A facile iodide-controlled fluorescent switch based on the interconversion between two- and three-coordinate copper(i) complexes

Article abstract of DOI:10.1039/b908765f

The first paradigm of halide-controlled interconversion between two- and three-coordinate copper(i) complexes, [Cu(L^Ph)](ClO₄) (1?ClO₄) and [Cu(L^Ph)I] (2), where L^Ph = 1,3-bis-(3,5-dimethyl-pyrazol-1-

Full text of DOI:10.1039/b908765f

View Article Online / Journal Homepage / Table of Contents for this issue
COMMUNICATION
www.rsc.org/chemcomm | ChemComm
A facile iodide-controlled fluorescent switch based on the interconversion
between two- and three-coordinate copper(I) complexesw
Chang-Chuan Chou,* Hsueh-Ju Liu and Lucas Hung-Chieh Chao
Received (in Cambridge, UK) 5th May 2009, Accepted 17th September 2009
First published as an Advance Article on the web 5th October 2009
DOI: 10.1039/b908765f
The first paradigm of halide-controlled interconversion between
two- and three-coordinate copper(I) complexes, [Cu(LPh)](ClO4)
(1ꢀClO4) and [Cu(LPh)I] (2), where LPh = 1,3-bis-(3,5-dimethyl-
pyrazol-1-ylmethyl)-2-phenyl-2,3-dihydro-1H-perimidine, was
presented, which can result in reversible fluorescence changes.
provide a useful spectroscopic probe upon interacting with
the copper(I) center.
The mononucleating ligand LPh was prepared by treating
1,8-naphthalenediamine with 1 equivalent of benzaldehyde
and 2 molar equivalents of 1-(hydroxymethyl)-3,5-dimethyl-
pyrazole in a 63% yield. The crystal structure of LPh, shown in
Fig. S1,wz reveals that the puckered bridging methylene
H2C(7) produced a six-membered C4N2 heterocycle. The five
atoms N3, C7, C12, C13 and N4 were coplanar and may have
been involved in the conjugation framework of the perimidine.
Based on the flexible coordination numbers of transition metal
and the lability of non-covalent interactions, the issue of
reversible structural interconversion controlled by an external
input (photon, electron, proton and other chemical species)
has attracted considerable attention because it may offer some
feasible ideas for constructing functional molecules.1–4
Accordingly, we recently developed an effective supramolecular
fluorescent switch based on the proton-controlled assembling/
disassembling process between 1-D polymeric and helicate
dimeric copper(II) complexes.5 Herein, we present the first
example of halide-controlled reversible system based simply
on the interconversion between monomeric linear two-coordinate
copper(I) complex [Cu(LPh)](ClO4) 1ꢀClO4 and T-shaped
three-coordinate copper(I) complex [Cu(LPh)I] 2, which is
accompanied by a reversible change in fluorescence (ca. 5-fold
The neutral LPh ligand featured only a single set of 1H and 13
C
signals (Fig. S2w), which indicated a symmetrical structure in
solution.
Complexes 1ꢀClO4 and 2 were synthesized from the reaction
of the LPh ligand with [Cu(CH3CN)4](ClO4) and CuI, respectively,
in yields of 73% and 85%. Complex 2 can also be crystallized
from a mixed CH2Cl2 solution of 1ꢀClO4 and n-Bu4NI. The
elemental analyses and ESI-MS were consistent with the
proposed formulas. The structures of complex cation 1 (1+)
and 2 are shown in Fig. 1 and 2, respectively.z As expected, the
coordinated LPh in 1+ and 2 behaved as a trans-chelating
ligand which placed two coordinated pyrazole rings close to
coplanar. The dihedral angles of the two pyrazoles were
6.9(2)1 for 1+ and 19.9(3)1 for 2. On the whole, five carbon
atoms, C11, C12, C17, C24 and C27, and the copper center,
Cu1, were approximately situated on a pseudo-plane of
symmetry. Similar to LPh, both 1+ and 2 also displayed
symmetrical structures when the 1H and 13C spectra
contrast fluorescence emission). The employed ligand LPh
,
shown in Scheme 1, is a novel trans pyrazolyl chelator containing
a perimidine fluorophore because the pyrazolyl-derivatives are
suitable supporting ligands for stabilizing low coordinate
copper(I) complexes,6–8 and the perimidine nucleus could
Scheme 1 Formation and reversibility of complex cation 1+ and 2.
Fig. 1 Molecular structure of 1+ (hydrogen atoms have been omitted
for clarity). Selected bond distances (A) and bond angles (1): Cu1–N1
1.878 (3), Cu1–N6 1.875 (3), Cu1ꢀ ꢀ ꢀN3 2.851 (3), Cu1ꢀ ꢀ ꢀN4 2.816 (2),
C7–N3 1.395 (4), C6–N3 1.429 (4), C17–N3 1.450 (4), C13–N4 1.404
(4), C17–N4 1.454 (4), C18–N4 1.432 (4); N1–Cu1–N6 169.0 (1),
C6–N3–C7 122.1 (2), C7–N3–C17 116.1 (2), C6–N3–C17 119.9 (2),
C13–N4–C17 115.7 (2), C13–N4–C18 122.4 (2), C17–N4–C18 119.3
(2), N3–C17–N4 107.4 (2).
Center for General Education, Chang Gung Institute of Technology,
Tao-Yuan 333, Taiwan, R.O.C. E-mail: ccchou@mail.cgit.edu.tw;
Fax: +886-3-2118866; Tel: +886-3-2118999 ext. 5583
w Electronic supplementary information (ESI) available: Experimental
details, crystal structure of LPh and related 1H&13C NMR spectra,
absorption and emission spectra. CCDC 722446–722448. For ESI and
crystallographic data in CIF or other electronic format see DOI:
10.1039/b908765f
ꢁc
This journal is The Royal Society of Chemistry 2009
6382 | Chem. Commun., 2009, 6382–6384

View Article Online
binding, which gave rise to a 13.01 increment of the dihedral
angle of the coordinated pyrazole rings. The Cu(I)–N(Pz0)
bond distances of 1.942 and 1.955 A were much longer than
those of the previous three-coordinate T-shape copper(I)-
pyrazole complexes (1.89–1.92 A).8 The terminal Cu(I)–I bond
distance of 2.7172(2) A was strikingly longer than that of a
trigonal planar anion [CuI3]2ꢂ at 2.55 A,9 which is a typical
T-shaped binding characteristic similar to the related copper(I)
complex [CuI(2,6-Me2-py)2] (2.66 A).10 Also, three noticeable
intramolecular C–Hꢀ ꢀ ꢀI hydrogen bonds,11 as shown in Fig. 3
(C6ꢀ ꢀ ꢀI = 3.902(6) A, H6Bꢀ ꢀ ꢀI = 3.172(4) A, C6–H6Bꢀ ꢀ ꢀI =
131.9(4)1; C17ꢀ ꢀ ꢀI = 3.908(6) A, H17Aꢀ ꢀ ꢀI = 3.031(5) A,
C17–H17Aꢀ ꢀ ꢀI = 1470.1(3)1; and, C18ꢀ ꢀ ꢀI = 4.056(6) A,
H18Aꢀ ꢀ ꢀI = 3.297(5) A, C18–H18Aꢀ ꢀ ꢀI = 134.8(3)1), appears
to help stablize the iodide in 2. To the best of our knowledge,
complex 2 is the first example of a structurally characterized,
three-coordinate copper(I) halide complex with an N-donor
chelate ligand. In contrast to 1+, the diastereotopic nature of
the methylenes H2C(6) and H2C(18) in 2 displayed two sets of
doublets at d 5.93 and 5.78 (Fig. S5w) in CH2Cl2 solution,
indicating a rigid structure for 2.
Fig. 2 Molecular structure of complex 2. Selected bond distances (A)
and bond angles (1): Cu1–N1 1.955 (5), Cu1–N6 1.942 (5), Cu1ꢀ ꢀ ꢀN3
2.896 (4), Cu1ꢀ ꢀ ꢀN4 3.069 (5), Cu1–I1 2.7172 (9), C7–N3 1.399 (8),
C6–N3 1.435 (7), C17–N3 1.463 (7), C13–N4 1.386 (8), C17–N4 1.453
(7), C18–N4 1.445 (7); N1–Cu1–N6 147.0 (2), N6–Cu1–I1 109.4 (2),
N1–Cu1–I1 103.3 (2), C6–N3–C7 121.8 (5), C7–N3–C17 115.0 (4),
C6–N3–C17 119.3 (5), C13–N4–C17 116.3 (5), C13–N4–C18 122.5 (5),
C17–N4–C18 120.7 (5), N3–C17–N4 107.6 (4).
(Fig. S3–5w) were inspected, which is in agreement with the
solid state structures.
The reversible reaction of 1+ and 2 were readily performed
For cation 1+ (Fig. 1), the copper(I) ion was coordinated
1
and investigated by H NMR spectra. When complex 1ꢀClO4
by two pyrazole nitrogen atoms of the LPh with
a
reacted stoichiometrically with n-Bu4NI, neutral complex 2
was generated nearly quantitatively (Fig. S6w). On the other
N(Pz0)–Cu–N(Pz0) bond angle of 169.0 (1)1 toward C17, which
formed a ten-membered metallocycle. The contacts of
hand, when complex
2 reacted stoichiometrically with
Cu(I)ꢀ ꢀ ꢀN(amine) were 2.816 and 2.851 A, indicating probable
weak N(amine)ꢀ ꢀ ꢀCu(I) interactions. The Cu(I)–N(Pz0)
distances of 1.875 and 1.878 A were in the normal range
of common two-coordinate copper(I)-pyrazole complexes
(1.87–1.88 A).7 Interestingly, the diastereotopic nature of the
methylenes H2C(6) and H2C(18) solely exhibited single peak at
d 5.96 in the 1H-NMR spectrum, indicating a remarkable
fluxional behavior for 1+ that was demonstrated further in
Ag(ClO4) to eliminate the coordinated iodide, complex
1ꢀClO4 was afforded again. If complex 1ꢀClO4 first reacted
with a stoichiometric amount of n-Bu4NI then a stoichiometric
amount of Ag(ClO4) was introduced, only the peaks of 1+ and
the n-butyl group were observed in the solution 1H NMR
spectrum (Fig. S7w), which manifested reversibility between
1+ and 2.
The fluorescence emission profiles originating from the
ligand-centered p–p* transitions of the perimidine moiety are
compared and shown in Fig. 3. The fluorescent properties of
LPh (lmax = 394 nm, Ff = 0.097) and of complexes 1ꢀClO4
(lmax = 380 nm, Ff = 0.005) and 2 (lmax = 394 nm, Ff =
0.031) in CH2Cl2 were examined when excited at l = 340 nm.
The ratio of fluorescence intensities were ca. 12.5 : 1.0 : 5.2
(for LPh : 1ꢀClO4 : 2, respectively). In fluorescence titration
experiments (see ESI for detailsw), complexes 1ꢀClO4 and 2 did
exhibit different degrees of quenching (Fig. S8–S10w).
In addition, fluorescence enhancement took place upon intro-
ducing Iꢂ to 1+ (Fig. 4. Inset), indicating that 1+ changes
from an iodide-unbound two-coordinated species to an iodide-
bound three-coordinated species 2. By monitoring the change
in fluorescent spectra, the interconversion of 1+ and 2 was
reversible in the presence (ON) and absence (OFF) of Iꢂ,
giving an ON 2 OFF emission switch.
1
variable-temperature H-NMR spectroscopic analyses with a
coalescence temperature Tc = 295.6 K (S3w). Therefore 1+ is
unequivocally a new stereochemically nonrigid monomeric
two-coordinate copper(I) complex. The fluxional process of
1+ is under investigation.
For 2 (Fig. 3), the N(Pz0)–Cu–N(Pz0) bond angle of
147.0(2)1 severely deviated from linearity due to the iodide
For complex 1ꢀClO4, a remarkable quenching effect and
substantial blue shift of 14 nm in the emission profile implies
an electronic perturbation in the delocalized p network of the
fluorophore, which is related to the existence of the weak
interaction between the lone pair electrons of the N(amine)
and the Cu(I) center because it could restrain the conjugation
of the perimidine nucleus and enlarge the energy levels of
p–p*. Besides, we were convinced that the influence of the
Cu(I)ꢀ ꢀ ꢀN(amine) interaction in solution could be pronounced
Fig. 3 Fluorescence spectra of ligand LPh, complexes 1ꢀClO4 and 2 in
CH2Cl2 excited at 340 nm at room temperature with a concentration
ꢂ5
of 6.32 ꢃ 10
M. Inset: the spectral change of fluorescence spectra
upon a gradual addition of n-Bu4NI (from 0.0 to 1.0 eq.) to complex 1.
ꢁc
This journal is The Royal Society of Chemistry 2009
Chem. Commun., 2009, 6382–6384 | 6383

View Article Online
coordination geometry could exist besides linear structure.
Further investigations are currently in progress.
Financial support of the National Science Council of the
Republic of China is greatly appreciated. We thank the
referee’s valuable comments. We thank Prof. I.-J. Chang
for helpful discussion. We also thank Mr. T.-S. Kuo and
Miss C.-H. He for assistance with collecting X-ray data and
variable-temperature NMR data, respectively.
Notes and references
z Crystal data for LPh: C29H30N6, M = 462.59, monoclinic, space
group P21/n, a = 10.7905(2), b = 19.1349(4), c = 13.3567(3) A, a =
901, b = 113.474 (1)1, g = 901, V = 2529.6(1) A3, Z = 4, Dc
=
1.215 Mg/m3, F(000) = 984, l(Mo-Ka) = 0.71073 A, 23 998 reflections
measured (Bruker Kappa CCD diffractometer) in the y range 2.07 to
25.021, 4448 unique (Rint = 0.0740), 317 parameters refined on F2
Fig. 4 Absorption spectra of ligand LPh (dash line), complexes
1ꢀClO4 (red line) and 2 (blue line) in CH2Cl2 solution at room
temperature.
using 4448 reflections to final indices: Rf [I 4 2s(I)] = 0.0727, Rw
=
0.1932. E.A. results: calcd. C 75.30, N 18.17, H 6.54%; found C 75.37,
N 18.16, H 6.60%. CCDC 722446. Crystal data for 1ꢀClO4ꢀ2CH3CN:
C33H36ClCuN8O4, M = 707.69, monoclinic, space group P21/n, a =
10.6294(2), b = 17.6905(3), c = 17.6917(3) A, a = 901, b =
96.005(1)1, g = 901, V = 3308.5(1) A3, Z = 4, Dc = 1.421 Mg/m3,
F(000) = 1472, l(Mo-Ka) = 0.71073 A, 23 078 reflections measured
(Bruker Smart CCD diffractometer) in the y range 1.63 to 25.021, 5821
unique (Rint = 0.0242), 426 parameters refined on F2 using 5821
reflections to final indices: Rf [I 4 2s(I)] = 0.0470, Rw = 0.1412. E.A.
results of 1: calcd. C 55.68, N 13.43, H 4.83%; found C 55.59, N 13.89,
H 4.63%. CCDC 726447. Crystal data for 2ꢀCH2Cl2: C30H32CuCl2N6I,
M = 737.96, monoclinic, space group P21/c, a = 13.2775(5), b =
15.5804(6), c = 14.6968(6) A, a = 901, b = 99.069(1)1, g = 901,
V = 3002.3(2) A3, Z = 4, Dc = 1.633 Mg/m3, F(000) = 1480,
l(Mo-Ka) = 0.71073 A, 21 778 reflections measured (Bruker Smart
due to the wriggle of the perimidine framework, which may
result in an alternatively N(amine) atom approaching toward
the Cu(I) center.12 For complex 2, the emission profile partially
retrieved to that of ligand LPh, suggesting a less p–p*
perturbation, because the N(amine)ꢀ ꢀ ꢀCu(I) interaction was
further weakened by the coordination of iodide. As shown in
Fig. 2, the average distance of N(amine)ꢀ ꢀ ꢀCu(I) was getting
longer at ca. 0.15 A.
The absorption spectra of LPh, 1ꢀClO4 and 2 are shown in
Fig. 4 and Fig. S11.w Prominent absorption peaks for these
compounds are indeed a little different each other, indicating
that the vibronic p–p* transitions of the perimidine nucleus in
1+ and 2 was really affected. For complex 2, a broad shoulder
was shown at 271 nm, which can be assigned to the Cu(I) to
pyrazole MLCT transition (ds* - p*).13 The absorption
envelope of the p–p* transition of the perimidine nucleus of
2 changed back to that of the free ligand to a large extent
because the perturbation of the p–p* transition is lessened
by the iodide coordination, which was consistent with the
emission spectra.
CCD diffractometer) in the y range 1.55 to 25.031, 5312 unique (Rint
=
0.0391), 361 parameters refined on F2 using 5312 reflections to final
indices: Rf [I 4 2s(I)] = 0.0497, Rw = 0.1476. E.A. results of 2: calcd.
C 48.83, N 11.39, H 4.37%; found C 49.10, N 11.72, H 4.58%. CCDC
726448.
1 B. Champin, P. Mobian and J.-P. Sauvage, Chem. Soc. Rev., 2007,
36, 358; J.-P. Sauvage, Chem. Commun., 2005, 1507.
2 A. Petitjean, N. Kyritsakas and J.-M. Lehn, Chem.–Eur. J., 2005,
11, 6818.
3 V. Amendola, L. Fabbrizzi, C. Mangano, H. Miller, P. Pallavicini,
A. Perotti and A. Taglietti, Angew. Chem., Int. Ed., 2002, 41, 2553.
4 D. Kalny, M. Elhabiri, T. Moav, A. Vaskevich, I. Rubinstein,
A. Shanzer and A. M. Albrecht-Gary, Chem. Commun., 2002, 1426.
5 H.-J. Liu, Y.-H. Hung, C.-C. Chou and C.-C. Su, Chem. Commun.,
2007, 495.
6 C.-C. Chou, H.-J. Liu and C.-C. Su, Dalton Trans., 2008, 3358;
C.-C. Chou, C.-C. Su and A. Yeh, Inorg. Chem., 2005, 44, 6122.
7 T. N. Sorrell and D. L. Jameson, J. Am. Chem. Soc., 1983, 105,
6013; T. N. Sorrell and D. L. Jameson, J. Am. Chem. Soc., 1982,
104, 2053.
8 T. N. Sorrell, M. R. Malachowski and D. L. Jameson, Inorg.
Chem., 1982, 21, 3250; T. N. Sorrell and M. R. Malachowski,
Inorg. Chem., 1983, 22, 1883.
In addition to the influence of the electronic perturbation
imposed on perimidine, fluxionality could be also an
important factor for significant change in fluorescence.14
Therefore, it is rational that nonrigid complex 1ꢀClO4 has a
relatively low emission intensity with respect to the rigid ligand
LPh while the rigidification of 2 by an iodide binding leads to
an enhancement in emission intensity. For 2, the emission
intensity was not fully retrieved to that of LPh suggest that an
effect of the electronic perturbation is not entirely eliminated
and the motion of the chromophoric skeleton was not
completely ceased in solution.
In conclusion, a new fluorescent trans-chelator, LPh, and its
two- and three-coordinate copper(I) derivatives 1ꢀClO4 and 2
were synthesized and characterized. Also, the implementation
of controllable interconversion between linear two-coordinate
and T-shaped three-coordinate copper(I) complexes was first
realized, which may result in a chemical fluorescent switch
when an iodide is used as the modulator.15 For ligand LPh, the
emission decreases significantly with other divalent metal
ions like Ni2+, Cu2+, and Zn2+ with a probable M : L
stoichiometry of 1 : 2 (Fig. S12–14w), implying that different
9 G. A. Bowmaker, G. R. Clark, D. A. Roger, A. Camus and
N. Marsich, J. Chem. Soc., Dalton Trans., 1984, 37.
10 P. C. Healy, C. Pakawatchai and A. H. White, J. Chem. Soc.,
Dalton Trans., 1983, 1917.
11 H. Dong, J. Yang, X. Liu and S. Gou, Inorg. Chem., 2008, 47,
2913.
12 In a separate experiment, we have found such a phenomenon by
using an analogous ligand. Unpublished results.
13 T. N. Sorrell and A. S. Borovik, Inorg. Chem., 1987, 26, 1957.
14 J. Shao, Y.-H. Qiao, H. Lin and H.-K. Lin, J. Inclusion Phenom.
Macrocyclic Chem., 2008, 62, 99.
15 Preliminary results for the binding of 1+ toward other halides
(F, Cl and Br) show that only bromide can make a T-shaped
adduct similar to 2, whereas the fluoride and chloride cannot.
ꢁc
This journal is The Royal Society of Chemistry 2009
6384 | Chem. Commun., 2009, 6382–6384