Synthesis, structure, and ion-binding studies of cobalt(II) complexes with aza-crown substituted salicylaldimine Schiff base ligand

Article abstract of DOI:10.1016/S0020-1693(02)01391-9

A series of cobalt(II) complexes with azacrown ether-containing salicylaldimine Schiff base ligand Co(L1), Co(L2)₂ and Co(L3)₂ has been successfully synthesized. The cation-binding properties of the complexes have been studied and the stability constants with alkali and alkaline earth metal cations determined. Synthesis of the complexes with monoaza-12-crown-4, Co(L1) and Co(L2)₂, allows for a direct comparison of the cation binding properties between the mono- and bis-Schiff base systems as well as with the complex containing the monoaza-15-crown-5 pendant, i.e. Co(L3)₂, which has a different crown size. The X-ray crystal structure of Co(L3)₂ has also been determined.

Full text of DOI:10.1016/S0020-1693(02)01391-9

Inorganica Chimica Acta 346 (2003) 49ꢁ56
/
www.elsevier.com/locate/ica
Synthesis, structure, and ion-binding studies of cobalt(II) complexes
with aza-crown substituted salicylaldimine Schiff base ligand
Xiao-Xia Lu a,b, Sheng-Ying Qin b,*, Zhong-Yuan Zhou c, Vivian Wing-Wah Yam a,*
a Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong
b Department of Chemistry, Sichuan University, Chengdu, Sichuan, People’s Republic of China
c Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
Received 18 June 2002; accepted 14 October 2002
Abstract
A series of cobalt(II) complexes with azacrown ether-containing salicylaldimine Schiff base ligand Co(L1), Co(L2)2 and Co(L3)2
has been successfully synthesized. The cation-binding properties of the complexes have been studied and the stability constants with
alkali and alkaline earth metal cations determined. Synthesis of the complexes with monoaza-12-crown-4, Co(L1) and Co(L2)2,
allows for a direct comparison of the cation binding properties between the mono- and bis-Schiff base systems as well as with the
complex containing the monoaza-15-crown-5 pendant, i.e. Co(L3)2, which has a different crown size. The X-ray crystal structure of
Co(L3)2 has also been determined.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Ion-binding; Cobalt(II) complexes; Aza-crown; Salicyladimine; Schiff base
1. Introduction
oxygen-binding properties. Recent works by us [8] and
others [9] have shown that Schiff base ligands with
crown ether pendants are good receptors for alkali and
transition metal guest cations. Stable dioxygen adducts
of Co(II) complexes of (15-crown-5)salophen [10] and
(18-crown-6)disalophen [11] have successfully been pre-
pared. Oxygenation constants and thermodynamic
parameters of transition metal complexes with (15-
crown-5)salophen were measured and the complexes
have been employed to catalyze the epoxidation of
styrene [12]. Compared with the crown-free analogues,
the dioxygen affinities and catalytic activities of those
complexes with crown ethers are higher. However, up to
date, all the Co(II) complexes with crown ether-contain-
ing Schiff base ligands are limited to those of oxacrown
moieties. Recently, we became interested in crown
systems other than that involving all oxygen donor
atoms, such as the azaoxacrown systems as shown in
Chart 1. Herein are described the synthesis and char-
acterization of several azaoxacrown-containing Schiff
base ligands and their complexes of cobalt(II). The
cation-binding properties of these complexes have been
studied. The complexes with monoaza-12-crown-4, i.e.
Co(L1) and Co(L2)2, together with the complex contain-
Synthetic oxygen carriers [1] are of great interest as
models to mimic oxygen carrying metalloenzymes [2]
and oxygenases, such as hemoglobin and cytochrome P-
450 [3], which play important roles in the catalytic
oxygenation mechanism of organic substrates [4]. Schiff
bases represent one of the most successful classes of
ligands for synthetic oxygen carriers due to their
structural similarity to those found in biological systems
[1,5]. The thermodynamic [5a], theoretical [6], and
catalytic aspects [7] of this class of compounds have
been extensively studied. Recently, Schiff bases contain-
ing a secondary site for coordination have attracted
special attention. Crown ether-containing Schiff bases
are known to bind cations in the crown ether cavity in
addition to the coordination of a transition metal center
through the N2O2 donor atoms. Co-complexation of a
hard cation close to the transition-metal center is
believed to play an important role in perturbing its
* Corresponding authors. Tel.: ꢀ
1586.
E-mail address: wwyam@hkucc.hku.hk (V.W.-W. Yam).
/
852-2859 7919; fax: ꢀ852-2857
/
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 1 3 9 1 - 9

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X.-X. Lu et al. / Inorganica Chimica Acta 346 (2003) 49ꢁ56
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(300 MHz) Fourier-transform NMR spectrometer,
while 13C{1H} NMR spectra were recorded on a Bruker
DRX-500 Fourier-transform NMR spectrometer. Che-
1
mical shifts (ppm) of H and 13C NMR spectra were
recorded relative to tetramethylsilane (Me4Si). Electron-
impact (EI) and positive-ion FAB mass spectra were
recorded on a Finnigan MAT95 mass spectrometer.
Elemental analyses of the newly synthesized compounds
were performed on a Carlo Erba 1106 elemental
analyzer at the Institute of Chemistry, Chinese Academy
of Sciences.
Electronic absorption spectral titration studies for
binding constant determination were performed on a
HewlettꢁPackard 8452A diode array spectrophotometer
/
at 25 8C, which was controlled by a Lauda RM6
compact low-temperature thermostat. Supporting elec-
trolyte (0.1 mol dmꢂ3 nBu4NPF6) was added to main-
tain a constant ionic strength of the sample solution in
order to prevent any changes arising from a change in
the ionic strength of the medium. Binding constants for
1:1 complexation were obtained by a nonlinear least-
squares fit [15] of the absorbance (X) versus the
concentration of the metal ion added (cM) according to:
Chart 1.
ing the monoaza-15-crown-5 pendant, Co(L3)2, provide
a direct comparison of the cation binding properties
between the mono- and bis-Schiff base systems as well as
those with different crown sizes. The X-ray crystal
structure of Co(L3)2 has also been determined.
Xlim ꢂ X0
X ꢃX0 ꢀ
2c0
2. Experimental
 [c0 ꢀcM ꢀ1=KS
ꢂ[(c0 ꢀcM ꢀ1=KS)2 ꢂ4c0cM]1=2
]
(1)
2.1. Reagents and materials
where X0 and X are the absorbances of complex Co(L1)
at a selected wavelength in the absence and presence of
the metal cation, respectively, c0 is the initial concentra-
tion of complex Co(L1), cM is the concentration of the
metal cation Mnꢀ, Xlim is the limiting value of
absorbance in the presence of excess metal ion, and KS
is the stability constant.
4-Aminoacetanilide, N-phenyldiethanolamine, re-
duced iron powder and salicylaldehyde were obtained
from Lancaster Synthesis Ltd. Cobalt(II) acetate tetra-
hydrate was obtained from Merck. Tetra-n-butylammo-
nium hexafluorophosphate (nBu4NPF6) (Aldrich, 98%)
was purified by recrystallization from hot ethanol three
times and vacuum dried for 12 h before use. Lithium
perchlorate, sodium perchlorate and potassium hexa-
fluorophosphate were recrystallized from hot methanol
and vacuum dried before use. The compounds N,N?-(4-
nitro-1,2-phenylene)bisacetamide [13] and 1,11-diiodo-
3,6,9-trioxaundecane [14] were synthesized according to
literature procedures. Acetonitrile was distilled over
calcium hydride before use. All other reagents and
solvents were of analytical grade and were used as
received.
2.2.1. Synthesis of N,N?-(4-amino-1,2-
phenylene)bisacetamide
To boiling water (200 ml) in a 500 ml beaker was
added in one portion the ground mixture of N,N?-(4-
nitro-1,2-phenylene)bisacetamide (13.0 g, 0.055 mol)
and reduced iron powder (5.0 g, 0.089 mol), with a
few drops of acetic acid. The resulting mixtures were
stirred and maintained at this temperature for 1 h. After
which, to the solution was added ammonia solution
(35%) until pH 8 was obtained. The solution was boiled
and filtered while it was still warm. The filtrate was
evaporated until solid appeared. After cooling, the white
solid was collected by filtration. Yield: 10.25 g, 90%. 1H
NMR (300 MHz, CD3COCD3, 298 K, relative to
Me4Si): d 1.91 (s, 6H, CH3CO), 4.47 (s, 2H, NH2),
2.2. Physical measurements and instrumentation
UVꢁ
/
Vis spectra were obtained on a HewlettꢁPackard
/
8452A diode array spectrophotometer, and steady-state
excitation and emission spectra on a Spex Fluorolog 111
spectrofluorometer equipped with a Hamamatsu R-928
photomultiplier tube. Low-temperature (77 K) spectra
were recorded by using an optical Dewar sample holder.
1H NMR spectra were recorded on a Bruker DPX-300
6.27ꢁ
6.90ꢁ
CONH), 8.71 (s, 1H, CONH). EI MS: (m/z): 207
/
6.31 (dd, 1H, Jꢃ
/
8.4 Hz and Jꢃ/1.9 Hz, C6H3),
/
6.93 (d, 2H, Jꢃ/8.4 Hz, C6H3), 8.55 (s, 1H,

X.-X. Lu et al. / Inorganica Chimica Acta 346 (2003) 49ꢁ
/56
51
{Mꢀ}. Elemental analyses, Found: C, 57.78; H, 6.37; N,
20.24. Calc. for C10H13N3O2: C, 57.96; H, 6.32; N,
20.28%.
no)benzo-15-crown-5 [16]. To a heated solution of N-
(3,4-diaminophenyl)aza-12-crown-4 (1.00 g, 3.56 mmol)
in 10 ml ethanol was added salicylaldehyde (0.87 g, 7.12
mmol) dissolved in 10 ml of the same solvent. The color
of the solution immediately turned bright yellow. The
solution was refluxed for 5 h and was then evaporated to
dryness. Subsequent recrystallization from ethanol gave
the product as bright yellow needles. Yield: 1.39 g, 80%.
1H NMR (300 MHz, CDCl3, 298 K, relative to Me4Si):
2.2.2. Synthesis of N-(3,4-diacetylphenyl)aza-12-crown-
4
This was prepared by modification of a literature
method for the related N-phenylaza-12-crown-4 [14]. A
stirred solution of 1,11-diiodo-3,6,9-trioxaundecane
(20.50 g, 0.05 mol) and N?,N?-(4-amino-1,2-phenyl-
ene)bisacetamide (10.35 g, 0.05 mol) in 700 ml dry
acetonitrile containing suspended powdered anhydrous
sodium carbonate (21.20 g, 0.20 mol) was heated to
reflux under an atmosphere of nitrogen for 15 days.
After cooling, the solid was filtered and washed with
acetonitrile, and the filtrate was evaporated to dryness
on a rotary evaporator. The residue was then dissolved
in dichloromethane, purified by column chromatogra-
phy on silica gel using CHCl3 as eluent and the product
d 3.62ꢁ
(m, 4H, crown ether protons), 6.52ꢁ
phenyl protons), 8.58 (s, 1H, ꢀCHꢁNꢀ
CHꢁNꢀ), 13.12 (s, 1H, ꢀOH, disappeared upon D2O
OH, disappeared upon D2O
/
3.65 (m, 12H, crown ether protons), 3.88ꢁ
7.40 (m, 11H,
), 8.63 (s, 1H,
/
3.92
/
/
/
/
ꢀ
/
/
/
/
exchange), 13.41 (s, 1H, ꢀ
/
exchange). 13C NMR (125 MHz, CDCl3, 298 K, relative
to Me4Si): d 160.88, 157.28, 147.11, 136.59, 131.94,
131.46, 122.41, 119.79, 118.79, 111.87, 71.35, 70.26,
70.16, 68.53, 52.72. IR (Nujol mull, KBr, n cmꢂ1): 1618
n(Cꢁ
Found: C, 67.22; H, 6.53; N, 8.44. Calc. for
C28H31N3O5×1/2 H2O: C, 67.45; H, 6.47; N, 8.43%.
/
N). EI MS: m/z 489 {Mꢀ}. Elemental analyses,
1
was obtained as a white solid. Yield: 7.66 g, 42%. H
NMR (300 MHz, CDCl3 298 K, relative to Me4Si): d
/
2.09 (s, 3H, CH3CO), 2.12 (s, 3H, CH3CO), 3.51ꢁ
(m, 12H, crown ether protons), 3.74ꢁ3.80 (m, 4H,
crown ether protons), 6.54ꢁ6.57 (d, 1H, Jꢃ8.4 Hz
C6H3), 6.75 (s, 1H, C6H3), 7.02ꢁ7.05 (d, 1H, Jꢃ8.4 Hz,
/
3.67
/
2.2.5. Synthesis of N-(4-acetylphenyl)aza-12-crown-4
This was prepared by modification of a literature
method for the related N-phenylaza-12-crown-4 [14]. A
stirred solution of 1,11-diiodo-3,6,9-trioxaundecane
(20.50 g, 0.05 mol) and 4-aminoacetanilide (7.50 g,
0.05 mol) in 700 ml dry acetonitrile containing sus-
pended powdered anhydrous sodium carbonate (19.50
g, 0.18 mol) was heated under reflux under an atmo-
sphere of nitrogen for 20 days. After cooling, the solid
was filtered and washed with acetonitrile, and the
filtrate was concentrated on a rotary evaporator. The
residue was then dissolved in dichloromethane and
purified by column chromatography on silica gel, using
ethyl acetate as eluent. A white solid was obtained.
/
/
/
/
C6H3), 8.00 (s, 1H, CONH), 8.35 (s, 1H, CONH). EI
MS: m/z 365 {Mꢀ}. Elemental analyses, Found: C,
59.48; H, 7.51; N, 11.44. Calc. for C18H27N3O5: C,
59.16; H, 7.45; N, 11.50%.
2.2.3. Synthesis of N-(3,4-diaminophenyl)aza-12-crown-
4
In a 50 ml three-necked flask were placed N-(3,4-
diacetylphenyl)aza-12-crown-4 (1.46 g, 4.00 mmol) and
Claisen’s alkali (40 ml). The mixture was stirred and
allowed to heat to reflux for 24 h under a nitrogen
atmosphere. The resulting mixture was concentrated
under reduced pressure and extracted with dichloro-
methane. The solvent was evaporated to dryness and to
give a brown-colored oil. Subsequent recrystallization
from acetonitrile gave the product as brown crystals.
Yield: 1.00 g, 89%. 1H NMR (300 MHz, CDCl3, 298 K,
1
Yield: 7.45 g, 42%. H NMR (300 MHz, CDCl3 298 K,
relative to Me4Si): d 3.50ꢁ
protons), 3.81ꢁ3.84 (t, 4H, Jꢃ
protons), 6.64ꢁ6.67 (d, 2H, Jꢃ8.8 Hz, phenyl protons),
7.33ꢁ7.35 (d, 1H, Jꢃ8.8 Hz, phenyl protons), 7.87 (s,
/3.74 (m, 12H, crown ether
/
/5.0 Hz, crown ether
/
/
/
/
1H, NHCO). EI MS: m/z 355 {Mꢀ}. Elemental
analyses, Found: C, 62.67; H, 7.79; N, 9.22. Calc. for
C16H24N2O4: C, 62.32; H, 7.84; N, 9.08%.
relative to Me4Si): d 3.38ꢁ
protons), 3.54ꢁ3.67 (m, 8H, crown ether protons), 3.78ꢁ
3.86 (m, 4H, crown ether protons), 5.30 (s, 4H, NH2),
6.22ꢁ6.23 (d, Jꢃ2.5 Hz, 1H, C6H3), 6.59ꢁ6.62 (d, Jꢃ
8.3 Hz, 1H, C6H3), 6.74ꢁ6.78 (dd, Jꢃ8.3 Hz and Jꢃ
/3.44 (m, 4H, crown ether
/
/
/
/
/
/
2.2.6. Synthesis of N?-(4-aminophenyl)aza-12-crown-4
In a 50 ml three-necked flask were placed N-
(4-acetylphenyl)aza-12-crown-4 (1.77 g, 5.00 mmol)
and Claisen’s alkali (40 ml). The mixture was allowed
to reflux while stirring for 24 h under a nitrogen atmos-
phere. The resulting mixture was concentrated under
reduced pressure and extracted with dichloromethane.
The solvent was removed to give a brown-colored oil.
Subsequent recrystallization from acetonitrile gave the
product as brown crystals. Yield: 1.09 g, 82%. 1H NMR
/
/
/
2.5 Hz 1H, C6H3). EI MS: m/z 281 {Mꢀ}. Elemental
analyses, Found: C, 59.58; H, 8.27; N, 14.99. Calc. for
C14H23N3O3: C, 59.76; H, 8.24; N, 14.94%.
2.2.4. Synthesis of N?,Nƒ-bis(2-
hydroxyphenylmethylideneimino)-N-phenylaza-12-
crown-4 (H2L1)
This was prepared by modification of a literature
procedure for 4?,5?-bis(2-hydroxyphenylmethylideneimi-
(300 MHz, CDCl3, 298 K, relative to Me4Si): d 3.43ꢁ
/

52
X.-X. Lu et al. / Inorganica Chimica Acta 346 (2003) 49ꢁ56
/
3.46 (m, 4H, crown ether protons), 3.62ꢁ
crown ether protons), 3.77ꢁ3.81 (m, 4H, crown ether
6.68 (m, 4H, phenyl
/
3.68 (m, 8H,
2.2.9. Synthesis of N-(4-nitrosophenyl)aza-15-crown-5
This was prepared by modification of a literature
procedure [17]. N-Phenylaza-15-crown-5 (2.95 g, 10.00
mmol) was dissolved in 5 ml warmed hydrochloric acid
(37%), and ice (8.00 g) was then added and the mixture
was stirred at temperature below 5 8C. An aqueous
solution of NaNO2 (0.70 g, 10.00 mmol) in 2 ml H2O
was slowly added. After addition, the mixture was
stirred for 20 min. The mixture separated into two
layers upon addition of ice water (30 ml) and dichlor-
omethane (20 ml). The mixture was adjusted to basic
conditions upon vigorous stirring using saturated
Na2CO3. The aqueous layer was extracted with dichlor-
omethane several times. The dichloromethane extracts
that were green in color were combined, and dried over
anhydrous magnesium sulfate. After filtration, the
solvent was evaporated to dryness, leaving behind a
green residue. The residue was then dissolved in 15 ml
warmed acetone, and 20 ml petroleum ether was quickly
added. After cooling, green crystals were obtained.
/
protons), 5.30 (s, 2H, NH2), 6.64ꢁ
/
protons). EI MS: m/z 266 {Mꢀ}. Elemental analyses,
Found: C, 63.27; H, 8.29; N, 10.62. Calc. for
C14H22N2O3: C, 63.13; H, 8.33; N, 10.52%.
2.2.7. Synthesis of N?-(2-
hydroxyphenylmethylideneimino)-N-phenylaza-12-
crown-4 (HL2)
This procedure was similar to that described for the
synthesis of H2L1, except that N?-(4-aminophenyl)aza-
12-crown-4 (0.95 g, 3.56 mmol) was used in place of N-
(3,4-diaminophenyl)aza-12-crown-4 to react with salicy-
laldehyde (0.435 g, 3.56 mmol) to give bright yellow
needles. Yield: 1.12 g, 85%. 1H NMR (300 MHz, CDCl3,
298 K, relative to Me4Si): d 3.59ꢁ
ether protons), 3.86ꢁ3.89 (m, 4H, crown ether protons),
6.76ꢁ6.79 (d, 2H, Jꢃ9.0 Hz, phenyl protons), 6.88ꢁ
6.93 (t, 1H, Jꢃ7.4 Hz, phenyl protons), 6.98ꢁ7.00 (d,
1H, Jꢃ8.3 Hz, phenyl protons), 7.23ꢁ7.26 (d, 2H, Jꢃ
9.0 Hz, phenyl protons), 7.26ꢁ7.29 (d, 1H, Jꢃ8.3 Hz,
phenyl protons), 7.32ꢁ7.36 (t, 1H, Jꢃ7.4 Hz, phenyl
N), 13.77 (s, 1H, OH,
/3.65 (m, 12H, crown
/
/
/
/
1
/
/
Yield: 2.50 g, 77%. H NMR (300 MHz, CDCl3, 298
/
/
/
K, relative to Me4Si): d 3.60ꢁ
protons), 3.67ꢁ3.70 (m, 8H, crown ether protons), 3.73ꢁ
3.77 (m, 4H, crown ether protons), 3.79ꢁ3.85 (m, 4H,
6.72 (m, 4H, phenyl pro-
/3.63 (m, 4H, crown ether
/
/
/
/
/
/
/
protons), 8.61 (s, 1H, CHꢁ
/
crown ether protons), 6.69ꢁ
/
disappeared upon D2O exchange). 13C NMR (125
MHz, CDCl3, 298 K, relative to Me4Si): d 155.46,
154.87, 149.52, 147.35, 138.89, 136.48, 124.23, 123.18,
121.34, 111.73, 71.35, 70.24, 70.15, 68.57, 52.73. IR
tons). EI MS: m/z 324 {Mꢀ}.
2.2.10. Synthesis of N-(4-aminophenyl)aza-15-crown-5
This was prepared by modification of a literature
procedure [17]. SnCl2 (2.60 g, 14.00 mmol) was dissolved
in 3 ml hydrochloric acid (37%) and 1.6 ml water. N-(4-
Nitrosophenyl)aza-15-crown-5 (1.60 g, 4.90 mmol) was
then added in portions under stirring at 40 8C. Water
(20 ml) was added to dilute the solution after 20 min and
the mixture was allowed to continue stirring for another
30 min. After addition of NaOH (40%), the crude
product appeared as a brown oil. The mixture was
extracted with dichloromethane several times and the
combined dichloromethane extracts were dried over
anhydrous magnesium sulfate. After filtration, the
solvent was evaporated to dryness leaving brown oils.
Subsequent recrystallization from acetonitrile gave the
(Nujol mull, KBr, n cmꢂ1): 1616 (s) n(Cꢁ
/
N). EI MS: m/
z at 370 {Mꢀ}. Elemental analyses, Found: C, 67.98; H,
7.04; N, 7.54. Calc. for C21H26N2O4: C, 68.09; H, 7.07;
N, 7.56%.
2.2.8. Synthesis of N-phenylaza-15-crown-5
This was prepared by modification of a literature
procedure [17]. A two-necked flask equipped with a
dropping funnel was evacuated and refilled with nitro-
gen, and then 300 ml dry THF and NaH (6.40 g, 0.16
mol) were added and refluxed. N-phenyldiethanolamine
(13.57 g, 0.08 mol) and diethylene glycol ditosylate
(34.39 g, 0.08 mol) were dissolved in 300 ml dry THF
and then slowly added dropwise to the reaction mixture.
Addition was completed in 3 h, and refluxing was
continued for another 24 h. After cooling, the solid
was filtered and washed with THF, and the filtrate was
concentrated on a rotary evaporator. The red residue
was then dissolved in dichloromethane and purified by
column chromatography on silica gel, using diethyl
ether as eluent. Yield, 7.45 g, 42%. 1H NMR (300
1
product as brown crystals. Yield: 1.2 g, 78%. H NMR
(300 MHz, CDCl3, 298 K, relative to Me4Si): d 3.42ꢁ
3.50 (m, 4H, crown ether protons), 3.63ꢁ3.74 (m, 16H,
6.63 (m,
/
/
crown ether protons), 5.30 (s, 2H, NH2), 6.55ꢁ
/
4H, phenyl protons). EI MS: m/z 310 {Mꢀ}.
2.2.11. Synthesis of N?-(2-
hydroxyphenylmethylideneimino)-N-phenylaza-15-
crown-5 (HL3)
MHz, CDCl3 298 K, relative to Me4Si): d 3.57ꢁ
16H, crown ether protons), 3.68ꢁ3.77 (m, 4H, crown
ether protons), 6.63ꢁ6.67 (m, 3H, phenyl protons),
7.17ꢁ7.25 (d, 1H, Jꢃ7.3 Hz, phenyl protons). EI MS:
m/z 295 {Mꢀ}.
/
3.65 (m,
This procedure was similar to that described for the
synthesis of H2L1, except N?-(4-aminophenyl)aza-15-
crown-5 (1.10 g, 3.56 mmol) was used in place of N-(3,4-
diaminophenyl)aza-12-crown-4 to give bright yellow
needles. Yield: 1.24 g, 84%. 1H NMR (300 MHz,
/
/
/
/

X.-X. Lu et al. / Inorganica Chimica Acta 346 (2003) 49ꢁ
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53
CDCl3, 298 K, relative to Me4Si): d 3.6 (m, 16H, crown
ether protons), 3.8 (m, 4H, crown ether protons), 6.68ꢁ
6.71 (d, 2H, Jꢃ8.9 Hz, phenyl protons), 6.88ꢁ6.93 (t,
1H, Jꢃ7.5 Hz, phenyl protons), 6.98ꢁ7.00 (d, 1H, Jꢃ
8.2 Hz, phenyl protons), 7.24ꢁ7.27 (d, 2H, Jꢃ8.9 Hz,
phenyl protons), 7.27ꢁ7.28 (d, 1H, Jꢃ8.2 Hz, phenyl
protons), 7.31ꢁ7.36 (t, 1H, Jꢃ7.5 Hz, phenyl protons),
8.6 (s, 1H, CHꢁN), 13.8 (s, 1H, ꢀOH, disappeared upon
2.3. Crystal structure determination
/
/
/
Crystal
[C46H58N4O10Co], F.W.ꢃ
data
for
Co(L3)2:
885.89, monoclinic, space
formulaꢃ
/
/
/
/
/
˚
˚
/
/
group Cc, aꢃ
/
21.552(5) A, bꢃ
908, bꢃ129.724(4)8, gꢃ
1.275 g cmꢂ3, m(Mo Ka)ꢃ
1876, Tꢃ294(2) K; Rꢃ0.0616, wRꢃ
0.1197 for 9435 reflections with I ꢀ2s(I), goodness-of-
fitꢃ1.038. A crystal with dimensions of 0.16ꢄ0.14ꢄ
0.10 mm was mounted on a Bruker CCD area detector
/
19.148(4) A, cꢃ
908, Vꢃ4613.9(18)
4.32
/14.536
˚
/
/
(3) A, aꢃ
/
/
/
/
3
˚
/
/
A , Zꢃ
/
4, Dcalc
ꢃ
/
/
/
/
cmꢂ1, F(000)ꢃ
/
/
/
/
D2O exchange). 13C NMR (125 MHz, CDCl3, 298 K,
relative to Me4Si): d 160.88, 157.28, 147.11, 136.59,
131.94, 131.46, 122.41, 119.79, 118.79, 111.87, 71.35,
70.26, 70.16, 68.53, 52.72. IR (Nujol mull, KBr, n
/
/
/
/
˚
diffractometer using Mo Ka radiation (lꢃ
from generator operating at 50 kV, 30 mA condition.
The intensity data were collected in the range of 2uꢃ
2.80ꢁ27.568; h: ꢂ27ꢁ27; k: ꢂ24ꢁ17; l: ꢂ18ꢁ17 with
oscillation frames of f and V in the range 0ꢁ1808.
/
0.71073 A)
cmꢂ1): 1616 n(Cꢁ
Elemental analyses, Found: C, 63.57; H, 7.47; N, 6.34.
Calc. for C23H30N2O5×H2O: C, 63.87; H, 7.46; N,
6.48%.
/
N). EI MS: m/z at 414 {Mꢀ}.
/
/
/
/
/
/
/
/
/
/
Frames of 1876 were taken in four shells. A self-
consistent absorption correction of SADABS program
[18] based on Fourier coefficient fitting was applied. The
structure was determined by the direct method, which
yielded the positions of part of the non-hydrogen atoms
and subsequent difference Fourier syntheses were em-
ployed to locate all of the remaining non-hydrogen
atoms, which did not show up in the initial structure. All
2.2.12. Synthesis of Co(L1)
This complex was prepared by modification of a
literature procedure for the related [Co(salen)] com-
plexes [16]. Co(OAc)2×
/
4H2O (51 mg, 0.20 mmol) dis-
solved in ethanol (100 ml) was added to H2L1 (100 mg,
0.20 mmol) dissolved in 10 ml ethanol. The mixture was
refluxed for 8 h under nitrogen atmosphere. After
evaporation of the solvent, the red brown residue was
dissolved in dichloromethane, and the solution was
filtered through Celite to remove metallic cobalt. The
filtrate was reduced in volume to 5 ml, and subsequent
diffusion of diethyl ether vapor into the concentrated
solution gave Co(L1) as red crystals. Yield: 95 mg, 87%.
non-hydrogen atoms were refined anisotropically with
(0.0300p)2ꢀ
0.0000p]
2
weight function wꢃ
/
1/[s2(F0 )ꢀ
/
/
2
2
(pꢃ
/
(F0 ꢀ2Fc )/3), except the C and O atoms of the
/
disordered aza-crown ethers which were refined isotro-
pically. Hydrogen atoms were located based on differ-
ence Fourier syntheses coupled with geometrical
analysis. All the analyses and computations were
performed on a PC computer using the programs of
Bruker Smart and Bruker SHELXTL package [18]. The
final difference Fourier map was featureless, with
IR (Nujol mull, KBr, n cmꢂ1): 1614 (s) n(Cꢁ
/
N).
Positive FAB MS: m/z at 547 {Mꢀ}. Elemental
analyses, Found: C, 61.50; H, 5.27; N, 7.88. Calc. for
C28H29N3O5Co: C, 61.54; H, 5.35; N, 7.69%.
maximum positive and negative peaks of 0.343 and
˚
ꢂ
/
0.229 e Aꢂ3, respectively.
2.2.13. Synthesis of Co(L2)2
3. Results and discussion
The procedure was similar to that described for the
preparation of Co(L1) except HL2 (148 mg, 0.40 mmol)
was used in place of H2L1 to give red crystals. Yield: 116
Three new azacrown-ether substituted salicylaldimine
Schiff base ligands, namely H2L1, HL2 and HL3, have
been synthesized, which represents an extension of the
work on the all-oxygen crown ether ligands previously
reported by Qin and co-workers [11,12,16]. For the
synthesis of H2L1, which consisted of a monoaza-12-
crown-4, the first step was the reduction of the N,N?-(4-
nitro-1,2-phenylene)bisacetamide using iron powder in
the presence of a few drops of acetic acid as catalyst
(Scheme 1). The incorporation of the monoaza-12-
crown-4 pendant is simple and straightforward, involv-
ing the reaction between primary amines and 1,11-
diiodo-3,6,9-trioxaundecane in acetonitrile solution con-
taining Na2CO3. Cyclization of N,N?-(4-amino-1,2-
phenylene)bisacetamide, followed by hydrolysis using
mg, 73%. IR (Nujol mull, KBr, n cmꢂ1): 1610 (s) n(Cꢁ
/
N). Positive FAB MS: m/z at 798 {Mꢀ}. Elemental
analyses, Found: C, 63.10; H, 6.43; N, 6.99. Calc. for
C42H50N3O5Co: C, 63.23; H, 6.32; N, 7.02%.
2.2.14. Synthesis of Co(L3)2
The procedure was similar to that described for the
preparation of Co(L1), except HL3 (166 mg, 0.40 mmol)
was used in place of H2L1 to give red crystals. Yield: 133
mg, 75%. IR (Nujol mull, KBr, n cmꢂ1): 1610 (s) n(Cꢁ
/
N). Positive FAB MS: m/z at 886 {Mꢀ}. Elemental
analyses, Found: C, 62.37; H, 6.73; N, 6.33. Calc. for
C46H58N4O10Co: C, 62.36; H, 6.60; N, 6.32%.
the Claisen’s alkali (KOH:H2O:MeOHꢃ8:63:250)
/

54
X.-X. Lu et al. / Inorganica Chimica Acta 346 (2003) 49ꢁ56
/
Scheme 3. Synthetic scheme of N?-(2-hydroxyphenylmethylideneimi-
no)-N-phenylaza-15-crown-5 (HL3).
3.1. Crystal structure determination
Scheme 1. Synthetic scheme of N?,Nƒ-bis(2-hydroxyphenylmethylide-
neimino)-N-phenylaza-12-crown-4 (H2L1).
Single crystals of Co(L3)2 were obtained by vapor
diffusion of diethyl ether into a concentrated dichlor-
omethane solution of the complex. The perspective
drawing of Co(L3)2 with atomic numbering is depicted
in Fig. 2. The crystal structure determination data are
summarized in Table 1 and selected bond distances and
angles tabulated in Table 2. During the structure
determination, attempts to select a space group of
higher symmetry (C2/c) have been made because of
the symmetric nature of the molecular structure. How-
ever, the highly disordered nature of the atoms in the
aza-crown ether moieties and the unusually high R value
(ca. 0.32) obtained, indicate that the C2/c space group
was not appropriate, and a space group of lower
symmetry (Cc) was chosen instead. The bond lengths
would give the key intermediate N-(3,4-diaminophen-
yl)aza-12-crown-4. The condensation of N-(3,4-diami-
nophenyl)aza-12-crown-4 with salicylaldehyde gave the
ligand as an N2O2 donor with a monoaza-12-crown-4
unit. HL2 was similarly obtained (Scheme 2). For N?-(4-
aminophenyl)aza-12-crown-4 and N-(3,4-diaminophe-
nyl)aza-12-crown-4, the amino groups were first intro-
duced into the benzene ring using mono-protected 4-
aminoacetanilide or biprotected N,N?-(4-amino-1,2-
phenylene)bisacetamide as the starting material. How-
ever, for N?-(4-aminophenyl)aza-15-crown-5, the amino
group was introduced into the benzene ring after
cyclization of N-phenyldiethanolamine. After cycliza-
tion of N-phenyldiethanolamine, direct nitration fol-
lowed by a reduction of nitroaza-15-crown-5 according
to modification of a literature method [17] gave the
aminoaza-15-crown-5 (Scheme 3). The complexes
Co(L1) was prepared in good yield from the reaction
Table 1
Crystal and structure determination data for Co(L3)2
Formula
Formula weight
Temperature (K)
C46H58N4O10Co
885.89
294(2)
of Co(OAc)2×
ratio of 1:1 in ethanol under reflux condition. Reaction
of Co(OAc)2×4H2O with the corresponding ligands in
/4H2O and the corresponding ligand in the
˚
a (A)
21.552(5)
19.148(4)
14.536(3)
90
˚
/
b (A)
˚
c (A)
the ratio of 1:2 under the same condition gave Co(L2)2
and Co(L3)2. The IR, FAB mass spectra and elemental
analyses of compounds Co(L1), Co(L2)2 and Co(L3)2
confirmed the formation of the cobalt(II) complexes
with azacrown-ether substituted salicylaldimine Schiff
base ligands. The IR spectra (KBr discs) of the
complexes show bands that occur almost at the same
frequencies as the ligand absorptions with the exception
a (8)
b (8)
g (8)
129.724(4)
90
3
˚
V (A )
4613.9(18)
monoclinic
Cc
Crystal system
Space group
Z
4
1876
F(000)
Dcalc (g cmꢂ3
)
1.275
Crystal dimensions (mm)
0.16ꢄ
l (A) (graphite monochromated, Mo Ka) 0.71073
m (Mo Ka) (cmꢂ1
4.32
2.80ꢁ
24ꢁ
/
0.14ꢄ0.10
/
of the n(Cꢁ
/
N) stretch, which is shifted slightly (ca. 5ꢁ10
/
˚
cmꢂ1) to lower frequency after complex formation.
)
Collection range (8)
/
27.56 (h: ꢂ
17; l: ꢂ18ꢁ
/
27ꢁ
/
27; k:
ꢂ/
/
/
/
17)
Number of data collected
Number of unique data
Number of data used in refinement, m
Number of parameters refined, p
Ra
15 335
9435
9435 [Rint
635
ꢃ/0.0487]
0.0616
0.1197
1.038
Rwa
Goodness-of-fit, S
Residual extrema in final difference
ꢂ3
ꢀ
/
0.343 and ꢂ0.229
/
˚
map (e A
Scheme 2. Synthetic scheme of N?-(2-hydroxyphenylmethylideneimi-
no)-N-phenylaza-12-crown-4 (HL2).
)

X.-X. Lu et al. / Inorganica Chimica Acta 346 (2003) 49ꢁ
/56
55
Table 2
Selected bond lengths (A) and bond angles (8) for Co(L3)2
Table 3
Electronic absorption spectral data for crown ether-containing cobal-
t(II) complexes in acetonitrile at 298 K
˚
Coꢀ
Coꢀ
O(1)ꢀ
N(1)ꢀ
N(2)ꢀ
C(6)ꢀ
C(1)ꢀ
/
N(1)
1.9086(19) Coꢀ
/
N(2)
2.0329(19)
1.883(2)
1.316(2)
1.496(3)
1.408(3)
1.375(4)
1.395(3)
/O(1)
1.898(2)
Coꢀ
/O(2)
Compound Absorption l (nm) o (dm3 molꢂ1 cmꢂ1
)
/C(1)
1.2938(19) O(2)ꢀC(24)
/
H2L1
Co(L1)
HL2
262 (21 000), 346 (14 600), 396 (17 900)
/
C(7)
C(30)
C(7)
C(6)
1.299(2)
1.307(2)
1.532(4)
1.398(3)
N(1)ꢀ
/C(8)
256 (30 000), 320 (9700), 390 (12 400), 428(11 600)
251 (24 700), 332 (7400), 392 (24 700)
251(41 600), 331 (16 500), 414 (33 900)
250 (15 200), 330 (7650), 390 (24 280)
250 (22 120), 330 (9100), 408 (17 830)
/
N(2)ꢀ
/C(31)
/
C(29)ꢀ
C(24)ꢀ
/C(30)
Co(L2)2
HL3
Co(L3)2
/
/C(29)
N(1)ꢀ
O(1)ꢀ
O(2)ꢀ
CoꢀO(1)ꢀ
CoꢀN(1)ꢀ
O(1)ꢀC(1)ꢀ
O(1)ꢀC(1)ꢀ
/
Coꢀ
Coꢀ
Coꢀ
/
N(2)
110.54(7)
96.49(8)
O(1)ꢀ
O(1)ꢀ
/
Coꢀ
Coꢀ
Coꢀ
O(2)ꢀ
N(2)ꢀ
O(2)ꢀC(24)ꢀ
O(2)ꢀC(24)ꢀ
/
O(2)
N(2)
N(2)
C(24)
116.87(7)
118.27(10)
97.30(8)
/
/
N(1)
N(1)
C(1)
/
/
/
/
118.63(10) O(2)ꢀ
126.40(17) Coꢀ
125.7(2)
117.6(2)
125.1(2)
/
/
/
/
/
/
124.26(18)
117.46(19)
119.0(2)
ture of Co(L3)2 shown in Fig. 1 indicates that the two
Schiff base ligands with crown ether pendants are linked
by cobalt atom to form a rare butterfly structure.
/
/
C(7)
C(2)
C(6)
Coꢀ
/
/
C(30)
C(25)
C(29)
/
/
/
/
/
/
/
/
125.3(2)
3.2. Absorption spectra
from both nitrogen atoms to the cobalt center are
˚
slightly different [Coꢀ
/
N(1) 1.9086 A, Coꢀ/N(2) 2.0329
The UVꢁVis spectral dates for the free and com-
/
˚
A]. Similar findings were observed for those found from
plexed azacrown-ether substituted salicylaldimine Schiff
base are shown in Table 3. All the compounds show
low-energy absorption bands at approximately 390ꢁ
nm and high energy bands at approximately 250ꢁ
nm. With reference to Khalaf et al. [20], the electronic
absorption spectra of the cobalt(II) complexes are
˚
both oxygen atoms [Coꢀ
/
O(1) 1.898 A, Coꢀ
A]. The six bond angles, N(1)ꢀCoꢀN(2), O(1)ꢀ
O(2), O(1)ꢀCoꢀN(1), O(1)ꢀCoꢀN(2), O(2)ꢀCoꢀ
and O(2)ꢀCoꢀN(2), are 110.54, 116.87, 96.49, 118.27,
/
O(2) 1.883
Coꢀ
N(1)
˚
/
/
/
/
/
430
262
/
/
/
/
/
/
/
/
/
118.63 and 97.308, respectively. The coordination geo-
metry at the cobalt atom of Co(L3)2 may best be
described as distorted tetrahedral with two bidentate
Schiff base ligands containing crown ether pendants
coordinated to the metal center. This is different from
that of the Schiff base cobalt complexes bridged by
ethylenediamine [19], in which the coordination about
the cobalt is essentially squared planar with the two
salicylideneiminate residues approaching approximate
dominated by the ligand-centerd pꢁ
transitions of the Schiff base ligands.
/
p* and nꢁp*
/
3.3. Cation-binding studies
Upon addition of LiClO4 to a solution of Co(L1) in
acetonitrile (0.1 mol dmꢂ3 nBu4NPF6), the electronic
absorption spectra showed UVꢁVis spectral changes
with well-defined isosbestic points (Fig. 2), while the
addition of NaClO4 and KPF6 caused only minor
changes in the absorption spectra. This suggests the
/
coplanarity. However, the plane formed by Coꢀ
C(1) in Co(L3)2 is approximately perpendicular to the
plane formed by CoꢀO(2)ꢀC(24). The molecular struc-
/
O(1)ꢀ
/
/
/
Fig. 1. Perspective drawing of Co(L3)2 with atomic numbering. Hydrogen atoms have been omitted for clarity. Thermal ellipsoids were shown at the
40% probability level.

56
X.-X. Lu et al. / Inorganica Chimica Acta 346 (2003) 49ꢁ56
/
Acknowledgements
V.W.-W.Y. acknowledges financial support from the
Research Grants Council and The University of Hong
Kong.
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˚
˚
1.5 A) [21], formation
the cavity size of 12-crown-4 (1.2ꢁ
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˚
˚
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/
upon addition of alkali and alkaline earth metal ions in
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Crystallographic data for the structural analysis have
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CB2
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
1EZ
(fax:
ꢀ
/
44-1223-336-033;
e-mail:
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¨