Alkali- and alkaline-earth metal–organic networks based on a tetra(4-carboxyphenyl)bimesitylene-linker

Article abstract of DOI:10.1016/j.poly.2019.114128

Four new 3D-metal–organic and supramolecular frameworks based on the 3,3′,5,5′-tetrakis(4-carboxyphenyl)-2,2′,4,4′,6,6′-hexamethyl-1,1′-biphenyl ligand (H₄L) namely: [Na₂(H₄L)(H₂L)(DMF)₂(H₂

Full text of DOI:10.1016/j.poly.2019.114128

Polyhedron 173 (2019) 114128
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Alkali- and alkaline-earth metal–organic networks based on a
tetra(4-carboxyphenyl)bimesitylene-linker
Lucian Gabriel Bahrin a, Dana Bejan a, Sergiu Shova a, Maria Gdaniec b, Marek Fronc c, Vasile Lozan a,d,
,
⇑
Christoph Janiak e,
⇑
a ‘‘Petru Poni” Institute of Macromolecular Chemistry, Aleea Gr. Ghica Voda 41A, RO 700487 Iasi, Romania
b Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b, 61-614 Poznan, Poland
c Slovak University of Technology, Faculty of Chemical and Food Technology, Institute of Physical Chemistry and Chemical Physics, Radlinského 9, SK-812 37 Bratislava, Slovakia
d Institute of Chemistry of MECR, Academiei Str. 3, MD2028 Chisinau, Republic of Moldova
e Institut für Anorganische Chemie und Strukturchemie, Heinrich-Heine-Universität Düsseldorf, Universitätsstr. 1, D 40225 Düsseldorf, Germany
a r t i c l e i n f o
a b s t r a c t
Four new 3D-metal–organic and supramolecular frameworks based on the 3,30,5,50-tetrakis(4-car-
boxyphenyl)-2,20,4,40,6,60-hexamethyl-1,10-biphenyl ligand (H4L) namely: [Na2(H4L)(H2L)(DMF)2(H2O)2]n
(1), 2[Mg(H2O)6]ꢀ2H3LꢀH2L (2), [Mg2L(DMF)2(H2O)]ꢀ2.5DMF (3), and 2[Ca(H2L)(H2O)4.5(DMF)0.5]ꢀ[Ca(H2L)
(H2O)5]nꢀ2H2O (4) were obtained and fully characterized. The sodium ion in compound 1 is coordinated
by six oxygen atoms in a distorted octahedral geometry, with the oxygen atoms provided by four mon-
odentate carboxylate groups, one water and one DMF molecule. The polycarboxylate ligand acts as a
bridge between four Na ions to form an extended 3D coordination network with (4,4) topology. In com-
pound 2 two crystallographically independent [Mg(H2O)6]2+ complex cations and three non-coordinated
mono- and doubly deprotonated tetracarboxylic acid molecules form a 3D supramolecular network
consolidated by a multiple system of OAHꢀ ꢀ ꢀO hydrogen bonds. Compound 3 consists of two Mg2+ cations,
one L4ꢁ tetra-anion, two coordinated DMF molecules and one aqua ligand to form a 3D coordination
polymer. The crystal structure of compound 4 includes three crystallographically independent and
chemically non-equivalent molecular entities: two molecular complexes [Ca(H2L)(H2O)4.5(DMF)0.5] and
a coordination-polymeric helical strand of repeating formula unit [Ca(H2L)(H2O)5]n. The crystal structure
of compound 4 is described as a supramolecular architecture where 1D coordination polymers [Ca(H2L)
(H2O)5]n and two molecular units [Ca(H2L)(H2O)4.5(DMF)0.5] are linked through numerous intermolecular
H-bonds.
Article history:
Received 26 June 2019
Accepted 21 August 2019
Available online 26 August 2019
Keywords:
Tetra(4-carboxyphenyl)bimesitylene
Alkaline metal
Alkaline earth metal
Metal–organic framework
Supramolecular network
Ó 2019 Elsevier Ltd. All rights reserved.
1. Introduction
ous structure with 5-fold interpenetration. When reacted with
copper(II), it forms three-dimensional metal–organic frameworks
Metal–organic frameworks (MOFs) are hybrid organic–inor-
ganic porous materials consisting of metal nodes or clusters,
known as secondary building units, bridged together by organic
linkers [1,2]. Depending on the nature of the organic linkers and
the metals used, MOFs can in theory be tailor-made for a specific
purpose. Amongst the many organic di- and tricarboxylate bridg-
ing ligands, also tetracarboxylate ligands are more and more
employed for constructing stable MOFs with permanent porosity
[3]. The robust organic framework formed by 3,30,5,50-tetrakis-(4-
carboxyphenyl)-1,10-biphenyl (H4BFTC) (cf. Fig. 1) [4] has a 3D por-
which exhibit double- and non-interpenetrated structures that
can be used for separation of gases [5–7]. The Zn and Cd porous
coordination polymers with derivatives of BFTC were employed
as efficient catalysts for the acetylation of phenols [8]. By using a
post-synthetic metal exchange in anionic Cd–MOF with derivatives
of BFTC, a series of isostructural MOFs containing different metal
ions with varying ionic radii have been characterized [9]. A design
strategy based on the geometric analysis of the tetratopic linker
shape and flexibility was developed to achieve predictable differ-
ent topologies of Zr–MOFs [10,11]. A series of three-dimensional
MOFs of copper(II) and zinc(II) based on derivatives of BFTC show
different framework structures and topologies [12–14]. The unique
partially interpenetrated metal–organic framework formed
by BFTC4ꢁ with indium(III) represents a new class of dynamic
⇑
Corresponding authors at: Institute of Chemistry of MECR, Academiei Str. 3,
MD2028 Chisinau, Republic of Moldova (V. Lozan).
E-mail addresses: vasilelozan@gmail.com (V. Lozan), janiak@hhu.de (C. Janiak).
https://doi.org/10.1016/j.poly.2019.114128
0277-5387/Ó 2019 Elsevier Ltd. All rights reserved.

2
L.G. Bahrin et al. / Polyhedron 173 (2019) 114128
2. Experimental
2.1. Analysis and physical measurements
All reactions were performed using standard Schlenk techniques
under a nitrogen atmosphere. Solvents were dried by standard pro-
cedures. All materials were purchased from commercial suppliers
and used as received. Thermogravimetric (TG) measurements were
performed using a STA 449F1 JUPITER (Netzsch, Germany) device.
Temperature and sensitivity calibrations in the temperature range
of 30–700 °C were carried out with indium. About 5.0 mg of the
solid samples were weighed and placed in alumina pans for TG
measurements. The temperature range used was between 30 and
700 °C with a heating rate of 5–10 °C minꢁ1, under an atmosphere
of dry nitrogen at a flow rate of 50 mL minꢁ1. The data were pro-
cessed with the NETZSCH PROTENS 4.2 software. Infrared (IR) spec-
tra were recorded on a BRUKER VERTEX 70 FTIR spectrometer
(Bruker Optics, Germany). The measurements were performed in
ATR (Attenuated Total Reflectance) mode in the 600–4000 cmꢁ1
range at room temperature with a resolution of 4 cmꢁ1 and accu-
mulation of 64 scans. C, H, N elemental analysis was performed
on a VARIO-EL-III elemental analyzer. Nitrogen sorption experi-
ments were carried out with a Quantrachrome NOVA volumetric
gas sorption instrument. Prior to N2 isotherm measurements at
77 K, samples were outgassed under a high vacuum. For the sorp-
tion measurements, 40–70 mg of the synthesized samples were
weighed and degassed at 150 °C under high vacuum for 6 h.
Fig. 1. The chemical structure with the spatial arrangement of 3,30,5,50-tetrakis(4-
carboxyphenyl)-2,20,4,40,6,60-hexamethyl-1,10-biphenyl
H4BFTC.
– H4L, a derivative of
materials that undergoes pronounced framework phase transitions
on desolvation [15].
When it comes to alkaline earth metals, only one MOF, formed
by BFTC with Ba2+ ions, is known. This structure was shown to have
1D channels with a diameter of 15.1 Å [16]. Thus, most of the cur-
rent research on the BFTC linker and its derivatives is focused on
MOFs with transition metal or rare earth ions. The use of the alka-
line earth metal ions in MOFs at large is less explored but has
recently received more attention. Alkaline earth metal ions have
a relatively large radius and are strongly oxophilic, providing
unique opportunities for the formation of diverse inorganic–
organic hybrids exhibiting rich structural topologies, good thermal
stabilities, and interesting properties [16].
Over the last decade, many researchers have focused their
attention on the synthesis of metal–organic networks with alkaline
and alkaline earth metals, because they play an important role in
nature and find application as materials in a wide range of fields:
catalysts, ferroelectrics, metallic conductors and superconductor
materials [17]. Thereby, a few alkaline earth metal complexes with
2,20,6,60-tetracarboxybiphenyl have been synthesized, and these
species exhibit good water stability and proton conductivity, and
are also highly thermally stable [18]. The other four 3D frame-
works of Ba(II) and Ca(II) based on benzene-1,2,4,5-tetracarboxylic
acid and its derivative reveal high thermal stability, and the com-
pounds also possess photoluminescent properties [19].
Under mild solvothermal conditions 3D MOFs have been syn-
thesized based on alkaline earth metal ions and aromatic car-
boxylic linkers. The crystal structures of these MOFs show
intriguing physical features such as chirality or large voids occu-
pied by solvent molecules, and also persistent photoluminescence,
which lasts for seconds [20].
Our interest in MOFs prompted us to investigate the use of the
tetrahedral bimesitylene core in the synthesis of multitopic
organic ligands [21]. Recently, one such linker, namely 3,30,5,50-
tetrakis(4-carboxyphenyl)-2,20,4,40,6,60-hexamethyl-1,10-biphenyl
(H4L, Fig. 1), was used to obtain two new structures incorporating
Zr and Hf secondary building units which demonstrated the nega-
tive linear compressibility without changing the network topology
and structure [22].
2.2. Synthesis of the ligand 3,30,5,50-tetrakis(4-carboxyphenyl)-
2,20,4,40,6,60-hexamethyl-1,10-biphenyl (H4L)
To a solution of potassium carbonate (3.04 g, 22.0 mmol) in
water (10.0 mL), ethanol (10.0 mL) and 1,4-dioxane (20.0 mL) were
added. Nitrogen was then bubbled for 15 min into the resulting
mixture, followed by the addition of 3,30,5,50-tetraiodobimesityl
(0.74 g, 1.0 mmol), 4-carboxyphenylboronic acid (0.90 g,
5.40 mmol) and tetrakis (triphenyl-phosphine)palladium(0) (0.2 g,
0.17 mmol). The mixture was refluxed for 48 hours under a nitro-
gen atmosphere and then filtered in order to remove the black solid
that formed. To the filtrate, water (100 mL) was added, followed by
the addition of 37% hydrochloric acid, until the pH of the solution
was 1–2. The precipitate thus formed was suction-filtered, washed
thoroughly with water and once more suspended in water
(100 mL). To the suspension, 20% ammonium hydroxide was added
until the precipitate dissolved and the pH of the mixture was 9–10.
The slightly opalescent solution was then kept under mechanical
stirring for 30 min and filtered through a fine filter paper. The clear
filtrate was acidified using 37% hydrochloric acid, until the pH was
1–2. The formed, white precipitate was suction-filtered, washed
thoroughly with water, acetone (5–10 mL) and air-dried. Yield
0.65 g (90%). 1H NMR (400 MHz, DMSO-d6): d 12.98 (bs, 4H),
8.05–7.99 (m, 8H), 7.39–7.31 (m, 8H), 1.65 (s, 12H), 1.63 (s, 6H)
ppm. 13C NMR (100 MHz, DMSO-d6): d 167.6, 146.5, 139.6, 138.6,
132.3, 131.4, 130.5, 130.1, 129.8, 19.5, 18.6 ppm. Elemental analysis
Calc (%) for C46H38O8 (M = 718 79 g/mol): C, 76.86; H, 5.33; found:
C, 76.82; H, 5.30. IR (ATR):
m
(cmꢁ1) = 3417(m), 3070(m), 3037
(m), 2998(m), 2922(m), 2659(m), 2547(m), 1693(s), 1607(s), 1564
(m), 1510(w), 1408(s), 1272(s), 1175(s), 1102(m), 1017(m), 860
(m), 783(m), 738(m), 715(m), 543(w), 514(w).
In the present contribution, we report the synthesis and charac-
terization of four new metal–organic networks by using 3,30,5,50-
tetrakis(4-carboxyphenyl)-2,20,4,40,6,60-hexamethyl-1,10-biphenyl
as linker (Fig. 1) and the main-group metals Na, Mg and Ca as
nodes.
2.3. Synthesis of the coordination polymers
2.3.1. Synthesis of [Na2(H4L)(H2L)(DMF)2(H2O)2]n (1)
To a solution of H4L (72.0 mg, 0.10 mmol) in DMF (5.0 mL), in a
20 mL screw-cap vial was added NaNO3 (68.0 mg, 0.80 mmol)

L.G. Bahrin et al. / Polyhedron 173 (2019) 114128
3
dissolved in water (0,5 mL) at room temperature. The vial was
sealed and mixture was kept under static conditions for 3 days at
80 °C. After cooling, the colorless crystalline needles were collected
by filtration and washed with DMF. Finally, the crystals were dried
at room temperature (66 mg, Yield 79%). Elemental analysis Calc.
(%) for C98H92N2O20Na2 (M = 1663.76 g/mol): C, 70.75; H, 5.57; N,
for 100 s over 1° scan width. Data processing was carried out using
the CRYSALIS package [24]. The relatively high Rint values for 1, 2 and
4 are solely caused by the not very good quality and low diffraction
capacity of the MOF-type crystals with large volumes of disordered
solvent molecules. The structures were solved by direct methods
using OLEX2 [25] and refined by full-matrix least-squares on F2 with
1.68; found: C, 70.78; H, 5.53; N, 1.65. IR (ATR):
m
(cmꢁ1) = 3432
SHELXL-2015 [26] using an anisotropic model for non-hydrogen atoms.
(s), 2924(m), 2505(w), 1940(w), 1699(s), 1668(s), 1607(s), 1585
(s), 1538(s), 1388(s), 1311(s), 1270(s), 1173(m), 1102(m), 1016
(m), 863(w), 784(m), 718(w), 524(w).
All C-bonded
H atoms were placed in idealized positions
(dCH = 0.96 Å) and refined using the riding model with Uiso(H) = x
Ueq(C) where x = 1.5 for methyl H atoms and x = 1.2 in the other
cases. Positions of the H atoms of COOH groups were deduced from
the geometry of the carboxylic groups and the analysis of inter-
molecular interactions. Whenever necessary, restraints were
imposed on geometry and displacement parameters of disordered
molecules. For 1, which crystallizes in the Sohnke P21212 space
group, inversion twinning was checked by the refinement of the
BASF parameter, however the value of 0.5(3) gave no conclusive
answer. All crystal structures contained large areas filled with
strongly disordered solvent molecules that could not be modeled
using atomic sites. For 1–3 the Mask option of OLEX2 was used to
model the contribution of disordered solvent molecules to struc-
ture factors. In 1 where the solvent accessible volume is 18% of
the unit-cell volume and the highest residual peak was 0.5 eÅ3,
the use of the Mask option in the refinement process reduced the
R1 factor from 0.0736 to 0.0668. In 2 and 3 the effect of using this
option was much stronger as the R1 values dropped from 0.235 to
0.0959 and from 0.199 to 0.0888, respectively. All crystal struc-
tures were checked for possible twinning by pseudomerohedry
but only crystals of 4 exhibited this kind of twinning with the twin
components related by 180° rotation about the [1 0 0] direct lattice
direction. The twin component ratio refined at 0.76:0.24. A disor-
dered solvent contribution for 4, due to crystal twinning, was
extracted from structure factors using the SQUEEZE routine of
PLATON [26]. The use of SQUEEZE routine led to the reduction of
the R1 factor from 0.1353 to 0.0848. This program generated a
modified hkl file that was subsequently used for the refinement
with SHELXL-2015. For calculations with Mask or SQUEEZE routines the
probe radius of 1.2 Å and a resolution of 0.2 Å were applied. Exactly
the same values of parameters were employed in the calculation of
the solvent accessible areas in 1–4 using OLEX2. The molecular plots
were obtained with the OLEX2 program. The crystallographic data
and refinement details are given in Table 1.
2.3.2. Synthesis of 2[Mg(H2O)6]ꢀ2H3LꢀH2L (2)
To a solution of H4L (72.0 mg, 0.10 mmol) in DMF (4.0 mL) in a
20 mL screw-cap vial was added Mg(NO3)2ꢀ6H2O (200.0 mg,
0.80 mmol) dissolved in water (2 mL) at room temperature. The
vial was sealed and mixture was kept under static conditions for
3 days at 80 °C. After cooling, the colorless crystalline needles were
collected by filtration and washed with DMF. Finally, the crystals
were dried at room temperature (65 mg, Yield 81%). Elemental
analysis Calc. (%) for
68.57; H, 5.59; found: C, 68.54; H, 5.57. IR (ATR):
C
138H134O36Mg2 (M = 2417.13 g/mol): C,
m
(cmꢁ1) = 3439
(s), 2923(m), 1666(s), 1607(s), 1584(s), 1536(s), 1391(s), 1311
(m),1258(s), 1173(m), 1102(m), 1016(m), 864(m), 784(m), 718
(m), 664(m), 521(w).
2.3.3. Synthesis of [Mg2L(DMF)2(H2O)]ꢀ2.5DMF (3)
To a solution of H4L (72.0 mg, 0.10 mmol) in dry DMF (4.0 mL),
in a 20 mL screw-cap vial was added Mg(NO3)2ꢀ6H2O (100.0 mg,
0.40 mmol) and acetic anhydride (60 lL, 0.6 mmol) at room tem-
perature. The vial was sealed and mixture was kept under static
conditions for 2 days at 120 °C. After cooling, the colorless crys-
talline blocks were collected by filtration and washed with DMF.
Finally, the crystals were dried at room temperature (75 mg, Yield
81%). Elemental analysis Calc. (%) for
(M = 1104.32 g/mol): C, 64.17; H, 6.16; N, 5.68; found: C, 64.14;
H, 6.17, N, 5.69. IR (ATR):
(cmꢁ1) = 3405(s), 2926(m), 1662(s),
C59.5H67.5Mg2N4.5O13.5
m
1606(s), 1588(s), 1537(s), 1388(s), 1255(m), 1102(m), 1016(m),
795(m), 757(m), 724(m), 457(w).
2.3.4. Synthesis of 2[Ca(H2L)(H2O)4.5(DMF)0.5][Ca(H2L)(H2O)5]nꢀ2H2O
(4)
To a solution of H4L (72.0 mg, 0.10 mmol) in DMF (4.0 mL) in a
20 mL screw-cap vial was added CaCl2 (88.7 mg, 0.80 mmol) dis-
solved in water (2 mL) at room temperature. The vial was sealed
and mixture was kept under static conditions for 3 days at 80 °C.
After cooling, the colorless crystalline needles were collected by fil-
tration and washed with DMF. Finally, the crystals were dried at
room temperature (74 mg, Yield 85%). Elemental analysis Calc.
(%) for C141H149O41NCa3 (M = 2633.94 g/mol): C, 64.30; H, 5.70;
3. Results and discussion
3.1. Synthesis
Although the synthesis of H4L was previously reported [21], a
different route, involving the Suzuki coupling of 3,30,5,50-
tetraiodobimesitylene with 4-carboxyphenylboronic acid, was
used here (Scheme 1). The reaction was performed using potas-
sium carbonate as a base and a mixture of water, ethanol and diox-
ane as solvent, to afford H4L in a 90% yield (Lit. 82%).
N, 0.53; found: C, 64.42; H, 5.78; N, 0.52. IR (ATR):
m )
(cmꢁ1
= 3446(m), 2924(m), 1658(s), 1607(s), 1586(s), 1538(s), 1396(s),
1312(m), 1257(s), 1173(m), 1102(m), 1016(m), 863(m), 784(m),
718(m), 670(m), 526(w).
2.4. Single crystal X-ray diffraction
The solvothermal reaction of H4L with NaNO3 in a mixture of
DMF/H2O at 80 °C for 72 h, followed by a period of seven days at
room temperature, yielded crystals of 1 in the form of colorless
needles (Scheme 2). By using Mg(NO3)2ꢀ6H2O or CaCl2 instead of
NaNO3, colorless needles of 2 and 4 were obtained after 72 h at
80 °C. Because 2 was obtained as a supramolecular framework,
where the Mg2+ nodes are coordinated by water molecules, we
speculated that by eliminating the water from the synthesis, a
new compound might be obtained with a different crystal struc-
ture. This was achieved by using only dry DMF as a solvent and
by adding a drop of acetic anhydride to the reaction mixture, which
should, in theory, react with the water molecules of the metal salt.
X-ray diffraction measurements for compounds 1, 2 and 4 were
performed on a STOE STADI VARI diffractometer, by microsource
Cu Ka radiation (k = 1.54186 Å) at 100 K. The crystals were posi-
tioned at a distance of 40 mm from the detector and 9362, 9569
and 9613 frames were recorded for 1, 2 and 4, respectively. The
data were processed using STOE X-RED32 [23] software package.
Diffraction data for compound 3 were collected with an Oxford-
Diffraction XCALIBUR E diffractometer using graphite-monochro-
mated Mo K
a radiation. The crystal was positioned at a distance
of 40 mm from the detector and 516 frames were recorded each

4
L.G. Bahrin et al. / Polyhedron 173 (2019) 114128
Table 1
Crystal data and details of data collection for 1–4.
Compound
[Na2(H4L)(H2L)
(DMF)2(H2O)2]n (1)
2[Mg(H2O)6]ꢀ
2H3LꢀH2L (2)
[Mg2L(DMF)2(H2O)]ꢀ
2.5DMF (3)
2[Ca(H2L)(H2O)4.5(DMF)0.5]
[Ca(H2L)(H2O)5]nꢀ2H2O (4)
Empirical formula
Fw
Space group
C
98H92N2Na2O20
C138H134Mg2O36
2417.06
Pnnm
C59.5H67.5Mg2N4.5O13.5
C141H149Ca3NO41
2633.84
P21/c
1663.71
P21212
1110.30
ꢁ
P 1
Unit cell dimensions
a (Å)
b (Å)
c (Å)
a (°)
b (°)
g (°)
V (Å3)
Z
7.16510(10)
23.9148(5)
29.7829(5)
90
90
90
5103.36(15)
2
1.083
21.2563(3)
23.9889(4)
36.9208(6)
90
90
90
18826.5(5)
4
0.853
16.0786(10)
16.60111(11)
16.8145(11)
108.474(6)
105.860(5)
105.663(5)
3771.4(5)
2
22.37240(10)
23.90450(10)
35.8723(2)
90
107.9450(8)
90
18251.27(15)
4
0.959
Dcalc (g cmꢁ3
)
0.960
Crystal size (mm)
0.46 ꢂ 0.08 ꢂ 0.06
0.38 ꢂ 0.07 ꢂ 0.05
0.30 ꢂ 0.25 ꢂ 0.20
0.60 ꢂ 0.20 ꢂ 0.10
T (K)
100
100
180
100
l
(mmꢁ1
)
0.689
0.566
0.082
1.300
2
H
range
5.936–133.134
286 911
9046 [Rint = 0.1374]
9046/14/543
0.0668
4.798–130.174
590 834
16 039 [Rint = 0.1794]
16 039/0/803
0.0959
3.004–49.424
34 944
12 667 [Rint = 0.0619]
12 667/61/580
0.0888
5.53–133.202
999 338
32 575 [Rint = 0.1242]
32 575/8/1678
0.0848
Reflections collected
Independent reflections
Data/restraints/parameters
a
R1
b
wR2
0.2112
0.989
0.2992
1.001
0.2602
0.964
0.2191
1.046
GOFc
The highest peak before SQUEEZE
Largest difference peak/hole (e Åꢁ3
Void electron count (e)d
0.5
2.6
3.4
1.31
)
0.26/ꢁ0.27
0.36/ꢁ0.34
0.67/ꢁ0.70
0.69/ꢁ0.61
76.6
2048
516
1532
Void, solvent accessible volume (Å3),
% unit cell volumed
916.6, 18
8026, 42
1789, 47
5744, 31
Flack parametere
0.5(3)
–
–
–
a
b
c
R1
wR2 = {
GOF = {
=
R
||Fo| ꢁ |Fc||/
R|Fo|.
R
[w(F2o ꢁ F2c)2]/
R .
[w(F2o)2]}1/2
R
[w(Fo2 ꢁ Fc2)2]/(n ꢁ p)}1/2, where n is the number of reflections and p is the total number of parameters refined.
d
Recovered number of electrons in the void, solvent accessible volume; both found by using the ‘‘Solvent Mask” routine in OLEX2
.
HOOC
COOH
COOH
I
I
I
I
Pd(PPh3)4, K2CO3
90%
+ 4
B(OH)2
H4L
HOOC
Scheme 1. The synthesis of the ligand H4L.
COOH
Scheme 2. Overview on syntheses and formulae of compounds 1–4.

L.G. Bahrin et al. / Polyhedron 173 (2019) 114128
5
Fig. 2. Extended view of the asymmetric part and coordination environment around Na+ in 1 along with the atom labeling scheme; thermal ellipsoids are shown at the 40%
probability level. Symmetry generated fragments and an alternative position of the DMF molecule are shown semi-transparent. Symmetry codes: i = ꢁ0.5 + x, ꢁ0.5 ꢁ y,
ꢁ1 ꢁ z; ii = ꢁ1.5 + x, ꢁ0.5 ꢁ y, ꢁz.
Fig. 3. The three-dimensional framework in 1. (a) Ball-and-stick presentation and (b) space filling presentation viewed along the a axis; (c) ball-and-stick view along the b
axis; (d) topology of the binodal (4,4)-connected 3-periodic net in 1.

6
L.G. Bahrin et al. / Polyhedron 173 (2019) 114128
When the reaction was run at 80 °C for 72 h, no change could be
observed. However, by raising the temperature to 120 °C for 48 h,
prism-shaped colorless crystals of 3 formed.
can be associated with asymmetric COOꢁ vibration, and peaks at
1408–1388 cmꢁ1 – with symmetric COOꢁ vibration of the carboxy-
late groups. For compounds 1–4 there are broad bands between
3600 and 3200 cmꢁ1 corresponding to asymmetric and symmetric
OAH stretching vibrations of water molecules [27]. The moderate
intense bands between 1408 and 1388 cmꢁ1 can be associated
with symmetric deformation vibration of CH3-group.
3.2. Thermogravimetric analysis (TGA)
Thermogravimetric analysis of the synthesized materials was
performed to evaluate the thermal stability of the new synthesized
compounds. The thermograms of compounds 1–4 are given in
Figs. S6–S10, Supplementary material. Compound 1 suffers a
weight loss of 12% between 40 and 280 °C, which corresponds to
2 coordinated DMF molecules and 2 coordinated water molecules
(theor. 11%). The framework is stable up to around 370 °C, above
which it decomposes. When heated up to 280 °C, 2 undergoes a
weight loss of 13%, which corresponds to the 12 water molecules
(theor. 9%) that are coordinated to the two Mg2+ cations. Between
280 and 420 °C, compound 2 is stable, but begins to decompose
above 420 °C. Framework 3 suffers a weight loss of 26% between
40 and 280 °C, slightly less that the theoretical value of 31% corre-
sponding to the 4.5 DMF molecules and the one coordinated water
molecule. It is stable up to approximately 490 °C, but decomposes
when heated above this temperature. Framework 4 undergoes a
weight loss of 12% when heated up to 280 °C, which correlates to
the coordinated 0.5 DMF molecule and overall 16 water molecules
(theor. 12%), and is stable up to 400 °C, above which it decomposes.
3.4. Description of crystal structures
[Na2(H4L)(H2L)(DMF)2(H2O)2]n (1): X-ray crystallography
revealed that compound 1 possesses a 3D neutral porous frame-
work that consists of Na+ ion, neutral and doubly deprotonated
ligands H4L and H2L2ꢁ having crystallographically imposed C2 sym-
metry and one DMF and one water molecule (Fig. 2). The coordi-
nated DMF molecule is disordered over two sites with equal
occupancy. The sodium ion is coordinated by six oxygen atoms:
two from the carboxylic and two from the carboxylate groups,
one from water and one from the DMF molecule. The coordination
geometry around the metal center is distorted octahedral. All car-
boxylic or carboxylate groups of the H4L and H2L2ꢁ ligands act in a
monodentate mode. Each linker coordinates to four Na+ ions and
the metal ions are linked to four carboxylic/carboxylate ligands.
All carboxylic groups are involved in short OAHꢀ ꢀ ꢀO hydrogen
bonds to O atoms of the carboxylate groups, stabilizing the coordi-
nation environment around the metal ions. According to the
TOPOSPRO [28] analysis the tetratopic ligands bonded to sodium
ions generate a new type of 3-periodic net that is 4,4,4-connected
with (4-c)(4-c)(4-c)2 stoichiometry and {8^6} point symbol. The
crystal packing of 1 and the topology of the network are illustrated
in Fig. 3. As can be seen in Fig. 3 the [Na2(H4L)(H2L)(DMF)2(H2O)2]n
3.3. IR-spectroscopy
The infrared spectra of the ligand (H4L) and the four new frame-
works are similar and are given in Figs. S1–S5, in the Supplemen-
tary material. The strong absorption peaks at 1693–1607 cmꢁ1
Fig. 4. Extended asymmetric unit and the coordination environment of Mg2+ in 2. Labels are shown for selected atoms and thermal ellipsoids are drawn at the 30% probability
level. C-bonded H atoms are omitted for clarity. Symmetry generated atoms are shown semi-transparent. Symmetry codes: i = x, y, ꢁz; ii = ꢁ1 ꢁ x, 1 ꢁ y, z.

L.G. Bahrin et al. / Polyhedron 173 (2019) 114128
7
framework is potentially porous with wide channels directed along
the a and b-axis (filled with disordered solvent molecules; solvent
molecules not included into the structural model – see Section 2).
The channels encompass 18% of the crystal volume as calculated
with OLEX2 using the probe radius of 1.2 Å and 0.2 Å resolution of
the map.
neutral supramolecular framework. This hydrogen-bonded frame-
work of 2 is potentially porous with crossing channels of different
diameter parallel to the c and a axis (Fig. 5a and c) such that the
largest channels are directed along the a axis. The solvent-filled
or potentially empty channels occupy 42% of the crystal volume.
[Mg2L(DMF)2(H2O)]ꢀ2.5DMF (3): Modification of the reaction
conditions, which led to compound 2, by elimination of water from
the reaction system and raising the temperature to 120 °C resulted
in the product 3, that, as shown by X-ray crystallography, has a
framework with the formula [Mg2L(DMF)2(H2O)]n (Fig. 6). The
asymmetric part of the unit cell consists of two Mg2+ cations, one
L4ꢁ tetra-anion, two coordinated DMF molecules and one aqua
ligand. These entities form a 3D coordination polymer with the
L4ꢁ ligand bridging four metal clusters formed from two Mg2+
cations, four carboxylate groups and solvent molecules coordi-
nated to one of the metal centers. The Mg2+ ions are bridged by
2[Mg(H2O)6]ꢀ2H3LꢀH2L (2): In contrast to the 3D metal–ligand
network 1, the magnesium compound 2 is not a coordination poly-
mer (Fig. 4). The asymmetric part of 2 comprises two halves of the
centrosymmetric [Mg(H2O)6]2+ hexaaqua complex cations and 1.5
uncoordinated tetracarboxylic anions, one of which is doubly
deprotonated and located around the twofold symmetry axis and
the other is monodeprotonated and located in a general position.
The hexaaqua-coordinated cations have a typical octahedral struc-
ture with MgAO distances in the range 2.017(6) ꢃ 2.115(6) Å. Two
carboxylic groups of H3Lꢁ and two carboxylic groups of H2L2ꢁ
anions act as H-bond donors to the carboxylate groups or, in one
case, to the carboxylic group in strong charge-assisted OAHꢀ ꢀ ꢀO
hydrogen bonds. These connections generate two very similar
but symmetry independent 2D anionic networks parallel to the
(0 0 1) plane that are interpenetrated to a 2D net (Fig. 5). The inter-
penetrated networks are shifted by a vector of 7.4 Å. These anionic
2D-interpenetrated assemblies are bridged by hydrogen bonds
formed with the hexaaquamagnesium cations generating a 3D
two carboxylate groups acting in a
l
2-r2O:O0 mode and one COO2ꢁ
group coordinating in a
l
2-r3O,O0:O tridentate mode. The fourth
carboxylate group coordinates to Mg2 in a r2O,O0 bidentate-chelat-
ing mode. The Mg1ꢀ ꢀ ꢀMg2 separation is 3.501(3) Å. The coordina-
tion polyhedron of the two Mg ions is also different. The Mg1
metal center adopts a distorted octahedral coordination geometry
being coordinated by six oxygen atoms provided by three bridging
carboxylate ligands, two DMF ligands and one water molecule.
Fig. 5. (a and b) Two interpenetrated 2D anionic H-bonded networks viewed along the c axis in 2. (c and d) Three-dimensional supramolecular network with the [Mg
(H2O)6]2+ cations included via hydrogen bonds; (b) and d) are the space filling representation for (a) and c), respectively. Non-relevant H-atoms are omitted for clarity.

8
L.G. Bahrin et al. / Polyhedron 173 (2019) 114128
Considering that chelating carboxylate groups occupy only one
coordination position, the coordination geometry of Mg2 can be
described as distorted tetrahedral.
As illustrated in Fig. 6, each carboxylate group of the tetracar-
boxylate linker L4ꢁ is coordinated to a dinuclear magnesium unit
and, therefore, the crystal structure packing results in the
Fig. 6. Extended asymmetric unit and magnesium coordination environment in the crystal structure of 3 along with partial atom labeling scheme and thermal ellipsoids at
30% probability level. Atoms obtained by symmetry are shown with 50% transparency. Symmetry codes: i = 1 + x, y, z; ii = x, y, ꢁ1 + z; iii = x, ꢁ1 + y, ꢁ1 + z.
Fig. 7. (a and b) One of the two interpenetrated 3D coordination networks in the crystal structure of 3. Hydrogen atoms are omitted for clarity; (c and d) Two interpenetrated
networks; (b) and d) are the space filling representation for (a) and (c), respectively.

L.G. Bahrin et al. / Polyhedron 173 (2019) 114128
9
formation of a three-dimensional coordination polymer, as shown
in Fig. 7a and b. Further examination revealed the interpenetration
of symmetry-related three-dimensional coordination polymers in
the crystal (Fig. 7c and d).
2[Ca(H2L)(H2O)4.5(DMF)0.5]ꢀ[Ca(H2L)(H2O)5]nꢀ2H2O (4): An asym-
metric unit of 4 consists of two crystallographically independent
repeat units [Ca(H2L)(H2O)4.5(DMF)0.5] (denoted as A and B) of
coordination chains and a monomeric fragment of a 1D coordina-
tion polymer with the formula [Ca(H2L)(H2O)5]n (denoted as C).
All three units are shown separately in Fig. 8. In the two chemically
identical building blocks A and B, the Ca2+ ion is coordinated by one
bidentate-chelating carboxylate group, four aqua ligands and one
DMF molecule. The position of the DMF ligand is shared with a fifth
aqua ligand with equal site occupation factor (s.o.f.) of 0.5. The cal-
cium atoms Ca1A and Ca1B exhibit a distorted octahedral geome-
try if one assumes that the carboxylate group occupies one
coordination site. In the third, coordination polymeric [Ca(H2L)
(H2O)5]n part of the asymmetric unit, the Ca atom is coordinated
by one monodentate carboxylate group and five water molecules.
The coordination environment is completed by bonding to an addi-
tional oxygen atom of the carboxylate group of the neighboring [Ca
(H2L)(H2O)5]n entity leading to the formation of a 1D coordination
polymer, as shown in Fig. 9. As the result, the coordination geom-
etry of the Ca1C atom is described as a distorted pentagonal
bipyramid. In the crystal, the helical chains are assembled via
OAHꢀ ꢀ ꢀO hydrogen bonding to a two-dimensional supramolecular
layer. The main crystal structure packing motif in 4 is described as
a supramolecular architecture where 1D coordination polymers
[Ca(H2L)(H2O)5]n and two molecular units [Ca(H2L)(H2O)4.5
(DMF)0.5] are linked through numerous intermolecular H-bonds
(Fig. S15, in Supp. Inf.). Selected views of the crystal packing are
shown in Fig. 10.
3.5. Gas sorption studies
Figs. S11–S14 present the N2 sorption isotherms for the synthe-
sized compounds in the Supporting Information. Because the com-
pounds are three-dimensional metal–organic or supramolecular
frameworks with solvent-filled voids, the potential of permanent
porosity has been investigated by nitrogen sorption measurements
at 77 K. The surface area of compound 1 was SBET = 130 m2/g, for
Fig. 8. Asymmetric units in the crystal structure of 4 with labeling of selected
atoms and thermal ellipsoids at the 50% probability level. Non-relevant atoms are
omitted. (a and b) Structures of the [Ca(H2L)(H2O)4.5(DMF)0.5] A and B molecular
units, respectively. (c) Section of the [Ca(H2L)(H2O)5]n, C unit. Atoms obtained by
symmetry are shown with 50% transparency. Symmetry code: i) x, 0.5 + y, 1.5 ꢁ z.
Fig. 9. 1D coordination polymeric moiety [Ca(H2L)(H2O)5]n in 4 in (a) ball-and-stick
and (b) space filling representation.

10
L.G. Bahrin et al. / Polyhedron 173 (2019) 114128
Fig. 10. Crystal packing for 4. (a and b) 2D supramolecular layer formed by H-bonded coordination polymers [Ca(H2L)(H2O)5]n; (c) partial packing diagram viewed along the c
axis; (b) and (d) are the space filling representation for (a) and (c), respectively.
compound 3 SBET = 583 m2/g and compound 4 SBET = 284 m2/g. For
the supramolecular framework compound 2 no porosity was
observed upon degassing at room temperature. A surface area
was only measured when this compound was degassed at
T = 150 °C (SBET = 495 m2/g).
coordinated ligands. Compound 3 consists of two Mg2+ cations,
one L4ꢁ tetra-anion, two coordinated DMF molecules and one aqua
ligand to form a 3D coordination polymer. The two Mg atoms in
compound 3 are bridged by two carboxylate ligands having differ-
ent coordination functions. One of the Mg ions is in a distorted
octahedral, while the other one is in a slightly distorted tetrahedral
environment. The crystal structure of 4 includes three crystallo-
graphically independent and chemically non-equivalent molecular
4. Conclusions
entities: two molecular complex units [Ca(H2L)(H2O)4.5(DMF)0.5
and a helical chain [Ca(H2L)(H2O)5]n which are linked through
numerous intermolecular H-bonds.
]
Four new 3D-metal–organic and supramolecular frameworks
based on the 3,30,5,50-tetrakis(4-carboxyphenyl)-2,20,4,40,6,60-
hexamethyl-1,10-biphenyl ligand were obtained and structurally
It is evident that in coordination polymers or (porous) MOF
structures of multicarboxylate ligands with alkaline and alkaline
earth metals, metal–ligand bonding and hydrogen bonding are
equally important for the construction of the 3D structure. The
metal coordination sphere consists not only of the ligand carboxy-
late groups but also of solvent, especially aqua ligands. Thereby, the
3D structures seem to present an even larger variety than transition
metal MOF structures. It is difficult to foresee the extent of coordi-
nation polymeric and hydrogen bonding contribution in the 3D
(supramolecular) networks. The present results suggest that an
assembly of MOFs with other alkaline and alkaline earth metals will
attract even more of our attention, taking into account an important
role they play in nature. On the other hand, the pillar-ligand exten-
sion strategy will be used to synthesize new 3D polymers of alka-
line and alkaline earth metals with impressive structures.
characterized,
namely:
[Na2(H4L)(H2L)(DMF)2(H2O)2]n
(1),
2[Mg(H2O)6]ꢀ2H3LꢀH2L (2), [Mg2L(DMF)2(H2O)]ꢀ2.5DMF (3), and 2
[Ca(H2L)(H2O)4.5(DMF)0.5]ꢀ[Ca(H2L)(H2O)5]nꢀ2H2O (4). The sodium
ion in compound 1 is coordinated by six oxygen atoms in a dis-
torted octahedral geometry, which is provided by four carboxylate
groups, one water and one DMF molecule as monodentate ligands.
In the crystal, the Na ions are inter-connected by four carboxylate
ligands. In turn, the polycarboxylate ligands act as bridges between
four Na atoms to form an extended 3D coordination network with
(4,4) topology. In compound 2 two crystallographically indepen-
dent [Mg(H2O)6]2+ complex cations were found and three non-
coordinated deprotonated polycarboxylate ligands. The crystal
structure is described as a 3D supramolecular network consoli-
dated by a system of multiple OAHꢀ ꢀ ꢀO hydrogen bonds between
coordinated water molecules and carboxylate atoms of the non-

L.G. Bahrin et al. / Polyhedron 173 (2019) 114128
[8] S. Seth, P. Venugopalan, J.N. Moorthy, Chem. Eur. J. 21 (2015) 2241.
11
Acknowledgements
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The financial support of European Social Fund for Regional
Development, Competitiveness Operational Programme Axis 1 –
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104810) is gratefully acknowledged.
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CCDC 1911283–1911286 contains the supplementary crystallo-
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Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
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