Permanent porosity and role of sulfonate groups in coordination networks constructed from a new polyfunctional phosphonato-sulfonate linker molecule

Article abstract of DOI:10.1039/c9dt04571f

The new linker molecule (H₂O₃PCH₂)₂N-CH₂C₆H₄SO₃H, (4-{[bis(phosphonomethyl)amino]methyl}benzene-sulfonic acid, H₅L), bearing both phosphonic and sulfonic acid groups, was employed for the synthesis of new coordination polymers (CPs). Four new CPs of composition [Mg(H₃L)(H₂O)₂]·H₂O (1), [Mg₂(HL)(H₂O)₆]·2H₂O (2), [Ba(H₃L)(H₂O)]·H₂O (3) and [Pb₂(HL)]·H₂O (4), were discovered using high-throughput methods and all structures were determined by single-crystal X-ray diffraction (SCXRD). With increasing ionic radius of the metal ion, an increase in coordination number from CN = 6 (Mg²⁺) to CN = 9 (Ba²⁺) and an increase in the dimensionality of the network from 1D to 3D is observed. This is reflected in the composition of the IBU and the number of metal ions that are connected by each linker molecule, i.e. from three in 1 to ten in 4. The connection of the IBUs leads to 1D and 2D structures in 1 and 2 with non-coordinating sulfonate groups, while 3 and 4 crystallise in MOF-type structures and coordination of the sulfonate groups is observed. The compounds exhibit thermal stabilities between 200 (2) and 345 °C (4) as proven by variable temperature powder X-ray diffraction (VT-PXRD) measurements. Title compound 4 contains micropores of 4 × 2 ? and reversible H₂O uptake of 50 mg g^-1 was demonstrated by vapour sorption measurements, making it the first porous metal phosphonatosulfonate. Detailed characterisation, i.e. CHNS and TG analysis as well as NMR and IR spectroscopy measurements confirm the phase purity of the title compounds.

Full text of DOI:10.1039/c9dt04571f

Dalton
Transactions
View Article Online
View Journal
PAPER
Permanent porosity and role of sulfonate groups in
coordination networks constructed from a new
polyfunctional phosphonato-sulfonate linker
molecule†
Cite this: DOI: 10.1039/c9dt04571f
b
Stephan Wöhlbrandt,a Angela Igeska,a Erik Svensson Grape,
Sigurd Øien-Ødegaard,c A. Ken Inge b and Norbert Stock
*
a
The new linker molecule (H2O3PCH2)2N-CH2C6H4SO3H, (4-{[bis(phosphonomethyl)amino]methyl}
benzene-sulfonic acid, H5L), bearing both phosphonic and sulfonic acid groups, was employed for the
synthesis of new coordination polymers (CPs). Four new CPs of composition [Mg(H3L)(H2O)2]·H2O (1),
[Mg2(HL)(H2O)6]·2H2O (2), [Ba(H3L)(H2O)]·H2O (3) and [Pb2(HL)]·H2O (4), were discovered using high-
throughput methods and all structures were determined by single-crystal X-ray diffraction (SCXRD). With
increasing ionic radius of the metal ion, an increase in coordination number from CN = 6 (Mg2+) to CN =
9 (Ba2+) and an increase in the dimensionality of the network from 1D to 3D is observed. This is reflected
in the composition of the IBU and the number of metal ions that are connected by each linker molecule,
i.e. from three in 1 to ten in 4. The connection of the IBUs leads to 1D and 2D structures in 1 and 2 with
non-coordinating sulfonate groups, while 3 and 4 crystallise in MOF-type structures and coordination of
the sulfonate groups is observed. The compounds exhibit thermal stabilities between 200 (2) and 345 °C
(4) as proven by variable temperature powder X-ray diffraction (VT-PXRD) measurements. Title compound
4 contains micropores of 4 × 2 Å and reversible H2O uptake of 50 mg g−1 was demonstrated by vapour
sorption measurements, making it the first porous metal phosphonatosulfonate. Detailed characterisation,
i.e. CHNS and TG analysis as well as NMR and IR spectroscopy measurements confirm the phase purity of
the title compounds.
Received 28th November 2019,
Accepted 6th February 2020
DOI: 10.1039/c9dt04571f
rsc.li/dalton
function and a suitable metal salt is needed. This variability
results in compounds with various magnetic, luminescent,
1. Introduction
The field of metal organophosphonates is a diverse and ever- ion-exchange
and
proton-conducting
properties.7
growing field of research.1–3 Most of the compounds are Furthermore, metal phosphonates were among the first porous
coordination polymers (CPs) featuring inorganic building coordination polymers,8 a field that is nowadays dominated by
units (IBUs) which can occur as isolated MOx polyhedra in the metal carboxylates.9 Nevertheless, recently important contri-
structure, but also as dimers (M2Ox), chains or layers.4 These butions to the field of porous metal phosphonates have been
IBUs are connected via organic linker molecules into crystal- reported by various groups.1,3
line networks, each with unique properties.5,6 The number of
The introduction of additional functionalities to the
theoretical combinations is virtually limitless since for the syn- organic linker, like amino, fluoro, methyl, or carboxylic
thesis only an organic linker molecule with a phosphonic acid groups, was carried out to study their influence on the for-
mation of crystalline metal phosphonates. Many beautiful yet
complex crystal structures were reported ranging from 0D-com-
plexes to 2D-layered networks and 3D-connected porous
frameworks.10
aInstitut für Anorganische Chemie, Christian-Albrechts-Universität zu Kiel,
24098 Kiel, Germany. E-mail: stock@ac.uni-kiel.de
bDepartment of Materials and Environmental Chemistry, Stockholm University,
Stockholm 10691, Sweden
Organic linker molecules containing alkylamine groups
have also been extensively used as starting materials for the
synthesis of metal organophosphonates,11 since the amino
group can be straightforwardly converted into bis(phosphono-
methyl)-amine groups ((H2O3PCH2)2N–). A dominant struc-
tural motif in these compounds are inorganic layers comprised
cDepartment of Chemistry, University of Oslo, P.O. Box 1033, N-0315 Oslo, Norway
†Electronic supplementary information (ESI) available: PXRD patterns, crystallo-
graphic data, 1H NMR and IR spectroscopy, TGA and sorption data, CHNS ana-
lysis. CCDC 1968802–1968805. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c9dt04571f
This journal is © The Royal Society of Chemistry 2020
Dalton Trans.

View Article Online
Paper
Dalton Transactions
of alternating MOx polyhedra and phosphonate groups, which lity of the sample during the sorption experiment was con-
are separated by the organic part of the linker molecule, thus firmed by PXRD measurements.
forming a hydrophobic region. The polarity of this region can
2.2 Synthetic procedures
be modified through the introduction of additional functional
groups, such as –CH3, –F and –COOH. Especially the addition
2.2.1 Synthesis
of
H5L.
The
linker
of –COOH groups proved to be interesting due to a possible (H2O3PCH2)2N-CH2C6H4SO3H was synthesized in a two-step
interconnection of the layers and extended hydrogen bonding. reaction. In the first step, benzylamine (240 ml, 2.196 mol)
This concept can be taken further through the addition of a sul- was added dropwise to conc. H2SO4 (240 ml) under ice cooling
fonic acid function, which has previously not been introduced within 1 h. After letting the mixture warm up to room tempera-
into the chemistry of the arylbis(phosphonomethyl)-amines.
ture, 720 ml fuming sulphuric acid (30%) was added slowly.
Here we report our results on the incorporation of a sulfo- The mixture was heated up and stirred for two hours at 100 °C.
nic acid function into
(H2O3PCH2)2N– group and the use of this new linker in the
a
linker molecule containing
a
Filtration gave 114.63 g of 4-sulfo-benzylamine, yield: 33.4%.
In the second step, 4-sulfo-benzylamine (114.63 g,
synthesis of metal phosphonatosulfonates. Thus the linker 612.3 mmol) was dissolved in 925 ml of 5.2 M hydrochloric
molecule (CH3PO3H2)2NCH2C6H4SO3H (H5L) was successfully acid and subsequently, 72 g phosphonic acid (882 mmol, 3
synthesized and a high-throughput investigation resulted in eq.) was added. The resulting mixture was heated to reflux and
the four new coordination polymers [Mg(H3L)(H2O)2]·H2O (1), formaldehyde (130 ml 37% aqueous solution, 1.61 mol, 5 eq.)
[Mg2(HL)(H2O)6]·2H2O (2), [Ba(H3L)(H2O)]·H2O (3) and was added dropwise over two hours. The solution was kept at
[Pb2(HL)]·H2O (4). The syntheses, crystal structures and full reflux for 72 hours and the solvent was removed under
characterization of these compounds are presented in detail.
reduced pressure. The resulting honey-textured product was
repeatedly refluxed in 10 × 150 ml of acetone, which resulted
in a grey powder. The crude product was stirred in 0.5 l of
ethanol to give a white powder of H5L (210.42 g, 91%).
1H NMR (400 MHz, D2O, TMS, 300 K): δ = 7.74 (d, 2H, Ar–
H), 7.57 (d, 2H, Ar–H), 4.64 (s, 2H, Ar–CH2–N), 3.35 (d, 4H, N–
CH2–P) ppm.
2. Experimental
2.1 Materials and methods
All metal salts and solvents were used as received.
High-throughput powder X-ray diffraction (PXRD) patterns
Elemental analysis: calcd (%): C 28.61, H 4.03, N 3.73, S
were measured in transmission geometry using Cu-Kα1 (λ = 8.55; found (%): C 28.55, H 4.13, N 3.61, S 8.29.
1.54056 Å, Mythen detector) radiation and employing a Stoe
2.2.2 High-throughput investigation, discovery of the title
Stadi P Combi diffractometer equipped with a motorized XY compounds. High-throughput (HT) syntheses were carried out
stage. PXRD patterns used for in-depth analysis were recorded using a custom made 24-multiclave reactor system with a total
on a Stoe Stadi P diffractometer in transmission geometry using volume of 2 ml and a filling volume of 1 ml as described pre-
Cu-Kα1 (λ = 1.54056 Å, Mythen detector) radiation. Conventional, viously.12 Starting materials, molar ratios, solvent compo-
in-house single-crystal X-ray diffraction (SCXRD) data were sitions and various counter ions of the metal salts were investi-
recorded with a Bruker APEX-II CCD diffractometer using Mo-Kα gated. A complete overview of the experiments and the discov-
radiation (λ = 0.71073 Å) or a Bruker D8 Venture equipped with a ery of the title compounds is given in Tables S1 and S2.†
PHOTON 100 CPAD detector, using Mo-Kα radiation.
Synchrotron SCXRD data were obtained at BioMAX, Max4 of reaction conditions optimized by HT methods by a factor of
synchrotron, Lund. 20 was easily accomplished. First the linker H5L was intro-
2.2.3 Synthesis scale-up of the title compounds. Scale-up
Variable temperature (VT) PXRD measurements were duced into a 30 ml autoclave as a powder. Subsequently water,
recorded on a Stoe Stadi P Combi diffractometer (Cu-Kα1 radi- ethanol, base and a solution of the respective metal salt were
ation, λ = 1.54056 Å, Mythen detector) equipped with a capil- added in the given order. The reactor was closed and heated
lary furnace. For the measurements, the samples were trans- up to 150 °C for six hours, kept at 150 °C for 24 hours and
ferred into 0.5 mm quartz capillaries and heated up in steps of cooled down to room temperature within twelve hours. The
10 K between 25 and 500 °C and measured for 5 minutes each. obtained products were filtered off and dried at room tempera-
Thermogravimetric analyses were carried out with
a
ture. Exact amounts, stoichiometry and yields are given in
Netzsch STA-409CD analyser under air stream with a flow rate Table 1.
of 75 ml min−1 and a heating rate of 4 K min−1. NMR spectra
Elemental analysis for 1 ([Mg(H3L)(H2O)2]·H2O): calcd (%):
were recorded on a Bruker Avance III spectrometer and IR C 23.94, H 4.24, N 3.10, S 7.10; found (%): C 23.94, H 4.17, N
spectra on a Bruker ALPHA-P A220/D-01 Fourier transform 3.12, S 7.71.
infrared (FTIR) spectrometer equipped with an attenuated
Elemental analysis for 2 ([Mg2(HL)(H2O)6]·2H2O): calcd (%):
total reflection (ATR) unit. Elemental analyses were carried out C 19.17, H 4.83, N 2.48, S 5.69; found (%): C 17.48, H 4.90, N
using a Euro EA 3000 analyser.
2.11, S 4.88.
Elemental analysis for 3 ([Ba(H3L)(H2O)]·H2O): calcd (%):C
For the sorption measurements, the sample was activated
for 16 hours at 120 °C under reduced pressure (10−2 kPa). The 19.70, H 3.49, N 2.55, S 5.85; found (%): C 20.07, H 3.04, N
H2O sorption experiment was carried out at 298 K. The stabi- 2.44, S 5.71.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2020

View Article Online
Dalton Transactions
Paper
Table 1 Overview of the optimized synthesis conditions for the title compounds. The yield given in the last column is based on the linker
2 mol l−1
Compound
Metal source
MgCl2·6H2O
M [mg] M [ml] Ratio metal Linker [mg] H2O [ml] EtOH [ml] NaOH [ml] Yield [%]
1 ([Mg(H3L)(H2O)2]·H2O)
2 ([Mg2(HL)(H2O)6]·2H2O) Mg(OAc)2·3H2O 428
3 ([Ba(H3L)(H2O)]·H2O)
4 ([Pb2(HL)]·H2O)
1218
2
2
2
2
4
4
2
1
564
188
188
188
6.5
8
8
10
10
10
10
1.5
0
0
64.8
79
41.1
41.8
BaCl2·2H2O
Pb(OAc)2·3H2O
244
189
8
0
Elemental analysis for 4 ([Pb2(HL)]·H2O): calcd (%):C 13.45, H
1.63, N 1.74, S 3.99; found (%): C 13.70, H 1.82, N 1.80, S 3.54.
2.3 Crystal structure determination
Compounds 1, 2 and 3 were obtained as single crystals suitable
for conventional single-crystal X-ray diffraction (SCXRD). The
single crystal structures were solved using the program
SHELXT13 and refined with SHELXL14 using Olex215 as GUI.
Title compound 4 formed dendritic crystals with very small
dagger-shaped crystallites. Thus, data sets were acquired at the
BioMAX beamline at Max4. The crystals endured severe radi-
ation damage during the experiments, losing high angle
diffraction (<1 Å) very fast and all diffraction after approxi-
mately one minute in the beam. The disordered nature of the
crystals and the radiation damage gave very noisy data, but the
structure could nevertheless be obtained by ab initio methods.
In the data sets of the Mg-based compounds 1 and 2,
H-atoms could unequivocally be observed in the Fourier map
and were subsequently refined. While in 1, all H-atoms were
refined freely, during the structure refinement of 2 the
H-atoms connected to the aromatic ring and free water mole-
cules had to be added via AFIX instructions and refined using
Fig. 1 Reaction scheme for the synthesis of H5L, starting from
benzylamine.
3.2 Synthesis of the coordination polymers
All metal phosphonatosulfonates were synthesized under
solvothermal reaction conditions employing a water/ethanol
mixture as solvent. A high-throughput (HT) screening experi-
ment using 20 different divalent metal salts with ionic radii
varying between 0.72 and 1.47 Å was carried out in order to
discover new CPs. A list of all metal salts and the exact syn-
thesis parameters are given in section S2 in the ESI.† The use
of ethanol as a co-solvent proved mandatory for obtaining crys-
talline reaction products and coordination polymers contain-
ing Mg2+, Ba2+ and Pb2+ ions were obtained. For the formation
of 1, the concentration of the reactants had to be increased by
a factor of three in order to obtain enough material for a full
characterization.
The use of the different magnesium salts, i.e. MgCl2·6H2O
and Mg(OAc2)·4H2O resulted in the formation of 1 and 2,
respectively. To investigate the influence of the addition of
acid or base on the formation of either 1 or 2, a systematic
acid/base-screening was carried out. Synthetic details and
results are summarized in Fig. S5.† Starting with MgCl2·6H2O
as the metal source and adding NaOH (2 mol l−1), the for-
mation of 2 was observed, while the use of Mg(OAc)2·3H2O
and adding HCl (2 mol l−1) results in the formation of 1.
a
riding model, the other H-atoms were refined using
restraints. In 3 and 4, the H-atoms could not be localized at all
from the Fourier map due to the influence of Ba and Pb ions
as heavy scatterers. H-atoms connected to carbon were added
via AFIX instructions and refined using a riding model.
3. Results and discussion
3.1 Synthesis
3.1.1 Synthesis of H5L, (H2O3PCH2)2N-CH2C6H4SO3H. The
new linker molecule H5L was obtained in a two-step reaction
as shown in Fig. 1. The first step, the sulfonation, was carried
out according to Hubbuch et al. starting from benzylamine.16
For the second step, the phosphonomethylation, the procedure
3.3 Crystal structures
first described by Moedritzer and Irani17 was adapted with Since all four compounds were obtained as single crystalline
modified stoichiometry. The reported work-up procedure materials, their crystal structures were determined by single-
based on precipitation of the product upon addition of hot crystal X-ray diffraction. Crystallographic details are given in
ethanol did not change the honey-like texture of H5L. Thus, a Table 2.
different work-up procedure had to be evaluated, where
Compound 1, [Mg(H3L)(H2O)2]·H2O, exhibits the lowest
repeated refluxing in acetone proved to be sufficient for con- degree of linker connectivity in all of the presented com-
verting the product into a solid powder. Further impurities pounds, which is reflected in the IBU and the connection
were removed by stirring the powder in ethanol. NMR pattern of the linker. The asymmetric unit (Fig. S7†) contains
spectra (Fig. S12†) as well as CHNS analysis confirmed chemi- one Mg2+ cation, three water molecules and a threefold proto-
cal purity.
nated linker molecule. Isolated MgO6 polyhedra are observed
This journal is © The Royal Society of Chemistry 2020
Dalton Trans.

View Article Online
Paper
Dalton Transactions
Table 2 Crystallographic data of the title compounds
1 ([Mg(H3L)(H2O)2]·H2O)
2 ([Mg2(HL)(H2O)6]·2H2O)
3 ([Ba(H3L)(H2O)]·H2O)
4 ([Pb2(HL)]·H2O)
Sum formula
Crystal system
λ [Å]
a [Å]
b [Å]
c [Å]
α [°]
MgC9H19NO12P2S
Monoclinic
0.71073
7.654(2)
8.098(2)
26.554(5)
90
Mg2C9H27NO17P2S
Monoclinic
0.71073
18.8531(8)
5.3729(2)
23.791(1)
90
BaC9H17NO11P2S
Orthorhombic
0.71073
15.569(3)
24.683(5)
8.749(2)
90
Pb2C9H11NO9P2S
Monoclinic
0.72932
5.3434(1)
23.6346(3)
13.1707(2)
90
β [°]
γ [°]
90.64(3)
90
113.180(1)
90
90
90
91.839(1)
90
Space group
Tot., uniq. data, Rint
R1, wR2 [I > 2σ(I)]
Observed data [I > 2σ(I)]
GOF
P21/c
P21/n
Ama2
P21/c
24123, 3752, 4.25
3.22, 8.61
3489
25674, 5014, 5.28
5.36, 14.74
3763
20223, 4303, 17.17
6.6, 18.5
3882
2337, 2337, 38.56
16.8, 38.7
1362
1.053
1.025
1.089
1.603
Fig. 3 Crystal structure of [Mg2(HL)(H2O)6]·2H2O (2), (a) coordination
environment of Mg1, (b) coordination environment of Mg2, (c) coordi-
nation mode of the linker molecule; and one-dimensional structure of 2,
(d) view along [100], (e) view along [010]. General colour scheme: C
(black), O (red), N (blue), P and P–O-tetrahedra (violet), S and S–O-tetra-
hedra (yellow), Mg (light blue) and Mg–O-polyhedra (blue). Hydrogen
atoms were omitted for clarity.
Fig. 2 Crystal structure of [Mg(H3L)(H2O)2]·H2O (1), (a) coordination
environment of Mg2+-ions, (b) connectivity of the linker molecule, and
two-dimensional network of 1 (c) along [010], (d) along [100]. General
colour scheme: C (black), O (red), N (blue), P and P–O-tetrahedra
(violet), S and S–O-tetrahedra (yellow), Mg (light blue) and Mg–O-octa-
hedra (blue). Hydrogen atoms were omitted for clarity.
with oxygen atoms from two coordinating water molecules and Harris notation,5 while the sulfonate group does not coordi-
four oxygen atoms of two H3L2− ions (Fig. 2). Each linker mole- nate. The acidic proton could be located from the Fourier map
cule connects three Mg2+ cations in a [2,110] fashion, accord- and was successfully refined. It is connected to the nitrogen
ing to the Harris notation.5 The third water molecule of the atom of the linker and it is involved in hydrogen bonding
asymmetric unit is located between the layers forming several (Table S6†). In addition to the six coordinating water mole-
H-bonds (Fig. 8c and Table S4†). The remaining three acidic cules, electron density in the Fourier map indicated the pres-
protons of the linker could be unequivocally localized from the ence of additional water molecules. The non-coordinating
Fourier map and were successfully refined. Zwitterions are water molecules are localized through hydrogen bonds and
−
present in the structure with –PO3H−, –SO3 and ammonium their presence is confirmed by the excellent agreement with
groups. Extensive hydrogen bonding (Fig. 8c and Table S4) the analytical data (sections 3.7 and S4†). Extended hydrogen
leads to a supramolecular 3D-structure.
bonding (Table S6†) leads to the formation of a 3D supramole-
Compound 2 features a slightly higher degree of linker con- cular structure.
nectivity and M–O condensation (Fig. 3). The asymmetric unit
In contrast, the crystal structure of compound 3, [Ba(H3L)
consists of two Mg2+ cations, six coordinating water molecules (H2O)]·H2O, shows a clear increase in condensation in the IBU
and a monoprotonated linker molecule (Fig. S8†). One linker and linker connectivity and thus does not resemble the interdi-
connects five Mg2+ cations via the phosphonate groups coordi- gitated structural motif found in 1 and 2. This is due to the
nating in a [3,210] and a [3,111] fashion according to the fact that the dimensionality of the IBU is increased and chains
Dalton Trans.
This journal is © The Royal Society of Chemistry 2020

View Article Online
Dalton Transactions
Paper
Fig. 4 Crystal structure of [Ba(H3L)(H2O)]·H2O (3), (a) chain of edge-
sharing BaO9-polyhedra, (b) coordination mode of the linker molecule,
(c) three-dimensional network of 3, view along [001]. General colour
scheme: C (black), O (red), N (blue), P and P–O-tetrahedra (violet), S and
S–O-tetrahedra (yellow), Ba and Ba–O-polyhedra (green). Hydrogen
atoms were omitted for clarity.
Fig. 5 Crystal structure of [Pb2(HL)]·H2O (4), (a) coordination environ-
ment of Pb1, (b) coordination environment of Pb2, (c) chain of edge-
and corner-sharing Pb–O-polyhedra along [001], (d) coordination mode
of the linker molecule, (e) three-dimensional network of 4. General
colour scheme: C (black), O (red), N (blue), P and P–O-tetrahedra
(violet), S and S–O-tetrahedra (yellow), Pb and Pb–O-polyhedra (grey).
Hydrogen atoms were omitted for clarity.
of interconnected BaO9 polyhedra are formed (Fig. 4). The
asymmetric unit consists of one Ba atom, two oxygen atoms
assigned to water molecules and two linker molecules on
special positions (Fig. S9†). The Ba centre is coordinated by
nine oxygen atoms, forming a monocapped square antiprism
and edge-sharing of the BaO9 polyhedra leads to zigzag-chains
along [001]. This fact, combined with a coordinating sulfonate
group, leads to the formation of a three-dimensional coordi-
nation polymer. The presence of hydrogen phosphonate
groups is indicated by a P–O bond length of 1.551(10) Å which
hydrogen atoms could be located from the Fourier map and
thus they were placed on idealized positions and refined using
a riding model. In order to achieve charge balance, the linker
must be monoprotonated. Based on the observed bond length
and the coordinating properties of the linker we conclude that
the acidic proton is probably located on the nitrogen atom as
observed in the other title compounds.
3.4 Structure discussion
is in excellent agreement with the P–O bond lengths found for Several similarities between the crystal structures can be
the P–OH groups in 1 (1.589(1) Å and 1.569(1) Å). The hydro- observed. First, similarities between both Mg-based com-
gen phosphonate and sulfonate groups coordinate in a [2,110] pounds (1 and 2) will be discussed, followed by the heavy
fashion, according to the Harris notation.5 Thus, each linker metal-containing compounds (3 and 4); subsequently, the
molecule connects six Ba2+ cations in total and is only twofold section will be concluded with a comparison to the structures
deprotonated. The third remaining proton is bonded to the already reported in the literature.
nitrogen atom, thus forming a zwitterionic molecule.
In all four compounds, zwitterionic linker molecules are
Compound 4, [Pb2(HL)]·H2O, exhibits similar structural fea- found due to the deprotonation of the –SO3H group, a variable
tures as 3. In Fig. 5, similarities such as a one-dimensional degree of deprotonation of the –PO3H2 groups, and the proto-
chain of M–O-polyhedra and the coordination of the sulfonate nation of the tertiary amine.
group to the metal ion is shown. Yet, there are still differences
Both 1 and 2 contain octahedrally surrounded Mg2+ cations
regarding the structural motif found in 4. The asymmetric unit with a minimum of two water molecules in their coordination
is composed of two Pb2+ cations and one linker molecule. The environment. While only isolated MgO6 polyhedra are
Pb1 atom is coordinated by seven oxygen atoms in a distorted observed in 1, an IBU with higher degree of condensation, i.e.
pentagonal bipyramidal fashion, while Pb2 is coordinated by dimeric Mg2O10 units are found in 2. Both compounds exhibit
five oxygen atoms and exhibits a distorted square-pyramidal a similar structural motif, layers with interdigitated aromatic
coordination environment. The polyhedra of Pb1 and Pb2 are cores and non-coordinating sulfonate groups. This results in a
linked by edge-sharing to dimers, which are further connected 2D-layered structure for 1 and a 1D-chain structure for 2. The
via corner-sharing into chains along [001]. These chains are high amount of crystal water in the coordination sphere of
linked by phosphonate and sulfonate groups to layers which Mg2 in 2 leads to a lower dimensionality, since it prevents the
are further interconnected into a 3D framework by the organic linker molecule from connecting the chains further.
part of the linker molecules. The increase in linker connec-
The increase in ionic radius from 0.72 (Mg2+) to 1.23 (Ba2+)
tivity is reflected in the coordination of the two phosphonate and 1.47 Å (Pb2+) leads to an increase in the coordination
and the sulfonate groups ([4,211], [3,211] and [4,211], respect- number in 3 and 4 and thus a more variable coordination
ively, according to the Harris notation).5 The compound exhi- environment. One-dimensional chains of edge-/corner-sharing
bits a stereochemically active electron pair pointing into the M–O polyhedra are observed in 3 and 4 and the higher degree
pore. Due to the presence of lead as a heavy scatterer, no of condensation of the IBU in combination with coordinating
This journal is © The Royal Society of Chemistry 2020
Dalton Trans.

View Article Online
Paper
Dalton Transactions
ters and phosphonate groups (motif A, Fig. 8, top left). The
organic part of the linker molecules, the phenyl ring, is
located between the layers, which leads to interdigitation.18
The crystal structure of 1 fits nicely into this pattern and the
−
presence of the –SO3 groups results in the formation of
hydrogen bonds between the layers. The second motif (motif
B, Fig. 8, top right) can be found in 2 but instead of 2D in-
organic layers, interdigitated 1D-chains are formed. Due to the
presence of sulfonate groups, coordinating water molecules
and water of crystallisation, 1 and 2 exhibit an extensive
network of hydrogen bonds. There are a few linker molecules
of similar geometry (Fig. 7) that have also been used for the
synthesis of coordination polymers. Interestingly, their crystal
structures can be categorized according to the two motifs
observed in the title compounds 1 and 2. Details are given in
the ESI, Table S12.†
Regarding the structure of 3 and 4, the sulfonate group now
takes part in the coordination of metal ions. This results in a
3D network structure. To the best of our knowledge, compar-
able structural motifs are not known to this date. Although
there are several reports of a coordinating carboxylate group,
the crystal structures arising thereof are best to be described
as 2D-layered.19
Fig. 6 Coordination modes of the linker molecules in the four title
compounds, which reflects the increase in connectivity. (a) [Mg(H3L)
(H2O)2]·H2O (1), (b) [Mg2(HL)(H2O)6]·2H2O (2), (c) [Ba(H3L)(H2O)]·H2O (3),
(d) [Pb2(HL)]·H2O (4).
sulfonate groups (Fig. 6) results in the formation of three-
dimensional open framework structures with one-dimensional
channel systems.
As previously stated, the dominant structural motif found
in compounds containing amino bismethylenphosphonate
groups are inorganic layers comprised of metal–oxygen-clus-
3.5 Hirshfeld surface analysis
Hirshfeld surface analysis is a powerful tool for studying inter-
molecular interactions between molecules in crystalline solids,
resolving various interatomic distances in a single picture.
Fig. 7 Linker molecules of similar geometries and containing
(H2O3PCH2)2N– groups, which were employed in previous studies.19,20
Fig. 8 Detailed insight into the structures of the Mg-based compounds (hydrogen bonds are represented through dashed lines), (a) simplified 2D-
layered motif of 1 (motif A), (b) simplified 1D-layered chain-like motif of 2 (motif B), (c) network of hydrogen bonds in 1, (d) network of hydrogen
bonds in 2.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2020

View Article Online
Dalton Transactions
Paper
This allows for detailed studies of the interactions which lead
to a certain crystal packing, such as van der Waals-interactions,
hydrogen bonds and other types. In order to study the nature
of interactions between the layers in 1 and the chains in 2 in
more detail, we carried out a Hirshfeld surface analysis. The
calculations were performed using the Crystal Explorer17
program20 and Hirshfeld surfaces were mapped using the nor-
malized contact distance dnorm which is calculated according
to the equation:
di ꢀ rivdW de ꢀ revdW
dnorm
¼
þ
rivdW
revdW
where dnorm is the normalized contact distance, derived from de
(the nearest atom outside the Hirshfeld surface), di (the nearest
atom inside the Hirshfeld surface) and their respective van der
Waals (vdW) radii.21 The 3D surfaces were mapped for dnorm
and are shown in Fig. 9 using the standard red-white-blue
colour scheme. Contacts shorter than van der Waals-radii are
encoded in red and are characteristic for hydrogen bonds and
other types of internuclear interactions. Close inspection of the
Hirshfeld surfaces for 1 and 2 reveals that hydrogen bonding
occurs at the sulfonic acid groups and the water molecules
attached to the metal centres. This provides additional evidence
for the extent of hydrogen bonding discussed in section 3.4.
Fig. 11 TG curves of the title compounds under air.
3.6 Porosity and sorption
Since the crystal structure determination of 4 revealed the
existence of pores, a sorption experiment was carried out. A
detailed view of the pore, the water sorption isotherm and
PXRD patterns of the sample before and after measurement
are shown in Fig. 10. While compound 4 is non-porous to
nitrogen at 77 K, a water uptake of 50 mg g−1 at 298 K was
detected which corresponds to 2.2 water molecules per
formula unit. PXRD measurements confirmed the stability of
the compounds towards H2O de- and adsorption (Fig. 10c).
3.7 Thermal analysis
For all compounds, thermogravimetric analyses were carried
out in order to verify the formulas deduced from the SCXRD
experiments and to investigate the thermal stabilities between
30 and 1000 °C. The TG curves are shown in Fig. 11 and the
assignment of the weight losses are given in Table 3. For each
compound various weight losses are observed and the first one
is related to the loss of water molecules while the second step
corresponds to linker decomposition. For 1, the loss of water
is divided into two steps: the first step up to 150 °C corres-
ponds to one water molecule per formula unit and can be
assigned to the water of crystallisation, while the second step
Fig. 9 (a) Hirshfeld surface of 1, view along [100], (b) Hirshfeld surface
of 2, view along [010]. Contacts shorter than van der Waals contacts (i.e.
covalent bonds and hydrogen bonds) are encoded in red, contacts
longer than van der Waals interactions are encoded in blue. Details on
the chosen structure sector are given in Fig. S16.†
Fig. 10 (a) Pores in the structure of 4, (b) water sorption curve of 4, (c) PXRD pattern of 4 before and after sorption measurement.
This journal is © The Royal Society of Chemistry 2020
Dalton Trans.

View Article Online
Paper
Dalton Transactions
Table 3 Overview of the TG analysis results
Mass loss H2O
Mass loss linker decomposition
Residual mass
Compound
Obs. [%]
Calc. [%]
ΔT [°C]
Obs. [%]
Calc. [%]
ΔT [°C]
Obs. [%]
Calc. [%]
1 ([Mg(H3L)(H2O)2]·H2O)
2 ([Mg2(HL)(H2O)6]·2H2O)
3 ([Ba(H3L)(H2O)]·H2O)
4 ([Pb2(HL)]·H2O)
13.7
26.4
5.8
11.97
25.6
6.5
25–370
25–400
25–185
25–100
43.56
34.7
40.4
26.4
47.67
35
39.61
—
370–1000
400–850
310–600
360–640
42.74
38.9
53.8
71
40.36
39.4
53.82
—
1.7
2.2
between 150 and 370 °C, presumably corresponds to the loss mation vibration) and the strong band at 1647 cm−1 observed
of the coordinating water molecules. for 1 and 2 corresponds to deformation vibrations of the water
For each compound, the thermogravimetric analysis leads molecules. This band can be also be observed in the spectrum
to a sum formula which is in good agreement with the results of 3, but as expected from the composition with much smaller
of the structure determination. A detailed comparison between intensity.
calculated and measured values is given in Table 3. These
results are further confirmed by elemental analyses.
The full assignment of the bands corresponding to the
–SO3 and –PO3 groups is not straightforward, but trends are
visible. The S–O and P–O stretching vibrations are anticipated
3.8 IR-spectroscopy
between 1000 and 1300 cm−1 22
. In comparison to the bands
observed in H5L many shifts and changes in intensity are
observed due to the coordination of these functional groups,
the different degrees of protonation and their involvement in
hydrogen bonding (section S5†). For compound 4 only one
broad band is observed in this region which is in line with its
crystal structure, i.e. the full deprotonation of the acid func-
tions and the involvement of all oxygen atoms in the coordi-
nation of the Pb2+ ions (Fig. 6d).
The IR spectra of the title compounds and the linker molecule
H5L are shown in Fig. 12. The complete assignment of the
bands is given in Table S11†22 and selected bands are dis-
cussed in this section. For the linker molecule, the strong and
broad absorption bands between 3000 and 2000 cm−1 can be
assigned to the OH-stretching vibration of the sulfonic and
phosphonic acid groups. In the structures of the CPs this
group are partially or fully deprotonated, which leads to lower
intensities or the absence of these bands in the IR spectra.
Other broad adsorption bands between 3660 and 3100 cm−1
can be assigned to the OH-valence vibration of the water mole-
cules. An assignment of the bands to coordinating and non-
coordinating water molecules is not possible since the water
molecules are involved in hydrogen bonding (section S5†).
Nevertheless, the intensity of these bands correlates with the
amount of water molecules found within the structures via
SCXRD and TG analysis. The weak bands at 1413 and
1431 cm−1 can be assigned to the P–CH2–R-groups (CH2 defor-
4. Conclusions
The use of the new polyfunctional linker molecule
(CH2PO3H2)2N-CH2C6H4SO3H led to the discovery of four new
coordination polymers. While compounds 1 and 2 exhibit
layered structures, for compound 3 and 4 3D-framework struc-
tures are observed. The latter is a result of coordinating sulfo-
nate groups, connecting two and four metal ions, respectively.
Both framework compounds are potentially porous and perma-
nent porosity was confirmed for 4 by water sorption measure-
ments. In addition to the synthetic study and the crystal struc-
ture determinations presented herein, the full characterization
of all title compounds is given.
The inclusion of a sulfonic acid group in linker molecules
containing the (H2O3PCH2)2N– moiety can result in the for-
mation of 3D CPs due to the coordination of the –SO3 group.
However, when the sulfonate group does not coordinate to the
metal ions, the resulting structure resembles the layered,
interdigitated motifs found for linker molecules containing
the (H2O3PCH2)2N– moiety and –H, –CH3, –F, –COOH
functions.
Thus, the compounds presented herein are excellent
examples for inorganic–organic hybrid materials with
mixed functionalities. We have demonstrated that the use
of these linker molecules can lead to the formation of free
acid functionalities and porous materials. The anticipation
of the structural motif remains a challenging task due to
Fig. 12 IR spectra of H5L and the title compounds.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2020

View Article Online
Dalton Transactions
Paper
the many unknown factors which control the formation of
the final structure. Nevertheless, the reported title com-
pounds will contribute to a better understanding of the
A. Peraio and T. Rega, Solid State Ionics, 1995, 77, 229–233;
(d) G. Alberti, Solid State Ionics, 1996, 84, 97–104;
(e) R. M. P. Colodrero, P. Olivera-Pastor, E. R. Losilla,
D. Hernández-Alonso, M. A. G. Aranda, L. Leon-Reina,
J. Rius, K. D. Demadis, B. Moreau, D. Villemin,
M. Palomino, F. Rey and A. Cabeza, Inorg. Chem., 2012, 51,
7689–7698; (f) J. M. Taylor, K. W. Dawson and
G. K. H. Shimizu, J. Am. Chem. Soc., 2013, 135, 1193–1196.
8 G. Alberti, U. Costantino, F. Marmottini, R. Vivani and
P. Zappelli, Angew. Chem., Int. Ed. Engl., 1993, 32, 1357–
1359.
chemistry
of
metal
phosphonates
and
metal
phosphonatosulfonates.
Conflicts of interest
There are no conflicts to declare.
9 K. Adil, Y. Belmabkhout, R. S. Pillai, A. Cadiau, P. M. Bhatt,
A. H. Assen, G. Maurin and M. Eddaoudi, Chem. Soc. Rev.,
2017, 46, 3402–3430.
Acknowledgements
The authors would like to thank Inke Jeß for the collection of
single-crystal X-ray data and Prof. Christian Näther for helpful
comments concerning the structure elucidations. E. S. G and
A. K. I acknowledge support from the Swedish Foundation for
Strategic Research. Financial support by the Deutsche
Forschungsgemeinschaft (DFG, SPP 1928) is gratefully
acknowledged.
10 (a) W.-Q. Kan, J.-F. Ma, Y.-Y. Liu, J. Yang and B. Liu,
CrystEngComm, 2012, 14, 2268; (b) Q. Yue, J. Yang, G.-H. Li,
G.-D. Li and J.-S. Chen, Inorg. Chem., 2006, 45, 4431–4439;
(c) K. D. Demadis, Z. Anagnostou, A. Panera, G. Mezei,
M. V. Kirillova and A. M. Kirillov, RSC Adv., 2017, 7, 17788–
17799; (d) N. Hermer and N. Stock, Dalton Trans., 2015, 44,
3720–3723; (e) T. Rhauderwiek, H. Zhao, P. Hirschle,
M. Döblinger, B. Bueken, H. Reinsch, D. de Vos, S. Wuttke,
U. Kolb and N. Stock, Chem. Sci., 2018, 9, 5467–5478.
11 (a) R. M. P. Colodrero, G. K. Angeli, M. Bazaga-Garcia,
P. Olivera-Pastor, D. Villemin, E. R. Losilla, E. Q. Martos,
G. B. Hix, M. A. G. Aranda, K. D. Demadis and A. Cabeza,
Inorg. Chem., 2013, 52, 8770–8783; (b) M. Feyand,
C. F. Seidler, C. Deiter, A. Rothkirch, A. Lieb, M. Wark and
N. Stock, Dalton Trans., 2013, 42, 8761–8770; (c) M. Taddei,
F. Costantino, A. Ienco, A. Comotti, P. V. Dau and
S. M. Cohen, Chem. Commun., 2013, 49, 1315–1317.
12 N. Stock, Microporous Mesoporous Mater., 2010, 129, 287–
295.
References
1 G. Yücesan, Y. Zorlu, M. Stricker and J. Beckmann, Coord.
Chem. Rev., 2018, 369, 105–122.
2 S. J. I. Shearan, N. Stock, F. Emmerling, J. Demel,
P. A. Wright, K. D. Demadis, M. Vassaki, F. Costantino,
R. Vivani, S. Sallard, I. Ruiz Salcedo, A. Cabeza and
M. Taddei, Crystals, 2019, 9, 270.
3 M. Taddei, F. Costantino and R. Vivani, Eur. J. Inorg. Chem.,
2016, 2016, 4300–4309.
4 (a) B. Wang, T. Rhauderwiek, A. K. Inge, H. Xu, T. Yang,
Z. Huang, N. Stock and X. Zou, Chem. – Eur. J., 2018, 24, 13 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Adv., 2015,
17429–17433; (b) P. Ramaswamy, N. E. Wong, B. S. Gelfand 71, 3–8.
and G. K. H. Shimizu, J. Am. Chem. Soc., 2015, 137, 7640– 14 G. M. Sheldrick, Acta Crystallogr., Sect. C: Struct. Chem.,
7643; (c) J. M. Taylor, R. Vaidhyanathan, S. S. Iremonger 2015, 71, 3–8.
and G. K. H. Shimizu, J. Am. Chem. Soc., 2012, 134, 14338– 15 O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard
14340.
and H. Puschmann, J. Appl. Crystallogr., 2009, 42,
339–341.
5 A. Clearfield and K. Demadis, Metal Phosphonate Chemistry.
From Synthesis to Applications, Royal Society of Chemistry, 16 A. Hubbuch, R. Bindewald, J. Föhles, V. K. Naithani and
2012. H. Zahn, Angew. Chem., 1980, 92, 394–395.
6 (a) E. Armakola, R. M. P. Colodrero, M. Bazaga-García, 17 K. Moedritzer and R. R. Irani, J. Org. Chem., 1966, 31, 1603–
I. R. Salcedo, D. Choquesillo-Lazarte, A. Cabeza, 1607.
M. V. Kirillova, A. M. Kirillov and K. D. Demadis, Inorg. 18 (a) Y.-Q. Guo, S.-F. Tang, B.-P. Yang and J.-G. Mao, J. Solid
Chem., 2018, 57, 10656–10666; (b) K. D. Demadis,
E. Armakola, K. E. Papathanasiou, G. Mezei and
A. M. Kirillov, Cryst. Growth Des., 2014, 14, 5234–5243;
(c) K. D. Demadis, A. Panera, Z. Anagnostou, D. Varouhas,
A. M. Kirillov and I. Císařová, Cryst. Growth Des., 2013, 13,
4480–4489.
7 (a) Y. Zorlu, D. Erbahar, A. Çetinkaya, A. Bulut, T. S. Erkal,
A. O. Yazaydin, J. Beckmann and G. Yücesan, Chem.
Commun., 2019, 55, 3053–3056; (b) M. D. Allendorf,
C. A. Bauer, R. K. Bhakta and R. J. T. Houk, Chem. Soc. Rev.,
2009, 38, 1330–1352; (c) M. Casciola, U. Costantino,
State Chem., 2008, 181, 2713–2718; (b) Z.-M. Sun, J.-G. Mao
and Z.-C. Dong, Polyhedron, 2005, 24, 571–577;
(c) Z.-M. Sun, J.-G. Mao, Y.-Q. Sun, H.-Y. Zeng and
A. Clearfield, New J. Chem., 2003, 27, 1326; (d) Z.-M. Sun,
J.-G. Mao, B.-P. Yang and S.-M. Ying, Solid State Sci., 2004,
6, 295–300; (e) Z.-M. Sun, B.-P. Yang, Y.-Q. Sun, J.-G. Mao
and A. Clearfield, J. Solid State Chem., 2003, 176, 62–68;
(f) R. Vivani, F. Costantino, M. Nocchetti and G. D. Gatta,
J. Solid State Chem., 2004, 177, 4013–4022; (g) R. Zeng,
X. Fu, Y. Sui, X. Yang, M. Sun and J. Chen, J. Organomet.
Chem., 2008, 693, 2666–2672; (h) Y.-Y. Zhu, Z.-G. Sun,
This journal is © The Royal Society of Chemistry 2020
Dalton Trans.

View Article Online
Paper
F. Tong, Z.-M. Liu, C.-Y. Huang, W.-N. Wang, C.-Q. Jiao,
Dalton Transactions
4, 49892–49899; (e) J.-L. Song and J.-G. Mao, J. Mol. Struct.,
2005, 740, 181–186; (f) S.-F. Tang, J.-L. Song and J.-G. Mao,
Eur. J. Inorg. Chem., 2006, 2006, 2011–2019; (g) W. Zhou,
J. Zhang, Z.-G. Sun, Y.-Y. Zhu, C.-Q. Jiao, S.-P. Shi, L.-L. Dai,
T. Sun, W.-Z. Li, M.-X. Ma and H. Luo, Inorg. Chem.
Commun., 2014, 47, 37–41; (h) W. Zhou, Y.-Y. Zhu,
C.-Q. Jiao, Z.-G. Sun, S.-P. Shi, L.-L. Dai, T. Sun, W.-Z. Li,
M.-X. Ma and H. Luo, CrystEngComm, 2014, 16, 1174.
C.-L. Wang, C. Li and K. Chen, Dalton Trans., 2011, 40,
5584–5590; (i) Z.-M. Sun, J.-G. Mao and Z.-C. Dong,
Polyhedron, 2005, 24, 571–577; ( j) Z.-M. Sun, B.-P. Yang,
Y.-Q. Sun, J.-G. Mao and A. Clearfield, J. Solid State Chem.,
2003, 176, 62–68; (k) H. Xu, H. Zhou, L. Feng, Q. Wang,
R. Chen, W. Huang and X. Wu, Dalton Trans., 2018, 47,
11226–11238.
19 (a) S. Bauer, T. Bein and N. Stock, Inorg. Chem., 2005, 44, 20 M. J. Turner, J. J. McKinnon, S. K. Wolff, D. J. Grimwood,
5882–5889; (b) S. Bauer, J. Marrot, T. Devic, G. Férey and
N. Stock, Inorg. Chem., 2007, 46, 9998–10002; (c) H. Luo,
P. R. Spackman, D. Jayatilaka and M. A. Spackman,
CrystalExplorer17, 2017.
C. Ma, C.-Q. Jiao, Z.-G. Sun, T. Sun, M.-X. Ma, Y.-Y. Zhu, 21 M. A. Spackman and D. Jayatilaka, CrystEngComm, 2009,
W.-Z. Li, M.-L. Wang and X.-W. Zhang, New J. Chem., 2015, 11, 19–32.
39, 6611–6622; (d) H. Luo, Y.-Y. Zhu, Z.-G. Sun, C.-Q. Jiao, 22 George Socrates, Infrared and Raman Characteristic
G.-N. Zhang, T. Sun, M.-X. Ma and W.-Z. Li, RSC Adv., 2014, Frequencies: Tables and Charts, Wiley, 2004.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2020