Inorganica Chimica Acta 381 (2012) 85–94

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Inorganica Chimica Acta

journal homepage: www.elsevier .com/locate / ica

Novel emissive phenylurea-based macrocyclic chemosensor: Synthesis,fluorescent and complexation studies

Cristina Núñez a,b,⇑, Anxela Aldrey c, Verónica García c, Rufina Bastida c,⇑, Alejandro Macías c,Carlos Lodeiro a,b

a Grupo BIOSCOPE, Departamento de Química Física, Facultade de Ciencias, Universidade de Vigo, Campus de Ourense, E32004 Ourense, Spainb REQUIMTE-CQFB, Departamento de Química, FCT-Universidade NOVA de Lisboa, 2829 Monte de Caparica, Portugalc Departamento de Química Inorgánica, Facultade de Química, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Spain

a r t i c l e i n f o a b s t r a c t

Article history:Available online 13 June 2011

Fluorescence Spectroscopy: from SingleChemosensors to Nanoparticles Science –Special Issue

Keywords:Fluorescence sensorPhenylureaExciplexMacrocyclesMetal complexesAnion recognition

0020-1693/$ - see front matter � 2011 Elsevier B.V. Adoi:10.1016/j.ica.2011.05.031

⇑ Corresponding authors at: Grupo BIOSCOPE, DepFacultade de Ciencias, Universidade de Vigo, CampusSpain (C. Núñez).

E-mail addresses: cristina.nunez@dq.fct.unl.pt (@usc.es (R. Bastida).

A new emissive macrocycle ligand bearing three phenylurea groups (L1) has been synthesized and fullycharacterised. Several mononuclear complexes with nitrate, perchlorate and tetrafluoroborate salts oftransition and post-transition metals (Cu2+, Ni2+, Co2+, Zn2+ and Cd2+) were synthesized and characterized.For comparative purposes, the coordination ability of two nonfluorescent macrocyclic ligands (L2 and L3)containing three nitrophenylurea pendant-arms towards the same metal ions were studied. The interac-tion with transition and post-transition metal ions, and anions was explored in solution by UV–Vis andemission spectroscopy with ligand L1. All new compounds were characterised by microanalysis, IR, UV–Vis and fluorescence emission, FAB and ESI mass spectrometry and conductivity measurements.

� 2011 Elsevier B.V. All rights reserved.

1. Introduction and thiourea groups are excellent receptors for oxoanions such

The development of new molecules whose properties can bemodulated by interaction with anions [1] and cations [2] hasreceived considerable attention in the recent years. The use of mac-rocyclic ligands for this strategic purpose reduces conformationalflexibility as compared with acyclic molecules [3].

The introduction of functionalised pendant coordinating armsinto the macrocyclic framework can lead to important changes inthe complexation capability of the ligands providing: (i) additionalcoordinating functions, (ii) enhancing the metal-ion selectivity andthe stability of metal complexes or (iii) promoting the formation ofsupramolecular structures with different properties and applica-tions [4].

Investigations into synthetic anion receptors have attractedgrowing attention from chemists due to the key roles played byanions during the chemical, biological and environmental pro-cesses [5]. The binding units of anion receptors are often composedof amide [6], urea [7], thiourea [8], sulfonamide [9], pyrrole [10]and indole [11] groups. Among all the systems explored, ureas

ll rights reserved.

artamento de Química Física,de Ourense, E32004 Ourense,

C. Núñez), mrufina.bastida

as carboxylates and phosphates to which they can donate twohydrogen bonds [12].

Host structures that possess a rigid scaffold and urea [13] orthiourea [14] functional groups as side-arms, have been reportedto be very effective in the binding of anions. A great number of sys-tems containing nitrophenylurea groups were published and thedeprotonation processes presented can be used to colorimetricallysense anions [15].

With this idea in mind, very recently we have reported two newcolorimetric ligands (L2 and L3) based on macrocyclic structureslinked to three nitrophenylurea groups as colorimetric anionicchemosensors for fluoride, hydroxide, cyanide, and dihydrogenphosphate in a DMSO solution [15h].

As a part of our ongoing research into the design and synthesisof new fluorescence macrocyclic chemosensors [16], here we pres-ent a new fluorescence macrocyclic ligand L1, containing threephenylurea groups as chromophores as well as its transition andpost-transition metal complexes.

2. Results and discussion

Ligand L1 was isolated as air-stable yellow oil in 65% yield bythe condensation of the previous synthesized ligand L with phenylisocyanate (see Scheme 1). Ligand L2 and L3 were isolated as air-

NO O

O O

Abs. EtOH

N NH2

NH2

H2N

NO O

NHHN N

H2N

L

L1

NOO

N NN

HNHN O

HN

O

HN

O

N NN

NHONH

OO

NH HN

NO2

O2N

O2N

OO

O O

OO

HN NHN

NH2

OO

O O O

N NN

NHO

NH

OO

NH HN

NO2

O2N

O2N

O O O

HN NHN

NH2

O O O

O O

L2

L3

L''

L'

N C O

Abs. EtOH

N C OO2N

N C OO2N

CH2Cl2

CH2Cl2

MeOH MeOH

2.NaBH4

1.N NH2

NH2

H2N

2.NaBH4

1. N NH2

NH2

H2N

2.NaBH4

1.

Scheme 1. Synthetic pathway of macrocyclic ligands L1–L3.

86 C. Núñez et al. / Inorganica Chimica Acta 381 (2012) 85–94

stable yellow solids in a 65% and 60% yield, respectively, by thecondensation of L0 and L00 with 4-nitrophenylisocyanate, respec-tively, by a previously published procedure [15h].

The infrared spectrum (KBr disc) of L1 shows bands at 1726 and1639 cm�1 assigned to the vibration modes m(C@O). The absorp-tion bands corresponding to m(C@N) and m(C@C) vibrations of thepyridine groups appear in their expected positions at 1597 and1444 cm�1, respectively. The FAB mass spectrum of L1 presentsan intense peak at m/z 819 (100%) corresponding to the molecularion [L1+H]+, thus confirming the integrity of the ligand in thistechnique.

The presence of 13 potential donor atoms (N8O5) in the ligandstructure gives L1 strong coordination ability towards metal ions.In order to explore the potential uses in the synthesis of newmultifunctional emissive materials, many solid metal complexeswere synthesized in a 1:1, 1:2 and 1:3 ligand-to-metal molar ra-tios. All attempts to obtain the polynuclear metal complexes in so-lid state were unsuccessful. In all cases non-analytical pureproducts were isolated. In these cases mixtures of the differentcomplexes were obtained. Only when the 1:1 M ratio wasachieved, pure mononuclear complexes were characterised.

The coordination ability of ligand L1 with hydrated nitrate andperchlorate salts of Co2+, Ni2+, Cu2+, Zn2+ and Cd2+ was studied.The reaction of L1 with metal salts in a 1:1 metal-to-ligand ratioin absolute ethanol led to compounds of formula [ML1](ClO4)2�x-H2O (M = Co2+, Ni2+, Cu2+, Zn2+, Cd2+) and [ML1](NO3)2�xH2O(M = Co2+, Ni2+, Cu2+, Zn2+, Cd2+) in good yield (43–67%). The coor-

dination ability of ligand L2 with hydrated nitrate and tetrafluoro-borate salts [M = Co2+, Ni2+, Cu2+, Zn2+ and Cd2+] was also studied.The reaction of L2 with metal salts in a 1:1 metal-to-ligand ratioin acetonitrile led to compounds of formula [ML2](BF4)2�xH2O([M = Co2+, Ni2+, Cu2+ and Zn2+], [ML2](NO3)2�xH2O [M = Co2+, Ni2+,Zn2+ and Cd2+] and [Cu2L2](NO3)4�9H2O in 60–70% yields. A similarreaction with L3 and metal salts in a 1:1 metal-to-ligand ratio inacetonitrile led to compounds of formula [ML3](BF4)2�xH2O[M = Co2+, Ni2+, Zn2+) [CuL3](BF4)2�xCH3CN and [ML3](NO3)2�xH2O[M = Co2+, Ni2+, Cu2+, Zn2+] in 62–90%yields.

The metal complexes are soluble in absolute ethanol (L1 com-plexes) and DMSO (L2 and L3 complexes) but insoluble in othercommon organic solvents. All the compounds were characterisedby elemental analysis, IR, and UV–Vis spectroscopy, and ESI andFAB MS spectrometry.

The IR spectra were recorded as KBr discs. The bands due to them(C@N) and m(C@C) stretching modes of the pyridine rings on thecomplexes derived from ligand L1 appeared in the same positionwhen compared with the spectrum of the free ligand, suggestingthe absence of interaction between the pyridyl group and the me-tal ions [17]. The carbonyl and amine stretching vibrations in thefree ligand L1 were shifted to higher frequencies in the spectra ofthe metal complexes, and the carbonyl stretching vibration in thefree ligands L2 (at ca. 1672 cm�1) and L3 (at ca. 1670 cm�1) wasshifted to lower frequencies in the spectra of the metal complexes,suggesting an interaction between the pendant groups and the-metal ions.

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Fig. 2. Absorption (left) and fluorescence emission (right) titrations of absoluteethanol solution of L1 as a function of increasing amounts of HBF4. The inset showsthe normalised fluorescence intensity at 307 nm (monomer) and 423 nm (exciples)bands. ([L1] = 1.00 � 10�5 M, kexc = 270 nm).

C. Núñez et al. / Inorganica Chimica Acta 381 (2012) 85–94 87

As far as the counterions were concerned, in all the nitrate com-plexes an intense band at 1380 cm�1, with a shoulder at ca.1300 cm�1 was observed, suggesting the presence of both coordi-nate and ionic nitrate groups [18]. In the perchlorate complexesthe intense band at 1100 cm�1, associated with the presence ofionic perchlorate, was accompanied by several other bands in theregion associated with perchlorate vibrations and these clearlyidentify the coordinated perchlorate groups [19]. The IR spectraof the tetrafluoroborate complexes showed the presence of severalbands in the region associated with the BF4

� vibrations, suggestingcoordination to the metal ion or due to hydrogen bond interactions[20].

Molar conductivity data, measured at room temperature usingethanol (L1) and DMSO (L2 and L3) as solvents, showed the pres-ence of ionic counterions, since they are in the range reported forsolvents for 1:1 and 2:1 electrolytes. FAB and ESI mass spectra ofmost compounds display peaks corresponding to [ML]+, [MLX]+,[MLX2]+ and [M2LX3]+ fragments, which indicated the integrity ofthe ligand, and the presence of the metal ions in the complexes.

The electronic spectra of the complexes were measured in EtOH(L1) and in DMSO (L2 and L3) at room temperature and all data aresummarised in Section 3.1.

1H NMR spectra of compounds [ZnL2](BF4)2�4H2O (17),[ZnL2](NO3)2�2H2O (18), [CdL2](NO3)2�H2O (19) and [ZnL3](NO3)2

(27) were recorded in DMSO-d6. In general, all of the proton signalsare shifted downfield in comparison to those in the free ligand.

1H NMR spectra of compounds [ZnL1](ClO4)2�2H2O (4), [CdL1](ClO4)2�2H2O (5), [ZnL1](NO3)2�5H2O (9), [CdL1](NO3)2�H2O (10)and [ZnL3](BF4)2�4H2O (26) are more complicated, probably dueto the existence of different species in solution, and this makes itdifficult to study them by NMR spectroscopy.

2.1. Spectrophotometric studies

The absorption, emission and excitation spectra of L1 in abso-lute ethanol solution at 298 K are reported in Fig. 1.

The absorption spectrum of L1 in absolute ethanol solutionshows two bands at 240 nm assigned to the p–p⁄ transitions ofthe pyridine ring and at 270 nm assigned to the benzene rings ofthe ligand. This spectrum was coincident with the excitation spec-trum. Excitation at 240 nm gave an emission spectrum composedby a band centred at 308 nm, assigned to the aromatic groups ofthe phenylurea arms, and a red-shifted non-structured band witha maximum at 423 nm was also observed in absolute ethanol. Thislower energy band could be attributed to an exciplex band formedfrom the interaction of an excited phenyl moiety with other in theground-state. This exciplex (excited CT state) emission increasesupon complexation of the amines (see below). The identificationof this band was corroborated by the strong solvent dependenceof its emission maximum.

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A φ = 0.009

Fig. 1. Absorption (—), emission (–) and excitation (� � �) spectra of ligand L1 inabsolute ethanol. ([L1] = 1 � 10�5 M, kexc = 270 nm, kem = 308 nm).

The relative fluorescence quantum yield of ligand L1 was deter-mined in absolute ethanol using a solution of benzene in cyclohex-ane as standard (U = 0.05) and the value obtained was 0.009 [21].

The UV–Vis spectrophotometric characterisation of ligands L2

and L3 was described previously [15h]. The presence of nitrophenylgroups in the macrocyclic skeleton of both ligands made themnonemissive species, and unfortunately prevented any spectroflu-orimetric studies [22].

2.2. Effect on protonation of L1

Fig. 2 shows the absorption and emission spectra of L1 in abso-lute ethanol as a function of increasing amounts of HBF4 at roomtemperature. The absorption spectrum is slightly affected by pro-tonation, stabilizing after the addition of two protons. On the otherhand, the fluorescence intensity is strongly quenched upon proton-ation, and a new non-structured band appears centred at 423 nmas function of protons added. The inset shows the fluorescence at307 and 423 nm corresponding to the monomer emission andthe exciplex bands. In both cases, stabilisation was obtained afterthe addition of two protons.

In ligand L1, two photo-induced electron transfer (PET) pro-cesses compete simultaneously: (i) the intermolecular (PET) fromthe –NH groups and the PET from the protonated pyridine ring.The subsequent decrease in the monomer band can be attributedto the protonation of the pyridine nitrogen, which yields a pyridi-nium ion that is known to quench the fluorescence of aromaticcompounds [23].

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420 nm

[H+] / [L1]

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Fig. 3. Absorption (left) and fluorescence emission (right) titrations of acetonitrilesolution of L1 as a function of increasing amounts of HBF4. The inset shows thenormalised fluorescence intensity at 310 nm. ([L1] = 1.00 � 10�5 M, kexc = 270 nm).

Table 1Stability constants for compound L1 in the presence of HBF4 in ethanol oracetonitrile.⁄

Ligand Interaction R log b (Absorption) R log b (Emission)

L1 H+ (1:1) 5.30 ± 1.16 � 10�3 5.33 ± 4.11 � 10�2

H+ (1:2) 12.26 ± 9.47 � 10�4 12.37 ± 2.76 � 10�2

H+ (1:3) 24.61 ± 1.09 � 10�3 25.84 ± 1.22 � 10�2

H+ (1:4) 33.34 ± 1.38 � 10�3 32.18 ± 5.30 � 10�2

H+ (1:5) 37.55 ± 1.56 � 10�3 38.05 ± 6.22 � 10�2

*L1 ⁄H+ (1:1) – 3.58 ± 3.84 � 10�2

⁄H+ (1:2) – 8.50 ± 2.88 � 10�2

⁄H+ (1:3) – 13.06 ± 2.21 � 10�2

⁄H+ (1:4) – 17.57 ± 1.87 � 10�2

⁄H+ (1:5) – 22 � 10 ± 1.74 � 10�2

⁄H+ (1:6) – 26.66 ± 1.71 � 10�2

* Studies in acetonitrile solution.

88 C. Núñez et al. / Inorganica Chimica Acta 381 (2012) 85–94

In an attempt to identify the exciplex band, the studies of pro-tonation of ligand L1 were carried out in a less polar solvent such asacetonitrile (Fig. 3). In that case, an increase in the number ofequivalents of HBF4 was needed to achieve the equilibrium andthe band centred at 423 nm was less intense than in the studieswith ethanol. This result suggests that more positions of the ligandwere protonated leading to more charge repulsion. Therefore, theinteraction between the chromophores was more prevented.

Five protonation constants for the interaction of L1 in the pres-ence of H+ were predicted using HypSpec software and are summa-rised in Table 1 [24].

2.3. Metal ions titrations

In order to explore the behaviour of L1 towards metal ions (Co2+,Ni2+, Cu2+, Zn2+ and Cd2+) and anions, several titrations followed byabsorption and emission were performed. These sensing studieswere developed using protic (absolute ethanol) and/or aprotic(acetonitrile) solvents.

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[Cu2+] / [L1]

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0

0

0

0

0

Fig. 4. Absorption (left) and fluorescence emission (right) titrations of an ethanolic solutiand Cd(BF4)2 (D) ([L1] = 1.00 � 10�5 M, kexc = 270 nm).

Addition of increasing amounts of Co(BF4)2, Ni(BF4)2, Cu(BF4)2

and Cd(BF4)2 to an ethanolic solution of L1 (1.00 � 10�5 M), at298 K, led to a moderate increase in the absorption band centredat 240 nm, and the emission spectrum shows a decrease on theband centred at 310 nm achieving a plateau only after the additionof 2 equivalents of metals. At the same time, in all cases, the exci-plex red-shifted band centred at ca. 420 nm increases in intensity.This result suggests that coordination to the metal ion induced tothe intramolecular exciplex formation. Fig. 4 shows all metallictitrations.

In an attempt to evaluate the influence of the solvent in thetitration of L1 with metal ions, a protic (absolute ethanol) and anaprotic solvent (acetonitrile) were employed in the titration withZn2+. The addition of increasing amounts of Zn(BF4)2 to an etha-nolic (Fig. 5A) and an acetonitrile (Fig. 5B) solution of L1

(1.00 � 10�5 M), at 298 K, led to a decrease in the absorption bandcentred at 240 nm. The emission spectrum in both cases shows adecrease in intensity being more pronounced in acetonitrile. Atthe same time, the band centred at 420 nm assigned to the exciplexformed by the interaction of the phenylurea pendant groups wasalso observed, being less intense in the aprotic solvent (acetoni-trile). The spectrum in absolute ethanol shows one band centredat 310 nm that decreases with the addition of 2 equivalents ofZn2+ to achieve a plateau. Two equivalents of Zn2+ were necessaryto achieve a plateau in both metal titrations.

The stability constants for the interaction of L1 in the presenceof Co2+, Ni2+, Cu2+, Zn2+ and Cd2+ were calculated using HypSpecsoftware and are summarised in Table 2 [24].

Taking into account the values summarised in Table 2, thesequence of the strongest interaction expected for sensor L1

decreases in the follow order: Zn2þðCH3CNÞ > Zn2+

EtOH � Cu2+ > Ni2+

� Cd2+ > Co2+.

2.4. Anion interactions

Once ligand L1 presented three urea groups available to interactwith anions in solution, the sensing behaviour of L1 towards tetra-

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on of L1 as a function of increasing amounts of Co(BF4)2 (A), Ni(BF4)2 (B), Cu(BF4)2 (C)

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Fig. 5. Absorption (left) and fluorescence emission (right) titrations of an ethanolic (A) and acetonitrile (B) solutions of L1 as a function of increasing amounts of Zn(BF4)2. Theinset shows the normalised fluorescence intensity at 310 nm. ([L1] = 1.00 � 10�5 M, kexc = 270 nm). Room temperature.

Table 2Stability constants for compound L1 in the presence of some metal ions in ethanol oracetonitrile.⁄

Ligand Interaction R log b (Absorption) R log b (Emission)

L1 Co2+ (1:1) – 4.28 ± 5.85 � 10�3

Co2+ (1:2) – 9.08 ± 8.27 � 10�3

Co2+ (1:3) – 13.83 ± 1.05 � 10�3

L1 Ni2+ (1:1) – 4.73 ± 8.85 � 10�3

Ni2+ (1:2) – 9.54 ± 1.07 � 10�2

Ni2+ (1:3) – 14.40 ± 1.30 � 10�2

L1 Cu2+ (1:1) – 5.20 ± 1.41 � 10�2

Cu2+ (1:2) – 10.16 ± 9.95 � 10�3

Cu2+ (1:3) – 15.31 ± 1.21 � 10�2

L1 Zn2+ (1:1) 4.99 ± 5.22 � 10�4 5 � 10 ± 1.00 � 10�2

Zn2+ (1:2) 9.89 ± 5.35 � 10�4 10.02 ± 7.85 � 10�3

Zn2+ (1:3) 14.89 ± 5.79 � 10�4 15.09 ± 9.93 � 10�3

*L1 Zn2+ (1:1) 5.93 ± 1.52 � 10�3 6.00 ± 2.88 � 10�2

Zn2+ (1:2) 11.46 ± 1.20 � 10�3 11.55 ± 2.00 � 10�2

Zn2+ (1:3) 18.89 ± 1.06 � 10�3 19.50 ± 1.47 � 10�2

L1 Cd2+ (1:1) – 4.71 ± 4.79 � 10�2

Cd2+ (1:2) – 9.55 ± 4.65 � 10�3

Cd2+ (1:3) – 14.43 ± 5.20 � 10�3

* Studies in acetonitrile solution.

Table 3Stability constants for compound L1 in the presence of (PO4)3

� in acetonitrile.

Ligand Interaction R log b (Absorption) R log b (Emission)

L1 (PO4)3� (1:1) 2.66 ± 1.19 � 10�3 2.50 ± 1.43 � 10�3

(PO4)3� (1:2) 7.33 ± 1.47 � 10�3 7.76 ± 2.17 � 10�3

(PO4)3� (1:3) 11.28 ± 1.79 � 10�3 11.99 ± 3.06 � 10�3

C. Núñez et al. / Inorganica Chimica Acta 381 (2012) 85–94 89

butylammonium salts of some anions (F�, Cl�, Br�, CN�, NO3�,

ClO4�, P3O10

5� and PO43�) was explored using acetonitrile as an

aprotic solvent. Only in the case of PO43� (see Fig. 6) did the addi-

tion of increasing amounts of the anion to a solution of L1

(1.00 � 10�5 M), at 298 K, lead to an increase in the absorptionband centred at 240 nm as well as an increase in the emission bandcentred at 315 nm (monomer band). Interestingly, the exciplex

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Fig. 6. Absorption (A) and fluorescence emission (B) titrations of acetonitrile solution of270 nm, and the normalised fluorescence intensity at 315. ([L1] = 1.00 � 10�5 M, kexc = 2

band observed at 423 nm with the addition of metal ions wasnot developed upon interaction with the PO4

3� anion.The stability constants for the interaction of L1 in the presence

of PO43� were calculated using HypSpec software and are summa-

rised in Table 3 [24]. The stability constants for the interaction ofsimilar systems containing phenylurea groups in the presence ofH2PO4

� were found in the literature [22b,25], but no examplesfor PO4

3� were described.

2.5. NMR responses of sensor L1

1H NMR titration of receptor L1 with HBF4 and tetrabutylammo-nium salts of some anions (F�, Cl�, PO4

3�, NO3�) were performed in

order to understand the effect of these compounds on the NH pro-tons of receptor L1.

1H NMR spectra were registered in DMSO-d6-0.5% water solu-tion. The amide NH signals appear in compound L1 at 8.66, 8.58,8.47 and 8.38 (Figs. 7 and 8). Addition of 2 equivalents of HBF4 tothe solution of receptor L1 in DMSO-d6-0.5% water was enoughto stabilize the spectrum and all of the NH proton signals areshifted downfield in comparison to those in the free ligand(Fig. 7). This result is in agreement with the modification of absorp-tion and emission spectra by titration with HBF4.

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u.

L1 as a function of increasing amounts of (PO4)3�. The inset shows the absorption at70 nm).

6.87.07.27.47.67.88.08.28.48.68.89.09.29.49.69.8

NOO

N NN

HNHN O

HN

O

HN

O

L1

L1

NH

NH

NH

8.388.58 8.47

8.66

8.518.72 8.628.98

9.34 8.808.728.89 L1 + 2 equiv HBF4

L1 + 1 equiv HBF4

Fig. 7. 1H NMR spectra taken in the course of the titration of a DMSO-d6 solution 1.00 � 10�3 M in L1 with a standard solution of HBF4.

9.8

6.87.07.27.47.67.88.08.28.48.68.89.09.29.49.69.810.010.210.4

L1 + 1 equiv [Bu4N]3(PO4)

L1

L1 + 2 equiv [Bu4N]3(PO4)

NH

NH

NH

8.38

8.66

8.56

9.91 9.82

8.70 8.58

8.59

8.58 8.47

9.29

8.86 8.77

6.87.07.27.47.67.88.08.28.48.68.89.09.29.49.69.810.010.210.4

L1

L1 + 2 equiv [Bu4N](F)

8.38

8.66

8.58 8.47

L1 + 1 equiv [Bu4N](F)

NH

NH

NH

8.38 8.38 8.58 8.47

8.58 8.47

8.388.38

Fig. 8. (a) 1H NMR spectra taken in the course of the titration of a DMSO-d6 solution 1.00 � 10�3 M in L1 with a standard solution of [Bu4N]3(PO4) (top) and [Bu4N](F)(bottom).

90 C. Núñez et al. / Inorganica Chimica Acta 381 (2012) 85–94

C. Núñez et al. / Inorganica Chimica Acta 381 (2012) 85–94 91

After the addition of 2 equivalents of the selected anions (F�,Cl�, PO4

3�, NO3�) to the solution of receptor L1 in DMSO-d6-0.5%

water, all of the NH proton signals are shifted downfield in com-parison to those in the free ligand (Fig. 8). In the case of PO4

3�, thisresult is in agreement with the modification of absorption andemission spectra by titration with this anion.

No changes were observed by absorption and emission titrationof L1 with F�, Cl�, NO3

� in acetonitrile. The different behaviourobserved for L1 by 1H NMR titration with F�, Cl�, NO3

� anions inDMSO-d6-0.5% water could be explained because the solventemployed is not the same that in the case of absorption and emis-sion titrations.

We described in our previous work [15h] that the addition of1 equivalents of tetrabutylammonium fluoride to the solutions ofreceptors L2 and L3 in the same solvent was enough to promotethe complete deprotonation process [26]. Despite the presence ofthree nitrophenylurea groups, one fluoride anion was enough tostabilize the spectra. In those cases, the deprotonation of the ureasubunits induced two distinct effects on the aromatic substituentsproducing upfield and downfield shifts of C–H protons.

The addition of F�, Cl�, PO43�, NO3

� to the solutions of receptorL1 produced the same effect in all cases (Fig. 8). Deprotonation pro-cesses were not observed and aromatic C–H signals appeared inthe same position as in the free ligand. This effect could explainthe different behaviour observed and the emissive properties ofL1 compared to L2 and L3 ligands.

3. Conclusions

The introduction of three phenyl-urea groups to macrocycle Lleads to a new emissive substituted macrocycle L1. As parent sys-tems, macrocycles L2 and L3 containing three nitrophenylurea moi-eties were proved to be colorimetric anion chemosensors butunfortunately emissive properties were not observed in either cases.

The complexation of ligands L1 to L3 with divalent (Co2+, Ni2+,Cu2+, Zn2+ and Cd2+) metal ions leads to mononuclear solid com-plexes in all cases, except in the case of complex [Cu2L2](NO3)4�9H2O (16).

For L1, a notable decrease in the fluorescence emission bandcentred at ca. 310 nm was observed after protonation, metal com-plexation and anion interaction. The subsequent decrease in inten-sity can be attributed to the PET quenching mechanism involvingthe pyridine nitrogen, which is known to quench the fluorescenceof aromatic compounds. The most interesting results come fromthe developed band centred at ca. 420 nm assigned to an exciplexspecies. This increased emission could be attributed to the interac-tion of the phenylurea pendant groups with the proton and metalions in the excited state.

3.1. Experimental

3.1.1. Physical measurementsElemental analyses were performed in a Carlo-Erba EA micro-

analyser. Infra-red spectra were recorded as KBr discs on a Bio-Rad FTS 175-C spectrophotometer. ESI mass spectra were recordedusing a micrOTOF spectrometer connected to a DS90 data system.Conductivity measurements were carried out in 10�3 mol dm�3

acetonitrile solutions at r.t. using a Crison Basic 30 conductivime-ter. 1H, 13C, COSY, DEPT and HMQC 1H, 13C NMR spectra wererecorded on a Bruker AMX-500 spectrometer and DMSO was usedas the solvent in all cases.

3.1.2. Spectrophotometric and spectrofluorimetric measurementsUV–Vis absorption spectra (220–900 nm) were performed using

a JASCO-650 UV–Vis spectrophotometer and fluorescence spectra

on a HORIBA JOVIN-IBON Spectramax 4. The linearity of the fluo-rescence emission versus concentration was checked in the con-centration range used (10�5–10�6 M). A correction for theabsorbed light was performed when necessary. All spectrofluori-metric titrations were performed as follows: a stock solution ofthe ligand (ca. 1.00 � 10�3 M) was prepared by dissolving anappropriate amount of the ligand in a 50 mL volumetric flask anddiluting to the mark with absolute ethanol, acetonitrile or DMSOUVA-so. The titration solutions ([L1 = L2 = L3] = 1.00 � 10�6 and1.00 � 10�5 M) were prepared by appropriate dilution of the stocksolution. Titrations were carried out by addition of microliteramounts of standard solutions of the ions dissolved in ethanol, ace-tonitrile or DMSO.

All the measurements were performed at 298 K. Luminescencequantum yields were measured using a solution of benzene incyclohexane as a standard [/] = 0.05 and were corrected for differ-ent refraction indexes of solvents [27,28].

3.1.3. Chemicals and starting materialsPhenylisocyanate, 4-nitrophenylisocyanate and hydrated tetra-

fluoroborate, nitrate and perchlorate metal salts were commercialproducts (from Alfa and Aldrich). Tetrabutylammonium salts ofsome anions (F�, Cl�, Br�, CN�, NO3

�, ClO4�, P3O10

5� and PO43�)

were commercial products from Alfa. The solvents used were ofreagent grade and purified by the usual methods. DMSO wasobtained from Aldrich. The hexaazamacrocycles L [29], L0 [30]and L00 [31] were synthesized using the methods described in theliterature.

Caution: Although no problems were encountered during thecourse of this work, attention is drawn to the potentially explosivenature of perchlorates.

3.1.4. Synthesis of L1

A solution of phenylisocyanate (0.480 g, 4 mmol) in absoluteethanol (25 mL) was added dropwise to a refluxing solution ofthe precursor ligand L0 (0.460 g, 1 mmol) in the same solvent(75 mL). The resulting solution was gently refluxed with magneticstirring for ca. 4 h. The solution was allowed to cool and then evap-orated to dryness. The residue was extracted with water–chloro-form. The organic layer was dried over anhydrous Na2SO4 andevaporated to yield a yellow oil characterised as the ligand L1.

L1: Anal. Calc. for C48H50N8O5�0.5H2O: C, 69.6; H, 6.1; N, 13.5.Found: C, 69.3; H, 6.0; N, 12.9%. Yield: 69%. IR (KBr, cm�1): 1639[m(CO)], 1597, 1444 [m(C@N)py and m(C@C)], 3060 [m(NH)]. FAB-MS (m/z): 819 [L1+H]+. Colour: yellow. 1H NMR (400 MHz, DMSO)t 7.80 (t, 1H); 7.53 (d, 2H); 7.33–7.29 (m, 6H); 7.32–7.28 (m,6H); 7.25 (t, 2H), 7.20 (m, 6H); 7.07 (t, 1H); 6.98–6.82 (m, 8H);5.16 (s, 4H); 4.49 (s, 4H); 3.27–2.99 (m, 6H); 2.57–2.38 (m, 6H).13C NMR (400 MHz, DMSO) 140.39; 128.7; 128.6; 128.3; 123.3;122.3; 121.7; 119.9; 118.2; 117.7; 112.9; 71.2; 53.71; 52.46;45.31; 39.88.

3.1.5. Synthesis of metal complexes of L1

The syntheses of metal complexes were carried out in a 1:1ligand-to-metal molar ratio. The appropriate metal salt(0.04 mmol) in absolute ethanol (5 mL) was added dropwise to astirred solution of the ligand L1 (0.05 mmol) in the same solvent(25 mL). The resulting solution was heated and stirred for 4 h,and the solvent was partially removed to ca. 5 mL. Diethyl etherwas infused into the solution, producing powdery precipitates.The products were filtered off, washed with cold absolute ethanoland diethyl ether, and dried, yielding the metal complexes of theligand.

92 C. Núñez et al. / Inorganica Chimica Acta 381 (2012) 85–94

3.1.6. [CoL1](ClO4)2 (1)Anal. Calc. for C48H50Cl2CoN8O13 (MW: 1075.22): C, 53.5; H, 4.7;

N, 10.4. Found: C, 53.8; H, 4.3; N, 10.6%. Yield: 45%. IR (KBr, cm�1):1643 [m(C@O)], 1598, 1445 [m(C@N)py and m(C@C)], 625, 636, 1089,1109, 1121 [m(ClO4

�)], 3380 [m(NH)]. ESI-MS (m/z): 976 [CoL1

(ClO4)]+. KM/X�1 cm2 mol�1 (in EtOH): 75 (2:1). Colour: pink.UV–Vis in EtOH (k nm): bands at 240 nm (e � 31 235 M�1

cm�1); 260 (e � 21 096 M�1 cm�1); 314 (e � 4228 M�1 cm�1); 392(e � 1199 M�1 cm�1); 506 (e � 292 M�1 cm�1). Non-emissivecomplex.

3.1.7. [NiL1](ClO4)2 (2)Anal. Calc. for C48H50Cl2NiN8O13 (MW: 1076.56): C, 53.5; H, 4.7;

N, 10.4. Found: C, 53.2; H, 4.5; N, 10.7%. Yield: 55%. IR (KBr, cm�1):1645 [m(C@O)], 1599, 1446 [m(C@N)py and m(C@C)], 625, 636, 1089,1109, 1120 [m(ClO4

�)], 3382 [m(NH)]. ESI-MS (m/z): 941 [NiL1

(C2H6O)(H2O)]+. KM/X�1 cm2 mol�1 (in EtOH): 72 (2:1). Colour:white.

UV–Vis in EtOH (k nm): bands at 240 nm (e � 79 549 M�1

cm�1); 272 (e � 19 318 M�1 cm�1); 305 (e � 3419 M�1 cm�1).Non-emissive complex.

3.1.8. [CuL1](ClO4)2�5H2O (3)Anal. Calc. for C48H60Cl2CuN8O18 (MW: 1071.48): C, 49.2; H, 5.2;

N, 9.6. Found: C, 49.2; H, 4.9; N, 9.2%. Yield: 52%. IR (KBr, cm�1):1639 [m(C@O)], 1598, 1446 [m(C@N)py and m(C@C)], 625, 636,1091, 1109, 1121 [m(ClO4

�)], 3384 [m(NH)]. ESI-MS (m/z): 980[CuL1(ClO4)]+. KM/X�1 cm2 mol�1 (in EtOH): 79 (2:1). Colour:green.

UV–Vis in EtOH (k nm): bands at 240 nm (e � 47 888 M�1

cm�1); 272 (e � 16 691 M�1 cm�1); 312 (e � 4662 M�1 cm�1); 389(e � 1526 M�1 cm�1); 673 (e � 303 M�1 cm�1). Non-emissivecomplex.

3.1.9. [ZnL1](ClO4)2�2H2O (4)Anal. Calc. for C48H54Cl2ZnN8O15 (MW: 1119.28): C, 51.5; H, 4.9;

N, 10.0. Found: C, 51.7; H, 4.3; N, 9.7%. Yield: 59%. IR (KBr, cm�1):1639 [m(C@O)], 1598, 1446 [m(C@N)py and m(C@C)], 624, 663, 1108,1119 [m(ClO4

�)], 3382 [m(NH)]. ESI-MS (m/z): 819 [L1+H]+. KM/X�1 cm2 mol�1 (in EtOH): 79 (2:1). Colour: yellow.

UV–Vis in EtOH (k nm): bands at 244 nm(e � 45 848 M�1 cm�1); 268 (e � 15 075 M�1 cm�1); 279(e � 9546 M�1 cm�1). Emission spectrum in EtOH (kexc = 270 nm;kem = 314 nm). / = 0.012.

3.1.10. [CdL1](ClO4)2�2H2O (5)Anal. Calc. for C48H54CdCl2N8O15 (MW: 1166.21): C, 49.4; H, 4.7;

N, 9.6. Found: C, 49.3; H, 4.7; N, 9.4%. Yield: 65%. IR (KBr, cm�1):1637 [m(C@O)], 1599, 1448 [m(C@N)py and m(C@C)], 628, 660,1089, 1116 [m(ClO4

�)], 3394 [m(NH)]. ESI-MS (m/z): 819 [L1+H]+,1031 [CdL1(ClO4)2]+. KM/X�1 cm2 mol�1 (in EtOH): 75 (2:1). Col-our: yellow.

UV–Vis in EtOH (k nm): bands at 240 nm (e � 35 893 M�1

cm�1); 265 (e � 19 548 M�1 cm�1); 280 (e � 10 944 M�1 cm�1);319 (e � 2655 M�1 cm�1). Emission spectrum in EtOH(kexc = 270 nm; kem = 314 nm). / = 0.013.

3.1.11. [CoL1](NO3)2�3H2O (6)Anal. Calc. for C48H56CoN10O14 (MW: 1055.33): C, 54.6; H, 5.3;

N, 13.3. Found: C, 54.8; H, 5.0; N, 12.8%. Yield: 67%. IR (KBr,cm�1): 1650 [m(C@O)], 1598, 1446 [m(C@N)py and m(C@C)], 1384[m(NO3

�)], 3361 [m(NH)]. ESI-MS (m/z): 819 [L1+H]+, 878 [CoL1]+.KM/X�1 cm2 mol�1 (in EtOH): 80 (2:1). Colour: pink.

UV–Vis in EtOH (k nm): bands at 240 nm (e � 69 295 M�1

cm�1); 260 (e � 22 451 M�1 cm�1); 314 (e � 2693 M�1 cm�1); 510(e � 26 M�1 cm�1). Non-emissive complex.

3.1.12. [NiL1](NO3)2 (7)Anal. Calc. for C48H50NiN10O11 (MW: 1000.30): C, 57.6; H, 5.0; N,

14.0. Found: C, 57.1; H, 5.3; N, 13.9%. Yield: 66%. IR (KBr, cm�1):1655 [m(C@O)], 1597, 1445 [m(C@N)py and m(C@C)], 1384[m(NO3

�)], 3346 [m(NH)]. ESI-MS (m/z): 819 [L1+H]+, 911 [NiL1

(H2O)2]+. KM/X�1 cm2 mol�1 (in EtOH): 93 (2:1). Colour: white.UV–Vis in EtOH (k nm): bands at 240 nm (e � 64 656 M�1

cm�1); 272 (e � 16 694 M�1 cm�1); 305 (e � 3786 M�1 cm�1); 390(e � 1074 M�1 cm�1). Non-emissive complex.

3.1.13. [CuL1](NO3)2�10H2O (8)Anal. Calc. for C48H70CuN10O21 (MW: 1186.67): C, 48.6; H, 5.9;

N, 11.8. Found: C, 48.6; H, 5.8; N, 11.6%. Yield: 43%. IR (KBr,cm�1): 1641 [m(CO)], 1598, 1444 [m(C@N)py and m(C@C)], 1384[m(NO3

�)]. ESI-MS (m/z): 819 [L1+H]+, 881 [CuL1]+. KM/X�1 cm2 mol�1 (in EtOH): 88 (2:1). Colour: green.

UV–Vis in EtOH (k nm): bands at 240 nm (e � 90 149 M�1

cm�1); 272 (e � 23 369 M�1 cm�1); 312 (e � 4347 M�1 cm�1); 389(e � 1767 M�1 cm�1); 673 (e � 342 M�1 cm�1). Non-emissivecomplex.

3.1.14. [ZnL1](NO3)2�5H2O (9)Anal. Calc. for C48H50ZnN10O11 (MW: 1006.30): C, 57.2; H, 4.9;

N, 13.9. Found: C, 57.4; H, 5.1; N, 13.2%. Yield: 61%. IR (KBr,cm�1): 1649 [m(C@O)], 1598, 1445 [m(C@N)py and m(C@C)], 1384[m(NO3

�)], 3336 [m(NH)]. ESI-MS (m/z): 885 [ZnL1]+, 924[ZnL1(H2O)Na]+. KM/X�1 cm2 mol�1 (in EtOH): 83 (2:1). Colour:yellow.

UV–Vis in EtOH (k nm): bands at 244 nm (e � 59 611 M�1 cm�1);268 (e � 35 336 M�1 cm�1); 279 (e � 21 589 M�1 cm�1); 318(e � 4454 M�1 cm�1). Emission spectrum in EtOH (kexc = 270 nm;kem = 314 nm). / = 0.011.

3.1.15. [CdL1](NO3)2�H2O (10)Anal. Calc. for C48H52CdN10O12 (MW: 1074.28): C, 53.7; H, 4.8;

N, 13.0. Found: C, 53.8; H, 4.8; N, 12.6%. Yield: 48%. IR (KBr,cm�1): 1646 [m(C@O)], 1598, 1448 [m(C@N)py and m(C@C)], 1384[m(NO3

�)], 3395 [m(NH)]. ESI-MS (m/z): 819 [L1+H]+. KM/X�1 cm2 mol�1 (in EtOH): 72 (2:1). Colour: yellow.

UV–Vis in EtOH (k nm): bands at 241 nm (e � 49 845 M�1

cm�1); 265 (e � 20 957 M�1 cm�1); 280 (e � 11 124 M�1 cm�1);319 (e � 2941 M�1 cm�1). Emission spectrum in EtOH(kexc = 270 nm; kem = 314 nm). / = 0.010.

3.1.16. Synthesis of metal complexes of L2 and L3

The synthesis of ligands L2 and L3 has been previously reported[15h]. The syntheses of all metal complexes were carried out in a1:1 ligand-to-metal molar ratio. The appropriate metal salt(0.04 mmol) in acetonitrile (5 mL) was added dropwise to a stirredsolution of the ligand L1 (0.04 mmol) in the same solvent (25 mL).The resulting solutions were stirred for 4 h at room temperature,and the solvent was partially removed to ca. 5 mL. The resultingproduct was filtered off and dried under vacuum. In all cases, thecomplexes were obtained in a 1:1 ligand-to-metal molar ratio ex-cept copper nitrate complex of ligand L2. The complexes were allfound to be air-stable and soluble in acetone and dimethyl sulfox-ide and are, in general, insoluble in absolute ethanol, methanol,chloroform, dichloromethane, diethyl ether and water.

3.1.17. [CoL2](BF4)2�6H2O (11)Anal. Calc. for C43H56B2CoN10O17 (MW: 1217.50): C, 42.4; H, 4.6;

N, 11.5. Found: C, 42.3; H, 4.6; N, 11.7%. Yield: 70%. IR (KBr, cm�1):1656 [m(CO)], 1549 [m(NO2)as], 1305, 1331 [m(NO2)sim], 533, 1064,1084, 1112 [m(BF4)]. MS (FAB, m/z): 935 [CoL2]+. KM/X�1 cm2 mol�1 (in DMSO): 73 (2:1). Colour: orange. Non-emissivecomplex.

C. Núñez et al. / Inorganica Chimica Acta 381 (2012) 85–94 93

3.1.18. [CoL2](NO3)2�4H2O (12)Anal. Calc. for C43H52CoN12O21 (MW: 1131.27): C, 45.6; H, 4.6;

N, 14.8. Found: C, 45.3; H, 4.6; N, 14.9%. Yield: 65%. IR (KBr,cm�1): 1647 [m(CO)], 1544 [m(NO2)as], 1306, 1331 [m(NO2)sim],1112 [m(C–N)], 1050, 1384 [m(NO3

�)]. MS (FAB, m/z): 997 [CoL2

(NO3)]+. KM/X�1 cm2 mol�1 (in DMSO): 82 (2:1). Colour: brown.Non-emissive complex.

3.1.19. [NiL2](BF4)2�4H2O (13)Anal. Calc. for C43H52B2F8NiN10O15 (MW: 1180.30): C, 43.7; H,

4.4; N, 11.9. Found: C, 43.4; H, 4.4; N, 11.8%. Yield: 63%. IR (KBr,cm�1): 1650 [m(CO)], 1553 [m(NO2)as], 1305, 1331 [m(NO2)sim],533, 1063, 1084, 1112 [m(BF4)]. MS (FAB, m/z): 934 [NiL2]+. KM/X�1 cm2 mol�1 (in DMSO): 75 (2:1). Colour: green. Non-emissivecomplex.

3.1.20. [NiL2](NO3)2�3H2O (14)Anal. Calc. for C43H50NiN12O20 (MW: 1112.26): C, 46.4; H, 4.5;

N, 15.1. Found: C, 46.2; H, 4.5; N, 15.4%. Yield: 70%. IR (KBr,cm�1): 1654 [m(CO)], 1540 [m(NO2)as], 1306, 1331 [m(NO2)sim],1112 [m(C–N)], 1050, 1384 [m(NO3

�)]. MS (FAB, m/z): 996 [NiL2

(NO3)]+. KM/X�1 cm2 mol�1 (in DMSO): 81 (2:1). Colour: green.Non-emissive complex.

3.1.21. [CuL2](BF4)2�4H2O (15)Anal. Calc. for C43H52B2F8CuN10O15 (MW: 1185.30): C, 43.5; H,

4.4; N, 11.8. Found: C, 43.2; H, 4.4; N, 11.8%. Yield: 75%. IR (KBr,cm�1): 1656 [m(CO)], 1540 [m(NO2)as], 1306, 1331 [m(NO2)sim],533, 1064, 1084, 1112 [m(BF4)]. MS (FAB, m/z): 1026 [CuL2(BF4)]+.KM/X�1 cm2 mol�1 (in DMSO): 75 (2:1). Colour: green. Non-emis-sive complex.

3.1.22. [Cu2L2](NO3)4�9H2O (16)Anal. Calc. for C43H62Cu2N14O32 (MW: 1412.22): C, 36.5; H, 4.4;

N, 13.9. Found: C, 36.2; H, 3.9; N, 13.7%. Yield: 60%. IR (KBr, cm�1):1665 [m(CO)], 1544 [m(NO2)as], 1305, 1331 [m(NO2)sim], 1112 [m(C–N)], 1050, 1384 [m(NO3

�)]. MS (FAB, m/z): 1188 [Cu2L2(NO3)3]+.KM/X�1 cm2 mol�1 (in DMSO): 90 (2:1). Colour: green. Non-emis-sive complex.

3.1.23. [ZnL2](BF4)2�4H2O (17)Anal. Calc. for C43H52B2F8ZnN10O15 (MW: 1187.93): C, 43.5; H,

4.4; N, 11.8. Found: C, 43.7; H, 4.3; N, 11.8%. Yield: 70%. IR (KBr,cm�1): 1665 [m(CO)], 1546 [m(NO2)as], 1305, 1331 [m(NO2)sim],533, 1064, 1084, 1112 [m(BF4)]. MS (FAB, m/z): 940 [ZnL2]+. KM/X�1 cm2 mol�1 (in DMSO): 80 (2:1). Colour: yellow. 1H NMR(400 MHz, DMSO-d6): d 6.96–7.62 (m, 20H), 4.34–4.52 (m, 4H),3.82–4.09 (m, 4H), 3.37 (s, 4H), 2.80–2.98 (m, 4H), 2.54–2.77 (m,4H). Non-emissive complex.

3.1.24. [ZnL2](NO3)2�2H2O (18)Anal. Calc. for C43H48ZnN12O19 (MW: 1102.30): C, 46.8; H, 4.4;

N, 15.2. Found: C, 46.8; H, 4.6; N, 15.7%. Yield: 60%. IR (KBr,cm�1): 1663 [m(CO)], 1548 [m(NO2)as], 1305, 1331 [m(NO2)sim],1112 [m(C–N)], 1050, 1384 [m(NO3

�)]. MS (FAB, m/z): 1002[ZnL2(NO3)]+. KM/X�1 cm2 mol�1 (in DMSO): 83 (2:1). Colour:yellow. 1H NMR (400 MHz, DMSO-d6): d 6.98–8.24 (m, 20H),4.53–4.33 (m, 4H), 3.86–3.99 (m, 4H), 3.45–3.61 (m, 4H), 2.83–2.79 (m, 4H), 2.75–2.59 (m, 4H). Non-emissive complex.

3.1.25. [CdL2](NO3)2�H2O (19)Anal. Calc. for C43H46CdN12O18 (MW: 1132.21): C, 45.6; H, 4.1;

N, 14.9. Found: C, 45.8; H, 3.9; N, 15.1%. Yield: 66%. IR (KBr,cm�1): 1660 [m(CO)], 1545 [m(NO2)as], 1306, 1331 [m(NO2)sim],1111 [m(C–N)], 1050, 1384 [m(NO3

�)]. MS (FAB, m/z): 990 [CdL2]+.KM/X�1 cm2 mol�1 (in DMSO): 80 (2:1). Colour: yellow. 1H NMR

(400 MHz, DMSO-d6): d 6.90–8.17 (m, 20H), 4.72 (s, 4H), 4.20–4.46 (m, 4H), 3.61–3.84 (m, 4H), 3.45–3.55 (m, 4H), 3.20–3.42(m, 4H). Non-emissive complex.

3.1.26. [CoL3](BF4)2�9H2O (20)Anal. Calc. for C45H66B2F8CoN10O21 (MW: 1315.38): C, 41.1; H,

5.1; N, 10.7. Found: C, 40.9; H, 4.3; N, 10.7%. Yield: 79%. IR (KBr,cm�1): 1637 [m(C@O)], 1559 [m(NO2)as], 1306, 1331 [m(NO2)sim],534, 1063, 1084, 1113 [m(BF4)]. ESI-MS (m/z): 921 [L3+H]+. KM/X�1 cm2 mol�1 (in DMSO): 53 (1:1). Colour: orange. Non-emissivecomplex.

3.1.27. [CoL3](NO3)2�5H2O (21)Anal. Calc. for C45H58CoN12O23 (MW: 1193.31): C, 45.3; H, 4.9;

N, 14.1. Found: C, 45.2; H, 4.6; N, 14.2%. Yield: 62%. IR (KBr,cm�1): 1644 [m(C@O)], 1554 [m(NO2)as], 1305, 1331 [m(NO2)sim],1112 [m(C–N)], 1050, 1384 [m(NO3

�)]. ESI-MS (m/z): 921 [L3+H]+.KM/X�1 cm2 mol�1 (in DMSO): 52 (1:1). Colour: red. Non-emissivecomplex.

3.1.28. [NiL3](BF4)2�H2O (22)Anal. Calc. for C45H50B2F8NiN10O13 (MW: 1170.30): C, 46.1; H,

4.3; N, 11.9. Found: C, 46.2; H, 4.4; N, 11.7%. Yield: 81%. IR (KBr,cm�1): 1643 [m(C@O)], 1553 [m(NO2)as], 1305, 1331 [m(NO2)sim],533, 1063, 1084, 1113 [m(BF4)]. ESI-MS (m/z): 921 [L3+H]+. KM/X�1 cm2 mol�1 (in DMSO): 35 (1:1). Colour: yellow. Non-emissivecomplex.

3.1.29. [NiL3](NO3)2�7H2O (23)Anal. Calc. for C45H62NiN12O25 (MW: 1228.33): C, 43.9; H, 5.1; N,

13.8. Found: C, 43.2; H, 4.6; N, 13.9%. Yield: 78%. IR (KBr, cm�1):1640 [m(C@O)], 1554 [m(NO2)as], 1305, 1331 [m(NO2)sim], 1112[m(C–N)], 1050, 1384 [m(NO3

�)]. ESI-MS (m/z): 921 [L3+H]+. KM/X�1 cm2 mol�1 (in DMSO): 53 (1:1). Colour: green. Non-emissivecomplex.

3.1.30. [CuL3](BF4)2�2.5CH3CN (24)Anal. Calc. for C50H55.5B2F8CuN12.5O12 (MW: 1259.85): C, 48.0;

H, 4.4; N, 13.9. Found: C, 48.6; H, 4.4; N, 13.7%. Yield: 90%. IR(KBr, cm�1): 1662 [m(C@O)], 1551 [m(NO2)as], 1305, 1331 [m(NO2)-sim], 533, 1063, 1084, 1113 [m(BF4)]. ESI-MS (m/z): 921 [L3+H]+.KM/X�1 cm2 mol�1 (in DMSO): 60 (1:1). Colour: yellow. Non-emis-sive complex.

3.1.31. [CuL3](NO3)2�4H2O (25)Anal. Calc. for C45H56CuN12O22 (MW: 1179.29): C, 45.8; H, 4.8;

N, 14.3. Found: C, 45.7; H, 4.1; N, 14.7%. Yield: 90%. IR (KBr,cm�1): 1670 [m(C@O)], 1552 [m(NO2)as], 1305, 1331 [m(NO2)sim],1112 [m(C–N)], 1048, 1384 [m(NO3

�)]. ESI-MS (m/z): 921 [L3+H]+.KM/X�1 cm2 mol�1 (in DMSO): 59 (1:1). Colour: green. Non-emissive complex.

3.1.32. [ZnL3](BF4)2�4H2O (26)Anal. Calc. for C45H56B2F8ZnN10O16 (MW: 1230.32): C, 43.9; H,

4.6; N, 11.4. Found: C, 43.7; H, 4.2; N, 11.3%. Yield: 70%. IR (KBr,cm�1): 1655 [m(C@O)], 1552 [m(NO2)as], 1306, 1331 [m(NO2)sim],533, 1063, 1084, 1113 [m(BF4)]. ESI-MS (m/z): 921 [L3+H]+. KM/X�1 cm2 mol�1 (in DMSO): 40 (1:1). Colour: orange. Non-emissivecomplex.

3.1.33. [ZnL3](NO3)2 (27)Anal. Calc. for C45H48ZnN12O18 (MW: 1108.25): C, 48.8; H, 4.4;

N, 15.1. Found: C, 48.8; H, 4.8; N, 14.7%. Yield: 64%. IR (KBr,cm�1): 1642 [m(C@O)], 1553 [m(NO2)as], 1305, 1331 [m(NO2)sim],1112 [m(C–N)], 1052, 1384 [m(NO3

�)]. ESI-MS (m/z): 921 [L3+H]+.KM/X�1 cm2 mol�1 (in DMSO): 42 (1:1). 1H NMR (400 MHz,

94 C. Núñez et al. / Inorganica Chimica Acta 381 (2012) 85–94

DMSO-d6): d 3.12–3.62 (m, 8H), 3.69–3.99 (m, 4H), 4.01–4.28 (m,4H), 4.39–4.50 (m, 4H), 4.71–4.82 (d, 4H), 6.41–8.23 (m, 20H). Col-our: yellow. Non-emissive complex.

Acknowledgements

We are grateful to the Xunta de Galicia (Spain) for Grants10PXIB209028PR and IN845B-2010/057, University of Vigo INOU-ViCOU K914 (Spain) and REQUIMTE-FCT funds (Portugal-EU) forfinancial support. C.N. thanks the Fundação para a Ciência e aTecnologia/FEDER (Portugal/EU) Programme Postdoctoral Contract(SFRH/BPD/65367/2009). C.L. thanks the Xunta de Galicia for theIsidro Parga Pondal Research Programme.

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