Synthesis, luminescence and host-guest chemistry of copper(I) and zinc(II) complexes of dppzc (dppzc=dipyrido[3,2-a:2′,3′-c]phenazo-15-crown-5)

Article abstract of DOI:10.1016/S0020-1693(02)00809-5

Copper(I) and zinc(II) complexes containing dipyrido[3,2-a:2′,3′-c]phenazo-15-crown-5 (dppzc) ligand have been synthesized and characterized, and their photophysics and electrochemistry studied. The crystal structure of [Zn(SC₆H₄-CH₃-p)₂(dppzc)] (2) has been determined. The ion-binding properties of these complexes towards alkali metal ions have also been described.

Full text of DOI:10.1016/S0020-1693(02)00809-5

Inorganica Chimica Acta 335 (2002) 77ꢀ84
/
www.elsevier.com/locate/ica
Synthesis, luminescence and hostꢀ
/
guest chemistry of copper(I) and
zinc(II) complexes of dppzc (dppzcꢁdipyrido[3,2-a:2?,3?-c]phenazo-
/
15-crown-5)ꢀ
Vivian Wing-Wah Yam *, Yung-Lin Pui, Kung-Kai Cheung
Department of Chemistry and Open Laboratory of Chemical Biology of The Institute of Molecular Technology for Drug Discovery and Synthesis, The
University of Hong Kong, Pokfulam Road, Hong Kong
Received 19 October 2001; accepted 25 January 2002
Abstract
Copper(I) and zinc(II) complexes containing dipyrido[3,2-a:2?,3?-c]phenazo-15-crown-5 (dppzc) ligand have been synthesized and
characterized, and their photophysics and electrochemistry studied. The crystal structure of [Zn(SC6H4ꢀ
/CH3-p)2(dppzc)] (2) has
been determined. The ion-binding properties of these complexes towards alkali metal ions have also been described. # 2002
Elsevier Science B.V. All rights reserved.
Keywords: Crystal structure; Luminescence; Electrochemistry; Ion-binding
1. Introduction
physical and metal ion-binding properties [10]. In this
work, efforts have been made to study the binding of
copper(I) and zinc(II) crown ether-containing complexes
for lithium and sodium metal ions. The binding proper-
ties of these complexes were evaluated as a function of
crown ether size and solvent polarity.
The fruitful discovery of crown ether ligands [1] led to
numerous studies on cyclic and cage compounds that
are capable of binding cations, anions or neutral
molecules in their cavities and have led to the develop-
ment of new fields in current chemistry such as hostꢀ
/
Dipyrido[3,2-a:2?,3?-c]phenazine (dppz) is an interest-
ing ligand that has attracted growing attention in recent
guest and supramolecular chemistry [2] since Pedersen’s
initial observations [3] on the affinity of macrocyclic
polyethers to alkali and alkaline earth cations. Apart
from the successful applications of metal ion probes, pH
years [11aꢀc]. Its extended p-conjugation and planarity
/
of the molecule have made it a promising candidate as a
DNA intercalator. Recent works have focused on the
syntheses of metal complexes containing dppz ligand to
function as metallointercalators and DNA photoswitch
[11]. Recently, we prepared a crown ether-containing
dppz ligand, dipyrido[3,2-a:2?,3?-c]phenazo-15-crown-5
(dppzc), and studied the ion-binding properties of its
ruthenium (II) complexes [12]. As an extension of our
previous works on the binding studies of ruthenium
polypyridine complexes with crown ether pendants,
herein are reported the syntheses and characterization
of copper(I) and zinc(II) dppzc complexes (Scheme 1).
The electronic absorption, luminescence, electrochemis-
try and binding properties of these complexes towards
metal cations have also been studied.
sensors and molecular recognitions [4ꢀ7] in this field,
/
crown ethers have also been used for the photocontrol
of ion extraction and transport and construction of
chemical switches [8]. However, most of the work has
been confined to the organic host systems [3,9]. With the
aim of advancing chemical sensor technology, consider-
able recent attention has been focused on the design of
inorganic hosts with the awareness of interesting photo-
ꢀ Area of Excellence Scheme, University Grants Committee (Hong
Kong).
* Corresponding author. Tel.: ꢂ
1586.
E-mail address: wwyam@hku.hk (V.W.-W. Yam).
/
852-2859 2153; fax: ꢂ852-2857
/
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 0 8 0 9 - 5

78
V.W.-W. Yam et al. / Inorganica Chimica Acta 335 (2002) 77ꢀ84
/
yellow crystals. Yield: 70 mg (62%). 1H NMR (300
MHz, CDCl3): d 3.82 (m, 8H, CH2OCH2), 4.05 (t, 4H,
Jꢁ
C6H2OCH2), 7.25 (m, 24H, PPh3), 7.35 (m, 6H, PPh3),
7.68 (s, 2H, C6H2), 8.02 (q, 2H, Jꢁ13.1 Hz, pyridyl
H’s), 9.10 (dd, 2H, Jꢁ1.9 Hz, Jꢁ4.8 Hz, pyridyl H’s),
9.70 (dd, 2H, Jꢁ1.4 Hz, Jꢁ6.9 Hz, pyridyl H’s ortho
/
7.8 Hz, C6H2OCH2CH2), 4.45 (t, 4H, Jꢁ
/
3.9 Hz,
/
/
/
/
/
to N). Positive ESI MS (m/z): 1058 {M}ꢂ, 797 {Mꢀ
/
PPh3}ꢂ. Anal. Calc. for C62H54F6N4O5P3Cu: C, 61.77;
H, 4.52; N, 4.65. Found: C, 61.69; H, 4.43; N, 4.41%.
2.2.2. Synthesis of [Zn(SC6H4ꢀ
/
CH3-p)2(dppzc)] (2)
This was prepared by modification of a literature
procedure for related zinc(II) complexes [16]. A solution
of dppzc (129 mg, 0.27 mmol) in MeOH (5 ml) was
added dropwise to a mixture of Zn(OAc)2×/2H2O (60 mg,
0.27 mmol) and p-thiocresol (67 mg, 0.54 mmol) in
MeOH (10 ml) and the mixture was stirred at r.t. for 4 h
during which the solution changed from colorless to
yellow. The isolation of the complex was similar to that
for 1 to give 2 as yellow crystals. Yield: 105 mg (49%).
1H NMR (300 MHz, CDCl3): d 1.83 (s, 6H, CH3), 3.75
Scheme 1. Schematic drawing of copper(I) and zinc(II) complexes of
dppzc.
2. Experimental
2.1. Reagents and materials
(m, 8H, CH2OCH2), 4.00 (t, 4H, Jꢁ
C6H2OCH2CH2), 4.45 (t, 4H, Jꢁ7.9 Hz, C6H2OCH2),
6.45 (d, 4H, Jꢁ7.9 Hz, aryl H ortho to S), 7.00 (d, 4H,
Jꢁ8.0 Hz, aryl H meta to S), 7.50 (s, 2H, C6H2), 7.95
(q, 2H, Jꢁ13.1 Hz, pyridyl H’s), 8.98 (dd, 2H, Jꢁ1.4
Hz, Jꢁ4.5 Hz, pyridyl H’s), 9.65 (dd, 2H, Jꢁ1.5 Hz,
Jꢁ6.8 Hz, pyridyl H’s ortho to N). Positive FAB MS
(m/z): 659 {MꢀSC6H4ꢀ
CH3-p}ꢂ. Anal. Calc. for
/
7.9 Hz,
/
p-Thiocresol was obtained from Lancaster Synthesis
Ltd. Zinc acetate dihydrate was obtained from Peking
Reagent. Dipyrido[3,2-a:2?,3?-c]phenazine (dppz) [13],
dppzc [12], [Cu(PPh3)2(MeCN)2]PF6 [14a] and
[Cu(PPh3)2(dppz)]PF6 [14b] were prepared by a pub-
lished procedure. Tetra-n-butylammonium hexafluoro-
phosphate (nBu4NPF6) (Lancaster, 98%) was purified by
recrystallization from hot ethanol three times and
vacuum dried for over 24 h before use. Sodium
perchlorate (Aldrich, 98%), lithium perchlorate (Al-
drich, 99.9%) and potassium hexafluorophosphate
(Strem, 99.5%) were recrystallized from hot methanol
and vacuum dried before use. Acetonitrile was distilled
over calcium hydride before use. Dichloromethane was
washed with conc. H2SO4 and distilled over calcium
hydride. All other reagents were of analytical grade and
were used as received.
/
/
/
/
/
/
/
/
/
C40H38N4O5S2Zn: C, 60.02; H, 4.88; N, 7.14. Found:
C, 60.17; H, 4.76; N, 6.82%.
2.2.3. Synthesis of [Zn(SC6H4ꢀ
/
CH3-p)2(dppz)] (3)
Complex 3 was prepared similarly to 2 except dppz
was used in place of dppzc to give yellow crystals. Yield:
1
113 mg (70%). H NMR (300 MHz, CDCl3): d 1.81 (s,
6H, CH3), 6.45 (d, 4H, Jꢁ
6.98 (d, 4H, Jꢁ6.4 Hz, aryl H meta to S), 8.02 (m, 4H,
C6H4), 8.40 (q, 2H, Jꢁ17.3 Hz, pyridyl H’s), 9.02 (dd,
2H, Jꢁ3.4 Hz, Jꢁ6.2 Hz, pyridyl H’s), 9.73 (dd, 2H,
Jꢁ6.7 Hz, Jꢁ9.7 Hz, pyridyl H’s ortho to N). Positive
FAB MS (m/z): 469 {MꢀSC6H4ꢀ
CH3-p}ꢂ. Anal. Calc.
/7.8 Hz, aryl H ortho to S),
/
/
/
/
/
/
2.2. Synthesis of copper(I) and zinc (II) complexes of
dppzc ligand
/
/
for C32H24N4S2Zn: C, 64.70; H, 4.07; N, 9.43. Found:
C, 64.48; H, 3.91; N, 9.20%.
2.2.1. Synthesis of [Cu(PPh3)2(dppzc)]PF6 (1)
This was prepared by modification of a literature
procedure for related copper(I) complexes [15]. To a
solution of dppzc (47 mg, 0.1 mmol) in dichloromethane
(5 ml) was added a solution of [Cu(PPh3)2(MeCN)2]PF6
(120 mg, 0.1 mmol) in dichloromethane (5 ml) and the
mixture was stirred at room temperature (r.t.) for 1 h
during which the solution changed from colorless to
yellow. After evaporation of the solvent, the residue was
dissolved in dichloromethane and diffusion of diethyl
ether vapor into its concentrated solution gave 1 as
2.3. Crystal structure determination
Single crystals of 2 were obtained by vapor diffusion
of diethyl ether into a concentrated dichloromethane
solution of the complex.
Crystal data for 2: [C40H38N4O5S2Zn], Mꢁ
monoclinic, space group P21/c (No. 14), aꢁ12.796(2),
100.90(2)8, Uꢁ
1.433 g cmꢃ3, m(Mo Ka)ꢁ
1632, Tꢁ301 K. A pale yellow
/
784.26,
/
˚
bꢁ
3534(1) A , Zꢁ
8.42 cmꢃ1, F(000)ꢁ
/
12.411(2), cꢁ
/
23.304(3) A, bꢁ
/
/
3
˚
/2, Dcalc
ꢁ
/
/
/
/

V.W.-W. Yam et al. / Inorganica Chimica Acta 335 (2002) 77ꢀ
/84
79
crystal of dimensions 0.35ꢄ
on a glass fibre was used for data collection at 28 8C on
a MAR diffractometer with a 300 mm image plate
/
0.15ꢄ
/
0.07 mm mounted
separated from the working electrode compartment by a
Vycor glass bridge. A Agꢀ
AgNO3 (0.1 mol dmꢃ3 in
CH3CN) reference electrode was used. The
ferroceniumꢀ
ferrocene couple (FeCp2ꢂ/0) was used as
the internal reference in the electrochemical measure-
ments [18a]. The working electrode was a glassy
carbon (Atomergic Chemetals V25) electrode with a
platinum foil acting as the counter electrode. Treatment
of the electrode surfaces was as reported previously
[18b].
/
detector using graphite monochromatized Mo Ka
/
˚
0.71073 A). 6562 unique reflections were
obtained from a total of 28360 measured reflections
radiation (lꢁ
/
(Rint 0.062). 4076 reflections with I ꢀ3s(I) were
ꢁ
/
/
considered observed and used in the structural analysis.
The space group was uniquely determined based on
systematic absences and the structure was solved by
direct methods (SIR92) [17a] and expanded by Fourier
method and refinement by full-matrix least-squares
using the software package TEXSAN [17b] on a Silicon
Graphics Indy Computer. Convergence for 467 variable
Binding studies using UVꢀVis measurement were
/
performed by adding aliquots of the metal salt to a
solution of the copper (I) and zinc(II) crown ether-
containing complexes in the presence of supporting
electrolyte (0.1 mol dmꢃ3 nBu4NPF6) while maintaining
the concentration of the metal complexes constant.
Binding constants for 1:1 complexation were obtained
by a nonlinear least-squares fit [19a] of the absorbance
(X) versus the concentration of the metal ion added (cM)
according to Eq. (1):
parameters by least-squares refinement on F with wꢁ
/
4Fo /s2(Fo ), where s2(Fo )ꢁ
4076 reflections with I ꢀ3s(I) was reached at Rꢁ
0.052 and wRꢁ0.072 with a goodness-of-fit of 2.22
(D/s)max 0.05 except for the disordered C atoms. The
/
[s2(I)ꢂ
(0.020Fo ) ] for
/
2
2
2
2 2
/
/
/
ꢁ
/
final difference Fourier map was featureless, with
maximum positive and negative peaks of 0.93 and 0.32
e Aꢃ3, respectively.
Xlim ꢃ X
˚
X ꢁX0 ꢂ
0 [c0 ꢂcM ꢂ1=KS
2c0
ꢃ[(c0 ꢂcM ꢂ1=KS)2 ꢃ4c0cM]1=2
2.4. Physical measurements and instrumentation
]
(1)
where X0 and X are the absorbance of the complex at a
selected wavelength in the absence and presence of the
metal cation, respectively, c0 is the concentration of the
complex, cM is the concentration of the metal cation,
Xlim is the limiting value of absorbance in the presence
of excess metal ion and KS is the stability constant. The
experiments for binding studies were performed in
duplicate and the average binding constants obtained.
For proton NMR titration experiments, a solution of
Cu(I) crown ether-containing complex was prepared.
The initial 1H NMR spectrum was recorded and
aliquots of metal cations were added using a micro-
syringe. After each addition and mixing, the spectrum
was recorded and changes in the chemical shift of
certain protons were noted. The results of the experi-
ment were expressed as a plot of chemical shift as a
function of the amount of cation added, which was
subjected to analysis by curve fitting since the shape of
the titration curve is indicative of the stability constant
for the complex formation. The computer program
EQNMR [19b] was used which requires a knowledge of
the concentration of each component and the observed
chemical shift for each data point.
1H NMR spectra were recorded on a Bruker DPX-
300 FT-NMR spectrometer in CDCl3 at 298 K and
chemical shifts were reported relative to Me4Si. Positive
ion FAB MS were recorded on a Finnigan MAT95 mass
spectrometer and positive ESI MS on a Finnigan LCQ
mass spectrometer. Elemental analyses of the new
complexes were performed on a Carlo Erba 1106
elemental analyzer at the Institute of Chemistry, Chinese
Academy of Sciences.
UVꢀ/Vis absorption spectra in acetonitrile, acetone or
methanol were obtained on a Hewlettꢀ/Packard 8452A
diode array spectrophotometer, and steady-state excita-
tion and emission spectra on a Spex Fluorolog 111
spectrofluorimeter. The electronic absorption spectral
titration for binding constant determination was per-
formed with a HewlettꢀPackard 8452A diode array
/
spectrophotometer at 25 8C which was controlled by a
Lauda RM6 compact low-temperature thermostat.
Supporting electrolyte (0.1 mol dmꢃ3 nBu4NPF6) was
added to maintain the ionic strength of the sample
solution constant during the titration in order to avoid
any changes arising from a change in the ionic strength
of the medium. This is especially important for com-
plexes showing a charge transfer transition since their
absorption characteristics are usually rather sensitive to
the nature of the solution medium.
3. Results and discussion
Cyclic voltammetric measurements were performed
by using a CH Instruments, Inc. CHI 620 electrochemi-
cal analyzer interfaced to an IBM-compatible PC. The
electrolytic cell used was a conventional two-compart-
ment cell. The salt bridge of the reference electrode was
All the synthesized copper(I) and zinc(II) crown
1
complexes have been well characterized by H NMR
spectroscopy and positive ion FAB MS or ESI MS and
gave satisfactory elemental analyses. The coordination

80
V.W.-W. Yam et al. / Inorganica Chimica Acta 335 (2002) 77ꢀ84
/
Table 1
Crystal and structure determination data for 2
of ligands to the metals has been confirmed by the
1
down-field shift of H NMR signals for those protons
adjacent to nitrogen atoms (dppzc, 9.57 ppm; 1, 9.70
ppm; 2, 9.65 ppm; dppz, 9.63 ppm; 3, 9.73 ppm). The X-
ray crystal structure of 2 has also been determined.
Formula
Formula weight
T (K)
[C40H38N4O5S2Zn]
784.26
301
˚
a (A)
12.796(2)
12.411(2)
23.304(3)
100.90(2)
3534(1)
monoclinic
P21/c (No. 14)
2
˚
b (A)
˚
c (A)
3.1. Crystal structure
b (8)
3
V (A )
˚
The perspective drawing of 2 with atomic numbering
is depicted in Fig. 1. The crystallographic data of 2 are
˚
summarized in Table 1. Selected bond distances (A) and
Crystal system
Space group
Z
F(000)
Dcalc (g cmꢃ3
1632
1.433
bond angles (8) are displayed in Table 2. The Zn(II)
center adopts a distorted tetrahedral geometry with a
)
˚
l, A (graphite monochromated, Mo Ka)
Number of data collected
Number of unique data
8.42
28360
S(1)ꢀ
/
Zn(1)ꢀ
/
S(2) angle of 130.15(5)8 and a N(1)ꢀ
/
Zn(1)ꢀ
/
N(4) angle of 79.0(2)8. The average bond distances of
6562
4076
Number of data used in refinement, m
Number of parameters refined, p
467
0.052
a
R
a
Rw
0.072
2.22
0.05
Goodness-of-fit, S
Maximum shift, (D/s)max
Residual extrema in final different map (e A
ꢃ3
˚
)
ꢂ
/
0.93, ꢃ
/
0.32
4 Fo2/s2(Fo2), where s2(Fo2)ꢁ
/
[s2(I)ꢂ
/
(0.020Fo2)2] with I ]
/
a
wꢁ
/
3s(I).
Table 2
˚
Selected bond distances (A) and bond angles (8) for 2
Bond distances
Zn(1)ꢀ
Zn(1)ꢀ
S(1)ꢀ
O(1)ꢀ
O(5)ꢀ
/
S(1)
2.257(1)
2.115(4)
1.764(6)
1.369(5)
1.442(6)
Zn(1)ꢀ
Zn(1)ꢀ
S(2)ꢀ
O(1)ꢀ
O(5)ꢀ
/
S(2)
2.280(2)
2.101(4)
1.781(5)
1.436(6)
1.354(5)
/N(1)
/N(4)
/
C(27)
/
C(34)
/
C(8)
/
C(9)
/
C(16)
/
C(17)
Bond angles
S(1)ꢀZn(1)ꢀ
S(1)ꢀZn(1)ꢀ
S(2)ꢀZn(1)ꢀ
Zn(1)ꢀS(1)ꢀ
Zn(1)ꢀN(1)ꢀ
Zn(1)ꢀN(1)ꢀ
/
/
S(2)
130.15(5) S(1)ꢀ
/
Zn(1)ꢀ
Zn(1)ꢀ
N(1)ꢀZn(1)ꢀ
Zn(1)ꢀS(2)ꢀC(34)
Zn(1)ꢀN(1)ꢀ
Zn(1)ꢀN(4)ꢀ
/
N(1)
115.4(1)
104.5(1)
79.0(2)
/
/
N(4)
N(4)
C(27)
110.7(1)
105.0(1)
107.3(2)
128.2(3)
128.1(3)
S(2)ꢀ
/
/
N(1)
/
/
/
/
N(4)
/
/
/
/
98.3(2)
/
/C(1)
/
/
C(26)
C(25)
111.6(3)
112.4(3)
/
/C(24)
/
/
˚
N are 2.268(7) and 2.108(4) A, respec-
tively, which are found to be typical of related systems
Znꢀ
/
S and Znꢀ
/
[16b,20]. For complex 2, pꢀp stacking interactions
/
between the aromatic rings of thiolate ligand and dppzc
are observed with the interplanar separations in the
˚
3.60 A.
range of 3.09ꢀ
/
3.2. Electronic absorption and luminescence properties
The electronic absorption spectrum of complex 1
shows a higher energy band at :
vibronic-structured low-energy absorption band at :
384ꢀ408 nm in both acetonitrile and dichloromethane
solutions. The low-energy band with vibrational pro-
gressional spacings of :1260ꢀ
1290 cmꢃ1, typical of the
/
260ꢀ300 nm and a
/
/
/
Fig. 1. Perspective drawing of 2 with the atomic numbering scheme.
Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are
drawn at the 40% probability level.
/
/

V.W.-W. Yam et al. / Inorganica Chimica Acta 335 (2002) 77ꢀ
/84
81
skeletal vibrational mode of the aromatic ring in the
excited state, is tentatively assigned as metal-to-ligand
charge transfer [MLCT, dp(Cu)0p*(dppzc)] transition
with some mixing of an intraligand [IL, p0p* (dppzc)
or n 0p* (dppzc)] transition, as similar assignments
/
/
/
have been suggested in other related systems [15].
Complex 2 also displays similar vibronic-structured
low-energy absorption bands at approximately 384ꢀ
/
404 nm in the electronic absorption spectra in both
acetonitrile and dichloromethane solutions. The close
resemblance of the low-energy vibronic bands in com-
plexes 1 and 2 is suggestive of an electronic transition
that is dominated by the IL transition of dppzc. Similar
to other related Zn(II) complexes with thiolate and
diimine ligands [16,20c,21], the low-energy bands ob-
served in the visible region of the spectrum of 2 are likely
to involve some mixing of a ligand-to-ligand charge
Fig. 2. Emission spectrum of 1 in the solid state at 77 K. The inset
shows an electronic absorption spectrum in acetonitrile at 298 K.
transfer [LLCT, pp(SRꢃ)0
p*(dppzc)] character. The
/
electronic absorption spectral data are collected in Table
3.
3.3. Cation binding studies
Upon excitation of complexes 1 and 2 in the solid
state, glass, acetonitrile and dichloromethane solutions
Upon addition of lithium ions to 1 and 2 in
acetonitrile solution, an obvious electronic absorption
at l ꢀ
/
350 nm, emission bands at :
/
520ꢀ615 nm are
/
observed (Table 3). The emissions are tentatively
assigned as originating from the 3IL/3MLCT and
3IL/3LLCT mixed states for 1 and 2, respectively. Fig.
2 shows the emission spectrum of 1 in the solid state at
77 K. The inset shows the electronic absorption
spectrum in acetonitrile at 298 K. The close resemblance
of the emission band between 1 and 2 is again suggestive
of the domination of an IL character for their origin. A
spectral change was observed. The bands at :408 nm in
/
1 and 404 nm in 2 undergo a blue shift in energy with
increasing lithium ion concentration. Similar changes
were also observed upon addition of sodium ions. These
shifts were attributed to the binding of the cations to the
crown ether cavity as similar effects were absent for the
crown-free analogues, [Cu(PPh3)2(dppz)]PF6 and
[Zn(SC6H4ꢀ/CH3-p)2(dppz)]. The spectral changes were
vibrational progressional spacing of
:
/
1300ꢀ1354
/
reversible on addition of an excess of free dppzc ligands
to an acetonitrile solution of 1 and 2. With Kꢂ ions, no
satisfactory fits to Eq. (1) were obtained and no well-
defined isosbestic points could be found in the electronic
absorption spectral traces upon addition of potassium
ions to a solution of both complexes, indicative of the
formation of both 1:1 and 1:2 adducts in the solution
mixture. The electronic absorption spectral traces of 2
cmꢃ1, typical of the skeletal vibrational mode of the
aromatic ring in the ground state, together with the
emission pattern in the solid state and glass at 77 K
appearing as a mirror image of the absorption band, is
in accord with an IL assignment, probably with some
mixing of a 3MLCT character in 1 and a 3LLCT
character in 2.
Table 3
Photophysical data for complexes 1 and 2
Complex
Medium (T(K))
labs (nm) (o (dm3 molꢃ1 cmꢃ1))
lem (nm) (t0 (ms))
1
Solid (298)
Solid (77)
554 (B0.01)
/
b
535, 575sh
534, 572sh
a
b
Glass (77)
CH3CN (298)
CH2Cl2 (298)
Solid (298)
Solid (77)
260 (54,030), 290 (83,890), 384sh (28,450), 404 (42,700)
264 (43,130), 300 (68,560), 388sh (24,150), 408 (36,220)
534sh (B0.01)
/
615 (B
/
0.01)
0.01)
2
535 (B
/
b
562, 608sh
524, 564sh
a
b
Glass (77)
CH3CN (298)
CH2Cl2 (298)
265 (7,150), 292 (9,660), 385sh (4,530), 403 (6,480)
295 (17,650), 388sh (6,430), 404 (11,720)
520sh (B0.01)
ꢀ
/
c
/
a
EtOH, MeOHꢁ4:1 (v/v).
Vibronic-structured.
Non-emissive.
/
b
c

82
V.W.-W. Yam et al. / Inorganica Chimica Acta 335 (2002) 77ꢀ84
/
on sequential addition of Liꢂ to an acetonitrile solution
of the complex are shown in Fig. 3. The inset in Fig. 3
shows the changes of absorbance at 404 nm as a
function of lithium ion concentration. The curve shows
a gradual decrease in absorbance on increasing the
cation concentration, reaching saturation at higher
cation concentration. The binding constants of 1 and 2
are tabulated in Table 4.
The effect of solvents on the binding abilities was
investigated using identical methods at 298 K in three
different solvents with different polarity: acetonitrile,
acetone and methanol. The choice of solvents was
limited by the solubility of the complex, the alkali metal
ions and the bound species. It is found that the binding
constants for lithium and sodium ions in different
Table 4
Binding constants of complexes 1 and 2 for alkali metal ions in
different solvents (0.1 mol dmꢃ3 nBu4NPF6) at 298 K
log Ks
Complex
Medium
MeCN
Liꢂ
Naꢂ
a
b
a
b
a
b
a
b
a
b
a
1
3.379
3.079
1.979
1.759
/
0.02
0.01
0.01
0.01
2.729
3.009
2.519
2.419
1.589
1.669
3.369
/
0.04
0.01
0.02
0.01
0.03
0.01
0.02
/
/
Acetone
MeOH
MeCN
/
/
/
/
c
ꢀ/
/
/
a
2
3.769
/0.02
/
a
From UVꢀVis spectrophotometric method.
/
b
c
From 1H NMR spectroscopic method.
Cannot be determined.
solvents are in the order of acetonitrileꢀ
/
acetoneꢀ
/
therefore, the binding constants of 1 for Liꢂ ions in
acetonitrile and acetone would be larger than that in the
protic methanol solvent. The binding constants of the
metal cations to complexes 1 and 2 could not be
determined using emission spectrophotometric method
due to insignificant changes in the emission intensities
upon addition of metal ions. The stability constants
methanol. The binding constants of 1 for Liꢂ and
Naꢂ ions in acetonitrile and acetone are in the order:
Liꢂ ꢀ
/
Naꢂ and Naꢂ ꢀLiꢂ, respectively.
/
These findings are in line with that commonly
observed for benzo-15-crown-5 type compounds in
MeCN [9]. This is in close resemblance to the order of
charge density of the cations: Liꢂ ꢀNaꢂ. The small
/
1
obtained by H NMR spectroscopic method are com-
size of the lithium ion bears the highest charge density
while sodium cations of lower charge density also give
rise to large binding constant as the hole size of the
crown cavity would best fit that of sodium ions [3d].
Unlike the case of acetonitrile, the selectivity of metal
ion binding to the crown cavity in methanol was higher
in Naꢂ than that of Liꢂ. Methanol is of the highest
polarity among the three solvents studied. The extent of
solvation by solvent molecules is larger for Liꢂ ions
than that for Naꢂ ions. In view of this, Liꢂ cations are
well-solvated by methanol solvent molecules, and thus
seeking a binding site in the crown cavity was no longer
a necessity to stabilize the cations in methanol and,
parable to those determined using UVꢀVis spectro-
/
photometric method for complex 1 in acetonitrile,
acetone and methanol (Table 4). Since complex 2 is
not very soluble in acetone and methanol, the effect of
solvents on the binding abilities in this complex has not
been investigated.
3.4. Electrochemical properties
Fig. 4 depicts the cyclic voltammograms of 1 in
acetonitrile (0.1 mol dmꢃ3 nBu4NPF6). The electro-
chemical data are summarized in Table 5. The cyclic
voltammograms of 1 and 2 display a quasi-reversible
reduction couple at ꢃ
/
1.31 and ꢃ0.91 V versus SCE,
/
respectively, corresponding to the reduction of the
dppzc ligand. An irreversible oxidation wave occurs at
ꢂ1.25 V versus SCE in 1, tentatively assigned as the
/
metal-based oxidation, similar to related systems [15].
For 2, the irreversible and quasi-reversible oxidation
couples at ꢂ
/
1.60 to ꢂ1.87 V versus SCE are likely to be
/
derived from the thiolate ligand-centered oxidations
[21c].
The cation recognition properties of 1 were further
demonstrated by addition of Naꢂ into an acetonitrile
(0.1 mol dmꢃ3 nBu4NPF6) solution of the complexes.
Electrochemical changes were observed and included in
Table 5. It is interesting to note that changes occurred in
the potential of the crown-based reduction couples upon
addition of metal cations, with no obvious changes in
the oxidation waves. The crown-based reduction couple
was shifted anodically. The anodic shift observed may
Fig. 3. The electronic absorption spectral traces of 2 (4.7ꢄ
10ꢃ5 mol
/
dmꢃ3) in acetonitrile (0.1 mol dmꢃ3 nBu4NPF6) upon addition of Liꢂ
at 298 K. The inset shows a plot of absorbance versus [Liꢂ] monitored
at lꢁ
/
404 nm (j) and its theoretical fit (*).
/

V.W.-W. Yam et al. / Inorganica Chimica Acta 335 (2002) 77ꢀ
/84
83
4. Conclusion
[Cu(PPh3)2(dppzc)]PF6
1
and [Zn(SC6H4ꢀ
/
CH3-
p)2(dppzc)] 2 have been successfully synthesized. The
electronic absorption, emission, electrochemical and
binding properties of these systems have been studied.
The crystal structure of [Zn(SC6H4ꢀ
/
CH3-p)2(dppzc)]
has also been determined. The low energy absorptions
of the copper(I) and zinc(II) dppzc complexes were
assigned as predominantly intraligand [IL, p(L)0
/
p*(L)
or n 0p*(L)] transitions, probably with some mixing of
/
a MLCT and LLCT character in the copper(I) and
zinc(II) complexes, respectively. The binding of alkali
metal cations by the cavity of the crown ether-contain-
ing complexes has been investigated by electronic
1
absorption spectrophotometry, H NMR spectroscopy
and electrochemical measurements.
5. Supplementary material
Crystallographic data for the structural analysis for
complex 2 have been deposited with the Cambridge
Crystallographic Data Centre, CCDC no. 182397.
Copies of this information may be obtained from The
Director, CCDC, 12 Union Road, Cambridge CB2 1EZ,
Fig. 4. Cyclic voltammograms showing (a) the oxidation (scan rate,
100 mV sꢃ1) and (b) reduction (scan rate, 100 mV sꢃ1) of 1 in
acetonitrile (0.1 mol dmꢃ3 nBu4NPF6) in the absence of Naꢂ ions
(solid line) and in the presence of Naꢂ ions (dashed line).
UK (fax: ꢂ44-1233-336 033; e-mail: deposit@ccdc.
/
cam.ac.uk or www: http://www.ccdc.cam.ac.uk.
Table 5
Electrochemical data for complexes 1 and 2
a
Complex Oxidation, E1/2 or Epa b(V
Reduction, E1/2 a(V vs.
vs. SCE), (E1/2 in Naꢂ
)
SCE), (E1/2 in Naꢂ
)
c
c
Acknowledgements
b
c
c
1
2
ꢂ
/
1.25 (ꢂ
/
1.24)
ꢃ
/
1.31 (ꢃ
/
1.21)
V.W.-W.Y. acknowledges financial support from the
Research Grants Council (HKU 7097/01P) and the
Generic Drug Program of The University of Hong
Kong. Y.-L.P. acknowledges the receipt of a postgrad-
uate studentship, administered by The University of
Hong Kong. Dr. M.J. Hynes is gratefully acknowledged
for providing us with the EQNMR program.
a
ꢂ
/
1.87
ꢃ0.91
/
b
ꢂ
/
1.60
In acetonitrile (0.1 mol dmꢃ3 nBu4NPF6). Working electrode, glassy
Fc ranges from 63 to 64 mV; scan rate, 100 mV
carbon; DEp of Fcꢂ ꢀ
/
sꢃ1
.
a
E1/2
peak potentials of the quasi-reversible reduction and oxidation
ꢁ/
(EpaꢂEpc)/2 where Epa and Epc are the anodic and cathodic
/
couples.
b
Anodic peak potential of the irreversible oxidation wave.
E1/2 value vs. SCE in the presence of NaClO4 in acetonitrile (0.1
c
mol dmꢃ3 nBu4NPF6).
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