A new family of NxOx pyridine-containing macrocycles: Synthesis and characterization of their Y(III), Ln(III), Zn(II), and Cd(II) coordination compounds

Article abstract of DOI:10.1139/v03-214

Reaction between 2,6-bis(2-formylphenoxymethyl)pyridine and N,N-bis(3-aminopropyl)methylamine or tris(2-aminoethyl)amine has been used as the starting point for the synthesis of seven oxa-aza macrocyclic ligands, five of them never reported previously. They all feature different pendant arms, which provide a wide range of coordination possibilities. The Schiff base macrocycles L¹ and L⁴ and their reduced ligands L ² and L⁵ are derived from 2,6-bis(2-formylphenoxymethyl) pyridine and tris(2-aminoethyl)amine or N,N-bis(3-aminopropyl)methylamine, respectively. The reaction of L¹ with salicylaldehyde forms L ³, which features an imine bond in the pendant arm. The ligand L ⁵ has been the precursor for the pendant-armed L⁶ and L⁷, by alkylation of the free NH groups with methyl-imidazole or methyl-indole. By a template or a nontemplate approach, we have synthesized different mono- and dinuclear complexes with Y(III), Ln(III), Zn(II), and Cd(II) cations. Both the free macrocyclic ligands and their corresponding metal complexes have been characterized by microanalysis, IR, UV-vis, ¹H and ¹³C NMR spectroscopy, FAB mass spectrometry, MS electrospray, and conductivity measurements.

Full text of DOI:10.1139/v03-214

437
A new family of NxOy pyridine-containing
macrocycles: Synthesis and characterization of
their Y(III), Ln(III), Zn(II), and Cd(II) coordination
compounds
Carlos Lodeiro, Rufina Bastida, Emilia Bértolo, and Adolfo Rodríguez
Abstract: Reaction between 2,6-bis(2-formylphenoxymethyl)pyridine and N,N-bis(3-aminopropyl)methylamine or tris(2-
aminoethyl)amine has been used as the starting point for the synthesis of seven oxa-aza macrocyclic ligands, five of
them never reported previously. They all feature different pendant arms, which provide a wide range of coordination
possibilities. The Schiff base macrocycles L1 and L4 and their reduced ligands L2 and L5 are derived from 2,6-bis(2-
formylphenoxymethyl)pyridine and tris(2-aminoethyl)amine or N,N-bis(3-aminopropyl)methylamine, respectively. The
reaction of L1 with salicylaldehyde forms L3, which features an imine bond in the pendant arm. The ligand L5 has
been the precursor for the pendant-armed L6 and L7, by alkylation of the free NH groups with methyl-imidazole or
methyl-indole. By a template or a nontemplate approach, we have synthesized different mono- and dinuclear complexes
with Y(III), Ln(III), Zn(II), and Cd(II) cations. Both the free macrocyclic ligands and their corresponding metal com-
1
plexes have been characterized by microanalysis, IR, UV–vis, H and 13C NMR spectroscopy, FAB mass spectrometry,
MS electrospray, and conductivity measurements.
Key words: Schiff-base macrocycle, template synthesis, macrocyclic ligand complexes, lanthanide(III) complexes.
Résumé : On a utilisé la réaction de la 2,6-bis(2-formylphénoxyméthyl)pyridine avec la N,N-bis(3-aminopropyl)méthy-
lamine ou la tris(2-aminoéthyl)amine comme point de départ pour la synthèse de sept ligands oxa-aza macrocycliques,
dont cinq n’avaient pas été rapportés antérieurement. Ils comportent tous des bras pendants différents qui peuvent don-
ner lieu à des possibilités différentes de coordination. Les macrocycles à base de bases de Schiff, L1 et L4, ainsi que
leurs ligands réduits, L2 et L5, sont dérivés respectivement de la 2,6-bis(2-formylphénoxyméthyl)pyridine et de la tris(2-
aminoéthyl)amine ou de la N,N-bis(3-aminopropyl)méthylamine. La réaction du ligand L1 avec le salicylaldéhyde
conduit à la formation du ligand L3 qui comporte une liaison imine dans le bras pendant. Le ligand L5 est le précur-
seur des ligands L6 et L7 à bras pendant par l’alkylation des groupes NH libres à l’aide de méthyl-imidazole ou de mé-
thyl-indole. Utilisant des approches avec ou sans gabarit, on a réalisé la synthèse de différents complexes mono- et
dinucléaires comportant dans cations Y(III), Ln(III), Zn(II) et Cd(II). On a caractérisé les ligands macrocycliques libres
1
ainsi que leurs complexes métalliques correspondants par microanalyse, spectroscopies IR, UV–vis et RMN du H et
du 13C, par spectrométrie de masse par bombardement avec des atomes rapides (FAB) ou par ionisation par électroné-
bulisation.
Mots clés : base de Schiff macrocyclique, synthèse à l’aide de gabarit, complexes de ligands macrocycliques, com-
plexes de lanthanide(III).
[Traduit par la Rédaction] Lodeiro et al. 447
Introduction
macrocycles involving N-methyl-pyridine, N-methyl-indole,
or N-methyl-imidazole have been prepared and their coordi-
nation ability towards divalent and trivalent metal anions
evaluated (8–11).
The synthesis of new receptors with pendant arms that
have aromatic or aliphatic units is a fascinating area of re-
search because of the importance of these receptors both in
basic and applied chemistry. A subject of special interest is
Pyridine-containing macrocycles have always attracted
considerable interest because of their versatility. They can be
used as building blocks that lead to more complicated struc-
tures, including systems with more than one cavity, three-
dimensional cages, and ligands with additional functional
groups attached to the macrocyclic skeleton (1–7). Some
Received 18 September 2003. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on 16 February 2004.
C. Lodeiro,1,2 R. Bastida, E. Bértolo, and A. Rodríguez. Departamento de Química Inorgánica. Universidad de Santiago de
Compostela. Avda. das Ciencias s/n. 15782 Santiago de Compostela, Galicia, Spain.
1Present address: REQUIMTE-CQFB, Departamento de Química, Faculdade de Ciências e Tecnología, Universidade Nova de
Lisboa, Quinta da Torre, 2829-516 Monte de Caparica, Portugal.
2Corresponding author (e-mail: lodeiro@dq.fct.unl.pt).
Can. J. Chem. 82: 437–447 (2004)
doi: 10.1139/V03-214
© 2004 NRC Canada

438
Can. J. Chem. Vol. 82, 2004
the design of homo- or hetero-binuclear complexes for bio-
medical applications that require covalent attachment of the
macrocycle system to a recognition site (12–16). Cytotoxic
studies of transition metal ion concentrations (i.e., cop-
per(II), zinc(II), and cadmium(II)) have also been carried out
using macrocyclic ligands with pendant arms (17, 18).
Lanthanide(III) ions have been employed as effective tem-
plate agents (19, 20) in the synthesis of large macrocycles
with pyridine head units.
the Eu(III), Tb(III), and Zn(II) complexes were measured on
a SPEX F111 Fluorolog spectrofluorometer.
Chemicals and starting materials
2,6-Bis(2-formylphenoxymethyl)pyridine was prepared
according to the method reported by Fenton and co-workers
(22). N,N-bis(3-aminopropyl)methylamine and tris(2-amino-
ethyl)amine, Y(III), Ln(III), Zn(II), and Cd(II) metal nitrates
and perchlorates were commercial products from Alfa and
Aldrich and were used without further purification. Salicyl-
aldehyde was a commercial product from Carlo Erba. 5-
Chloromethyl-4-methylimidazole hydrochloride and 3-
chloromethylindole were synthesized according to the litera-
ture method (23). Solvents were of reagent grade and were
purified by the usual methods. The synthesis of the free
imine macrocyclic ligands L1 and L4 has been reported in a
previous paper (24). Caution: Perchlorate salts are poten-
tially explosive.
In the present work, we describe the synthesis and charac-
terization of a new group of oxa-aza macrocyclic ligands
containing a pyridine head and phenyl lateral units (see
Fig. 1). The heptadentate Schiff base macrocycle L1 and its
corresponding reduced ligand L2 are derived from the reac-
tion between 2,6-bis(2-formylphenoxymethyl)pyridine (I)
and tris(2-aminoethyl)amine. Both macrocycles have a flexi-
ble amine pendant arm, with potential to form new macro-
cyclic ligands by condensation with different carbonylic
species. Very recently we have reported a related compound
of ligand L1 (21). In those cases the stability of the com-
plexes was increased by coordination of the flexible amine
pendant arm to the metal ions. In this work, we present the
reaction of L1 with salicylaldehyde to form L3, which fea-
tures an imine bond. The Schiff base ligand L4 has been
obtained by reaction between 2,6-bis(2-formylphenoxy-
methyl)pyridine and N,N-bis(3-aminopropyl)methylamine
and subsequently reduced to obtain L5. The ligand L5 has
been the precursor for the pendant-armed macrocycles L6
and L7 by alkylation reaction of the NH groups with methyl-
imidazole or methyl-indole. This thus covalently introduces
a biological substrate in the macrocycle skeleton. We have
studied the coordination capability of the macrocyclic lig-
ands towards different metallic ions. We report the synthesis
of the corresponding homodinuclear or mononuclear Y(III),
Ln(III), Zn(II), and Cd(II) complexes, using nitrate or per-
chlorate as the counter ions. Both a direct route and a tem-
plate approach have been used as required.
Synthesis of the reduced macrocycles L2 and L5
The two ligands were prepared by a modification of the
method reported in refs. 22 and 25. The corresponding
aliphatic polyamine (4.0 mmol) in warm solvent (100 cm3)
was slowly added to a solution of 2,6-bis(2-formylphenoxy-
methyl)pyridine (4.0 mmol) and Ba(ClO4)2·xH2O (4.0 mmol)
in warm solvent (300 cm3). The reaction mixture was
refluxed for 6 h, allowed to cool down, and then put in an
ice bath. Solid NaBH4 (55.0 mmol) was added carefully in
solid incremental amounts, with stirring. After the efferves-
cence stopped, a white precipitate was removed by filtration.
The filtrate was reduced to dryness by rotary evaporation,
and chloroform (150 cm3) was added; the resulting solution
was then stirred for ca. 72 h. A grey precipitate was removed
by filtration; the filtrate was then dried over anhydrous so-
dium sulphate, and subsequently the sodium sulphate was
removed by filtration. The filtrate was concentrated to ca.
10–15 cm3 and diethyl ether was added, producing the prod-
uct, which was filtrated (L2) or decanted (L5) and dried in
vacuo.
Experimental section
L2
Methods
Yellow solid. Amine: tris(2-aminoethyl)amine. Solvent:
methanol. Yield 64%. Melting point: 195–200 °C. IR (KBr
disc) ν(NH) (cm–1): 3200; ν(NH2) (cm–1): 3064, ν(C=C) and
ν(C=N) (cm–1): 1597, 1453. UV–vis spectrum (in CH3CN)
Elemental analyses were performed by the University of
Santiago de Compostela Microanalytical Service in Carlo
Erba 1108 and Leco CNHS-932 microanalysers. Infrared
spectra were recorded as KBr discs or in CsCl windows,
using a Mattson Cygnus 100 spectrophotometer. Proton and
carbon NMR spectra were recorded using a Bruker WM-
300. Positive ion FAB mass spectra were recorded on a
Kratos MS50TC spectrometer, using 3-nitrobenzyl alcohol
(MNBA), glycerol, or 2-hydroxyethyl disulfide matrixes.
Electrospray mass spectra were recorded using acetonitrile
and acetic acid mixture as solvent. Melting points were car-
ried out using a BÜCHI melting point apparatus. Conductiv-
ity measurements were carried out in 10–3 mol dm–3
acetonitrile or DMF solutions at 25 °C using a WTW LF-3
conductivimeter. The electronic absorption spectra of some
complexes and ligands (MeCN solutions) were measured in
the 220–850 nm range using a PerkinElmer Lambda 6
spectrophotometer, and the fluorescence emission spectra of
1
(λ(mn), ε((mol L–1)–1·cm–1): 269, 5344. H NMR (CD3CN)
(ppm) δ: 8.6 (t), 1H, (Py); 8.3 (d), 2H, (Py); 7.6 (d) 2H,
(C6H6); 7.5 (t), 2H, (C6H6); 7.3 (d), 2H, (C6H6); 7.1(t), 2H,
(C6H6); 5.6(s), 4H, (Py-CH2-O); 4.4(s), 4H, (Ph-CH2-NH);
3.6–3.2(m), 12H, (-CH2CH2); 5.00(sw), (-NH). 13C NMR
(CD3CN) (ppm) δ: 156.8, 156.0, 155.4, 137.6, 131.2, 130.3.
129.2, 128.7, 128.1, 127.7, 127.1, 126.1, 122.6, 121.9,
120.6, 112.7, 112.1, 97.1, 71.3, 61.7, 54.1, 53.3, 48.3, 47.8,
47.0, 45.6, 44.3. FAB-MS (positive-ion) m/z: 462 ([L2
+
H]+). Anal. calcd. for C27H35N5O2·3.5H2O (%): C 61.85, H
8.05, N 13.30; found: C 61.50, H 7.95, N 12.50.
The ligand is air stable and soluble in acetonitrile, abso-
lute ethanol, chloroform, dimethylformamide, and dimethyl-
sulfoxide; it is moderately soluble in dichloromethane and
insoluble in diethyl ether, petroleum ether, and water.
© 2004 NRC Canada

Lodeiro et al.
439
Fig. 1. Schematic diagram showing the synthetic route to obtain the different ligands. L1: 2-[3.25-dioxa-11.14.17.31-tetrazatetracyclo-
[25.3.1.O4.9.O19.24]hentriaconta-1(31).4(9).5.7.10.17.19(24).20.22.27.29-undecaen-14-yl]-1-ethanamine. L2: 2-[3.25-dioxa-11.14.17.31-tetra-
zatetracyclo[25.3.1.O4.9.O19.24]hentriaconta-1(31).4(9).5.7.10.17.19(24).20.22.27.29-nonaen-14-yl]-1-ethanamine. L3: 2-[({2-[3.25.dioxa-
11.14.17.31-tetraazatetracyclo[25.3.1.O4.9.O19.24]hentriaconta-1(30).4(9).5.7.19(24).20.22.27(31).28-nonaen-14-yl]ethyl}imino)methyl]phe-
nol. L4: 15-methyl-3.27-dioxa-11.15.19.33-tetraazatetracyclo[27.3.1.O4.9.O21.26]tritiaconta-1(32).4(9).5.7.10.19.21(26).22.24.29(33).30-undecane.
L5: 15-methyl-3.27-dioxa-11.15.19.33-tetraazatetracyclo[27.3.1.O4.9.O21.26]tritiaconta-1(32).4(9).5.7.10.19.21(26).22.24.29(33).30-nonaene.
L6: 15-methyl-11.19-di[(5-methyl-1H-4-imidazolyl)methyl]-3.27-dioxa-11.15.19.33-tetraazatetracyclo[27.3.1.O4.9.O21.26]tritiaconta-
1(32).4(9).5.7.21(26).22.24.29(33).30-nonaene. L7: 11.19-di(1H-5-indolylmethyl)-15-methyl-3.27-dioxa-11.15.19.33-tetraazatetracyclo-
[27.3.1.O4.9.O21.26]tritiaconta-1(32).4(9).5.7.21(26).22.24.29(33).30-nonaene.
© 2004 NRC Canada

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Can. J. Chem. Vol. 82, 2004
ing 1 h. After the effervescence disappeared, 2 mmol of L5
dissolved in 50 cm3 of dry acetonitrile was slowly added.
The reaction was then kept at 50 °C in a silicone bath during
5 days, with vigorous stirring and under the nitrogen atmo-
sphere. After 5 days, the solution was filtered, and the fil-
trate was reduced to dryness. The crude product was then
dissolved in water–chloroform and extracted with 3 ×
25 cm3 of CHCl3. The organic phase was washed twice with
2 × 40 cm3 of water and dried with anhydrous Na2SO4. The
solution was then filtered and reduced to give an oil.
L5
Pale yellow oil. Amine: N,N-bis(3-aminopropyl)methyl-
amine. Solvent: absolute ethanol. Yield 58%. IR (CsCl win-
dows) ν(NH) (cm–1): 3290, ν(C=C) and ν(C=N) (cm–1):
1595, 1454. UV–vis spectrum (in CH3CN) (λ(mn),
ε((mol L–1)–1·cm–1)): 266, 3595. H NMR (CDCl3) (ppm) δ:
1
7.78 (t), 1H, (Py); 7.6 (d), 2H, (Py); 7.4–6.7 (m), 8H,
(C6H6); 5.0 (s) 4H, (Py-CH2-O); 3.7 (m) 4H, (Ph-CH2-NH);
2.5 (t), 4H, (-CH2CH2CH2); 2.3 (t), 4H, (-CH2CH2CH2); 1.5
(m), 4H, (-CH2CH2CH2); 1.7 (s), 3H, (-CH3). 13C NMR
(CDCl3) (ppm) δ: 155.2, 155.1, 154.8, 154.5, 135.9, 129.0,
128.2, 127.3, 127.1, 126.8, 126.4, 119.5, 119.2, 110.3,
109.8, 69.3, 55.0, 54.9, 54.5, 54.3, 54.0, 53.8, 49.2, 46.3,
40.6, 39.6, 38.9, 29.3. FAB-MS (positive-ion) m/z (%): 461
([L5 + H]+, 100), 921 ([2 + 2]+, 10). Anal. calcd. for
C28H36N4O2·3H2O (%): C 65.35, H 9.05, N 10.90; found: C
65.65, H 9.20, N 10.60.
L6
Orange-yellow oil. Yield 26%. IR (CsCl windows)
ν(NH)imid (cm–1): 3331, ν(C=C) and ν(C=N) (cm–1): 1597,
1456. H NMR (CDCl3) (ppm) δ: 7.70 (t), 1H, (Py); 7.3 (d),
1
1H, (NHCHNimid); 7.5–6.8 (m), 10H, (Py+C6H6); 5.1 (d)
4H, (Py-CH2-O); 3.9 (d) 4H, (Ph-CH2-N); 3.6 (d), 4H, (CH2Imi);
2.6 (m), 4H, (-CH2CH2CH2); 2.3 (m), 4H, (-CH2CH2CH2);
1.8 (m), 4H, (-CH2CH2CH2); 1.9 (s), 3H, (-CH3); 1.6 (s),
3H, (-CH3), 1.2 (s), 3H, (-CH3). 13C NMR (CDCl3) (ppm) δ:
157.4, 157.1, 156.8, 156.6, 156.0, 155.7, 155.3, 139.0,
132.5, 132.0, 131.8, 130.7, 128.4, 127.2, 126,5, 124.4,
123.8, 123.6, 122,6, 122.4, 121.6, 119.9, 119.8, 113.8, 77.5,
71.6, 55.9, 54.9, 53.9, 47.4, 46.3, 41.5, 40.4, 29.7, 22.9,
22.2, 9.8, 8.9. MS (electrospray) m/z (%): 650 ([L6 + H]+,
35), 555 ([L6 – (C5H6N2)]+, 25), 461 ([L6 – 2(C5H6N2)]+,
65). Anal. calcd. for C38H48N8O2·2H2O (%): C 66.65, H
7.65, N 16.35; found: C 66.65, H 7.70, N 16.65.
The ligand is air stable and soluble in acetonitrile, abso-
lute ethanol, chloroform, dimethylformamide, and dimethyl-
sulfoxide. It is moderately soluble in dichloromethane and
benzene and is insoluble in diethyl ether, petroleum ether, n-
hexane, and water.
Synthesis of the scorpionand macrocycle L3
A fresh solution of L1 (yellow oil) in absolute ethanol
(75 cm3) was refluxed during 30 min; an ethanolic solution
of salicylaldehyde (1.02 mmol) was then added dropwise.
The resulting solution, with an intense yellow colour, was
refluxed with magnetic stirring for ca. 4 h. After cooling
over ice, it was filtered off and reduced to dryness by rotary
evaporation. The intense yellow oil obtained was dried under
vacuum for 2 h.
L7
Dark yellow oil. Yield 31%. IR (CsCl windows)
ν(NH)indol (cm–1): 3408; δ(NH)indol (cm–1): 3266, ν(C=C) and
ν(C=N) (cm–1): 1596, 1454. H NMR (CDCl3) (ppm) δ: 7.9–
1
6.8 (t), 21H, (aromatics); 5.3 (d), 4H, (Py-CH2-O); 4.9 (s)
4H, (Ph-CH2-N); 3.9 (d) 4H, (CH2 . -Indol); 2.6–1.6 (m),
15H, (Aliphatics). 13C NMR (CD3CN) (ppm) δ: 169.2,
168.8, 168.6, 168.2, 149.7, 148.7, 142.7, 140.7, 140.4,
139.9, 139.2, 136.3, 133.5, 133.3, 133.2, 132.9, 132.8,
131.0, 130.8, 128.8, 124.2, 123.8, 123.5, 123.4, 90.3, 90.0,
89.9, 89.8, 89.3, 82.5, 82.2, 76.7, 76.4, 68.9, 68.2, 67.7,
62.2, 59.4, 53.6, 52.8, 38.8, 38.3, 33.9, 30.0, 27.1, 12.0. MS
L3
Yield 80%. Intense yellow oil. IR (CsCl windows) ν(OH)
(cm–1): 3412, ν(NH) (cm–1): 3292, ν(C=N)imi (cm–1): 1630,
ν(C=C) and ν(C=N) (cm–1): 1597, 1455. UV–vis spectrum
(in CH3CN) (λ(mn), ε((mol L–1)–1·cm–1)): 257, 12 444, 317,
1
2121. H NMR (CD3CN) (ppm) δ: 8.0 (s), 1H, (HC=Nimi);
7.6–6.6 (m), 15H, (aromatics); 4.9 (s) 4H, (Py-CH2-O); 4.8
(s), 4H, (Ph-CH2-NH); 3.5–3.4 (m), 12H, (-CH2CH2); 4.5
(sw), (-NH). 13C NMR (CD3CN) (ppm) δ: 166.4, 161.0,
160.9, 156.4, 156.3, 155.3, 138.1, 136.5, 133.3, 132.07,
131.3, 130.8, 129.6, 129.1, 126.6, 123.7, 121.1, 120.9,
120.3, 119.5, 118.1, 117.0, 112.6, 97.6, 69.9, 61.6, 59.0,
56.6, 55.7, 55.5, 48.7, 46.7, 45.7, 17.5. 13C NMR DEPT-135
(CD3CN) (ppm) (CH, CH3) δ: 167.2, 138.9, 137.4, 134.0,
132.8, 132.3, 132.1, 130.3, 129.9, 121.8, 121.1, 120.3,
117.96, 117.5, 113.5, 112.8, 97.9, (CH2) 71.5, 71.0, 62.2,
61.8, 57.4, 56.6, 53.9, 52.9, 51.9, 47.4, 46.0. FAB-MS
(positive-ion) m/z (%): 566 ([L3 + H]+, 100), 461 ([L3 –
(electrospray) m/z (%): 720 ([L7 + H]+, 25), 590 ([L7
–
(C9H8N)]+, 10), 461 ([L7 – 2(C9H8N)]+, 65). Anal. calcd. for
C46H50N6O2·3H2O (%): C 71.50, H 7.30, N 10.85; found: C
71.65, H 7.75, N 10.90.
The ligands are air stable and soluble in acetonitrile, abso-
lute ethanol, chloroform, dimethylformamide, and dimethyl-
sulfoxide. They are moderately soluble in dichloromethane
and insoluble in diethyl ether, petroleum ether, n-hexane,
and water.
Synthesis of the metal complexes
CH2N=CH(C6H4OH)],
33).
Anal.
calcd.
for
Template reaction of Schiff-base macrocycles L1 and L4
in the presence of metal ions: General procedure for
[ML][X]n (X = ClO4 or NO3 )
2,6-Bis(2-formylphenoxymethyl)pyridine (1 mmol) and
MXn·xH2O (1 mmol) (M = Y(III), Ln(III), Zn(II), or Cd(II))
were dissolved in hot methanol or absolute ethanol (30 cm3).
A solution of N,N-bis(3-aminopropyl)methylamine or tris(2-
aminoethyl)amine (1 mmol) in methanol or absolute ethanol
C34H39N5O3·3.5H2O (%): C 65.90, H 7.30, N 11.30; found:
C 65.85, H 7.45, N 10.60.
–
–
Synthesis of the di-pendant-armed macrocycles L6 and L7
Four millimoles of freshly prepared 5-chloromethyl-4-
methylimidazole hydrochloride or 3-chloromethylindole
were mixed with triethylamine in 50 cm3 of dry acetonitrile
under a nitrogen atmosphere. The mixture was refluxed dur-
© 2004 NRC Canada

Lodeiro et al.
441
Table 1. Analysis, yield, and molar conductance (in CH3CN) data for the complexes [MmL1–2–3][X]n·xH2O.
Elemental analysis (%)a
M
L
m
n
x
X
C
N
H
Yield (%) ΛM/Ω–1 (cm2·mol–1) Colour
(L1 = C27H31N5O2)
La
Zn
Cd
L1
L1
L1
1
1
2
3
2
4
10 ClO4
30.70 (30.20)
41.05 (40.85)
27.40 (27.70)
6.95 (6.50)
5.25 (4.80) 34
5.20 (4.95) 35
3.75 (3.50) 18
295
125
238
Yellow
–
–
–
4
5
ClO4
ClO4
9.10 (8.80)
5.50 (5.95)
Orange-yellow
Yellow
(L2 = C27H35N5O2)
L2
L2
1
1
1
1
1
1
1
3
3
3
3
3
3
3
2
5
6
9
2
8
5
NO3
NO3
NO3
42.35 (42.00) 14.75 (14.50) 5.25 (5.10) 43
37.45 (37.00) 12.95 (12.80) 4.50 (5.15) 18
35.55 (35.80) 12.30 (12.35) 4.95 (5.20) 59
119
123
121
222
236
247
285
Pale yellow
Pale yellow
Pale yellow
Yellow
–
Y
–
La
Sm L2
–
L2
L2
L2
L2
ClO4
ClO4
ClO4
ClO4
30.00 (30.55)
35.00 (34.65)
30.45 (30.55)
32.30 (31.90)
6.60 (6.60)
7.00 (7.50)
6.75 (6.60)
6.25 (6.85)
4.80 (5.05) 25
4.35 (4.20) 63
4.60 (4.85) 42
4.20 (4.45) 44
–
–
–
–
La
Ce
Gd
Er
Yellow-gold
Pale yellow
Yellow-orange
(L3 = C34H39N5O3)
L3
L3
L3
L3
1
1
1
2
1
2
3
3
3
6
3
4
7
6
5
5
7
4
NO3
NO3
ClO4
ClO4
ClO4
ClO4
39.50 (39.65) 10.70 (10.90) 5.35 (5.20) 52
39.80 (40.10) 10.25 (10.95) 4.85 (5.05) 46
137
127
277
369
284
265
Yellow
–
Eu
Tb
La
Pr
–
Dark yellow
Yellow
–
–
–
–
37.90 (37.35)
27.00 (26.60)
35.80 (35.80)
35.45 (35.00)
6.40 (6.40)
5.15 (4.55)
6.20 (6.15)
6.45 (6.00)
5.00 (4.55) 47
3.20 (3.20) 46
5.15 (4.70) 56
4.15 (4.05) 30
Yellow
Sm L3
Zn
L3
Yellow
Yellow
aRequired values are given in parentheses.
(25 cm3) was added dropwise; magnetic stirring and heating
was maintained during the addition. The solution was
refluxed for 3 to 4 h, allowed to cool to room temperature,
and then concentrated to ca. 15 cm3. The complexes precipi-
tated directly or after addition of diethyl ether (15 cm3); they
were filtered off and dried in vacuo. Microanalytical data are
given in Tables 1 and 2. The complexes are air stable and
soluble in acetone, dimethylformamide, methanol, acetoni-
trile, and dichloromethane. They are moderately soluble in
chloroform and insoluble in water and absolute ethanol.
Results and discussion
Synthesis of the free ligands
We have previously reported that direct reaction between
(I) with aliphatic or aromatic amines in the absence of tem-
plate agents is a valid method to obtain Schiff-base and oxa-
aza macrocyclic ligands (2, 19, 24). We now present seven
macrocyclic ligands derived from this dicarbonyl precursor
and two aliphatic diamines (mentioned in the starting mate-
rial section) and the study of the complexation capacity of
these ligands with a range of trivalent and divalent metal
ions. Ligands L1 and L4 were obtained by reaction of (I)
with both aliphatic diamines. These two macrocycles have
already been reported in a previous paper (24).
Direct synthesis between L2, L3, L5, L6, and L7 and
divalent and trivalent metal ions: General procedure for
–
–
[ML][X]n (X = ClO4 or NO3 )
Using L1 and L4 as the starting point, we have prepared
five new macrocyclic ligands with different donor atom ar-
rays (see Fig. 1). L2 was synthesized by reduction of L1,
formed in situ using barium perchlorate, with sodium boro-
hydride. In a similar way, L5 was obtained from L4. The
pendant-armed macrocycle L3 was obtained by a Schiff-base
reaction between L2 and salicylaldehyde, with formation of
an iminic bond in the pendant arm. The ligands L6 and L7
were obtained by reaction of L5 with 5-chloromethyl-4-
methylimidazole hydrochloride and 3-chloromethylindole,
respectively, following the method described in the experi-
mental section.
The appropriate metal salt MXn·xH2O (Y(III), Ln(III),
–
–
Zn(II), or Cd(II) and X = NO3 or ClO4 ) (0.50 mmol) was
dissolved in methanol (for L2, L3, L5, and L7) or absolute
ethanol (for L6) (20 cm3) and added to a solution of the
ligand (0.50 mmol) in methanol (L2, L3, and L5) or chloro-
form (L6 and L7) (50 cm3). The mixture was stirred during
24–72 h at room temperature and cooled. When a precipitate
did not developed immediately, the solution was partially
concentrated under vacuum to give a solid, although in some
cases the precipitation was aided by addition of some diethyl
ether (ca. 5–10 cm3). The products were filtered off, washed
with cold absolute ethanol or methanol, and dried in vacuo.
Microanalytical data are given in Tables 1, 2, and 3. The
complexes are air stable and are soluble in acetone, metha-
nol, acetonitrile, and dichloromethane. They are moderately
soluble in dimethylformamide and insoluble in chloroform,
water, and absolute ethanol.
We have found that the template approach is more effec-
tive for the preparation of L2 and L5, with yields of 64% and
58%, respectively. In previous papers, we have reported the
effectiveness of a direct approach in the synthesis of large
macrocycles, in which the presence of aromatic groups in
© 2004 NRC Canada

442
Can. J. Chem. Vol. 82, 2004
Table 2. Analysis, yield, and molar conductance (in CH3CN for L4 or in DMF for L5) data for the complexes [MmL4–5][X]n·xH2O.
Elemental analysis (%)a
M
L
m
n
x
X
C
N
H
Yield (%) ΛM/Ω–1 (cm2·mol–1) Colour
(L4 = C28H32N4O2)
Y
L4
L4
L4
L4
L4
L4
L4
L4
L4
L4
L4
1
2
1
1
1
1
1
1
1
2
1
3
6
3
3
3
3
3
3
3
4
2
5
NO3
NO3
NO3
NO3
NO3
NO3
40.45 (40.95) 12.20 (11.95) 5.05 (5.15) 53
30.05 (30.40) 12.30 (12.65) 2.90 (2.90) 58
42.25 (42.25) 11.50 (12.30) 4.50 (4.20) 87
42.75 (42.35) 11.90 (12.35) 3.90 (4.05) 57
38.80 (38.25) 11.05 (11.15) 5.00 (4.60) 91
40.06 (39.40) 11.05 (11.50) 4.05 (4.25) 51
158
264
144
124
137
147
247
232
224
220
158
Orange
Orange
Orange
Orange
Orange
Orange
Yellow
Yellow
Yellow
Yellow
Yellow
–
–
–
–
–
–
La
Nd
Eu
Ho
Lu
La
Ce
Er
—
0.5
—
4
2
–
–
–
–
–
4
ClO4
ClO4
ClO4
ClO4
ClO4
34.90 (34.80)
34.85 (34.80)
36.30 (35.75)
32.20 (32.90)
40.20 (40.05)
6.25 (5.80)
6.33 (5.80)
6.50 (5.95)
5.20 (5.50)
7.05 (6.70)
4.55 (4.15) 77
4.10 (4.20) 35
4.00 (3.65) 49
3.00 (3.55) 46
4.70 (4.80) 51
4
1
Zn
Cd
2
4
(L5 = C28H36N4O2)
L5
L5
L5
L5
L5
L5
L5
2
1
1
1
1
1
2
6
3
3
3
3
2
4
3
NO3
NO3
NO3
31.55 (31.60) 12.85 (13.15) 4.10 (4.00) 22
37.95 (37.85) 10.60 (11.00) 4.75 (5.20) 62
37.20 (36.80) 11.15 (10.70) 4.90 (5.30) 36
143
72
Pale yellow
Yellow
–
Y
–
Eu
Tb
La
Gd
Zn
Cd
5
–
6
67
Pale yellow
Yellow
–
–
–
–
6
ClO4
ClO4
ClO4
ClO4
33.15 (33.40)
34.90 (34.65)
46.00 (45.80)
31.40 (31.05)
5.90 (5.60)
5.85 (5.80)
7.65 (7.65)
5.70 (5.20)
4.60 (4.80) 68
4.20 (4.35) 39
4.80 (5.10) 68
3.25 (3.35) 43
172
179
79
3
Pale yellow
Yellow
0.5
—
67
Yellow
aRequired values are given in parentheses.
Table 3. Analysis, yield, and molar conductance (in DMF for L6 or in CH3CN for L7) data for the complexes [MmL6–7][X]n·xH2O.
Elemental analysis (%)a
M
L
m
n
x
X
C
N
H
Yield (%) ΛM/Ω–1 (cm2·mol–1)
Colour
(L6 = C38H48N8O2)
L6
L6
L6
2
2
1
6
6
3
5
4
7
NO3
NO3
35.35 (35.40)
32.40 (32.45)
37.70 (37.65)
15.30 (15.20)
13.90 (13.95)
9.35 (9.25)
4.55 (4.55)
4.50 (4.00)
5.30 (5.15)
22
26
31
236
274
240
Yellow
Yellow
Yellow
–
–
Y
Gd
La
–
ClO4
(L7 = C46H50N6O2)
L7
L7
2
6
4
7
ClO4
ClO4
32.00 (32.15)
44.75 (44.30)
5.25 (4.90)
7.15 (6.75)
4.10 (3.75)
3.60 (4.05)
63
32
365
273
Yellow
Yellow
–
–
La
Zn
2
—
aRequired values are given in parentheses.
both organic precursors helps to minimize the formation of
acyclic structures (19, 20). However, when the direct route
was used to prepare L2 and L5, the aliphatic nature of the
amine precursors seemed to increase the formation of unde-
sired acyclic compounds, and low yields were obtained for
both macrocycles. A template approach was thus chosen,
and we have found that the use of barium(II) as the template
agent increased the yields of the two macrocycles.
The FAB mass spectra for L2, L3, and L5, as well as the
electrospray mass spectra for L6 and L7, show the highest
molecular weight peaks at m/z 462 (L2), 566 (L3), 461 (L5),
650 (L6), and 720 (L7), corresponding to ([L + H]+). The IR
spectra feature the secondary amine N–H stretching band at
ca. 3200–3292 cm–1 (in L2, L3, and L5) or δ(NH)pyrrolic at ca.
3330–3400 cm–1 (in L6 and L7). The spectra for L2 and L5
do not show bands in the 1620–1640 cm–1 region, where
imine stretches are expected. The spectrum for L3 features a
band at ca. 1630 cm–1, owing to the imine group present in
the pendant arm. For L7 it is possible to observe a band at
ca. 3266 cm–1, attributable to δ(NH) of the indole group.
1
The H NMR spectra in CD3CN (for L2 and L3) and in
CDCl3 (for L5, L6, and L7) confirm the integrity of the lig-
ands in solution. The 13C NMR spectra for L2, L5, L6, and L7
feature 27, 28, 38, and 46 signals, respectively, one for each
C in the macrocyclic skeleton. This suggests that both the
reduction of the imine bonds and the presence of the pendant
arms lead to an increase in the ligand flexibility and unsym-
metrical behaviour of the ligands. UV–vis spectra in
acetonitrile were recorded for L2, L3, and L5. The broad ab-
sorption bands observed at 269 nm for L2, at 257 and
317 nm for L3, and at 266 nm for L5 can be attributed to the
π–π* transitions of the pyridine and phenyl groups.
© 2004 NRC Canada

Lodeiro et al.
443
cases, probably because of the small size of both ions when
compared with the lanthanide(III) cations. It is also notewor-
thy that the increase in the flexibility and complexity of the
ligands, from L1 to L3 and from L4 to L6 or L7, does not ap-
pear to affect especially the formation of the corresponding
complexes.
Molar conductivity data, measured at room temperature
using DMF or acetonitrile solutions, show the ionic nature
of all complexes in these solvents. The values are in accor-
dance with those expected for 1:1 or 1:2 electrolytes (for
complexes with L1, L2, L3, L4, and L5) or for 1:2 or 1:3 elec-
trolytes (L6 and L7 complexes) (26). The value for the com-
plex [Pr2L3](ClO4)6·5H2O, measured in acetonitrile, falls
between the ranges reported for 1:2 and 1:3 electrolytes.
Data for the different complexes are given in Tables 1, 2,
and 3. Molar conductivities were measured again 1 week af-
ter sample preparation for the complexes containing L2, L5,
and L6; a significant increase in the values was observed in
some complexes, suggesting the displacement of counter
ions from the coordination sphere by solvent molecules (26).
Metal complexes: Microanalytical and molar
conductivity data
Yttrium and lanthanide trivalent metal ions and divalent
zinc and cadmium have been used to explore the coordina-
tion behaviour of this new family of oxa-aza macrocycles.
Condensation between 2,6-bis(2-formylphenoxymethyl)py-
ridine and tris(2-aminoethyl)amine (L1) or N,N-bis(3-
aminopropyl)methylamine (L4) in the presence of the corre-
sponding hydrated metal salt, in a 1:1:1 molar ratio, leads
to the formation of mononuclear complexes formulated
as
[LaL1](ClO4)3·10H2O,
[ZnL1](ClO4)2·4H2O,
and
[ML4](X)n·xH2O (M = Y(III), Ce(III), Nd(III), Eu(III),
–
–
Ho(III), Er(III), Lu(III), and Cd(II); X = NO3 or ClO4 ) and
dinuclear complexes formulated as [Cd2L1](ClO4)4·5H2O
–
and [M2L4](X)n·xH2O (M = La(III); X = NO3 and M =
–
Zn(II); X = ClO4 ). Microanalytical data for these complexes
are shown in Table 1 (L1) and Table 2 (L4).
Only complexes with trivalent metal ions have been ob-
tained with L2, with the formula [ML2](X)3·xH2O (M =
Y(III), La(III), Ce(III), Sm(III), Gd(III), and Er(III); X =
–
–
ClO4 or NO3 ). Reaction between L5 and Y(III), La(III),
Gd(III), Eu(III), Tb(III), Zn(II), and Cd(II) leads to the for-
mation of mononuclear complexes, formulated as
[ML5](X)n·xH2O (M = La(III), Eu(III), Gd(III), Tb(III), and
Metal complexes: FAB and electrospray mass spectra
All mass spectra feature peaks attributable to the corre-
sponding macrocyclic ligand, confirming the stability of the
seven macrocycles in their metal complexes. Moreover, the
spectra show peaks at higher molecular weights, which in
some cases have also been assigned. The spectra for the
complexes with L1 contain peaks attributable to [ML1]+
(M = La(III) and Cd(II)) and [ZnL1(ClO4)]+. For the com-
plexes with L2, the spectra show peaks assignable to the
fragments [ML2(ClO4)]+ (M = La(III) and Ce(III)), and
[L2(ClO4)]+ and [LaL2(NO3)]+ are present. In the case of
the L3 complexes, peaks assignable to the fragments
[ML3(ClO4)]+ (M = La(III), Pr(III), Sm(III) and Zn(II)),
[ML3(NO3)]+ (M = Eu(III)), and [ML3]+ (M = Eu(III) and
Sm(III)) can be observed.
The spectrum of the dinuclear nitrate La(III) complex
with L4 contains peaks corresponding to the fragments
[La2L4(NO3)3]+ and [LaL4(H2O)]+. The mononuclear
Ce(III), La(III), and Nd(III) complexes exhibit peaks due to
the species [ML4(ClO4)2]+ (M = La(III) and Ce(III)) and
[NdL4(NO3)]+, confirming the presence of the metal ions in
the complexes. Peaks attributable to the fragment
[L4(ClO4)]+ are also present in the spectra of the complexes
with Ce(III) and Cd(II). For the complexes with L5, the mass
spectra feature peaks assignable to the fragments
–
–
Zn(II); X = ClO4 or NO3 ), as well as the dinuclear com-
–
plexes [M2L5](X)n·xH2O (M = Y(III); X = NO3 and M =
–
Cd(II); X = ClO4 ). Microanalytical data for these com-
plexes are shown in Table 1 (L2) and Table 2 (L5). The syn-
theses were also attempted with the perchlorates of Zn(II)
and Cd(II) for L2, as well as the nitrates of La(III) and the
perchlorates of Ce(III) and Eu(III) for L5; however, with
these metals only species with unsatisfactory analytical data
were obtained.
A direct method has been successfully used to synthesize
complexes with L3. Reaction of freshly prepared L3 in the
presence of the corresponding metal salt yielded
mononuclear complexes of formula [ML3](X)3·xH2O (M =
–
La(III) and Sm(III); X = ClO4 ; M = Eu(III) and Tb(III);
–
X = NO3 ) (see Table 1) and the dinuclear complexes
[Pr2L3](ClO4)6·5H2O and [Zn2L3](ClO4)4·4H2O. Under the
experimental conditions employed, it has been impossible to
isolate the expected metal complexes with the nitrates of
Y(III) and La(III) and with the perchlorate of Cd(II).
The reaction between equimolar amounts of freshly pre-
pared L6 and L7 and the perchlorates of La(III) and Zn(II),
as well as the nitrates of Y(III) and Gd(III), gave analyti-
cally pure products of formula [LaL6](ClO4)3·7H2O,
[ML5(NO3)2]+ (M
=
Y(III), Eu(III), and Tb(III)),
[ML5(ClO4)]+ (M = La(III), Gd(III), Zn(II), and Cd(II)), and
[ML5]+ (M = Y(III) and Zn(II)). The FAB mass spectra for
the L6 complexes show peaks assignable to the fragments
[ML6]+ and [L6(NO3)2]+, while for the L7 complexes, peaks
corresponding to the fragments [LaL7]+ and [ZnL7(H2O)]+
can be observed.
[M2L6](NO3)6·xH2O (M
=
Y(III) and Gd(III)), and
[M2L7](ClO4)n·H2O (M = La(III) and Zn(II)). The presence
of extra donor atoms in the pendant arms leads to the forma-
tion of binuclear species with the majority of the metal ions
employed. The syntheses were also attempted using the per-
chlorate of Cd(II) and the nitrates of Eu(III) and Tb(III), but
only a mixture of unreacted metal salt and free ligand were
recovered.
Infrared spectra
In the absence of crystal structures, which are decisive in
the elucidation of the coordinative environment of the metal
ions in these molecules, it is difficult to give an appropriate
explanation for the formation, depending on the ligand and
the metal ion, of di- or mononuclear complexes. Reaction
with Cd(II) and Zn(II) yields dinuclear complexes in most
The IR spectra for the complexes with L1, L2, L4, and L5
confirm the cyclic nature of the ligands in their metal com-
plexes. The spectra for the complexes with L1 and L4 show a
band at ca. 1639–1660 cm–1, attributable to the imine
groups, and no bands due to ν(C=O) vibrations. In the Cd(II)
complex with L1, a band at ca. 3227 cm–1, attributable to
© 2004 NRC Canada

444
Can. J. Chem. Vol. 82, 2004
1
Fig. 2. H NMR data (300 MHz) for [LaL2](ClO4)3·9H2O (in CD3CN), [LaL5](ClO4)3·6H2O (in CDCl3), and [La2L4](NO3)6 (in DMSO-d6).
ν(NH2), is also observed (27). The spectra exhibit medium
to strong bands at ca. 1603–1597 and 1458 cm–1, as ex-
pected for the ν(C=C)ar and ν(C=N)py ring vibrations (28).
The ν(C=N)py band, as well as those corresponding to the
imine groups, are generally shifted to higher wave numbers
when compared with those of the free ligands, suggesting
coordination via nitrogen atoms (29, 30). The IR spectral re-
sults for the complexes with L3 confirm that the imine group
is present in the pendant arm of the ligand, showing an in-
tense band at ca. 1630–1650 cm–1 that is attributable to
ν(C=N) and no bands due to ν(C=O) and ν(NH2) groups
(27). The bands attributable to ν(NH) in the complexes
of L2, L3, and L5 cannot be observed because of the exis-
tence of a broad band at ca. 3380–3520 cm–1, assignable to
the stretching and bending modes of water (31). For the
complexes with L2 and L5, the absence of bands at ca. 1620–
1660 cm–1 in the spectra confirms the reduction of the
iminic groups.
1121, 1115, and 1088 cm–1; the ν4 band also shows splitting
with maxima at ca. 636 and 626 cm–1 (36). The splitting of
these bands is indicative of coordination of at least one per-
chlorate anion to the metal.
NMR spectra
The 1H NMR spectra of some diamagnetic complexes
with Y(III), La(III), and Zn(II) were recorded immediately
after dissolution in CD3CN, DMSO-d6, or CD3OD at room
temperature.
The
spectra
of
the
complexes
[LaL1](ClO4)3·10H2O and [ZnL1](ClO4)2·4H2O (in CD3CN)
are complicated, showing more signals than expected. This
may be indicative of the following: (i) the co-existence of
additional processes in solution such as dimerization; (ii) the
existence of demetallation processes in solution or geometric
changes; and (or) (iii) the hydrolysis of the iminic groups.
We ran the spectra at the following different temperatures:
298.15, 313.15, and 323.15 K. In all cases the number of
signals never decreased notably, suggesting slow intersystem
changes. The complexes [LaL2](ClO4)3·9H2O and [La2L4](NO3)6
(in DMSO-d6) and [LaL5](ClO4)3·6H2O (in CD3CN) gave
the expected simple spectra, indicating the integrity of the
complexes in those solvents (see Fig. 2, Table 4).
The IR spectra of the complexes with L6 and L7 also con-
tain absorption bands characteristic of the ligand frame-
works. The sharp absorption band occurring in the region
3340–3060 cm–1 is attributable to ν(NH) of the indole or
imidazole groups. For the complexes of L6, the band at ca.
1648 cm–1 can be assigned to the δ(NH) of the imidazole
groups. Bands at ca. 1602 and 1458 cm–1, corresponding to
the aromatic ring vibrations, are also present. These bands
are shifted to lower energy when compared with their posi-
tion in the spectra of the free ligands, probably because of
coordination to the metal ion.
The spectra of the complexes [LaL3](ClO4)3·5H2O,
[YL4](NO3)3·5H2O, [Zn2L4](ClO4)4·2H2O, and [LaL4](ClO4)3·
4H2O (in CD3CN) are complicated and show more signals
than expected (complex and free ligand signals), which may
be indicative of the existence of demetallation processes in
solution or dimerization reactions in the dinuclear com-
plexes. Nevertheless, clear peaks at δ 9.20, 8.60, 9.00, and
9.20 ppm, corresponding to the imine protons in the ligands,
are present. The 1H NMR spectra of [Y2L6](NO3)6·5H2O and
[LaL6](ClO4)3·7H2O (in DMSO-d6) are also complicated,
maybe because of the nonsymmetric topology of the ligand.
Nevertheless, clear peaks at δ 7.8 and 8.8 ppm, correspond-
ing to the aromatic imidazol protons of the pendant arms, as
well as the signals attributable to aromatic rings of the
macrocycle (37), confirm the integrity of the ligand L6 in
both metal complexes.
The absorptions of the counter-ions provide some useful
structural information. The IR spectra for all nitrate com-
plexes show bands at ca. 1448–1460 (ν5), 1300 (ν1), and
1030 (ν2) cm–1, suggesting the existence of coordinated ni-
trate groups, as well as a band at ca. 1384 cm–1, attributable
–
to the presence of ionic NO3 (32, 33). Although the spectra
do not allow a clear-cut difference between mono- and
bidentate chelating nitrates, the separation between ν5 and ν1
(ca. 160 cm–1) suggests the presence of nitrate groups acting
as bidentate (34, 35). Regarding the perchlorate complexes,
bands attributable to the asymmetric Cl–O stretching mode
at ca. 1088 cm–1 (ν3) and the asymmetric Cl–O bending
mode (ν4) at ca. 625 cm–1 can be observed. The highest en-
ergy band consists in three well-resolved maxima at ca.
Electronic absorption spectra
The electronic spectra for L2, L3, L4, and L5, as well as some
of their corresponding metal complexes, were recorded at room
© 2004 NRC Canada

Lodeiro et al.
445
1
Table 4. H NMR data for the complexes [LaL2](ClO4)3·9H2O and [La2L4](NO3)6 (in DMSO-d6)
and [LaL5](ClO4)3·6H2O (in CD3CN).
δ integration (ppm)
[LaL2](ClO4)3·9H2O
Assignment
[LaL5](ClO4)3·6H2O
[La2L4](NO3)6
Ha
7.9 (t) — 1H
7.8 (t) — 1H
7.9 (t) — 1H
Hb, Hd–Hg
Hc
7.7–6.8 (m) — 10H
5.2 (s) — 4H
8.5–6.8 (m) — 10H
5.4 (s) — 4H
7.7–6.9 (m) — 10H
5.5 (s) — 4H
Hh
4.2 (s) — 4H
4.2 (s) — 4H
8.3 (s) — 2H
Hi, Hj, Hk, Hl
3.0–2.6 (m) — 12H
3.1–1.0 (m) — 15H
2.5–1.5 (m) — 15H
ca. 351 nm (ε ≈ 5930 mol–1·L·cm–1) for L4. In all cases,
these bands are associated with the π–π* and n–π* elec-
tronic transitions in the chromophores — pyridine and
phenyl rings — that are present in the macrocyclic skeletons
(38).
Fig. 3. Electronic spectra for L2, L4, and L5 (A) and some ML4
complexes (B) in acetonitrile solution. [L] = [ML] = 9.0 E–5 mol L–1.
The UV–vis spectra for some Y(III), Ln(III), and Zn(II)
nitrate and perchlorate complexes of L2 and L4 exhibit two
or three absorption bands in the regions 262–270, 315–325,
and 370–385 nm. The shift in the absorption maxima that is
observed when it is compared with those of the free macro-
cycles may be due to the presence of the metal in the species
and could be attributable to the π–π* and n–π* transitions of
the coordinated macrocycles. In some cases, the intensity of
the absorption bands changed slightly when the spectra were
recorded after 1 and 2 weeks, suggesting the displacement of
some coordinated anions or water molecules by acetonitrile
molecules. The spectral data for the complexes are given in
Table 5, and the electronic spectra for the free ligands L2,
L4, and L5 and some ML4 metal complexes are shown in
Fig. 3.
Fluorescence emission spectra
Room-temperature emission spectra were registered using
10–5–10–6 mol L–1 acetonitrile solutions for the Eu(III),
Tb(III), and Zn(II) complexes with L3, L4, and L5. Unfortu-
nately, no emission could be detected in these complexes,
probably because of (i) the presence of water molecules in
the complexes; (ii) the presence of free uncoordinated
amines with the lone-pair unoccupied; and (iii) the co-
existence of nonradiative mechanisms that quenched the
emission, in a similar way to those reported for other macro-
cycle ligands derived from similar aliphatic or aromatic pre-
cursor (2, 19, 24, 39).
Conclusions
Seven [1+1] oxa-aza macrocyclic ligands, five of them
new, have been prepared using 2,6-bis(2-formylphenoxy-
methyl)pyridine as the precursor. Treatment of the previ-
ously reported Schiff-base macrocycles L1 and L4 with
NaBH4, in the presence of Ba(II) as a template agent, gave
the corresponding reduced macrocycles L2 and L5. The more
sophisticated ligands L3, L6, and L7, provided with pendant
arms, have been synthesized by condensation or alkylation
reactions with the amine groups present in L2 and L5. Com-
plexes with these seven ligands have been prepared by tem-
plate reaction or direct methods, using the nitrates and (or)
perchlorates of Y(III), Ln(III), Cd(II), or Zn(II) ions.
temperature in acetonitrile solutions. The spectra for the re-
duced ligands L2 and L5 present one band at ca. 269–266 nm
(ε ≈ 5344 and 3595 mol–1·L·cm–1, respectively). The Schiff
base ligands L3 and L4 exhibits two bands, at ca. 257 nm (ε ≈
12 444 mol–1·L·cm–1) and ca. 317 nm (ε ≈ 2921 mol–1·L·cm–1)
for L3 and at ca. 303 nm (ε ≈ 16 066 mol–1·L·cm–1) and
The complexes are mono- or dinuclear, depending on the
macrocyclic ligand and (or) metal salt employed. Although
© 2004 NRC Canada

446
Can. J. Chem. Vol. 82, 2004
Table 5. UV–vis spectral data for the complexes with L2 and L4
in acetonitrile solution at room temperature.
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Complexes
λ (nm); ε ((mol L–1)–1·cm–1)
[YL2](NO3)3·2H2O
[LaL2](NO3)3·5H2O
[SmL2](NO3)3·6H2O
[LaL2](ClO4)3·9H2O
[CeL2](ClO4)3·2H2O
[GdL2](ClO4)3·8H2O
[ErL2](ClO4)3·5H2O
[YL4](NO3)3·5H2O
[La2L4](NO3)6
264 (9071); 312(sh) (3065)
266 (8528); 316(sh) (3113)
266 (6778)
267 (6796)
268(11249); 322(sh) (2559)
268 (7770)
267 (7298)
266 (8468); 319(sh) (3257)
266 (5313); 313(sh) (1744)
268 (4602); 339(sh) (999); 385(sh) (704)
267 (9871); 323(sh) (2355)
256 (10940); 316 (4426); 384(sh) (1102)
268 (10202); 320(4862); 379(sh) (401)
267 (5902); 324(4842); 379(sh) (527)
269 (7282); 335(sh) (4347)
[EuL4](NO3)3
[LuL4](NO3)3·2H2O
[LaL4](ClO4)3·4H2O
[CeL4](ClO4)3·4H2O
[ErL4](ClO4)3·H2O
[Zn2L4](ClO4)4·2H2O
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Note: [Complex] = 10–4–10–6 mol L–1; sh = shoulder.
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ion employed, it is worth mentioning that reaction with
Cd(II) and Zn(II) generally generates the dinuclear complex,
suggesting that the macrocyclic cavity in L1, L3, L4, and L5
is large enough to accommodate two of these metal cations.
The complexes obtained with L6 and L7, provided with two
lateral pendant arms, are always dinuclear except in one
case, suggesting that the increase in the number of donor at-
oms present in the macrocyclic skeleton facilitates the for-
mation of dinuclear compounds and showing the ability of
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Acknowledgements
Work supported in part by Xunta de Galicia
(PGIDT01PXI20901PR) (Spain) and the European Commu-
nity’s Human Potential Programme under contract HPRN-
CT-2000-00029 (Molecular Level Devices and Machines).
C.L. acknowledges the financial support provided through
the European Community’s Human Potential Programme un-
der contract HPRN-CT-2000-00029 (Molecular Level De-
vices and Machines).
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