Metal-organic coordination polymers with a new 3,5-(4-carboxybenzyloxy) benzoic acid linker

Article abstract of DOI:10.1039/c3nj00054k

New framework solids consisting of coordination polymers [Ce(L)(DMA)(H ₂O)]_n (1), [Nd(L)(DMA)(H₂O)]_n (2), [Cu₂(OH)(L)]_n (3) and [Cd₂(L) ₂(4,4′-bipyridyl)]_n·(CH₃NH ₂CH₃⁺)_2n (4) (H₃L = 3,5-(4-carboxybenzyloxy) benzoic acid; DMA = dimethyl acetamide) have been synthesized under hydro(solvo)thermal conditions and characterized by X-ray crystallography. They reveal two-dimensional and three-dimensional network architectures. Thermal analysis (TGA and DTA) features of 1-4 and solid-state variable temperature magnetic susceptibility data of 2 and 3 are reported as well.

Full text of DOI:10.1039/c3nj00054k

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Metal–organic coordination polymers with a new
3,5-(4-carboxybenzyloxy) benzoic acid linker†
Cite this: NewJ.Chem., 2013,
37, 1494
Ranjan Patra, Hatem M. Titi and Israel Goldberg*
New framework solids consisting of coordination polymers [Ce(L)(DMA)(H2O)]n (1), [Nd(L)(DMA)(H2O)]n
+
(2), [Cu2(OH)(L)]n (3) and [Cd2(L)2(4,40-bipyridyl)]nꢀ(CH3NH2CH3
)
2n
(4) (H3L = 3,5-(4-carboxybenzyloxy)
Received (in Victoria, Australia)
13th January 2013,
benzoic acid; DMA = dimethyl acetamide) have been synthesized under hydro(solvo)thermal conditions
and characterized by X-ray crystallography. They reveal two-dimensional and three-dimensional network
architectures. Thermal analysis (TGA and DTA) features of 1–4 and solid-state variable temperature
magnetic susceptibility data of 2 and 3 are reported as well.
Accepted 25th February 2013
DOI: 10.1039/c3nj00054k
www.rsc.org/njc
Introduction
Crystal engineering of novel coordination polymers has evoked
considerable attention in the past two decades, owing to their
versatile framework topologies as well as their potential
applications as functional materials in molecular magnetism,
catalysis, gas sorption, fluorescent sensing, and optoelectronic
devices.1–4 Construction of desired coordination architectures
is still subjective and cannot be generalized as the self-assembly
process is highly influenced by several factors, such as the
nature of the metal and ligand components,5 solvents,6
templates and counterions,7 as well as the applied reaction
conditions.8 Nevertheless, some coordination polymers with
specific topologies could be ‘‘designed’’ by the judicious selec-
tion of metal ions with definite coordination preferences and
robust organic ligands with preorganized functionality.9 It has
been shown recently that the use of flexible organic linkers
(that can assume different conformations upon coordination)
in the synthesis of coordination polymers can lead to new
coordination networks with dynamic structures (including
supramolecular isomerism), as well as interesting topologies
and properties.10,11 Following our earlier efforts in the synthesis
of metal–organic frameworks with the relatively rigid porphyrin
tetracarboxylic acids,12 we have also recently engaged in a
parallel avenue of crystal engineering investigations with more
flexible poly-carboxylate scaffolds.13 In the latter context we
report herein on the synthesis of a new tricarboxylic acid ligand
Scheme 1 Molecular structure of the title ligand H3L. Note the trigonal disposi-
tion of the carboxylic molecular recognition sites.
H3L, 3,5-(4-carboxybenzyloxy)benzoic acid (Scheme 1), and preli-
minary findings on its coordination behavior (as a de-protonated
tri-anion) with different d- and f-metal ions.14 Four new coordi-
nation network materials have been successfully synthesized
and characterized so far to this end: [Ce(L)(DMA)(H2O)]n (1),
and [Nd(L)(DMA)(H2O)]n (2), [Cu2(OH)(L)]n (3) and [Cd2(L)2-
+
(4,40-bipyridyl)]nꢀ(CH3NH2CH3 )2n (4). Crystals of 3 and 4 were
obtained in DMA solvated forms.
Results and discussion
The title ligand bears three carboxylic acid groups oriented in
diverging directions, which can be readily de-protonated in
basic environments into the corresponding anionic form, L3ꢁ
.
This favors 1 : 1 coordination stoichiometry with trivalent
cations (e.g., a common oxidation state of the lanthanoid ions),
and formation of extended coordination networks. Charge
balance in coordination of this ligand with divalent transition
metals would require either its incomplete de-protonation, a
more complex stoichiometry of the metal–ligand complexation,
or incorporation of additional ions into the resulting product.
The synthesis of the ligand was obtained by reacting under
School of Chemistry, Sackler Faculty of Exact Sciences, Tel-Aviv University,
Ramat-Aviv, 69978 Tel-Aviv, Israel. E-mail: ranjanpatra06@gmail.com,
goldberg@post.tau.ac.il
† Electronic supplementary information (ESI) available: FT-IR and TGA (for 1–4)
data. CCDC 918381–918384. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c3nj00054k
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reflux 3,5-dihydroxy-methylbenzoate with 4-bromo-methylbenzoate take the form of dinuclear (Ce/Nd)2(COOꢁ)6(H2O)2(DMA)2 clusters
under basic conditions (K2CO3 and NaOH). In the next step centered around crystallographic inversion, each one of them
conversion of the ester into the carboxylic acid group was associating with four different ligands (Fig. 1). The Ce/Nd-ions in
achieved by acidification with HCl. The available metal–organic the cluster are eight-coordinate, each binding to two carboxylates
polymeric materials 1–4 were obtained by reacting the H3L (the side carboxyphenyl groups of two neighboring ligands) in a
ligand under solvothermal conditions with the corresponding chelating bidentate mode, one water molecule, and one DMA
commercially available metal salts Ce(NO3)3ꢀ6H2O, Nd(NO3)3ꢀ species. In addition, the two nuclei are inter-connected by two
6H2O, Cu(NO3)2ꢀ2.5H2O and Cd(NO3)2ꢀ4H2O. A mixture of other carboxylates (the middle carboxyphenyls) of two different
DMA, methanol, water, and acetic/nitric acid served for solubi- ligands. Correspondingly, every linker species is coordinated to
lizing the reagents and adjusting the pH of the reaction three adjacent bi-metallic nodes. The coordination distances are
environment. Suitable single crystals of the cadmium com- Ce–O within 2.384–2.557(3) Å in 1 and Nd–O within 2.343–2.527(3) Å
pound could be obtained only upon addition of 4,40-bipyridine in 2. The CeꢀꢀꢀCe and NdꢀꢀꢀNd distances within the di-nuclear
to the crystallization mixture. The individual syntheses connectors are 5.124(1) and 5.112(1) Å, respectively.
were characterized by reasonably good yields (50–75%, see
the Experimental section).
The metal–ligand multiple coordination in 1 and 2 gives rise
to the formation of a flat two-dimensional grid metal–organic
The principal conformational degrees of freedom of the L network of 2/m symmetry (Fig. 1), with all the linker molecules
tri-carboxylate linker (in all the structures, the title ligand was aligned parallel to it and parallel to the (2,0,1) plane of the
found fully de-protonated) involve possible rotation of the two crystal. The metal-coordinated DMA and water moieties are
peripheral 4-carboxyphenyl rings with respect to the central one oriented in a normal direction, sticking out above and below
about the corresponding saturated bridging units. The three from the polymeric grid, which is perforated by wide internal
terminal carboxylate functions may also adapt a range of voids. These are filled effectively in the crystal by tight offset-
orientations with respect to the respective aryl residues they stacking of the network arrays along the normal direction,
are bound to, although co-planarity of these moieties is pre- where the DMA species of one layer protrude into the voids of
valent as it optimizes p-electron delocalization. Compounds 1 neighboring layers. In addition, the metal-bound water mole-
and 2 are isomorphous and isostructural, and the polymeric cules of one layer hydrogen-bond to the carboxylate functions
networks they form are illustrated in Fig. 1. In their crystals, the of the layers located above and below. The topology of this
ligand species is located on an axis of twofold rotation, and its coordination polymer has been analyzed with the TOPOS
molecular structure is essentially planar, the anti torsion angles (v. 4.0) software, reducing the complex structure to a simpler
about the Csp –O bonds being 174.2(4)1 in 1 and 174.6(3)1 in 2. node-and-linker net.15 It can be best represented as a (4)-connected
3
¨
The three carboxylate groups are coplanar with the corres- uni-nodal net with Schlafli symbol {44.62}.
ponding aryl rings, diverging in lateral directions. However,
The coordination scheme in compound 3 represents a
each of the two terminal carboxyphenyl rings is nearly continuous interaction synthon that propagates throughout
perpendicular to the middle one (the dihedral angle between the crystal lattice. The organic linkers L are tessellated to one
these planes being 89.71). Every organic linker coordinates to another by periodically spaced polymeric [Cu2(OH)-carboxylate]n
three different Ce/Nd metallic nodes. The inorganic connectors arrays that propagate along the c-direction (at x = 1/2, y = 0 and
x = 0, y = 1/2) and act as construction pillars (Fig. 2a). The
shortest Cuꢀ ꢀ ꢀCu distances with neighboring Cu atoms in this
polymer are 3.078(1) Å between ions related by the C2 axis and
3.303(1) Å between those related by inversion. Each of the metal
ions connects to three different carboxylate groups, and every
carboxylate bridges between two adjacent metal ions (in a
m2–Z1–Z1-bridging mode) of the poly-nuclear cluster. The
square pyramidal coordination sphere around every Cu ion
consists therefore of three COOꢁ ligands at Cu–O distances of
1.945–1.962(2) Å and two hydroxide moieties (located on a
twofold symmetry axis) at Cu–O = 1.919(1) Å (at the base of
the pyramid) and 2.450(2) Å (along its apex). The organic ligand
is characterized by a slightly twisted but still expanded con-
formation as in the previous examples, with nearly anti torsion
angles about the saturated Csp –O bonds of 164.9(2)1 and a twist
3
angle between the terminal and central aryl rings of 75.83(7)1.
Its three carboxylate functions connect to three different inor-
ganic pillars in the structure, ensuring the formation of a
supramolecular network of 3D topology (Fig. 2b).
Fig. 1 The 2D coordination network in the isostructural compounds 1 and 2.
The green spheres represent the Ce/Nd metal ions. The red spheres depict the
metal-coordinated DMA (only the O-atom is shown) and water moieties which
are aligned perpendicular (up and down) to the flat network array. In the crystal,
The polymeric lattice of crystalline 3 is characterized
by solvent-accessible channel voids (centered at x = 0, y = 0
the empty voids within the network are filled by the DMA units emerging from
the two adjacent layers above and below.
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Fig. 4 The bi-layered coordination network in 4, aligned parallel to the ab plane
of the crystal. The tri-carboxylate and bipyridyl linkers are marked by L and P
respectively. Note that the Cd nodes of the grid are seven coordinate. The
dimethyl ammonium counter ions, along with the DMA crystallization solvent,
are omitted.
Charge balance was maintained by co-crystallization of
dimethyl ammonium moieties obtained from hydrolysis of
DMA under the hydrothermal reactor conditions. The crystallo-
graphic analysis revealed the formation of polymeric bi-layers
in this case. The intermolecular organization of the latter can
be described as consisting of CdL layered grids with mono-
nuclear nodes, wherein every Cd-center coordinates to three
different carboxylate units (that bind to it in a chelating
bidentate mode) of three different linkers, each of which
connects in turn to three metallic centers in the layer (Fig. 4).
The open voids within this array are then lined by three
metallic nodes and three organic linkers. The Cd–O coordina-
tion bonds are within 2.306–2.439(4) Å around the Cd1 center
of one layer and 2.323–2.564(4) Å around the Cd2 node in the
second layer. Two neighboring coordination nets thus formed
are further cross linked by bipyridyl columns which coordinate
simultaneously to the Cd-centers (at Cd–N = 2.307(4) and
2.346(5) Å) of the lower and upper layers to yield a bi-layered
polymeric array aligned parallel to the ab plane of the crystal
(Fig. 4). In the resulting structure every Cd ion is seven-
coordinate. The organic ligand (both species are located in
general positions) adapted a somewhat more twisted conformation
than in the preceding examples. In one ligand of the asymmetric
Fig. 2 (a) The polymeric [Cu2(OH)(L)] coordination pillars in 3 propagating
along the c-axis of the crystal. Note the carboxylate functions of different organic
linkers that connect to it. The hydroxyls bridging between adjacent metal ions are
depicted in yellow. (b) View of the channeled (solvent omitted) crystal structure
approximately down c, showing how the organic linkers span in a trigonal
manner between three neighboring inorganic pillars of the structure.
and x = 1/2 and y = 1/2) that propagate through it parallel to the
c-axis. They consist of about 26% of the crystal volume, contain-
ing disordered DMA solvent. This framework solid can be best
described (by TOPOS, Fig. 3) as a (4,6,8)-connected 3-nodal net
15
¨
with Schlafli symbol {411.64}2{416.612}{45.6}.
The reaction product between the cadmium salt and H3L
could be obtained in the form of single crystals only in the presence
of 4,40-bipyridine (bpy) in the reaction mixture. The crystalline
networks are of ternary composition of 2 : 2 : 1 Cd2+ :L3ꢁ : bpy
stoichiometry (this is also the content of the asymmetric unit).
unit the torsions around the Csp –O bonds are 161.0(5) and
3
168.2(5)1 and the dihedral angles between the terminal and the
central aryl rings are 60.5(2) and 66.4(2)1. In the other crystallo-
graphically independent L-moiety the corresponding values are
164.5(6) and 176.9(7)1, and 64.5(2) and 76.5(3)1.
From the topological perspective, the coordinated pattern in
4 can be considered as a (2,3,4)-connected 3-nodal net with
15
¨
Schlafli symbol {63.83}2{63}2{8}. In the crystalline solid the
bi-layered polymers doubly interpenetrate into one another to
yield a three-dimensionally interweaved framework, as shown
in Fig. 5. The bipyridyl pillars of one bi-layer intrude through
the open voids of the lower part of the upper bilayer and the
upper part of the lower bilayer. The dimethyl ammonium
counter ions along with molecules of the DMA crystallization
solvent reside within voids between the layered networks.
Fig. 3 Simplified topological description of the 3-nodal polymeric framework in
3. The Cu-atoms are in green, organic linkers in blue and the bridging hydroxyls
in red.
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could arise from a selective depopulation of the Stark level or
indicates the presence of possible anti-ferromagnetic inter-
action between the Nd(III) ion through a carboxylate bridge.
Similar results were also obtained for previously reported
neodymium-containing coordination-polymeric compound.17
It is well-known that for systems containing Ln(III) ions the
effects of the magnetic exchange coupling are much weaker
than those of transition metal ions because the f orbitals are
well shielded by outer s and p orbitals and less extended than d
orbitals of transition metal ions. The spin–orbit coupling
plays an important role in the magnetism of lanthanide
complexes due to the internal nature of the valence f orbitals.
Theoretically, the lanthanide ions are characterized by the 4fn
configuration, which may be split into the 2S+1LJ state due to the
inter-electronic repulsion and spin–orbit coupling. Influenced
by the crystal field perturbation, each of these levels may be
further split into Stark sublevels which are thermally populated
at room temperature. By lowering the temperature, a depopu-
lation of these sublevels occurs, causing XMT decreases with
decreasing temperature. As a result, the nature of the inter-
action between Ln(III) with an orbital angular momentum
cannot be inferred clearly from the temperature dependence
of XMT in 2. Further difficulty is due to the fact that the
magnitude of the magnetic interaction between rare-earth ions
is usually comparable to that arising from the crystal field
effect and population of the first excited state for magnetic
contribution.16
Fig. 5 Topological description of the inter-weaved structure 4, viewed down
the a-axis of the crystal. The Cd nodes are marked in green, the tri-carboxylate
ligands in blue, and the bipyridyl bridges in purple.
The thermogravimetric analysis of the complexes was per-
formed under a N2 atmosphere. TGA curves (see Fig. S1 in the
ESI†) of compounds 1 and 2 show a weight loss of 12.9% and
13.4%, respectively at the temperature range 180–200 1C, which
corresponds to the release of coordinated DMA and water
molecules (the corresponding calculated values are 13.1%
and 13.6%). Decomposition of these coordination networks
was observed only above 450 1C. The TGA curve of compound
3 exhibits a gradual weight loss of 15.4% at the temperature of
150–180 1C due to an uncoordinated DMA molecule (calculated
14.9%) and the framework is stable up to 325 1C. Compound 4
exhibits weight loss of 9.4% within 150–180 1C due to escape of
the uncoordinated DMA and dimethyl amine (calculated
10.1%) molecules. Decomposition of this material occurs above
380 1C.
We also probed the magnetic behavior of compounds 2 and 3.
The variable-temperature magnetic susceptibilities were mea-
sured at an applied magnetic field of 500 Oe in the temperature
range of 5.0–300 K. The temperature dependence of the XM and
XMT product for 2 is shown in Fig. 6. XMT at 300 K is 1.59 cm3 K
molꢁ1, which is slightly lower than the expected value of 1.64
cm3 K molꢁ1 for a non interacting Nd(III) ion in the 4I9/2 ground
state (g = 8/11).16 As the temperature is lowered, the XMT
product decreases monotonously and slowly within the entire
temperature range and reaches 0.63 cm3 K molꢁ1 at 5 K.
Lowering the temperature caused a decrease in XMT, which
The presence of infinite Cu–OH–Cu bonds in 3 is expected to
give interesting magnetic behavior.18 The temperature depen-
dence of the XM and XMT product for 3 is shown in Fig. 7.
At room temperature, the XMT value of compound 3 is
0.74 cm3 molꢁ1 K for two Cu(II) ions (XMT = 0.375 cm3 molꢁ1
K
for a S = 1/2 system, single Cu(II) ions), which are close to the
value expected for two non coupled Cu(II) ions.16 Starting from
room temperature XMT values decrease quickly and approach
0.04 cm3 molꢁ1 K at 5 K, which indicates strong anti-ferromagnetic
interactions. The XM vs. T curve is also a typical one for an
anti-ferromagnetically coupled dinuclear system; it shows a
maximum at 100 K. The maximum appearing in the XM vs. T
curve indicates a significant anti-ferromagnetic couple between
Cu(II) ions through m-O bridges.19 The 1/XM vs. T data for
compound 3 fitted in the temperature range 80–300 K to the
Fig. 6 Plots of the temperature dependence of XMT and XM for compound 2.
Fig. 7 Plots of the temperature dependence of XMT and XM for compound 3.
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Curie–Weiss behavior, which gave a Weiss constant value linkers and denticity of the organic linker, as well as delicate
(y = ꢁ97.5 K). The highly negative values of Weiss constant tuning of the pH conditions during the reaction (preferably
obtained for compound 3 again indicate that the magnetic with the aid of non-coordinating reagents). Further evalua-
exchanges between the copper centers through the oxygen are tion of the metal–organic coordination polymers with the
strong. The short Cu–O distance (2.450 and 1.919 Å) and the H3L attractive building block will certainly throw more light
small angle of Cu–O–Cu (97.481) led to the very strong anti- on this issue.
ferromagnetic coupling through an oxo bridge. Similarly large
negative Weiss-constant values have been observed in other
Experimental section
copper-containing coordination compounds reported in the
literature.20
All chemicals for the syntheses were commercially available
reagents of analytical grade and were used without further
purification. The FT-IR spectra were recorded from KBr pellets
in the 4000–400 cmꢁ1 range on a Nicolet 5DX spectrometer.
Conclusions
In conclusion, the new tri-acid ligand reported herein provides Thermogravimetric analyses (TGA) were performed on a Perkin-
an excellent building block for the formulation of extended Elmer Pyris l (30–600 1C, 5 1C minꢁ1, flowing N2(g)). The
coordination-polymeric networks and frameworks both with magnetic data were collected on a Quantum Design MPMS
the oxophilic lanthanoid metal ions as well as d-shell transition SQUID-XL-5 magnetometer using crushed single-crystal
metals such as Cu or Cd. It has a mildly flexible conformation- samples. Magnetic data were corrected for the diamagnetic
tunable backbone and a bent shape, bearing three carboxylate contribution calculated from Pascal constants22 and a back-
(after de-protonation) ligating sites to transition metal ions ground of the sample holder.
oriented in diverging directions. The observed structures 1–4
differ in the nuclearity of the metal connectors, from poly-
Preparation of H3L
nuclear [Cu2OH]n arrays in 3, di-nuclear (Ce2/Nd2) clusters in 3,5-dihydroxy-methylbenzoate (185 mg, 1 mmol) was dissolved
1 and 2, to mono-nuclear Cd nodes in 4. The flexible nature of 20 mL of in acetonitrile, and then anhydrous K2CO3 was added.
H3L allows the ligand to conformationally adjust to the differ- The mixture was heated to reflux. After that 4-bromo-methyl
ent interaction types.
benzoate (460 mg, 2.01 mmol) was added. The reaction mixture
It is of particular interest to relate the above findings to was refluxed for 6 h. Then the solvent was removed and water
those reported recently for a closely related tripodal tricarboxylic was added, yielding a white solid. (Yield 358 mg, 75%.) In the
acid ligand, 3,5-bi(4-carboxyphenoxy)-benzoic acid (H3BCPBA), second step the isolated ester (1.79 g, 5 mmol) and NaOH (0.6 g,
and its coordination compounds with Co(II) ions.21 In that 15 mmol) were dissolved in 20 mL of ethanol : water (4 : 1). The
study, direct coordination of the ligand with the divalent reaction mixture was refluxed for 4 h at 80 1C, after which the
metal moiety resulted in the formation of a discrete 0D solvent was removed under reduced pressure, 10 mL of water
[Co(H2BCPBA)(H2O)4] complex. Formation of 2D and 3D was added into it and the solution was acidified (pH = 2) with
coordination polymers could be realized there only in the dilute HCl solution. The obtained white solid product H3L was
presence of additional auxiliary pyridyl ligands. The resulting filtered and washed with water until free from acid. Yield: 60%.
structures were characterized by diverse (metal : ligand: auxiliary FT-IR (KBr, cmꢁ1): 3286 (bs, gO–H), 2991 (mb, gC–H), 1680
ligand) stoichiometries, and represented coordination polymers (s, gCQO asymmetric), 1597 (s, gCQC), 1360 (m, gCQO symmetric),
of either two-dimensional or three-dimensional connectivity 1160 (s, gC–O), 1065 (w), 928 (s), 853 (w), 752 (s), 728 (w), 549 (m);
features of various topologies. Inter-weaving of the 2D and 3D 1H-NMR (DMSO-d6): 8.69 (4H, d), 7.68 (4H, d), 7.28 (2H, d), 7.06
polymeric arrays was observed as well. The H3BCPBA exhibited (1H, s), 5.35 (4H, s).
various degrees of de-protonation and conformational flexibility,
and the Co-centers in these compounds were of either mono-
Preparation of the coordination solids
nuclear, (m2-H2O)2-bridged di-nuclear, or (m2-H2O)4-bridged An important aspect of the solvothermal syntheses applied here
tri-nuclear nature.21
is to achieve conditions under which the rate of the ligand
It is apparent that, the inability to control the specific deprotonation matches that of the ligand–metal coordination
composition of the resulting materials, the metal–ligand binding bond formation. The DMA (as other related amides) solvent
modes, as well as the issue of network interpenetration, tends to undergo hydrolysis at the solvothermal conditions in
present a major weakness in this type of crystal engineering acidic environments, releasing amines capable of deprotonating
investigations. The possible take-home message from this and the carboxylic acid ligands and promote the reaction. Often,
preceding studies by others and us could be that in most cases addition of an inorganic acid is required along with other
it is relatively easy to design multi-dentate organic linkers with solvents (usually on an empirical basis for any given metal–
diverging molecular recognition groups for the construction ligand combination) to adjust the pH of the reaction mixture
of framework-polymeric solids. It is much more difficult to for optimal ligand deprotonation and dissociation of the
control the topology and constitution of the supramolecular metal–salt reactant.23 (1): A mixture of H3L (8.4 mg, 0.02 mmol)
architectures that form. This seems to require predominantly and Ce(NO3)3ꢀ6H2O (8.6 mg, 0.02 mmol) was dissolved in 8 mL
more careful matching between the valency of the metal of DMA/MeOH/water (1 : 1 : 0.5). A small amount of acetic acid
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was added to the mixture. The mixture was heated for 12 h in a maps but were not refined. Compounds 3 and 4 were found
bath-reactor at 100 1C, and after cooling to room temperature to contain disordered crystallization solvent within the intra-
colorless crystals were obtained, separated by filtration, washed lattice voids. The solvent species could be clearly recognized in
with water and DMA, and then dried in air. The yield was difference electron-density maps (per asymmetric unit: DMA in 3,
approximately 51% based on metal salt. FT-IR (KBr, cmꢁ1
,
and 4*DMA in 4), but could not be reliably modelled by
Fig. S2, ESI†): 2958 (mb, gC–H), 1579 (s, gCQO asymmetric), discrete atoms due to their severe disorder in the lattice.
1422 (s, gCQC), 1378 (m, gCQO symmetric), 1160 (s, gC–O), 1048 Correspondingly, the contribution of the disordered solvent
(w), 788 (s), 728 (w), 639 (m), 489 (w). (2): H3L (8.4 mg, moieties was subtracted from the diffraction pattern by the
0.02 mmol) and Nd(NO3)3ꢀ6H2O (8.7 mg, 0.02 mmol) were SQUEEZE procedure and PLATON software.26 The metal ions in
dissolved in 8 mL of DMA/MeOH/water (1 : 1 : 0.5). A small 1 and 2 are located at sites with crystallographically imposed
amount of acetic acid was added to the mixture. The latter mirror symmetry. The organic ligand species in 1–3 are located
was heated for 24 h in a bath-reactor at 120 1C, and after on axes of twofold rotation. The (OHꢁ) bridges in 4, required
cooling to room temperature colorless crystals were obtained, to balance the charge within the [Cu2(OH)-carboxylate]n
separated by filtration, washed with water and DMA, and then cluster originate most probably from the water solvent.
dried in air. The yield was approximately 49% based on metal Hydroxy-bridged poly-nuclear Cu-clusters have been observed
salt. FT-IR (KBr, cmꢁ1, Fig. S3, ESI†): 2942 (mb, gC–H), 1574 (s, frequently in coordination-polymeric assemblies involving
gCQO asymmetric), 1412 (s, gCQC), 1370 (m, gCQO symmetric), copper(II) ions.27
1160 (s, gC–O), 1041 (w), 780 (s), 710 (w), 630 (m), 479 (w). (3):
The crystal data for 1–4 are: (1) C27H26CeNO10, Mr = 664.61,
Cu(NO3)2ꢀ2.5H2O (9.2 mg, 0.04 mmol) and H3L (8.4 mg, monoclinic, space group C2/m, a = 13.7661(5), b = 24.6948(11),
0.02 mmol) were dissolved in 8 mL of DMA : water (1 : 1). c = 8.3773(10) Å, b = 105.686(5)1, V = 2741.8(4) Å3, T = 110 K, Z = 4,
A small amount of HNO3 was added to this mixture. The m(MoKa) = 1.717 mmꢁ1, rcalcd = 1.610 g cmꢁ3, 8843 reflec-
mixture was heated for 48 h in a bath-reactor at 95 1C, and tions measured to ymax = 25.321, of which 2508 were unique
after cooling to room temperature blue crystals were obtained, (Rint = 0.036) and 2189 with I 4 2s(I). Final R1 = 0.034 (wR2 =
separated by filtration, washed with water and DMA, and then 0.082) for the 2189 data above the intensity threshold, and R1 =
dried in air. Yield: 52% based on metal salt. FT-IR (KBr, cmꢁ1
Fig. S4, ESI†): 2922 (mb, gC–H), 1568 (s, gCQO asymmetric), 1409
(s, gCQC), 1364 (m, gCQO symmetric), 1160 (s, gC–O), 1048 (w), a = 13.6593(4), b = 24.5441(11), c = 8.4234(3) Å, b = 105.445(3)1,
766 (s), 715 (w), 602 (m), 458 (w). (4): H3L (8.4 mg, 0.02 mmol), V = 2722.0(2) Å3, T = 110 K, Z = 4, m(MoKa) = 1.965 mmꢁ1, rcalcd
,
0.043 (wR2 = 0.086) for all unique data. CCDC 918381. (2)
27H26NNdO10, Mr = 668.72, monoclinic, space group C2/m,
C
=
Cd(NO3)2ꢀ4H2O (12.3 mg, 0.04 mmol) and 4,40-bipyridine 1.632 g cmꢁ3, 10937 reflections measured to ymax = 27.861, of
(1.5 mg, 0.01 mmol) were dissolved in 8 mL of DMA : MeOH which 3241 were unique (Rint = 0.045) and 2734 with I 4 2s(I).
(1 : 1) and 0.05 mL of 12N HNO3 was added. This mixture was Final R1 = 0.040 (wR2 = 0.095) for the 2734 data above the
heated for 96 h in a bath-reactor at 100 1C, and after cooling to intensity threshold, and R1 = 0.052 (wR2 = 0.100) for all unique
room temperature colorless crystals were obtained, separated data. CCDC 918382. (3) C23H15Cu2O9ꢀ(C4H9NO) (the disordered
by filtration, washed with water and DMA, and then dried in air DMA solvent was excluded from the refined structural model),
(yield 55% based on metal salt). FT-IR (KBr, cmꢁ1, Fig. S5, ESI†): Mr = 649.55, monoclinic, space group C2/c, a = 17.8091(4),
2922 (mb, gC–H), 1580 (s, gCQO asymmetric), 1429 (s, gCQC), b = 25.5978(7), c = 5.7377(2) Å, b = 98.156(1)1, V = 2589.2(1) Å3,
1344 (m, gCQO symmetric), 1160 (s, gC–O), 1058 (w), 756 (s), T = 110 K, Z = 4, m(MoKa) = 1.704 mmꢁ1, rcalcd = 1.666 g cmꢁ3
,
705 (w), 612 (m), 448 (w). The uniform identity of the formed 14289 reflections measured to ymax = 27.821, of which 3075 were
crystal lattices in a given reaction were confirmed in each case unique (Rint = 0.048) and 2675 with I 4 2s(I). Final R1 = 0.040
by spectroscopic data as well as by uniform morphology of (wR2 = 0.110) for the 2675 data above the intensity threshold,
crystals in the bulk, repeated measurements of the unit-cell and R1 = 0.047 (wR2 = 0.114) for all unique data. CCDC 918383.
dimensions from different single crystallites, and powder X-ray (4) C56H38Cd2N2O16ꢀ2(C2H8N)ꢀ4(C4H9NO) (the disordered DMA
diffraction data (for 2 and 3; Fig. S6 and S7 in the ESI†).
solvent was excluded from the refined structural model),
%
Mr = 1660.36, triclinic, space group P1, a = 15.3997(9),
b = 15.4635(9), c = 17.2247(10) Å, a = 93.145(3), b = 114.157(2),
Crystal structure determination
The X-ray measurements (Nonius-Kappa CCD, MoKa radiation) g = 100.775(3)1, V = 3636.9(4) Å3, T = 110 K, Z = 2, m(MoKa) =
were carried out at ca. 110(2) K on crystals coated with a thin 0.665 mmꢁ1, rcalcd = 1.516 g cmꢁ3, 28 863 reflections measured
layer of amorphous oil to minimize crystal deterioration, to ymax = 25.051, of which 12 824 were unique (Rint = 0.077) and
possible structural disorder and related thermal motion effects, 8927 with I 4 2s(I). Final R1 = 0.068 (wR2 = 0.150) for the 8927
and to optimise the precision of the structural results. These data above the intensity threshold, and R1 = 0.098 (wR2 = 0.160)
structures were solved by direct methods and refined by full- for all unique data. CCDC 918384.
matrix least-squares (SIR-97 and SHELXL-97).24,25 All non-
hydrogen atoms were refined anisotropically. The hydrogen
atoms were located in idealized/calculated positions and
Acknowledgements
were refined using a riding model; some of those involved in This research was supported by The Israel Science Foundation
hydrogen bonds were located directly in difference-Fourier (Grant No. 502/08 and 108/12).
c
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