Mononuclear AlIII, GaIII and InIII, and heterodinuclear GaIIIMII (M = Zn, Cu, Ni, Co) complexes of a tetraiminodiphenol macrocyclic ligand

Article abstract of DOI:10.1039/b507484c

Mononuclear aluminium(III), gallium(III) and indium(III) complexes [M ^III(LH₂)(H₂O)Cl](ClO₄)₂ · nH₂O (1-3) of the tetraiminodiphenolate macrocyclic ligand L^2- have been synthesized. The two uncoordinated imine nitrogens of these compounds are protonated and hydrogen bonded to the metal-bound phenolate oxygens to stabilize them against hydrolytic cleavage. The gallium(III) compound, 2, forms the heterodinuclear complexes [Ga^IIIM ^IIL(μ-OAc)(OAc)(H₂O)][ClO₄] (M = Co, 4; Ni, 5) and [Ga^IIIM^IIL(μ-OAc)(OAc)][ClO₄]. 2H₂O (M = Cu, 6; Zn, 7). The presence of the core unit [Ga ^IIIM^IIL(μ-OAc)(OAc)]⁺ in all the compounds has been ascertained by ESI-MS measurements. Complexes 1-3 show luminescence at room temperature between 505 and 490 nm. Spectrofluorimetric titrations of 2 with Zn(OAc)₂ · 2H₂O and Cu(OAc)₂ · H₂O in acetonitrile have shown that the formation of a 1: 1 Ga^IIIZn^II complex occurs with the growth of luminescence intensity, while the formation of a Ga^IIICu^II complex leads to the complete quenching of luminescence. Complexes 1-7 have been further characterized by their proton NMR spectra. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2005.

Full text of DOI:10.1039/b507484c

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P A P E R
III
III
III
III
II
Mononuclear Al , Ga and In , and heterodinuclear Ga M
(M = Zn, Cu, Ni, Co) complexes of a tetraiminodiphenol
macrocyclic ligandw
Bula Dutta, Pradip Bag and Kamalaksha Nag*
Department of Inorganic Chemistry, Indian Association for the Cultivation of Science,
Jadavpur, Kolkata, 700 032, India. E-mail: ickn@iacs.res.in; Fax: þ91 33 2473 2805
Received (in Montpellier, France) 27th May 2005, Accepted 29th June 2005
First published as an Advance Article on the web 20th July 2005
III
Mononuclear aluminium(III), gallium(III) and indium(III) complexes [M (LH2)(H2O)Cl](ClO4)2 ꢀ nH2O (1–3)
of the tetraiminodiphenolate macrocyclic ligand L2ꢁ have been synthesized. The two uncoordinated imine
nitrogens of these compounds are protonated and hydrogen bonded to the metal-bound phenolate oxygens
to stabilize them against hydrolytic cleavage. The gallium(III) compound, 2, forms the heterodinuclear
III
II
III
II
complexes [Ga M L(m-OAc)(OAc)(H2O)][ClO4] (M ¼ Co, 4; Ni, 5) and [Ga M L(m-OAc)(OAc)][ClO4] ꢀ
1
III
II
2H2O (M ¼ Cu, 6; Zn, 7). The presence of the core unit [Ga M L(m-OAc)(OAc)] in all the compounds has
been ascertained by ESI-MS measurements. Complexes 1–3 show luminescence at room temperature between
505 and 490 nm. Spectrofluorimetric titrations of 2 with Zn(OAc)2 ꢀ 2H2O and Cu(OAc)2 ꢀ H2O in acetonitrile
III
II
have shown that the formation of a 1 : 1 Ga Zn complex occurs with the growth of luminescence
III
intensity, while the formation of a Ga Cu complex leads to the complete quenching of luminescence.
II
Complexes 1–7 have been further characterized by their proton NMR spectra.
metal ions. We have reported18 valence delocalization phenom-
Introduction
II
III
enon in the mixed-valence Fe Fe tetraiminodiphenol macro-
cyclic systems. More recently, we reported19 the efficient
proton-templated synthesis of a whole range of tetraiminodi-
phenol macrocyclic ligands as their perchlorate salts. These
macrocyclic ligands and their dizinc(II) complexes exhibit
strong luminescence.17,19 The present study is concerned with
the synthesis and spectroscopic characterization of the mono-
There is considerable current interest in the chemistry of
Group-13 metal elements because of their involvement in the
genesis and diagnosis of diseases. Aluminium(III) has been
suspected1 of inducing neurological dysfunctions such as Alz-
heimer’s disease, even though overwhelming medical evidence
still does not convincingly demonstrate even a causal relation-
ship between aluminium and the disease.2 On the other hand,
III
nuclear complexes [M (LH2)(H2O)Cl](ClO4)2 ꢀ nH2O (M ¼ Al,
III
II
complexes of gallium(III) and indium(III) have strong potential
as radiopharmaceuticals.3–5 The radioisotopes Ga (g, t ¼
Ga, In) and the heterodinuclear complexes [Ga M L(m-OAc)
(OAc)][ClO4] ꢀ nH2O (M ¼ Co, Ni, Cu, Zn) derived from the
macrocyclic ligand (L2ꢁ), I.
67
1
2
68
1
111
1
2
1
2
3.25 d), Ga (b , t ¼ 68 min) and In (g, t ¼ 2.80 d) have
appropriate energies and half-lives for g-ray imaging and
positron emission tomography. For effective transportation
of these radioisotopes to the target organs, the thermodynamic
stability of the complex species should be high, and could be
achieved by using polydentate ligands. To this end, extensive
studies have been made in recent years on the chemistry of
Group-13 metals with various polydentate ligands comprising
combinations of amino and phenolic units.6–9 Interestingly,
however, similar complexes of iminophenol ligands are not
reported. This is probably because the Lewis acidity of the
trivalent Group-13 metal ions induces hydrolytic cleavage of
the CH N bonds in these ligands. Nevertheless, a recent study
Q
has reported10 the structures of several gallium(III), indium(III)
and thalium(III) complexes of a hexadentate tripodal imino-
phenol ligand by synthesizing these complexes in an improved
way.
Experimental
Although numerous studies have been reported on the
phenoxo-bridged homodimetallic complexes of tetraiminodi-
phenolate macrocyclic ligands,11–17 non-availability of metal-
free macrocyclic ligands has restricted these studies to divalent
Materials
Reagent grade chemicals obtained from commercial sources
were used as received. Solvents were purified and dried accord-
ing to standard methods.20 The chloride salts of aluminium,
gallium and indium were prepared by treating the metal with
dilute HCl, followed by evaporation of the solution over a
steam bath. The residue was dissolved in water, filtered,
concentrated to a viscous liquid and kept in a desiccator over
w Electronic supplementary information (ESI) available: Simulated
and observed ESI-MS positive spectral patterns of 4, 5 and 7, absorp-
tion spectra of 4–6 and 1H NMR spectrum of 5. See http://dx.doi.org/
10.1039/b507484c
T h i s j o u r n a l i s & T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 5
1182
N e w J . C h e m . , 2 0 0 5 , 2 9 , 1 1 8 2 – 1 1 8 8

View Online
kept at ca. 5 1C for a few hours. The crystalline product that
deposited was collected by filtration and washed with diethyl
ether. The compounds rapidly lose crystallinity upon standing
in air.
dried silica gel. 2,6-diformyl-4-methylphenol was prepared
according to a literature method.21 [Pb(LH2)][ClO4]2 was
prepared as reported earlier.22
Preparation of the complexes
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II
[Ga Co L(l-OAc)(OAc)(H2O)][ClO4] (4). Brown com-
pound, yield 0.22 g (57%). Found C, 43.91; H, 4.40; N, 7.28.
C28H34N4O11GaCoCl requires C, 43.86; H, 4.44; N, 7.31%.
Caution! All the perchlorate salts reported in this study are
potentially explosive and therefore should be handled with
care.
III
II
MS (ESI positive in CH3CN) m/z ¼ 691 [Ga Co L(OAc)
1
(ClO4)]1, 649 [Ga Co L(OAc)2]
and 295.5 [Ga Co
III
II
III
II
L(OAc)]21. IR data on KBr (n/cmꢁ1) 3410br, 2925m, 2866w,
1644s, 1595sh, 1570s, 1443m, 1408m, 1322m, 1275w, 1117s,
1084s, 943w, 883w, 808w, 678w, 628m and 539w. dH (300
MHz, CD3CN) 144, 120, 96, 43.6, 19.9, 10.7, 6.9, 2.36, 2.04
and ꢁ6.2.
.
Mononuclear complexes [M(LH2)(H2O)Cl](ClO4)2 nH2O
[M = Al, Ga, In] (1–3). To a boiling acetonitrile solution (50
cm3) of [Pb(LH2)](ClO4)2 (0.81 g, 1 mmol) were added simul-
taneously acetonitrile solutions (20 cm3) of the metal chloride
(1 mmol) and sodium perchlorate (0.55 g, 4 mmol). The
resulting yellow solution was refluxed for 1 h, after which time
the precipitated PbCl2 was removed by filtration. The filtrate
was concentrated at 80 1C to a volume of ca. 40 cm3, at which
point an orange or yellow crystalline product began to separate
out. At this stage, the solution was kept overnight for slow
evaporation. The deposited crystalline compound was filtered
and washed with acetonitrile and diethyl ether.
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[Ga Ni L(l-OAc)(OAc)(H2O)][ClO4] (5). Light yellow com-
pound, yield 0.20 g (52%). Found C, 43.76; H, 4.46; N, 7.30.
C28H34N4O11GaNiCl requires C, 43.87; H, 4.44; N, 7.31%.
III
II
MS (ESI positive in CH3CN) m/z ¼ 690 [Ga Ni L(OAc)
1
1
21
III
II
III
II
(ClO4)] , 650 [Ga Ni L(OAc)2] and 296 [Ga Ni L(OAc)]
.
IR data on KBr (n/cmꢁ1) 3408br, 2925m, 2866w, 1650s, 1595w,
1572s, 1443m, 1407m, 1320m, 1274w, 1245w, 1209w,
1122s, 1083s, 937w, 883w, 808m, 771w, 628m and 525w. dH
(300 MHz, (CD3)2SO) 178, 120, 63, 24.2, 11.3, 9.3, 6.03, 4.72
and ꢁ5.59.
[Al(LH2)(H2O)Cl](ClO4)2 (1). Yield 0.36 g (53%). Found C,
42.56; H, 4.46; N, 7.98. C24H30N4O11AlCl3 requires C, 42.14;
H, 4.39; N, 8.19%. IR data on KBr (n/cmꢁ1) 3406br, 2932m,
2866w, 1646s, 1532s, 1460w, 1387w, 1337m, 1308w, 1210m,
1129s, 1088s, 996m, 883w, 678w, 629m and 572w. dH (300
III
II
.
[Ga Cu L(l-OAc)(OAc)][ClO4] 2H2O (6). Green com-
pound, yield 0.23 g (59%). Found C, 42.45; H, 4.52; N, 7.09;
C28H36N4O12GaCuCl requires C, 42.60; H, 4.56; N, 7.10%.
MHz, CD CN) 13.40 (2 H, s, N–Hꢀ ꢀ ꢀO), 8.26 (4 H, s, CH N),
Q
3
7.26 (4 H, s, Ar), 3.97 (8 H, s, a-CH2), 2.25 (4 H, s, b-CH2) and
2.11 (6 H, s, CH3).
III
II
MS (ESI positive in CH3CN) m/z ¼ 695 [Ga Cu L(OAc)
(ClO4)]1, 655 [Ga Cu L(OAc)2]
and 298.5 [Ga Cu
1
III
II
III
II
L(OAc)]21. IR data on KBr (n/cmꢁ1) 3409br, 2925m, 2860w,
1642s, 1576s, 1444m, 1415m, 1385m, 1322s, 1277w, 1243w,
1113s, 1086s, 931w, 878w, 816m, 763w, 667w, 627m and 523w.
dH (300 MHz, CD3CN) 22, 13.4, 11.2, 9.1, 4.9, 3.6, 3.05
and ꢁ9.6.
[Ga(LH2)(H2O)Cl](ClO4)2 (2). Yield 0.39 g (54%). Found C,
39.33; H, 4.12; N, 8.12. C24H30N4O11GaCl3 requires C, 39.65;
H, 4.13; N, 7.71%. IR data on KBr (n/cmꢁ1) 3408br, 2927m,
2866w, 1650s, 1556s, 1448m, 1352m, 1288m, 1236m, 1113s,
1088s, 870w, 830w, 685w, 629m and 525w. dH (300 MHz,
(CD ) SO) 11.86 (2 H, s, N–Hꢀ ꢀ ꢀO), 8.64 (2 H, s, CH N in
Q
the metal free site), 8.55 (2 H, s, CH N in the metal site), 7.59
3 2
Q
III
II
.
[Ga Zn L(l-OAc)(OAc)][ClO4] 2H2O (7). Yellow com-
pound, yield 0.25 g (64%). Found C, 42.49; H, 4.50; N, 7.10;
C28H36N4O12GaZnCl requires C, 42.50; H, 4.55; N, 7.08%.
(2 H, s, Ar in the metal free site), 7.55 (2 H, s, Ar in the metal
site), 3.99 (4 H, s, a-CH2 in the metal free site), 3.89 (4 H, s, a-
CH2 in the metal site), 2.28 (6 H, s, CH3), 2.15 (2 H, s, b-CH2 in
the metal free site) and 2.07 (2 H, s, b-CH2 in the metal site).
III
II
MS (ESI positive in CH3CN) m/z ¼ 696 [Ga Zn L(OAc)
(ClO4)]1, 656 [Ga Zn L(OAc)2] and 299 [Ga Zn
1
III
II
III
II
L(OAc)]21. IR data on KBr (n/cmꢁ1) 3432br, 2932m, 2859w,
1640s, 1590sh, 1567s, 1438m, 1416m, 1374m, 1334m, 1279w,
1243m, 1198w, 1088s, 1003w, 937w, 897w, 822m, 769, 623m
.
[In(LH2)(H2O)Cl](ClO4)2 2H2O (3). Yield 0.45 g (56%).
Found C, 35.61; H, 4.17; N, 6.81. C24H34N4O13InCl3 requires
C, 35.66; H, 4.21; N, 6.93%. IR data on KBr (n/cmꢁ1) 3410br,
2945m, 2859w, 1656s, 1551s, 1454m, 1348m, 1295w, 1248m,
1121s, 1086s, 923w, 877w, 811w, 685w, 628m and 519w. dH
(300 MHz, CD3CN) 12.37 (2 H, s, N–Hꢀ ꢀ ꢀO), 8.48 (2 H, s,
and 519w. dH (300 MHz, CD CN) 8.28 (2 H, s, CH N Ga
Q
site), 8.24 (2 H, s, CH N Zn site), 7.39 (4 H, s, Ar), 4.07 (4 H,
3
Q
s, a-CH2 Ga site), 3.98 (4 H, s, a-CH2 Zn site), 2.30 (6 H, s,
CH3), 2.18 (2 H, s, b-CH2 Ga site), 2.08 (2 H, s, b-CH2 Zn site)
and 1.54 (6 H, s, CH3 of OAc).
CH N in the metal free site), 8.27 (2 H, s, CH N in the
Q
Q
metal site), 7.62 (2 H, s, Ar in the metal free site), 7.54 (2 H, s,
Ar in the metal site), 4.37 (2 H, s, a-CH2 in the metal free site),
3.85 (2 H, s, a-CH2 in the metal free site), 4.20 (2 H, s, a-CH2
in the metal site), 4.12 (2 H, s, a-CH2 in the metal site), 2.28
(6 H, s, CH3) and 2.24 (2 H, s, b-CH2).
Physical measurements
Elemental C, H and N analyses were performed on a Perkin-
Elmer 2400II elemental analyzer. The 1H NMR (300 MHz)
spectra were performed in CD3CN (1, 3, 4, 6 and 7)
and (CD3)2SO solutions (2 and 5) on a Bruker Avance
DPX-300 spectrometer. Longitudinal relaxation times,
T1, were measured by the inversion recovery method. FTIR
spectra were recorded using KBr disks on a FT-IR Nexus
Nicolet spectrometer. The electronic spectra of 1–7 in
acetonitrile were measured in the range 250–1100 nm using
Shimadzu UV-2100 and 1601PC spectrophotometers. Emis-
sion spectral measurements were carried on a Perkin-Elmer
LS55 luminescence spectrometer with 10ꢁ5 mol dmꢁ3 acetoni-
trile solutions. Emission quantum yields, j, were measured
at room temperature in acetonitrile solution relative to per-
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.
[Ga M L(l-OAc)(OAc)][ClO4] nH2O
Heterodinuclear
complexes [M = Co, Ni, Cu and Zn] (4–7). To a stirred
acetonitrile solution (50 cm3) of 2 (0.36 g, 0.5 mmol) at room
temperature were added an acetonitrile solution (10 cm3) of
M(ClO4)2 ꢀ 6H2O (0.5 mmol) and solid sodium acetate (0.16 g,
2 mmol). The colour of the solution changed from yellow to
II
II
II
pink (for Co ), greenish-yellow (for Ni ) or green (for Cu ).
After stirring for 3 h, the solution was filtered and the filtrate
concentrated on a rotary evaporator to dryness. The residue
was extracted with dichloromethane (30 cm3) and the extract
concentrated to a volume of ca. 10 cm3. The solution was then
N e w J . C h e m . , 2 0 0 5 , 2 9 , 1 1 8 2 – 1 1 8 8
1183

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ylene as the standard.23 The quantum yields were calculated
using the relation24
and [Pb(LH2)][ClO4]2 produces the corresponding [M
III
(LH2)(H2O)Cl](ClO4)2 ꢀ nH2O complex, 1–3. The gallium(III)
complex, 2, on reaction with the hydrated perchlorate salts of
cobalt(II), nickel(II), copper(II) or zinc(II) in a 1 : 1 ratio, in the
presence of excess of sodium acetate, produces the acetate-
j ¼ jstd (Astd/A)(I/Istd)(Z2/Zs2td
)
where A, I, and Z refer to absorbance, integrated emission
intensity, and solution refractive index, respectively. The elec-
trospray ionization mass spectra (ESI-MS positive) of com-
pounds 4–7 were measured in acetonitrile on a Micromass Qtof
YA263 mass spectrometer.
III
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bridged heterodinuclear complexes [Ga M L(m-OAc)(OAc)]
[ClO4] ꢀ nH2O, 4–7. All the heterodinuclear complexes were
initially isolated in a crystalline form, however, attempts to
determine their crystal structures were unsuccessful as their
crystallinity was lost within a few minutes of being taken out of
the mother liquor. The composition of the compounds re-
ported here are based on analyses of products which were first
stored for ca. 24 h. Complexes 1–7 were found to be stable
toward hydrolytic decomposition. Although they were insolu-
ble in water, they could be recovered unchanged from a 1 : 1
acetonitrile–water solution.
Results and discussion
Synthesis
The cyclocondensation reaction between 2,6-diformyl-4-
methylphenol and 1,3-diaminopropane in the presence of the
chloride salts of aluminium(III), gallium(III) or indium(III) fail
to produce the corresponding dinuclear or mononuclear
41
1
III
III
Mass spectra
macrocyclic complexes [M2 L] and [M L] . The lack of
formation of the dinuclear complexes can be attributed to
Coulombic charge repulsion between the metal centres, while
The electrospray ionization mass spectra (ESI-MS positive) of
the heterodinuclear complexes 4–7 have been measured using
their acetonitrile solutions (ca. 10ꢁ4 mol dmꢁ3). All the com-
pounds exhibit similar spectral features, and are characterized
by the occurrence of three types of positively-charged species.
1
Namely, these are [Ga M L(OAc)(ClO4)] , [Ga M L
1
III
the failure to produce [M L] species seems to be due to the
susceptibility of the uncoordinated CH N bonds in such
Q
compounds to hydrolytic cleavage. We have reported19 that
the nucleophilic attack on uncoordinated CH N bonds can
Q
III
II
III
II
(OAc)2]1 and [Ga M L(OAc)]21, with the relative abundance
of the doubly-positive charged ion being the highest. Fig. 1
shows the cluster of peaks observed for the three types of
molecular cations of 6, along with their corresponding simu-
lated spectral patterns. It may be noted that the numbers of
peaks, m/z values and the relative peak heights observed for the
be prevented by protonating the imino nitrogens under mild
conditions. Thus, when one equivalent of lead(II) perchlorate is
reacted with two equivalents each of 2,6-diformyl-4-methyl-
phenol, 1,3-diaminopropane and acetic acid, the mononuclear
complex [Pb(LH2)][ClO4]2 is obtained in high yield.21 In this
compound, the two protonated imine nitrogens are hydrogen
bonded with the lead(II)-bound phenolate oxygens and the
compound in solution is stable towards hydrolysis. As shown
in Scheme 1, the metathetical reaction between the hydrated
chloride salts of aluminium(III), gallium(III) or indium(III)
III
II
1
1
III
II
III
II
cations [Ga Cu L(OAc)(ClO4)] , [Ga Cu L(OAc)2] and
21
III
II
[Ga Cu L(OAc)] are in excellent agreement with the calcu-
lated spectral patterns obtained by taking into consideration
the relative abundances of the isotopes of the constituent
elements. Similar observations are made for complexes 4, 5
and 7 (Figs. S1–S3).w From the mass spectral studies, it is clear
that all the heterodinuclear complexes contain the core cation
1
III
II
[Ga M L(m-OAc)(OAc)] .
Fig. 1 Electrospray ionization mass spectra (ESI-MS positive) of
[GaIIICuIIL(m-OAc)(OAc)][ClO4], 6, in acetonitrile. Simulated isotro-
pic spectral patterns are compared with the observed major positi-
vely-charged cationic species.
Scheme 1
1184
N e w J . C h e m . , 2 0 0 5 , 2 9 , 1 1 8 2 – 1 1 8 8

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Infrared spectra
The common IR spectral features observed for complexes 1–7
are a broad band due to water in the range 3500–3400 cmꢁ1
,
a strong band due to nCQ between 1655 and 1640 cmꢁ1 and
N
characteristic bands due to ionic perchlorate at ca. 1100 and
630 cmꢁ1. The heterodinuclear complexes 4–7 exhibit addi-
tional bands due to their coordinated acetates. Thus, the nasym
ꢁ
CO2 vibrations are observed as a shoulder and as a strong
band at about 1595 and 1570 cmꢁ1 respectively, whereas the
ꢁ
nsym CO2 vibrations are observed as two medium intensity
bands at about 1440 and 1410 cmꢁ1. The differences in
energies, D, of the nasym and nsym vibrations (1595 ꢁ 1410 ¼
185 cmꢁ1 and 1570 ꢁ 1440 ¼ 130 cmꢁ1) indicate the presence
of two types of acetate group. Generally for bidentate carbox-
ylates, the D value is less than 100 cmꢁ1, for unidentate acetate
D is greater than 150 cmꢁ1, while for bridging carboxylate the
D value is close to 150 cmꢁ1 25
On the basis of this classifica-
.
tion, the presence of both bridging and unidentate acetate in
4–7 may be anticipated.
Fig. 2 Luminescence spectra observed for the mononuclear com-
plexes 1–3 in acetonitrile at room temperature.
Absorption spectra
peak at 505 nm, when the excitation wavelength is 430 nm. On
the other hand for 2, lem occurs at 495 nm with lex ¼ 390 nm;
while for 3, the emission occurs at 490 nm when it is excited at
395 nm. The emission spectral characteristics of these com-
pounds are given in Table 1. It may be noted that the Stoke’s
shift decreases in the following way: 2 (5450 cmꢁ1) 4 3 (4900
cmꢁ1) 4 1 (3500 cmꢁ1). As shown in Fig. 2, at the appropriate
excitation wavelengths, the emission intensities of all the three
compounds are essentially the same. All the three compounds
lose luminescence when their solutions are treated with triethyl-
amine.
Spectrofluorimetric titrations carried out by adding an in-
cremental amount of an acetonitrile solution of Zn(OAc)2 ꢀ
2H2O to a solution of 2 in the same solvent, leading to the
formation of 7, is shown in Fig. 3. The growth of the emission
band at 435 nm, using 390 nm as the excitation wavelength,
was monitored. The inset of Fig. 3 shows that with the increase
in mole fraction of Zn(OAc)2 ꢀ 2H2O added, the luminescence
intensity increases smoothly and then tapers off in the vicinity
of a 1 : 1 ratio of gallium(III) and zinc(II). With the further
addition of zinc(II), no further change in luminescence intensity
occurs.
The absorption spectral data of complexes 1–7 in acetonitrile
are listed in Table 1. The mononuclear complexes 1–3 exhibit
two strong absorptions at 250–260 and 390–430 nm. Signifi-
cantly for the aluminium compound, the lower energy absorp-
tion band occurs at a considerably higher wavelength (430 nm)
compared to that of gallium (390 nm) and indium (395 nm).
In the heterodinuclear Ga M compounds 4–7, the posi-
tions of the two absorption bands in the UV region remain
practically unchanged for all the four compounds, and are
III
II
III
II
observed at about 255 and 365 nm. For the Ga Co com-
pound, 4, a weak broad absorption occurs at ca. 950 nm (e ¼ 8
dm3 molꢁ1 cmꢁ1). This band seems to be due to the 4T1(F) -
4T2g transition of the six-coordinated cobalt(II) centre. The
III
II
Ga Ni compound, 5, on the other hand, exhibits three
absorption bands in the visible region with lmax at 560 nm
(e ¼ 17 dm3 molꢁ1 cmꢁ1), 830 nm (e ¼ 3 dm3 molꢁ1 cmꢁ1) and
1070 nm (e ¼ 3 dm3 molꢁ1 cmꢁ1). These absorptions can be
3
3
3
related to A2g
-
3T1g (P), T1g and T2g transitions for
octahedral nickel(II), in decreasing order of energy. In the
III
II
Ga Cu complex, 6, the sole d–d band, typical of square
pyramidal copper(II), is observed at 645 nm (e ¼ 45 dm3 molꢁ1
cmꢁ1). As expected, the Ga Zn compound, 7, shows no
absorption in the visible region. The absorption spectra of
4–6 are available as supplementary information (Figs. S4–S6).w
III
II
Luminescence spectra
The mononuclear compounds show luminescence at room
temperature when their acetonitrile solutions are irradiated
with light in the wavelength range 390–430 nm. For compound
1, the intensity of luminescence becomes maximum, with a
Table 1 Absorption and emission spectral data for complexes 1–7a
Emission
Absorption
max/nm (e/dm3 molꢁ1 cmꢁ1
l
)
l
max/nm
j
Compounds
1
2
3
4
5
250 (26 500), 430 (15 700)
260 (30 200), 390 (12 400)
260 (24 600), 395 (9 800)
505
495
490
—
0.07
0.09
0.10
—
255 (49 600), 368 (9 200), 945 (8)
255 (57 300), 370 (11 100),
560 (17), 830 (3), 1070 (3)
—
—
Fig. 3 Spectrofluorimetric titration of [Ga(LH2)(H2O)Cl][ClO4]2 (1 ꢂ
10ꢁ5 mol dmꢁ3) with increasing equivalents of Zn(OAc)2 ꢀ 2H2O in
acetonitrile. The excitation wavelength used was 390 nm. The inset
shows the variation of luminescence intensity with the number of
equivalents of Zn(OAc)2 ꢀ 2H2O added.
6
7
255 (59 200), 368 (10 800), 650 (45)
255 (46 600), 370 (9 500)
—
435
—
—
a
In acetonitrile.
N e w J . C h e m . , 2 0 0 5 , 2 9 , 1 1 8 2 – 1 1 8 8
1185

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1
Fig. 6 H NMR spectrum of [GaIIICoIIL(m-OAc)(OAc)(H2O)][ClO4],
4, in CD3CN.
deconvoluted. Fig. 4(a) shows the presence of two peaks at
435 and 490 nm, while Fig. 4(b) shows that although the
position of the first peak remains unchanged, the second peak
is blue-shifted to 470 nm. Indeed, for all the emission spectra
obtained during titration, deconvolution shows that the emis-
sion peak observed at 490 nm for the solution containing
gallium(III) alone is gradually shifted to 470 nm when gallium
(III) to zinc(II) ratio becomes 1 : 1, without showing any
significant change of luminescence intensity. On the other
hand, as the gallium(III) to zinc(II) ratio changes from 1 : 0
to 1 : 1, the intensity of luminescence also increases, albeit the
peak position remains unchanged at 435 nm. Clearly, in the
III
II
heterodinuclear Ga Zn compound, the dual emission occurs
due to the non-equivalence of the structural sites. Fig. 4(b)
shows that relative to the gallium(III) site, the zinc(II) site is
more photoluminescent. We have recently reported 17 that the
dizinc(II) complex [Zn2L(m-OAc)][ClO4] ꢀ 2H2O shows strong
luminescence in acetonitrile, with lem at 430 nm when lex is 370
nm. Importantly, the observed normalized intensity of the
dizinc(II) complex is almost double that of the zinc(II) site in 7.
Fig.
4 Deconvoluted luminescence spectra for the mixture of
[Ga(LH2)(H2O)Cl][ClO4]2 and Zn(OAc)2 ꢀ 2H2O in acetonitrile in the
III
II
III
II
In contrast to the Ga Zn complex, 7, the other Ga M
ratio (a) 1 : 0.2 and (b) 1 : 1.
complexes, 4–6, are devoid of photoluminescence. The quench-
ing of the luminescence of 2 occurs when it is treated with a
transition metal(II) salt, and this is typically shown in Fig. 5—
where an acetonitrile solution of 2 is titrated with Cu(OAc)2 ꢀ
H2O. The inset of Fig. 5 shows that the total loss of lumines-
On careful examination, the luminescence spectra obtained
during the titration (Fig. 3) reveals the occurrence of dual
luminescence. This is illustrated in Fig. 4, where the spectra
observed for the solutions containing 2 and Zn(OAc)2 ꢀ 2H2O
in the ratios 1 : 0.2 (Fig. 4(a)) and 1 : 1(Fig. 4(b)) are
III
II
cence occurs with the formation of the Ga Cu complex, 6.
Proton NMR spectra
The 1H NMR spectra of 1, 3, 4, 6 and 7 were measured in
CD3CN, while for 2 and 5 their (CD3)2SO solutions were used.
For the diamagnetic compounds 1–3 and 7, the observed
chemical shifts and assignments are given in the Experimental
section. In the mononuclear compounds 1–3, the protonated
imine nitrogens, which are intramolecularly hydrogen bonded
with the phenolate oxygens, are observed as broad singlets at
13.40, 11.86 and 12.37 ppm respectively. As expected, the
III
II
Ga Zn compound, 7, shows small differences in the chem-
Fig. 5 Quenching of luminescence intensity during the titration of
[Ga(LH2)(H2O)Cl][ClO4]2 (1 ꢂ 10ꢁ5 mol dmꢁ3) with Cu(OAc)2 ꢀ H2O
in acetonitrile. The excitation wavelength used was 390 nm. The inset
shows the variation in emission intensity with the mole fraction of
Cu(OAc)2 ꢀ H2O added.
1
Fig. 7 H NMR spectrum of [GaIIICuIIL(m-OAc)(OAc)][ClO4] ꢀ 2H2O,
6, in CD3CN.
1186
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Table 2 Chemical shifts, T1 values, line widths and assignments for GaIIIMII compounds 4–6
GaIIICoII, 4
GaIIINiII, 5
GaIIICuII, 6
a
a
a
1
2
1
2
1
2
d/ppm
T1/ms
D /Hz
Assignment
d/ppm
D /Hz
Assignment
d/ppm
T1/ms
D /Hz
Assignment
144
120
96
—
—
220
1080
180
120
86
d0
178
120
63
1400
850
1200
112
170
142
135
27
d0
—
22
—
—
—
—
m-OAc
m-OAc
1300
350
190
175
70
m-OAc
3.4
8.2
b0
c
b0
c
13.4
11.2
9.1
—
b0
c
43.6
19.9
10.7
6.9
24.2
11.3
9.3
4.5
17.2
12.7
32.4
16.5
—
12.4
18.9
15.8
27.6
22.4
10.9
b
b
b
154
132
15
d
d
4.9
3.6
d
e
6.03
4.72
—
e
50
80
a
2.36
2.04
ꢁ6.2
a
a
a
3.05
—
e
18
130
OAc
e0
—
620
—
e0
—
2240
—
e0
ꢁ5.59
ꢁ9.6
—
Full width at half height.
Conclusion
The tendency of CH N bonds to be hydrolyzed in the
Q
presence of Group-13 metal (III) ions is the major deterrent
for the synthesis of Schiff base complexes of these metals.
III
Nevertheless, complexes of the type [M (LH2)(H2O)Cl][ClO4]2
have been obtained for aluminium(III), gallium(III) and indium
(III) with a tetraiminodiphenolate macrocyclic ligand, L2ꢁ. In
these compounds, the two uncoordinated imine nitrogens,
which are protonated and involved in intramolecular hydrogen
bonding with the phenolate oxygens, contribute to the reinfor-
cement of the stability of the compounds. Spectrofluorimetric
21
III
titrations of [Ga (LH2)(H2O)Cl] with the acetate salts of
zinc(II) and copper(II) have shown that the formation of 1 : 1
complex species is accompanied by the maximization of lumi-
nescence intensities for zinc and the complete quenching of
luminescence for copper. The heterodinuclear complexes
Scheme 2
[Ga M L(m-OAc)(OAc)]1 have been isolated as their perchlo-
III
II
ical shifts for the identical protons in proximity to the
gallium(III) and zinc(II) centres.
rate salts for cobalt(II), nickel(II), copper(II) and zinc(II). The
1
hyperfine-shifted H NMR spectral features of the paramag-
In the paramagnetic compounds, hyperfine-shifted reso-
nances are observed due to interactions between nuclear spins
and unpaired electron spins, in addition to the normal dia-
magnetic nuclear spin interactions. Electron and nuclear spin
interactions occurring through bonds give rise to a contact
shift, while through space interactions give rise to a dipolar or
pseudo-contact shift. The dipolar shift depends on the mag-
netic anisotropy of the system and the position in space of a
given proton. The contribution of the contact shift decreases
rapidly with the increase in the number of bonds connecting
the proton to the paramagnetic centre. However, when the
unpaired electron spin is delocalized, the interaction remains
significant for protons many bonds away from the metal
centre. For the assignment of signals in paramagnetic com-
pounds, measurement of longitudinal relaxation times, T1, and
transverse relaxation times, T2, are particularly important. T1
correlates the proximity of the proton to paramagnetic centre,
while T2 ¼ 1/p(fwh), where fwh is full width of a signal at its
half-height, correlates line width to the proximity of the proton
to the paramagnetic site. The closer the proximity of a proton
to the metal centre, the shorter the T1 and the broader the line
netic compounds have been analyzed using their longitudinal
relaxation times, T1, and line widths.
References
1
(a) Aluminium and Alzheimer’s Disease, ed. C. Exley, Elsevier
Science, Amsterdam, 2001; (b) M. Suwalsky, B. Norris, T. Kiss
and P. Zatta, Coord. Chem. Rev., 2002, 228, 225.
2
3
(a) C. Derouesne, Psychol. Neuropsychiatr. Vieil., 2004, 2, 76; (b)
Alzheimer’s Society Information Sheet, June 2, 2002.
(a) M. A. Green and M. J. Welch, Nucl. Med. Biol., 1989, 16, 435;
(b) M. A. Green, C. J. Mathias, W. L. Neumann, P. E. Fanwick,
M. Janin and E. A. Deutsch, J. Nucl. Med., 1993, 34, 228.
(a) S. L. Madsen, C. J. Bannochie, A. E. Martell, C. J. Mathias
and M. J. Welch, J. Nucl. Med., 1990, 31, 1662; (b) R. J.
Motekaitis, A. E. Martell and M. J. Welch, Inorg. Chem., 1990,
29, 1463.
4
5
6
(a) D. J. Clevette and C. Orvig, Polyhedron, 1990, 9, 151; (b) H. R.
Hoveyta, V. Karunaratne, S. J. Rettig and C. Orvig, Inorg. Chem.,
1992, 31, 5408.
(a) P. Caravan and C. Orvig, Inorg. Chem., 1997, 36, 236; (b) E.
Wong, P. Caravan, S. Liu, S. J. Rettig and C. Orvig, Inorg. Chem.,
1996, 35, 715; (c) E. Wong, S. Liu, S. J. Rettig and C. Orvig, Inorg.
width.26
Chem., 1995, 34, 3057; (d) E. Wong, S. Liu, T. Lugger, F. E. Hahn
¨
1
Fig. 6 and Fig. 7 show the H NMR spectra of Ga Co , 4,
III
II
and C. Orvig, Inorg. Chem., 1995, 34, 93; (e) S. Liu, E. Wong, S. J.
Rettig and C. Orvig, Inorg. Chem., 1993, 32, 4268; (f) S. Liu, E.
Wong, V. Karunaratne, S. J. Rettig and C. Orvig, Inorg. Chem.,
1993, 32, 1756; (g) S. Liu, S. J. Rettig and C. Orvig, Inorg. Chem.,
1992, 31, 5400.
III
and Ga Cu , 6, compounds respectively, while the spectrum of
II
III
II
Ga Ni , 5, is available as supplementary information (Fig.
S7).w The assignment of signals (the numbering scheme for the
protons is shown in Scheme 2) based on T1 values, line widths
and intensities are given in Table 2. It may be noted that of the
three compounds, the widths of the signals observed for the Ga
7
8
9
H. S. Sun, X. M. Wang, Y. J. Liu, X. Y. Huang and X. Z. You,
J. Coord. Chem., 1996, 39, 265.
J. E. Bollinger, J. T. Mague and D. M. Roundhill, Inorg. Chem.,
1994, 33, 1241.
D. K. Koggin, P. E. Fanwick and M. A. Green, J. Chem. Soc.,
Chem. Commun., 1993, 807.
III
II
Co compound are relatively lower, which is consistent with
II
the behaviour expected for high-spin Co , for which electronic
relaxation time is short.
N e w J . C h e m . , 2 0 0 5 , 2 9 , 1 1 8 2 – 1 1 8 8
1187

View Online
1996, 100, 2086; (c) S. M. Ostovsky, R. Werner, K. Nag and W.
Haase, Chem. Phys. Lett., 2000, 320, 295.
10 M. Figuet, M. T. Averbuch-Pouchot, A. M. d’Hardemare and
O. Jarjayes, Eur. J. Inorg. Chem., 2001, 2089.
11 N. H. Pilkington and R. Robson, Aust. J. Chem., 1970, 23, 2225.
12 (a) P. Zanello, S. Tamburini, P. A. Vigato and G. A. Mazzocchin,
Coord. Chem. Rev., 1987, 77, 165; (b) P. A. Vigato, S. Tamburini
and D. E. Fenton, Coord. Chem. Rev., 1990, 106, 205.
13 H. Okawa, H. Furutachi and D. E. Fenton, Coord. Chem. Rev.,
1998, 174, 51.
14 B. Bosnich, Inorg. Chem., 1999, 38, 2554.
15 L. K. Thompson, S. K. Mandal, S. S. Tandon, J. N. Bridson and
M. K. Park, Inorg. Chem., 1996, 35, 3317.
19 B. Dutta, P. Bag, B. Adhikary, U. Florke and K. Nag, J. Org.
Chem., 2004, 69, 5419.
¨
20 D. D. Perrin, W. L. Armarego and D. R. Perrin, Purification of
Laboratory Chemicals, Pergamon, Oxford, 2nd edn., 1980.
21 (a) R. R. Gagne, C. L. Spiro, T. J. Smith, C. A. Hamann, W. R.
Thies and A. K. Shiemke, J. Am. Chem. Soc., 1981, 103, 4073; (b)
F. Ullmann and K. Brittner, Chem. Ber., 1909, 42, 2539.
22 B. Dutta, B. Adhikary, P. Bag, U. Florke and K. Nag, J. Chem.
Soc., Dalton Trans., 2002, 2760.
¨
16 S. Mohanta, B. Adhikary, S. Baitalik and K. Nag, New. J. Chem.,
2001, 25, 1466.
23 H. Du, R. A. Fuh, J. Li, A. Corkan and J. S. Lindsay, Photochem.
Photobiol., 1998, 68, 141.
17 B. Dutta, P. Bag, U. Florke and K. Nag, Inorg. Chem., 2005, 44,
24 J. Van Houten and R. J. Watts, J. Am. Chem. Soc., 1976, 98, 4853.
25 K. Nakamoto, Infrared and Raman Spectra of Inorganic and
Coordination Compounds, John Wiley, New York, 5th edn., 1997.
26 (a) I. Bertini, P. Turano and A. Vila, Chem. Rev., 1993, 93, 2883;
(b) I. Bertini and C. Luchinat, NMR of Paramagnetic Substances,
Elsevier, Amsterdam, 1996.
¨
147.
18 (a) S. K. Dutta, J. Ensling, R. Werner, U. Florke, W. Haase, P.
¨
Gutlich and K. Nag, Angew. Chem., Int. Ed. Engl., 1997, 36, 152;
¨
(b) S. Mohanta, C. Saal, K. Nag, S. K. Dutta, R. Werner, W.
Haase, E. Duin and M. Johnson, Ber. Bunsen-Ges. Phys. Chem.,
1188
N e w J . C h e m . , 2 0 0 5 , 2 9 , 1 1 8 2 – 1 1 8 8