Cu(II)-containing cross-linked polymers for the hydrolysis of 4-nitrophenyl phosphate

Article abstract of DOI:10.1016/S0020-1693(00)00241-3

The protonation constants of N-(4-vinyl)benzyl ethylenediamine (L1), 1-(4-vinyl)benzyl diethylenetriamine (L2), 4-(4-vinyl)benzyl diethylenetriamine (L3), and the stability constants of their Cu(II) and Zn(II) complexes have been potentiometrically determined. The crystal structures of [Cu(L1)₂][ClO₄]₂ and [CuL₂(NO₃)₂]·CH₃CO₂C₂H₅ are reported. [Cu(L1)₂][ClO₄]₂ crystallizes in the monoclinic system with space group P2₁/c, having lattice parameters a = 12.48(2), b = 12.062(16), c = 9.188(15) A?, β = 97.46(7)°, and Z = 2. [CuL2(NO₃)₂]·CH₃CO₂C₂H₅ crystallizes in the monoclinic system with space group P2₁/n, having lattice parameters a = 10.239(2), b = 9.177(1), c = 24.096(4) A?, β = 95.99(1)°, and Z = 2. Kinetic studies show that the Cu(II)-containing cross-linked polymers made from incorporating [Cu(L1)₂]X₂ and [CuL3]X₂ (X = ClO₄^-, NO₃^-) catalyze the hydrolysis of 4-nitrophenyl phosphate with first-order rate constants 1.33 x 10^-5 and 1.04 x 10^-6 s^-1, respectively, at 55°C and pH 8.5. (C) 2000 Elsevier Science B.V.

Full text of DOI:10.1016/S0020-1693(00)00241-3

www.elsevier.nl/locate/ica
Inorganica Chimica Acta 309 (2000) 82–90
Cu(II)-containing cross-linked polymers for the hydrolysis of
4-nitrophenyl phosphate
Q. Lu a,b, Alok Singh a, Jeffrey R. Deschamps c, E.L. Chang a,*
a Na6al Research Laboratory, Code 6930, Washington, DC 20375-5348, USA
b Geo Centers, Inc., 10903 Indian Head Hwy., Ft. Washington, Washington, DC 20375, USA
c Na6al Research Laboratory, Code 6030, Washington, DC 20375-5348, USA
Received 17 March 2000; accepted 16 July 2000
Abstract
The protonation constants of N-(4-vinyl)benzyl ethylenediamine (L1), 1-(4-vinyl)benzyl diethylenetriamine (L2), 4-(4-vi-
nyl)benzyl diethylenetriamine (L3), and the stability constants of their Cu(II) and Zn(II) complexes have been potentiometrically
determined. The crystal structures of [Cu(L1)2][ClO4]2 and [CuL2(NO3)2]·CH3CO2C2H5 are reported. [Cu(L1)2][ClO4]2 crystallizes
,
in the monoclinic system with space group P21/c, having lattice parameters a=12.48(2), b=12.062(16), c=9.188(15) A,
i=97.46(7)°, and Z=2. [CuL2(NO3)2]·CH3CO2C2H5 crystallizes in the monoclinic system with space group P21/n, having lattice
,
parameters a=10.239(2), b=9.177(1), c=24.096(4) A, i=95.99(1)°, and Z=2. Kinetic studies show that the Cu(II)-containing
cross-linked polymers made from incorporating [Cu(L1)2]X2 and [CuL3]X2 (X=ClO4−, NO3−) catalyze the hydrolysis of
4-nitrophenyl phosphate with first-order rate constants 1.33×10−5 and 1.04×10−6 −1, respectively, at 55°C and pH 8.5.
s
© 2000 Elsevier Science B.V. All rights reserved.
Keywords: N-Alkylation; Crystal structures; Stability constants; Cross-linked polymers; Catalytic hydrolysis
synthesis and stability constants of the Cu(II) and
1. Introduction
Zn(II) complexes formed by the polymerizable ligands
L1–L3 (Scheme 1) and the catalytic hydrolysis of 4-ni-
trophenyl phosphate by the Cu(II)-containing cross-
linked polymers. These polymers are made by
incorporating Cu(II) complexes of L1–L3 into a
trimethylolpropane trimethacrylate (trim) matrix. The
crystal structures of [Cu(L1)2][ClO4]2 and [CuL2-
(NO3)2]·CH3CO2C2H5 are also described.
There has been extensive interest in the catalytic
hydrolysis of phosphate esters because of its relevance
to the breakdown of nucleic acids and potent
organophosphate pesticides. Many low molecular
weight metal complexes have been designed and synthe-
sized to promote the hydrolysis of phosphate esters,
and some of these model complexes provide enormous
rate acceleration for the hydrolysis reactions [1–8].
While homogenous catalysis is efficient, it suffers
from difficulty in separation of products from reac-
tants/catalysts. This shortcoming, however, can be
overcome by immobilizing the model compounds into a
polymeric matrix [9–11]. An often-overlooked addi-
tional advantage of incorporating the monomeric metal
complexes into a polymeric matrix is that the polymeric
structure may confer catalytic reactivity to the other-
wise non-reactive metal complexes. We report here the
2. Experimental
2.1. Materials
CuCl2·2H2O, KCl, trim, and CO2-free Dilut-it am-
poules of KOH were obtained from Sigma Chemical
Co., Fisher Scientific Co., TCI, and J.T. Baler Inc.,
respectively. All other chemicals including ethylenedi-
amine, diethylenetriamine, 4-vinylbenzyl chloride, and
4-nitrophenyl phosphate were purchased from Aldrich
Chemical Co.
* Corresponding author.
0020-1693/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(00)00241-3

Q. Lu et al. / Inorganica Chimica Acta 309 (2000) 82–90
83
2.2. Synthesis
mixture was stirred at r.t. for 4 h. Two mono-substi-
tuted isomers were separated by chromatography on
silica gel (9/1 MeOH–NH4OH). 1H NMR of 1-(4-vinyl)
benzyl diethylenetriamine trihydrochloride (D2O), l
(ppm): 3.28 (m, 8H), 4.06 (s, 2H), 5.11 (d, 1H), 5.64 (d,
1H), 6.54 (q, 1H), 7.20 (d, 2H), 7.32 (d, 2H). 13C NMR
(D2O), l (ppm): 35.23, 42.08, 43.75, 44.75, 51.5, 115.41,
127.08, 129.21, 130.30, 135.83, 138.92. 1H NMR of
4-(4-vinyl) benzyl diethylenetriamine trihydrochloride
(D2O), l (ppm): 3.34 (m, 4H), 3.47 (m, 4H), 4.38 (s,
2H), 5.27 (d, 1H), 5.81 (d, 1H), 6.69 (q, 1H), 7.40 (d,
2H), 7.50 (d, 2H). 13C NMR (D2O), l (ppm): 34.12,
49.68, 58.58, 116.44, 127.42, 127.77, 131.59, 135.89,
139.80.
2.2.1. N-(4-Vinyl)benzyl ethylenediamine (L1)
A solution of 4-vinylbenzyl chloride (1.52 g, 10
mmol) in dichloromethane (100 ml) was added drop-
wise to a stirred solution of ethylenediamine (2.4 g, 40
mmol) in dichloromethane (200 ml). The resulting mix-
ture was stirred at room temperature (r.t.) for 4 h. The
solvent was then removed on a rotary evaporator. The
residue was purified by chromatography on silica gel
(9/1 MeOH–NH4OH) to give N-(4-vinyl)benzyl
1
ethylenediamine as a brown oil (0.88 g, 50%). H NMR
of N-(4-vinyl)benzyl ethylenediamine dihydrochloride
(D2O), l (ppm): 3.32 (m, 2H), 3.38 (m, 2H), 4.23 (s,
2H), 5.31 (d, 1H), 5.83 (d, 1H), 6.76 (q, 1H), 7.39 (d,
2H), 7.51 (d, 2H). 13C NMR (D2O), l (ppm): 35.64,
43.78, 51.49, 116.19, 127.11, 129.52, 130.38, 136.00,
139.28.
2.3. Preparation of crystalline Cu(II) complexes for
X-ray analysis
2.3.1. [Cu(L1)2][ClO4]2
N-(4-Vinyl)benzyl ethylenediamine (0.3 mmol) in
methanol (10 ml) was mixed with a solution of
Cu(ClO4)2·6H2O (0.15 mmol) in acetonitrile (10 ml).
Purple plate-like crystals suitable for X-ray analysis
were collected after ether diffusion.
2.2.2. 1-(4-Vinyl) benzyl diethylenetriamine (L2) and
4-(4-6inyl) benzyl ditheylenetriamine (L3)
A solution of 4-vinylbenzyl chloride (1.52 g, 10
mmol) in dichloromethane (100 ml) was added drop-
wise to a stirred solution of diethylenetriamine (4.12 g,
40 mmol) in dichloromethane (300 ml). The resulting
2.3.2. [CuL2(NO3)2]·CH3CO2C2H5
1-(4-Vinyl)benzyl diethylenetriamine (0.15 mmol) in
methanol (10 ml) was mixed with a solution of
Cu(ClO4)2·6H2O (0.15 mmol) in acetonitrile (10 ml).
Ethyl acetate was diffused into the solution for several
days, after which purple rod-like crystals suitable for
X-ray analysis were collected.
2.4. Preparation of cross-linked polymers from Cu(II)
complexes of L1–L3 and trim
The following procedures were followed in the prepa-
ration of cross-linked polymers Poly1, Poly2, and Poly3
from the Cu(II) complexes of L1–L3 and trim. Substi-
tuted polyamine (1 mmol) was mixed with CuX2 (X=
ClO4−, NO3−) in a molar ratio of 1:1 or 2:1 in 25 ml
EtOH. The mixture was stirred at r.t. for 15 min before
trim (9 mmol in 10 ml EtOH) was added. The resulting
solution was heated to 70°C while at the same time
bubbling nitrogen. The initiator 2,2-azobisisobutyro-
nitrile (AIBN) (100 mg) was then added to start the
polymerization. Polymer formation could be seen
within 1 h. Cross-linked polymers containing 10 mol%
metal ion content to trim were isolated by filtration and
washed with solvents to remove any unreacted starting
materials.
Metal-free cross-linked polymers made from L1–L3
and trim were also synthesized by the same procedures
except without adding the Cu(II) salt.
Scheme 1.

84
Q. Lu et al. / Inorganica Chimica Acta 309 (2000) 82–90
Table 1
2.6. Crystallography
Crystal data and structure refinement parameters
X-ray diffraction data for [Cu(L1)2][ClO4]2 were col-
lected on an automated four-circle diffractometer
(Bruker P4) equipped with an incident beam graphite
monochrometer and a 1.0-mm collimator. Three reflec-
tions, used as standards, were measured after every 97
new measurements. These standards showed a random
variation of 2% over the period of data collection
(approximately 24 h).
Name
[Cu(L1)2][ClO4]2
[CuL2(NO3)2]·
CH3CO2C2H5
Color/shape
purple/plate
C22H32Cl2CuN4O8
614.96
223(2) K
monoclinic
P21/c
purple/rod
C17H29CuN5O8
494.99
198(2) K
monoclinic
P21/n
Empirical formula
Formula weight
Temperature
Crystal system
Space group
Unit cell dimensions
a (A)
b (A)
X-ray
diffraction
data
for
[CuL2(NO3)2]·
,
,
12.48(2)
12.062(16)
9.188(15)
97.46(7)
1372(4)
2
10.239(2)
9.177(1)
24.096(4)
95.99(1)
2251.8(6)
4
CH3CO2C2H5 were collected on a computer controlled
Siemens CCD 1K area detector system with a Bruker
platform goniometer, using a Rigaku rotating anode
source and Go¨bels mirrors (Cu Ka radiation, u=
,
c (A)
i (°)
3
,
V (A )
Z
,
1.54178 A). Data collection nominally covered a hemi-
Dcalc (g cm−3
)
1.489
1.042
1.460
1.832
sphere in reciprocal space by combining six sets of
exposures with different 2q and € angles: each exposure
covered a range of 0.25° in €. The crystal to detector
distance was 4.48 cm and the coverage of a unique set
Absorption coefficient
(mm−1
)
Diffractometer/scan
Radiation/wavelength
Bruker P4/q/2q
Mo Ka/0.71073
Bruker 1K CCD/ꢀ
Cu Ka/1.54178
,
(A)
,
was 94% complete to 1.0 A resolution. Crystal decay
F(000)
638
1036
0.15×0.11×0.04
mm
was monitored by repeating 60 of the initial frames at
the end of data collection. No crystal decay was found.
The CCD data was integrated using SAINT [12]. Correc-
tions were applied for Lorentz and polarization effects.
A face-indexed absorption correction was applied using
XPREP [13].
Crystal size
0.22×0.20×0.08
mm
2.36–25.08°
q Range for data
collection
Index ranges
3.69–56.54°
−145h514,
−145k53,
−25l510
2684
2428/922
face indexed
0.88–0.98
−85h510,
−95k59,
−265l516
7250
2600/2332
face indexed
0.76–0.92
Data collection, structure solution, and refinement
parameters for both crystal structures are summarized
in Table 1. The structures were solved by direct meth-
ods with the program XS [14] and refined on F2 using
all reflections with the program SHELXTL [15]. Weighted
R-factors (wR) and all goodness-of-fit parameters are
based on F2. Conventional R-factors (R) are based on
F, with F set to zero for negative F2.
For [Cu(L1)2][ClO4]2, despite low temperature data
collection, both the perchlorate and the 4-vinyl benzyl
side chain were disordered. Secondary positions for the
disorder were located in difference maps and refined
using SHELXTL. Restraints were applied to the atoms in
the perchlorate to preserve the geometry during the
refinement of the disorder. The crystal scattered weakly
with less than 40% of the data observed and R (|) was
13.43%. Despite these problems the structure refined to
a final R value of 8.08% for I\2|(I). The final R value
of [CuL2(NO3)2]·CH3CO2C2H5 is 5.67% for I\2|(I)
(R (|) for the data was 6.74% for the data).
Reflections collected
Independent/observed
Absorption correction
Transmission factor
range
Refinement method
full-matrix
full-matrix
least-squares on F2 least-squares on F2
Computing
XS [14], SHELXTL
[15]
2428/13/273
XS, [14] SHELXTL
[15]
2600/0/280
Data/restraints/
parameters
Goodness-of-fit (all
data)
SHELXL weight
parameters
R indices [I\2|(I)]
0.993
1.069
0.0968 0.0000
0.0968 0.0000
R1=0.0808
wR2=0.1791
R1=0.2179
wR2=0.2576
none
R1=0.0567
wR2=0.1461
R1=0.0635
wR2=0.1522
none
R indices (all data)
Extinction coefficient
Largest difference peak 0.310−0.284
and hole (e A
0.626−0.595
−3
,
)
2.7. Potentiometric measurements
2.5. NMR and UV–Vis spectra
Potentiometric studies of N-(4-vinyl)benzyl ethylene-
diamine dihydrochloride, 1-(4-vinyl)benzyl diethylene-
triamine trihydrochloride, and 4-(4-vinyl)benzyl
diethylenetriamine trihydrochloride in the absence and
presence of metal ions were carried out with a Orion
model 920A pH meter fitted with a Orion combined
1H and 13C spectra were recorded on a Bruker
AVANCE DRX 400 spectrometer. UV–Vis spectra
were recorded on a Varian CARY 2400 spectro-
photometer.

Q. Lu et al. / Inorganica Chimica Acta 309 (2000) 82–90
85
electrode. Each titration in aqueous solution was per-
3. Results and discussion
formed at 25.0°C and under nitrogen. The concentra-
tions of the experimental solutions were approximately
2×10−3 to 4×10−3 M. The stoichiometries of lig-
and–metal ion systems are 1:1 and 2:1. Equilibrium
constants were calculated with the program BEST [16].
The log Kw for the system, defined in terms of log [H+
][OH−], was found to be −13.78 at the ionic strength
employed and was fixed during the refinement of the
other constants. In all the potentiometric determina-
tions the |fit [16], which measures the deviation of the
experimental curve and the curve calculated from the
equilibrium constants, was less than 0.02[pH] units.
3.1. Crystal structure of [Cu(L1)2][ClO4]2
The complex crystallizes in a monoclinic space group
P21/c. The asymmetric unit contains one molecule of
N-(4-vinyl)benzyl ethylenediamine, half a Cu(II) ion,
and one perchlorate anion (Fig. 1). Bond lengths and
angles are given in Tables 2 and 3. The coordination
geometry around the Cu(II) ion is best described as
square planar. One oxygen atom from each perchlorate
anion is located above or below the plane at a distance
,
,
of 2.553 A. The bond length (2.05 A) between the
secondary nitrogen atom N2 and Cu(II) ion is slightly
longer than that between the primary nitrogen atom N1
2.8. Kinetic studies
,
and the Cu(II) ion (1.974 A), presumably due to the
steric hindrance caused by the bulky substituent.
The method of initial rates was used to determine the
rate constants of 4-nitrophenyl phosphate hydrolysis in
the presence of PolyL1, PolyL2, and PolyL3. In a
typical experimental run, 10 ml borate buffer (pH 8.5)
containing substrate (in the range of 10−4–10−3 M)
was capped in a 15 ml test tube and placed in a
thermostated bath (5590.5°C) equipped with a shaker.
The reaction was initiated by adding 0.05 g Cu(II)-con-
taining cross-linked polymer (ꢀ10−5 mol of Cu(II)
ion). Periodically 0.2 ml of the solution was taken out
by a syringe and diluted to 1 ml with borate buffer in a
cuvette. The hydrolysis of 4-nitrophenyl phosphate was
then followed through UV absorbance of 4-nitropheny-
late at 400 nm. A reference solution was similarly
prepared without the Cu-containing polymer in order
to eliminate the effect from the spontaneous hydrolysis
of 4-nitrophenyl phosphate. The initial rate of the
reaction was obtained from the plot of 4-nitrophenyl
phosphate concentration (calculated from the extinc-
3.2. Crystal structure of [CuL2(NO3)2]·CH3CO2C2H5
The complex crystallizes in a monoclinic space group
P21/n. The asymmetric unit shown in Fig. 2 contains
one molecule of 1-(4-vinyl)benzyl diethylenetriamine,
one Cu(II) ion, one molecule of ethyl acetate, and two
nitrate anions. Bond lengths and angles are listed in
Tables 4 and 5. The Cu(II) ion is penta-coordinated by
three nitrogen atoms from the tridentate polyamine and
two oxygen atoms from the nitrate anions, exhibiting a
square pyramidal geometry. The oxygen O1 from one
of the nitrate anions occupies the apical position with a
,
CuꢀO1 distance of 2.314 A. The bond length between
the Cu(II) ion and the secondary nitrogen atom N7 is
marginally longer than the other bond lengths between
the Cu(II) ion and the nitrogen donors. The copper(II)
,
cation is displaced 0.16 A from the square planar basal
plane.
tion coefficient of 4-nitrophenylate, 18700 l mol−1
)
versus time. All the measurements were done in dupli-
cate and the reactions were followed for less than 5%
hydrolysis of the substrate. For the purpose of com-
parison, the kinetics of monomeric Cu(II) complexes of
L1, L2, L3 and the metal-free cross-linked polymers
have also been also carried out under the same
conditions.
3.3. The effect of N-alkylation on the basicity of L1,
L2, L3, and the stability constants of their metal
complexes
The protonation constants of L1, L2, L3, and the
stability constants of their Cu(II) and Zn(II) complexes
Fig. 1. View of [Cu(L1)2][ClO4]2 showing the labeling of all non-hydrogen atoms. Thermal ellipsoids are shown at 20% probability level. H-atoms
are drawn as small circles of arbitrary radii. Disordered positions of the divinylbenzene side-chain and perchlorate were omitted for clarity.

86
Q. Lu et al. / Inorganica Chimica Acta 309 (2000) 82–90
Table 2
,
Bond lengths (A) for [Cu(L1)2][ClO4]2
Atom 1
Atom 2
Distance
Atom 1
Atom 2
Distance
Cu1
Cu1
Cu1
Cu1
Cu1
Cu1
N1
C1
C1
C2
N2
C3
C4
C4
C5
C6
C7
C7
C8
N1
N1 a
N2 a
N2
N2% a
N2%
C1
C2%
C2
N2
C3
C4
C5
C9
C6
C7
C8
C10
C9
1.974(8)
1.974(8)
2.05(3)
2.05(3)
2.05(4)
2.05(4)
1.433(18)
1.06(5)
1.55(3)
1.46(3)
1.44(2)
1.57(2)
1.3900
1.3900
1.3900
1.3900
1.3900
1.50(3)
1.3900
C2%
N2%
C3%
C4%
C4%
C5%
C6%
C7%
C7%
C8%
C10
Cl1
Cl1
Cl1
Cl1
Cl1%
Cl1%
Cl1%
Cl1%
N2%
C3%
C4%
C5%
C9%
C6%
C7%
C8%
C10
C9%
C11
O1
O3
O4
O2
O3%
O1%
O2%
O4%
1.55(5)
1.54(4)
1.56(3)
1.3900
1.3900
1.3900
1.3900
1.3900
1.61(3)
1.3900
1.224(17)
1.35(3)
1.35(2)
1.39(3)
1.40(2)
1.35(3)
1.34(3)
1.42(3)
1.44(3)
a −1−x, 1/2+y, 1/2−z
Table 3
Bond angles (°) for [Cu(L1)2][ClO4]2
Atom 1
Atom 2
Atom 3
Angle
Atom 1
Atom 2
Atom 3
Angle
N1
N1
N1 a
N1
N1 a
N2 a
N1
N1 a
N2 a
N2
N1
N1 a
N2 a
N2
N2% a
C1
C2%
C2%
N1
N2
C3
C3
C2
N2
C5
C5
Cu1 a
Cu1 a
Cu1 a
Cu1
Cu1
Cu1
Cu1 a
Cu1 a
Cu1 a
Cu1 a
Cu1
Cu1
Cu1
Cu1
Cu1
N1
C1
C1
C1
C2
N2
N2
N2
C3
N1
N2
N2
N2
N2
N2
N2%
N2%
N2%
N2%
N2%
N2%
N2%
N2%
N2%
Cu1
N1
C2
C2
C1
C2
Cu1
Cu1
C4
C9
C3
180.0 (1)
92.1(7)
87.9(7)
87.9(7)
92.1(7)
180.0 (1)
98.5(10)
81.5(10)
17.2(5)
162.8(5)
81.5(10)
98.5(10)
162.8(5)
17.2(5)
C7
C8
C1
C8
C9
C9
C4
120.0
120.0
C2%
N2%
N2%
N2%
C3%
C4%
C4%
C4%
C5%
C6%
C7%
C7%
C7%
C8%
C9%
C10
C10
C10
Cl1
Cl1
Cl1
Cl1
Cl1
Cl1
Cl1%
Cl1%
Cl1%
Cl1%
Cl1’
Cl1%
N2%
C3%
Cu1
Cu1
C4%
C9%
C3%
C3%
C6%
C7%
C6%
C10
C10
C9%
C4%
C7
C7%
C7%
O3
O4
O4
O2
O2
O2
124(3)
121(4)
101(2)
108.1(18)
108(2)
120.0
128(2)
112(2)
120.0
120.0
120.0
123(3)
115(3)
120.0
C2%
C2%
C3%
N2%
C5%
C5%
C9%
C4%
C5%
C8%
C8%
C6%
C7%
C8%
C11
C11
C7
O1
O1
O3
O1
O3
O4
O3%
O3%
O1%
O3%
O1%
O2%
180.0 (1)
111.8(7)
115(3)
120.0
46(3)
117(3)
116(3)
7.9(18)
107.2(19)
113(2)
109(2)
112(2)
110.5(19)
104.8(19)
117(3)
107.1(18)
113.2(18)
111.3(19)
103(2)
105(3)
109.0(14)
115.3(18)
118.1(19)
118.1(15)
104.5(14)
113.9(15)
120.0
119.2(16)
120.7(16)
120.0
C4
C4
C4
C5
C6
C7
C7
C7
C9
C6
C5
C6
C6
C8
C3
C4
C7
C8
C10
C10
O1%
O2%
O2%
O4%
O4%
O4’
120.0
120.0
123(2)
117(2)
a −1−x, 1/2+y, 1/2−z

Q. Lu et al. / Inorganica Chimica Acta 309 (2000) 82–90
87
have been determined by a potentiometric method.
They are given in Tables 6 and 7 together with the
corresponding constants of ethylenediamine (EN) and
diethylenetriamine (DIEN) [17]. It is noted that N-alky-
lation reduces the basicity of L1, L2, L3 and the
stability constants of their complexes, in comparison
with their parent polyamine ligands EN and DIEN.
These observations seem to be in contradiction to what
would be expected, as the 4-vinyl benzyl substituent is
an electron-donating group. However, there are factors
other than electron density that may exert an opposing
influence on the basicity of N-alkylated polyamine lig-
ands and the stability of their metal complexes. These
factors include the steric hindrance caused by the bulky
substituent that may elongate the MꢀN bonds, and the
disruption of the hydrogen bonding pattern in aqueous
solution, which may destabilize the positively-charged
species such as protonated ligands and their metal
complexes.
Crystal structure results show that the MꢀN bonds
involving the secondary nitrogen atoms attached to a
bulky substituent are only marginally longer than those
involving the primary nitrogen atoms. Therefore, the
steric factor may not be the most significant factor in
reducing the basicity of L1, L2, L3, and their respective
metal stability constants. Instead, the destabilization of
positively charged species in aqueous solution from the
disruption of the hydrogen bond is probably more
Fig. 2. View of [CuL2(NO3)2]·CH3CO2C2H5 showing the labeling of all non-hydrogen atoms. Thermal ellipsoids are shown at 20% probability
level. H-atoms are drawn as small circles of arbitrary radii.
Table 4
,
Bond lengths (A) for [CuL2(NO3)2]·CH3CO2C2H5
Atom 1
Atom 2
Distance
Atom 1
Atom 2
Distance
Cu1
Cu1
Cu1
C2
N4
C6
C8
C9
C11
C12
C15
N2
N4
O4
O1
C3
C5
1.993(4)
2.011(3)
2.314(3)
1.516(7)
1.474(6)
1.485(6)
1.502(7)
1.400(7)
1.399(8)
1.475(7)
1.305(9)
1.248(6)
1.235(5)
1.285(5)
1.199(7)
1.459(6)
Cu1
Cu1
N1
C3
C5
N7
C9
C10
C12
C13
N2
N2
N3
C1S
C2S
C3S
N1
N7
C2
N4
C6
C8
C14
C11
C13
C14
O2
O1
O6
C2S
O2S
C4S
1.996(4)
2.038(4)
1.482(6)
1.461(6)
1.520(7)
1.485(6)
1.384(7)
1.376(7)
1.369(8)
1.389(7)
1.228(6)
1.256(5)
1.241(5)
1.497(8)
1.337(7)
1.515(8)
N7
C9
C10
C12
C15
C16
O3
O5
O4
O1S
C3S
N3
N3
C2S
O2S

88
Q. Lu et al. / Inorganica Chimica Acta 309 (2000) 82–90
Table 5
Bond angles (°) for [CuL2(NO3)2]·CH3CO2C2H5
Atom 1
Atom 2
Atom 3
Angle
Atom 1
Atom 2
Atom 3
Angle
N4
N1
N1
N4
O4
C2
N4
C3
N4
C8
C6
C14
C10
C10
C13
C12
C16
O2
Cu1
Cu1
Cu1
Cu1
Cu1
N1
C3
N4
C5
N7
N7
C9
C9
C11
C12
C13
C15
N2
N1
O4
N7
O1
O1
Cu1
C2
Cu1
C6
C6
Cu1
C10
C8
C12
C15
C14
C12
O1
Cu1
O4
Cu1
C1S
C3S
84.50(15)
95.57(14)
162.4(2)
98.7(2)
N4
N4
O4
N1
N7
N1
C3
C5
N7
C8
N7
C14
C11
C13
C11
C9
O2
O3
O5
O6
O1S
O2S
O2S
Cu1
Cu1
Cu1
Cu1
Cu1
C2
N4
N4
C6
N7
O4
176.0(2)
85.6(2)
93.3(1)
98.5(2)
97.3(1)
N7
N7
O1
O1
C3
C5
Cu1
C5
Cu1
C9
C8
85.2(1)
109.2(3)
107.2(4)
108.9(3)
106.2(4)
113.7(4)
106.9(3)
118.0(5)
121.8(5)
121.6(5)
122.0(5)
121.3(5)
127.8(6)
121.7(4)
128.0(3)
118.6(4)
109.6(3)
125.2(5)
116.3(4)
106.4(4)
116.8(4)
107.2(3)
108.6(4)
114.6(3)
115.7(4)
120.2(5)
120.3(5)
117.8(5)
120.2(5)
121.0(5)
120.9(4)
117.4(5)
122.5(4)
118.8(4)
123.8(5)
111.0(5)
107.3(5)
C8
C9
C10
C12
C12
C14
N2
N2
N3
N3
C9
C11
C15
C13
O3
O1
O6
N2
O5
N3
O1S
C2S
O1
N3
O4
C2S
O2S
O4
C2S
C2S
C3S
O2S
C1S
C4S
Table 6
a
Stepwise protonation constants of L (v=0.10 M (KCl), 25.0°C, L=L1, L2, L3, EN, and DIEN, H=H+
)
Equilibrium quotient
Log K
L1
L2
L3
EN
DIEN
[LH]/[L][H]
[LH2]/[LH][H]
[LH3]/[LH2][H]
9.70(92)
6.50(91)
9.83(92)
8.49(92)
4.05(93)
9.92(94)
9.09(93)
B2.0
9.92(95)
7.08(94)
9.86(97)
9.02(96)
4.25(96)
a Standard deviations in parentheses.
Table 7
Stability constants a of LꢀCu(II) and LꢀZn(II) systems (v=0.10 M (KCl), 25.0°C; L=L1, L2, L3, EN, and DIEN; H=H+
)
Equilibrium quotient
Log K
L1
L2
L3
EN
DIEN
15.9(91)
8.82
[LCu]/[L][Cu]
[L2Cu]/[LCu][L]
[LZn]/[L][Zn]
[L2Zn]/[LZn][L]
8.99(91)
6.99(91)
4.30(93)
4.14(93)
14.92(94)
8.06(94)
14.12(91)
8.20(93)
10.50(96)
9.10(92)
5.7(91)
4.90(91)
a Standard deviations in parentheses.
important. The latter may also cause the increase in
acidity of the metal ion as a Lewis acid in the N-alky-
lated complexes [18]. Indeed, N-alkylated 1,4,7-trisiso-
propyl-1,4,7-triazacyclononane–Cu(II)Cl2 is a better
catalyst for the anaerobic catalyzed hydrolysis of DNA
than the parent compound, 1,4,7-triazacyclononane–
Cu(II)Cl2 [19].
3.4. Kinetics studies
The rates of 4-nitrophenyl phosphate hydrolysis in
the presence of either Cu(II) complexes of L1–L3 or
Cu(II)-containing cross-linked polymers, Poly1–Poly3,
and the metal-free cross-linked polymers have been
measured by UV–Vis spectroscopy at 55°C and pH 8.5.

Q. Lu et al. / Inorganica Chimica Acta 309 (2000) 82–90
89
Since each measurement was carried out relative to a
reference solution containing the same buffer and pre-
pared under the same conditions as for the sample
solution, the catalytic contribution, if any, from the
hydroxide or buffer may be ignored.
phosphate is not surprising. As has been observed in
previous studies [21], the catalytic reactivity of the
Cu(II) ion for hydrolysis decreases with increasing sta-
bility constants of the complexes. All three Cu(II) com-
plexes have relatively high stability constants,
indicating that the Cu(II) ions in the complexes are
poor Lewis acids that only react weakly with the sub-
strate. What is interesting is that the Cu(II)-containing
cross-linked polymers Poly1 and Poly3, contrary to the
monomers, do exhibit catalytic reactivity in the hydrol-
ysis of 4-nitrophenyl phosphate.
The electronic spectra (in Nujol mulls) of the Cu(II)
complexes of L1–L3 and the Cu(II)-containing cross-
linked polymers Poly1–Poly3 have been recorded. It is
seen from Table 8 that there are slight red-shifts in the
d–d transition bands of Poly1–Poly3, suggesting a
possible distortion in the coordination geometry or the
weakening of the CuꢀN bonds in the polymer. These
shifts in d–d transition bands, however, do not signify
a major change either in the coordination geometry
surrounding the Cu(II) ion or in the strength of the
CuꢀN bonds. Thus, the observed catalytic reactivity of
Poly1 and Poly3 probably arises from the combined
effect of the distortion of coordination geometry, the
weakening of the CuꢀN bonds, and the change in the
general environment around the Cu(II) ion in the poly-
mer matrix.
Of all the kinetic measurements taken, only Poly1
and Poly3 show observable reactivity with approximate
first-order rate constants of 1.33×10−5 (Fig. 3) and
1.04×10−6 −1, respectively (the kobs of the uncata-
s
lyzed hydrolysis of 4-nitrophenyl phosphate at 55°C
and pH 8.36 is 4.7×10−7 s−1 [7]). The reactions are
catalytic as judged by the amount of 4-nitrophenylate
produced under the conditions of a large excess of
substrate. Because some absorption of the 4-nitro-
phenylate anion by the polymers was observed [20], the
above rate constants are likely to be lower than the
actual values. In either case, the adsorption did not
appear to poison the catalytic centers within the poly-
mers. All other complexes showed no measurable rate
enhancement over the spontaneous hydrolysis of 4-ni-
trophenyl phosphate under the same conditions.
The inability of the monomeric Cu(II) complexes of
L1–L3 to catalyze the hydrolysis of 4-nitrophenyl
It is interesting to note that Poly1 shows higher
catalytic reactivity than Poly3 even through one would
expect the opposite by comparing the stability con-
stants of [Cu(L1)2]2+ and [CuL3]2+ (1015.98 versus
1014.12). The better catalytic reactivity of Poly1 may be
due to its more porous structure since the monomer
[Cu(L1)2]X2 contains one more polymerizable site than
[CuL3]X2. Obviously, a more porous structure will be
beneficial for the substrate to gain access to the Cu(II)
center.
Three conclusions may be drawn from the above
results. First, the presence of the Cu(II) ion is a neces-
sity for the observed catalytic reactivity since the metal-
free cross-linked polymers show no activity. Second, the
cross-linked polymer structure confers catalytic reactiv-
ity to the otherwise non-reactive Cu(II) centers, coordi-
nated either by two molecules of L1 or by one molecule
of L3. Finally, the direct coordination of the Cu(II) ion
to the substrate 4-nitrophenyl phosphate may be an
important step in the cleavage of the PꢀO bond.
Fig. 3. The plot of the natural logarithms of the initial rates (Rini) vs.
the natural logarithms of the initial concentrations of 4-nitrophenyl
phosphate for the system of Poly1–4-nitrophenyl phosphate (55°C,
pH 8.5).
Table 8
Electronic spectra a of Cu(II) complexes of L1–L3 and Cu-containing
cross-linked polymers
4. Supplementary material
Monomer
d–d transition 540
[Cu(L1)2][ClO4]2 [CuL2(NO3)2] [CuL3(NO3)2]
650
667
(umax, nm)
Polymer
d–d transition 566
(umax, nm)
Tables of anisotropic displacement parameters, H
atom coordinates and isotropic displacement parame-
ters for both crystal structures are available from the
authors upon request. Crystallographic data for the
structural analysis have been deposited with the Cam-
Poly1
Poly2
665
Poly3
688
a In Nujol mull.

90
Q. Lu et al. / Inorganica Chimica Acta 309 (2000) 82–90
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Copies of this information may be obtained free of
charge from: The Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (Fax: +44-1223-336033;
e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
Acknowledgements
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The authors would like to acknowledge partial sup-
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