Synthesis and structural characterization of new 2-bromo-1,3-bis(triazol-1- ylmethyl)benzene ligands. Study of their behavior as complexing agents for determination of nickel(II) by adsorptive stripping voltammetry

Article abstract of DOI:10.1080/00958972.2013.764997

Reaction of 2-bromo-1,3-bis(bromomethyl)benzene (1) with 1,2,3-triazole and benzotriazole yields 2-bromo-1,3-bis(triazol-1-ylmethyl)benzene (2) and 2-bromo-1,3-bis(benzotriazol-1-ylmethyl)benzene (3), isolated as white solids, air stable at room temperature, and characterized by elemental analysis, mass spectra, IR, and NMR (¹H, ¹³C) spectroscopy. The molecular structure of 3 was determined by single-crystal X-ray diffraction. These ligands were evaluated for determination of ultra-trace concentrations of nickel by adsorptive stripping voltammetry. The method is based on adsorptive accumulation of the Ni(II)-L complex onto a hanging mercury drop electrode, followed by reduction of the adsorbed species by voltammetric scan using square wave modulation. However, only with 2 was a signal observed at -0.81 V. Under the best experimental conditions (pH 5.5; ligand concentration 0.30 μmol L^-1; adsorptive potential (E_ads) -0.70 V and adsorptive time (t_ads) 80 s), the peak current is proportional to the Ni(II) concentration to 15.0 μg L^-1, with a 3 detection limit of 0.2 μg L^-1. The proposed method was validated by determining Ni(II) in certified reference waste water (SPS-WW1) with satisfactory results.

Full text of DOI:10.1080/00958972.2013.764997

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Synthesis and structural
characterization of new 2-bromo-1,3-
bis(triazol-1-ylmethyl)benzene ligands.
Study of their behavior as complexing
agents for determination of nickel(II)
by adsorptive stripping voltammetry
John Hurtado a , Edgar Nagles a , Verónica Arancibia a , René Rojas
a , Mauricio Valderrama a & Roland Fröhlich b
a Facultad de Química, Departamento de Química Inorgánica ,
Pontificia Universidad Católica de Chile , Santiago , Chile
b Organisch-Chemisches Institut der Universität Münster ,
Münster , Germany
Accepted author version posted online: 16 Jan 2013.Published
online: 25 Feb 2013.
To cite this article: John Hurtado , Edgar Nagles , Verónica Arancibia , René Rojas , Mauricio
Valderrama & Roland Fröhlich (2013) Synthesis and structural characterization of new 2-
bromo-1,3-bis(triazol-1-ylmethyl)benzene ligands. Study of their behavior as complexing agents for
determination of nickel(II) by adsorptive stripping voltammetry, Journal of Coordination Chemistry,
66:4, 592-601, DOI: 10.1080/00958972.2013.764997
To link to this article: http://dx.doi.org/10.1080/00958972.2013.764997
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Journal of Coordination Chemistry
Vol. 66, No. 4, 20 February 2013, 592–601
Synthesis and structural characterization of new 2-bromo-
1,3-bis(triazol-1-ylmethyl)benzene ligands. Study of their
behavior as complexing agents for determination of nickel(II)
by adsorptive stripping voltammetry
JOHN HURTADO†, EDGAR NAGLES†, VERÓNICA ARANCIBIA*†, RENÉ ROJAS†,
MAURICIO VALDERRAMA*† and ROLAND FRÖHLICH‡`
†Facultad de Química, Departamento de Química Inorgánica, Pontificia Universidad
Católica de Chile, Santiago, Chile
‡Organisch-Chemisches Institut der Universität Münster, Münster, Germany
(Received 16 August 2012; in final form 26 October 2012)
Reaction of 2-bromo-1,3-bis(bromomethyl)benzene (1) with 1,2,3-triazole and benzotriazole yields
2-bromo-1,3-bis(triazol-1-ylmethyl)benzene (2) and 2-bromo-1,3-bis(benzotriazol-1-ylmethyl)ben-
zene (3), isolated as white solids, air stable at room temperature, and characterized by elemental
analysis, mass spectra, IR, and NMR (1H, 13C) spectroscopy. The molecular structure of 3 was
determined by single-crystal X-ray diffraction. These ligands were evaluated for determination of
ultra-trace concentrations of nickel by adsorptive stripping voltammetry. The method is based on
adsorptive accumulation of the Ni(II)-L complex onto a hanging mercury drop electrode, followed
by reduction of the adsorbed species by voltammetric scan using square wave modulation. How-
ever, only with 2 was a signal observed at À0.81 V. Under the best experimental conditions (pH
5.5; ligand concentration 0.30 μmol LÀ1; adsorptive potential (Eads) À0.70 V and adsorptive time
(tads) 80 s), the peak current is proportional to the Ni(II) concentration to 15.0 μg LÀ1, with a 3
detection limit of 0.2 μg LÀ1. The proposed method was validated by determining Ni(II) in certified
reference waste water (SPS–WW1) with satisfactory results.
Keywords: Nickel; Adsorptive stripping voltammetry; Bidentate ligands
1. Introduction
Multidentate ligands [(N–C–N)Br] have been developed to control the coordination sphere
of metallic species [1–6]. The nature of the N donor and their substituents can control
accessibility of the metal and the electron density around the metal center to potentiate
their reactivity in the complexes. Van Koten et al. prepared the diamagnetic [BrNi(N–C–
N)] compounds using 2-bromo-1,3-bis[(dimethylamino)methyl]benzene and [Ni(cod)2]
(cod = 1,5-cyclooctadiene) (scheme 1).
The square-planar nickel(II) compounds are very stable due to formation of two
five-membered metallocycles that provide additional stabilization of the carbon–metal bond
*Corresponding authors. Email: jmvalder@puc.cl (M. Valderrama); darancim@uc.cl (V. Arancibia)
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online Ó 2013 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2013.764997

Complexing agent for nickel(II)
593
R
R
Ni(cod)2
oxidative addition
Me2N
Br
NMe2
Me2N
Ni
Br
NMe2
Scheme 1. R=H, NO2, NH2, MeO, Cl, MeC(O).
[7–9]. These complexes have been used as catalysts in the Kharasch addition reaction [10]
and for synthesis of metallodendrimers [11]. Recently, our research focused on the
synthesis of new ligands of the [(N–C–N)Br] type. In this context, we report the synthesis
and characterization of nickel(II) bromide complexes bearing 2-bromo-1,3-bis(3,5-dim-
ethylpirazol-1-ylmethyl)benzene (figure 1(A)) and 2-bromo-1,3-bis(indazol-2-ylmethyl)ben-
zene (figure 1(B)) [12].
Nickel is a moderately toxic element compared with other transition metals, but different
studies have shown chronic effects of nickel exposure, such as inhibition of growth and
reproduction in invertebrates. Since the concentration of nickel in environmental and bio-
logical samples is low (pristine streams, rivers, and lakes are between 0.2 and 10 μg LÀ1),
development of adequate methods for determination of trace amounts is required [13]. In
trace analysis of metal ions, anodic stripping voltammetry has been the most popular
electroanalytical technique because of its speed, good selectivity and sensitivity, and low
instrumentation cost compared to other techniques. Traditionally, the hanging mercury drop
electrode (HMDE), due to its sensitivity, has been used most widely as the working
electrode. However, nickel does not form amalgams with mercury. In these cases, adsorp-
tive stripping voltammetry (AdSV) is the technique for their determination in a variety of
matrices. Complexing agents such as dimethylglyoxime [14–19], 1-nitroso-2-naftol [20],
pyridoxal salicyloylhydrazone [21], N-2-pyridyl-benzamidine [22], eriochrome black T
[23], and others have been used.
The purpose of the present study was to report the synthesis and structural
characterization of new 2-bromo-1,3-bis(triazol-1-ylmethyl)benzene ligands and posterior
application as complexing agents for determination of Ni(II) by AdSV. To our knowledge,
similar results have not yet been reported.
Figure 1. Schematic structure of bis(diazolate) ligands.

594
J.Hurtado et al.
2. Experimental
2.1. General procedures
The reactions were carried out under an atmosphere of purified nitrogen. All reagent-grade
solvents were dried, distilled, and stored under nitrogen. The starting compound 2-bromo-
1,3-bis(bromomethyl)benzene (1) was synthesized according to literature procedures [24].
Other reagents were purchased from commercial sources and used without purification.
Elemental analyses (C, H, N) were made on a Fisons EA 1108 CHNS-O microanalyzer.
FTIR spectra were recorded throughout the 4000–250 cmÀ1 region, with samples prepared
as KBr disks on a Bruker Vector-22 spectrophotometer. NMR spectra were recorded on
Bruker AC-200P and Avance-400 spectrometers and chemical shifts are reported in ppm
relative to SiMe4 (1H, 13C). Mass spectra were obtained on a Micromass Quattro LC-Z
electrospray mass spectrometer. Melting points were determined using an electrothermal
melting point apparatus in open capillary tubes and are uncorrected.
2.2. Electroanalytical studies
2.2.1. Reagents. Water used for sample preparation, dilution of the reagents, and rinsing
purposes was obtained in a Milli-Q system (18.2 M. Millipore, USA). All chemicals (nitric
acid, acetic acid, sodium hydroxide, etc.) were analytical grade from Merck (Darmstadt,
Germany). Standard Ni(II) solutions were prepared by diluting commercial standard con-
taining 1000 mg LÀ1, Merck (Darmstadt, Germany). Ligand solutions were prepared by
dissolving appropriate amounts in methanol. Britton Robinson (BR) buffer solutions were
used to investigate pH from 4.0 to 10.0. These buffers (0.4 mol LÀ1) were prepared by
mixing equal volumes of orthophosphoric acid, acetic acid, and boric acid, adjusting to the
required pH with 2.0 mol LÀ1 NaOH solution. Certified reference waste water (SPS–WW1)
containing Al 2.00, As 0.1, Cd 0.02, Co 0.06, Cr 0.20, Cu 0.40, Fe 1.00, Mn 0.4, Ni 1.0,
P 1.00, Pb 0.1, V 0.1, and Zn 5.00 mg LÀ1 was used for validation studies. Dissolved
oxygen was removed from the studied solutions by purging with water-saturated nitrogen
(99.99%).
2.2.2. Instrumentation. Voltammograms were obtained on a Metrohm model 797 VA
Computrace in a three-electrode configuration. The HMDE was used as working electrodes
with a Ag/AgCl/KCl 3 mol LÀ1 reference electrode, and a platinum wire auxiliary elec-
trode. The pH measurements were carried out with Orion-430 digital pH/mV meters
equipped with combined pH glass electrode.
2.2.3. Voltamperometric procedure. Ten milliliter of deionized water (or 50 μL of
certified waste water), 0.1 mL of BR buffer solution (0.4 mol LÀ1), 10–40 μL of ligand
(0.15 mmol LÀ1), and aliquots of Ni(II) solution (0.5 mg LÀ1) were pipetted into the
voltammetric cell. The solution was purged with nitrogen (saturated with water vapor) for
5 min in the first cycle and for 60 s for each successive cycle. The standard measuring
procedure was performed using square wave stripping voltammetry. A mercury drop was
formed and accumulation of the Ni(II)-L complex was carried out at À0.7 V for 80 s from

Complexing agent for nickel(II)
595
stirred solution. At the end of the accumulation time, the stirrer was switched off, and after
the equilibration time of 5 s, a square wave voltammogram was recorded, while the poten-
tial was scanned from À0.1 to À1.3 V with 0.01 V step amplitude, 0.04 V pulse amplitude,
and a frequency of 25 Hz. Each voltammogram was repeated three times. The standard
additions method was used to determine Ni(II) in the certified water and to check linearity
of response. All experiments were carried out at room temperature.
2.3. Synthesis of ligands
2.3.1. Synthesis of 2-bromo-1,3-bis(triazol-1-ylmethyl)benzene (2). Triazole (332 mg,
4.66 mmol), 2-bromo(1,3-bis(bromomethyl)benzene (800 mg, 2.33 mmol), Et3N (2 mL),
and toluene (40 mL) were placed in a Schlenk flask provided with a reflux condenser and
the mixture was refluxed for 48 h. The resulting mixture was treated with water and
extracted with CHCl3. The organic layer was separated and dried with magnesium sulfate.
The solution was evaporated to dryness to give a white solid that was crystallized from
chloroform–diethyl ether. Yield 302 mg (41%). m.p.: 139–141 °C. Anal. Calcd for
C12H11N6Br: C, 45.2; N, 26.3; H, 3.5%. Found: C, 45.0; N, 25.9; H, 3.9%. MS–ESI (m/z,
ES+): 319.16 [M]+, 342.15 [M + Na]+. IR (KBr, cmÀ1): ν 1417s, 1290s, 1216s, 1092s,
1066s, 805s, 768s, 3091m, 1464m, 1365m, 1119m, 1111m, 1026m.
Atom numbering for ligand 2 is as follows:
NMR (CDCl3, 295 K): 1H, δ 5.7 (s, 4H, CH2), 6.8 (d, 2H2,6, J(HH) = 7.6 Hz), 7.2
(t, 1H1, J(HH) = 7.6 Hz), 7.6 (d, 2H7,7, J(HH) = 8.0 Hz) and 7.7 (d, 2H8,8, J(HH) = 8.0 Hz)
ppm. 13C{1H}, δ 54 (CH2), 124 (C7, 7′), 124 (C4), 129 (C1), 130 (C2, C6), 134 (C8, 8′)
and 137 (C3, C5) ppm.
2.3.2. Synthesis of 2-bromo-1,3-bis(benzotriazol-1-ylmethyl)benzene (3). Benzotria-
zole (414 mg, 3.48 mmol), 2-bromo(1,3-bis(bromomethyl)benzene (610 mg, 1.74 mmol),
and toluene (25 mL) were placed in a Schlenk flask provided with a reflux condenser and
the mixture was refluxed for 48 h. The resulting mixture was filtered and the toluene
solution was cooled to yield a white solid. The solid was chromatographed on silica gel,
eluting with CHCl3 : ethyl acetate 2 : 1 to give a pure compound. Yield: 270 mg (66%). m.

596
J.Hurtado et al.
p.: 144–145 °C. Anal. Calcd for C20H15N6Br: C, 57.3; N, 20.0; H, 3.6%. Found: C, 57.2;
N, 20.0; H, 3.9%. MS–ESI (m/z, ES+): 418.05 [M]+, 441.04 [M + Na]+. IR (KBr, cmÀ1): ν
1229s, 1089s, 748s, 1455m, 1424m, 1265m, 1163m, 1028m, 944m.
Atom numbering for ligand 3 is as follows:
1
NMR (CDCl3, 295 K): H, δ 5.9 (s, 4H, CH2), 6.7 (d, 2H4,6, J(HH) = 7.8 Hz), 7.0 (t, H5,
J(HH) = 7.8 Hz), 7.3 (m, 6H, H10,11,12) and 8.0 (d, 2H9,9, J(HH) = 8.0 Hz) ppm. 13C{1H}, δ
58 (CH2), 110 (C11,11′), 120 (C9,9′), 123 (C2), 124 (C10,10′), 128 (C12,12′), 128 (C5),
129 (C4, C6), 133 (C13,13′), 135 (C1, C3) and 146 (C8, 8′) ppm.
2.4. Crystal structure determination of ligand 3
Crystals of 3 were grown by slow diffusion of diethyl ether into a dichloromethane solu-
tion. Intensity data were collected with a Nonius Kappa CCD diffractometer. The structure
was solved using SHELXS-97 [25](a) and refinement using SHELXL [25](b).
C20H15BrClN6·0.5 CH2Cl2, MW = 461.75, colorless crystal 0.25 Â 0.20 Â 0.10 mm in size,
monoclinic, space group P2(1)/c, a = 10.5782(5), b = 8.4977(4), c = 21.9778(10) Å,
β = 95.977(3)°, V = 1964.9(2) Å3, Z = 4, Dc = 1.561 Mg mÀ3, μ(Cu Kα) = 4.261 mmÀ1, F
(0 0 0) = 932. Limiting indices À12 < =h < =12, À9 < =k < =10, À25 < =l < =25. Reflections
collected/unique 15,108/3442 [R(int) = 0.039]. Semi-empirical absorption correction is
from equivalents. Refinement method: full-matrix least squares on F2. Final R indices
[I > 2(I)] (I) R1 = 0.0375, wR2 = 0.0961. R indices (all data) R1 = 0.0407, wR2 = 0.0984.
Solvent CH2Cl2 is disordered, refined with restraints, and hydrogens are calculated and
refined as riding atoms.
3. Results and discussion
3.1. Synthesis of ligands
2-Bromo-1,3-bis(triazol-1-ylmethyl)benzene (2) was synthesized by reaction of 2-bromo-
1,3-bis(bromomethyl)benzene with two equivalents of 1,2,3-triazole in toluene under
reflux. The compound was isolated as air stable white solid at room temperature, soluble
in dichloromethane and chloroform, and characterized by elemental analysis, mass spectra,

Complexing agent for nickel(II)
597
IR, and NMR spectroscopy. The electron spray mass spectra showed the molecular ion,
with the highest ion at 342.15 m/z with isotopic distributions that matched with those
calculated for [C12H11N6Br]Na+.
1
The H and 13C NMR spectra are consistent with formation of a single isomer. The for-
1
mulation was established on the basis of H and 13C NMR data and elemental analyses.
1
1
The H and 13C chemical shifts were assigned with the aid of H–1H1 (COSY), DEPT,
1H-13C (HMQC), HMBC, and NOESY experiments. Diagnostic peaks include (in ppm): δ
5.7 (s, 4 H, CH2) and 7.7 (s, 2H, H8,8’-triazolyl). As shown in scheme 2, the triazolyl
groups are connected to methylene spacers through N1.
The reaction of 3,5-bis(bromomethyl)toluene with two equivalents of benzotriazole in
refluxing toluene gives 2-bromo-1,3-bis(benzotriazol-1-ylmethyl)benzene (3) in 66% yield.
The compound was isolated as white solid, air stable at room temperature, and fully char-
acterized by microanalysis, mass spectra, FTIR, and NMR spectroscopy. The electron
spray mass spectra showed the molecular ion, with the highest ion at 441.04 m/z with iso-
topic distributions that matched with those calculated for [C20H15N6Br]Na+. NMR spectra
of this complex are consistent with the proposed formulation. As shown in scheme 2, the
1
triazolyl groups are connected to methylene spacers through N1. The H and 13C chemical
1
1
shifts were assigned with the aid of H–1H (COSY), DEPT, H–13C (HMQC), HMBC,
and NOESY experiments. In order to determine the molecular structure of 3, an X-ray dif-
fraction study was undertaken. Suitable crystals for structural determination were grown
by slow diffusion of diethyl ether into a dichloromethane solution of 3. A perspective view
of the molecule is shown in figure 2.
As can be seen, in the solid-state, the phenyl and benzotriazole rings are planar and the
benzotriazole and methylene groups are placed on the same side of the phenyl plane. All
bond distances and angles fall within the expected ranges.
Ligands 2 and 3 rapidly react with Ni(II) salts in methanol solution to give green
solutions. Unfortunately, all attempts to isolate the formed complexes as pure samples were
unsuccessful. However, we use their coordination properties in determination of Ni(II) at
low concentrations.
NH
toluene
Br
(1)
+
N
N
N
N
N
N
N
N
(2)
H
N
(1)
N
+
toluene
N
N
N
N
Br
N
N
N
(3)
Scheme 2. Schematic structure of bis(triazolate) ligands (2,3).

598
J.Hurtado et al.
C4
C5
C3
N6
C20
C11
N5
N4
C12
C10
C6
C19
C2
C1
C13
C9
C15
C8
Br1
N3
C14
C7
C18
N1
C16
N2
C17
Figure 2. ORTEP-style plot of 3. Thermal ellipsoids are shown at the 50% probability level. The numbering is
arbitrary and different from that used in the 13C NMR spectrum. Selected bond distances (Å) and angles (°): N
(4)–N(5), 1.358 (3); N(5)–N(6), 1.299(3); N(6)–C(20), 1.376(4); N(4)–C(15), 1.358(3); N(4)–C(14), 1.452(4); C
(15)–C(20), 1.392(4); C(8)–Br(1), 1.905(3); C(9)–C(10), 1.391(4); C(10)–C(11), 1.380(4); C(12)–C(13), 1.381(4);
C(19)–C(20), 1.401(4); C(17)–C(18), 1.399(5); N(2)–N(1)–C(1), 108.5(2); C(7)–N(3)–C(6), 129.7(2); N(5)–N(4)–
C(14), 120.0(2); N(4)–N(5)–N(6), 108.7(2); Br(1)–C(8)–C(9), 119.2(2); Br(1)–C(8)–C(13), 118.1(2); N(5)–N(6)–C
(20), 108.4(2); C(8)–C(13)–C(14), 119.7(2); N(4)–C(14)–C(13), 113.0(2).
3.2. Determination of Ni(II) in the presence of the new ligands [(N–C–N)Br]
Because of the existence of reduction signals for the ligands, not only their complexing
capacity with nickel needed to be taken into account, but also the possibility of overlap-
ping peaks between the free ligand and the Ni-L complex peaks. Charge of the complex at
different pH values is important due to changes in adsorption properties. The two ligands
form complexes with Ni(II), however only with 2, a sensitivity peak of Ni(II)-L complex
appeared at about À0.81 V, while three peaks corresponding to a reduction process of free
ligand were observed to À0.30, À0.40, and À1.20 V, respectively (figure 3).
To determine the M : L stoichiometry, cyclic voltammograms were recorded with
3.0 mmol LÀ1 of 2 in the presence of Ni(II) 1.0, 1.5, and 3.0 mmol LÀ1 obtaining the high-
est current with the Ni(II) : 2 ratio of 1 : 1. In order to find the optimum conditions with
highest sensitivity for determination of Ni(II) with HMDE, influence of various parameters
such as pH, CL(2), tads, Eads on peak current were studied; pH of 4.0–10.0 was investigated.
Figure 3. Adsorptive voltammograms corresponding to free 2 (- - -) and metal complex with Ni(II) (__ __).
Conditions: pH = 5.5; Ni(II) = 4.9 μg LÀ1; CL(2) = 0.30 μmol LÀ1; Eads = À0.10 V; tads = 80 s.

Complexing agent for nickel(II)
599
The peak potentials of both nickel and the nearest ligand peak shifted more negative with
increasing pH, but higher peak resolution was obtained between pH 4.0 and 7.0 with max-
imum peak current at pH 5.5. For study of ligand concentration, the concentration of 2 in
solution ranged from 0.15 to 0.80 μmol LÀ1. As the nickel peak increases, the free ligand
peak decreases. For low Ni(II) concentration (1.0 μg LÀ1), a 0.15 μmol LÀ1 2 concentration
is adequate to obtain good sensitivity, however, if Ni(II) concentration is higher or the
sample contains other metal ions, concentration of 2 of 0.60 or 0.8 μmol LÀ1 is needed.
Dependence of the nickel peak current on accumulation potential was examined from
À0.1 to À1.3 V, and peak height was almost constant between À0.3 and À0.7 V, with
À0.7 V providing the maximum peak height and was selected for measurements. Variation
of the accumulation time showed that peak current increased linearly with accumulation
time up to 300 s; an adsorption time of 80 s was used for the optimization study, and a
higher adsorption time with the samples.
3.2.1. Analytical parameters. The calibration graph for determination of nickel was
obtained under optimized conditions (figure 4): pH 5.5 (100 μL of 0.4 mol LÀ1 BR buffer);
CL(2) 0.15 μmol LÀ1; tads 80 s; Eads À0.70 V. If CL(2) is 0.15 μmol LÀ1, adsorptive curves of
Ni(II) at concentrations from 0.1 to 5.0 μg LÀ1 produce a linear calibration plot (r = 0.998),
but if CL(2) is 0.3 μmol LÀ1, the plot is linear until 15.0 μmol LÀ1. The precision expressed
as the relative standard deviation (RSD) was 0.60% for seven successive measurements of
the same sample containing 4.9 μg LÀ1 of Ni(II). The limit of detection (LOD) was calcu-
lated according to Miller [26] and was 0.2 μg LÀ1. These results are similar (0.1 μg L-1) to
those obtained by us using the commercial ligand 1-nitroso-2-napthol [20].
3.2.2. Interference studies and validation of the method. The usefulness of the
present method was evaluated by determining Ni(II) in certified reference waste water
Figure 4. Adsorptive voltammograms (top) and corresponding calibration plot (bottom) of Ni(II) standard
solutions. Conditions: pH = 5.5; CL(2) = 0.15 μmol LÀ1; Eads = À0.70 V; tads = 80 s.

600
J.Hurtado et al.
(SPS–WW1) containing 1000 μg LÀ1 of Ni in the presence of Al, As, Cd, Co, Cr, Cu, Fe,
Mn, P, Pb, V, and Zn. An aliquot of 50 μL of water sample (4.9 μg LÀ1 of Ni in solution)
and aliquots of ligand were added into the electrochemical cell to observe the signal of
free ligand. Ni(II) was quantified by standard addition method obtaining 5.2 0.4 μg LÀ1
(RE 6.1%). Experimental conditions: pH 5.5; CL: 0.3 μmol LÀ1, tads: 80 s; Eads: À0.70 V.
However, only with 2 was it possible to carry out this analytical application. Probably, 3
does not form a complex with nickel under these experimental conditions or the formed
complex has a different charge and is not adsorbed onto the electrode.
Metal ions can interfere with the measurement by complexing with 2, and this consumes
the ligand or both by complexing and producing reduction peaks that overlap with, or even
completely suppress, the Ni-L(2) complex peak. The first problem was solved by adding
excess ligand and using the standard addition method for the determination. In voltammetric
determination of Ni(II), the main interferences may be caused by the presence of Co(II), Al
(III), and Zn(II) because their reduction potentials are close to that of Ni(II). However, in
this case in the presence of 2 no signals were observed due to these metal ions.
4. Conclusions
We have synthesized and characterized two new [(N–C–N)Br] ligands formed by reacting
2-bromo-1,3-bis(bromomethyl)benzene with 1,2,3-triazole and benzotriazole. The molecu-
lar structure of 2-bromo-1,3-bis(benzotriazol-1-ylmethyl)benzene (3) was confirmed by
X-ray diffraction. 2-Bromo-1,3-bis(triazol-1-ylmethyl)benzene (2) gave the best results in
analysis of Ni(II). The present work shows that these new ligands can be explored for
trace metal analysis, and further studies with the other ligands are in progress in our
laboratory.
Supplementary material
Crystallographic data for the structural analysis have been deposited with the Cambridge
Crystallographic Data Centre, CCDC-806476. Copies of this information may be obtained
free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
(Fax: /44-1223-336-033; E-mail: deposit@ccdc.cam.ac.uk or www: http://www.ccdc.cam.
ac.uk).
Acknowledgments
We thank “Fondo de Desarrollo Científico y Tecnológico” (FONDECYT), Chile, for
financial support under projects Nos. 1060597 11980002 and 1080524. JH and EN
acknowledge Pontificia Universidad Católica de Chile (VRAI), CONICYT and MECESUP
for doctoral fellowships.
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