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An international journal of inorganic chemistry
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Volume 40 | Number 21 | 7 June 2011 | Pages 5633–5796
ISSN 1477-9226
COVER ARTICLE
Wu, Janiak et al.
Anion binding by metallo-receptors
of 5,5’-dicarbamate-2,2’-bipyridine
ligands
1477-9226(2011)40:21;1-X
Dalton
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PAPER
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Anion binding by metallo-receptors of 5,5¢-dicarbamate-2,2¢-bipyridine
ligands†
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Published on 16 February 2011 on http://pubs.rsc.org | doi:10.1039/C0DT01561J
Biao Wu,*a Jin Yang,b Xiaojuan Huang,c Shaoguang Li,c Chuandong Jia,c Xiao-Juan Yang,c Ning Tangb and
Christoph Janiak*d
Received 11th November 2010, Accepted 11th January 2011
DOI: 10.1039/c0dt01561j
Three 5,5¢-dicarbamate-2,2¢-bipyridine ligands (L = L1 –L3 ) bearing ethyl, isopropyl or tert-butyl
terminals, respectively, on the carbamate substituents were synthesized. Reaction of the ligands L with
the transition metal ions M = Fe2+ , Cu2+ , Zn2+ or Ru2+ gave the complexes MLn X2 ·xG (1–12, n = 1–3;
X = Cl, NO3 , ClO4 , BF4 , PF6 , 12 SO4 ; G = Et2 O, DMSO, CH3 OH, H2 O), of which [Fe(L2 )3 … SO4 ]·8.5H2 O
(2), [Fe(L1 )3 … (BF4 )2 ]·2CH3 OH (7), [Fe(L2 )3 … (Et2 O)2 ](BF4 )2 ·2CH3 OH (8), [ZnCl2 (L1 )][ZnCl2 (L1 )(DMSO)]·2DMSO (9), [Zn(L1 )3 … (NO3 )2 ]·2H2 O (10), [Zn(L2 )3 … (ClO4 )(Et2 O)]ClO4 ·Et2 O·2CH3 OH·
1.5H2 O (11), and [Cu(L1 )2 (DMSO)](ClO4 )2 ·2DMSO (12) were elucidated by single-crystal X-ray
crystallography. In the complexes MLn X2 ·xG the metal ion is coordinated by n = 1, 2 or 3 chelating
bipyridine moieties (with other anionic or solvent ligands for n = 1 and 2) depending on the transition
metal and reaction conditions. Interestingly, the carbamate functionalities are involved in hydrogen
bonding with various guests (anions or solvents), especially in the tris(chelate) complexes which feature
the well-organized C 3 -clefts for effective guest inclusion. Moreover, the anion binding behavior of the
pre-organized tris(chelate) complexes was investigated in solution by fluorescence titration using the
emissive [RuL3 ]2+ moiety as a probe. The results show that fluorescent recognition of anion in solution
can be achieved by the RuII complexes which exhibit good selectivities for SO4 2- .
Introduction
Anion binding is an active research field in supramolecular
chemistry because of the potential applications of anion receptors
in pollutant sequestration and biomedical and environmental
monitoring.1 A vast number of different synthetic systems which
are capable of acting as receptors for a range of anions have been
reported, in which metal complexes have also been designed to
recognize anions in parallel with organic anion receptors. Metalassembled anion receptors are constructed from metal ions and
properly functionalized ligands in which the hydrogen bond donor
substituents may converge to offer complementary binding sites
for the anion.2,3 This assembly of MLx metallo-ligand receptors
a
Key Laboratory of Synthetic and Natural Functional Molecule Chemistry
of the Ministry of Education, College of Chemistry and Materials Science,
Northwest University, Xi¢an, 710069, China. E-mail: [email protected]
b
State Key Laboratory of Applied Organic Chemistry, College of Chemistry
and Chemical Engineering, Lanzhou University, Lanzhou, 730000, China
c
State Key Laboratory for Oxo Synthesis & Selective Oxidation, Lanzhou
Institute of Chemical Physics, CAS, Lanzhou, 730000, China
d
Institut für Anorganische Chemie und Strukturchemie, Universität
Düsseldorf, Universitätsstr., 1, D-40225, Düsseldorf, Germany. E-mail:
[email protected]
† Electronic supplementary information (ESI) available: Fluorescence
titration data. CCDC reference numbers 800531–800537. For ESI and
crystallographic data in CIF or other electronic format see DOI:
10.1039/c0dt01561j
This journal is © The Royal Society of Chemistry 2011
for anions is attractive because various relatively simple ligands
are available for coordination about metal centers with different
coordination geometries, thus resulting in desirable cages, clefts
or cavities to accommodate anions.4 On the other hand, such an
accumulation of hydrogen bonding donors around a metal atom
in a metallo ligand can be regarded as a similar procedure to
the incorporation of multiple anion-binding groups into a single
organic ligand. The synthesis of a metallo ligand is, however,
less synthetically challenging compared to the synthesis of purely
organic receptors.
2,2¢-Bipyridine (bipy) and its derivatives are of significant
interest in coordination chemistry due to their ability to form
complexes with a range of transition metals.5 When functionalized
with hydrogen bond donors, these ligands may serve as good
candidates for the construction of coordination-driven anion
receptors. For instance, Beer and coworkers6a–d have designed a
variety of 4,4¢-disubstituted bipy ligands with hydrogen donors
(e.g. amide), and obtained the corresponding metal-assembled
anion receptors. They have also studied the anion binding properties of ruthenium(II) 5,5¢-diamide-2,2¢-bipyridine receptors.6e,f
Williams et al.7 have reported some iron and cobalt complexes
of amino acid-substituted bipy ligands which can encapsulate
chloride ions in the clefts upon protonation of the amine groups.
We8 have reported that the pre-organization of the octahedral
metal ion Fe2+ with the carbamate-functionalized bipy ligand 5,5¢-bis(ethoxy-carbonylamino)-2,2¢-bipyridine (L1 ) creates a
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Scheme 1 Overview of the metal complexes formed by the 5,5¢-dicarbamate-2,2¢-bipyridine ligands L (= L1 –L3 ) and metal salts.
C 3 -symmetric cavity at each end of the complex, which incorporates the oxoanions (sulfate, nitrate or perchlorate) by hydrogen
bonds from the carbamate functional groups.
In an extended investigation of the anion-binding properties
of metal-assisted systems with 5,5¢-dicarbamate-2,2¢-bipyridine
ligands, we synthesized two new carbamate-functionalized bipy
ligands, 5,5¢-bis(isopropoxy-carbonylamino)-2,2¢-bipyridine (L2 )
and 5,5¢-bis(tert-butoxycarbonylamino)-2,2¢-bipyridine (L3 ) by
varying the terminal groups (Scheme 1). Reaction of the ligands L1 –L3 with various metal salts gave a series of complexes
with different metal-to-ligand ratios, in which anion binding was
achieved by the pre-organization of the carbamate groups. Herein
we report the syntheses and structures of these anion-binding
metal complexes, as well as the solution anion-binding properties
of the tris(chelate) ruthenium(II) complexes by using fluorescence
emission spectroscopy.
Results and discussion
The synthesis of the ligands L1 –L3 involved a Curtius rearrangement of 5,5¢-diacylazide-2,2¢-bipyridine and coupling of the resulting 5,5¢-diisocyanate-2,2¢-bipyridine with ethanol, isopropanol
and tert-butanol, respectively.9 Transition metal complexes (1–
14) were obtained by the reaction of the ligands with the
corresponding metal salts in methanol (Scheme 1) or by anion
metathesis (for the tetrafluoroborate and hexafluorophosphate
complexes). The compounds were characterized by NMR, IR,
elemental analysis, and single-crystal X-ray diffraction (for 1,8 2
and 7–12, Table 1). The dimethylsulfoxide (DMSO)-containing
compounds were obtained from crystallization from DMSO–
methanol solutions.
1
H NMR studies on the sulfate-binding in the tris(chelate) FeII
complexes 1, 2 and 3
As reported previously, reaction of Fe2+ with the ethyl-substituted
ligand L1 yielded a complex which contains one C 3 -symmetric
cleft at each end of the molecule, and the sulfate anion is
encapsulated within one of the cavities in the solid state (with
three hydrogen bonds between sulfate and the three NH groups).8
To evaluate the solution anion-binding behavior of such systems,
5688 | Dalton Trans., 2011, 40, 5687–5696
Fig. 1 1 H NMR spectra (400 MHz, DMSO-d 6 , 298 K) of (a) L1 ; (b)
[Fe(L1 )3 … SO4 ] (1); (c) L2 ; (d) [Fe(L2 )3 … SO4 ] (2); (e) L3 ; (f) [Fe(L3 )3 … SO4 ]
(3).
1
H NMR investigations were performed for the Fe complexes of
the ligands L1 –L3 (Fig. 1) with sulfate as the counter-anion.
The 1 H NMR spectra of the iron(II) complexes 1, 2 and 3 in
DMSO-d 6 show two sets of signals. One of them occurs at almost
the same positions as the free ligand L, and the other (which is
marked with the asterisk *) is shifted upfield (for H6) or downfield
(H3, H4), which is attributed to the complex formation. The
intensity/integral of the second set is about one half of those of
the first set. These results suggest that the complexes may partially
decompose under such conditions, that is, the bipy ligands are
replaced by the solvent DMSO and sulfate ion, thus leading to
a slow dynamic equilibrium between the complex and the free
ligand. This has also been described in our previous report.8
Nevertheless, compared with the free ligand, the NH protons of
the complexes are downfield-shifted by ca. 0.24 ppm due to the
binding of sulfate ion (through hydrogen bonds) by the NH groups.
The complexes are stable in methanol as a solvent in the presence
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of sulfate, but rapid exchanges of acidic protons preclude seeing
the diagnostic NH protons.
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Fluorescence studies on the anion-binding properties of the
tris(chelate) RuII complexes 4, 5 and 6
As mentioned above, the FeII complexes of the ligands L1 –
L3 decomposed partially in DMSO solution in the presence of
the sulfate ion, which restrained further investigation of their
anion-binding behavior. Hence, we changed the metal center to
ruthenium, which has the same coordination mode with the 2,2¢bipyridyl ligand as iron but is much more kinetically stable in
solution. However, the NMR studies once again failed because
of the poor solubility of the RuII complexes with sulfate even
in DMSO. Fortunately, it was possible to carry out fluorescence
titration at more dilute solutions by using the RuII polypyridyl
complexes, which have a relatively long wavelength MLCT emission band and proved to be very useful in the investigation of anion
binding.10,11 In this work, the binding affinities of the complex
Ru(L1 )3 (PF6 )2 (4) to various anions were studied by fluorescence
titration in CH3 CN at room temperature. Upon excitation at
374 nm, complex 4 showed an emission band at l max = 571 nm.
On addition of 1 equiv. of SO4 2- , F- , HSO4 - and OAc- anion,
a decrease of the emission intensity was observed, while other
anions such as NO3 - , ClO4 - , Cl- , Br- and I- induced no significant
changes of the emission intensity (Fig. 2). Notably, the addition
of 1 equiv. of SO4 2- caused drastic quenching of the emission (ca.
80%), suggesting that complex 4 has an excellent anion-binding
ability for SO4 2- anion due to the good complementarity between
the anion and binding sites, and also a favorable electrostatic
attraction for the dianionic sulfate ion with the cationic metalloreceptor compared to monoanionic anions.2f,3b
Fig. 2 Fluorescence emission spectra of the complex Ru(L1 )3 (PF6 )2 (4)
(1.0 ¥ 10-5 M in CH3 CN) upon addition of 1 equiv. of anions (as their
tetrabutylammonium salts): F- , Cl- , Br- , I- , ClO4 - , NO3 - , H2 PO4 - , HSO4 - ,
OAc- and SO4 2- . Excitation at 374 nm. Inset: bar profiles of normalized
fluorescence intensity for complex 4 in the absence and presence of different
anions.
Quantitative investigations of the binding affinity of receptor 4
with SO4 2- ion have been carried out in CH3 CN by fluorescence
titration (Fig. 3). The fluorescence intensity of 4 decreased
gradually with increasing SO4 2- concentration. An approximate
This journal is © The Royal Society of Chemistry 2011
Fig. 3 (a) Fluorescence titration of the complex Ru(L1 )3 (PF6 )2 (4) (1.0 ¥
10-5 M in CH3 CN) with SO4 2- (up to 8.0 ¥ 10-5 M); (b) Variation of the
fluorescence intensity as a function of the molar ratio of SO4 2- to the
receptor Ru(L1 )3 (PF6 )2 .
plateau was observed at the 1 : 1 molar ratio, corresponding to the
formation of a 1 : 1 anion–host adduct in solution. The stability
constant K was calculated by the nonlinear least-squares analysis
(Table 2).12a The binding of 4 toward HSO4 - , F- and OAc- ion
was also studied. For the HSO4 - anion, the fluorescence titration
showed a 1 : 1 binding mode with a slightly smaller stability
constant than that of the SO4 2- ion. The results imply that the
HSO4 - ion might be converted to SO4 2- during the binding, which
has also been observed with a tripodal tris-urea receptor.13 The
titration of the other two anions (F- and OAc- ) to receptor 4
revealed a 1 : 2 (host–guest) binding mode (Fig. S1†), which is in
accordance with the solid-state structure of the complexes of the
receptors with some monovalent anions, such as 7 and 10. The
binding constants were obtained for the 1 : 2 complexes with the
data fitted by the Dynafit program.12b
For comparison, analogous fluorescence titrations of the receptor Ru(L2 )3 (PF6 )2 (5) and Ru(L3 )3 (PF6 )2 (6) with SO4 2- were also
performed (Fig. S2†). Also for complexes 5 and 6 the decrease of
emission intensity levels off at a SO4 2- -to-complex molar ratio of
1 : 1, indicating again the formation of a 1 : 1 anion–host adduct
in solution. It is noteworthy that all complexes exhibit a strong
binding ability toward SO4 2- ions, and the binding strength is
dependent on the substituent of the receptor (K = 1.04 ¥ 106 M-1
for 5 and 7.05 ¥ 105 M-1 for 6). With increasing terminal steric
hindrance, the association constant decreases, which may be
attributed to the larger repulsion of the substituents that can
Dalton Trans., 2011, 40, 5687–5696 | 5689
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Table 1 Crystal data for complexes 2 and 7–12
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Formula
Fw
Crystal system
Space group
a/Å
b/Å
c/Å
a/◦
b/◦
g /◦
V /Å3
Z
T
Dcalc /g cm-3
F(000)
m (Mo Ka)/mm-1
Reflections collected
Independent reflections
Observed reflections [I > 2s (I)]
Rint
Refined parameters
GOF
R1 [I > 2s(I)]
wR2 (all data)
2
7
8
9
10
11
12
C108 H166 Fe2 N24 O49 S2
2760.47
Triclinic
P1̄
13.853(18)
16.35(2)
17.75(2)
109.45(2)
95.93(2)
106.38(2)
3549(8)
1
293
1.292
1458
0.323
17218
11832
3921
0.1146
838
0.881
0.1182
0.3450
C50 H62 B2 F8 FeN12 O14
1284.59
Monoclinic
C2/c
18.774(17)
25.57(2)
15.47(2)
90.00
117.83(3)
90.00
6567(12)
4
293
1.299
2664
0.318
13912
4686
2435
0.0903
398
1.004
0.0771
0.2478
C64 H94 B2 F8 FeN12 O16
1516.98
Monoclinic
P21 /c
18.4694(16)
19.7057(17)
23.748(2)
90.00
108.239(1)
90.00
8209.0(12)
4
293
1.227
3192
0.266
37981
8777
5911
0.0496
948
1.036
0.0740
0.2390
C38 H54 Cl4 N8 O11 S3 Zn2
1167.61
Triclinic
P1̄
13.422(4)
14.320(4)
14.365(4)
73.397(4)
77.928(4)
80.200(4)
2569.4(13)
2
293
1.509
1204
1.324
17277
8854
5908
0.0435
623
1.015
0.0435
0.1166
C48 H58 N14 O20 Zn
1216.45
Trigonal
P3̄1 c
13.499(2)
13.499(2)
18.540(3)
90.00
90.00
120.00
2925.9(8)
2
293
1.381
1268
0.504
14489
1736
1138
0.0357
142
1.078
0.0760
0.2847
C128 H194 Cl4 N24 O51 Zn2
3157.61
Triclinic
P1̄
16.8995(14)
17.5045(15)
17.6189(15)
62.561(1)
63.352(1)
79.811(2)
4131.4(6)
1
173
1.269
1666
0.439
21137
14401
9964
0.0283
992
1.028
0.0722
0.2279
C38 H54 Cl2 CuN8 O19 S3
1157.51
Triclinic
P1̄
9.5168(11)
15.5544(19)
18.715(2)
75.716(2)
89.987(2)
79.958(2)
2641.0(5)
2
293
1.456
1202
0.710
17772
9137
6799
0.0228
635
1.016
0.0528
0.1562
Table 2 Binding constants (K, M-1 ) of 4 with different anionsa
Anion
SO4 2-
HSO4 -
OAc-
F-
K1
K2
3.59 ¥ 106
—
1.13 ¥ 106
—
5.50 ¥ 102
1.49 ¥ 103
5.47 ¥ 102
2.36 ¥ 103
a
T = 25 ◦ C; [Host] = 1 ¥ 10-5 M, in CH3 CN; errors estimated to be £10%.
weaken the hydrogen bonding contacts of the NH groups with
the anionic guest.
The solid-state structures of the complexes 2 and 7–12
The anion-binding modes of the complexes with different
metal ions were also investigated in the solid state by
single-crystal X-ray diffraction analysis.10 Seven complexes
were structurally characterized: [Fe(L2 )3 … SO4 ]·8.5H2 O (2),
(7),
[Fe(L2 )3 … (Et2 O)2 ](BF4 )2 ·
[Fe(L1 )3 … (BF4 )2 ]·2CH3 OH
2CH3 OH (8), [ZnCl2 (L1 )][ZnCl2 (L1 )(DMSO)]·2DMSO (9),
(10),
[Zn(L2 )3 … (ClO4 )(Et2 O)]
[Zn(L1 )3 … (NO3 )2 ]·2H2 O
ClO4 ·Et2 O·2CH3 OH·1.5H2 O (11), [Cu(L1 )2 (DMSO)](ClO4 )2 ·
2DMSO (12). The complexes feature the typical bipyridine–metal
coordination, while the carbamate functionality is not involved
in metal coordination but forms hydrogen-bonding interactions
with various anions or solvents. Notably, all the iron(II) complexes
(2, 7, 8) show a ligand-to-metal ratio of 3 : 1, but the zinc(II)
complexes have both mono(chelate) (9) and tris(chelate) (10, 11)
modes, and the copper(II) complex 12 displays a ligand-to-metal
ratio of 2 : 1, which is dependent on the coordination preferences
of the metal ions.8,14
[Fe(L2 )3 … SO4 ]·8.5H2 O (2). Red crystals of the iron complex
2 were obtained by slow evaporation of a solution in methanol–
water. The skeletal structure of 2 consists of an iron(II) ion and
three L2 molecules, which chelate the FeII center to form two clefts
5690 | Dalton Trans., 2011, 40, 5687–5696
at the ends of the octahedral complex [Fe–N distances 1.955(7)–
1.991(7) Å]. The tris(chelate) structure around the iron(II) center
is common, as in a sizeable number of tris(bipy)–metal complexes
described in the literature. A sulfate anion is encapsulated within
one of the clefts through three hydrogen bonds with the three
NH groups, while the fourth oxygen atom (O16) of sulfate points
outward along the pseudo C 3 -axis of the complex molecule.15 As
required by the charge balance, the other cleft is empty (Fig. 4).
This structure is similar to the previously reported complex
[Fe(L1 )3 … SO4 ] (1).8 However, with increasing steric hindrance
of the terminal group (from ethyl in L1 to isopropyl in L2 ), the
interactions between the sulfate anion and the NH groups in the
cleft tend to decrease, as indicated by the N–H ◊ ◊ ◊ O hydrogen
bond lengths which are elongated from 2.735–2.813 Å in 1 to
Fig. 4 (a) Sulfate encapsulation in the molecular structure of
[Fe(L2 )3 … SO4 ] (2); (b) View of the molecule along the C 3 axis. Selected
bond distances (Å): mean Fe–N, 1.971; N2 ◊ ◊ ◊ O13, 2.792(11); N6 ◊ ◊ ◊ O14,
2.881(11); N10 ◊ ◊ ◊ O15, 2.788(11). Non-interacting hydrogen atoms and
solvent molecules are omitted for clarity.
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2.788–2.881 Å in 2. Furthermore, the distance from Fe atom to
the S atom of sulfate is also elongated from 5.539 Å in 1 to 5.592 Å
in 2, indicating that the sulfate anion is located further away from
the cleft.
[Fe(L1 )3 … (BF4 )2 ]·2CH3 OH (7). Complex 7 was synthesized
from a methanolic solution of L1 and FeCl2 ·4H2 O in the presence
of NaBF4 . Red crystals were obtained by slow diffusion of diethyl
ether into the methanol solution of the complex. The metal ion
sits on an inversion center and has a six-coordinate, distorted
octahedral environment being bonded by three bidentate L1
ligands [Fe–N distances 1.990(4)–1.996(5) Å] (Fig. 5). In contrast
to the sulfate complexes, both of the C 3 -clefts are occupied by
a BF4 - monoanion. Notably, only one of the fluorine atoms of
the BF4 - ion is involved in the N–H ◊ ◊ ◊ F hydrogen bonding with
a carbamate NH group of the receptor [N3 ◊ ◊ ◊ F2b, 2.943(9) Å;
∠N3–H ◊ ◊ ◊ F2b, 168(1)◦ ).16 The second F atom (F4) forms a
hydrogen bond with the CH3 OH molecule of crystallization
[F4b ◊ ◊ ◊ O, 2.928(13) Å, not shown], while the third one (F1) is
located between the other two carbamate arms and forms a weak
hydrogen bond with one CH group of a neighboring complex unit
(not shown), and the remaining F atom (F3) points outward of
the cleft with no hydrogen bonding contacts. Meanwhile, the other
two NH donors of the carbamate moieties are also free from
the binding with the anion. This binding mode is similar to the
perchlorate complex of the same ligand, [Fe(L1 )3 … (ClO4 )2 ], in
which the anions are encapsulated within both clefts through one
hydrogen bond.8
Fig. 5 Molecular structure of [Fe(L1 )3 … (BF4 )2 ] (7) with the two encapsulated BF4 - ions. Mean Fe–N 1.992 Å; symmetry codes: a) 1 - x, y, 0.5 z; b) 0.5 + x, 0.5 - y, 0.5 + z; c) 0.5 - x, 0.5 - y, -z.
[Fe(L2 )3 … 2Et2 O](BF4 )2 ·2CH3 OH (8). By changing the terminal substituent from ethyl to isopropyl, an analogous 3 : 1
(ligand-to-metal) complex to compound 7 was obtained as deepred crystals from FeCl2 ·4H2 O, L2 , and NaBF4 under similar
conditions. The tris(chelate) structure around the iron(II) center
(Fig. 6) is as seen before, and the Fe–N bond lengths [1.964(5)–
This journal is © The Royal Society of Chemistry 2011
Fig. 6 Molecular structure of [Fe(L2 )3 … 2Et2 O](BF4 )2 ·2CH3 OH (8)
showing the inclusion of two diethyl ether molecules. Mean Fe–N 1.971 Å;
symmetry code: a) x, 0.5 - y, -0.5 + z.
1.982(5) Å] in 8 are slightly shorter than those in the complex
7. Most surprisingly, the two tetrafluoroborate anions are not
encapsulated within the clefts of the complex as in 7, but are
placed on the outside of the Fe(L2 )3 unit in 8. Instead, two diethyl
ether molecules are trapped within the clefts through N–H ◊ ◊ ◊ O
hydrogen bonds [N4 ◊ ◊ ◊ O14, 2.866(8) Å, ∠N4–H ◊ ◊ ◊ O14, 176◦ ;
N7 ◊ ◊ ◊ O13, 2.935(14) Å, ∠N7–H ◊ ◊ ◊ O13, 170◦ ] between the NH
groups and the oxygen atom of the Et2 O molecule. Compared
with complex 7, it appears that there is competitive binding for the
NH groups between the solvent Et2 O and the tetrafluoroborate
anion in the binding sites. With increasing steric hindrance of the
terminal group, the tetrahedral BF4 - anion could not fit in the
cleft, and the linear Et2 O molecules are included.
(9). Pale-yellow
[ZnCl2 (L1 )][ZnCl2 (L1 )(DMSO)]·2DMSO
crystals of 9 were obtained by slow diffusion of diethyl ether into
a DMSO–methanol solution of the complex. The structure of
9 consists of zinc(II) ions and L1 ligands in a 1 : 1 molar ratio.
There are two crystallographically independent zinc atoms in
complex 9 (Fig. 7a). The Zn1 atom is four-coordinated by one
bipyridine ligand L1 and two Cl atoms in a distorted tetrahedral
coordination geometry, whereas the other metal center, Zn2, is
five-coordinated by one ligand, two Cl atoms and an oxygen
atom from a DMSO molecule. The geometry around Zn2 can
be described as distorted square pyramidal, with an Addison
parameter t = 0.38 (t = 0.0 for an ideal square pyramid and t =
1.0 for an ideal trigonal bipyramid).17 There are also two DMSO
molecules of crystallization in the crystal lattice. The carbamate
groups are not involved in the hydrogen bonding with anions, but
form strong hydrogen bonds with the solvent DMSO molecules
(N ◊ ◊ ◊ O distances, 2.814(8) and 2.864(8) Å; N–H ◊ ◊ ◊ O angles,
162◦ and 154◦ , respectively).
In the extended structure, the Cl2 atom in the [Zn(1)Cl2 L1 ] unit
forms an intermolecular N–H ◊ ◊ ◊ Cl hydrogen bond [N3 ◊ ◊ ◊ Cl2a,
3.417(3) Å; ∠N3–H ◊ ◊ ◊ Cl2A, 148◦ ] with the NH group of a
neighboring unit. Two adjacent [Zn(1)Cl2 L1 ] units are thus held
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Fig. 7 (a) Molecular structure of 9 showing the different coordination geometry of the two zinc(II) centers. Hydrogen atoms and solvent molecules are
omitted for clarity. Selected bond distances (Å): Zn1–N1, 2.061(3); Zn1–N2, 2.068(3); Zn1–Cl1, 2.191(1); Zn1–Cl2, 2.221(1); Zn2–O9, 2.108(3); Zn2–N5,
2.163(3); Zn2–N6, 2.178(3); Zn2–Cl3 2.285(1); Zn2–Cl4 2.294(1); (b, c) View of the [Zn(1)Cl2 L1 ]2 and [Zn(2)Cl2 L1 (DMSO)]2 dimeric units constructed
by N–H ◊ ◊ ◊ Cl hydrogen bonds. (d) Section of the tape structure formed by intermolecular N–H ◊ ◊ ◊ Cl and C–H ◊ ◊ ◊ O hydrogen bonding interactions.
Symmetry codes: a) 1 - x, 1 - y, -z; b) 1 - x, -y, 1 - z; c) x, y - 1, z; d) x, 1 + y, z.
together (Fig. 7b). Meanwhile, two neighboring five-coordinate
[Zn(2)Cl2 L1 (DMSO)] units also form a dimer through a pair
of N–H ◊ ◊ ◊ Cl hydrogen bonds [N8 ◊ ◊ ◊ Cl3B, 3.302(3) Å; ∠N8–
H ◊ ◊ ◊ Cl3B, 168◦ ] (Fig. 7c). Finally, the two different dimeric units
are further linked by an R2 2 (10) ring18 of C–H ◊ ◊ ◊ O contacts
(C31 ◊ ◊ ◊ O1c, 3.245(5) Å; ∠C31–H ◊ ◊ ◊ O1c, 129◦ ; C12 ◊ ◊ ◊ O7d,
3.156(5) Å, ∠C12–H ◊ ◊ ◊ O7d, 129◦ ) to form an infinite tape
structure (Fig. 7d).
[Zn(L1 )3 … (NO3 )2 ]·2H2 O (10). Crystals of complex 10 suitable
for X-ray structure determination were obtained through slow
diffusion of diethyl ether into a methanol solution. Compound
10 crystallizes in the trigonal space group P3̄1 c with a crystallographically imposed D3 symmetry. The tris(chelate) structure
around the zinc center (Fig. 8) is the same with the complex
[Fe(L1 )3 … (NO3 )2 ] 7 in which two nitrate anions were encapsulated
within both clefts of the complex. Notably, one of the N–O bonds
of the nitrate anions coincides with the crystallographic C 3 -axis,
and thus the other two oxygen atoms are distributed in three
positions. Although both the iron and zinc complexes show the
inclusion of two nitrates ions at both ends of the molecule, there
are differences between the anion-binding modes. In the case of
[Fe(L1 )3 … (NO3 )2 ] each nitrate ion is close to one of the ligand
arms and forms only one hydrogen bond with the host, while the
other two oxygen atoms of the nitrate ion display only very weak
interactions with the NH groups. However, in the complex 10,
one of the oxygen atoms (O4) which sits on the C 3 -axis accepts
three hydrogen bonds from all the three NH groups of the ligands
within the cleft (N2 ◊ ◊ ◊ O4, 3.327(7) Å, ∠N2–H ◊ ◊ ◊ O4, 118◦ ) in an
approximately trigonal arrangement. The O4 atom is displaced
5692 | Dalton Trans., 2011, 40, 5687–5696
Fig. 8 (a) Molecular structure of [Zn(L1 )3 … (NO3 )2 ]·2H2 O (10) with the
encapsulation of two NO3 - ions; (b) View along the C 3 axis. Selected bond
distance Zn–N 2.179(4) Å. Symmetry codes: a) 1 - x + y, 1 - x, z; b) 1 - y,
x - y, z; c) 1 - y, 1 - x, 0.5 - z; d) x, x - y, 0.5 - z; e) 1 - x + y, y, 0.5 - z.
slightly out of the plane defined by the three N2 atoms of the NH
group (by 0.556 Å), being away from the zinc atom with a distance
of 4.972 Å.
[Zn(L2 )3 … (Et2 O)·(ClO4 )]ClO4 ·Et2 O·2CH3 OH·1.5H2 O (11).
The complex 11 was obtained from Zn(ClO4 )2 and L2 through
slow diffusion of diethyl ether into a methanol solution. The
tris(chelate) structure around the zinc atom is found again [Zn–N
2.124(3)–2.194(3) Å]. Different from the preceding structures is
the guest inclusion in the two clefts (Fig. 9). A perchlorate anion
is encapsulated within one of the clefts through one hydrogen
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Fig. 10 Molecular structure of 12. Selected bond distances (Å): Cu1–O9,
2.061(3); Cu1–N1, 2.066(1); Cu1–N2, 1.958(1); Cu1–N5, 1.970(3);
Cu1–N6, 2.094(3). Symmetry code: a) x - 1, y, z.
Conclusions
Fig. 9 Molecular structure of 11 showing the inclusion of one ClO4 anion and one diethyl ether molecule. Mean Zn–N, 2.152(4) Å.
bond between one oxygen atom and NH group [N12 ◊ ◊ ◊ O14,
2.908(6) Å, ∠N12–H ◊ ◊ ◊ O14, 179◦ ]. Another oxygen atom (O16)
of the anion is oriented toward the zinc atom and forms a weak
C–H ◊ ◊ ◊ O hydrogen bond with a ligand (not shown), while the
remaining two oxygen atoms (O13 and O15) point out of the
cleft. In contrast to the complex [Fe(L1 )3 … (ClO4 )2 ] in which both
cavities encapsulate an anion, the other perchlorate anion is not
encapsulated within the cleft, but stays outside. Surprisingly,
a diethyl ether molecule is encapsulated within the other cleft
[N5 ◊ ◊ ◊ O22, 2.855(5) Å, ∠N5–H ◊ ◊ ◊ O22, 171◦ ]. The result again
suggests very similar supramolecular interaction energies of the
perchlorate anion and diethyl ether solvent in forming hydrogen
bonds within the clefts where the NH donors are located.
[Cu(L1 )2 (DMSO)](ClO4 )2 ·2DMSO (12). Bottle-green crystals
of 12 were obtained by slow diffusion of diethyl ether into the
DMSO–methanol solution of the complex. The skeletal structure
of 12 consists of copper ions and L1 in a 1 : 2 molar ratio.
The copper atom is five-coordinated by two bidentate ligands
and a DMSO molecule (Fig. 10). The coordination geometry
of the complex is best described as a slightly distorted trigonal
bipyramid (t = 0.86)17 with the atoms N1, N6 and O9 defining
the equatorial coordination plane and N2 and N5 occupying the
axial sites. The two Cu–N distances of a given ligand are slightly
different. In the complex, the two perchlorate anions participate
in different hydrogen bonding contacts with the ligands. The
carbamate NH donor (N7) and a neighboring CH group (C21)
of one ligand form N–H ◊ ◊ ◊ O and C–H ◊ ◊ ◊ O hydrogen bonds with
two oxygen atoms of perchlorate, resulting in an R2 2 (8) motif18
[N7 ◊ ◊ ◊ O10a, 3.039(5) Å, ∠N7–H ◊ ◊ ◊ O10, 167◦ ; C21 ◊ ◊ ◊ O11a,
3.273(5) Å, ∠C21–H ◊ ◊ ◊ O11a, 146◦ ]. In contrast, the other ligand
of the complex donates one N–H ◊ ◊ ◊ O bond and one C–H ◊ ◊ ◊ O
bond to only one oxygen atom of the other perchlorate anion, with
an R2 1 (6) ring18 [N4 ◊ ◊ ◊ O15, 2.871(6) Å, ∠N4–H ◊ ◊ ◊ O15, 167◦ ;
C8 ◊ ◊ ◊ O15, 3.339(7) Å, ∠C8–H8 ◊ ◊ ◊ O15, 135◦ ] (Fig. 10).
This journal is © The Royal Society of Chemistry 2011
A series of 5,5¢-dicarbamate-2,2¢-bipyridine ligands and their
mono-, bis-, and tris-chelating transition metal complexes were
synthesized. The carbamate functionality is not involved in metal
coordination but participates in hydrogen bonding with various
anions or solvents. In particular, the tris(chelate) complexes
display the expected guest inclusion behavior within the clefts
formed by three ligand arms. Moreover, the anion-binding ability
of the photoactive tris(chelate) RuII complexes in solution was
investigated by fluorescence emission spectroscopy, and they are
found to exhibit prominent selectivity for SO4 2- ions in their
fluorescence response.
Experimental
General
All chemicals and solvents were commercially available and were
used without further purification. The syntheses of ligand L1 –
L3 are straightforward, involving a simple Curtius rearrangement
reaction of 2,2¢-bipyridine-5,5¢-dicarboxylic diazide and coupling
of the resulting 2,2¢-bipyridine-5,5¢-diisocyanate with EtOH, iPrOH and t-BuOH respectively. Metal complexes were obtained
by reaction of the ligands with the corresponding metal salts in
methanol solution. Elemental analyses were performed on an
Elementar VarioEL instrument. IR spectra were recorded on a
Bruker IFS 120HR spectrometer as KBr disks. NMR spectra were
recorded at ambient temperature on a Mercury Plus 400 MHz
FT spectrometer. EI-MS were recorded on a Finnigan MAT
311 mass spectrometer. ESI-MS measurements were carried out
using a Waters ZQ4000 spectrometer with methanol being the
solvent. Melting points were detected on an X-4 Digital Vision
MP Instrument.
Synthesis
L1 . The ligand L1 was prepared in a similar way as reported
previously.3b To a solution of 5,5¢-diisocyanato-2,2¢-bipyridine
(2.0 g, 8.5 mmol) in xylene (50 mL) was added 50 mL ethanol.
The mixture was then refluxed for 12 h to give a clear yellow
solution. Upon cooling, yellowish crystals were obtained which
after filtration were recrystallized from ethanol as a colorless
product. Yield: 6.5 g (97%).
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L2 . The synthesis of L2 was similar to that of L1 , except that
50 mL i-PrOH was used instead of EtOH. Yield: 3.9 g, 64%. M.p.
> 300 ◦ C. 1 H NMR (400 MHz, DMSO-d 6 ): d = 1.26 (d, 12H, J =
6.4 Hz, CH3 ), 4.91 (m, 2H, J = 6.4 Hz, CHMe2 ), 7.98 (dd, 2H, J =
8.8 Hz and 2.4 Hz, H4), 8.20 (d, 2H, J = 8.8 Hz, H3), 8.68 (d, 2H,
J = 2.4 Hz, H6), 9.93 (s, 2H, NH). 13 C NMR (100 MHz, DMSOd 6 ): d = 21.86, 68.03, 119.81, 125.61, 135.81, 139.15, 149.21, 153.14.
IR (KBr, cm-1 ): 3308 (br, N–H), 2973 m, 1698 (s, C O), 1513 (s,
N–H), 1254 m, 1225 (s, O C–OR), 1108 m, 1074 s, 1022 m, 842 m.
Anal. Calc. for C18 H22 N4 O4 (358.39): C, 60.32; H, 6.19; N, 15.63%.
Found: C, 60.51; H, 6.30; N, 15.48%.
L3 . The synthesis of L3 was similar to that of L1 , except that
50 mL t-BuOH was used instead of EtOH. Yield: 3.8 g, 58%. M.p.
> 300 ◦ C. 1 H NMR (400 MHz, DMSO-d 6 ): d = 1.47 (s, 18H, CH3 ),
7.98 (dd, 2H, J = 8.4 Hz and 2.0 Hz, H4), 8.17 (d, 2H, J = 8.8 Hz,
H3), 8.63 (d, 2H, J = 2.4 Hz, H6), 9.69 (s, 2H, NH). 13 C NMR
(100 MHz, DMSO-d 6 ): d = 27.99, 79.67, 119.66, 125.49, 135.92,
139.10, 149.04, 152.67. IR (KBr, cm-1 ): 3375 (br, N–H), 2983 m,
1700 (s, C O), 1505 (s, N–H), 1254 m, 1250 (s, O COR), 1154
m, 1072 s, 1018 m, 840 m. Anal. Calc. for C20 H26 N4 O4 (386.44): C,
62.16; H, 6.78; N, 14.50%. Found: C, 62.41; H, 6.46; N, 14.72%.
(1–3). FeSO4 ·7H2 O
(9.5
mg,
[Fe(L)3 … SO4 ]·xH2 O
0.034 mmol) and the ligand L (0.10 mmol) were added to
10 mL of hot methanol to give a clear solution. Methanol
was removed under vacuum to yield a red solid. The complex
[Fe(L1 )3 … SO4 ]·3.2H2 O·0.5CH3 OH (1) was prepared as reported
previously.8 For [Fe(L2 )3 … SO4 ]·8.5H2 O (2): Yield: 35.8 mg
(87%). 1 H NMR (400 MHz, DMSO-d 6 ): d = 1.18 (m, 6H, J =
6.4 Hz, CH3 , 2), 1.26 (m, 6H, J = 6.4 Hz, CH3 , L2 ), 4.81 (m, 1H,
J = 6.0 Hz, CHMe2 , 2), 4.91 (m, 1H, J = 6.4 Hz, CHMe2 , L2 ),
7.36 (s, 1H, H6, 2), 7.98 (s, 1H, J = 8.4 Hz, H4, L2 ), 8.20 (d,
1H, J = 8.8 Hz, H3, L2 ), 8.34 (s, 1H, H4, 2), 8.55 (s, 1H, H3,
2), 8.68 (s, 1H, H6, L2 ), 9.93 (s, 1H, NH, L2 ), 10.25 (s, 1H, NH,
2). IR (KBr, cm-1 ): 3397, 2981, 1725 (s, C O), 1609, 1586 (s,
N–H), 1486, 1386, 1260, 1226 (s, O COR), 1180, 1108. ESI-MS:
m/z 565.6 [M - SO4 2- ]2+ . Anal. Calc. for Fe(L2 )3 SO4 ·8H2 O
(C54 H66 FeN12 O16 S·8H2 O, 1371.20): C, 47.30; H, 6.03; N, 12.26%.
Found: C, 47.46; H, 6.12; N, 11.98%. For Fe(L3 )3 SO4 (3): Yield:
38.5 mg (88%). 1 H NMR (400 MHz, DMSO-d 6 ): d = 1.38 (s, 9H,
CH3 , 3), 1.47 (s, 9H, CH3 , L3 ), 7.37 (s, 1H, H6, 3), 7.97 (d, 1H,
J = 8.4 Hz, H4, L3 ), 8.17 (d, 1H, J = 8.8 Hz, H3, L3 ), 8.29 (s,
1H, H4, 3), 8.51 (s, 1H, H3, 3), 8.62 (s, 1H, H6, L3 ), 9.71 (s, 1H,
NH, L3 ), 9.95 (s, 2H, NH, 3). IR (KBr, cm-1 ): 3222, 2979, 1723
(s, C O), 1608, 1586, 1544 (s, N–H), 1487, 1391, 1369, 1232 (s,
O COR), 1156, 1076. ESI-MS: m/z 607.7 [M - SO4 2- ]2+ . Anal.
Calc. for Fe(L3 )SO4 ·8H2 O (C60 H78 FeN12 O16 S·8H2 O, 1455.36): C,
49.52; H, 6.51; N, 11.55%. Found: C, 49.88; H, 6.17; N, 11.79%.
Ru(L3 )(PF6 )2 (4–6). Ru(DMSO)4 Cl2 (16.2 mg, 0.033 mmol)
and L (0.10 mmol) were refluxed in ethanol (10 mL) under argon
for 8 h. The volume was reduced to half under vacuum and a
saturated NH4 PF6 solution was then added to the solution until
no further precipitate was observed. The yellow solid was filtered
off and washed with water. For Ru(L1 )3 (PF6 )2 (4): Yield: 16.7 mg
(35%). 1 H NMR (400 MHz, DMSO-d 6 ): d = 1.18 (t, 6H, J =
7.2 Hz, CH2 CH 3 ), 4.08 (q, 4H, J = 7.2 Hz, CH 2 CH3 ), 7.76 (d,
2H, J = 2.4 Hz, H6), 8.25 (dd, 2H, J = 9.2, 2.0 Hz, H4), 8.57 (d,
2H, J = 9.2 Hz, H3), 10.25 (s, 2H, NH). IR (KBr, cm-1 ): 3317,
5694 | Dalton Trans., 2011, 40, 5687–5696
2981, 1731 (s, C O), 1608, 1586, 1543 (s, N–H), 1486, 1384,
1259 m, 1226 (s, O COR), 1085 s, 1049 m. ESI-MS: m/z 546.3
[M - 2PF6 - ]2+ , 1237.5 [M - PF6 - ]+ . Anal. Calc. for Ru(L1 )3 (PF6 )2
(C48 H54 F12 N12 O12 P2 Ru, 1382.01): C, 41.72; H, 3.94; N, 12.16%.
Found: C, 41.66; H, 3.99; N, 12.24%. For Ru(L2 )3 (PF6 )2 (5):
Yield: 17.8 mg (49%). 1 H NMR (400 MHz, DMSO-d 6 ): d = 1.18
(d, 12H, J = 6.4 Hz, CH3 ), 4.83 (m, 2H, J = 6.4 Hz, CHMe2 ), 7.69
(d, 2H, J = 2.0 Hz, H6), 8.30 (dd, 2H, J = 8.8, 2.0 Hz, H4), 8.56
(d, 2H, J = 9.2 Hz, H3), 10.15 (s, 2H, NH). IR (KBr, cm-1 ): 3356,
2981, 1728 (s, C O), 1610, 1587, 1541 (s, N–H), 1488, 1385,
1261, 1224 (s, O COR), 1107, 1042. ESI-MS: m/z 588.4 [M 2PF6 - ]2+ , 1321.3 [M - PF6 - ]+ . Anal. Calc. for C54 H66 F12 N12 O12 P2 Ru
(1466.17): C, 44.24; H, 4.54; N, 11.46%. Found: C, 44.16; H,
4.67; N, 11.28%. For Ru(L3 )3 (PF6 )2 (6): Yield: 19.2 mg (37%).
1
H NMR (400 MHz, DMSO-d 6 ): d = 1.41 (s, 9H, CH3 ), 7.74 (s,
2H, H6), 8.28 (dd, 2H, J = 8.8, 1.6 Hz, H4), 8.53 (d, 2H, J =
8.8 Hz, H3), 9.97 (s, 2H, NH). IR (KBr, cm-1 ): 3347, 2982, 1725
(s, C O), 1618, 1583, 1550 (s, N–H), 1489, 1386, 1265, 1228 (s,
O COR), 1109, 1050. ESI-MS: m/z 630.5 [M - 2PF6 - ]2+ , 1405.8
[M - PF6 - ]+ . Anal. Calc. for C60 H78 F12 N12 O12 P2 Ru (1550.33): C,
46.48; H, 5.07; N, 10.84%. Found: C, 46.15; H, 5.15; N, 10.59%.
(7). FeCl2 ·4H2 O
(7.0
mg,
[Fe(L1 )3 ](BF4 )2 ·2CH3 OH
0.034 mmol) and L1 (0.10 mmol) were refluxed in 10 mL
methanol for 5 min to give a clear solution. The volume was
reduced to half under vacuum and a saturated NaBF4 solution
was then added to the solution until no further precipitate was
observed. The red solid was filtered off, washed with water and
diethyl ether, and dried in vacuum. Yield: 32.2 mg (78%). Single
crystals of the methanol adduct were obtained by slow diffusion
of diethyl ether into a MeOH solution. 1 H NMR (400 MHz,
DMSO-d 6 ): d = 1.15 (t, 6H, J = 7.2 Hz, CH2 CH 3 ), 4.03 (q, 4H, J =
7.2 Hz, CH 2 CH3 ), 7.39 (s, 2H, H6), 8.25 (d, 2H, J = 8.0 Hz, H4),
8.54 (d, 2H, J = 8.4 Hz, H3), 10.23 (s, 2H, NH). IR (KBr, cm-1 ):
3331, 2983, 1730 (s, C O), 1609, 1586, 1544 (s, N–H), 1484,
1385, 1257, 1220 (s, O COR), 1082, 1053. ESI-MS: m/z 523.6
[M - 2BF4 - ]2+ , 1133.8 [M - BF4 - ]+ . Anal. Calc. for Fe(L1 )3 (BF4 )2
(C48 H54 B2 F8 FeN12 O12 , 1220.47): C, 47.24; H, 4.46; N, 13.77%.
Found: C, 47.36; H, 4.59; N, 13.56%.
[Fe(L2 )3 ](BF4 )2 ·2Et2 O·2CH3 OH (8). Compound 8 was synthesized by a similar method for [Fe(L1 )3 ](BF4 )2 ·2CH3 OH (7)
except that L2 was used instead of L1 . Yield: 34.8 mg (79%). Single
crystals of the methanol and diethyl ether adduct were obtained
by slow diffusion of diethyl ether into a MeOH solution. 1 H NMR
(400 MHz, DMSO-d 6 ): d = 1.16 (d, 12H, J = 5.2 Hz, CH3 ), 4.80
(m, 2H, J = 6.4 Hz, CHMe2 ), 7.33 (s, 2H, H6), 8.32 (d, 2H, J =
8.8 Hz, H4), 8.54 (d, 2H, J = 9.2 Hz, H3), 10.15 (s, 2H, NH).
IR (KBr, cm-1 ): 3344, 2982, 1727 (s, C O), 1609, 1585, 1540 (s,
N–H), 1486, 1386, 1261, 1222 (s, O COR), 1109, 1042. ESI-MS:
m/z 565.6 [M - 2BF4 - ]2+ , 1217.9 [M - BF4 - ]+ . Anal. Calc. for
Fe(L2 )3 (BF4 )2 (C54 H66 B2 F8 FeN12 O12 , 1304.63): C, 49.71; H, 5.10;
N, 12.88%. Found: C, 49.36; H, 4.98; N, 12.65%.
(9). ZnCl2
[ZnCl2 (L1 )][ZnCl2 (L1 )(DMSO)]·2DMSO
(13.6 mg, 0.10 mmol) and L1 (33.0 mg, 0.10 mmol) were
added to 10 mL methanol. A yellow precipitate formed
immediately. After stirring for 10 min, the precipitate was filtered
and washed with methanol. Pale-yellow crystals of the DMSO
adduct were obtained by slow diffusion of diethyl ether into
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the DMSO–methanol solution of the complex. Yield: 32.7 mg
(56%). 1 H NMR (400 MHz, DMSO-d 6 ): d = 1.12 (t, 6H, J =
7.2 Hz, CH2 CH 3 ), 4.10 (q, 4H, J = 7.2 Hz, CH 2 CH3 ), 7.66 (s,
2H, H6), 8.25 (d, 2H, J = 8.4 Hz, H4), 8.60 (d, 2H, J = 8.4 Hz,
H3), 10.03 (s, 2H, NH). IR (KBr, cm-1 ): 3276 (br, N–H), 1730
(s, C O), 1587, 1541 (s, N–H), 1500, 1485, 1380, 1320, 1265,
1229 (s, O C–OR), 1086 s, 1044 m, 1031, 1012, 838. ESI-MS:
m/z 429.3 [ZnL1 Cl]+ . Anal. Calc. for Zn2 (L1 )2 Cl4 ·3DMSO
(C32 H36 Cl4 N8 O8 Zn2 ·3DMSO, 1167.65): C, 39.09; H, 4.66; N,
9.60%. Found: C, 39.18; H, 4.38; N, 9.85%.
[Zn(L1 )3 ](NO3 )2 ·2H2 O (10). Zn(NO3 )2 ·6H2 O (10.0 mg,
0.033 mmol) and L1 (33.0 mg, 0.10 mmol) were added to 10 mL
methanol to give a clear solution. The solvent was removed under
vacuum to yield a white solid. Single crystals were obtained by
slow diffusion of diethyl ether into a MeOH solution. Yield:
28.7 mg (74%). 1 H NMR (400 MHz, DMSO-d 6 ): d = 1.16 (t, 6H,
J = 7.2 Hz, CH2 CH 3 ), 4.05 (q, 4H, J = 7.2 Hz, CH 2 CH3 ), 7.49 (s,
2H, H6), 8.25 (d, 2H, J = 8.4 Hz, H4), 8.56 (d, 2H, J = 8.4 Hz,
H3), 10.22 (s, 2H, NH). IR (KBr, cm-1 ): 3241 (br, N–H), 2980
m, 1732 (s, C O), 1607, 1593, 1545 (s, N–H), 1500, 1487, 1383
(NO3 - ), 1315, 1259 m, 1222 (s, O C–OR), 1083 s, 1052 m, 845
m, 770. ESI-MS: m/z 527.3 [M - 2NO3 - ]2+ , 1116.7 [M - NO3 - ]+ .
Anal. Calc. for Zn(L1 )3 (NO3 )2 ·2H2 O (C48 H54 N14 O18 Zn·2H2 O,
1216.44): C, 47.39; H, 4.81; N, 16.12%. Found: C, 47.67; H, 4.44;
N, 16.53%.
[Zn(L2 )3 ](ClO4 )2 ·2Et2 O·2CH3 OH·1.5H2 O (11). Zn(ClO4 )2 ·
6H2 O (12.5 mg, 0.033 mmol) and L2 (35.8 mg, 0.10 mmol) were
added to 10 mL methanol to give a clear solution. The solvent
was then removed under vacuum and the white solid thus formed
was collected. Single crystals were obtained by slow diffusion of
diethyl ether into a MeOH solution. Yield: 30.0 mg (67%). 1 H
NMR (400 MHz, DMSO-d 6 ): d = 1.17 (d, 12H, J = 6.0 Hz, CH3 ),
4.82 (m, 2H, CHMe2 ), 7.55 (d, 2H, J = 2.0 Hz, H6), 8.31 (dd,
2H, J = 8.8, 2.0 Hz, H4), 8.55 (d, 2H, J = 8.8 Hz, H3), 10.16
(s, 2H, NH). IR (KBr, cm-1 ): 3305 (br, N–H), 2981 m, 1732 (s,
C O), 1614, 1591, 1539 (s, N–H), 1492, 1384, 1317, 1260 m,
1224 (s, O C–OR), 1180, 1106 s, 1043 m, 931, 846. ESI-MS:
m/z 569.3 [M - 2ClO4 - ]2+ , 1237.6 [M - ClO4 - ]+ . Anal. Calc.
for Zn(L2 )3 (ClO4 )2 ·H2 O (C54 H66 Cl2 N12 O20 Zn·H2 O, 1357.47):
C, 47.78; H, 5.05; N, 12.38%. Found: C, 47.61; H, 4.69; N,
12.55%.
[Cu(L1 )2 ](ClO4 )2 ·3DMSO (12). In a similar manner,
Cu(ClO4 )2 ·6H2 O (12.5 mg, 0.033 mmol) and L1 (33.0 mg,
0.10 mmol) were reacted to yield the complex 12 (34.7 mg,
83%). Single crystals were obtained by slow diffusion of diethyl
ether into a DMSO–MeOH solution. Yield: 45.7 mg (79%).
IR (KBr, cm-1 ): 3298, 2982, 1730 (s, C O), 1609, 1585, 1540
(s, N–H), 1486, 1386, 1260, 1221 (s, O COR), 1108. ESI-MS:
m/z 361.7 [M - 2ClO4 - ]2+ , 822.3 [M - ClO4 - ]+ . Anal. Calc. for
Cu(L1 )2 (ClO4 )2 ·3DMSO (C32 H36 Cl2 CuN8 O16 ·3DMSO, 1157.52):
C, 39.43; H, 4.70; N, 9.68%. Found: C, 39.17; H, 4.33; N, 9.74%.
X-Ray crystallography
Data collection was performed on a Bruker-AXS SMART CCD
area detector diffractometer at 293 K using w rotation scans with
a scan width of 0.3◦ and Mo Ka radiation (l = 0.71073 Å).
Multi-scan corrections were applied using SADABS.19 Structure
This journal is © The Royal Society of Chemistry 2011
solutions and refinements were performed with the SHELX-97
package.20 All non-hydrogen atoms were refined anisotropically
by full-matrix least-squares on F 2 . The hydrogen atoms were
included in idealized geometric positions with thermal parameters
equivalent to 1.2 times those of carbon and nitrogen atoms.
Hydrogen atoms of water molecules in some complexes were not
included. The wR2 values for complexes 2, 7, 8, and 10 are quite
high, which may be due to the presence of a considerable amount
of weak diffraction. Crystallographic data for the compounds are
summarized in Table 1.
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (Grant No. 20872149).
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