl
C10–O7
1.478(10)
1.217(7)
Fig. 1. H-bonding modes of the phosphonate group P1 in
H(HO3PCH2)2NH-CH2C6H4-COOH.
Table 4
Selected bond distances (A) for Ca(H(O3PCH2)2NH-CH2C6H4-
˚
COOH) ꢀ H2O (2)
P1
Ca–O
2.303 (2)–2.442 (2) P–C
1.836(2)–1.834(2)
1.534 (2)
1.505 (2)
1.527(2)
P1–O1
P1–O2
P1–O3
N–C
1.488 (2)
1.510(2)
1.562 (2)
P2–O4
O4
P2
P2–O5
P2–O6
C3–C4
C7–C10
O8–C10
O2
O5
1.501(3)–1.519(3)
1.384(4)–1.393(3)
1.317(3)
1.507(3)
1.500(3)
1.199(3)
O6
O5
C–Cphenyl
O7–C10
P2
O4
P1
O3
Table 5
Selected bond distances (A) and angles (deg) for Ca((HO3PCH2)NH-
P1
˚
CH2C6H4-COOH)2 ꢀ 4H2O
Ca–O
2.280(2)–2.384(2)
1.488(2)
1.512(2)
P–C
1.827(3)–1.828(3)
1.571(2)
1.486(2)
P
O
N
C
P1–O1
P1–O2
P1–O3
C–N
P2–O4
P2–O5
P2–O6
C3–C4
C7–C10
O8–C10
Fig. 2. H-bonding modes of the phosphonate group P2 in
H(HO3PCH2)2NH-CH2C6H4-COOH.
1.567(2)
1.512(2)
1.512(4)
1.516(4)–1.528(4)
1.386(5)–1.397(5)
1.323(4)
C–Cphenyl
O7–C10
1.498(4)
1.214(4)
dimers. These different kinds of H-bonding schemes result
in a structure that can be described as hydrogen-
phosphonate layers in the a,c-plane (Fig. 3) that are
zipper-like interconnected via H-bonding of aryl-car-
boxylic acid groups (Fig. 4). The different H-bonds are
well reflected in the P–O and C–O bond distances obtained
from the crystal structure determination.
˚
atoms with O6 and O4 (O2-H?O6:2.477(2) A; O3-
˚
H?O4: 2.597(2) A) of two different monohydrogen-
phosphonate groups (P2). The oxygen O1 is a twofold H-
acceptor, interacting with N1-H and O8-H from the
˚
carboxylic acid group (N1-H?O1: 2.792(2) A; O8-H?O1:
˚
2.854(2) A). The H-bonding modes of the monohydrogen-
phosphonate group (P2) are shown in Fig. 2. Only oxygen
O5 is protonated and by employing oxygen O4 and O5, the
phosphonate groups (P2) form a hydrogen bonding pattern
4.1.2. Crystal structure of Sm[(O3PCH2)2NH-CH2C6H4-
COOH] ꢀ H2O (1)
The asymmetric unit of Sm[(O3PCH2)2NH-CH2C6H4
COOH] ꢀ H2O is shown in Fig. S2. It consists of one Sm3+
˚
(O5-H?O4: 2.591(2) A) well-known from carboxylic acid

ARTICLE IN PRESS
S. Bauer et al. / Journal of Solid State Chemistry 179 (2006) 145–155
149
O4
O6
P2
O2
O5
P1
O1
O3
a
c
c
a
P
O
N
C
Fig. 5. Chains of SmO8-polyhedra are connected via phosphonate groups
to form a samarium phosphonate layer parallel to the a,c-plane as
observed in Sm[(O3PCH2)2NH-CH2C6H4-COOH] ꢀ H2O (1). The SmO8-
polyhedra are presented in light gray.
Fig. 3. Hydrogen-phosphonate layer in the a,c-plane as observed in
H(HO3PCH2)2NH-CH2C6H4-COOH. The gray tetrahedra describe the
PCO3-group.
Fig. 4. Zipper-like interconnection of the hydrogen phosphonate layers
via aryl-carboxylic acid groups in H(HO3PCH2)2NH-CH2C6H4-COOH.
The gray tetrahedra describe the PCO3-group.
Fig. 6. Zipper-like interconnection of adjacent samarium phosphonate
layers by hydrogen bonding (dashed lines) between carboxylic acid and
phosphonate groups in Sm[(O3PCH2)2NH-CH2C6H4-COOH] ꢀ H2O (1).
The SmO8-polyhedra are presented in light gray.
ion, one [(O3PCH2)2NH-CH2C6H4COOH]3ꢁ zwitterion,
and one water molecule. The hydrogen atom bonded to
nitrogen and one hydrogen atom bonded to the water
molecule (O9) could be located from difference Fourier
maps. The samarium ions are coordinated by seven oxygen
atoms belonging to phosphonate groups and the water
molecule. Edge-sharing SmO8-polyhedra form chains
along the a-axis that are further stabilized by the
phosphonate group (Fig. 5). The phosphonic acid groups
are fully deprotonated and all phosphonate oxygens except
oxygen O1 are involved in the coordination of the metal
centers. Whereas the oxygen atoms O2 and O3 of the
phosphonate group around P1 are each bound to only one
samarium ion, the phosphonate group around P2 acts as a
chelating ligand through oxygen O4 and O5 and at the
same time these oxygen atoms bridge to adjacent samarium
ions (m2 oxygen). The interconnection of these chains is
accomplished through the coordination of an oxygen atom
(O6) to a samarium ion of an adjacent chain (Fig. 5). The
organic units are arranged in a zipper-like fashion with
the carboxylic acid groups pointing to neighboring layers
(Fig. 6). Thus, hydrogen bonds between the carboxylic acid
group (O7-H) and the oxygen atom O1 of the phosphonate
group P1 of a adjacent layer are formed. The proton of the
carboxylic acid group could not be located from the
difference Fourier map. However, the bond distances in the
˚
carboxylic acid group (C10-O7: 1.329(8) A, C10-O8:
˚
1.217(7) A) strongly suggest that oxygen O7 is protonated
and acts as proton donor in the hydrogen bonding scheme
O7H?O1 (Table S3). The short interatomic distance
˚
(2.547 A) implies a strong hydrogen bond [18]. The

ARTICLE IN PRESS
S. Bauer et al. / Journal of Solid State Chemistry 179 (2006) 145–155
150
structure is further stabilized via extensive N–H?O and
O–H?O hydrogen bonding (Fig. S3 in the Supplementary
Material).
(Fig. 9). These layers are stabilized by extensive N–H?O
and O–H?O hydrogen bonding (Fig. S5 and Table S4 in
the Supplementary Material). The organic units point into
the interlayer space with the carboxylic acid groups
directed to the adjacent layers. Thus, a zipper-like
connection of neighboring layers stabilized by hydrogen
bonding between the carboxylic acid oxygen O7 and
phosphonate oxygen O6 is observed (Fig. 10). This theme
is very similar to that observed in the structures of
H(HO3P)2NH-CH2C6H4-COOH and Sm[(O3PCH2)2NH-
CH2C6H4-COOH] ꢀ H2O.
4.1.3. Crystal structure of Ca[H(O3PCH2)2NH-CH2C6H4-
COOH] ꢀ H2O (2)
The asymmetric unit of 2 consists of one Ca2+ ion, one
[H(O3PCH2)2NH-CH2C6H4-COOH]2ꢁ zwitterion, and one
water molecule (Fig. S4). All positions of the hydrogen
atoms were unambiguously derived from the difference
Fourier map. The Ca2+ ion are octahedrally surrounded
by five oxygen atoms of the phosphonate and one water
molecule. Two edge-sharing CaO6 octahedra connect to
form centrosymmetric Ca2O10 units (Fig. 7). The coordina-
tion behavior of the organic unit is given in Fig. 8. Two
oxygen atoms of each phosphonate group are involved in
the coordination of Ca2+ ions. Oxygens O1, O2, and O5
are only binding to a single Ca2+ ion, whereas oxygen O4
acts as a m2 ligand bridging two Ca2+ ions of the Ca2O10
units. Thus, Ca2O10 units are connected by phosphonate
groups to form Ca-phosphonate layers in the a,b-plane
4.1.4. Crystal structure of Ca[(HO3PCH2)2NH-CH2C6H4-
COOH]2 ꢀ 4H2O (3)
The asymmetric unit of 3 is given in Fig. S6. It is
comprised of one [(HO3PCH2)2NH-CH2C6H4-COOH]ꢁ
O5
O2
O4
O1
O9
O9
O1
Ca1
Ca1
O4
a
O2
O5
b
Fig. 7. Two edge-sharing CaO6 octahedra form centrosymmetric Ca2O10
units, as observed in Ca[H(O3PCH2)2NH-CH2C6H4-COOH] ꢀ H2O (2).
Fig. 9. In Ca[H(O3PCH2)2NH-CH2C6H4-COOH] ꢀ H2O (2), the Ca2O10
units are connected via phosphonate groups to form Ca-phosphonate
layers in the a,b-plane. The layers are further stabilized by hydrogen
bonding (dashed lines).
O6
O5
O4
O2
O3
O1
Ca
P
O
N
C
Fig. 8. Coordination behavior of the organic unit in Ca[H(O3PCH2)2NH-
CH2C6H4-COOH] ꢀ H2O (2).
Fig. 10. Zipper-like connection of adjacent Ca-phosphonate layers in
Ca[H(O3PCH2)2NH-CH2C6H4-COOH] ꢀ H2O (2).

ARTICLE IN PRESS
S. Bauer et al. / Journal of Solid State Chemistry 179 (2006) 145–155
151
zwitterion, one Ca2+ ion on a special position, and two
water molecules. The Ca2+ ions are octahedrally coordi-
nated by four oxygen atoms of the phosphonate groups
and two water molecules (Fig. S11). The Ca–O distances
along the c-axis by intensive hydrogen bonding. Thus, the
CaO6 are arranged in a layer parallel to the b,c-plane
(Fig. 12). A view along the b-axis shows that the organic
units are again arranged in a zipper-like fashion and point
to adjacent layers. In contrast to the other compounds, the
carboxylic acid unit can form two hydrogen bonds,
connecting two neighboring chains of CaO6 octahedra
(Fig. 13). Fig. S7 and Table S5 in the Supplementary
Material show all hydrogen bonds formed by the organic
unit.
˚
(2.280(2)–2.331(2) A) are comparable to those found in the
˚
title compound 2 (2.303 (2)–2.442 (2) A). Only one oxygen
atom of each phosphonate group (O1 and O5) takes part in
the coordination of Ca2+ ions. Thus, two adjacent CaO6
octahedra are connected at a time by two iminobis(methyl-
phosphonic acid)-units and one-dimensional chains of
rings of isolated octahedra along the b-axis are formed
(Fig. 11). These chains are further stabilized and connected
4.2. IR spectroscopy
All four title compounds were studied by IR spectro-
scopy (Fig. 14). In the following only bands related to the
a
b
Ca
P
O
N
C
Fig. 11. One-dimensional chain of CaO6 octahedra along the b-axis as
observed in Ca[(HO3PCH2)2NH-CH2C6H4-COOH]2 ꢀ 4H2O (3). CaO6
octahedra are shaded in light gray and PO3C tetrahedra are shaded in
dark gray. Hydrogen bonds are presented in dashed lines.
Fig. 13. The organic units are arranged in a zipper-like fashion and point
to adjacent layers as observed in Ca[(HO3PCH2)2NH-CH2C6H4-
COOH]2 ꢀ 4H2O (3). CaO6 octahedra are shaded in light gray and PO3C
tetrahedra are shaded in dark gray.
c
b
Ca
P
O
N
C
Fig. 12. The CaO6 octahedra are arranged in the b,c-plane as observed in Ca[(HO3PCH2)2NH-CH2C6H4-COOH]2 ꢀ 4H2O (3). CaO6 octahedra are shaded
in light gray and PO3C tetrahedra are shaded in dark gray.

ARTICLE IN PRESS
S. Bauer et al. / Journal of Solid State Chemistry 179 (2006) 145–155
152
ing deformation band appears at 1655 cmꢁ1. The aromatic
(a)
(b)
(c)
and aliphatic C–H stretching vibrations result in a set of
sharp bands in the region from 3096 to 2975 cmꢁ1. Several
broad bands of low intensity in the region from 2845 to
2200 cmꢁ1 are due to O–H stretching vibrations of the
hydrogen phosphonate and the carboxylic acid groups
involved in hydrogen bonding. The CQO stretching
vibration of the carboxylic acid group can be assigned to
the sharp band at 1706 cmꢁ1. The higher frequency in
comparison to the CQO stretching vibration in com-
pound 1 is in agreement with the shorter CQO bond
(d)
˚
distance (1.199(3) and 1.217(7) A, respectively).
The sharp and well-defined band at 3613 cmꢁ1 in the IR
spectrum of Ca[(HO3PCH2)2NH-CH2C6H4-COOH]2 ꢀ
4H2O (3) can be assigned to O–H stretching vibration of
one of the water molecules with the hydrogen atoms not
being involved in hydrogen bonding. This is in accordance
with crystallographic results. The broad band from 3483 to
3358 cmꢁ1 clearly indicates the presence of the other water
molecules that are involved in hydrogen bonding. The C–H
stretching vibrations of the aromatic and aliphatic groups
can be assigned to the set of sharp bands in the region
between 3047 and 2950 cmꢁ1. Several bands in the region
from 2854 to 2291 cmꢁ1 indicate an extensive scheme of
hydrogen bonding. The sharp band at 1696 cmꢁ1 is due to
the CQO stretching vibration of the carboxylic acid
group.
3500
3000
2500
2000
1500
1000
500
Wavenumber / cm-1
Fig. 14. IR-spectra for (a) H(HO3PCH2)2NH-CH2C6H4-COOH (H5L), (b)
Sm[(O3PCH2)2NH-CH2C6H4-COOH] ꢀ H2O (1), (c) Ca[H(O3PCH2)2NH-
CH2C6H4-COOH] ꢀ H2O (2), and (d) Ca[(HO3PCH2)2NH-CH2C6H4-
COOH]2 ꢀ 4H2O.
presence of water molecules, hydrogen bonding, and
carboxylic acid groups are discussed in detail, since
they give valuable structural information. The IR-
spectra of all compounds exhibit typical bands in the
region between 1250 and 980 cmꢁ1 that are due to the P–C
and P–O stretching vibrations of the tetrahedral CPO3-
group.
In the IR-spectrum of H(HO3PCH2)2NH-CH2C6H4-
COOH (H5L) the absence of bands due the vibrations of
water molecules is in accordance with crystallographic
results. Several broad bands of low intensity in the region
between 2900 and 2200 cmꢁ1 are due to O–H stretching
vibrations involved in H-bonding of the hydrogen phos-
phonate groups [19]. The band corresponding to the CQO
stretching vibration of the carboxylic acid group is located
at 1717 cmꢁ1, which is a typical value for carboxylic groups
involved in hydrogen bonding.
4.3. Thermal properties
The thermal properties of the title compounds were
studied using TG analysis (Fig. 15). Additionally,
Sm[(O3PCH2)2NH-CH2C6H4-COOH] ꢀ H2O (1) was char-
acterized using temperature-dependent X-ray powder
diffraction (Fig. 16).
In accordance with the crystallographic results that the
water molecules in Sm[(O3PCH2)2NH-CH2C6H4-COOH] ꢀ
H2O (1) are involved in a complex hydrogen-bonding
scheme, a broad band at 3373 cmꢁ1 is present. The
(a)
corresponding deformation band appears at 1615 cmꢁ1
.
Bands in the region from 3079 to 2950 cmꢁ1 are due to
aromatic and aliphatic C–H stretching vibrations. Several
broad bands from 2800 to 2500 cmꢁ1 may be assigned to
O–H stretching vibrations of the carboxylic acid groups
involved in hydrogen bonding. The CQO stretching
vibration of the carboxylic acid group appears as a rather
(b)
(c)
(d)
100
200
300
400
500
600
700
800
broad band at 1693 cmꢁ1
.
Temperature / °C
The presence of two broad bands at 3475 and 3396 cmꢁ1
in the IR spectrum of Ca[H(O3PCH2)2NH-CH2C6H4-
COOH] ꢀ H2O (2) clearly indicates that hydrogen-bonded
water molecules are part of the structure. The correspond-
Fig. 15. TG curves for (a) H(HO3PCH2)2NH-CH2C6H4-COOH (H5L), (b)
Sm[(O3PCH2)2NH-CH2C6H4-COOH] ꢀ H2O (1), (c) Ca[H(O3PCH2)2NH-
CH2C6H4-COOH] ꢀ H2O (2), and (d) Ca[HO3PCH2)2NH-CH2C6H4-
COOH]2 ꢀ 4H2O.

ARTICLE IN PRESS
S. Bauer et al. / Journal of Solid State Chemistry 179 (2006) 145–155
153
Fig. 16. Temperature-dependent X-ray diffraction of Sm[(O3PCH2)2NH-CH2C6H4-COOH] ꢀ H2O (1).
In the TG diagram of H5L up to 235 1C no weight loss is
observed. The decomposition of the compound due to
condensation of the phosphonic and carboxylic acid
groups and the pyrolysis upon further heating proceeds
in two major steps. Up to 520 1C a weight loss of 28% is
observed followed by weight loss of 63%, which is
completed at 750 1C.
The TG diagram of Sm[(O3PCH2)2NH-CH2C6H4-
COOH] ꢀ H2O (1) shows no significant weight loss up to
210 1C. From 210 to 300 a weight loss of 3.7%, which
corresponds to the release of the lattice water molecule
(calcd. 3.6%). With increasing temperature a steady loss is
observed. Thus, the departure of water, which is completed
at 290 1C according to TG measurement, leads to a change
in the structure. A new, unknown crystalline phase appears
from 290 1C on and is present to 480 1C. Beyond 480 1C the
sample is X-ray amorphous.
According to TG measurements, Ca[H(O3PCH2)2NH-
CH2C6H4-COOH] ꢀ H2O (2) is stable up to 200 1C (Fig. 15).
Thus, no weight loss is observed. From 200 to 290 1C a one
step loss of 5.7% occurs. The calculated value for the
release of one lattice water molecule is 4.6% indicating that
in this step condensation of hydrogen phosphonate and
carboxylic acid groups takes place. Upon further heating a
continuous weight loss due to decomposition of the sample
is observed.
In Ca[(HO3PCH2)2NH-CH2C6H4-COOH]2 ꢀ 4H2O (3) a
single-step weight loss is observed from 120 to 280 1C. The
value 11.3% (calcd. 11.4%) corresponds to the departure
of five water molecules per formula unit (Fig. 15). Thus,
not only the lattice water molecules are released but also
water from the condensation of hydrogen phosphonate and
carboxylic acid groups resulting in a collapse of the
structure. Upon further heating a continuous weight loss
due to further condensation and pyrolysis of the organic
part is observed.
5. Conclusions
Single-crystal structure determination of the organic
building block H(HO3PCH2)2NH-CH2C6H4-COOH re-
vealed that the crystal structure is composed of zwitterions
formed by the protonation of the nitrogen atom. This
compound was successfully employed in the synthesis of
new metal phosphonates and in all cases the protonation of
the nitrogen in metal phosphonates was observed. This is in
accordance with the work of other groups employing
iminobis(methylphosphonic acid) and its derivatives
[20–22]. Comparing the metal phosphonates, Sm[(O3
PCH2)2NH-CH2C6H4-COOH] ꢀ H2O (1), Ca[H(O3PCH2)2
NH-CH2C6H4-COOH] ꢀ H2O (2), and Ca[(HO3PCH2)2
NH-CH2C6H4-COOH]2 ꢀ 4H2O (3), all exhibit a similar
zipper-like arrangement of the rigid phenyl carboxylic acid
(Fig. 17). The structures are stabilized through the
formation of H-bonding between the carboxylic acid group
and a phosphonate or the amine group (C-OH?OQP,
C-OH?N, respectively). But, due to different oxidation
states and ionic radii of the cations as well as different
synthesis temperatures a variation in the dimensionality of
the inorganic building units are observed. In the case of
Sm3+ ions (coordination number: 8; ionic radius: 1.219 A
˚
[23]), the higher ionic charge in comparison to Ca2+ permits
the complete deprotonation of the phosphonic acid groups,
which leads to a higher dimensionality of the network. Thus,
chains of SmO8 polyhedra are formed, which are further
connected via phosphonate groups to form a samarium
phosphonate layer. At the same reaction temperature
(150 1C), Ca[H(O3PCH2)2NH-CH2C6H4-COOH] ꢀ H2O was

ARTICLE IN PRESS
S. Bauer et al. / Journal of Solid State Chemistry 179 (2006) 145–155
154
Fig. 17. Zipper-like arrangement of the rigid phenyl carboxylic acid moiety in H(O3PCH2)2NH-CH2C6H4-COOH (H5L) (top), Ca[H(O3PCH2)2NH-
CH2C6H4-COOH] ꢀ H2O (2) (middle left), Ca[(HO3PCH2)2NH-CH2C6H4-COOH]2 ꢀ 4H2O (3) (middle right), Sm[(O3PCH2)2NH-CH2C6H4-COOH] ꢀ H2O
(1) (bottom left), and Co2[(O3PCH2)2N-CH2C6H4-COOH] ꢀ H2O (bottom, right) [9]. Metal-oxygen polyhedra are shaded in light gray and PO3C
tetrahedra are shaded in dark gray.
formed (ionic radius of six fold coordinated Ca2+: 1.14 A
[22]). In this compound one phosphonic acid group
remains mono-protonated. The metal-oxygen building
units are of lower dimensionality compared to those in
the Sm-compound. Ca2O6 units are present, which are
connected via phosphonate groups and thus, a Ca-
phosphonate layer further stabilized by hydrogen bonding
is formed. In the case of Ca[(HO3PCH2)2NH-CH2C6H4-
COOH]2 ꢀ 4H2O, which is formed at lower temperatures
(100 1C), both phosphonic acid groups remain mono-
protonated and the dimensionality of the inorganic
building units is therefore even lower (isolated CaO6
octahedra). In addition, more water molecules are incor-
porated into the structure. The fact that with elevated
temperature for identical initial compositions the formed
structures exhibit a higher grade of condensation and less
water molecules are found to be incorporated into the
structure is also observed in a recent systematic investiga-
tion on the formation of Cobalt succinates under hydro-
thermal conditions [24].
˚
The phosphonocarboxylic acid, H5L, has shown to
be a versatile and flexible starting material in the
synthesis of new metal phosphonates. In addition
to the recently obtained open-framework compound
Ba3[O3PCH2NH2CH2PO3]2 ꢀ 7H2O [8], which is a reaction
product of the in situ decomposition of H5L and several
new cobalt carboxy-phosphonates [9], we were able to
synthesize three new metal carboxy-phosphonates, employ-
ing Sm3+ and Ca2+. In all observed structures, derived
from H(HO3PCH2)2NH-CH2C6H4-COOH, the carboxylic
acid group remained protonated.
A
carboxylate
group involved in the coordination of metal ions should
lead to a higher dimensionality that is mandatory for an
open framework structure. In order to study this effect
reactions under more basic conditions are currently
performed.

ARTICLE IN PRESS
S. Bauer et al. / Journal of Solid State Chemistry 179 (2006) 145–155
155
Supplementary material: CCDC 285963 (H(HO3
PCH2)2NH-CH2C6H4-COOH), CCDC 285964 (Sm[(O3
PCH2)2NH-CH2C6H4COOH] ꢀ H2O (1)), CCDC 285965
(Ca[H(O3PCH2)2NH-CH2C6H4-COOH] ꢀ H2O (2)), and
CCDC 285966 (Ca[(HO3PCH2)2NH-CH2C6H4-COOH]2
ꢀ 4H2O (3)) contain the supplementary crystallographic
data for this paper. These data can be obtained free of
charge from the Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif. In addition, the
molar ratios xSm:yH5L:zNaOH in the high-throughput
experiment and the figures of the asymmetric units of
(H(HO3PCH2)2NH-CH2C6H4-COOH), 1, 2, and 3, as well
as the tables describing the hydrogen bonding in the latter
compounds (Tables S2–S5) are given. Furthermore, the
experimental and theoretical XRD powder patterns of
compounds 1–3 are presented.
[2] M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M. O’Keeffe,
O.M. Yaghi, Science 295 (2002) 469.
[3] K. Maeda, Microporous Mesoporous Mater. 73 (2004) 47.
[4] T. Bein, Angew. Chem. Int. Ed. 38 (1999) 323.
[5] K. Choi, D. Gardner, N. Hilbrandt, T. Bein, Angew. Chem. Int. Ed.
38 (1999) 2891.
[6] N. Stock, T. Bein, Angew. Chem. 116 (2004) 767;
N. Stock, T. Bein, Angew. Chem. Int. Ed. 43 (2004) 749.
[7] N. Stock, T. Bein, J. Mater. Chem. 15 (2005) 1384.
[8] S. Bauer, H. Muller, T. Bein, N. Stock, Inorg. Chem., in press,
¨
doi:10.1021/ic050935m.
[9] S. Bauer, T. Bein, N. Stock, Inorg. Chem. 44 (2005) 5882.
[10] N. Stock, M. Rauscher, T. Bein, J. Solid State Chem. 177 (2004)
642.
[11] N. Stock, A. Stoll, T. Bein, Microporous Mesoporous Mater. 69
(2004) 65.
[12] J.-L. Song, A.V. Prosvirin, H.-H. Zhao, J.-G. Mao, Eur. J. Inorg.
Chem. (2004) 3706.
[13] J.-L. Song, J.-G. Mao, J. Mol. Struct. 740 (2005) 181.
[14] K. Moedritzer, R.R. Irani, J. Org. Chem. 31 (1966) 1603.
[15] N. Stock, T. Bein, Solid State Sci. 5 (2003) 1207.
[16] XRED, data reduction and absorption correction program version
1.09 for Windows, Stoe & Cie GmbH, Darmstadt, 1997.
[17] G.M. Sheldrick, SHELXTL-PLUS Crystallographic System, Sie-
mens, Analytical X-ray Instruments Inc., Madison, WI, 1992.
[18] G.A. Jeffrey, in: D.G. Truhlar (Ed.), Topics in Physical Chemistry:
An Introduction to Hydrogen Bonding, Oxford University Press,
New York, 1997.
Acknowledgments
The authors thank Dr. P. Mayer for the acquisition of
the single-crystal data of (HO3PCH2)2NH-CH2C6H4-
COOH, 1, and 2, and Priv.-Doz. Dr. Christian Nather
for the acquisition of the single-crystal data of 3.
¨
[19] L.J. Bellamy, Infrared Spectra of Complex Molecules, Wiley,
New York, 1958 (Chapter 18).
Appendix A. Supplementary materials
[20] J.-L. Song, J.-G. Mao, Y.-Q. Sun, H.-Y. Zeng, R.K. Kremer,
A. Clearfield, J. Solid State Chem. 177 (2004) 633.
[21] R. Vivani, U. Costantino, M. Nocchetti, J. Mater. Chem. 12 (2002)
3254.
Supplementary data associated with this article can be
found in the online version at doi:10.1016/j.jssc.2005.10.008.
[22] A. Cabeza, S. Bruque, A. Guagliardi, M.A.G. Aranda, J. Solid State
Chem. 160 (2001) 278.
References
[23] R.D. Shannon, C.T. Prewitt, Acta Crystallogr. B25 (1969)
925.
[24] P.M. Forster, N. Stock, A.K. Cheetham, Angew. Chem. Int. Ed.
2005, in press, doi:10.1002/ange.200501766.
´
[1] A.K. Cheetham, G. Ferey, T. Loiseau, Angew. Chem. Int. Ed. 38
(1999) 3268.