In situ selective N-alkylation of pendant pyridyl functionality in mixed-valence copper complexes with methanol and copper(ii) bromide

Article abstract of DOI:10.1039/c2dt12081j

The reactions of CuBr₂ with pyridyl 2,2′:6′, 2′′-terpyridine ligands in methanol yielded four copper complexes under solvothermal conditions. The self-assembly processes were accompanied by designing bitopic precursor ligands and increasing the stoichiometric metal-ligand ratio. In the four resulting complexes, the pendant pyridyl groups of pyridylterpyridine were selectively in situ N-methylated and yielded the 4′-(N-methylpyridinium)-2,2′:6′,2′′-terpyridine cations, including the 2-position pyridyl group which is difficult to be N-alkylated due to the steric problem. Partial divalent copper atoms were reduced to cuprous ones in the solvothermal reactions, which made the mixed-valence copper atoms coexist in each compound. The mixed-valence complexes have a varied dimensionality (from 2D to 0D) and the Cu^IBr cluster, which can be controlled by changing the metal-ligand ratio. Theoretical studies show that the nucleophilic attack of the nitrogen atom in the pendant pyridyl is more facile than others of terpyridine. A possible mechanism was also proposed. The Royal Society of Chemistry 2012.

Full text of DOI:10.1039/c2dt12081j

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PAPER
In situ selective N-alkylation of pendant pyridyl functionality in
mixed-valence copper complexes with methanol and copper(II) bromide†
Da-Qian Feng, Xiao-Ping Zhou, Ji Zheng, Guang-hui Chen, Xiao-Chun Huang and Dan Li*
Received 2nd November 2011, Accepted 6th February 2012
DOI: 10.1039/c2dt12081j
The reactions of CuBr with pyridyl 2,2′:6′,2′′-terpyridine ligands in methanol yielded four copper
2
complexes under solvothermal conditions. The self-assembly processes were accompanied by designing
bitopic precursor ligands and increasing the stoichiometric metal–ligand ratio. In the four resulting
complexes, the pendant pyridyl groups of pyridylterpyridine were selectively in situ N-methylated and
yielded the 4′-(N-methylpyridinium)-2,2′:6′,2′′-terpyridine cations, including the 2-position pyridyl group
which is difficult to be N-alkylated due to the steric problem. Partial divalent copper atoms were reduced
to cuprous ones in the solvothermal reactions, which made the mixed-valence copper atoms coexist in
each compound. The mixed-valence complexes have a varied dimensionality (from 2D to 0D) and the
I
Cu Br cluster, which can be controlled by changing the metal–ligand ratio. Theoretical studies show that
the nucleophilic attack of the nitrogen atom in the pendant pyridyl is more facile than others of
terpyridine. A possible mechanism was also proposed.
1
5,16
Introduction
alkylating agents.
They found that the pendant pyridyl
groups in the former two terpyridine complexes underwent
partial N-alkylation and obtained mono- and bis-N-methylated
derivatives even in harsher reaction conditions (higher tempera-
ture, longer time and excess of CH I) due to sterical hindrances.
We are interested in constructing coordination polymers using
In situ metal–ligand reactions under solvo(hydro)thermal con-
ditions are of topical interest in coordination chemistry and
organic chemistry. As a powerful non-conventional approach,
lots of unusual metal–ligand reactions have been found in high
pressure and at relatively high temperature.
products in such conditions may be inaccessible by traditional
organic synthesis. N-alkylation of amine is one of the most
fundamental and important reactions in synthetic organic chem-
istry. The normal method for N-alkylation is to use alkyl halides,
which is undesirable from an environmental point of view. Intro-
ducing alcohols as substitutes should be more attractive.
However, the actualization of the N-alkylation processes usually
3
1
–8
Some reaction
2
,2′:6′,2′′-terpyridine and its derivatives as linkers, particularly
functionalizing the 4′-position of the central pyridine of terpyri-
1,2
17–21
dine to bring a pendant pyridyl donor site.
-pyridyl functionality terpyridines are employed as rational
starting materials for in situ alkylation reactions. On the other
hand, it has been reported that Cu ions can be reduced to Cu
by 4,4′-bipyridine and pyridine derivatives under hydrothermal
conditions. It is possible to design bifunctional precursory
ligands which are capable of accommodating the coordination
modes of metal ions and active organic reaction. Our strategy is
to construct building blocks through selective N-alkylation reac-
tions of pendant pyridyl functionality in situ. We synthesized a
The pendant
4
II
I
17
9
,10
needs expensive Ru or Ir organometallic catalysts.
others have developed new in situ N-alkylation reactions includ-
We and
11
12
ing N-alkylation of triazole, pyridine-4-thiol, 4,4′-bipyri-
1
3
14
dine and 4-(4-aminobenzyl)benzenamine using alcohols in
the presence of cheap metal halides under solvothermal
conditions.
II
+
series of mixed-valence copper complexes [(Cu Br L1Me) -
2
I
−
II
+
I
−
II
4 5 n 2 3 4 n 2
(
Cu Br ) ] (1), [(Cu Br L1Me) (Cu Br ) ] (2), [(Cu Br -
+
I
−
II
+
I
−
As one of the most important tridentate ligands, terpyridine
and its subsequently substituted analogues have been widely
investigated in coordination chemistry. Constable et al.
implemented a systematic investigation of N-alkylation of a
series of mononuclear complexes of 4′-(2-pyridyl)-, 4′-(3-
L1Me ) (Cu Br ) ] (3), and [(Cu Br L2Me) (Cu 2.68Br3.68) ]
2
2
2
2
2
(
4) (L1 = 4′-(4-pyridyl)-2,2′:6′,2′′-terpyridine, L2 = 4′-(2-
pyridyl)-2,2′:6′,2′′-terpyridine, Chart 1). The Cu –Cu
I
II
pyridyl)- and 4′-(4-pyridyl)-2,2′:6′,2′′-terpyridine using CH I as
3
Department of Chemistry, Shantou University, Guangdong 515063,
P. R. China. E-mail: dli@stu.edu.cn
†
Electronic supplementary information (ESI) available. CCDC reference
numbers 806444–806447. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c2dt12081j
Chart 1
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 4255–4261 | 4255

compounds were obtained by reactions of corresponding terpyri-
dines with CuBr2 in methanol. In these compounds, all the
pendant pyridyl groups are in situ N-methylated selectively,
2
+
while the other three pyridyl groups chelate Cu centers. The
advantage of using alcohols instead of alkyl halides is obvious
because alcohols are not only cheaper and more ready available,
but are also environmental friendly.
Results and discussion
In situ N-methylation products
Complexes 1–4 were obtained by reacting CuBr with L1 or L2
2
under identical solvothermal conditions (methanol as solvent,
temperature at 140 °C, see Experimental section). X-ray single-
I
crystal analyses reveal that complexes 1–4 contain varied Cu Br
anionic aggregations (see below for structure description) and
4
′-(N-methylpyridinium)-2,2′:6′,2′′-terpyridine ligands, where
the pendant pyridyl groups were selectively N-methylated,
II
chelating to Cu atoms. The distances between the carbon atoms
of methyl groups and the nitrogen atoms of the pyridinium
are 1.454(13)–1.494(13) Å, which are typical C–N bonds for
N-alkylated pyridinium.
II
+
1
5,16
Fig. 1 The structure of 1. (a) View of the Cu Br
Cu Br cluster. (b) 2D grid-like network view along the b axis. Hydro-
gen atoms are omitted for clarity.
2
L1Me sections and
4
4
The in situ N-methylation of the pendant pyridyl group was
also proved by the featuring C–H stretching vibrations of the
−1
−1
methyl groups (2927 cm –2850 cm ) in their IR spectra. The
UV-vis absorption data (Fig. S1, ESI†) of reaction filtrates in
reaction for copper ions often occurs under hydro(solvo)thermal
conditions. The Cu Br clusters are linked by the μ -Br4 atoms
to form a 1D anionic [Cu Br5 ] chain. Then the chains are
further extended to a 2D grid-like network by the Cu Br L1Me
1
CH OH solutions show that the reaction products are signifi-
3
4
4
2
−
cantly different from the starting materials. The spectrometry
further demonstrates that the N-alkylation approach with alcohol
under solvothermal conditions is successful and practicable. In
4
n
II
+
2
through Cu–Br coordination bonds, as shown in Fig. 1b.
1
–4, the planar character of the tridentate motif of the terpyridyl
Although distorted cubic Cu Br clusters were well documented,
4
4
ligands is critical in keeping the divalent copper ion at this site,
in situ methylation of the monodentate pyridyl to methylpyridi-
nium was observed. Thermogravimetric analyses of all com-
pounds in argon demonstrate the mass loss as shown in Fig. S2
being embedded into a mixed-valence 2D network is rarely
reported.
II
+
Similar to 1, complex 2 also contains the Cu Br L1Me frag-
2
I
ment and anionic Cu Br chains. However, both of them have
(ESI†) indicating the complexes are thermally stable up to
their differences. The pendant pyridinium ring twist at an angle
3
00–400 °C.
of 34.2° to the central pyridyl ring in 2, and the angle in 1 is
1
4.1°. Unlike that adopting a trigonal bipyramid geometry in 1,
the divalent Cu1 atom in 2 adopts a more likely distorted square
pyramidal geometry (Fig. 2a). The three N atoms and one
Br atom (Br1) bonding to the Cu1 atom form the square base
(Cu–N, 1.9366(1)–2.0246(1) Å, and Cu–Br, 2.3352(1) Å), and
an additional Br2 atom occupies the apex through a lengthened
coordination bond (Cu1–Br2 2.8765(2) Å) to complete the
square pyramidal geometry. The cuprous atoms binding with Br
Crystal structures
Complex 1 features two dimensional grid-like networks based on
the linkage of Cu Br L1Me sections to [Cu Br ]n inorganic
II
+
−
2
4
5
anionic chains. The asymmetric portions of the unit cell contains
.5 copper atoms (Cu1, Cu2 and Cu3, Cu1 located on the C2
2
+
axis with sites occupancy 0.5), half of the L1Me cation, and
−
3
.5 Br anions (Br1, Br2, Br3, and Br4, Br4 is disordered with
atoms form a Cu
3
Br
3
cluster (Fig. 2a). Similar Cu
3
Br
3
clusters
(2,3-
The trinuclear clusters were
further linked by the bridging Br atoms (Br6) to form a
sites occupancy 0.5). The divalent Cu1 is chelated by the three
nitrogen atoms and bound by additional two Br ions, adopting
a distorted trigonal bipyramid geometry (Cu–N 1.930(2)–2.0235
were found in the previous reported compounds Cu
3
−
22
23
dmpz)
Br
and Cu Br (dpmt) .
3 3 2
2
3
−
(3) Å, Cu–Br 2.517(3) Å; N–Cu–N 79.849(3)°, N–Cu–Br
[Cu
Br ] anionic chain like in 1 and then extend to a triple-
3 4 n
9
4.781(4)–126.52(3)°, Br–Cu–Br(1) 106.95(5)°). The two Cu2
rung ladder structure. Interestingly, only one Br atom (Br2)
for each Cu Br L1Me bridges to the [Cu Br ] chain (Br1 as
2 3 4 n
a terminal coordination) leading to the formation of a ribbon
structure rather than a 2D one.
−
II
+
−
and two Cu3 atoms are bound by four Br ions to construct a
distorted cubic Cu Br cluster (Fig. 1a), in which the Br ions
adopt a μ -bridging mode and copper atoms adopt a tetrahedron
4
4
3
geometry (completed by an additional μ -Br atom, Br1 or Br4,
Complex 3 features a relatively simple oligonuclear structure
compared with the polymeric structures in 1 and 2, as shown in
Fig. 3. The L1Me chelates the divalent Cu1 with three nitrogen
2
(Cu–Br 2.473(2)–2.669(2) Å), respectively. The tetrahedron geo-
+
metry of Cu2 and Cu3 indicates that they are cuprous atoms, in
accordance with the requirement of charge balance. The redox
atoms like those in 1 and 2, and the divalent Cu1 adopts a
4256 | Dalton Trans., 2012, 41, 4255–4261
This journal is © The Royal Society of Chemistry 2012

Fig. 4 The structure of 4. Hydrogen atoms are omitted for clarity.
CuBr –L1 increase from 2 : 1 to 8 : 1. No doubt the metal–
2
ligand ratio (stoichiometry) plays an important role in controlling
the assembly of the complexes. However, in the reported results,
the metal–ligand ratios in the products are always consistent
2
4–26
with the reacting ratios.
Here, this difference may be caused
2+
+
−
by the large excess of Cu atoms, which affect the Cu and Br
aggregations. Under the same solvothermal conditions, the quan-
tity of Cu through reducing Cu will probably be identical.
Therefore, the non-reducing Cu atoms (partial Cu atoms
are coordinated by the L1Me ) in the reacting system during the
+
2+
2+
2+
+
formation of 3 will largely exceed those used than when forming
2
+
1
(probably 4 fold or more). The excess non-reacting Cu may
I
disturb the formation of the Cu Br anionic cluster and the self-
assembly of the resulting complexes will take place through elec-
trostatic interaction. For example, the large CuBr anionic clusters
Fig. 2 The structure of 2. (a) The asymmetric unit of complex 2. (b)
The 1D ribbon structure of 2. Hydrogen atoms are omitted for clarity.
2+
may hardly form when it is surrounded by abundant Cu ions
2+
+
(
the Cu ions are probably preferred more than Cu because
of the more positive charge). Such a condition leads to the
lower dimensionality, smaller CuBr anionic cluster and a lower
metal–ligand ratio like in 3.
The synthesis of complex 4 is similar to 2 except replacing L1
II
+
with L2. In the structure of 4, two Cu Br L2Me units are
2
bridged by an oligonuclear cuprous bromide cluster, as shown in
Fig. 4. The pendant pyridyl of L2 was also N-methylated like
L1 in complexes 1–3. The divalent Cu1 displays a distorted
square pyramidal coordination geometry (similar to the structure
of complex 2), which is comprised of three N donors from the
terpyridine ligand and two bromine ions (Cu–N, 1.950(6)–2.050
(7) Å, Cu–Br, 2.3734(14)–2.7520(14) Å). The dihedral angle
between the pendant pyridinium and the central pyridyl of
Fig. 3 The structure of 3. Hydrogen atoms are omitted for clarity.
distorted trigonal bipyramid geometry completed by two
additional Br atoms (Cu–N, 1.9646(2)–2.0326(3) Å, Cu–Br,
2
9
.4757(3)–2.4897(3) Å, N–Cu–N 79.13(1)–79.43(1)°, N–Cu–Br
1.46(1)–120.04° and Br1–Cu1–Br2 109.38(1)°). The positive
+
L2Me is 78.45°, which approaches a vertical angle. The value
II
+
I
−
Cu Br L1Me is linked to the Cu Br anionic unit (Cu–Br,
is obviously larger than the corresponding dihedral angle value
2
2
+
2
.3722(3)–2.2799(3) Å) through Br2 bridging to Cu2 (2.5243(3)
of L1Me in complexes 1–3 (10.51° to 34.2°) and the non-
Å), and then a dinuclear complex is formed. Interestingly, the
dinuclear complex is further interacted to an adjacent dinuclear
complex forming a tetranuclear adduct with two weaker Cu–Br
coordination bonds (3.0047 (4) Å, Fig. 3). The bond distance is
just slightly shorter than the sum of the Van der Waals radius of
Cu (1.40 Å) and Br (1.85 Å).
N-alkylated L2 in a previous reported mixed-valence complex
[Cu (L2)(SCN) ] (12.7°). The large twisting of the pendant
2 3 n
17
pyridinium ring avoids the steric problem, and helps implement
the N-methylation on the 2-position of the pyridyl group. This
structural feature indicates that the L2 needs additional energy
to rotate the pendant ring to finish the N-methylation, and
also visually shows the difficulty of N-methylation of L2. This is
In the syntheses of complexes 1–3, we try to tune the struc-
I
tures (e.g., dimensionality and the size of Cu Br cluster) by
consistent with the difficult N-methylation of [Ru(L2)
2
][PF
in the presence of >1000-fold excess of CH I. The central
3
6 2
]
15
changing the metal–ligand ratio. In complexes 1–3, the dimen-
I
II
+
sionality decreases from 2D to 0D and the Cu Br cluster size
copper bromide cluster between the two Cu Br L2Me sections
2
decreases from tetranuclear to mononuclear when the metal–
ligand ratio increases. On the other hand, the metal–ligand ratios
was slightly intricate. Both Cu2 and Cu4 atoms disorder with
two positions (with a ratio of 0.677 : 0.323, and 0.51 : 0.49,
respectively), when Cu3 and Br3 atoms are only partially occu-
pied (refined as a 0.677 site occupation). Therefore, the overall
formula of complex 4 determined from X-ray diffraction can
in the products are in large disagreement with the ratios in the
+
starting reagents. The ratios of CuBr –L1Me in products 1–3
2
are degressive from 5 : 1 to 2 : 1 while the reacting ratios of
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 4255–4261 | 4257

Table 1 NBO charge (in e) analysis
Cu
N
A
N
B
N
C
N
D
L1
L2
Cu-L1
Cu-L2
—
—
1.080
1.079
−0.447
−0.452
−0.377
−0.458
−0.465
−0.467
−0.499
−0.499
−0.465
−0.466
−0.560
−0.560
−0.465
−0.457
−0.560
−0.561
Fig. 5 The optimized structures of L1, L2 and their complexes with
Cu.
Scheme 1 Possible mechanism of alkylation of complex 1.
thus be represented as [(Cu Br L2Me) (Cu 2.68Br3.68)−] . As
II
+
I
2
2
15
This was verified by a recent report, in which [Ru(L2) ][PF ]
I
2
6 2
shown in Fig. 4, the Cu atoms are coordinated by the Br atoms
and form a Cu Br anionic cluster, which further links to two
Cu Br L2Me species giving the eight-nuclear mixed-valence
copper complex 4. Unlike 1 and 2, complex 4 is not further
is hardly N-alkylated (25 h at reflux in the presence of >1000-
I
−
6
8
fold excess of MeI). In contrast, our present work shows that the
N-alkylation of L2 was successfully carried out even with
alcohol under solvothermal conditions, where unusual organic
reactions may happen.
II
+
2
−
linked to Br to form a coordination polymer.
DFT calculations
Possible mechanism
The selective N-methylation of the pendant pyridyl group (NA
II
over N , N and N , Fig. 5) is considered as the result of the
Hydrothermal reactions of Cu with pyridylterpyridyl ligands
B
C
D
I
II
nucleophilic attack of N to the cationic methyl group generated
in situ generate mixed-valence Cu Cu compounds, where
metal ions as redox agents may be crucial in promoting the
ligand reactions. Self-assembly reactions of metal ions and the
neutral pyridine-based 2,2′:6′,2′′-terpyridine ligands adopted a
unconventional solution method under extreme conditions,
involving a simultaneous redox, N-methylation reactions. A
rational assumption of the solvothermal reactions is similar to
the situation previously reported by Yao et al. Undoubtedly,
the methyl group comes from methanol. Methanol acts directly
as a sort of alkylation reagent. Another possible indirect sort of
alkylation agent is MeBr when methanol was activated by Br2
and H O. Br is an important intermediate as oxidation products
oxidated by Cu ions. ESI-MS analyses confirmed that corre-
sponding N-methylated compounds did exist in the reaction
filtrates (Fig. S3, ESI†). As the UV-vis spectrum curves (Fig. S1,
ESI†) display, ligand L1 has three peaks at 240 nm, 276 nm,
312 nm, respectively while ligand L2 has peaks at 241 nm,
279 nm, 312 nm. The spectra suggest that the reactions should
produce new compounds because the curve of complex 1 has the
new unique peak located in approximately 330 nm compared
with the curves of the component and even the similar mixture
A
from methanol. In this selective nucleophilic reaction, two poss-
ible effects should not be ruled out for consideration: (i) does the
electronic effect play a role, along with the steric effect, in this
selectivity; (ii) does the copper coordination affect this selectiv-
ity? To gain insight into these aspects, preliminary density func-
tional theory (DFT) calculations were performed. The optimized
structures of the ligands and complexes are shown in Fig. 5, and
the NBO (Natural Bond Order) charges of the N and Cu atoms
are summarized in Table 1.
12
For (i), we have found, in both L1 and L2, the negative
charge of NA does not differ drastically from those of N , NC
B
2
2
2+
and N ; in fact, the NBO charges of N , N and N are even
D
B
C
D
slightly more negative. Also the charges of NA in L1 and L2
show no notable difference from each other, indicating the elec-
tronic effect may not be responsible for the selective N-methyl-
ation, which has to be majorly attributed to the steric effect. For
(ii), the chelating effect enables the conformational adjustment
of N , N and N when coordinating to Cu (Fig. 5). The reactiv-
B
C
D
ity of NA in Cu-L1 is reduced (negative charge from −0.447 to
0.377 e), and in Cu-L2 maintains largely unchanged (negative
−
charge from −0.452 to −0.458 e). This hints that the selective
N-methylation may take place simultaneously to, or before, the
coordination of Cu.
with L1 and CuBr at room temperature. Regioselective alky-
lation of pendant pyridyl functionality in situ for complex mol-
ecule synthesis gave rise to Cu Br L1 Me, and anionic
clusters which took the roles of charge balance
(Scheme 1, complex 1 as an example).
2
II
+
2
I
−
Because of the large steric hindrance in L2, the N-alkylation
of L2 should be an arduous task under traditional conditions.
Cu Br
n
n+1
4258 | Dalton Trans., 2012, 41, 4255–4261
This journal is © The Royal Society of Chemistry 2012

Conclusion
1548 m, 1467 m, 1393 m, 1070 w, 993 m, 780 m, in agreement
with the literature data.
27,28
In summary, we demonstrate a synthetic method to achieve
homometallic mixed-valence
4′-(2-Pyridyl)-2,2′:6′,2′′-terpyridine (L2). It was prepared
copper(I/II)
pyridine-based
analogously to L1 by replacing 4-acetylpyridine with 2-acetyl-
pyridine in the same mole ratio. As a result, a yellow crystalline
solid was obtained in 25% yield. m.p. 232 °C. Anal. Calc for
terpyridyl compounds formed by simultaneous in situ alkylation
reactions of neutral ligands and redox cupric halides under sol-
vothermal conditions in alcohol. All complexes were constructed
II
+
I
−
C H N : C, 77.40%; H, 4.55%; N, 18.05%. Found: C,
of the Cu Br L1 Me components and anionic Cu Br clus-
n+1
20 14 4
2
n
1
7
=
7.45%; H, 4.51%; N, 18.01%. H NMR (400 MHz, CDCl ): δ
3
9.11 (s, 2H), 8.81 (d, 1H, J = 6.53 Hz), 8.75(d, 2H, J = 7.43
ters as counterions. These results show that the bifunctional
ligand can accommodate both selective N-alkylation and coordi-
nation of added metal ions. In particular, the successful N-alky-
lation of the pendant 2-pyridyl of L2 with a large steric
hindrance suggests that such a method may be especially suitable
and useful for enhancing some difficult organic reactions (e.g.
the reagents or precursors with steric problems). Inspired by the
successful N-alkylation of L1 and L2 with alcohol, the further
N-alkylation on more amine molecules will be foreseen
and exploited by the use of alcohol as the alkyl source under
solvothermal conditions.
3
3
3
3
Hz), 8.67(d, 2H, J = 7.95 Hz), 8.08(d, 1H, J = 7.96 Hz), 7.86
1
(
m, 3H), 7.35 (m, 3H). IR (KBr, cm− ): 3045 w, 1581 s,
1
562 m, 1467 m, 1393 m, 1071 w, 982 m, 790 m.
II
+
I
−
[
(Cu Br
2
L1Me) (Cu
4
Br
5
) ]
n
(1). A mixture of CuBr2
(0.045 g, 0.2 mmol) and ligand L1 (0.031 g, 0.1 mmol) in
methanol (8 mL) was sealed in a 15 mL Teflon-lined reactor,
heated to 140 °C for 72 h, and then cooled to room temperature
−1
at a rate of 6 °C h . X-ray-quality black crystals of compound 1
were obtained in ca. 55% yield based on L1. Anal. Calcd for
C H Cu N Br : C, 20.96%; H, 1.43%; N, 4.68%. Found: C,
2
1
17
5
4
7
−1
2
2
1.01%; H, 1.41%; N, 4.66%. IR (KBr, cm ): 3035 w, 2922 w,
850 w, 1635 m, 1614 m, 1558 s, 1472 w, 1415 m, 1242 s,
Experimental section
Materials and physical measurements
1017 m, 781 m, 508 m.
II
+
I
−
Chemicals and solvents used in this work were of analytical
grade and used as purchased without further purification. NMR
spectra were recorded on a Bruker AVANCE400 spectrometer
and referenced to TMS. Infrared spectra were collected from a
KBr disk on a Nicolet Avatar 360 FTIR spectrometer in the
[(Cu Br L1Me) (Cu Br ) ] (2). It was prepared analo-
2 3 4 n
gously to compound 1 with double amounts of CuBr (0.09 g,
0.4 mmol). Black crystals of compound 2 were obtained in ca.
25% yield (based on L1). Anal. Calcd for C H Cu N Br : C,
23.81%; H, 1.65%; N, 5.27%. Found: C, 23.79%; H, 1.62%; N,
5.31%. IR (KBr, cm ): 3055 w, 2927 w, 2855 w, 1718 w,
2
21
17
4
4
6
−1
−1
range of 4000–400 cm . Elemental analyses of C, H, and N
were determined with a Perkin-Elmer 2400C elemental analyzer.
Thermogravimetric analysis (TGA) was carried out under argon
1699 m, 1636 m, 1559 m, 1541 s, 1410 w, 1228 m, 1016 s,
781 m, 705 m.
−1
atmosphere with the heating rate of 10 °C min from room
temperature to 800 °C on a Seiko Extar 6000 TG/DTA equip-
ment. UV-vis measurements were performed using a Perkin-
Elmer Lambda 35 spectrophotometer. ESI-MS analyses were
carried out using an ABI4000 Q TRAP liquid chromatography-
mass spectrometer.
II
2 2
(Cu Br L1Me) (Cu Br
)−] (3). It was prepared analogously
+
I
[
to compound 1 using CuBr of 0.18 g (0.8 mmol). Black crystals
of compound 3 were obtained in ca. 20% yield (based on L1).
Anal. Calcd for C H Cu N Br : C, 32.68%; H, 2.25%; N,
.21%. Found: C, 32.64%; H, 2.28%; N, 7.26%. IR (KBr,
cm ): 3037 w, 2924 w, 2851 w, 1635 w, 1605 m, 1559 m, 1472
s, 1411 w, 1242 m, 1015 s, 783 m, 506 m.
2
21
17
2
4
4
7
−1
Preparations
II
+
I
−
[
2 2
(Cu Br L2Me) (Cu 2.68Br3.68) ] (4). It was prepared analo-
gously to compound 2 by replacing ligand L1 with L2. Black
crystals of compound 4 were obtained in ca. 45% yield based on
4
′-(4-pyridyl)-2,2′:6′,2′′-terpyridine (L1). A mixture of 4-
pyridinecarboxaldehyde (3.21 g, 30 mmol), 2-acetylpyridine
7.26 g, 60 mmol) and solid NaOH (2.58 g, 62 mmol) was pre-
L2. Anal. Calcd for C H Br11.36Cu N : C, 24.90%; H,
(
42 34
7.36 8
1
.69%; N, 5.53%. Found: C, 24.82%; H, 1.62%; N, 5.49%. IR
pared using a pestle and mortar, the yellow medium aggregated
until a yellow powder was formed (ca. 10 min) and then was
further ground for 30 min. The powder was transferred to a sus-
pension of ammonium acetate (20 g, excess) in glacial acetic
acid (50 mL) and heated to reflux. After reaction for 3 h, a
mixture of ethanol (30 mL) and water (40 mL) was added with
stirring. Upon cooling, the crystalline product was precipitated
from the solution, collected and recrystallized in ethanol to yield
yellow crystals of L1. Yield: 4.28 g (46%, 13.8 mmol). m.
p. 235 °C. Anal. Calcd for C H N : C, 77.40%; H, 4.55%; N,
−1
(KBr, cm ): 3040 w, 2922 w, 2852 w, 1654 w, 1636 m,
1
7
599 m, 1560 s, 1466 w, 1408 m,1245 m, 1016 s, 776 m,
21 m.
X-ray crystallography
Suitable crystals of 1–4 were mounted with glue at the end of a
glass fiber, respectively. Diffraction data was collected at 293(2)
K with a Bruker-AXS SMART CCD area detector diffractometer
using ω rotation scans with a scan width of 0.3° and Mo-Kα
radiation (λ = 0.71073 Å). Multi-scan absorptions were applied.
Reflection intensities were integrated using SAINT software, and
an absorption correction was applied. The structures were solved
by the direct methods and refined by full-matrix least-squares
2
0 14 4
1
1
(
8.05%. Found: C, 77.44%; H, 4.52%; N, 18.03%. H NMR
400 MHz, CDCl ) (Fig. S4, ESI†): δ = 8.79 (d, 2H, J = 6.12
Hz), 8.09 (d, 2H, J = 6.18 Hz), 8.01(s, 2H), 7.99(d, 2H, J =
.60 Hz), 7.87(d, 2H, J = 8.42 Hz), 7.59 (m, 2H), 7.52 (m, 2H).
3
3
3
3
3
8
−1
IR (KBr, cm ) (Fig. S5, ESI†): 3052 w, 3007 w, 1581 s,
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 4255–4261 | 4259

Table 2 Crystal data and structure refinement parameters for complexes 1–4
1
2
3
4
Formula
C
21
H
17Br
7
Cu
5
N
4
C
21
H
17Br
6
Cu
4
N
4
C
21
H
17Br
4
Cu
2
N
4
C
42 8
H34Br11.36Cu7.36N
M
r
1202.46
Monoclinic
C2/c
10.3551(9)
27.263(2)
11.1239(10)
90
1059.01
772.11
Triclinic
P1ˉ
2026.18
Monoclinic
C2/c
33.656(8)
9.029(2)
18.153(4)
90
Cryst syst
Space group
a (Å)
b (Å)
c (Å)
Monoclinic
P2(1)/c
9.3227(8)
8.3368(8)
35.520(3)
90
9.724(2)
11.040(3)
12.238(3)
71.211(4)
α (°)
β (°)
γ (°)
V (Å )
112.780(2)
90
2895.5(4)
4
2.758
13.294
8883
91.218(2)
90
2760.0(4)
4
83.308(4)
65.455(4)
1131.2(5)
2
2.267
8.962
90.725(4)
90
5516(2)
4
3
Z
D
−
3
c
(g cm
)
2.549
2.439
−
1
μ (mm
No. of reflns collected
No. of unique reflns
)
11.746
13 831
4830
11.045
15 330
4696
8156
3952
3264
R
int
0.0443
1.048
0.0484
0.1214
0.0757
0.1466
0.0533
1.082
0.0504
0.1283
0.0729
0.1468
0.0359
0.975
0.0395
0.0885
0.0564
0.0975
0.0573
1.054
0.0546
0.1401
0.0813
0.1596
GOF
[I > 2σ(I)]
a
R
1
b
wR
R
wR
2
[I > 2σ(I)]
a
1
[all data]
b
2
[all data]
a
b
2
o
2 2
2 2 1/2
R
1
= ∑(||F | − |F
o
c
||) / ∑|F
o
|. wR
2
= [∑w(F
− F
c
o
) /∑w(F ) ] .
2
refinements based on F . All non-hydrogen atoms were refined
with anisotropic thermal parameters, and all hydrogen atoms
were included in calculated positions and refined with isotropic
thermal parameters riding on those of the parent atoms. Structure
solutions and refinements were performed with the SHELXL-97
X. H. Zhao, X. D. Chen, Q. Yu and M. Du, Cryst. Growth Des., 2010,
0, 5034.
N. Zheng, X. Bu and P. Feng, J. Am. Chem. Soc., 2002, 124, 9688.
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K. I. Fujita, Z. Li, N. Ozekib and R. Yamaguchib, Tetrahedron Lett.,
1
5
6
7
29
package. The parameters and experimental details of crystals
–4 are summarized in Table 2.
8
9
1
2003, 44, 2687.
10 S. Bähn, S. Imm, K. Mevius, L. Neubert, A. Tillack, J. M. J. Williams
DFT calculation
and M. Beller, Chem.–Eur. J., 2010, 16, 3590.
1
1 (a) T. Wu, M. Li, D. Li and X. C. Huang, Cryst. Growth Des., 2008, 8,
68; (b) Y. Cheng, P. Xu, Y. B. Ding and Y. G. Yin, CrystEngComm,
2011, 13, 2644; (c) Y. Du, S. Oishi and S. Saito, Chem.–Eur. J., 2011,
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5
Density functional theory calculations were performed using
the Gaussian09 A.02 program package at the B3LYP level.
3
0
31
1
3
2
For the geometric optimization and NBO charge analysis, the
3
3
6
-31G(d) basis set was used for C, N and H elements, while
12 J. K. Cheng, Y. G. Yao, J. Zhang, Z. J. Li, Z. W. Cai, X. Y. Zhang,
Z. N. Chen, Y. B. Chen, Y. Kang, Y. Y. Qin and Y. H. Wen, J. Am. Chem.
Soc., 2004, 126, 7796.
3 G. Xu, G. C. Guo, M. S. Wang, Z. J. Zhang, W. T. Chen and J. S. Huang,
Angew. Chem., Int. Ed., 2007, 46, 3249.
4 Z. J. Zhang, S. C. Xiang, G. C. Guo, G. Xu, M. S. Wang, J. P. Zou,
S. P. Guo and J. S. Huang, Angew. Chem., Int. Ed., 2008, 47, 4149.
5 J. E. Beves, E. I. Dunphy, E. C. Constable, C. E. Housecroft,
C. J. Kepert, M. Neuburger, D. J. Price and S. Schaffner, Dalton Trans.,
34
the SDD effective core potential (ECP) and basis set were used
for Cu element.
1
1
1
Acknowledgements
This work was financially supported by the National Science
Foundation for Distinguished Young Scholars of China (Grant
No. 20825102) and the National Natural Science Foundation of
China (Grant Nos. 20771072, 21171114 and 21101103).
2008, 386.
1
6 E. C. Constable, E. L. Dunphy, C. E. Housecroft, W. Kylberg,
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