Urea-based flexible dicarboxylate linkers for three-dimensional metal-organic frameworks

Article abstract of DOI:10.1016/j.ica.2017.09.029

The metal-organic frameworks (MOFs) 3D-[Mn₂(L1)₂(DMF)]·2DMF (1), 3D-[Cd₂(L2)₂(DMF)₃] (3), [Zn₂(L2)₂(DMF)₃] (4) and 3D-[Mn₂(L2)₂(DMF)₃] (5) are the first examples of three-dimensional metal-organic networks constructed from a single ditopic dicarboxylate linker (i.e., without bridging co-ligands) with an urea group in the linker axis (L1^2? = 4,4′-(carbonylbis(azanediyl))dibenzoate; L2^2? = 4,4′-(carbonylbis(azanediyl))bis(3-methylbenzoate), DMF = dimethylformamide). From Cd²⁺and L1^2? a 1D coordination polymer 1D-[Cd(L1)(DMF)₃] (2) is formed. The urea group is engaged in hydrogen bonding with the C(4)[R¹₂(6)] motif to an oxygen atom of a DMF solvent (in 1) or a metal-coordinated carboxylate group (in 3–5). Network 1 has infinite channels with parallelepiped cross sections and 30% solvent-filled volume. The 3 D frameworks 3–5 are of diamond (6,6), dia topology with a single framework having large voids with 17.6 ? and 19.7 ? nodal separation. Thus, four symmetry-related nets interpenetrate, organized via H-bonds in the C(4)[R¹₂(6)] motif, still leaving about 50% solvent-filled void volume in the fourfold interpenetrated structure.

Full text of DOI:10.1016/j.ica.2017.09.029

Accepted Manuscript
Urea-based flexible dicarboxylate linkers for three-dimensionalmetal-organic
frameworks
Sebastian Glomb, Gamall Makhloufi, Irina Gruber, Christoph Janiak
PII:
S0020-1693(17)31028-9
http://dx.doi.org/10.1016/j.ica.2017.09.029
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DOI:
Reference:
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11 September 2017
Please cite this article as: S. Glomb, G. Makhloufi, I. Gruber, C. Janiak, Urea-based flexible dicarboxylate linkers
for three-dimensionalmetal-organic frameworks, Inorganica Chimica Acta (2017), doi: http://dx.doi.org/10.1016/
j.ica.2017.09.029
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Urea-based flexible dicarboxylate linkers for three-dimensionalmetal-organic
frameworks
Sebastian Glomb, Gamall Makhloufi, Irina Gruber, Christoph Janiak*
Institut für Anorganische Chemie und Strukturchemie, Heinrich-Heine-Universität
Düsseldorf, 40204 Düsseldorf, Germany. Email: janiak@uni-duesseldorf.de
* Corresponding author:
C. Janiak
Tel.: +49 211 81 12286; fax: +49 211 81 12287. E-mail address:
janiak@hhu.de
Dedicated to Prof. Ionel Haiduc on the occasion of his 80th birthday.
Keywords:
MOFs,
metal-organic
frameworks;
urea
function;
four-fold;
4,4’-(carbonylbis(azanediyl))dibenzoic
acid; interpenetration,
diamondoiddiatopology; hydrogen bonding
Abstract
The
metal-organic
frameworks
(MOFs)3D-[Mn2(L1)2(DMF)]·2 DMF(1),
3D-
[Cd2(L2)2(DMF)3](3), [Zn2(L2)2(DMF)3](4) and 3D-[Mn2(L2)2(DMF)3] (5) are the first
examples of three-dimensional metal-organic networks constructed from a single
ditopic dicarboxylate linker (i.e., without bridging co-ligands) with an urea group in the
linker axis(L12–
=
4,4'-(carbonylbis(azanediyl))dibenzoate; L22–
=
4,4'-
(carbonylbis(azanediyl))bis(3-methylbenzoate), DMF = dimethylformamide). From
Cd2+ and L12– a 1D coordination polymer 1D-[Cd(L1)(DMF)3] (2) is formed.The urea
group is engaged in hydrogen bonding with the C(4)[R1 (6)] motif to an oxygen atom
2
of a DMF solvent (in 1) or a metal-coordinated carboxylate group (in 3-5).
Network1has infinite channels with parallelepiped cross sections and 30% solvent-
filled volume. The 3D frameworks 3-5 are of diamond (6,6),dia topology with a single
framework having large voids with 17.6 Å and 19.7 Å nodal separation. Thus, four
symmetry-related nets interpenetrate, organized via H-bonds in the C(4)[R1 (6)] motif,
2
still leaving about 50% solvent-filled void volume in the four-fold interpenetrated
structure.
1

1. Introduction
−organic frameworks (MOFs)
Metal
attractcontinuousinterestfor their open network
topologies associated with potential applications, mainly based on porosity and
reversible guest exchange [1,2, 3] with recently also water adsorption for heat
transformation [4].The interest in urea-based porous organic frameworks increased in
the last years due to possible applications for hydrogen-bond-donating catalysis
[5,6,7], anion recognition [8]and their high selectivity for CO2 adsorption [9,10].
In the literature, there are only few examples known ofMOFs with urea-
functionalizedcarboxylate ligands [8,11,12]although the urea groupwith their H-bond
donor and/or acceptor functions would be predestined for the separation of toxic
gases such as SO2, NH3 or H2S.
Possible andreported positions for the urea function in the linker can bein the main
chain of the linker [8,12,13] orin theside chain of the ligand (Figure 1) [5].In the latter
case, the urea function can also be introducedby postsynthetic modification [6,7].
Figure 1.Schematic presentation of possible positions of the urea function
indicarboxylate-linker MOFs. Left: Urea group in the main chain of the linker
[8,12],right: in the side chain of a linker [5].
Urea-based linkers with the urea group in the main chain are not rigid because of the
rotational flexibility of the urea group that can assume different conformations. The
synthesis of flexible MOFs ismore dependent on reaction parameters such as
solvent, temperature, concentration, pH etc. [14,15,16].
2

For all published syntheses of three-dimensional MOFs from linear urea-based
dicarboxylate linkers, a further co-ligand had been required in order to obtain
crystalline products for structure elucidation [8,11,12]. Roberts et al.[11] were the first
to form a three-dimensional, porous urea-functionalized MOF (NU-601) by usingthe
5,5'-(carbonylbis(azanediyl))diisophthalate linker and 4,4'-bipyridine as co-ligand
(Figure 2). Tehrani et al. employedthe ditopic4,4'-(carbonylbis(azanediyl))dibenzoate
(L12–) ligand and obtained with 4,4'-bipyridine (bipy), 2-bis(4-pyridyl)ethane (bpe) or
1,3-di(pyridin-4-yl)urea the mixed-ligand MOFs TMU-18, -19 [12] and -31 [8],
respectively for the use as Lewis acid catalysts orfor sensing of nitro-substituted
compounds (Figure 2).
(a)
(b)
Figure 2. Thelinker (as protonated forms) 5,5'-(carbonylbis(azanediyl))diisophthalic
acid (a) for NU-601 [11] and 4,4’-(carbonylbis(azanediyl))dibenzoic acid (H2L1,(b))
used for the syntheses TMU-18, -19 and -31 [8,12].
Wang [9]and Li [10]et al. were able to obtain theporous networks Cu-UBTA
andCu-TUH based on the trigonal hexacarboxyllinkersH6UBTA and H6TUH (Figure 3)
with urea groups in the main chain and Cu2+ as a metal with a high adsorption
capacity for CO2 (165 cm3·g-1and37 cm3·g-1).
3

Figure 3.Schematic presentation of theurea-functionalized linkers (protonated
form)H6UBTA and H6TUH for the syntheses of the MOFs Cu-UBTA [9] and Cu-TUH
[10].
In this work, we introduce five new metal-organic networks of zinc, cadmium, and
manganese with the linkers4,4'-(carbonylbis(azanediyl))dibenzoate (L12–)and4,4'-
(carbonylbis(azanediyl))bis(3-methylbenzoate) (L22–) (Figure 1).To the best of our
knowledge thisis the first report ofsingle-ligand three-dimensional metal-organic
networks constructed from a linear dicarboxylate linker with an urea group in the main
chain,that is without co-ligands.
2. Results and Discussion
2.1 Linker synthesis
The urea-containingligands4,4'-(carbonylbis(azanediyl))dibenzoic acid(H2L1) [17] and
4,4'-(carbonylbis(azanediyl))bis(3-methylbenzoic acid)(H2L2)were synthesizedina
one-step synthesis in a buffer system of aqueous boric acid and sodium hydroxide by
the reaction of the aminobenzoic acid with triphosgene in THF (Scheme 1). Crystals
of 4,4'-(carbonylbis(azanediyl))dibenzoic acid (H2L1) were obtained by dissolving the
ligand in a solution of water/ammonia, followed by slow evaporation of ammonia
fromthe solution.
4

Scheme 1.Reaction scheme of the reaction of aminobenzoic acid with triphosgene in
a buffer system of boric acid to the urea ligands H2L1 and H2L2.
The thermal stability of both ligands H2L1 and H2L2 was investigated by
thermogravimetric analysis (Figure S1). Both ligands are stable up to 220 °C.
2.2
Metal-organic framework synthesis
The compounds 1-5 could be crystallized from the solvothermal reaction of the Linker
H2L1or H2L2 in DMF with different metal salts (Scheme 2). Due to the insolubilityof
the linkers in other solvents (H2O, alcoholsand nonpolar solvents) the crystallization
processes were limited to basic, organic solvents likedimethylformamide, DMF.
Compounds 1, 2 and 5 were synthesized by reacting one equivalent of the metal
nitrate salt with one equivalent of the dicarboxylic acid whereascrystals of compounds
3 and 4 were obtained with an excess of the metal salt in a molar ratio of 3 : 1 to the
linker.Compound 4 can also be obtained by the reaction of Zn(SO4)·7 H2O as the
metal salt source at 50 °C.
Theinfrared spectral bands forthe carboxyl C=O vibrations for the linkers at
1420 cm-1and 1377 cm-1are shifted to lower wavenumbers upon metal compound
formation which indicates the complete deprotonation of the linkers and the
coordination at the metal centers.
For the example of compound 4, the chemical stability during the activation processof
the isoreticular compounds 3-5was tested in more detail. The attempted exchange
against other solvents (CHCl3, EtOH and H2O) yielded a white powder (investigated
by PXRD, cf. Fig. S12 in Supp. Info.). For all compounds the crystals are stable in
DMF and DMF can also be used as a washing solvent. Exposure to other solvents for
solvent exchange as part of the attempted activation led to loss of crystallinity or to an
undefinable crystalline state (cf. Fig. S12).Cadmium compound 3 was unstable in
ambient air as indicated by powder X-ray diffraction (see below).For the analytical
measurements the crystals of 3 were taken directly from the mother liquor and dried
in a stream ofdinitrogen to avoid degradation by air humidity. Attempted reaction of
the linkers H2L1 and H2L2 with different metal salts (Co(NO3)2·6 H2O,
5

Ni(NO3)2·6 H2O, La(NO3)2·6 H2O) gave no crystalline products. The reaction with
Cu(NO3)·3 H2O in different solvents (DMF, diethylformamide (DEF), dibutylformamide
(DBF), dimethylacetamide(DMA)) gave microcrystalline plates whosestructure could
not be solved, however, and whose PXRD did not match with the known structures
simulated from the single crystal structure of compounds 1-5. For compound 4 the
synthesis was also investigated in differentsolvents (DEF, DBF, DMA) but no crystals
could be obtained.
Scheme 2. Overview about synthesis and formulae of compounds 1-5. Only the
found and refined solvent molecules are given in the formulae. In the structures of
compounds 1, 3-5 the electron density contribution of additional solvent of
crystallization was included in the recovered number of electrons in the voids by the
SQUEEZE routine in PLATON [18].
Taking compound 4 as an example, the thermal stability was investigated by a TGA
under a continuous flow of nitrogen (Figure S2).
In the range up to 200 °C, the DMF solvent of crystallization as well the metal-
coordinated DMF molecules (see below) are evaporated (theor. 30.4 wt% (see
below), exp. 27.8 wt%).Following a short plateau around 200 °C, in the range
between 200 °C and 300 °C, the coordinated three DMF molecules (theor. 15.2 wt%,
exp. 12.6 wt%) are lostfollowing by linker decomposition which is not finished at
600 °C. A ZnO residue would amount to only 5.6 wt% for a formula unit of
[Zn2(L2)2(DMF)3]·6DMF.
The unit cell void electron count of 1076 e in 4 can be tried to match to potential
solvent molecules according to Z x Σi(solvent molecule i electron count x number of
solvent molecules i in formula unit). With the DMF (C3H7NO) electron count of 40 e
this gives an estimated 6 DMF molecules per formula unit in 4 (Z = 4). In the resulting
formula unit of[Zn2(L2)2(DMF)3]·6DMF (C43H49N7O13Zn2·6(C3H7NO)) with M = 1441.3
g/mol the six DMF crystal solvent molecules would amount to 30.4 wt%, the three
coordinated DMF molecules to 15.2 wt%.
6

2.2 Crystal structures
2.2.1 Crystal structure of H2L1
The
asymmetric
unit
of
the
structure
of
the
ligand4,4'-
(carbonylbis(azanediyl))dibenzoic acid,H2L1 consists of half of the ligand molecule
with a two-fold axis passing through the urea C=O bond (Figure 4a). The carboxylic
acids are nearly coplanar to theiraryl rings with dihedral angles of ~6°. The plane of
the urea group is twisted to the planes of the adjacent aryl rings each by 45 °.
Consequentlyboth carboxylic acid groups and aryl rings assumedihedral angles of
71.3(1)°and 82.5(1)°, respectively.
(a)
(b)
Figure 4.a)Extended asymmetric unit of H2L1 (50% thermal ellipsoids, H atoms with
arbitrary radii). b) Section of the packing diagram in the H2L1 structure with strong O-
H···O and N-H···O H-bonding interactions indicated as orange dashed lines, see
Table S1 in Supp. Info. for details. Symmetry transformation: i=-x, y, 3/2-z.
The supramolecular crystal packing in the structure of H2L1 is organized by classic O-
H···Oand N-H···Ohydrogen bonds.The -COOH groups form tail-to-tail hydrogen
bondsof the R2 (8) motif in the Etter-notation (Figure 4b) [19]. The urea N-H groups
2
adopt the anti-relationship to their carbonyl group and form the expected three-center
bond to the urea carbonyl group of an adjacent molecule with the C(4)[R1 (6)] motif
2
(Figure 4b) [19].
These strong H-bond interactions explain the low solubility of carboxylic
acid/urea-molecules in water and in most common organic solvents. Dissolution of
H2L1
is
only
possible
in
basic
solvent
mixtures
like
dimethylformamide(DMF)/dimethylsulfoxide(DMSO)/ dimethylacetamide(DMA) andin

apH-basic water solution, where is it possible to dissociatethe H-bonds between the
carboxylic acids by deprotonation in order to dissolve the molecule.
2.2.2 Crystal structure of compound3D-[Mn2(L1)2(DMF)]·2 DMF(1)
Colorless crystals were obtained by the reaction of H2L1 and manganese(II)-nitrate
tetrahydrate in DMF after 24 days at a temperature of 105 °C. The compound 1
crystallizes in the triclinic crystal system with the space group P¯ 1.The asymmetric
unit of 1 consists of two deprotonated L12–ligands, two manganese atoms and three
molecules ofdimethylformamide. One dimethylformamidemolecule is coordinatedto
the Mn2 atom, the other two molecules are connected via H-bonds to the hydrogen
atoms of the urea group.However, only the O and C atom of this coordinatedDMF
solvent could be found and refined. The remaining N(CH3)2 part of the molecule was
not found and is included in the recovered number of electronsin the void using the
SQUEEZE routine in PLATON [18]. The coordination sphere is a distorted square
pyramid for Mn1 and a distorted octahedron for Mn2 (Figure 5).
(a)
(b)
Figure 5.Extended asymmetric unit of compound 1 (50 % thermal ellipsoids) (a);
polyhedraof the coordination environment of the two crystallographically different
manganese atoms (b).Symmetry transformations: i = x, y+1, z-1; ii = x+1, y, z-1; iii
= -x+1, -y+2, -z; iv = -x+2, -y+2, -z; v = -x+1, -y+2, -z+1; vi = x-1, y, z+1; vii = x, y-1,
z+1.Selected geometric parameters in Table S2 and S3, Supp. Info.
The Mn1 atom is coordinated by five oxygen atoms from the carboxylate groups from
five different L1 ligands. Two oxygen atoms O1 bridge between two Mn1 atoms in a
rhombic Mn(µ-O)2Mn fragment (Figure 6a). The bond lengths for the Mn1-O bonds

are in the range of2.134 Å to 2.183 Å and the angles are between 78.44° and
113.34°for the oxygen atoms in cis-position and 168.03°and 171.64°for the atoms
in trans-position.
The Mn2 atom is coordinated by five carboxylate oxygen atoms from five different L1
ligands and one oxygen atom of coordinated dimethylformamide. Two oxygen atoms
O5bridge between two Mn2 metal centers, forming again a rhombic Mn(µ-O)2Mn
fragment. The oxygen atom O5 is trans to the DMF ligand.The remaining three oxy-
gen atoms belong tocarboxylate groups which bridge as bidentate ligandsbetween
the metal atoms Mn1 and Mn2 (Figure 6a). The bond lengths for the Mn2-O bonds
are in the range from 2.100 Å (Mn2-O10i) and 2.223 Å (Mn2-O5v) and the angles are
between 81.12°and 99.32°for the atoms in cis-position as well 166.18°and 175.76°
for the atoms in trans-position.
The manganese-carboxylatesubstructureform one dimensional chainsparallel to the a
direction (Figure 6a) while the L1ligands connect these metal-carboxylate chains in
two other dimensions along the b and b(–c) direction to a three-dimensional network
without any interpenetration (Figure 6b). The network has infinite channels in the
a-direction, while the other two directions are blocked by the ligands. The channels
have anopening of 4.6 x 19.6 Å along the diagonalsof the parallelepiped cross-
section (taking into account the van der Waals surface) (Figure 6c).
9

(a)
(b)
(c)
Figure 6.(a) Infinite one-dimensional chain formed by the manganese atoms and the
deprotonated carboxylic acids in 1. (b) and (c) Sections of the packing diagram of
1,with (b) view along the c-axis, and(b) along the a-axis looking downthe channels of
the network (space-filling model with unit cell outline).
2.2.3 Crystal structure of compound 1D-[Cd(L1)(DMF)3] (2)
Colorless crystals were obtained by the reaction of H2L1and cadmium(II)-nitrate
tetrahydrate in DMF. Compound 2 crystallizes in the monoclinic crystal system with
the space group P21/n. The asymmetric unit of 2 consists of one cadmium atom, one
ligand L12- and three coordinatedmolecules of dimethylformamide at the cadmium
atom(Figure 7).

(a)
(b)
Figure 7.(a) Asymmetric unit of compound 2 (50% thermal ellipsoids); (b)
pentagonal-bipyramidal coordination sphere of the central cadmium atom in 2 with
the three dimethylformamide ligands. Symmetry transformations: i=-1+x, -1+y, z;
ii=1+x, 1+y, z.Selected geometric parameters in Table S4, Supp. Info.
The cadmium atom is coordinated by seven oxygen atomsfrom which three below to
coordinated dimethylformamide and four oxygen atoms are part of two different
carboxylate groups of the L12–ligand. Each carboxylate groupcoordinates in a
bidentate chelating mode so that the ligand bridges between two Cd atoms. The
coordination sphere for the central cadmium atom is pentagonal bipyramidal (Figure
7b).The lengths of the cadmium-oxygen bonds are in the range between 2.297 Å and
2.425 Å and the angles in the range between 83.7°and 97.3°for the angles between
the atoms in the axial and equatorial positions. The O-Cd-O angles between the cis-
positioned O atoms in the equatorial plane are 54.9° and 55.2° for carboxylate
chelate rings and 82.4° and 86.4° for the DMF O-atom to the carboxylate groups
(Table S4).
The ligand and the cadmium atom form one-dimensional, linear chains where the
distance between two cadmium atoms is 17.93 Å. The angle between two arylrings
from the ligand is 31.40° (Figure 8). Parallel chains are arranged in double layers
running either parallel to the ab axis or to the (–a)b axis (Figure 8a). Chains running
parallel to the different axes cross at an acute angle of 60°. Crossing chains are
connected by N-H···O bonds (Figure 8b, Table S5).

(a)
(b)
Figure 8.(a)Section of the packing diagram in 2 withthe differentchains indicated by
different color. Yellow-red-pink colors indicate chains running along the ab axis. Blue-
green colors indicate chains running along the (–a)b direction. (b) Connection of
crossing chains by N-H···O bonds (orange dashed lines) (details in Table S5, Supp.
Info.).
2.2.4 Crystal
structures
of
compounds3D-[Cd2(L2)2(DMF)3](3),
3D-
[Zn2(L2)2(DMF)3](4) and 3D-[Mn2(L2)2(DMF)3] (5)
Compounds3,4and 5 are isoreticular albeit not fully isotypic or isostructural as the
space group of the room-temperature structure 3(orthorhombic Pna21) is different to
the space group of the structure 4 and 5 (monoclinic P21/n). However, the
asymmetric unit, secondary building unit and network topology including the fourfold
interpenetration of all three structures is identical (see below). Hence, we present and
discuss here the structure of 3 as the example to the structures of 3-5.
The asymmetric unit of 3 (Figure 9) consists of two crystallographically different urea
ligandsL22-and two cadmium atoms as well three dimethylformamidemolecules

coordinated to Cd1. From these three DMF ligands only the oxygen donor atoms
(O11, O12 and O13) could be found and refined. The remaining -CH-N(CH3)2 part of
the DMF ligand was strongly disordered and, hence,was included together with the
non-coordinated solvent molecules in the recovered number of electronsin the void
using the SQUEEZE routine in PLATON [18]. There are four formula units in the unit
cell (Z = 4).
(a)
(b)
Figure 9.(a) Extended asymmetric unit of compound 3 (30% thermal ellipsoids, room
temperature structure). (b) Coordination polyhedra of the cadmium atoms. Oxygen
atoms O11, O12, O13 are the donor atoms of three strongly disordered (hence
'squeezed') DMF ligands. Symmetry transformations: i =3/2-x, 1/2+y, 1/2+z;
ii=1/2-x, -1/2+y, 1/2+z; iii=1/2-x, 1/2+y, -1/2+z; iv=3/2-x,-1/2+y, -1/2+z.Selected
geometric parameters in Table S6, Supp. Info.See Figures S5 and S6 for the
corresponding asymmetric units of compounds4 and 5, respectively.
Both cadmiums atoms Cd1 and Cd2 are coordinated by six oxygen atoms, each.The
coordination sphere of Cd1 still appears asa rather regular octahedron in O-Cd-O
bond angles (deviation less than 5.5°from 90°) but has different terms of Cd-O bond
distances (range 2.172-2.414 Å) (Table S6). The coordination sphere of Cd2 is
distorteddue to two chelating carboxylate groups with distances between
2.139 Å (Cd2-O2)to2.627 Å (Cd2-O9) and angles between 52.6°(O9-Cd2-O10) and
168.4°(O7-Cd2-O9), giving a more trigonal-prismatic coordination polyhedron
[20 ,21, 22 ] (Table S6, Figure 9b). Both cadmium atoms are bridged by three
carboxylate groups, with two of them bridging bis-monodentate (κO:O') and one is
chelating and bridging (κO,O':O') (Figure 12b). In addition, Cd1 is coordinated by
three DMF solvent ligands, Cd2 is coordinated by achelating bidentate carboxylate
group from a bridging L22- ligand.The secondary building unit in 3can be ascribed as
{Cd2(O2C-)4}with the four carboxylate carbon atoms at the vertices of a flattened and
distorted tetrahedronwith near C2v symmetry (Figure 10a). Overall, the L22- ligand

with the carboxylate oxygen atoms O1-O5 bridges between three cadmium atoms,
the ligand with O6-O10 bridges between four cadmium atoms.
(a)
(b)
–O
O
= {M2}-SBU
with M =
Mn2+, Zn2+, Cd2+
HN
HN
O
HN
HN
O
O
–O
L22–
(c)
Figure 10.(a) Secondary building unit (SBU){Cd2(O2C-)4} showing the four
carboxylate carbon atoms as the vertices of a flattened and distorted tetrahedron
from which (b) the 3D network of diamondoid (dia) topology originates. Three
adamantane cages of the dia network are depicted in (b) together with the SBU
centroid connections as dark blue lines and the unit cell outline of 3(identical in 4 and
5). (c) Schematic representation of the diamondoid network with the ligand L22–.
Thereby, the Cd atoms and the ligand form a three-dimensional network of
diamondoid (6,6), dia-topology [23]topology (Figure 10b). The 3D network has large
openings as channels in different directions. The node separation between the
{Cd2(O2C-)4} SBUs of 17.6 Å and 19.7 Å gives rise to large voids in asingle 3D

network (Figure 10b). Thus, four symmetry-related nets interpenetrate (Figure 14)
[ 24 , 25 ].The individual networks in this four-fold interpenetrated structure are
organized via H-bonds in the C(4)[R1 (6)] motif [19] from the urea group tothe
2
carboxylate oxygen atoms O5 or O9 (Figure 12, Table 2). Oxygen atoms O5 and O9
are the weakly coordinated donor atoms of the chelating carboxylate groups to Cd2,
that is, have the longest Cd2-O bond distance (Table S7). Examples of porous MOF
structures
with
four-fold
interpenetration
appear
rare:
3D-[Cu(I)3(4,4’-bipy)5]2[H2SiW11O39]·5H2O (4,4’-bipy = bipyridine) [26], the diamondoid
network [Co(pybz)2]·2 DMF (pybz- = 4-(4-pyridyl)benzoate anion) in which the DMF
crystal solvent can be removed from the channels to give a potentially porous
framework that however shows no N2-uptake [ 27 ]; the diamondoid MOF
{[Ni4(44pba)8]·sol}n, (44pba = 4-(4-pyridyl)benzoate), which was investigated for the
adsorption of a wide range of solvents like methanol, ethanol, benzene or
dimethylformamide [28] and the diamondoid network ([Zn4O{Cu(L)2}2] (L = bis(N-
heterocyclic) complex) [29]. Thus, a four-fold interpenetration seems to correlate
closely with dia network topology.
15

(a)
(b)
Figure 11.Section of the fourfold interpenetrated symmetry-related networks in
compound 3 (identical in 4 and 5) with each network represented by a single
adamantane cage in different color. The space-filling mode illustrates that despite the
interpenetration a potential porosity (~50% solvent-filled void space of unit-cell
volume) is retained in 3-5. View approximately along (a) a axis, (b) ab axis.

Figure 12.Connection of symmetry related networks by N-H···O bonds (orange
dashed lines) in compound 3(identical in 4 and 5) (details in Table S7, S9 and S12,
respectively, Supp. Info.).
The four-fold interpenetrated networks in 3-5 still have open channels, primarily in the
a-direction. The channels provide a solvent accessible volume of about 50% of the
total unit cell volume (cf. Table 1). The electron density coming from disordered DMF
solvent in these voids was recovered by the SQUEEZE option in PLATON [18].
To the best of ourknowledge, compounds 1 and 3-5 are the first three-dimensional
networks with an urea group in the main chain of the ligand and without an additional
co-linker like 4,4’-bipyridin [30].Although other groups have also attempted to get
crystal structures with the ligand H2L1 no single-ligand network structure is known in
the literature with this ligand [13].
Powder X-ray diffractometry (PXRD) confirmed the reproducible synthesis (Fig. S11,
Supp. Info.), phase purity and representative nature of the single crystals. For the
representative nature and phase purity it is crucial to be aware that the simulated
diffractograms were derived from crystal data where the considerable amount of
solvent-derived electron density in the voids had been removed by the SQUEEZE
option in PLATON [18]. In structure 1 and 3-5 also part of the coordinated DMF
ligands were included in SQUEEZE because of unrefinable disorder. Even if the DMF
crystal solvent in the voids is disordered its electron density still contributes to
diffraction. Hence, the experimental diffractograms on the as-synthesized samples
differ in their intensities (Fig. S9 and S10, Supp. Info.). In the case of sample 4 a
single-crystal data set beforeSQUEEZE was refined to the stage where most of the

solvent electron density was assigned to individual atoms. Consequently, the
simulated diffractogram now gave a better match to the PXRD of the as-synthesized
sample (Fig. S10, Supp. Info.).
Powder X-ray diffractometry also showed that the crystallinity of the samples started
to get lost when kept in ambient air for 24 h (Fig. S9) and when the DMF solvent was
tried to exchange against ethanol or chloroform or when the samples were dried
under vacuum as part of the activation procedure before gas sorption studies (Fig.
S12 in Supp. Info.).
For the measurement of the N2-adsorption isotherm at 77 K, the as-synthesized
sample of 4 was degassed for 12 h at 120 °C under continuous vacuum. After the
activation, loss of crystallinity possibly with a change in the structure of the compound
was observed by PXRD (Fig. S12). For the activated sample of 4, no nitrogen uptake
was seen; hence no BET-surface area could be determined.
Also a dye sorption experiment did not confirm the potential porosity. As-synthesized
crystals of compound 4(2 mg) were added to a solution of methylene blue (MB) in
DMF (c = 0.02 g/L) in a cuvette. The UV-Vis absorption was measured immediately
after the addition and again after 24 h. Neither spectrometrically (Fig. S13a in Supp.
Info.) nor visually (Fig. S13b) could a change in absorption intensity be observed. The
crystals of compound 4 remained colorless.
3. Experimental section
3.1 Materials and methods
The chemicals used were obtained from commercial sources and no further
purification has been carried out.For aqueous solutions doubly de-ionized water was
used. Organic solvents were of reagent grade and dried over molar sieve. The
ligandswere synthesized starting from the aminobenzoic acids in a one-step-
synthesis. CHN analysis was performed with a Perkin Elmer CHN 2400. Fourier-
transform infrared (FT-IR)-spectra were recorded on a Bruker Tensor 37 IR
spectrometer as KBr pellet or with attenuated total reflection (ATR) unit(Platinum
ATR-QL, Diamond).The intensity of absorption is indicated as strong (s), medium (m),
weak (w) and broad (br). Thermogravimetric analysis (TGA) was done with a Netzsch
TG 209 F3 Tarsus in the range from 20 to 600 °C, equipped with Al-crucible and
applying a heating rate of 3 K·min-1under inert atmosphere (N2).Prior to
measurement, the MOF sample was exposed to a continuous stream of nitrogenin an
open Schlenk tube for one hour to remove any outer-surface solvent
molecules.Powder X-ray diffractograms (PXRDs) weremeasured on a Bruker D2
Phaser with a flat silicon, low background sample holder, at 30 kV, 10 mA, a scan
18

speed of 0.2 s/step and a step size of 0.02°(2θ)withCu-Kradiation (λ= 1.5418 Å).In all
.
diffractograms, the most intensive reflection was normalized to 1.NMR spectra were
measured with a Bruker Avance DRX-600 spectrometer. Electron-spray ionization
mass spectra (ESI-MS) were collected with aUHR-QTOF maXis 4G from Bruker
Daltonics.
3.2 Syntheses
3.2.1 Synthesis of 4,4'-(carbonylbis(azanediyl))dibenzoic acid (C15H12N2O5, H2L1)
H2L1has been described in the literaturewith a multistep synthesis [17].HereH2L1 has
been synthesized different to the known literatureprocedure with the
reagenttriphosgene,which is highly selective for amide formation from amino
groups.Therefore no additional protection of the carboxylic acid was needed for the
following synthesis [31].
4-Aminobenzoic acid (C7H7NO2,1.65 g, 12.0 mmol), boric acid (H3BO3, 43.2 mmol,
2.67 g) and sodium hydroxide (NaOH, 33.6 mmol, 1.32 g) were dissolved in water
(150 mL) to obtain a buffer solution with a pH of ~9. To this, a solution of triphosgene
(C3Cl6O3, 3.00 mmol, 0.89 g) in THF (20 mL) was added over a period of 30 minutes.
The solution was stirred for 10 additional minutes and conc. HCl(2 mL) was added.
The withe precipitate was filtered off (pore 4 filter) and washed with water (2×50 mL)
and once with THF (50 mL). The white solid was dried under vacuum for 4 h at
120 °C. Yield: 1.26 g (4.19 mmol, 70 % based on 4-aminobenzoic acid).
Crystals of H2L1were obtained by suspending H2L1in water and dissolving it by
adding a few drops of aqueous ammonia solution. By slow evaporation of the
ammonia, single crystalswere obtained after about 3 weeks.
FT-IR (KBr, cm-1): 3321 (m), 3185 (w), 3074 (w), 2983 (w), 2831 (w), 2669 (w),
2554(w), 2362(w), 1666(s), 1596(m), 1539(s), 1420(m), 1305(s), 1224(m), 1176(m),
1120(w), 935(w), 864(w), 760(m), 651(w), 608(w), 547(w), 510(w).
1H-NMR (300 MHz, DMSO-d6, ppm): δ = 12.63 (s, 1H), 9.15 (s, 1H), 7.88 (d, J = 8.8
Hz, 2H), 7.58 (d, J = 8.8 Hz, 2H).
13C{1H}-NMR (300 MHz, DMSO-d6): δ = 167.35, 152.31, 144.00, 130.91, 124.37,
117.81.
MS (ESI[+]): m/z = 301.1 [M + H]+ (calc.: 301.1).
Elemental analysis (C15H12N2O5, 300.27): calc. C 60.00, H 4.03, N 9.33 %; found
C 59.82, H 4.08, N 9.14 %.
19

3.2.2 Synthesis
of
4,4'-(carbonylbis(azanediyl))bis(3-methylbenzoic
acid)
(C17H16N2O5, H2L2)
4-Amino-3-methylbenzoic acid (C8H9NO2,1.81 g, 12.00 mmol), boric acid (H3BO3,
43.20 mmol, 2.67 g) and sodium hydroxide (NaOH, 33.00 mmol, 1.32 g) were
dissolved in water (150 mL) asa buffer system with a pH of ~9. To this a solution of
triphosgene (C3Cl6O3, 3.00 mmol, 0.89 g) in THF (20 mL) was added over a period of
30 minutes. The solution was stirred for 10 additional minutes and conc. HCl (2 mL)
was added. The witheprecipitate was filtered off (pore 4 filter) and washed two times
with water (2×50 mL) and once with THF (50 mL). The white solid was dried for 18 h
at 80 °C. Yield: 1.38 g (4.19 mmol, 70 % based on 4-amino-3-methylbenzoic
acid).FT-IR (KBr, cm-1): 3281(m), 2971 (m), 1696 (s), 1637 (s), 1587 (m), 1547 (s),
1429 (m), 1308 (m), 1271 (m), 1184 (m), 1127 (w), 937 (w), 977 (w), 837 (w),
764 (m), 656 (w), 563 (w).
1H-NMR (300 MHz, DMSO-d6, ppm): δ = 12.61 (s, 1H), 8.67 (s, 1H), 8.09 (d, J = 8.5
Hz, 1H), 7.84 – 7.67 (m, 2H), 2.34 (s, 3H).
13C{1H}-NMR (300 MHz, DMSO-d6, ppm): δ = 167.15, 152.23, 141.68, 131.52,
127.86, 126.57, 124.29, 119.62, 18.13.
MS (ESI[+]): m/z = 329.3 [M + H]+ (calc.: 329.3).
Elemental analysis (C17H16N2O5, 328.32): calc. C 62.19, H 4.91, N 8.53 %; found
C 62.09, H 4.84, N 8.25 %.
3.2.3 Synthesis of [Mn2(L1)2(DMF)]·2 DMF(1)
In
a
DURAN
glass
vial,
Mn(NO3)2·4H2O
(5.0 mg,
20 µmol)
and
H2L1 (6.0 mg, 20 µmol) were dissolved in DMF (2.5 mL). The vial was sealed,
sonicated in an ultrasound bath for 10 min and the crystals were allowed to grow at a
temperature of 105 °C for 24 days. After this time, a small amount of colorless
crystals had formed (yield ~1.2 mg, 7 %) together with a brownish precipitate of
MnO2. An attempted scale-up of this procedure resulted only in a white powder but no
crystals anymore.
FT-IR (ATR, cm-1): 3344 (w), 3301 (w), 1712 (w), 1647 (m), 1599 (m), 1571 (m),
1526 (m), 1385 (s), 1307 (m), 1233 (m), 1200 (m), 1172 (s), 1102 (m), 1061 (w),
1013 (w), 900 (w), 860 (m), 782 (m), 701 (w), 664 (m), 635 (w), 618 (m), 567 (w).
3.2.4 Synthesis of [Cd(L1)(DMF)3] (2)
In
a
DURAN
glass
vial,
Cd(NO3)2·4H2O
(6.1 mg,
20 µmol)
and
H2L1 (6.0 mg, 20 µmol) were dissolved in DMF (2.5 mL). The vial was sealed,
20

sonicated in an ultrasound bath for 10 min and the crystals were allowed to grow at a
temperature of 105 °C for 14 days. After this time, colorless crystals had formed
(yield ~1.5 mg, 24 %).
FT-IR (ATR, cm-1): 3284 (w), 2931 (w), 1705 (w), 1638 (s), 1598 (s), 1557 (m),
1507 (m), 1436 (w), 1391 (s), 1304 (s), 1238 (m), 1210 (m), 1171 (s), 1141 (w),
1103 (m), 1061 (w), 1035 (w), 900 (w), 860 (m), 832 (w), 783 (s), 750 (w), 702 (w),
672 (m), 621 (m).
3.2.5 Synthesis of [Cd2(L2)2(DMF)3](3)
In
a
DURAN glass vial,
Cd(NO3)2·4H2O (18.4 mg,
60 µmol)
and
H2L2 (6.6 mg, 20 µmol) were dissolved in DMF (5.0 mL). The vial was sealed,
sonicated in an ultrasound bath for 10 min and the crystals were allowed to grow at a
temperature of 80 °C for 5 days. After this time, colorless cubic crystals were
collected (Figure S3), (yield ~1.4 mg, 8 %).
FT-IR (ATR, cm-1): 3281 (m), 1641 (m), 1594 (m), 1559 (m), 1517 (s), 1492 (m),
1406 (s), 1391 (s), 1308 (m), 1278 (m), 1258 (m), 1224 (w), 1192 (m), 1139 (m),
1112 (m), 1051 (w), 1036 (w), 1005 (w), 924 (w), 918 (w), 886 (w), 856 (w), 843 (w),
823 (m), 777 (s), 747 (m), 714 (w), 672 (m), 633 (m), 568 (w).
3.2.6 Synthesis of [Zn2(L2)2(DMF)3](4)
In a DURAN glass vial,Zn(NO3)2·6H2O(6.0 mg, 20 µmol) and H2L2 (6.6 mg, 20 µmol)
were dissolved in DMF (2.5 mL). The vial was sealed, sonicated in an ultrasound
bath for 10 min and the crystals were allowed to grow at a temperature of 50 °C for
14 days. After several days, colorless cubic crystals were collected (yield ~8.0 mg, 42
%)(Figure S4). In contrast to the synthesis at 50 °C, the synthesis at 105 °C gives
crystals of compound4 after three days.
FT-IR (ATR, cm-1): 3346 (m), 2924 (w), 1656 (s), 1623 (s), 1592 (s), 1526 (s),
1418 (s), 1382 (s), 1308 (m), 1269 (m), 1247 (m), 1205 (m), 1181 (m), 1136 (m),
1100 (m), 810 (s), 782 (m), 661 (w), 636 (w).
3.2.7 Synthesis of [Mn2(L2)2(DMF)3](5)
In
a
DURAN
glass
vial,
Mn(NO3)2·4H2O
(5.0 mg,
20 µmol)
and
H2L2 (6.6 mg, 20 µmol) were dissolved in DMF (2.5 mL). The vial was sealed,
sonicated in an ultrasound bath for 10 min and the crystals were allowed to grow at a
temperature of 105 °C for 11 days. After this time, a small amount of colorless
crystals had formed (yield ~1.4 mg, 8 %) together with a brownish precipitate of
21

MnO2.Only a low amount of small crystals were obtained. Due to the low yield, no
powder diffractogram could be recorded.
FT-IR (KBr, cm-1): 3345 (w), 3294 (w), 1700 (w), 1647 (m), 1616 (w), 1593 (m),
1518 (m), 1416 (m), 1379 (s), 1310 (m), 1273 (m), 1249 (m), 1209 (w), 1184 (m),
1141 (w), 1106 (m), 1004 (w), 940 (w), 910 (w), 808 (m), 779 (m), 664 (m), 634 (m).
3.2.8 Single Crystal X-ray structures
Suitable crystals for measurement were carefully selected under a polarizing
microscope, covered with protective oiland mounted on a glass loop. Unit cell
parameters were determined by a least-squares fit of 2θ values and intensity data
were measured on a Bruker Kappa DUO with APEX II CCD area detector equipped
with microfocus sealed tube, Mo-Kα radiation (λ = 0.71073 Å) and multilayer mirror
monochromator.Data collection by ω- and φ-scans with APEX II [32], cell refinement
with SMART, data reduction with SAINT [33]. The intensities were corrected for
empirical absorption based on multi-scan technique using the SADABS program
[34].Structure analysis and refinement:The structures were solved by direct methods
and refined by full-matrix least-squares fitting on F2 by SHELX 97 [35]. All non-
hydrogen atoms were refined with anisotropic thermal parameters, except in the
structure of 5 which was only refined isotropically due to low number of
data.Hydrogen atoms were positioned geometrically and refined using riding models
[AFIX 43 for aromatic CH with C-H = 0.95 Å, Uiso(H) = 1.2Ueq(C), AFIX 137 for CH3
with C-H = 0.98 Å and Uiso(H) = 1.5Ueq(C)]. The hydrogen atoms on the urea nitrogen
atoms were positioned geometrically(N-H = 0.88 Å) and refined using a riding
model(AFIX 43) with Uiso(H) = 1.2Ueq(N). In the structure of the ligand H2L1 he N-H
and carboxyl O-H atoms have been found and refinedwith Uiso(H) = 1.5Ueq(N,O).
Crystallographic data are summarized in Table 1. For the X-ray structure analyses of
the metal compounds 1-5we picked the largest crystals we could locate in the
compounds. Even these were mostly of very small size (cf. Table 1). It is known that
very small crystals diffract weaker than larger crystals, resulting in lower data quality
and subsequent problems during refinement [36]. Some of the checkcif alerts are due
to the small crystal size, e.g., poor data/parameter ratio.For each compound 1-5 two
to three crystals each were mounted on the diffractometer and data sets were
collected, giving the same cell constants and upon structure solution and refinement
the same structure. The refinement of the best data set is reported here. Some
atomic displacement parameters in compound 1 indicate prolate thermal ellipsoids
which can be traced to motion perpendicular to the plane through the atoms, as
indicated by the larger temperature factors in this (perpendicular) direction. In
22

compound 1only the O and C atom of the manganese-coordinatedDMF solvent could
be found and refined. The remaining N(CH3)2 part of the molecule is included in the
recovered number of electronsin the void using the SQUEEZE routine in PLATON
[18]. Compound 2 crystallized in the centrosymmetric space group P21/n but was
refined as a 2-component twin, based on the two-foldrotation axis(0 0 1) [1 0 5] (in
reciprocal space)[in direct space] using the twin law -1 0 0 0 -1 0 0 0 1 with HKLF 5
and a HKL-file generated from PLATON graphical menu though 'twinrotmat' yielding
BASF 0.16.In the structures of3-5the value of sin(theta_max)/wavelength is less than
0.550. The porous MOF structures contain solvent-filled voids of comprising more
than 50% of the unit cell volumes. Like in many other porous MOFs, also here the
crystals did not diffract above theta 20°.Crystals of 5 did even diffract only to 2theta
angles of 13°.In compound 3 and 4RIGU restraints were applied with RIGU s1[0.004]
s2[0.004] for all non-hydrogen atoms as enhanced rigid bond restraints with esds s1
for 1,2-distances and s2 for 1,3 [37].Also, in 3 the single oxygen atoms O11, O12 and
O13 on Cd1 are the donor atoms of coordinated DMF ligand molecules, which could
not be refined due to disorder. Therefore the related electron density was removed
with further residual electron density in the pores using the SQUEEZE routine in
PLATON [18].In compound 3-5 the flexible linker will assume slightly different
conformations leading to disorder as indicated by different Ueq values of neighboring
atoms, longer C-C bond lengths etc. Yet, the topology of the 3D metal-ligand network
in 3-5 could be unequivocally determined.
Graphics were drawn with DIAMOND [38].The crystallographic data have been
deposited with the Cambridge Crystallographic Data Center (CCDC-numbers
1559378-1559382 for H2L12, 4, 1 and 3, respectively).These data can be obtained
free of charge viawww.ccdc.cam.ac.uk/data_request/cif. For the structure of 5
refinement details are only reported here without structure deposition at CCDC due to
low structure quality. See Supporting Informationfor further details of structure 5.
23

Table 1: Crystal data and structure refinement for compounds H2L1 and1-5.
1
C31H20Mn2N4O11·2(C3H7N
O)e
2
Compound
H2L1
f
Chemical formula
C15H12N2O5
C24H31CdN5O8
M/g·mol−1
300.27
880.58
629.94
Crystal system, space group
Monoclinic, C2/c
Triclinic, P¯ 1
Monoclinic, P21/n
Temperature/K
140
13.5100(11)
4.7129(3)
19.8387(16)
90
150
9.6545(6)
17.2717(10)
17.326(1)
66.504(3)
77.105(4)
83.163(3)
2581.3(3)
2
100
9.2718(7)
15.3481(11)
19.9685(15)
90.00
a/Å
b/Å
c/Å
α/°
β/°
91.425(5)
90
94.808(4)
90.00
γ/°
V/Å3
1262.76(17)
4
2831.6(4)
4
Z
Dcalc/g cm−3
1.579
1.133
1.478
µ (mm-1)
0.121
0.54
0.82
0.10 × 0.10 ×
0.01
Crystal size (mm)
0.16 × 0.10 × 0.04
0.11 × 0.10 × 0.08
F(000)
624
904
1288
absorpt. correct.Tmin, Tmax
0.666, 0.753
0.669, 0.745
0.669, 0.745
Reflections collected, indepen-
20524, 2848, 2266
30330, 8159, 6118
9963, 5601, 4583
dent and observed [I > 2σ(I)]
Rint
0.043
2848/107/0
--
0.049
8159/527/0
0.58
0.058
5601/350/0
0.619
Data/parameters/restraints
(sin θ/λ)max (Å-1)
∆ρmax, ∆ρmin (e Å-3)
0.519, -0.402
0.63, -0.75
3.55, -2.58
R1/wR2 [I>2σ(I)] b
R1/wR2 (all data)b
Goodness-of-fit on F2 c
0.0390/0.1123
0.0521/0.1221
1.050
0.0497/1380
0.705/0.1505
1.050
0.0705/0.1492
0.0889/0.1553
1.130
Void electron count/e d
--
351
--
Void, solvent accessible vo-
lume/Å3(% unit cell volume)d
a Largest difference peak and hole.
--
826 (32%)
--
2 2
b R1= [∑(||Fo| − |Fc||)/∑|Fo|]; wR2 = [∑[w(Fo2 − Fc2)2]/∑[w(Fo ) ]]1/2
.
2 2
c Goodness-of-fit = [∑[w(Fo2 − Fc ) ]/(n − p)]1/2
.
dRecovered number of electrons in the void, solvent accessible volume; both found by using the
SQUEEZE routine in PLATON (probe radius 1.2 Å) [18].The unit cell void electron count can be tried to
match to potential solvent molecules according to Z x Σi(solvent molecule i electron count x number of
solvent molecules i in formula unit). Electron count for solvent molecules i: DMF (C3H7NO) 40 e.
eOnly the O and C atom of this coordinated DMF solvent could be found and refined. The remaining
N(CH3)2 part of the molecule was not found and is included in the recovered number of electrons in the
void using the SQUEEZE routine in PLATON [18].
24

f refined as a 2-component twin, see text in section 3.2.8.
Table 2. Crystal data and structure refinement for compounds H2L1 and1-5 (contd.).
3
4
5
g
i
C34H28Cd2N4O13
C40H42N6O13Zn2h
C40H42Mn2N6O13
925.4
945.53
924.67
g
Orthorhombic, Pna21
Monoclinic, P21/n
Monoclinic, P21/n
293
14.730(3)
28.473(7)
18.577(5)
90.00
100
14.232(5)
20.366(7)
26.441(9)
90.00
100
14.571(5)
18.145(6)
28.255(9)
90.00
90.00
90.884(13)
90.00
91.663(7)
90.00
90.00
7791(3)
4
7663(5)
4
7467(4)
4
0.789
0.820
0.822
0.58
0.30 × 0.30 × 0.08
1840
0.67
0.08 × 0.08 × 0.06
1952
0.38
0.06 × 0.03 × 0.02
1908
0.590, 0.745
0.636, 0.744
--
71896, 7554, 6842
30835, 5698, 4501
9868, 2091, 1533
0.096
7554/483/427
0.493
0.068
5698/558/480
0.450
0.081
2091/252/0
0.324
2.00, -0.77
0.60, -0.66
0.44, -0.75
0.0487/0.1210
0.0547/0.1261
1.056
0.0983/0.2541
0.1177/0.2787
1.071
0.1201/0.3435
0.1473/0.3657
1.593
1113
1076
734
4798 (62%)
4245 (55%)
3921 (52%)
g
In an attempted low-temperature data set different ligand conformations were frozen which lead to
increased disorder so that the quality of refinement became even lower. Further, the structure of 3 in the
non-centrosymmetric space groupPna21 was refined as an inversion twin with a Flack parameter of
0.48(4) [39]. From the three coordinated DMF molecules only the O donor atoms were found and
refined.
hThe atoms of two of the three metal-coordinated DMF ligands were found and refined. For the third
coordinated DMF only the O donor atom was found and refined.
i Despite the low data quality the topology of the 3D metal-ligand network in 5 could be unequivocally
determined, including the atoms of two of the three metal-coordinated DMF ligands. For the third
coordinated DMF only the O donor atom was found and refined.
25

4. Conclusions
A ditopic dicarboxylate linker with an urea group built in gives rise to coordination
polymeric and metal-organic framework structures. For the linker L22– = 4,4'-
(carbonylbis(azanediyl))bis(3-methylbenzoate) isostructural or isoreticular MOF
structures are obtained for the different metal atoms Mn2+, Zn2+ and Cd2+, indicating
the exerted structure control by the linker. The dimensions of the linker create large
voids in diamondoid, dia networks. Despite the resulting four-fold interpenetration,
which is rare in MOF-structures, about 50% of solvent accessible volume remains. In
order to obtain permanently porous structures with urea-functionality in the linker the
framework stability needs to be increased, however. At present, the inherent linker
flexibility around the urea group gives rise to loss of crystallinity and void volume
upon activation through solvent exchange and drying. We will now tackle this problem
through judicious linker modification with rigidification.
Acknowledgements
The work was supported by the German Science Foundation (DFG) through grant Ja-
466/29-1.
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(c) K. K. Gangu, S. Maddila, S. B. Mukkamala, S.B. Jonnalagadda, Inorg. Chim. Acta
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(d) S. Quaresma, V. Andre, A. Fernandes, M.T. Duarte, Inorg.Chim. Acta 455 (2017)
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[2] (a) K. Adil, Y. Belmabkhout, R.S. Pillai, A. Cadiau, P.M. Bhatt, A.H. Assen, G.
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(b) W.P. Lustig, S. Mukherjee, N.D. Rudd, A.V. Desai, J. Li, S.K. Ghosh, Chem. Soc.
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