Homo- and heteronuclear compounds with a symmetrical bis-hydrazone ligand: Synthesis, structural studies, and luminescent properties

Article abstract of DOI:10.1002/chem.201405962

Nine new coordination compounds have been synthesized by the reaction of salts of bivalent metal ions (a=Zn^II, b=Cu^II, c=Ni^II, d=Co^II) with the bis(benzoylhydrazone) derivative of 4,6-diacetylresorcinol (H₄

Full text of DOI:10.1002/chem.201405962

DOI: 10.1002/chem.201405962
Full Paper
&
Complex Formation
Homo- and Heteronuclear Compounds with a Symmetrical Bis-
hydrazone Ligand: Synthesis, Structural Studies, and Luminescent
Properties
[
a, b]
[a]
[a]
[c]
Sabina Rodrꢀguez-Hermida,
Ana B. Lago, Rosa Carballo, Oscar Fabelo, and
[a]
Ezequiel M. Vꢁzquez-Lꢂpez*
Abstract: Nine new coordination compounds have been
by single-crystal X-ray diffraction. The ligand shows lumines-
II
synthesized by the reaction of salts of bivalent metal ions
cence properties and its fluorimetric behavior towards M
II
II
II
II
(
a=Zn , b=Cu , c=Ni , d=Co ) with the bis(benzoylhydra-
metals (M=Zn, Cu, Ni and Co) has been studied. Further-
more, the solid-state luminescence properties of the ligand
and compounds have been determined at room tempera-
zone) derivative of 4,6-diacetylresorcinol (H L). Three kinds
4
of complexes have been obtained: homodinuclear com-
1
pounds [M (H L) ]·nH O (1a, 1b, 1c, and 1d), homotetranu-
ture. H NMR spectroscopic monitoring of the reaction of
2
2
2
2
II
clear compounds [M (L) ]·n(solv) (2a and 2c), and heterote-
H L with Zn showed the deprotonation sequence of the
4
2
4
tranuclear compounds [Zn M (L) ]·n(solv) (2ab, 2ac, and
OH/NH groups upon metal coordination. Heteronuclear reac-
tions have also been monitored by using ESI-MS and spec-
trofluorimetric techniques.
2
2
2
2
ad). The structures of the free ligand H L·2DMSO and its
4
complexes [Zn (H L) (DMSO) ] (1a*), [Zn (L) (DMSO) ] (2a*),
2
2
2
2
4
2
6
and [Zn0.45Cu3.55(L) (DMSO) ]·2DMSO (2ab*) were elucidated
2
6
Introduction
construct compounds with the desired topologies and these
depend on the appropriate choice of metal ions, in terms of
their coordination number and geometry, and bridging ligands
with a suitable shape, size, flexibility, and denticity. The metal
ions play both a structural role (directing and sustaining the
solid-state architecture) and a functional one (through magnet-
The preparation of solids with useful functionalities is one of
the main goals of crystal engineering. Fluorescent chemosen-
sors are of interest in many research areas, such as environ-
[
1]
[2]
mental control, medical diagnostics, and biological stud-
[
3]
[5]
ies. Nevertheless, many of the fluorescent materials prepared
to date cannot fluoresce efficiently in the aggregated or solid
state because the intrinsic radiative decay pathway of the fluo-
rophore is often disturbed by intermolecular contacts. In this
context, it is necessary to overcome this concentration quench-
ic, optical or redox properties).
Schiff base ligands are commonly used as fluorescence
[6]
probes because of their ease of functionalization and conven-
ient metal-coordination and, consequently, the possibility of
modifying their optical properties. The use of tridentate Schiff
bases to modulate the oxidation state of the metal ion has re-
[4]
ing to obtain efficient solid-state emissive compounds.
[7a]
Control of the coordination architecture is a crucial factor
that determines the chemical and physical properties of the re-
sulting materials. Appropriate synthetic routes are required to
cently been reported, but, although their properties in the
[7b]
formation of dynamic metallosupramolecular polymers and
[7c]
constitutional libraries were reported by the Lehn group
almost a decade ago, tridentate poly-hydrazone ligands have
[7d,e]
been less widely studied.
In the latter ligands, the presence
[a] Dr. S. Rodrꢀguez-Hermida, Dr. A. B. Lago, Prof. R. Carballo,
Prof. E. M. Vꢁzquez-Lꢂpez
Instituto de Investigaciꢂn Biomꢃdica, Universidade de Vigo
Departamento de Quꢀmica Inorgꢁnica, Facultade de Quꢀmica
of two or more reactive sites (which may provide additional
properties to the molecule, such as fluorescence) provides an
additional option through which to tune the molecular re-
3
6310 Vigo, Galicia (Spain)
[8]
sponse towards various chemical species. In this way, hetero-
metallic transition-metal complexes can be synthesized with
polydentate ligands because one approach to isolate hetero-
nuclear compounds is the use of metalloligands that incorpo-
rate different and separate binding sites in the organic skele-
ton or through a bridging-coordinative mode of the donor
E-mail: ezequiel@uvigo.es
[
b] Dr. S. Rodrꢀguez-Hermida
Current address:
ICN2-Institut Catala de Nanociencia i Nanotecnologia
Campus UAB, 08193 Bellaterra, Barcelona (Spain)
[
c] Dr. O. Fabelo
Institut Laue Langevin, Diffraction Group
[9]
groups.
7
1 avenue des Martyrs, 38000 Grenoble (France)
In this study we selected H L (Scheme 1), which is a multi-
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201405962.
4
site coordinating ligand that contains six donor atoms separat-
Chem. Eur. J. 2015, 21, 1 – 13
1
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of two clearly defined coordinative sites allowed us to explore
the effect of the gradual coordination of different ions on the
luminescence properties. Simultaneously, the ability of the hy-
[13]
droxyl group to establish bridges between two metal cen-
ters allowed us to isolate complexes with different nuclearity
(
Scheme 2).
Results and Discussion
Scheme 1. Schematic representation of H
H···N interactions and the two tridentate binding pockets.
4
L showing the intramolecular Oꢀ
Synthesis and characterization
H L was synthesized by a modification of the method previous-
4
[
12]
ed by an aromatic ring to define two symmetrical coordination
pockets. The intramolecular hydrogen bonds associated with
the salicyl and the hydrazone groups preorganize the pockets
towards a cisoid conformation (see for example the different
conformation observed in the non-hydroxylated and in the
ly published by Kotali
but using ethanol in an acidic
medium as the solvent. The symmetrical, ditopic and potential-
ly tridentate double-Schiff base ligand was obtained in good
yield. The ligand is stable in air and is soluble in N,N-dimethyl-
formamide (DMF) and dimethyl sulfoxide (DMSO). The ligand
[
10]
1
mono-hydroxylated ligands ), whereas the methyl group at
both C=N hydrazone groups leads to metal attack only on the
same side of the ligand molecule. Preorganization of the hy-
was characterized by H NMR and IR spectroscopy, by elemen-
+
tal and MS (ESI ) analyses, and its structure was confirmed by
X-ray diffraction analysis. The optical properties (UV/Vis absorp-
tion and emission) were measured in solution and in the solid
state.
[7c]
drazone groups may play a relevant role in the stability and
[
9d]
reactivity of the hydrazone complexes. An additional proper-
ty associated with the presence of salicylaldimine groups is lu-
minescence based on the existence of an excited-state intra-
Three different types of complex based on the M/H L (M=
4
II
II
II
II
Zn , Cu , Ni , and Co ) system were obtained by adjusting the
synthetic conditions (Scheme 2), although the complexes were
isolated from reactions carried out with an equimolar metal
acetate/ligand ratio (1:1:1 in heteronuclear compounds) using
methanol as solvent.
[
11]
molecular proton transfer mechanism (ESIPT). In the work
described here, we explored the coordinative behavior and lu-
[12]
minescent response of this ditopic hydrazone ligand (H L)
4
towards different first-row transition-metal ions. The presence
Scheme 2. Top: Schematic representation of the compounds isolated. Bottom: Those characterized by X-ray diffraction. Some of the DMSO molecules are
omitted for clarity.
&
&
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The different levels of deprotonation were achieved without
ꢀOH and ꢀNH groups were observed at 13.99 and 11.30 ppm,
2ꢀ
additional base under conventional (complexes of H2L ; i.e.,
respectively, for H L (the atomic numbering schemes used in
4
compounds 1a, 1b, 1c, and 1d) or solvothermal (complexes
this paper are shown in Scheme 4, see the experimental sec-
tion). In 1a, these signals were shifted to slightly higher field
and the integration was half, which is consistent with the si-
multaneous deprotonation of the ꢀNH and ꢀOH of one bind-
ing pocket. In the spectrum of freshly prepared solutions of
2a, the absence of these signals in the set of main signals is
consistent with the tetra-anionic character of the ligand and
the coordination of two metal centers by the two pockets.
Nevertheless, very weak signals due to traces of 1a could be
detected and this suggests an equilibrium in solution between
2a and 1a (see below).
4ꢀ
of L ; i.e., compounds 2a and 2c) conditions. Solvothermal
II
II
reactions with Cu and Co yielded unidentified products. All of
the compounds were characterized by elemental analysis,
+
mass spectrometry (ESI ), infrared, diffuse reflectance, and
1
H NMR spectroscopy in the case of the diamagnetic com-
pounds. Attempts to obtain single crystals of the compounds
from the mother liquor were unsuccessful, although single
II
crystals of Zn complexes 1a*, 2a*, and the heteronuclear
II
II
complex Zn /Cu 2ab* were obtained from DMSO solutions.
The results of spectroscopic studies (see below) suggest that
replacement of water present in the as-synthesized com-
pounds by DMSO in the single crystals did not lead to signifi-
cant modifications in the coordinative characteristics of the
metal–ligand core.
Peaks in the ESI mass spectrum at m/z 985, 983, and 974 in
1a, 1b, and 1d, respectively, can be assigned to the molecular
+
ion [M (H L) ꢀH] , thus suggesting the robustness of the dinu-
2
2
2
clear species even in DMSO solutions.
The IR spectra of the complexes provide information about
the involvement of one or two ligand pockets in the coordina-
tion to the corresponding metal ion. The structurally significant
IR bands for the free ligand and its complexes are listed in
Table S1 in the Supporting Information. The infrared spectrum
of the free ligand contains bands centered at 1641, 1513, and
Bearing in mind the frequent occurrence of the di-m-hy-
droxy-bridge core motif (M O ) in the complexes of Schiff base
2
2
[13]
ligands derived from salicylaldehyde (Scheme 2, see below),
we believe that the same structural motif is present in all of
the isolated structures and is a key factor in the stability of the
compounds. As a consequence, the behavior of compounds
ꢀ
1
1
278 cm , which are attributed to n (C=O), n (C=N), and n (Cꢀ 1 is very different to that of the asymmetric ligand recently re-
N), respectively. In the IR spectrum of the homodinuclear com-
pounds 1a–d, two bands corresponding to amide I (n (C=O))
are observed. This behavior has been related to the coexis-
tence of coordinated and uncoordinated carbonyl groups in
ported by us (only an ꢀOH group is present in the aromatic
spacer) because coordination polymers were exclusively isolat-
II
[10b]
ed for a 1:1 (M /L) stoichiometry.
On the other hand, the
isolation of homotetranuclear compounds (2a, 2c) under sol-
vothermal conditions and their reluctance to retain their dis-
crete nature, encouraged us to study the {Zn (H L) } system as
[
10b]
other ditopic dihydrazones.
By contrast, the IR spectra of
2
a and 2c each contain a single redshifted vibration attributed
2
2
2
ꢀ
1
to amide I at 1627 and 1623 cm , respectively, indicating that
both binding pockets are coordinated to metal centers. The
diffuse reflectance spectra contain bands attributed to d-d
transitions of metal atoms (Table S2 in the Supporting Informa-
tion) in 1b–d and 2c in addition to bands with charge transfer
metalloligand for the synthesis of new heterometallic com-
plexes. This hypothesis was reinforced by the ESI-TOF charac-
terization of the reaction solutions (DMSO) between 1a
II
(formed in situ) and equimolar amounts of M acetates
(Table S13 in the Supporting Information). The results of spec-
trofluorimetric studies (see below) on these reaction media are
consistent with the spectrometry results.
(CT) or intra-ligand (IL) character that are common to all of the
complexes.
The thermal stability of compounds 1a–d, 2a, and 2c was
studied by thermogravimetric analysis (Figure S6–S8 in the Sup-
porting Information). The compounds were stable up to 250–
The mononuclear and homodinuclear species [M(H L) ] and
3
2
[M (H L) ] (M=Zn, Co, Ni) were detected in the mass spectra
2
2
2
(Figure S5, Table S13 in the Supporting Information) along with
the heterodinuclear species [ZnCo(H L) ] and [ZnNi(H L) ], al-
3008C, at which point decomposition took place. The thermal
2
2
2
2
II
II
behavior seems to be independent of the di-/tetra-nuclear met-
allic nature. The thermal analysis results helped to assign the
different number of trapped solvent molecules and the conclu-
sions were consistent with the elemental analysis data. It was
observed that all of the compounds seem to be stabilized with
different numbers of water or methanol molecules, and this is
also evident in the isolated single crystals, in which DMSO mol-
ecules are present in all cases. However, the results do not
allow unequivocal determination of the true role of solvents in
the structure. Consequently, the compounds were formulated
as solvate complexes although the coordination of water, for
example in compounds 1a and 2a, is very plausible.
though the Zn cation seems to be replaced by Cu , and only
mono- and di-copper species [Cu(H L) ] and [Cu (H L) ] were
3
2
2
2
2
observed.
Finally, two heterotetranuclear compounds [Zn M (L) ]·n(solv)
2
2
2
II
II
(M=Cu , 2ab and Ni , 2ac) were isolated from the preformed
dimeric compound [Zn (H L) ]. In addition, the resulting solids
2
2
2
were characterized by inductively coupled plasma optical emis-
sion spectrometry (ICP-OES) and energy-dispersive X-ray spec-
troscopy (EDS) analysis. Both techniques indicated an equimo-
lar metal-to-metal ratio within the bulk materials.
II
Interestingly, the resulting materials of the reaction with Co
(described as 2ad in the experimental section) are quite stable
+
NMR studies (on the free ligand and its zinc complexes) and
electrospray ionization (ESI) mass spectrometry were per-
in solution because species such as [ZnCo(H L) +H] was de-
2
2
tected in the ESI-MS. Nevertheless, the lack agreement in the
II
II
formed on [D ]DMSO solutions due to the low solubility of the
Zn /Co molar ratio found by EDS (1:0.6) with ICP-OES (1:0.5)
suggests a nonhomogeneous nature of the materials.
6
1
compounds in other solvents. The H NMR signals due to the
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Moreover, a single shifted amide I band was observed in the
IR spectra (Table S1 in the Supporting Information), which sug-
gests a coordination mode involving both binding pockets.
The diffuse reflectance spectra of the heterotetranuclear com-
plexes confirm the presence of the two metal centers, with
[
14]
II
broad bands that are characteristic of d-d transitions of Cu
II
II
(
2ab), Ni (2ac), and Co (2ad) (Table S2 in the Supporting In-
formation). The bimetallic nature of this kind of compound
could also be studied by X-ray diffraction of single crystals of
2
2
ab*, obtained by slow evaporation of a DMSO solution of
ab. This system can be modulated by exchange of the metal
ion, as observed in the crystal structure of 2ab* in which re-
placement of the zinc atom by copper was detected. This type
of modularity is helpful in the design of new materials because
it allows the physical properties to be tuned without changing
[
15]
the structure of the material.
Structural studies
Structure of the ligand H L·2DMSO
4
The molecular structure of H L·2DMSO is represented in
4
Figure 1 together with the atomic numbering scheme. Select-
ed bond distances and angles are listed in Table S4 in the Sup-
porting Information. The ligand crystallizes with two crystallo-
graphically independent and distorted DMSO molecules in the
monoclinic P2 space group. The molecule is almost planar:
1
the angles between the planes defined by the three rings are
21.99(12)8 and 27.73(13)8, with the aromatic rings clearly locat-
Figure 1. Top: Molecular structure of H
4
L·2DMSO showing the atomic num-
ed in planar segments with rms values ranging from 0.0039 to
bering. Middle: Supramolecular arrangement of H L·2DMSO. Bottom: details
4
of the NꢀH···O and CꢀH···O interactions and the OꢀH···N intramolecular inter-
0
.0067. The C(6)ꢀN(6) and C(6)ꢀO(6) bond distances are typical
action.
of the amide resonance form (Table S4 in the Supporting Infor-
mation).
An interesting parameter that highlights differences be-
tween the free ligand and its complexes is the length of the in-
tramolecular OꢀH···N hydrogen bond. The structural parame-
ters in the interaction O(3)ꢀH···N(5) are indicative of an interac-
Structures of complexes 1a*, 2a*, and 2ab*
Crystal data and selected bond distances and angles for 1a*,
2a*, and 2ab* are listed in Tables S3 and S5–S7, respectively.
Compound 2a* crystallizes in the triclinic P 1¯ space group and
[16]
tion between a strong and moderate hydrogen bond
(
Table S9 in the Supporting Information) to generate six-mem-
bered rings [rms=0.0338 (N5a-C5a-C4a-C3a-O3a-H3a) and
.0498 (N5b-C5b-C4b-C3b-O3b-H3b)]. These intramolecular H-
bonds are of particular interest for a number of reasons:
) they are probably responsible for the planar arrangement of
1a* and 2ab* crystallize in the monoclinic P2 /c and P2 /n
1
1
space groups, respectively. Compound 1a* is a homodinuclear
dimer with an uncoordinated pocket. Compounds 2a* and
2ab*, neither of which have uncoordinated pockets, are homo-
tetra- and heterotetranuclear compounds, respectively.
0
1
[
10]
the molecular structure of the free ligand; 2) they are re-
The structures correspond to neutral discrete compounds in
which DMSO solvent molecules complete the coordination
sphere and also contribute to the supramolecular association
sponsible for the luminescence of H L (see below)—a property
4
that should be affected by the metal coordination.
The molecular association in the crystal structure is achieved
by means of weak H-bonds involving aromatic CꢀH groups
and hydroxyl groups (Table S9 in the Supporting Information,
Figure 1) and the DMSO solvent molecules, which act as
a ‘glue’ between the ligand molecules: as H-donors with the
ligand oxygen atoms O(3) and O(6) and as acceptors with the
by establishing different interactions (see below; Scheme 2).
II
All M cations are {NO } pentacoordinated through O(3),
4
N(5), and O(6) atoms of one ligand molecule to generate five-
and six-membered chelate rings and by an oxygen atom of
a DMSO molecule. The fifth position is occupied by one O(3)
atom belonging to a neighboring ligand (coordination sphere
N(6)-H groups. These interactions are reinforced by C(12)ꢀ A, Figure 2) [in 1a* the Zn(1) atom of 2a* and in M(1) and
H···O(s) and C(13)ꢀH···O(s) interactions (Table S9 in the Support-
M(3) in 2ab*] or by another DMSO molecule [Zn(2) in 2a* and
Cu(2) and Cu(4) in 2ab*] (coordination sphere B).
ing Information) in a similar way to that observed in a previous-
[
10b]
ly published asymmetrical dihydrazone.
In addition, C(11)ꢀ
The geometry around the metallic centers can be described
[17]
H···O(6) and CꢀH···p interactions are also observed in the
as a square pyramid because the Addison parameter (t)
supramolecular arrangement.
values are within the range 0.008–0.355 (Table S8 in the Sup-
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The ligand moiety retains its planarity after coordination in
2
ab* (29.18, 5.04, 6.38, and 30.348), whereas in 1a* and 2a*
the terminal phenyl rings are rotated and this planarity is
broken (14.98, 27.66, 54.41, and 2.028 for 1a*, and 14.45 and
57.598 for 2a*). In 1a* and 2a*, the ligand moieties are ar-
ranged in a parallel manner (the angles between the planes
formed by the central aromatic ring of both ligand molecules
is 9.09 and 08, respectively). By contrast, in 2ab*, the ligands
form an angle of 50.358, which is similar to the H-bond angle
N(6b)-H-O(6b) established in 1a* (see below).
Coordination prevents the formation of the OꢀH···N intramo-
lecular H-bonds observed in the free ligand and in the uncoor-
dinated pocket of 1a*. Moreover, the deprotonation of NH
groups upon coordination implies the presence of the enol
form in the carboxamide fragments in the coordinated pock-
ets, as deduced from the bond distances (Tables S5–S7).
The protonated nature of the -NH group in the uncoordinat-
ed pocket of 1a* allows the interaction with the oxygen atom
of a DMSO molecule of a neighboring unit. The -NH and -CH
groups of the ligand act as donors and the oxygen atom of
the DMSO molecule acts as an acceptor in this interaction
(Figure 3). This situation leads to the formation of the stable
synthon observed in the free ligand and in a previous study
with a related asymmetrical ligand (Table S10 in the Support-
Figure 2. Schematic representation and main structural differences in com-
plexes 1a*, 2a*, and 2ab*.
porting Information). The main distortion is found in the outer
zinc metal atoms coordinated to two DMSO molecules in com-
pound 2a*. The apical position is occupied by a DMSO mole-
cule in the three structures, with MꢀO distances in the range
[10b]
2.016–2.461 ꢄ for M=Zn and 2.045–2.236 ꢄ for M=Cu.
ing Information).
Zig-zag chains are formed by C(10b)ꢀ
In the homodinuclear compound 1a*, the ligand is bidepro-
H···O(6d) interactions along the crystallographic b axis. These
chains are interconnected in a double strand by the supra-
molecular N(6b)ꢀH···O(6b) synthon and this arrangement is re-
inforced by CꢀH···p interactions (Figure 3, Table S10 in the Sup-
porting Information). These double-strand chains are intercon-
nected by means of N(6d)ꢀH···O(2s) interactions with the
DMSO molecules.
tonated to form a dianionic binding site in one pocket, which
leads to a dimeric structure in which two metal–ligand units
are linked by a m-phenolate-bridged Zn O core. In 2a* and
2
2
2
ab* the ligand is tetradeprotonated and adopts the m-
3
3
k O,N,O’:kO’ and k O,N,O’ coordination modes. The bridging
coordinative behavior of the O(3) atom allows the formation of
M O2 cores. This core is
2
a common structural motif in all
of the structures. The Zn···M
II
II
(
M=Zn or Cu ) distance is
3
.102, 3.184, and 3.058 ꢄ in 1a*,
a*, and 2ab*, respectively. In
[
13]
2
all cases, this core is coplanar
with the planar ligand binding
pocket. This structural feature
has been observed previously in
aroylhydrazone complexes with
M···M distances in a similar range
[
13b,18]
(3.058–3.184 ꢄ).
This unit is
always composed of zinc atoms
except in 2ab*, in which the
structural disorder in the central
core was interpreted as a partial
replacement of zinc atoms
(
using EADP Shelxl instruc-
[
19]
tions
)
from
the
initial
[
Zn (H L) ] precursor by copper
2 2 2
atoms to generate ((Cu/Zn) ꢀO )
2
2
units, whereas the two external
pockets are exclusively occupied
by copper atoms.
Figure 3. Supramolecular association in 1a* showing details of the supramolecular synthon.
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Similar hydrogen-bonding interactions, based on a donor
NꢀH group, are not possible due to the deprotonated charac-
ter of the ligand in 2a* and 2ab*. Indeed, in these complexes,
nitrogen atoms act as acceptors and establish interactions with
the CꢀH groups [C(11b)ꢀH and C(43s)ꢀH] in 2a*. Moreover,
C(9b)ꢀH···O(2s) interactions established with DMSO solvent
molecules are observed (Figure S1, Table S11 in the Supporting
Information). In 2ab*, DMSO molecules (coordinated and un-
coordinated) are responsible for the supramolecular associa-
tion through DMSO···DMSO, DMSO···O(6), and C(9)ꢀH···DMSO
interactions (Figure S1, Table S12 in the Supporting Informa-
tion).
assigned to p–p* absorptions associated with the C=N azome-
[7a]
thine bond ) in the solid state has a tail at approximately
400 nm, whereas a clear band was observed in the solution
spectrum with a maximum at 420 nm. This bathochromic shift
is interesting because this band is associated with the emis-
sion: upon excitation at 430 nm (and 350 nm), the emission
bands in solid state and in solution are centered at lmax 535
and 500 nm, respectively.
The differences between the two states are probably due to
different intermolecular interactions involving the solvent
(DMSO) in the ground and excited states. However, it is not
easy to establish correlations between the two states because
the intrinsic radiative decay pathway is often disturbed by in-
[4]
termolecular contacts in the aggregate or the solid state.
Gradual addition of NaOH to the H L solution led to an in-
crease in the intensity of the absorption band around 430 nm
Figure S3A in the Supporting Information). More interestingly,
Fluorescence studies
4
The two intramolecular OꢀH···N hydrogen bonds associated
(
with the ketimine groups of the ligand H L encouraged us to
4
although the intensity of the emission (along with splitting of
the band) was initially observed, after reaching the maximum
explore the luminescence properties, because this intramolecu-
lar hydrogen bond allows triggered emission through an excit-
ed state intramolecular proton transfer mechanism (ESIPT; Fig-
intensity at a 1:1 ratio of H L/NaOH, the emission was finally
4
quenched when a 1:2 molar ratio was reached (Figure S3B in
the Supporting Information). Although the first process can be
[
11,16,20]
ure S2 in the Supporting Information).
The ESIPT process
involves transfer of the hydroxyl proton to an imine nitrogen
located less than 2 ꢄ away through a pre-existing six-mem-
ꢀ
attributed to the improved protonation transfer in the H3L
species as a result of resonance stabilization induced by the
deprotonated pocket, similar to the effects that were observed
[
21]
bered-ring hydrogen-bonding configuration. ESIPT dyes gen-
erally have large Stokes shifts and are ideal candidates for use
[23]
by Xu and Pang in bis(benzoxazole) derivatives, the small
value of the Stokes shift casts doubt on the true origin of this
[
22]
as fluorescence labels.
The photophysical properties of H L were studied at room
4
ꢀ
emission in H L . The final quenching at a 1:2 ratio of H L/
3
4
temperature in DMSO solution, because of the lack of solubility
in other solvents, and in the solid state (Figure 4) to confirm
the structural integrity in solution.
2ꢀ
NaOH suggests the formation of H2L by deprotonation of
both phenolic OH groups—a situation that is consistent with
the higher acidity observed for this group in the salicylaldimine
hydrazones.
Three absorption bands were observed in the spectrum of
H L in DMSO solution: two intense bands at 295 and 350 nm
4
The addition of M(AcO) (M=Zn, Co, Cu and Ni) to H L in
2
4
and a weak absorption at 420 nm. The solid diffuse reflectance
DMSO at room temperature also caused changes in the ab-
spectrum of H L exhibits intense absorptions at l
260 and
4
max
II
sorption spectra (Figure 5 and 6). The addition of the M cat-
3
35 nm. The highest energy band is probably due to a p!p*
transition of aromatic rings whereas the intense band above
00 nm is assigned to the n!p* transition of the hydrazone
azomethine) chromophore. The latter band (which is usually
ions led to a progressive increase in the intensity of the band
at 420 nm and this change was accompanied by a decrease in
the absorption bands at 295 and 350 nm along with the emer-
gence of a new band at approximately 320 nm. The presence
of an isosbestic point in all experiments (ca. 375 nm) suggests
the formation of new species during the additions.
3
(
It was possible to distinguish two kinds of fluorescence re-
II
sponse of H L depending on the electronic nature of the M
4
II
II
cations. The addition of increasing amounts of Co , Ni , and
II
Cu led to a quenching in the emission intensity, which was
complete when a 1:1 molar ratio was reached (Figure 5). This
feature can be related to the paramagnetic nature of the metal
[24]
atoms, which play a relevant role in the quenching process.
On the other hand, this quenching occurs at the equimolar
point; therefore, the formation of a coordination polymer of
[10b]
n
the type [M(H L)]
cannot be ruled out.
2
II
The behavior was completely different when Zn was used.
Fortunately, the diamagnetic nature of this cation allowed the
1
reaction in [D ]DMSO to be monitored by H NMR spectrosco-
6
py (Figure S4 in the Supporting Information). In this experi-
4
Figure 4. Absorption (left) and emission (right) spectrum at RT of H L (solid
ment, signals were observed for the OꢀH and NꢀH groups
line) in the solid state, and (dashed line) in DMSO solution
ꢀ
5
II
([H
4
L]=1ꢅ10 m). lex =430 nm (black lines); lex =350 nm (gray lines).
(13.49 and 11.12 ppm, respectively) at a 1:1 H L/Zn molar ratio
4
&
&
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II
II
II
Figure 5. Spectrophotometric (top) and fluorimetric (bottom) monitoring of the reactions of H
at RT [H L]=1·10 m, [M ]=1ꢅ10 m. lex =430 nm.
4
4
L with (left) Co , (middle) Ni , and (right) Cu cations in DMSO
ꢀ5
II
ꢀ2
and only when a 1:2 ratio was reached were these signals
absent.
sensitivity of fluorescence spectroscopy provided evidence for
the existence of a protonation–chelation equilibrium in solu-
tion on the second pocket (Scheme 3).
Spectrofluorometric monitoring of the reaction showed
a marked increase in the emission intensity (ca. 60-fold en-
hancement), upon addition of one equivalent of zinc acetate
The formation of heterotetranuclear [Zn M (L) ] complexes
2
2
2
from [Zn (H L) ] was also monitored by using spectrofluorimet-
2
2
2
(
Figure 6). The ESI-TOF mass spectra of the reaction mixtures at
ric techniques. In these studies, zinc acetate was added to H4L
until a 1:1 molar ratio was reached and increasing amounts of
+
this molar ratio contained signals due to [Zn (H L) ] and
2
2
2
+
II
[
Zn(H L)] , which suggests the predominance of species based
the other M acetate (M=Cu, Ni, Co) were then added
2
on 1a. The solid-state fluorescence spectrum of 1a displays
(Figure 7).
a broad band centered at 475 nm and a shoulder at 535 nm
The initial increase in the emission intensity is consistent
with the formation of [Zn (H L) ] at a 1:1 molar ratio, and this
(
Figure 6) and this matches reasonably well with the spectra of
2
2
2
II
the Zn /H L solutions in a 1:1 molar ratio. Once again, deproto-
was followed by a gradual decrease in fluorescence on addi-
4
II
nation, and probably coordination in the present case, of one
of the pockets seems to increase the basic character of the ni-
trogen atom in the other pocket, thus improving the emis-
tion of M until the L/Zn/M molar ratio was 1:1:1. When copper
or cobalt acetates were added, a plateau appeared in the spec-
trum and fluorescence quenching was observed. It is notewor-
thy that the point at which the fluorescence is switched off
was only reached at a 1:1:3 ratio when nickel acetate was
added.
[
25]
sion.
The addition of more zinc acetate caused changes in the ab-
sorption and emission spectra, which is consistent with the in-
II
teraction of the second Zn with the free pocket of the species
The switch-off in fluorescence emission can be attributed to
1
a formed in solution. An interesting aspect of this reaction is
the replacement of the Zn by Cu or Co (with behavior analo-
II
that although the fluorescence intensity decreases when more
gous to that observed in the direct reaction of H L and Cu or
4
II
II
Zn is added, it is still higher compared with that of the free
Co ) or to the formation of 1:1:1 (L/Zn/M) complexes, in which
II
ligand [25-fold enhancement when a 1:2 (H L/Zn ) molar ratio
the paramagnetic nature of M may influence the final quench-
ing. In agreement with the latter hypothesis, signals attributa-
ble to heterodinuclear species were observed in the ESI-TOF
4
is reached]. Although the NMR spectrum of this medium
showed only very small signals for the -OH proton, the better
Chem. Eur. J. 2015, 21, 1 – 13
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7
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Scheme 3. Representation of the ESIPT mechanism of 1a and the equilibri-
um between 1a and 2a in solution.
Scheme 4. Schematic representation of the ligand and its complexes show-
ing the atomic labeling used.
spectra of the H L/Zn/Co reaction medium but they were
4
absent in the H L/Zn/Cu system. Consequently, a different be-
4
II
II
havior of [Zn (H L) ] in conjunction with Co or Cu cannot be
2
2
2
II
ruled out. Nevertheless, the case of Ni warrants further consid-
Figure 6. Top: Spectrophotometric and fluorimetric monitoring of the reac-
II
ꢀ5
II
ꢀ2
tion of H
Bottom: Fluorimetric measurement of H
dashed line) at RT in the solid state. lex =430 nm.
4
L with Zn in DMSO at RT ([H
4
L]=1·10 m, [Zn ]=1ꢅ10 m).
4
L (black), 1a (gray), and 2a (gray
&
&
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Figure 7. Top: Schematic representation of the coordination sequence. Bottom: Spectrophotometric (upper) and fluorimetric (lower) monitoring of the reac-
II
II
II
II
tions of H
4
L (black lines) with Zn (gray solid lines) to a 1:1 molar ratio and then with Co (A), Ni (B), Cu (C) cations (gray dashed lines) in DMSO at RT
ꢀ
5
II
ꢀ2
(
[H L]=1·10 m, [M ]=1ꢅ10 m, lex =430 nm).
4
eration because: 1) the ESI-TOF spectra of the reaction media
display signals due to Ni/Zn species (Figure S5 in the Support-
ing Information); 2) in the absence of Zn, the reaction with the
free ligand led to quenching of the fluorescence (see above);
heterotetranuclear compounds. The structural parameters of
these three types of compounds in the solid state were ana-
lyzed by X-ray diffraction. It was demonstrated that the fluores-
cence behavior of H L depends on the coordination of the
4
3
) in the presence of [Zn (H L) ], additional overconcentration
{ONO} binding pockets because this emission is based on an
excited state intramolecular proton transfer (ESIPT) mechanism.
Deprotonation of one of the pockets on addition of a base or
2
2
2
is necessary to quench the fluorescence. In fact, the behavior
in this case was similar to that observed in the reaction of
II
II
[Zn (H L) ] with Zn .
by coordination of Zn gives rise to an extraordinary enhance-
2
2
2
ment in the emission intensity and only if deprotonation of
the second pocket is achieved is the emission finally
quenched. The results of ESI-TOF mass spectrometry studies
on the zinc-containing reaction media suggest the presence of
dimeric species, and the X-ray structures of [Zn (H L) (DMSO) ]
Conclusion
The nature of the symmetrical and multi-site coordinating hy-
drazone ligand H L allowed the isolation, from different reac-
4
2
2
2
2
tions with a variety of divalent metal atoms, of three different
kinds of complexes: homodinuclear, homotetranuclear, and
(1a*) and [Zn (L) (DMSO) ] (2a*) confirm this hypothesis. In
4 2 6
both cases, the association of the two units is based on the di-
Chem. Eur. J. 2015, 21, 1 – 13
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9
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&
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amond-shaped Zn O core formed by the bridging phenolate
solution was heated to reflux for 2 h and the resulting white solid
2
2
was filtered off and vacuum-dried over CaCl /NaOH. Suitable crys-
groups.
2
II
II
tals of H L·2DMSO were obtained after storing a DMSO solution at
The fluorimetric response of the ligand H L towards Co , Ni ,
4
4
1
II
RT for 20 days. Yield: 0.190 g (86%); H NMR (400 MHz, [D
]DMSO,
6
and Cu is completely different because a gradual decrease in
2
7
58C): d=13.99 (s, 2H; O3-H), 11.30 (s, 2H; N6-H), 7.94 (d, J=
.2 Hz, 4H; C8-H+C12-H), 7.83 (s, 1H; C2-H), 7.63 (t, J=7.3 Hz, 2H;
the emission intensity was observed on addition of the metal.
Although the formation of polymeric compounds in which
both binding pockets are used in the metal coordination
cannot be ruled out, ESI-TOF studies on the reaction media
suggest the formation of compounds based on dimeric
C10-H), 7.53 (t, J=7.4 Hz, 4H; C9-H+C11-H), 6.37 (s, 1H; C1-H),
.55 ppm (s, 6H; C13-H); IR (KBr): n˜ =3434 + 3224 (m; OH-NH),
2
ꢀ
1
1641 (vs; C=O), 1513 (m; C=N), 1278 (s) cm (CꢀN); MS (ESI): m/z
+
(%): 431 (100) [H
L ]; elemental analysis calcd (%) for C24
H
N
4
O
4
: C
5
22
6
6.97, H 5.15, N 13.02; found: C 66.65, H 5.17, N 12.97.
[
M (H L) ] units.
2 2 2
The ability of the fragment {Zn (H L) } to act as a metalloli-
Synthesis of homodinuclear complexes of general formula
2
2
2
II
II
II
II
II
[
M (H L) ]·nH O: 1a (Zn ), 1b (Cu ), 1c (Ni ), and 1d (Co ): A solu-
gand was also tested against M and several heterotetranuclear
compounds were isolated. The reactions were monitored by
ESI-TOF MS, with peaks due to heterodinuclear species ob-
served, and by analysis of the spectrophotometric and fluori-
metric response. The fluorimetric responses of {Zn (H L) }
2 2 2 2
tion of M(AcO) ·nH O (0.22 mmol) in MeOH (10 mL) was added to
2
2
a suspension of H L (0.1 g, 0.23 mmol) in MeOH (20 mL). The sus-
4
pension was heated to reflux for 2 h and the resulting solid was fil-
tered off and vacuum-dried over CaCl /NaOH.
2
2
2
2
Data for [Zn (H L) ]·2(H O) (1a): Yield: 0.102 g (43%); dark yellow.
II
2
2
2
2
(
which is different to that of H L) towards the different M cat-
1
4
H NMR (400 MHz, [D ]DMSO, 258C): d=13.43 (s, 1H; O3a-H), 11.09
6
ions were not identical. The fluorescence was completely
(s, 1H; N6a-H), 8.09 (s, 2H; C8a-H+C12a-H), 7.94 (s, 2H; C8b-H+
II
II
quenched at 1:1:1 (H L/Zn/M) ratios when M=Co and Cu ,
4
C12b-H), 7.71 (s, 1H; C2-H), 7.61–7.40 (m, 6H; C9a-H+C9b-H+
C10a-H+C10b-H+C11a-H+C911-H), 6.03 (s, 1H; C1-H), 2.73 ppm
(s, 6H; C13a-H+C13b-H). IR (KBr): n˜ =3442, 3226 (m; OHꢀNH),
II
whereas an excess of Ni was necessary to achieve quenching.
Although these results suggest that the reacting metal cations
interact with the free pocket of the metalloligand, the isolation
of single crystals of [Zn0.45Cu3.55(L) (DMSO) ]·2DMSO (2ab*)
ꢀ
1
1
641 (vs) + 1625 (vs; C=O), 1508 (vs; C=N), 1276 (s) cm (CꢀN);
+
+
MS (ESI): m/z (%): 431 (29) [H L] , 571 (10) [Zn(H L)(DMSO)] , 923
5
3
2
6
+
+
(
30) [Zn(H L) +H] , 985 (17) [Zn (H L) +H] ; elemental analysis
3 2 2 2 2
proves that replacement of the metal in the original Zn O dia-
2
2
calcd (%) for C H N O Zn ·2H O: C 56.32, H 4.33, N 10.95; found:
48
40
8
8
2
2
mond is also possible. The bimetallic nature of these materials
could also be analyzed in the solid state by using EDS and
OIC-PC techniques.
C 56.29, H 4.68, N 10.88.
[
Zn (H L) (DMSO) ] (1a*): The DMSO solvate of this complex was
2
2
2
2
obtained as single crystals by slow evaporation (1 month) at RT of
a DMSO solution of 1a.
Data for [Cu (H L) ]·4(H O) (1b): Yield: 0.109 g (45%); green; IR
2
2
2
2
Experimental Section
(
KBr): n˜ =3438 (vs; OH-NH), 1646 (m) + 1618 (vs; C=O), 1517 (vs;
ꢀ1
+
C=N), 1267 (s) cm (CꢀN); MS (ESI): m/z (%): 431 (6) [H L] , 492 (7)
Materials and physical measurements
5
+
+
+
[
Cu(H L)] , 570 (100) [Cu(H L)(DMSO)] , 631 (27) [Cu (HL)(DMSO)] ,
922 (27) [Cu(H L) +H] , 983 (11) [Cu (H L) +H] ; elemental analy-
3 2 2 2 2
3
3
2
+
+
Metallic salts and solvents were obtained commercially and were
used as supplied. Elemental analyses (C, H, N) were carried out
with a Fisons EA-1108 microanalyser. IR spectra were recorded
sis calcd (%) for C H N O Cu ·4H O: C 54.59, H 4.58, N 10.61;
48
40
8
8
2
2
found: C 54.64, H 4.23, N 10.48.
ꢀ
1
from KBr discs (4000–400 cm ) with a Bruker Vector 22 spectro-
Data for [Ni (H L) ]·5(H O) (1c): Yield: 0.108 g (42%); dark-orange;
2
2
2
2
1
photometer. H NMR spectra were obtained with a Bruker AMX 400
IR (KBr): n˜ =3401 (m; OHꢀNH), 1622 (sh) + 1592 (s; C=O), 1524 (vs;
spectrometer. Mass spectra were recorded with a Hewlett–Packard
ꢀ1
+
C=N), 1275 (s) cm (CꢀN); MS (ESI): m/z (%): 431 (29) [H L] , 565
5
5
989A spectrometer. TGA was performed with a SETSYS Evolution
+
+
(
96) [Ni(H L)(DMSO)] , 917 (100) [Ni(H L) +H] ; elemental analysis
3
3
2
Setaram thermogravimetric analyser in a flow of N with a heating
2
calcd (%) for C H N O Ni ·5H O: C 54.17, H 4.74, N 10.53; found:
ꢀ1
48 40
8
8
2
2
rate of 108Cmin . UV/Vis absorption and emission spectra were
obtained with HP 8453 and Horiba-Jobin–Yvon Fluoromax-3 TCSPC
spectrophotometers in DMSO at RT; excitation and emission slits of
C 54.55, H 4.30, N 10.33.
Data for [Co (H L) ]·8(H O) (1d): Yield: 0.110 g (43%); dark-brown.
2
2
2
2
IR (KBr): n˜ =3417 (m; OHꢀNH), 1625 (m) + 1577 (vs; C=O), 1521
2
.0 or 5.0 nm were used for the measurements. Spectrofluorimetric
measurements in the solid state were collected with a Jasco-FP-
300 spectrofluorimeter with excitation and emission bandwidths
ꢀ
1
+
(
4
vs; C=N), 1276 (m) cm (CꢀN). MS (ESI): m/z (%): 431 (7) [H L] ,
5
+
+
87 (7) [Co(H L)] , 566 (27) [Co(H L)(DMSO)] , 916 (6) [Co(H L) +
3 3 3 2
8
+
+
II
II
II
II
H] , 974 (11) [Co
(H L) +H] ; elemental analysis calcd (%) for
2 2 2
of 5 nm. Determination of metals [Co , Ni , Cu , Zn ] in heterome-
tallic compounds was carried out with a PerkinElmer Optima 4300
DV Optical Inductively Coupled Plasma Spectrometer (OIC-PC). The
heterometallic nature of the compounds was also confirmed with
a JEOL JSM6700F Field Emission Scanning Electron Microscope (FE-
SEM) equipped with an Oxford Inca Energy SEM 300 X-ray detector
C H N O Co ·8H O: C 51.53, H 5.04, N 10.01, C 51.22, H 4.46, N
48
40
8
8
2
2
9
.60.
Synthesis of homotetranuclear complexes of general formula
II
II
[M
(L) ]·n(solv): 2a (Zn ) and 2c (Ni ): The reaction performed
2
4
under solvothermal conditions (heating at 1108C for 24 h followed
ꢀ1
(
EDS).
by slow cooling to RT at a rate of 0.608Ch ) of H
L (0.1 g,
4
0
.23 mmol) and M(AcO) ·nH O (0.22 mmol) in MeOH (40 mL) afford-
2
2
ed homogeneous precipitates in both syntheses. The solids were
Synthesis of the compounds
filtered off and vacuum-dried over CaCl /NaOH.
2
Synthesis of H L: A warm colorless solution of 4,6-diacetylresorci-
Data for [Zn (L) ]·2(H O) (2a): Yield: 0.058 g (21%); yellow.
4
4
2
2
1
nol (0.1 g, 0.51 mmol) in EtOH (20 mL) was added dropwise to a so-
lution of benzoic hydrazide (0.208 g, 1.53 mmol) in EtOH (20 mL).
Immediately, 1 drop of concentrated HCl was added. The colorless
H NMR (400 MHz, [D ]DMSO, 258C): d=8.20–7.38 (m, 12H; C1-H+
6
C2-H, C8-H+C9-H+C10-H+C11-H+C12-H), 2.79–2.67 ppm (m,
6H; C13-H); IR (KBr): n˜ =3430 (s; OH), 1627 (s; C=O), 1539 (s; C=N),
&
&
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Full Paper
ꢀ
1
+
1
259 (m) cm (CꢀN); MS (ESI): m/z (%): 431 (9) [H L] , 493 (11)
The structures were solved by direct methods using the program
SHELXS97. All non-hydrogen atoms were refined with anisotrop-
5
+
+
[29]
[
[
Zn(H L)] ,
571
(14)
[Zn(H L)(DMSO)] ,
730
(11)
3
3
+
+
Zn (HL)(H O)(DMSO) ] , 923 (15) [Zn(H L) +H] ; elemental analy-
sis calcd (%) for C H N O Zn ·2H O: C 50.11, H 3.50, N 9.74;
ic thermal parameters by full-matrix least-squares calculations on
2
2
2
3
2
2
[19]
F using the program SHELXL2013/2.
4
8
36
8
8
4
2
found: C 50.39, H 3.87, N 9.61.
Hydrogen atoms were inserted at calculated positions and con-
strained with isotropic thermal parameters, except for the hydro-
gen atoms of the -NH and -OH groups, which were located from
[
Zn (L) (DMSO) ] (2a*): The DMSO solvate of this complex was ob-
4
2
6
tained as single crystals by slow evaporation (1 month) at RT of
a DMSO solution of 2a.
difference Fourier maps in H L·2DMSO and 1a*.
4
Data for [Ni (L) ]·2(MeOH)·4(H O) (2c): Yield: 0.056 g (23%);
In 2ab*, the AEDP command was used to refine the metal center
positions, giving rise to 90% and 65% occupancy for Cu(1) and
Cu(3), and 10% and 35% for Zn(1) and Zn(3), respectively. Draw-
4
2
2
brown; IR (KBr): n˜ =3413 (m; OH), 1623 (s; C=O), 1536 (m; C=N),
ꢀ
1
+
1
[
260 (m) cm (CꢀN); MS (ESI): m/z (%): 431 (4) [H L] , 543 (44)
5
+
+
[30]
Ni (HL)] , 917 (4) [Ni(H L) +H] ; elemental analysis calcd (%) for
ings were produced with MERCURY and special computations
2
3
2
C H N O Ni ·2MeOH·4H O: C 49.07, H 4.28, N 9.16; found: C 49.02,
H 4.51, N 9.51.
for the crystal structure discussions were carried out with
PLATON.
4
8
36
8
8
4
2
[31]
Synthesis of heterotetranuclear complexes of general formula
CCDC 1032627 (H L·2DMSO), 1032628 (1a*), 1032629 (2a*) and
4
II
II
[
Zn M (L) ]·n(solv): 2ab (M=Cu ), 2ac (M=Ni ), and 2ad (M=
1032630 (2ab*) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif. Selected bond lengths and angles and hydrogen
bond lengths for the crystal structures are listed in Tables S4–S12
in the Supporting Information.
2
II
2
2
Co ): A solution of Zn(AcO) ·2H O (0.056 g, 0.26 mmol) in MeOH
2
2
(
10 mL) was added to a suspension of H L (0.114 g, 0.26 mmol) in
4
the same solvent (20 mL). The yellow suspension was heated to
reflux for 2 h, then the suspension was cooled to RT and a solution
of M(AcO) ·nH O (0.26 mmol; 0.057 g of Co(AcO) ·4H O, 0.045 g of
2
2
2
2
Cu(AcO) ·H O, or 0.064 g of Ni(AcO) ·4H O) in MeOH (10 mL) was
2
2
2
2
added. The mixture was heated to reflux for 2 h and the resulting
solids were filtered off and dried under vacuum over CaCl /NaOH.
2
Acknowledgements
Data for [Zn Cu (L) ]·2(H O) (2ab): Yield: 0.132 g (41%); pale-
2
2
2
2
green; IR (KBr): n˜ =3446 (m; OH), 1590 (s; C=O), 1564 (s; C=N),
Financial support from the Spanish Ministry of Education and
Science (project CTQ2010–19386/BQU) is gratefully acknowl-
edged. We acknowledge the Spanish BM16 beamline (Dr. A.
Labrador) facility at the ESRF (Grenoble, France) for provision
of synchrotron radiation beam time under project 16–01–747.
A. B. L. thanks the Xunta de Galicia for a postdoctoral contract
under the “ꢆngelesAlvariÇo” program.
ꢀ1
+
1
266 (m) cm (CꢀN); MS (ESI): m/z (%): 431 (5) [H L] , 570 (69)
5
+
+
[
Cu(H L)(DMSO)] , 631 (9) [Cu (HL)(DMSO)] , 922 (100) [Cu(H L) +
3 2 3 2
+
H] ; elemental analysis calcd (%) for C H N O Zn Cu ·2H O: C
48
36
8
8
2
2
2
5
9
0.27, H 3.52, N 9.77, Cu 10.47, Zn 10.63; found: C 50.16, H 3.91, N
.65, Cu 11.08, Zn 11.40.
[
Zn0.45Cu3.55(L) (DMSO) ]·2DMSO (2ab*): The DMSO solvate of this
2 6
complex was obtained as single crystals by storing a DMSO solu-
tion of 2ab at RT for 1 month. Insufficient crystals were obtained
for elemental analysis or a meaningful estimation of yield.
Keywords: copper · hydrazones · luminescence · nickel · zinc
Data for [Zn Ni (L) ]·4(H O)·2(MeOH) (2ac): Yield: 0.122 g (38%);
2
2
2
2
dark yellow; IR (KBr): n˜ =3411 (m; OH), 1594 (s; C=O), 1565 (s; C=
ꢀ1
+
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(
[
83) [Ni(H L)(DMSO)] , 571 (16) [Zn(H L)(DMSO)] , 917 (70)
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2
2
2
2
99–108.
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ꢀ
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Received: November 5, 2014
Published online on && &&, 0000
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&
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ꢃ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
FULL PAPER
All in the metal: Reactions of bis(ben-
&
Complex Formation
zoylhydrazone) derivatives of 4,6-diace-
2
+
S. Rodrꢀguez-Hermida, A. B. Lago,
R. Carballo, O. Fabelo,
tylresorcinol with M (M=Zn, Cu, Ni,
Co) yield three kinds of complexes: ho-
modinuclear [M (H L) ], homotetranu-
E. M. Vꢁzquez-Lꢂpez*
2
2
2
clear [M (L) ], and heterotetranuclear
4
2
&& – &&
compounds [Zn M (L) ] (see figure). The
2
2
2
ligand luminescence properties and its
Homo- and Heteronuclear Compounds
with a Symmetrical Bis-hydrazone
Ligand: Synthesis, Structural Studies,
and Luminescent Properties
2
+
fluorimetric behavior towards M
metals (M=Zn, Cu, Ni and Co) has been
studied.
Chem. Eur. J. 2015, 21, 1 – 13
www.chemeurj.org
13
ꢃ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ