Isomer-selective complexation of copper(I) ionic salts towards 1- and 2-allylbenzotriazoles. Synthesis and characterization of CuBF 4·2-all-bta·H2O, CuClO4·2- all-bta, CuClO4·1-all-bta·2-all-bta and CuHSO 4·2-all-bta - The first known example of CuHSO4 π-complexes

Article abstract of DOI:10.1016/j.jorganchem.2012.02.024

The alternating current electrochemical synthesis starting from ethanol solution of Cu(ClO₄)₂·6H₂O, CuSO ₄·5H₂O and Cu(BF₄)₂· 6H₂O with the equimolar mixture of 1- and 2-allylbenzotriazole (all-bta) has led to a formation of Cu[2-all-bta]ClO₄ (I), Cu[2-all-bta]HSO₄ (II) and Cu[2-all-bta]BF₄·H ₂O (III) compounds. The direct interaction between Cu(ClO ₄)₂·6H₂O and the mixture of 1- and 2-allylbenzotriazole in ethanol solution results in an appearance of Cu[(1-all-bta)(2-all-bta)]ClO₄ (IV) compound. These results are strikingly different from earlier performed syntheses using the same ligands mixture and copper(II) halides, and producing coordination compounds with 1-allylbenzotriazole only. Compounds I and II are isotypical and crystallize in a monoclinic space group Cc. I: a = 9.5413(10) , b = 12.3171(9) , c = 10.3264(10) , β = 111.155(4)°, V = 1131.78(18) ³, Z = 4. II: a = 9.1707(17) , b = 13.6639(17) , c = 9.4543(17) , β = 105.555(7)°, V = 1141.3(3) ³, Z = 4. The main feature of structures I and II is a chelate-bridging role of the ligand moiety, bonded to one copper ion via CC-bond of the allyl group and nitrogen atom of the triazole core, and to the second Cu⁺ centre by another N atom. Trigonal-pyramidal copper environment comprises of two nitrogen atoms from different ligand units, CC-bond and oxygen atom at the apical position. The bridging function of both Cu⁺ cations and 2-all-bta molecules results in the formation of infinite chains. High affinity of BF₄^- anion to the H₂O leads to a formation of compound III including water molecule. It crystallizes in an orthorhombic Pbca space group, a = 13.502(8) b = 11.299(5) c = 16.124(8) , V = 2460(2) ³, Z = 8. The ligand moiety plays the same as in I and II chelate-bridging function, but Cu⁺, being also bonded to CC group and to two N atoms, is connected with the disordered BF₄^- anion through the water bridge. In the crystal structure IV the metal ion possesses mixed-isomer surrounding, being bound to N-atom and CC-bond of 2-all-bta molecule, N-atom of 1-all-bta-moiety and O(ClO₄ ^-) atom at apical position. IR spectra confirm rather effective Cu-(CC) bonding.

Full text of DOI:10.1016/j.jorganchem.2012.02.024

Journal of Organometallic Chemistry 710 (2012) 1e5
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Communication
Isomer-selective complexation of copper(I) ionic salts towards
1- and 2-allylbenzotriazoles. Synthesis and characterization
of CuBF4$2-all-bta$H2O, CuClO4$2-all-bta, CuClO4$1-all-bta$2-all-bta
and CuHSO4$2-all-bta e The first known example of CuHSO4
p-complexes
,
a
b
b
E.A. Goreshnik a , A.A. Vakulka , Yu. I. Slyvka , M.G. Mys’kiv
*
a
ꢀ
Department of Inorganic Chemistry and Technology, Institute Jozef Stefan, Jamova 39, 1000 Ljubljana, Slovenia
b Department of Inorganic Chemistry, Ivan Franko National University, L’viv, Ukraine
a r t i c l e i n f o
a b s t r a c t
Article history:
The alternating current electrochemical synthesis starting from ethanol solution of Cu(ClO4)2$6H2O,
CuSO4$5H2O and Cu(BF4)2$6H2O with the equimolar mixture of 1- and 2-allylbenzotriazole (all-bta) has led
to a formation of Cu[2-all-bta]ClO4 (I), Cu[2-all-bta]HSO4 (II) and Cu[2-all-bta]BF4$H2O (III) compounds.
The direct interaction between Cu(ClO4)2$6H2O and the mixture of 1- and 2-allylbenzotriazole in ethanol
solution results in an appearance of Cu[(1-all-bta)(2-all-bta)]ClO4 (IV) compound. These results are
strikingly different from earlier performed syntheses using the same ligands mixture and copper(II)
halides, and producing coordination compounds with 1-allylbenzotriazole only. Compounds I and II are
isotypical and crystallize in a monoclinic space group Cc. I: a ¼ 9.5413(10) Å, b ¼ 12.3171(9) Å,
Received 14 November 2011
Received in revised form
17 February 2012
Accepted 21 February 2012
Keywords:
Copper
Coordination chemistry
Heterocycles
h2-Interaction
c ¼ 10.3264(10) Å,
c ¼ 9.4543(17) Å,
b
¼ 111.155(4)ꢀ, V ¼ 1131.78(18) Å3, Z ¼ 4. II: a ¼ 9.1707(17) Å, b ¼ 13.6639(17) Å,
b
¼ 105.555(7)ꢀ, V ¼ 1141.3(3) Å3, Z ¼ 4. The main feature of structures I and II is a chelate-
bridging role of the ligand moiety, bonded to one copper ion via C]C-bond of the allyl group and nitrogen
atom of the triazole core, and to the second Cuþ centre by another N atom. Trigonal-pyramidal copper
environment comprises of two nitrogen atoms from different ligand units, C]C-bond and oxygen atom at
the apical position. The bridging function of both Cuþ cations and 2-all-bta molecules results in the
formation of infinite chains. High affinity of BFꢁ4 anion to the H2O leads to a formation of compound III
including water molecule. It crystallizes in an orthorhombic Pbca space group, a ¼ 13.502(8) Å
b ¼ 11.299(5) Å c ¼ 16.124(8) Å, V ¼ 2460(2) Å3, Z ¼ 8. The ligand moiety plays the same as in I and II chelate-
bridging function, but Cuþ, being also bonded to C]C group and to two N atoms, is connected with the
disordered BFꢁ4 anion through the water bridge. In the crystal structure IV the metal ion possesses mixed-
isomer surrounding, being bound to N-atom and C]C-bond of 2-all-bta molecule, N-atom of 1-all-bta-
moiety and O(ClOꢁ4 ) atom at apical position. IR spectra confirm rather effective Cue(C]C) bonding.
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
a mixture of 1- and 2-N-allylbenzotriazole isomers as a starting
material. Unexpectedly, using the same mixture of 1- and 2-N-allyl-
benzotriazoles, complexes of copper(I) ionic salts containing
predominantly 2-isomer have been synthesized. The results are
represented in this paper.
Cuþ is a well-known cation capable to h2-coordination with
a double carbonecarbon bond. Due to instability of copper-olefin
adducts, substituted derivatives of unsaturated hydrocarbons
appear to be more suitable ligands for obtaining and investigations of
copper(I) e
p-adducts. N-allylbenzotriazole attracts an attention as
2. Material and methods
a potential ligand with various coordination abilities. Earlier some
complexes of copper-halides derivatives of 1-allylbenzotriazole have
been obtained and X-ray structurally investigated [1e3] using
2.1. Synthesis
2.1.1. Synthesis of N-allylbenzotriazole
The ligand was synthesized (according to a procedure similar to
that described in [4]) from the equimolar amounts of benzotriazole
* Corresponding author. Fax: þ386 1 477 31 55.
E-mail address: evgeny.goreshnik@ijs.si (E.A. Goreshnik).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2012.02.024

2
E.A. Goreshnik et al. / Journal of Organometallic Chemistry 710 (2012) 1e5
(Reachim), freshly distilled allyl chloride, and NaHCO3 in ethanol
(Fig. 1). The mixture was boiled for 11 days (with breaks for nights)
with a reflux condenser and then filtered. A NMR spectrum of used
ligand, agreed well with earlier described one, has shown the
presence of both 1- and 2-isomers of N-allylbenzotriazole in
approximately equimolar ratio. A concentrated solution of the
mixture of 1-allylbenzotriazole and 2-allylbenzotriazole was used
for syntheses of compounds IeIV.
and further the mixtures were pressed into the pellets which had
nearly 1 mm of width. Prepared pellets were used to record the
spectra of the above mentioned complexes. To record the spectrum
of liquid ligand L 0.1 mm potassium bromide cell has been used.
2.3.1. Ligand L (mixture of 1- and 2-allyl derivatives)
IR:
n
¼
3088(m), 3067(m), 3022(m), 2988(m), 2933(m),
1645(m), 1615(m), 1591(w), 1566(m), 1496(m), 1454(m), 1435(w),
1422(m), 1327(m), 1277(m), 1266(m), 1230(m), 1192(w), 1160(m),
2.1.2. Synthesis of IeIII compounds
1093(w), 990(m), 935(s), 850(m), 783(m), 746(s), 432(w) cmꢁ1
.
High-quality single crystals of all three compounds were
obtained by alternating current electrochemical synthesis [5] in
ethanol. Solutions contained Cu(ClO4)2$6H2O, CuSO4$5H2O and
Cu(BF4)2$6H2O respectively (1.0 mmol) and N-allylbenzotriazole
(2.0 mmol) were placed in small test-tubes. A copper wire was
wrapped into a spiral of w1 cm diameter. A straight copper wire
was placed inside the spiral. These copper electrodes were inserted
in cork and immersed in the above mentioned solutions. Syntheses
were performed using alternating current of 50 Hz, voltage 0.4 V
was applied both wire electrodes. After two weeks, colourless
crystals of compounds appeared on the electrodes.
2.3.2. Compounds I-IV
I: IR (KBr):
n
¼ 3494(s), 3101(w), 3037(w), 2975(m), 2926(m),
2844(m), 2723(w), 1895(w), 1724(m), 1635(s), 1591(m), 1557(w),
1499(m), 1449(s), 1413(w), 1376(w), 1360(w), 1297(w), 1271(w),
1239(m), 1085(s), 998(w), 947(w), 841(m), 786(m), 768(s), 665(w),
577(w), 534(w), 522(m), 434(m) cmꢁ1
.
II: IR (KBr):
n
¼ 3092(w), 2975(m), 2929(m), 2872(m), 2842(m),
2723(w), 1725(s), 1645(w), 1572(m), 1444(s), 1377(m), 1329(m),
1167(s), 1108(m), 1061(m), 998(m), 973(m), 949(m), 841(m), 747(s),
620(s), 592(m) cmꢁ1
III: IR (KBr):
.
n
¼ 3090 (m), 3064 (m), 3031 (m), 2983 (m), 1645
2.1.3. Synthesis of compound IV
(m), 1614 (m), 1607 (m), 1594 (m), 1572 (s), 1496 (m), 1456 (s), 1444
(m), 1422 (m), 1328 (m), 1318 (m), 1306 (m), 1283 (s), 1230 (s), 1200
(w), 1088 (s), 948 (m), 854 (m), 787 (m), 747 (s), 534 (s), 522 (s).
The reaction conditions were identical to those in the case of I,
but current was not applied. Colourless crystals have grown on the
copper wire after one month. Crystals appear to be enough stable in
dry atmosphere. The density of the crystals measured by the
flotation method in a mixture of chloroformebromoform was 1.88,
1.85, 1.77 and 1.61 g/cm3 for IeIV respectively.
IV: IR (KBr):
n
¼ 3170 (w), 3100 (w), 3035 (w), 2984 (w), 2954
(w), 2924 (m), 2871 (w), 2854 (m), 1644 (m), 1617 (w), 1611 (w),
1594 (m), 1579 (m), 1572 (m), 1495 (m), 1458 (m), 1444 (m), 1423
(m), 1296 (m), 1282 (m), 1230 (m), 1072 (s), 952 (m), 855 (m), 788
(m), 747 (s), 678 (m), 533 (s), 522 (s).
2.2. Crystallography
2.4. NMR measurements
Single-crystal data were collected on a Rigaku AFC7 diffrac-
tometer equipped by Mercury CCD area detector using graphite
1H NMR spectra (300 MHz) for IeIII compounds dissolved in
DMSO-d6 were recorded using an Inova 300 Varian spectrometer.
Unfortunately, all three compounds are low-soluble in “soft”
solvents, including THF-d8 and acetone-d6. The signals from eCH]
CH2 protons were found at the same positions as in free ligand,
indicating unquestionably breaking the CuIe(C]C) bond because
of strong solvating abilities of used solvent. The data were not
further analysed, and there is no more discussion about these
results.
monochromatized MoK
a radiation. Data treatments were per-
formed using Rigaku CrystalClear software suite program package
[6]. All structures were solved by direct methods using SIR-92 [7]
program (teXan crystallographic software package of Molecular
Structure Corporation [8]) and refined with SHELXL-97 [9] soft-
ware, implemented in program package WinGX [10]. Hydrogen
atoms of ligand moieties were included on idealized positions and
refined with geometrical restrictions, H-atoms of water molecule in
III and HSOꢁ4 anion in II were found on the difference Fourier maps.
Figures were prepared using DIAMOND 3.1 software [11].
3. Results and discussion
3.1. Crystal structure
2.3. IR spectroscopy
In structures I and II 2-allylbenzotriazole fully realizes its
coordination abilities, being bound to one of metal atoms through
the N1 atom of triazole core and by C]C-bond of allyl group, and to
another metal centre through the N3 atom (Fig. 1). Therefore, the
ligand moiety plays in these structures chelating e bridging role.
Copper environment comprises two nitrogen atoms from two
ligand moieties, the C]C group and the oxygen atom from the
anion. In both I and II compounds the metal coordination sphere
FTIR spectra of L and complexes IeIV were recorded with using
of Perkin Elmer GX spectrometer. The resolution in each
experiment was 2 cmꢁ1. 1e2 mg of each complex was mixed and
grinded with 100 mg of potassium bromide (spectroscopic purity)
demonstrates strong tetrahedral motiff, more common for Cuþ
complexes rather than for
-derivatives. In I the CueO (ClOꢁ4 )
s-
p
distance is slightly elongated in comparison with both CueN bond
lengths, in II the CueO (HSOꢁ4 ) bond length appears to be practi-
cally equal to both CueN distances (Fig. 2, Tables 1 and 2). The Cu
atom is removed from the N1, N3, m (m is a mid-point of C8]C9
bond) plane for 0.38 Å in I and 0.54 Å in II, and the C]C-bond is
tilted from the basal plane of coordination polyhedron on 14ꢀ in I
and 11ꢀ in II respectively. A small elongation of coordinated C]C-
bonds and tetrahedral rather than trigonal-pyramidal shape of the
Fig. 1. Scheme of the ligand synthesis.

E.A. Goreshnik et al. / Journal of Organometallic Chemistry 710 (2012) 1e5
3
Table 2
Selected bond distances (Å) and angles (ꢀ) in structures IeIV.
I
Cu1eN3
Cu1eN1a
Cu1eC8a
Cu1eC9a
Cu1eO4
Cu1em
Cl1eO2
Cl1eO3
Cl1eO1
Cl1eO4
1.959(5)
2.034(6)
2.095(6)
2.172(6)
2.234(5)
2.025(6)
1.404(6)
1.422(6)
1.426(6)
1.437(5)
N3eCu1eN1a
N3eCu1em
N1aeCu1em
N3eCu1eO4
N1aeCu1eO4
meCu1eO4
C8aeCu1eC9a
121.7(2)
127.9(2)
99.2(2)
95.9(2)
99.3(2)
108.6(2)
36.8 (3)
II
Cu1eN3
Cu1eN1a
Cu1eO4
Cu1eC8a
Cu1eC9a
Cu1em
S1eO3
S1eO2
S1eO4
S1eO1
O1eH1
1.973(5)
2.072(5)
2.111(4)
2.135(7)
2.166(7)
2.040(8)
1.426(6)
1.436(5)
1.448(5)
1.579(5)
0.95
N3eCu1eN1a
N3eCu1eO4
N1aeCu1eO4
meCu1eO4
N1aeCu1em
N3eCu1em
C8aeCu1eC9a
120.8(2)
101.1(2)
104.3(2)
111.3(1)
98.7(2)
119.9(2)
36.9(3)
Fig. 2. Metal coordination and ligand surrounding in crystal structure II (structure I
differs only by the presence of ClOꢁ4 anion instead of HSO4ꢁ one).
coordination surrounding indicate a weakness of the Cue(C]C)
interaction. Such a conclusion has an additional confirmation in
a rather small (24 cmꢁ1 and 42 cmꢁ1 in I and II respectively) shift of
the C]C stretching frequency. This frequency decreases up to
100 cmꢁ1 in copper(I) complexes with ethylen [12]. The steric
hindrances lead to a marked difference in values of O4eCu1eN3
and O4eCu1eN1 angles (Table 2). Due to the bridging function of
both Cuþ cations and 2-all-bta molecules infinite V-shaped chains
oriented along [101] direction appear. Each two benzotriazole
skeletons from two ligand moieties attached to the same copper
atom are tilted on 57ꢀ. These chains, in turn, are associated into 3D
structure by non-valent interactions. Perchlorate-anions, being
attached to the chains via the only one oxygen atom demonstrate
a noticeable libration, resultated in the enlarged thermal parame-
ters of other three O atoms.
III
IV
Cu1eN1
Cu1eN3b
Cu1eC8b
Cu1eC9b
Cu1eO1
Cuem
1.976(3)
2.055(3)
2.095 (4)
2.141(4)
2.166(3)
2.007(4)
N1eCu1eN3b
N1eCu1em
N3beCu1em
N1eCu1eO1
N3beCu1eO1
meCu1eO1
118.24(14)
129.0(1)
98.59(9)
97.8(1)
96.7(1)
112.32(8)
37.3(2)
C8beCu1eC9b
Cu1eN11
Cu1eN21
Cu1eC28
Cu1eC29
Cu1eO4
Cu1em
Cl1eO2
Cl1eO3
Cl1eO1
Cl1eO4
1.947(3)
2.020(3)
2.058(4)
2.094(4)
2.452(4)
1.962(7)
1.383(4)
1.386(5)
1.429(3)
1.442(3)
N11eCu1eN21
N11eCu1em
N21eCu1em
N11eCu1eO4
N21eCu1eO4
meCu1eO4
112.47(14)
141.3(1)
100.17(8)
92.3(1)
101.0(1)
101.6(8)
38.1(2)
C28eCu1eC29
In III the ligand unit plays the same chelating-bridged role
(Fig. 3) as in previously described compounds I and II. But rather
common tendency of BF4ꢁ units to be bound with the 3d10 metal
cations through the water bridges [13,14] involves oxygen atom of
the water molecule into copper coordination sphere. Despite
a
Symmetry codes: (a) x þ 1/2, ꢁy þ 1/2, z þ 1/2.
Symmetry codes: (b) ꢁx þ 3/2, y ꢁ 1/2, z.
b
Table 1
Details of experimental and crystallographic data for compounds IeIV.
Compound
I
II
III
IV
Formula
Fw
T (K)
C9H9ClCuN3O4 C9H10CuN3O4S C9H11BCuF4N3O C18H18ClCuN6O4
322.18
200
319.8
293
327.56
200
481.38
200
Crystal
system
Space
group
a (Å)
Monoclinic
Monoclinic
Orthorhombic
Triclinic
ꢁ
Cc
Cc
Pbca
P1
9.5413(10)
12.3171(9)
10.3264(10)
9.1707(17)
13.6639(17)
9.4543(17)
13.502(8)
11.299(5)
16.124(8)
7.8621(6)
10.2633(7)
13.1327(10)
97.485(2)
106.141(3)
99.838(2)
985.10(13)
2
b (Å)
c (Å)
a
b
g
(deg)
(deg)
(deg)
111.155(4)
105.555(7)
V (Å3)
1131.78(18)
4
1141.3(3)
4
2460(2)
8
Z
l
(Å)
0.71069
2.176
1.891
0.71069
2.107
1.861
0.71069
1.819
1.769
0.71069
1.284
1.623
m
(mmꢁ1
)
Dcalcd
(g/cm3)
b
R1
0.0511
0.1067
1.088
0.0455
0.1147
1.133
0.0682
0.2048
1.208
0.0694
0.2104
1.147
c
wR2
GOFa
P
P
a
R1
¼
jjFoj ꢁ jFcj =jjFoj
P
P
P
wR2 ¼ ½ wðFo2 ꢁ Fc2Þ2= ðwðFo2Þ2Þꢂ1=2
.
b
c
GOF ¼ ½ wðFo2 ꢁ Fc2Þ2=ðNo ꢁ NpÞꢂ1=2, where No ¼ no. of reflns and Np ¼ no. of
refined parameters.
Fig. 3. Metal coordination and ligand surrounding in crystal structure III.

4
E.A. Goreshnik et al. / Journal of Organometallic Chemistry 710 (2012) 1e5
a neutral state this oxygen atom forms rather short (2.166(3) Å)
CueO bond. This value is close to the earlier observed one of
2.145(7) Å in the structure of CuBF4$2C6H4N3(OC3H5)$H2O [13]. The
metal coordination sphere is very similar to those in I and II and
also demonstrates strong tetrahedral distortion with copper atom
removed from the basal plane by 0.44 Å. The coordinated C]C-
bond is moderately elongated to 1.353(6) Å. The C]C stretching
frequency is shifted on 42 cmꢁ1, similarly to that in I and II. The BF4ꢁ
anion demonstrates rather common orientantional disorder.
Infinite (CuBF4$2-all-bta)n chains are interconnected by OeH/F
hydrogen bonds into layers lying in (110) plane.
Contrary to the above compounds discussed with 2-all-btz as
a ligand the complex IV represents an unusual case of mixed-
isomer coordination compound. In contrast to compounds IeIII,
the 2-allylbenzotriazole molecule acts in the structure of IV as
a chelate ligand, being bonded to the copper atom through the
nitrogen atom and a C]C-bond of allyl group. Two other places in
the metal surrounding are occupied by nitrogen atom from the
molecule of 1-allylbenzotriazole and by moderately removed
oxygen atom belonging to perchlorate-anion (Fig. 4, Table 2). The
CueO(ClO4) distance of 2.425(5) Å noticeably differs from that in
compound I. This value, as same as earlier observed CueO (ClO4)
distance of 2.69(1) Å in Cu(C7H10N2)ClO4 [15] agrees much better
than that in I with the hardness, using Pearson terms, of ClOꢁ4 anion
and softness of Cuþ cation [16]. Two benzotriazole cores belong to
1- and 2-allylbenzotriazole units, attached to the same copper
centre, are mutually tilted on 22.9(1)ꢀ. Because 1-all-bta moiety is
bound with the metal centre via N atom only, uncoordinated allyl
group undergoes small disordering, which is seen in an apparent
shortening of C28]C29 bond to 1.25 Å. Because of the presence in
this structure both coordinated and uncoordinated allyl groups the
IR spectrum of IV contains peaks at 1617 cmꢁ1 (uncoordinated) and
1572 cmꢁ1 C]C stretching frequencies. Isolated [Cu(1-all-bta)(2-
all-bta)ClO4] units are interconnected by weak interactions only.
derivatives [17]. An NMR experiment has confirmed a presence of
both isomers in the product. This mixture was used for further
synthesis of coordination compounds of copper(I) chloride,
bromide, nitrate, tetrafluoroborate, perchlorate and hydrosulfate.
Under very similar reaction conditions the only derivatives of 1-
all-bta with CuCl, Cu(Cl, Br), and CuNO3 were obtained. Contrary,
electrochemical synthesis using copper(II) perchlorate, tetra-
fluoroborate and sulphate resulting in a formation of complexes
with 2-allylbenzotriazole. One may suggest that the main reason
of such selectivity is an entropy factor. In the case of weakly
bonded anions e ClOꢁ4 , BF4ꢁ and HSOꢁ4 , because of high accessibility
of the metal centre 2-allylbenzotriazole fully realizes it coordina-
tion abilities and plays chelate-bridging role. It is well known, that
chelate-effect strongly increases complex stability. Such chelate-
bridging coordination mode requires three places (from four
available) in the copper environment. On the other hand, halide-
anions in the structure play usually bridging role, occupy at least
two places in the metal coordination sphere and, therefore, retains
only two places in metal surrounding, preventing energetically
favourable chelate-bridging ligand coordination. The nitrate-anion
frequently behaves in the same manner. Presence of two acces-
sible places in the Cuþ coordination sphere promotes coordination
of either one ligand moiety in chelate mode or two ligands in
bridging manner, in the last case an adduct should be less soluble
and, consequently, easier crystallized. One may also note, that the
1-allylbenzotriazole is more suitable ligand for the bridging
coordination mode (which requires usually one or two places in
copper environment) because of higher spatial accessibility of the
N1 atom of triazole core comparatively with that for 2-isomer.
That is the reason why only 1-all-bta derivatives appear with
copper(I) halides and nitrate.
The formation of two different (I and IV) compounds from the
same starting materials attracts an additional attention. The stan-
dard electrode potentials for the Cu2þ/Cuþ pair is 0.16 V (in aqueous
media). Because of 1) specific coordination ability of Cuþ towards
carbon C]C double bond, and 2) sharp increase of formation
constants in the case of N, C]C e chelate metal coordination one
may suppose, that this electrode potential could easily be shifted
into negative area, i.e. reaction may run without applying addi-
tional voltage. But such a reaction should be much slower than that
under applied tension. It means that Cuþ concentration in solution
is much lower than the concentration of the ligand, resulting in
a high probability of a formation of single (solvated and/or coor-
dinated by ligand) metal ions. Coordination under such conditions
should produce the most thermodynamically stable moieties, i.e.
bonded in a N, C]C-chelate manner metal centres. The presence of
anion in copper coordination sphere is a requirement of the charge
balance. The molecule of 1-allylbenzotriazole could compete more
successfully for the fourth place in the metal environment because
of higher spatial accessibility of the N3 atom comparatively with
the 2-derivative. Finally, one may expect a formation of isolated
complex units, as was in reality observed. The reaction under
applied tension should run much quicker and generate higher
amount of Cuþ ions. These conditions are favourable for a coordi-
nation of ligand moiety with more than one metal ion and,
consequently, for the appearing of polymeric structures. There are
two reasons why under such conditions only crystals of 2-
allylbenzotriazole complex appear. At first, mentioned above
thermodynamic stability of the complex with chelate metal coor-
dination. Additionally, bridging function of 1-allylbenzotriazole in
hypothetical (Cu e 1-allylbenzotriazole)n chains requires only two
places in the copper coordination sphere. All these points increase
the probability of appearance during electrochemical synthesis
Cu(I)-complexes of 2-allylbenzotriazole, as was also observed
experimentally.
3.2. Isomer-selective complexation
As it is known, the simplest technique to obtain an N-allyl-
benzotriazole
e a reaction between benzotriazole and allyl
halides, resulting in a formation of a mixture of 1- and 2-allyl
Fig. 4. Metal coordination and ligand surrounding in crystal structure IV.

E.A. Goreshnik et al. / Journal of Organometallic Chemistry 710 (2012) 1e5
5
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Acknowledgements
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The authors gratefully acknowledge the Slovenian Research
Agency (ARRS) for the financial support of the present study within
the research program: P1-0045 Inorganic Chemistry and
Technology.
Appendix A. Supplementary material
CCDC 853613 (I), 853615 (II), 853612 (III), 853614 (IV) contains
the supplementary crystallographic data for this paper. These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/ retrieving.html (or from the CCDC, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: þ44 1223 336033; e-mail: deposit@ccdc.
cam.ac.uk).
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