Anionic bipyridyl ligands for applications in metallasupramolecular chemistry

Article abstract of DOI:10.1002/chem.201400285

The facile synthesis of anionic bipyridyl ligands with dinuclear clathrochelate cores is described. These metalloligands can be obtained in high yields by the reactions of M(ClO₄)₂(H₂O) ₆ (M: Zn, Mn, or Co) with 4-pyridylboronic acid and 2,6-diformyl-4-methylphenol oxime or 2,6-diformyl-4-tert-butylphenol oxime, followed by deprotonation. The ligands are interesting building blocks for metallasupramolecular chemistry, as evidenced by the formation of a Pt-based molecular square and four coordination polymers with 2D or 3D network structures. Competition experiments reveal that the utilization of anionic bipyridyl ligands can result in significantly more stable assemblies. Its good to be negative: Anionic bipyridyl ligands with dinuclear clathrochelate cores (see scheme) are easily obtained from simple starting materials. These ligands are interesting building blocks for metallasupramolecular chemistry. The utilization of anionic bipyridyl ligands can result in significantly more stable assemblies.

Full text of DOI:10.1002/chem.201400285

DOI: 10.1002/chem.201400285
Full Paper
&
Supramolecular Chemistry
Anionic Bipyridyl Ligands for Applications in
Metallasupramolecular Chemistry
Mirela Pascu,[a] Mathieu Marmier,[a] Clꢀment Schouwey,[a] Rosario Scopelliti,[a]
Julian J. Holstein,[b] Gꢀrard Bricogne,[b] and Kay Severin*[a]
Abstract: The facile synthesis of anionic bipyridyl ligands
with dinuclear clathrochelate cores is described. These
metalloligands can be obtained in high yields by the reac-
tions of M(ClO4)2(H2O)6 (M: Zn, Mn, or Co) with 4-pyridylbor-
onic acid and 2,6-diformyl-4-methylphenol oxime or 2,6-di-
formyl-4-tert-butylphenol oxime, followed by deprotonation.
The ligands are interesting building blocks for metallasupra-
molecular chemistry, as evidenced by the formation of a Pt-
based molecular square and four coordination polymers
with 2D or 3D network structures. Competition experiments
reveal that the utilization of anionic bipyridyl ligands can
result in significantly more stable assemblies.
Introduction
Bipyridyl ligands are among the most frequently used building
blocks for supramolecular coordination chemistry.[1] The simple
4,4’-bipyridine (bpy) ligand has been employed for a long
time, as exemplified by the molecular square [{(en)Pd(bpy)}4]8+
(en: ethylenediamine) published in 1990.[2] Today, one can find
more than 1000 entries for structures of the type LnM(bpy)MLn
in the Cambridge Structural Database.[3] Of course, many struc-
tural variants of 4,4’-bipyridine have been explored over time.
Bipyridyl ligands containing metal ions (“metalloligands”) are
an interesting subclass in this context.[1,4] The metal ions can
add novel properties, such as color, redox activity, magnetism,
molecular-recognition sites, or catalytic activity. Furthermore,
the metal ions can facilitate the synthesis of the bipyridyl
ligand if metal-templated reactions are employed. Some repre-
sentative examples of metal-containing bipyridyl ligands are
depicted in Figure 1. Complexes of type A have mainly been
used as “expanded ligands” for structural investigations.[4a,e]
Metallaporphyrins of type B[4d,f] and salen-type complexes of
type C possess accessible metal sites, which can be used for
molecular recognition (for example, in sensing applications)[5]
or for catalysis.[6] We have recently introduced clathrochelate-
based bipyridyl ligands of types D and E.[7] These ligands are
rigid, long (approximately 3.2 nm for E with n=2), well soluble,
and easily accessible in a one-pot reaction from commercially
Figure 1. Examples of metal-containing bipyridyl ligands.
available starting materials. Below, we describe a different class
of clathrochelate complexes with terminal pyridyl groups. The
new bipyridyl ligands display an interesting characteristic for
applications in metallasupramolecular chemistry: they are neg-
atively charged.
[a] Dr. M. Pascu, M. Marmier, C. Schouwey, Dr. R. Scopelliti, Prof. K. Severin
Institut des Sciences et Ingꢀnierie Chimiques
ꢁcole Polytechnique Fꢀdꢀrale de Lausanne (EPFL)
1015 Lausanne (Switzerland)
E-mail: kay.severin@epfl.ch
[b] Dr. J. J. Holstein, Dr. G. Bricogne
Global Phasing Ltd., Sheraton House
Castle Park, Cambridge CB3 0AX (UK)
Results and Discussion
In 2006, Chaudhuri and co-workers reported the synthesis and
structure characterization of a dinuclear MnII clathrochelate
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201400285.
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complex with bridging phenolatodioximato ligands and cap-
ping methylboronate esters.[8] We hypothesized that similar di-
nuclear complexes could be used to build bipyridyl ligands.
Indeed, macrobicyclic MII tris(dioximato) complexes (M: Zn, Co,
or Mn) with terminal pyridyl groups were obtained by subcom-
ponent self-assembly[9] of three compounds, M(ClO4)2(H2O)6,
4-pyridylboronic acid, and 2,6-diformyl-4-methylphenol oxime
(L1) or 2,6-diformyl-4-tert-butylphenol oxime (L2), in dichloro-
methane/ethanol (Scheme 1). Products 1–6 precipitated from
Single-crystal X-ray structure analyses of 4 and 5 confirmed
the presence of dinuclear clathrochelate cores with terminal
pyridyl groups. A graphical representation of the structure of
complex 4 is given in Figure 2, and selected bonds lengths
and angles for 4 and 5 are summarized in Table 1. The two MII
Figure 2. Molecular structure of complex 4 in the crystal. Most of the hydro-
gen atoms have been omitted for clarity.
Table 1. Selected distances [ꢂ] and angles [8] for the complexes 4, 5, 7,
and 8.
M···M [ꢂ]
MÀNav [ꢂ]
MÀOav [ꢂ]
MÀOÀMav [8]
NÀMÀOav [8]
4
5
7
8
2.9401(17)
2.9591(10)
2.9436(8)
2.9080(10)
2.12
2.10
2.12
2.18
2.10
2.10
2.10
2.14
88.9
89.6
88.8
85.6
82.4
83.0
82.4
80.7
Scheme 1. Synthesis of the clathrochelates 1–6.
the reaction mixtures in the form of microcrystalline materials.
All of the complexes were obtained in high yield (>80%), with
the exception of complex 6, for which a somewhat lower yield
of 65% was observed. The reactions were performed without
the addition of a base, so the products were obtained in the
diprotonated form with perchlorate as the counteranion. The
cationic complexes are only soluble in polar organic solvents
such as DMF or DMSO.
ions in 4 and 5 are coordinated in a trigonal prismatic fashion
by three nitrogen and three oxygen atoms. The latter bridge
the two metal ions, which results in M···M distances of
2.9401(17) ꢂ (4) and 2.9591(10) ꢂ (5). At 1.490 ꢂ, the average
BÀO bond length of the tetragonal boronate esters is similar
to what is found for mononuclear chlathrochelates with
boronate ester caps.[7,10] The N atoms of the pyridyl groups in
4 and 5 are 17.91 ꢂ and 17.87 ꢂ apart from each other, respec-
tively. The clathrochelate ligands are thus substantially longer
than mononuclear clathrochelates of type D (14.95 ꢂ; Figure 1).
The NH groups of the protonated pyridyl groups are involved
in hydrogen bonding to the perchlorate anion (NH···O in 4:
2.729 ꢂ; NH···O in 5: 2.817 ꢂ).
The cationic clathrochelates can be deprotonated by the ad-
dition of a base: when triethylamine or tetraethylammonium
hydroxide was added to a solution of 1, 3, or 4 in acetonitrile/
methanol, the anionic complexes 7–9 were obtained in high
yield (Scheme 2). The solubility of the anionic complexes is
higher than that of the cationic perchlorates: the complexes
display a good solubility (>10 mgmLÀ1) in acetonitrile/meth-
anol (1:1), acetone, or CHCl3.
Clathrochelates 1–6 were analyzed by elemental analysis
and mass spectrometry. The diamagnetic Zn complexes 1 and
4 were also characterized by NMR spectroscopy. As expected,
only one set of signals was observed for the three phenolato-
dioximato ligands. The “free” ligands L1 and L2 showed lumi-
nescence with emission maxima at 392 nm (L1) and 387 nm
(L2; in DMF; lex =340 nm). Solutions of the Co and Mn com-
plexes did not show significant luminescence, presumably due
to quenching by the paramagnetic metal ions. The Zn com-
plexes 1 and 4 however, were highly emissive, with maxima at
451 nm for 1 and 445 nm for 4 (in DMF; lex =340 nm). Due to
the inert character of the Zn2+ ions, the photoluminescence
can be assigned to intraligand (IL) and/or ligand-to-ligand
charge transfer (LLCT) emissions. The magnetic properties of
the Co and Mn complexes were not investigated. However, it
is expected that the Mn complexes 3 and 6 show very similar
behavior to that of the previously reported clathrochelate with
methylboronate ester end groups. For the latter, a magnetic
moment of 7.13 mB (290 K) and antiferromagnetic exchange
coupling between the two paramagnetic MnII centers was ob-
served.[8]
Crystallographic analyses of 7 and 8 show that the deproto-
nation has only a minor influence on the structure: the bond
lengths and angles observed for the anions of 7 and 8 are very
similar to those of the cations of 4 and 5 (Figure 3). The N···N
distances in 7 (17.99 ꢂ) and 8 (17.98 ꢂ) are marginally longer
than those found for 4 and 5.
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Scheme 2. Synthesis of the anionic bipyridyl ligands 7–9.
Figure 3. Molecular structure of complex 8 in the crystal. Most of the hydro-
gen atoms have been omitted for clarity.
Scheme 3. Synthesis of the molecular square 10.
After having established a facile synthetic route for the syn-
thesis of anionic clathrochelates with pyridyl end groups, we
examined the potential of these bipyridyl ligands in structural
supramolecular chemistry. It is well known that rigid, linear bi-
pyridyl ligands react with cis-protected square-planar Pd and
Pt complexes to form square-shaped structures.[1e,11] We postu-
lated that our new ligands would react in a similar fashion,
and we therefore studied the reaction of 9 with Pt(dppp)(OTf)2
(dppp: 1,3-bis(diphenylphosphino)propane; OTf: trifluorometh-
anesulfonate). Complex 9 was chosen because it is diamagnet-
ic and because of its superior solubility compared to that of 7.
Multinuclear NMR analysis of a 1:1 solution of 9 and Pt(dppp)-
(OTf)2 in DMSO indicated the formation of a single product
possessing a high degree of symmetry. Isolation of the product
as a pale yellow amorphous powder was achieved by precipi-
tation upon addition of CHCl3. Complex 10 displays poor solu-
bility in most common solvents, with the exception of polar
aprotic solvents such as DMSO and DMF. The analytical data of
10 (NMR, elemental analysis, and ESI-MS) confirmed the forma-
tion of a molecular square (Scheme 3).
Scheme 4. Disruption of the molecular squares 10 and 11 by addition of
pyridine ([D5]pyridine was used for the NMR experiments).
The presence of a negative charge on the clathrochelate
ligand was expected to result in a more stable assembly.[12] To
investigate this hypothesis, we compared the stability of 10
with that of the known bpy analogue [(dppp)Pt(bpy)]4(OTf)8
(11).[13] Increasing amounts of the N-donor [D5]pyridine were
added to solutions of 10 or 11 in [D6]DMSO (Scheme 4). Pyri-
dine competes with the bridging ligand for complexation to
the Pt centers and therefore results in rupture of the assembly.
The amount of remaining square complex was then deter-
1
mined by H or 31P NMR spectroscopy. The results are summar-
ized in Figure 4. Addition of only one equivalent of [D5]pyridine
to a solution of 11 resulted in significant ligand exchange, and
no starting material could be observed after the addition of
approximately seven equivalents. In contrast, more than 50%
of square 10 was still present after addition of approximately
10 equivalents of [D5]pyridine, and more than 100 equivalents
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upon heating to generate a basic medium.[14] The base can de-
protonate the pyridyl groups of 1 and 4. In this way, the net-
work is formed slowly and crystallizes directly from the reac-
tion mixture. Attempts to perform the same reaction with the
deprotonated metalloligands 7 or 9 resulted in the immediate
formation of powders.
Crystallographic analyses of the coordination polymers 12
and 13 revealed 2D square-grid-type layer structures with
square dimensions of 22.3ꢃ22.3 ꢂ (Figure 5). Four metallo-
Figure 4. Ratio of starting material 11 (*) or 10 (*) present in solution rela-
tive to the initial 2.0 mm concentration in [D6]DMSO upon an increase in the
concentration of the competitor [D5]pyridine.
were needed before the concentration of square 10 dropped
below 5% of the initial concentration. The complexity of the
equilibria involved in the formation and disruption of these
molecular squares made it impossible to accurately derive the
thermodynamic parameters. However, the results clearly show
that the assembly between (dppp)Pt2+ and the clathrochelate-
based bipyridyl ligand 9 is significantly more stable than the
square formed between (dppp)Pt2+ and the standard bpy
ligand.
Figure 5. Part of the layer structure of coordination polymer 12 with a view
along the crystallographic z axis. Hydrogen atoms and solvent molecules
have been omitted for clarity. C: grey; O: red; N: blue; B: green; Zn: cyan.
Bipyridyl ligands have been used extensively for the con-
struction of metal–organic frameworks (MOFs).[1d] To demon-
strate that our clathrochelate-based bipyridyl ligands can also
be used in this area, we have investigated the reactions of
1 and 4 with Zn2+ and Cd2+ ions. Heating of a mixture of Zn-
(NO3)2(H2O)6 and the protonated metalloligands 1 or 4 in DMF
in a sealed vial resulted in the formation of the crystalline coor-
dination polymers 12 and 13 (yields of 66 and 89%, respec-
tively; Scheme 5). It is known that DMF decomposes slowly
ligands are connected through ZnII ions. The latter have an oc-
tahedral coordination geometry with two additional DMF mol-
ecules in the trans positions. Overall, the networks are neutral,
because the anionic clathrochelate ligands compensate for the
charge of the ZnII ions. It is worth mentioning that MII-based
MOFs with square-grid-type layer structures have been report-
ed previously in the literature.[15] In contrast to 12 and 13, the
square substructures are typically smaller and the anions are
coordinated to the bridging M2+ ions (Figure 5).
The 2D networks of 12 and 13 both show an ABAB-type
packing arrangement (Figure 6). Due to the presence of the
bulky tert-butyl groups, the interlayer distance of the planes
defined by the bridging Zn2+ ions is larger for 13 (23.7 ꢂ) than
for 12 (18.6 ꢂ). The solvent-accessible volume, as calculated by
the PLATON software,[16] is larger for 12 (25%) than for 13
(21%).
Figure 6. Space filling representation of the structures of 12 (left) and 13
(right) highlighting the packing of two adjacent layers. Solvent molecules
have been omitted for clarity.
Scheme 5. Syntheses of the two-dimensional coordination polymers 12 and
13.
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In order to avoid scrambling of the metal ions, reactions of
Zn-based clathrochelates with Cd2+ ions were performed
under milder conditions. Large single crystals of the coordina-
tion polymers 14 and 15 (yield for both: 80%) were obtained
by slow diffusion of a methanolic solution of Cd(ClO4)2(H2O)6
into a DMF solution of the deprotonated metalloligands 7 or 9
(Scheme 6). A crystallographic analysis of the heterometallic
Scheme 6. Syntheses of the coordination polymers 14 and 15.
coordination polymer 15 revealed a layer structure that is very
similar to what was observed for 13. Four metalloligands are
connected through octahedral Cd(DMF)2 units to form 22.2ꢃ
22.8 ꢂ squares. In contrast to what was found for 13, an ABBA-
type packing arrangement is observed. The interlayer distance
is 10.6 ꢂ, and the calculated solvent-accessible volume is 30%.
The crystallographic analysis of polymer 14 was hindered by
disorder of the Cd ions and their coordinated clathrochelate li-
gands. Located next to a special position (inversion center),
the occupancies are split 50:50. Key to a successful refinement
was the utilization of stereochemical restraints for the clathro-
chelate ligand, which were generated by the GRADE pro-
gram.[17,18] This macromolecular refinement technique has
been adapted to be used in the SHELXL program.[19] Its first ap-
plication in a supramolecular chemistry context was the refine-
ment of a tetranuclear coordination cage.[20] The method dras-
tically increases the robustness of the refinement, especially if
it is combined with the new rigid bond restraint in the SHELXL
2013 (RIGU) program.[21] The ShelXle program,[22] which sup-
ports the macromolecular residue grouping, was used as
a graphical user interface (GUI). More crystallographic details
can be found in the Experimental Section.
Figure 7. Part of the 3D network structure of coordination polymer 14. Hy-
drogen atoms and solvent molecules have been omitted for clarity. C: grey;
O: red; N: blue; B: green; Zn: cyan; Cd: pink.
mic shift can be observed relative to the solid state spectra of
the protonated metalloligands 1 (lmax =515 nm) and 4 (lmax
=
469 nm). This shift is probably induced by the coordination of
the pyridyl groups to the Zn2+ and Cd2+ ions.
Thermogravimetric analyses of 12–15 show that the struc-
turally related networks 12, 13, and 15 are all thermally stable
up to approximately 3008C. Coordination polymer 14 was
found to be more susceptible to thermal degradation, which
confirmed indirectly that it possesses a unique structure.
BET surface measurements (N2, 77 K) after drying under
vacuum gave low values for the coordination polymers 12
(54 m2 gÀ1) and 14 (10 m2 gÀ1), both of which are based on
a clathrochelate ligand with methyl substituents on the pheno-
latodioximato ligand. Significantly higher values were observed
for the tert-butyl-containing 13 (556 m2 gÀ1) and 15
(700 m2 gÀ1; pore volume=0.412 cm3gÀ1). These differences
show that the lateral size of the clathrochelates can have a pro-
nounced influence on the physical properties of the resulting
assemblies.
Surprisingly, coordination polymer 14 shows a completely
different structure than the analogous Zn network 12. A 3D
network structure with two types of octahedral Cd nodes is
observed. Both Cd centers are bound to four pyridyl groups,
but one is bound to two DMF molecules in the trans positions
(“Cd1”), whereas the other one features two DMF ligands in cis
positions (“Cd2”). This arrangement gives rise to a 3D network,
with layers of (Cd1)2(Cd2)2 rhombuses, which are linked
through Cd2 centers by two clathrochelate metalloligands
(Figure 7). The latter are oriented perpendicular to the plane
defined by the Cd atoms. The network is neutral, because the
anionic bipyridyl ligands compensate for the charge of the
Cd2+ ions. The framework is twofold interpenetrated. The cal-
culated solvent-accessible volume is 45% of the unit cell
volume.
Conclusion
We have described the synthesis of dinuclear ZnII, MnII, and CoII
clathrochelates with terminal pyridyl groups. These complexes
were obtained in high yield by one-pot reactions of M(ClO4)2
salts with phenolatodioximato ligands and pyridylboronic acid.
Upon deprotonation, anionic bipyridyl ligands are obtained.
These ligands have interesting characteristics for applications
in supramolecular coordination chemistry: 1) they are robust,
rigid, and relatively long; 2) the lateral size and the solubility of
the ligands can be modified by variation of the phenolatodiox-
imato ligand; 3) the Zn-based clathrochelates are luminescent;
and 4) it is possible to incorporate diamagnetic or paramagnet-
ic metal ions. To demonstrate that these ligands are indeed
useful building blocks in metallasupramolecular chemistry, we
have synthesized the molecular square 10 as an example of
a molecularly defined nanostructure, as well as the coordina-
tion polymers 12–15. By using competition experiments, we
The Zn-based clathrochelates are luminescent, so we have
also investigated the photoluminescence of the coordination
polymers 12 and 15 in the solid state. The Zn-based polymer
12 exhibits an emission maximum at 467 nm (lex =380 nm),
and the heterometallic Zn/Cd coordination polymer 15 shows
an emission maximum at 455 nm (lex =390 nm). A hypsochro-
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perchlorate are potentially explosive and should be handled
with care!
were able to demonstrate that complex 10 is significantly
more stable than an analogous assembly with the standard
4,4-bipyridine ligand. The increased stability is attributed to
the presence of an anionic charge on the clathrochelate, which
reduces the overall charge of the metallamacrocycle. The pos-
sibility to make more stable metal-based assemblies is certainly
an interesting aspect of this new class of ligands. The success-
ful synthesis of the coordination polymers 12–15 is the first
evidence for the utility of clathrochelate-based pyridyl ligands
in the field of metal–organic frameworks. The negative charge
of the metalloligands is again an important point, because it
reduces or even eliminates the need for anionic coligands to
compensate for the charge of the metal ions. The lateral size
of the clathrochelate ligands can be controlled by the choice
of the phenolatodioximato ligands. So far, we have explored
methyl- and tert-butyl substituents on the phenolato ligand.
The importance of such modifications was evidenced by the
pronounced differences that were observed for the specific
surface areas of 12 and 13. Overall, we think that dinuclear cla-
throchelates are an interesting new class of metalloligands
with a lot of potential for applications in molecular nano-
science.
General procedure for the synthesis of 1–3
A mixture of ligand L1 (201 mg, 108 mmol) and 4-pyridylboronic
acid (88 mg, 720 mmol) was heated in a mixture of dichlorometh-
ane/ethanol (1:1, 20 mL) until all of the boronic acid had dissolved.
Solid M(ClO4)2(H2O)6 (M: Zn, 268 mg, 720 mmol; M: Co, 263 mg,
720 mmol; M: Mn, 260 mg, 720 mmol) was then added, and the so-
lution was stirred for 1 h. The yellow (1 and 3) or orange (2) micro-
crystalline precipitate was filtered, washed with cold ethanol, and
dried under vacuum.
Complex 1: Yield: 0.31 g, 81%; 1H NMR (400 MHz, [D7]DMF): d=
2.20 (s, 9H, CH3), 7.21 (s, 6H, CHar), 8.38 (d, 4H, J=6.4 Hz, CHpy),
8.42 (s, 6H, CHim), 9.00 ppm (d, 4H, J=6.6 Hz, CHpy); 13C NMR
(100 MHz, [D7]DMF): d=163.77 (CÀOPh), 155.51 (C=N), 139.97 (CHar),
136.96 (Car), 130.39 (CHar), 124.34 (Car), 119.29 (CHar), 19.55 ppm
(CH3) (BÀC was not observed); ESI-MS: m/z: 883.0644 [M+2H]+; el-
emental analysis: calcd (%) for Zn2C37H31N8B2O9(ClO4)(CH2Cl2)
(1068.47 gmolÀ1): C 42.71, H 3.11, N 10.48; found: C 42.83, H 3.42,
N 10.47; FTIR: n˜max: 3413 (br), 2928 (br), 1615 (m), 1594 (m), 1554
(m), 1445 (s), 1321 (s), 1186 (m), 1084 (s), 997 (vs), 935 (vs), 815 (vs),
758 (s), 621 cmÀ1 (s).
Complex 2: Yield: 0.30 g, 83%; ESI-MS: m/z: 871.1042 [M+2H]+;
elemental analysis: calcd (%) for Co2C37H31N8B2O9(ClO4)(CH2Cl2)0.5
(1013.09 gmolÀ1): C 44.45, H 3.18, N 11.06; found: C 44.60, H 3.32,
N 11.07; FTIR: n˜max: 3248 (br), 1614 (m), 1591 (m), 1556 (m), 1445
(s), 1313 (s), 1201 (m), 1089 (s), 1000 (vs), 937 (vs), 816 (vs), 761 (s),
620 cmÀ1 (s).
Experimental Section
General
All reagents were obtained from commercial sources. Ligand L1
was prepared according to a literature procedure.[8] The synthesis
of ligand L2 and Pt(dppp)Cl2 is described in the Supporting Infor-
mation. Pt(dppp)(OTf)2 and the molecular square 11 were synthe-
sized as described in the literature.[13] 1H and 13C NMR spectra were
obtained on a Bruker Avance instrument (1H: 400 MHz; 13C:
Complex 3: Yield: 0.25 g, 87%; ESI-MS: m/z: 861.1017 [M+2H]+;
elemental analysis: calcd (%) for Mn2C37H31N8B2O9(ClO4)(CH2Cl2)2
(1132.50 gmolÀ1): C 41.36, H 3.11, N 9.89; found: C 41.39, H 3.08, N
10.31; FTIR: n˜max: 2982 (br), 1603 (m), 1578 (m), 1545 (m), 1473 (s),
1321 (s), 1200 (m), 1181 (m), 1029 (s), 991 (vs), 927 (vs), 819 (vs),
758 (s), 684 cmÀ1 (s).
1
100 MHz). H and 13C chemical shifts (d) are reported in parts per
million (ppm) referenced to the internal solvent. All spectra were
recorded at room temperature. Electrospray-ionization MS data
were acquired on a Q-Tof Ultima mass spectrometer (Waters) oper-
ated in the positive ionization mode, and data were processed by
using the MassLynx 4.1 software. APPI-FT-ICR experiments were
performed on a hybrid linear ion trap Fourier transform ion cyclo-
tron resonance mass spectrometer (LTQ FT-ICR MS, Thermo Scien-
tific, Bremen, Germany) equipped with a 10 T superconducting
magnet (Oxford Instruments Nanoscience, Abingdon, UK). Data
analysis was carried out by using XCalibur software (Thermo Scien-
tific, Bremen, Germany). IR spectra were recorded on a Perkin–
Elmer Spectrum One Golden Gate FT/IR spectrometer. Combustion
analysis was performed with a Thermo Scientific Flash 2000 Organ-
ic elemental analyzer. Diffuse reflectance spectra were carried out
by using a Perkin–Elmer Lambda 900 UV/VIS/NIR spectrometer
with a PELA-1000 accessory within the wavelength range of 200–
800 nm. Emission spectra were recorded with Varian Cary Eclipse
or Perkin–Elmer LS-50 spectrofluorimeters. Thermogravimetric anal-
ysis was performed on a Mettler-Toledo TGA/SDTA851e instrument
equipped with a TSO800GC1 gas control unit. Data were collected
by using the STARe software and processed in Microsoft Excel. The
sample was heated from 35 to 6008C at a rate of 28C per minute
in an alumina crucible under a 60 mLminÀ1 flow of N2. Nitrogen-
sorption measurements were performed on a Quantachrome Auto-
sorb iQ surface area analyzer. Before the measurements, the poly-
mers were dried under a high vacuum for 12 h at 1208C. The BET
analyses were performed at 77.3 K. Note: compounds containing
General procedure for the synthesis of 4–6
A mixture of ligand L2 (0.66 g, 2.79 mmol) and 4-pyridylboronic
acid (0.23 g, 1.86 mmol) was heated in a mixture of dichlorometh-
ane/ethanol (1:1, 20 mL) until all of the boronic acid had dissolved.
Solid M(ClO4)2(H2O)6 (M: Zn, 0.69 g, 1.86 mmol; M: Co, 0.68 g,
1.86 mmol; M: Mn, 0.67 g, 1.86 mmol) was then added, and the so-
lution stirred for 1 h. The yellow (4 and 6) or orange (5) microcrys-
talline precipitate was filtered, washed with cold ethanol, and
dried under vacuum.
Complex 4: Yield: 0.98 g, 88%; X-ray-quality crystals were formed
by slow evaporation of the mother liquor; 1H NMR (400 MHz,
[D6]DMSO): d=1.22 (s, 27H, (CH3)3), 7.37 (s, 6H, CHar), 8.20 (d, 4H,
J=6.5 Hz, CHpy), 8.44 (s, 6H, CHim), 8.79 ppm (d, 4H, J=6.5 Hz,
CHpy); 13C NMR (100 MHz, [D6]DMSO): d=162.56 (CÀOPh), 155.10
(C=N), 139.17 (CHar), 137.36 (Car), 132.97 (CHar), 129.46 (Car), 117.99
(CHar), 33.44(C(CH3)3), 31.11 ppm (C(CH3)3), (BÀC was not observed);
ESI-MS: m/z: 1009.2392 [M+H]+; elemental analysis: calcd (%) for
Zn2C46H49N8B2O9(ClO4) (1109.78 gmolÀ1): C 49.79, H 4.45, N 10.10;
found: C 50.35, H 4.51, N 10.23; FTIR: n˜max: 3242 (br), 2949 (m),
1612 (m), 1550 (m), 1444 (s), 1326 (s), 1221 (s), 1198 (s), 1075 (s),
1035 (s), 998 (vs), 938 (vs), 838 (m), 771 (s), 695 (s), 618 cmÀ1 (s).
Complex 5: Yield: 0.90 g, 89%; X-ray-quality crystals were formed
by slow evaporation of the mother liquor; ESI-MS: m/z: 499.1277
[M+2H]2+; elemental analysis: calcd (%) for Co2C46H49N8O9(ClO4)
(1075.44 gmolÀ1): C 51.38, H 4.59, N 10.42; found: C 51.00, H 4.40,
Chem. Eur. J. 2014, 20, 5592 – 5600
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N 10.41; FTIR: n˜max: 2955 (br), 1610 (m), 1550 (m), 1445 (s), 1365
(m), 1325 (s), 1285 (m), 1200 (m), 1080 (s), 1035 (vs), 940 (vs), 840
(vs), 770 (s), 620 cmÀ1 (s).
Complex 6: Yield: 0.57 g, 65%; ESI-MS: m/z: 989.2579 [M+2H]+;
elemental analysis: calcd (%) for Mn2C46H49N8B2O9(ClO4)
(1088.87 gmolÀ1): C 50.74, H 4.54, N 10.29; found: C 50.91, H 4.62,
N 10.44; FTIR: n˜max: 2955 (br), 1630 (m), 1580 (m), 1545 (m), 1445
(s), 1330 (s), 1280 (m), 1195 (m), 1020 (s), 990 (vs), 935 (vs), 805 (vs),
780 (s), 690 cmÀ1 (s).
d=1.10 (s, 108H, CH3), 1.98 (br, 8H, CH2), 3.26 (br, 16H, CH2), 7.25
(s, 24H, Ar-H), 7.30 (d, 16H, Ar-H), 7.47 (t, 32H, Ar-H), 7.60 (t, 16H,
Ar-H), 7.73 (t, 32H, Ar-H), 8.26 (s, 24H, CH), 8.49 ppm (d, 16H, Ar-
H); 13C NMR (150 MHz, [D6]DMSO): d=17.3 (CH2), 21.5 (CH2), 31.1
(CH3), 33.3 (Cq), 118.0 (Cq), 125.0 (Cq), 125.4 (Cq), 129.2 (CH), 129.3
(CH), 132.4 (CH), 132.6 (CH), 132.9 (CH), 137.1 (Cq), 147.1 (CH), 154.7
1
(CH), 162.4 ppm (Cq); 31P NMR: d=À12.7 (t, JPtÀP =1512 Hz); HRMS
(ESI+): m/z calcd for [C292H292B8N32O36P8Pt4Zn8]4+: 1615.5895; found:
1615.5914 [MÀ(OTf)4]4+
;
elemental analysis: calcd (%) for
C296H292B8F12N32O48P8Pt4S4Zn8 (7059.6 gmolÀ1): C 50.36, H 4.17, N
6.35; found: C 50.50, H 4.12, N 6.33.
General procedure for the synthesis of 7 and 8
Et3N (88 mL, 0.6 mmol) was added to a suspension of 1 (0.33 g,
0.31 mmol) or 3 (0.27 g, 0.31 mmol) in acetonitrile/methanol (1:1,
20 mL). The mixture was stirred until all of solid had dissolved. The
volume of the solvent was reduced under vacuum to 3 mL, and
a yellow solid formed. The product was filtered, washed with cold
acetonitrile, and dried under vacuum.
Complex 7: Yield: 0.29 g, 85%; 1H NMR (400 MHz, [D7]DMF): d=
1.29–1.35 (m, 12H), 2.18 (s, 9H, CH3), 3.43 (q, J=7.3 Hz, 8H), 7.14
(s, 6H, CHar), 7.66 (d, 4H, J=5.7 Hz, CHpy), 8.35 (s, 6H, CHim),
8.46 ppm (d, 4H, J=5.6 Hz, CHpy); 13C NMR (100 MHz, [D7]DMF): d=
164.25 (CÀOPh), 155.20 (C=N), 148.95 (CHar), 136.91 (Car), 128.49
(CHar), 124.53 (Car), 120.11 (CHar), 53.01 (CH2), 20.16 (CH3), 7.95 ppm
(CH3) (BÀC was not observed); ESI-MS: m/z: 883.1703 [M+2H]+; el-
emental analysis: calcd (%) for Zn2C37H31N8B2O9(C6H16N)(CH2Cl2)
(1060.13 gmolÀ1): C 49.84, H 3.61, N 11.89; found: C 48.66, H 4.89,
N 11.37; FTIR: n˜max: 3208 (br), 2988 (br), 1613 (m), 1592 (m), 1553
(m), 1444 (s), 1322 (s), 1202 (s), 1085 (m), 1034 (vs), 998 (vs), 935
(vs), 817 (s), 761 (s), 688 cmÀ1 (s).
Coordination polymer 12
Polymer 12 was prepared in multiple batches. The individual reac-
tions were carried out in sealed 20 mL microwave vials as follows.
Zn(NO3)2(H2O)6 (6.0 mg, 20 mmol) was added to a solution of com-
plex 1 (32 mg, 30 mmol) in DMF (6.0 mL). The resulting mixture was
briefly sonicated before the vial was placed for 24 h into an oil
bath at 808C. The vial was then allowed to cool to room tempera-
ture to induce crystallization. After 3 d, the resulting yellow crystals
were washed with DMF (3ꢃ5 mL) before being isolated by filtra-
tion and dried under vacuum for 3 d. Yield: 20 mg, 62%; elemental
analysis:
calcd
(%)
for
(Zn2C37H29B2N8O9)2Zn(DMF)4(H2O)3
(2175.96 gmolÀ1): C 47.47, H 4.26, N 12.87; found: C 47.64, H 3.84,
N 12.23; FTIR: n˜max: 3317 (br), 2924 (m), 1650 (vs), 1613 (s), 1592
(m), 1554 (m), 1444 (vs), 1384 (m), 1321 (s), 1204 (m), 1086 (m),
1036 (s), 998 (vs), 940 (vs), 822 (s), 765 (s), 694 (s), 659 cmÀ1 (s).
Complex 8: Yield: 0.25 g, 87%; ESI-MS: m/z: 861.1017 [M+2H]+;
elemental analysis: calcd (%) for Mn2C37H31N8B2O9(C6H16N)(CH2Cl2)
(1039.23 gmolÀ1): C 50.85, H 3.68, N 12.13; found: C 50.01, H 3.52,
N 12.30; FTIR: n˜max: 2982 (br), 1603 (m), 1578 (m), 1545 (m), 1473
(s), 1321 (s), 1200 (m), 1181 (m), 1029 (s), 991 (vs), 927 (vs), 819 (vs),
758 (s), 684 cmÀ1 (s).
Coordination polymer 13
Polymer 13 was prepared in multiple batches. The individual reac-
tions were carried out in sealed 7 mL microwave vials as follows.
Zn(ClO4)2(H2O)6 (20 mg, 54 mmol) was added to a solution of com-
plex 4 (30 mg, 27 mmol) in DMF (5.0 mL). The resulting mixture was
briefly sonicated before the vial was placed for 48 h into an oil
bath at 1208C. The vial was then allowed to cool to room tempera-
ture to induce crystallization. After 2 d, the resulting yellow crystals
were washed with DMF (3ꢃ5 mL) before being isolated by filtra-
tion and dried under vacuum for 3 d. Yield: 31 mg, 89%; elemental
analysis: calcd (%) for sample after the heating under vacuum
(Zn2C46H48B2N8O9)2Zn(H2O)4 (2156.09 gmolÀ1): C 51.24, H 4.86, N
10.39; found: C 51.03, H 4.84, N 12.23; FTIR: n˜max: 2950 (m), 1670
(s), 1610 (m), 1445 (s), 1385 (m), 1329 (s), 1220 (m), 1202 (s), 1080
(m), 1035 (s), 995 (vs), 931 (vs), 838 (m), 785 (vs), 770 (vs), 700 (s),
660 cmÀ1 (m).
Complex 9: Et4NOH (1.0 mL, 1.7 mmol, 25% in MeOH) was added
to a suspension of 4 (0.98 g, 0.88 mmol) in acetonitrile/methanol
(1:1, 20 mL). The mixture was stirred until the entire solid had dis-
solved. A few more drops of the Et4NOH solution were added, and
a yellow solid started to form. The product was filtered, washed
with cold methanol, and dried under vacuum. Yield: 0.92 g, 92%;
1H NMR (400 MHz, [D7]DMF): d=1.27 (s, 27H, (CH3)3), 1.32 (t, J=
8.2 Hz, 12H, CH3), 3.43 (q, J=7.3 Hz, 8H, CH2), 7.38 (s, 6H, CHar),
7.67 (d, 4H, J=5.6 Hz, CHpy), 8.42 (s, 6H, CHim), 8.46 ppm (d, 4H,
J=5.7 Hz, CHpy); 13C NMR (100 MHz, [D7]DMF): d=164.15 (CÀOPh),
155.53 (C=N), 148.92 (CHar), 138.41 (Car), 133.61 (CHar), 128.51 (Car),
119.79 (CHar), 52.94 (CH2), 34.55 (C(CH3)3), 31.93 (CH3), 7.94 ppm
(CH3) (BÀC was not observed); ESI-MS: m/z: 1009.2791 [M+H]+; el-
emental analysis: calcd (%) for Zn2C46H48B2N8O9(C8H21N)(H2O)2.5
(1186.62 gmolÀ1): C 54.86, H 6.18, N 10.66; found: C 54.73, H 5.98,
N 10.66; FTIR: n˜max: 2949 (m), 1611 (m), 1590 (m), 1550 (m), 1446
(s), 1331 (s), 1221 (s), 1202 (s), 1079 (s), 1036 (s), 996 (vs), 919 (vs),
781 (vs), 772 (s), 696 cmÀ1 (s).
Coordination polymer 14
A solution of complex 7 (28 mg, 26 mmol) in DMF (4.0 mL) in a test
tube (diameter=15 mm) was layered with a solution of Cd(ClO4)2-
(H2O)6 (6.0 mg, 19 mmol) in MeOH (4.0 mL), separated by a buffer
layer of DMF/MeOH (1:1, 2 mL). After 2 weeks, yellow crystals had
formed. The crystals were washed with DMF (3ꢃ5 mL) before
being isolated by filtration and dried under vacuum for 3 d. Yield:
20 mg, 80%; elemental analysis: calcd (%) for (Zn2C37H29B2N8O9)2Cd-
(DMF)2(H2O)6 (2130.84 gmolÀ1): C 45.09, H 3.97, N 11.83; found: C
43.90, H 3.76, N 11.79; FTIR: n˜max: 3344 (br), 2952 (m), 1652 (s),
1610 (s), 1552 (m), 1445 (vs), 1384 (m), 1327 (s), 1203 (m), 1080 (m),
1035 (s), 985 (vs), 929 (vs), 839 (s), 782 (vs), 698 (vs), 659 cmÀ1 (m).
Molecular square 10
A solution of Pt(dppp)(OTf)2 (100 mg, 110 mmol) and complex 9
(125 mg, 110 mmol) in DMSO (10 mL) was stirred for 1 h. CHCl3
(20 mL) was then added, which caused the precipitation of a pale-
yellow amorphous powder. The product was isolated by centrifu-
gation, washed with CHCl3 (3ꢃ5 mL) and Et2O (3ꢃ5 mL), and dried
1
under vacuum. Yield: 133 mg, 68%; H NMR (600 MHz, [D6]DMSO):
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Coordination polymer 15
A solution of complex 9 (30 mg, 26 mmol) in DMF (4.0 mL) in a test
tube (diameter=15 mm) was layered with a solution of Cd(ClO4)2-
(H2O)6 (6.0 mg, 19 mmol) in MeOH (4.0 mL), separated by a buffer
layer of DMF/MeOH (1:1, 2 mL). After 1 week, yellow single crystals
had formed. The crystals were washed with DMF (3ꢃ5 mL) before
being isolated by filtration and dried under vacuum for 3 d. Yield:
24 mg, 80%; elemental analysis: calcd (%) for sample after heating
under vacuum (Zn2C46H48B2N8O9)2Cd(H2O)9 (2293.19 gmolÀ1):
48.18, H 5.01, N 9.77; found: C 47.95, H 4.49, N 9.84; FTIR: n˜max
3344 (br), 2952 (m), 1652 (s), 1610 (s), 1552 (m), 1445 (vs), 1384
(m), 1327 (s), 1203 (m), 1080 (m), 1035 (s), 985 (vs), 929 (vs), 839 (s),
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Intensity data were collected by using an Oxford Diffraction KM-4
CCD diffractometer, a Bruker APEX II CCD system, or a marmx
system, with graphite monochromated Mo-Ka radiation (l=
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graphic data for this paper. These data can be obtained free of
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The work was supported by Marie Curie fellowships for M.P.
(IEF-2009-252716) and J.J.H. (ITN-2010-264645), the Swiss Na-
tional Science Foundation, and by the EPFL. Oliver Smart is
thanked for writing and adapting the GRADE program, which
was applied in the X-ray analysis.
Keywords: boronic acid
· clathrochelates · coordination
polymers · nanostructures · supramolecular chemistry
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Received: January 23, 2014
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Published online on April 2, 2014
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