2-tert-Butyl-5-(2-pyridyl)-2H-tetrazole as a chelating ligand in the direct synthesis of novel Cu(ii) and heterobimetallic Cu(ii)/Mn(ii) complexes

Article abstract of DOI:10.1039/c2dt32512h

For the first time, a representative of the 2,5-disubstituted tetrazoles, namely, 2-tert-butyl-5-(2-pyridyl)-2H-tetrazole (L), has been found to participate in oxidative dissolution of copper powder in homometalic systems Cu⁰-L-NH₄X-DMSO (X = Cl, SCN, ClO₄) and heterobimetallic ones Cu⁰-Mn(OAc)₂-L-NH ₄OAc-Solv (Solv = DMSO, DMF), providing the formation of molecular homometallic complexes [CuL₂Cl₂] (1), [CuL ₂(SCN)₂] (2), and [CuL₂(H₂O)] (ClO₄)₂ (3), heterobimetallic complex [Cu ₂MnL₂(OAc)₆] (4) from DMF solution and its mixture with complex [Cu₂MnL₂(OAc)₆] ·2DMSO (5) from DMSO solution. Free ligand L and complexes 1-4 were characterized by elemental analysis, IR spectroscopy, thermal and X-ray single crystal analyses, whereas complex 5 was characterized by X-ray analysis only. Compounds 1-3 are mononuclear complexes, with chelating coordination mode of L via the tetrazole ring N4 and pyridine ring N7 atoms. Heterobimetallic complexes 4 and 5 possess trinuclear structures, with a linear Cu-Mn-Cu arrangement of the metal atoms, linked by the acetate anions; each copper(ii) atom is decorated by a chelating unit of L via the tetrazole ring N1 and pyridine ring N7 atoms in complex 4, and via the N4, N7 atoms in complex 5. Temperature-dependent magnetic susceptibility measurements of complex 4 revealed a weak antiferromagnetic coupling between the paramagnetic copper(ii) and manganese(ii) ions (J = -2.5 cm^-1, g_Cu = 2.25 and g_Mn = 2.01), with magnetic exchange through the acetato bridges.

Full text of DOI:10.1039/c2dt32512h

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2-tert-Butyl-5-(2-pyridyl)-2H-tetrazole as a chelating
ligand in the direct synthesis of novel Cu(II) and
Cite this: Dalton Trans., 2013, 42, 2985
heterobimetallic Cu(II)/Mn(II) complexes†
a
a
a
Anastasiya P. Mosalkova, Sergei V. Voitekhovich,* Alexander S. Lyakhov,
a
b
b
a
Ludmila S. Ivashkevich, Jochen Lach, Berthold Kersting, Pavel N. Gaponik and
a
Oleg A. Ivashkevich
For the first time, a representative of the 2,5-disubstituted tetrazoles, namely, 2-tert-butyl-5-(2-pyridyl)-
2
H-tetrazole (L), has been found to participate in oxidative dissolution of copper powder in homometalic
0
0
systems Cu –L–NH
Solv (Solv = DMSO, DMF), providing the formation of molecular homometallic complexes [CuL
CuL (SCN) ] (2), and [CuL (H O)](ClO (3), heterobimetallic complex [Cu MnL (OAc) ] (4) from DMF
solution and its mixture with complex [Cu MnL (OAc) ]·2DMSO (5) from DMSO solution. Free ligand L
4
X–DMSO (X = Cl, SCN, ClO
4
) and heterobimetallic ones Cu –Mn(OAc)
2
–L–NH
4
OAc–
2
2
Cl ] (1),
[
2
2
2
2
4
)
2
2
2
6
2
2
6
and complexes 1–4 were characterized by elemental analysis, IR spectroscopy, thermal and X-ray single
crystal analyses, whereas complex 5 was characterized by X-ray analysis only. Compounds 1–3 are mono-
nuclear complexes, with chelating coordination mode of L via the tetrazole ring N4 and pyridine ring N7
atoms. Heterobimetallic complexes 4 and 5 possess trinuclear structures, with a linear Cu–Mn–Cu
arrangement of the metal atoms, linked by the acetate anions; each copper(II) atom is decorated by a
chelating unit of L via the tetrazole ring N1 and pyridine ring N7 atoms in complex 4, and via the N4, N7
atoms in complex 5. Temperature-dependent magnetic susceptibility measurements of complex 4
revealed a weak antiferromagnetic coupling between the paramagnetic copper(II) and manganese(II)
ions (J = −2.5 cm− , gCu = 2.25 and gMn = 2.01), with magnetic exchange through the acetato bridges.
Received 21st October 2012,
Accepted 19th November 2012
DOI: 10.1039/c2dt32512h
1
www.rsc.org/dalton
Introduction
Tetrazoles, containing six-membered nitrogen heterocyclic
substituents, are promising multifunctional ligands, with the N
1–5
atoms of both rings being able to bind to metal atoms. This
allows formation of diverse coordination frameworks, resulting
in coordination compounds with different structural motifs and
important applications in the areas of single molecule
5–8
9
10
11,12
Scheme 1 5-R-tetrazoles with heterocyclic R substituents (A), 1-substituted (B)
and 2-substituted (C) 5-(2-pyridyl)tetrazoles.
magnetism,
sensors, storage, nonlinear optics,
light-
13–15
16
emitting
and dielectric devices. Among such ligands, the
anionic forms of 5-(2-pyridyl)-, 5-(pyrimidyl)- and 5-(pyrazinyl)-
tetrazoles (Scheme 1, A) have been mainly investigated. They
have been found to act as chelating agents as well as linkers,
assembling chelating motifs in unusual polymeric structures.
Coordination properties of analogous N-substituted derivatives
have been investigated to a lesser extent. Only a few complexes
with 1- and 2-substituted 5-(2-pyridyl)tetrazoles (Scheme 1, B
1–16
17–23
and C) have been structurally characterized until now,
and
some spectroscopic assumptions concerning the structures of
2
4,25
such complexes have been made.
More intensive investi-
a
Research Institute for Physical Chemical Problems, Belarusian State University,
gations in this area are retarded by the absence of convenient
methods for synthesis of such tetrazole ligands.
The most common pathway for obtaining high-nuclearity
transition-metal complexes as well as polymeric complexes of
various dimensionalities with NH-tetrazoles and N-substituted
ones is based on the self-assembly of ligands together with the
Leningradskaya 14, 220030 Minsk, Belarus. E-mail: azole@tut.by;
Fax: +375 17 2264696; Tel: +375 17 2095198
b
Institut für Anorganische Chemie, Universität Leipzig, Johannisallee 29, D-04103
Leipzig, Germany. E-mail: b.kersting@uni-leipzig.de
†
CCDC 904342–904347. For crystallographic data in CIF or other electronic
format see DOI: 10.1039/c2dt32512h
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1
transition-metal salts. Among the factors to affect the syn- procedures were carried out in vessels open to air. Elemental
thetic process (the ligand, the counterion, the solvent, and the analyses (C, H, N, S) were performed on a VARIO EL-elemental
1
13
3 2
reaction conditions etc.), the modification of reaction con- analyzer. H and C NMR spectra were recorded in (CD ) SO
ditions is presently the most attractive approach to producing on a Bruker Avance 500 spectrometer. The observed chemical
novel topologies and intriguing frameworks. It has long been shifts were referenced to solvent signals (δH 2.50, δ 39.43).
c
known that coordination compounds can be prepared easily Infrared spectra were recorded with a Nicolet Thermo Avatar
through the so-called “direct synthesis of coordination com- 330 FT-IR system over the 400–4000 cm− range (SiC cavities),
1
pounds” – a one-pot oxidative dissolution of a metal powder or and with
a
Bruker Optik GmbH Vertex 70 over the
−
1
metal oxide with a complex-forming agent in non-aqueous 50–400 cm range (between two polyethylene plates). The TG
2
6
solution in air. It has been shown that metal oxidation and and DSC curves were obtained with a NETZSCH STA429 ther-
complexation were conditioned by proton- and/or anion-donat- moanalyzer in a dynamic nitrogen atmosphere (heating rate:
ing reagents and air oxygen. Thus, this approach is very prom- 10 K min− , aluminum oxide, mass 5–6 mg and temperature
ising since the formation of new compounds with unexpected range from room temperature up to 600 °C). Temperature-
stoichiometry, diverse dimensionality and properties starts dependent magnetic susceptibility for a powder sample of 4
from easily available materials under usual conditions with was measured between 2 and 330 K using a MPMS 7XL SQUID
1
2
7–29
good repeatability and high yield.
Moreover, this straight- magnetometer (Quantum Design) in an applied external mag-
forward approach has been extended to the preparation of netic field of 500 G. The experimental susceptibility was cor-
heterobi- and trimetallic systems that are of current interest rected for the diamagnetism of the constituent atoms by using
owing to their unique electronic, electrochemical, magnetic, Pascal’s tables.
3
0–33
catalytic and biological properties.
Quantum chemical calculations have been carried out
Recently, to explore the possibilities of a “direct synthesis” within density functional theory with Becke’s three parameter
approach for the preparation of tetrazole-containing complexes hybrid method employing the Lee–Yang–Parr correlation func-
4
5
of transition metals, we have tested a number of 5-substituted tional (B3LYP) and 6-31+G(d,p) basis set. The solvent effect
tetrazoles as both proton- and anion-donating agents, and has been incorporated by using the polarizable continuum
4
6
1
-substituted tetrazoles in the presence of proton-donating model. The geometry of both syn-L and anti-L rotamers was
substances in the oxidative dissolution of metal powder. fully optimized in the presence of solvent. For all structures
A series of novel 5-R-tetrazolato-bridged Zn(II), Cu(II) and the the force constants have been calculated to verify whether the
first Cu(II)/Zn(II) heterobimetallic complexes, as well as com- optimized structures were minima on the potential energy
plexes of Co(II) and Cu(II) based on 1-substituted tetrazoles, surface. All the calculations have been performed using the
3
4–37
47
have been isolated and structurally characterized.
Gaussian 03 program.
Considering this approach in combination with our earlier
synthetic and structural investigations of metal complexes
Single crystal X-ray diffraction study
3
4,35,38–40
with 5-substituted tetrazoles
and their N-deri- X-ray data were collected on a SMART APEX II diffractometer
3
6,37,41–43
vatives,
we were interested to clear up the behavior of using graphite monochromated Mo-Kα radiation (λ
=
potentially chelating 2-tert-butyl-5-(2-pyridyl)-2H-tetrazole (L) 0.71073 Å). The reflection data were corrected on absorption.
in oxidative dissolution of copper powder in homometalic The structures were solved by direct methods with the
0
48
2
4 4
systems Cu –L–NH X–DMSO (X = Cl, SCN, ClO ) and hetero- program SIR2004 and refined on F by full-matrix least
0
49
bimetallic ones Cu –Mn(OAc) –L–NH OAc–Solv (Solv = DMSO squares technique with SHELXL-97. All non-hydrogen atoms
2
4
or DMF), where ammonium salts were used as both proton- were refined in anisotropic approximation. For complexes 1–5,
and anion-donating agents. Herein, we report a facile route for the hydrogen atoms at carbon atoms were placed in calculated
the synthesis of L, its molecular and crystal structure, and positions and refined using a “riding” model, with Uiso(H) =
present the crystal structures, spectroscopic, thermal and mag- 1.5Ueq(C) for the methyl groups and Uiso(H) = 1.2Ueq(C) for
2 2
netic properties of new homometallic complexes [CuL Cl ] (1), others. For compound L and water molecules in complex 3,
[
CuL (SCN) ] (2), [CuL (H O)](ClO ) (3), and heterobimetallic the hydrogen atoms were localized from Fourier maps and
2
2
2
2
4 2
ones [Cu
2
MnL
2
(OAc)
6
] (4) and [Cu
2
MnL
2
(OAc)
6
]·2DMSO (5).
refined isotropically. Molecular graphics was performed with
5
0
51
the programs ORTEP-3 for Windows and PLATON. X-ray
powder diffraction data of polycrystalline compounds were
used to control their purity. The patterns were recorded with a
HZG 4A diffractometer (Carl Zeiss, Jena) using Cu-Kα radiation
Experimental
General methods, equipment and chemicals used
(
Ni-filter) at 298 K.
5
5
-(2-Pyridyl)-1H-tetrazole, used for the synthesis of 2-tert-butyl-
-(2-pyridyl)-2H-tetrazole, was prepared by the reaction of
Synthesis of 2-tert-butyl-5-(2-pyridyl)-2H-tetrazole (L)
sodium azide with 2-cyanopyridine according to a common tert-Butanol (1.3 mL, 14 mmol) was added dropwise with stir-
4
4
procedure. Copper powder (particle size 13.2 ± 1.1 μm), ring to a suspension of 5-(2-pyridyl)-2H-tetrazole (2.06 g,
other chemicals and solvents were of analytical grade and used 14 mmol) in aqueous 65% perchloric acid (5 mL). The solution
as purchased without further purification. All synthetic obtained was kept at room temperature for 2 h and then
2
986 | Dalton Trans., 2013, 42, 2985–2997
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neutralized with 1 M NaOH to pH 7–8. The precipitate was fil- copper powder was observed for 30 min. Blue crystals of 3 suit-
tered off, washed with cold water, and dried on air. Recrystalli- able for X-ray analysis were formed directly from the reaction
zation from water solution gave colorless crystals L, suitable mixture within two months.
for X-ray analysis.
Yield: 200 mg (58%). Elemental analysis (%): found (calcu-
Yield: 2.37 g (83%). Melting point: 140–142 °C. Elemental lated for C H Cl CuN O ): C 34.76 (34.97); H 4.05 (4.11);
2
0
28
2
10 9
1
analysis (%): found (calculated for C10
H
13
N
5
): C 59.00 (59.10); N 20.30 (20.39). FT-IR (KBr): ν (cm− ): 3391 (br), 3119 (sh),
1
6
H 6.27 (6.245); N 34.35 (34.46). H NMR (500 MHz, DMSO-d ) 3055 (m), 3021 (w), 2989 (m), 2952 (w), 2886 (w), 1623 (m).
δ: 8.77 (1H, d, J = 7.6 Hz), 8.21 (1H, d, J = 7.6 Hz), 8.10 (1H, t, 1567 (m), 1462 (s), 1380 (m), 1305 (m), 1285 (m), 1237 (m),
1
3
J = 7.6 Hz), 7.63 (1H, t, J = 7.6 Hz), 1.75 (9H, s, t-Bu) ppm;
C
1207 (m), 1180 (m), 1107 (vs), 1041 (vs), 980 (w), 924 (m),
6
NMR (100 MHz, DMSO-d ) δ: 162.9 (CN
4
), 149.2, 145.5, 138.7, 818 (m), 796 (s), 758 (s), 724 (s), 645 (m), 621 (vs), 594 (m),
1
1
3
25.5, 122.7, 64.4, 28.8 ppm. FT-IR (KBr): ν (cm− ): 3091 (s), 513 (m), 460 (vw), 422 (s), 353 (s), 275 (vs), 232 (m), 162 (m),
055 (s), 2987 (s), 2941 (m), 2913 (vw), 2879 (w), 1613 (s), 1592 134 (s), 76 (w).
(
1
9
s), 1531 (m), 1473 (s), 1423 (s), 1371 (s), 1304 (s), 1251 (s),
204 (s), 1164 (w), 1081 (vs, br), 1051 (w), 1011 (w), 983 (w),
38 (w), 917 (w), 802 (s), 755 (s), 724 (s), 644 (m), 621 (s), 588 A mixture of copper powder (56 mg, 0.9 mmol), Mn(OAc)2·
Synthesis of [Cu MnL (OAc) ] (complex 4)
2
2
6
(
m), 520 (sh), 462 (w), 433 (m), 403 (s), 280 (s), 175 (m), 98 (s), 4H O (220 mg, 0.9 mmol), 2-tert-butyl-5-(2-pyridyl)-2H-tetra-
2
7
5 (s).
zole (370 mg, 1.8 mmol), ammonium acetate (270 mg,
.6 mmol) and DMF (5 mL) was heated at 70–80 °C under stir-
ring for 30 min until total dissolution of copper powder. Blue
A mixture of copper powder (32 mg, 0.5 mmol), 2-tert-butyl- crystals of complex 4 suitable for X-ray diffraction were
3
Synthesis of [CuL Cl ] (complex 1)
2
2
5
-(2-pyridyl)-2H-tetrazole (203 mg, 1 mmol), ammonium chlo- obtained directly from the reaction mixture the next day.
0
ride (54 mg, 1 mmol) and DMSO (5 mL) was heated at
Yield: 265 mg (62.5%, based on Cu ). Elemental analysis
7
0–80 °C with stirring for 70 min until total dissolution of (%): found (calculated for C H Cu MnN O ): C 40.54
32 44 2 10 12
−
1
copper. After cooling the solution to room temperature, green- (40.77); H 4.43 (4.70); N 15.08 (14.86). FT-IR (KBr): ν (cm ):
ish-blue fine polycrystalline complex 1 was precipitated. 3107 (m), 3077 (w), 3050 (vw), 2985 (s), 2938 (m), 2880 (vw),
Filtered mother solution was allowed to stand for two days to 1595 (vs, sh), 1476 (w), 1410 (vs, sh), 1340 (w), 1304 (m), 1274
give green crystals of 1 suitable for X-ray analysis.
(w), 1252 (w), 1201 (m), 1174 (m), 1103 (m), 1041 (s), 1015 (w),
Yield: 115 mg (43%). Elemental analysis (%): found (calcu- 979 (vw), 934 (m), 903 (w), 822 (m), 798 (s), 755 (s), 727 (s),
lated for C H Cl CuN ): C 44.20 (44.41); H 4.67 (4.84); 668 (vs), 616 (m), 592 (w), 523 (m), 489 (w), 457 (w), 430 (m),
2
0
26
2
10
−
1
N 25.75 (25.89). FT-IR (KBr): ν (cm ): 3072 (w), 3043 (w, sh), 409 (w), 332 (s), 271 (m), 178 (s), 70 (m).
2
1
1
9
5
1
987 (s), 2942 (m), 2881 (w), 1608 (vs), 1574 (s), 1535 (m),
445 (sh), 1402 (m), 1372 (vs), 1301 (vs), 1269 (m), 1239 (m), Synthesis of [Cu MnL (OAc) ]·2DMSO (complex 5)
2 2 6
193 (sh), 1160 (m), 1107 (s), 1037 (vs, br), 981 (m), 943 (sh),
04 (m), 823 (s), 802 (vs), 758 (vs), 725 (vs), 650 (vs), 598 (vs),
18 (s), 438 (m), 410 (s), 353 (w), 275 (vs), 232 (m), 162 (m),
34 (vs), 76 (w).
Blue crystals of complex 5 suitable for X-ray analysis were sepa-
rated off from the mixture of complexes 4 and 5 obtained
according to the procedure described above for complex 4
using DMSO instead of DMF.
Synthesis of [CuL
Complex 2 was prepared by analogy with complex 1, but using
NH SCN (76 mg, 1 mmol) in place of NH Cl. Dissolution of
copper powder was observed for 1 h. Green crystals of complex
2 2
(SCN) ] (complex 2)
Results
Synthesis of ligand and complexes
4
4
2
suitable for X-ray analysis were obtained directly from the 2-tert-Butyl-5-(2-pyridyl)-2H-tetrazole was obtained in 83%
reaction mixture the next day. yield by alkylation of 5-(2-pyridyl)-1H-tetrazole with tert-butyl
Yield: 170 mg (58%). Elemental analysis (%): found (calcu- alcohol in 65% aqueous perchloric acid. t-BuOH–HClO4 was
lated for C22 ): C 44.90 (45.08); H 4.36 (4.47); chosen for alkylation in connection with our recent success in
N 28.54 (28.67); S 10.88 (10.94). FT-IR (KBr): ν (cm ): adjusting the regioselectivity of N-functionalization of azoles
H
26CuN12S
2
−
1
3
1
1
1
7
3
084 (m), 3053 (m), 2987 (s), 2937 (m, sh), 2877 (w), 2086 (vs), using this system. In particular, it is an efficient tool for intro-
605 (vs), 1574 (s), 1533 (m), 1441 (vs), 1371 (vs), 1302 (m), ducing a lipophilic tert-butyl group into the N2 position of the
5
2,53
266 (m), 1187 (sh), 1157 (m), 1100 (m), 1058 (s), 1045 (w), tetrazole cycle.
The regioselectivity of alkylation of 5-R-
023 (w), 981 (w), 951 (m), 903 (w), 821 (s), 800 (s), 7569 (s), tetrazoles is explained by protonation of latter on the N4 atom,
24 (s), 6469s), 593 (s), 515 (m), 468 (m), 431 (m), 410 (m), resulting in formation of 5-R-1H-tetrazol-4-ium cations, in
05 (s), 262 (s), 235 (s), 169 (s), 78 (m).
which only equivalent N2 and N3 atoms are accessible for
attack by carbenium cations generated from the alkylation
agents, like olefins and alcohols. The same mechanism can
Synthesis of [CuL (H O)](ClO ) (complex 3)
54
2
2
4 2
Complex 3 was prepared by analogy with complex 1, but using be proposed for tert-butylation of 5-(2-pyridyl)-1H-tetrazole.
NH ClO (120 mg, 1 mmol) in place of NH Cl. Dissolution of In this case, however, primary protonation on the pyridine
4
4
4
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5
5
N atom should be taken into account as well. Therefore, the
2
Direct synthesis of complexes 1–5 have been carried out
0
0
-(1H-tetrazol-4-ium-5-yl)pyridinium dication can act as an in systems Cu –L–NH X–DMSO (X = Cl, SCN, ClO ) and Cu –
4
4
alkylation substrate in highly acidic mediums (Scheme 2).
Mn(OAc)
2
4
–L–NH OAc–Solv (Solv = DMSO or DMF), where
The obtained compound was attributed to 2,5-disubstituted ammonium salts were used as both proton- and anion-donat-
13
tetrazoles based on C NMR chemical shifts of the tetrazole ing agents. The interaction of copper powder with L and
ring C5 atom, in accordance with the data on the related tetra- ammonium salts in DMSO, using a molar ratio of Cu : L : NH X =
] (complex 1, X = Cl; complex
solution of the compound, confirmed the formation of L and 2, X = SCN) and [CuL (H O)](ClO ) (complex 3, X = ClO ). It
4
1
7,24,25
zoles.
2 2
X-ray analysis of single crystals, grown from water 1 : 2 : 2, gave compounds [CuL X
2
2
4 2
4
showed that the molecules were in the anti conformation in should be noted that complexes 2 and 3 can be also prepared
the solid (Scheme 2). However, due to possible rotation of both from DMF solutions.
heterocycles around the exocyclic C–C bond, the syn confor-
Heterobimetallic compound [Cu MnL (OAc) ] (complex 4)
2 2 6
mation of L is also possible. Conformational changes can be has been synthesized by the reaction of L, copper powder,
caused by specific interactions of the molecules with solvents manganese(II) acetate and ammonium acetate in DMF, with a
of different polarity and protic abilities under recrystallization molar ratio of the components Cu : Mn(OAc) : L : NH OAc =
2
4
or complexation conditions. Quantum chemical calculations 1 : 1 : 2 : 4 in open air. The use of DMSO instead of DMF results
of the total energy of both rotamers in DMSO and DMF show in a mixture (∼1 : 1) of complex 4 and its solvated analogue
almost equal total energies of conformers in both solvents. [Cu MnL (OAc) ]·2DMSO (complex 5). It should be noted that
2
2
6
−
1
The total energy of syn-L is about 1 kJ mol lower than that of ligand L in complexes 4 and 5 exists in different rotameric
anti-L. As a result, not only anti, but also syn conformation of forms, namely syn and anti, respectively (see Scheme 2).
the ligand molecule were realized in complexes synthesized in
this work (see below).
The complexes 1–4 have been isolated directly from the
reaction mixtures as crystalline products. Their moderate
yields of 40–60% are due to their high solubility in the
solvents used (DMSO or DMF). At the same time, these com-
plexes are soluble in water, ethyl alcohol, and acetonitrile.
They have been characterized by elemental analysis, IR spectro-
scopy, thermal and X-ray analyses. Complex 5, obtained in a
mixture with complex 4, has been characterized by X-ray
analysis only.
Crystal structures of L and complexes 1–5
Crystal data, data collection, and refinement details for the
structures reported are summarized in Table 1.
Scheme 2 tert-Butylation of 5-(2-pyridyl)-1H-tetrazole and formation of rota-
meric forms of 2-tert-butyl-5-(2-pyridyl)-2H-tetrazole.
a
Table 1 Main crystal data and structure refinement details for L and complexes 1–5
L
Complex 1
CuN10
Complex 2
Complex 3
CuN10
Complex 4
MnN10
Complex 5
Formula
Formula weight 203.25
T/K
Crystal system
Space group
C
H N
10 13 5
C
20
H
26Cl
2
C
22
H26CuN12
S
2
C
20
H
28Cl
2
O
9
C
32
H
44Cu
2
O
12
36 2 14 2
C H56Cu MnN10O S
540.95
100(2)
Monoclinic
586.21
100(2)
Monoclinic
686.96
100(2)
Monoclinic
942.79
100(2)
Monoclinic
Pˉ1
1099.05
100(2)
Monoclinic
Pˉ1
100(2)
Monoclinic
P2 /c
1
Pc
P2
1
/c
C2/c
Crystal size/mm 0.40 × 0.20 × 0.20 0.25 × 0.25 × 0.12 0.30 × 0.20 × 0.20 0.20 × 0.20 × 0.02
0.19 × 0.15 × 0.05
8.5655(4)
9.9404(5)
12.7777(7)
81.761(2)
75.090(2)
70.822(2)
990.91(9)
1
0.25 × 0.25 × 0.52
8.34040(10)
8.63110(10)
17.2045(2)
93.7780(10)
93.0760(10)
98.7330(10)
1218.93(2)
1
a/Å
b/Å
c/Å
α/°
β/°
γ/°
V/Å
Z
9.8402(6)
10.5972(6)
11.2157(7)
90
116.8140(10)
90
1043.80(11)
4
1.293
10.2378(8)
8.6284(7)
14.6102(12)
90
110.1260(10)
90
1211.80(17)
2
1.483
10.2627(4)
9.3012(4)
15.2346(8)
90
109.8770(10)
90
1367.59(11)
2
1.424
26.510(2)
6.9403(6)
15.2164(13)
90
95.384(2)
90
2787.2(4)
4
1.637
3
−
3
D
c
/g cm
1.580
1.449
1.497
1.275
−
1
μ/mm
0.085
1.152
0.987
1.044
Reflections
Restraints
Parameters
2392
0
188
5393
2
305
0.0314/0.0848
0.0328/0.0860
1.035
2687
36
203
0.0230/0.0655
0.0246/0.0667
1.010
3191
0
198
0.0345/0.0764
0.0583/0.0851
1.014
4525
0
265
0.0233/0.0571
0.0290/0.0605
0.999
5592
21
311
0.0217/0.0603
0.0232/0.0613
1.020
R
R
1
/wR
/wR
2
[I > 2σ(I)] 0.0359/0.0905
[all data] 0.0428/0.0959
1
2
Goodness-of-fit
1.012
a
c 1 2
V = volume of the unit cell; Z = number of formula units in unit cell; D = calculated density; μ = linear absorption coefficient; R and wR are
discrepancy factors.
2
988 | Dalton Trans., 2013, 42, 2985–2997
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-tert-Butyl-5-(2-pyridyl)-2H-tetrazole (L). The compound
Paper
2
crystallizes in the monoclinic space group P2 /c, with four
1
molecules in the unit cell. The asymmetric unit of L comprises
one molecule, showing anti conformation (Scheme 2, Fig. 1).
In the molecule, the tetrazole and pyridine rings are inclined
at 21.30(5)°. Bond lengths and valence angles in the molecule
are in the expected ranges [Cambridge structural Database
(CSD), version 5.33, November 2011]. In the tetrazole ring, for-
mally single bond N4–C5 of 1.3537(13) Å is the longest bond,
while the remaining ones lie in a narrow range of 1.3263(13)–
1
.3326(13) Å. In the pyridine ring, C–C bonds are in a narrow
range of 1.3868(15)–1.3914(14) Å, and the two N–C bonds are
close in length [1.3419(14) and 1.3456(13) Å]. The bridge bond
C5–C6 is 1.4758(14) Å. Intermolecular non-classic hydrogen
a
bonds C11–H11⋯N7 [symmetry code: (a) x, −y−1/2, z + 1/2;
a
hydrogen bond geometry: C11⋯N7 = 3.3890(14) Å, C11–
a
H11⋯N7 = 138.0(10)°] between the pyridine H and N atoms
Fig. 3 Complex molecule of 1, with the atom-numbering scheme. Displace-
of neighbouring molecules form polymeric chains running ment ellipsoids are drawn at the 50% probability level. The hydrogen atoms are
shown as spheres of arbitrary radii.
along the c axis (Fig. 2). Only van der Waals interactions are
between the chains.
[
CuL
monoclinic space group Pc and presents a molecular complex. The asymmetric unit is composed of one complex molecule
one Cu and two Cl atoms, and two ligands L). In complex 1,
2 2
Cl ] (complex 1). The compound 1 crystallizes in the
(
ligand molecules L show anti conformation (Fig. 3).
The copper environment contains a planar arrangement of
two chelating ligands L, coordinated via the tetrazole ring N41
(
N42) and pyridine ring N71 (N72) nitrogen atoms. Two chlo-
rine atoms complete the coordination environment to a dis-
torted octahedron, with distances Cu1–N41 = 2.422(2), Cu1–
N42 = 2.493(2), Cu1–N71 = 1.993(2), Cu1–N72 = 2.005(2), Cu1–
Cl1 = 2.3253(7), and Cu1–Cl2 = 2.3234(7) Å. As seen, the tetra-
zole ring nitrogen atoms are more distant from the copper
atom compared with the pyridine nitrogen atoms. Most of
coordination angles around the copper atom are very close to
9
0° or 180°, except for the angles N42–Cu1–N72 = 76.52(8)°,
Fig. 1 The molecular structure of L, showing the atom-numbering scheme.
Displacement ellipsoids are drawn at the 50% probability level. The hydrogen N42–Cu1–N71 = 103.46(8)°, N41–Cu1–N71 = 77.72(8)° and
atoms are shown as spheres of arbitrary radii.
N41–Cu1–N72 = 102.30(8)°.
In both molecules of L, the structural units composed of
the pyridine and tetrazole rings are considerably flattened as
compared with that in free ligand L. So, the least squares
planes of the tetrazole ring N11/C51 and the pyridine ring
C61/C111 are inclined at 4.97(15)°; for the rings N12/C52 and
C62/C112, the angle between the planes is of 3.56(15)°. In the
tetrazole and pyridine rings, the bonds lengths and valence
angles are usual.
b
Intermolecular non-classic hydrogen bonds C92–H92⋯Cl1
[
symmetry code: (b) x, −y, z − 1/2; hydrogen bond geometry:
b
b
C92⋯Cl1 = 3.682(3) Å, C92–H92⋯Cl1 = 164°] between the
pyridine ring hydrogen atom and the chlorine atom of neigh-
bouring complex molecules form polymeric chains running
along the c axis (Fig. 4).
[
CuL (SCN) ] (complex 2). Compound 2, crystallizing in the
2 2
monoclinic space group P2
1
/c, presents a molecular complex
symmetry imposed by
(
Fig. 5). The complex molecule has C
i
position of the copper atom lying on inversion centre. The
Fig. 2 Crystal packing of L viewed along the b axis. Dashed lines indicate
hydrogen bonds.
ligand molecule L shows anti conformation.
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Fig. 4 Crystal packing of 1, viewed along the b axis. Dashed lines show hydro-
gen bonds. The tert-butyl groups are omitted for clarity.
2
+
2 2
Fig. 6 The cation [CuL (H O)] and perchlorate anion in the crystal structure
of 3. The atom-numbering scheme is given for the asymmetric unit. Displace-
ment ellipsoids are drawn at the 50% probability level. The hydrogen atoms are
shown as spheres of arbitrary radii.
[CuL
2 2 4 2
(H O)](ClO ) (complex 3). Compound 3 (monoclinic,
the space group C2/c) is composed of complex cations
2
+
[
CuL (H O)] and perchlorate anions (Fig. 6). The ligand L is
2 2
in the anti conformation.
The copper and water oxygen atoms lie on a two-fold axis,
imposing C symmetry on the cation. The copper atom coordi-
2
nates four nitrogen atoms of two chelating ligands L and one
water oxygen atom, forming a square pyramid. The basal bond
d
lengths are Cu1–N4(N4 ) = 1.9928(19) Å for the tetrazole ring
Fig. 5 Complex molecule of 2, with the atom-numbering scheme for the asym-
d
metric unit and displacement ellipsoids at the 50% probability level. The hydro- nitrogen atoms and Cu1–N7(N7 ) = 2.0377(18) Å for the pyri-
gen atoms are shown as spheres of arbitrary radii. For the disordered tert-butyl
dine ring nitrogen atoms [symmetry code: (d) 1 − x, y, 1/2 − z].
Water oxygen atom lies in the apical site, with bond lengths
group, only the atoms being in sites of higher occupancy are shown.
Cu1–O1W = 2.190(3) Å. The coordination angles O1W–Cu1–N4
d
d
An elongated octahedral environment around the copper (N4 ) and O1W–Cu1–N7(N7 ) take on the values 93.27(5)° and
d
d
atom is formed by four nitrogen atoms of two ligands L, co- 94.61(5)°, respectively. The angle N4–Cu1–N7 (N4 –Cu1–N7 )
ordinated in a bidentate chelating mode, and two nitrogen of 80.78(7)° is considerably less than 90°, whereas the angle
d
d
atoms of two monodentate thiocyanate ligands. The Cu–N N4–Cu1–N7 (N4 –Cu1–N7) of 98.70(7)° is greater than 90°.
bonds of the tetrazole nitrogen atoms, lying in the axial posi-
In ligand molecule L, the tetrazole and pyridine rings are
c
tions [Cu1–N4(N4 ) = 2.3944 (12) Å], are considerably longer close to co-planarity, with the dihedral angle of 1.80(1)°
c
compared to those for the pyridine [Cu1–N7(N7 ) = 2.0540 (12) Å] between their least squares planes.
c
and the thiocyanate [Cu1–N7S(N7S ) = 1.9628 (13) Å] nitrogen
In the crystal structure of complex 3, intermolecular hydro-
atoms, occupying the equatorial sites [symmetry code: (c) −x, gen bonds of perchlorate oxygen atoms with the pyridine ring
c
e
f
−
y, −z + 1]. The coordination angles N4–Cu1–N7 and N4 – H atoms, C10–H10⋯O4 and C11–H11⋯O2 [symmetry codes:
c
c
Cu1–N7 are of 76.60(4)° (as a consequence, the angles N4 – (e) 1 − x, 1 − y, −z; (f) x, 1 − y, z − 1/2; hydrogen bonds geome-
c
e
e
f
Cu1–N7 and N4–Cu1–N7 are of 103.40(4)°). All remaining try: C10–⋯O4 = 3.304(3) Å, C10–H10⋯O4 = 138°, C11⋯O2 =
f
coordination angles are very close to 90° or 180°.
3.386(3) Å, C11–H11⋯O2 = 159°], connect the anions and
In complex 2, the tert-butyl group of ligand L is disordered cations into polymeric chains running along the c axis. The
over two positions, with occupancies 0.622(9) and 0.378(9). chains are located around the planes x = 0 and x = 1/2.
The tetrazole and pyridine rings are practically co-planar in
the molecule, with the dihedral angle of 0.12(8)° between their anions, O1W–H1W⋯O2 [symmetry code: (g) x, y − 1, z; hydro-
least squares planes. There are no hydrogen bonds in the gen bond geometry: O1W⋯O2 = 2.769(2) Å, O1W–H1W⋯O2 =
crystal structure of 2, and its crystal packing is defined by 173(3)°], combine the above chains in double-chains. An
Hydrogen bonds of water molecules with perchlorate
g
g
g
van-der-Waals interactions only.
arrangement of the chains located around the plane x = 1/2 is
2
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Paper
Fig. 8 Complex molecule of 4, with the atom-numbering scheme for the asym-
metric unit and displacement ellipsoids at the 50% probability level. The hydro-
gen atoms are shown as spheres of arbitrary radii. Dashed lines show semi-
coordinated Cu–O bonds.
Fig. 7 An arrangement of hydrogen-bonded polymeric double-chains, located
around the plane x = 1/2, in the crystal structure of complex 3. The tert-butyl
groups are omitted for clarity.
Cu1–O6 = 2.7920(13) Å, which can be considered as semi-
coordinated. They complete the copper environment to an
octahedron with a bifurcated vertex (O3, O6). In the copper
polyhedron, N1–Cu1–N7 = 76.76(5)°, O1–Cu1–N7 = 171.97(5)°,
O4–Cu1–O5 = 172.13(5)°, and all remaining angles (except for
h
shown in Fig. 7. Intramolecular hydrogen bonds C8–H8⋯N3
[
symmetry code: (h) 1 − x, y, 1/2 − z; hydrogen bond geometry: those including the atoms O3 and O6) lie in the range
C8⋯N3 = 3.187(3) Å, C8–H8⋯N3 = 143°] between the pyri- 89.87(5)–94.95(4)°.
h
h
dine H atom and the tetrazole ring N atom, belonging to
Both heterorings of ligand L show the usual bond lengths
different ligands L of the same complex molecule, are and valence angles. The tetrazole and pyridine rings are
additional in the chains.
inclined at 10.86(11)°.
j
[
Cu MnL (OAc) ] (complex 4). Heterobimetallic compound
In complex 4, non-classic hydrogen bonds C10–H10⋯O5
crystallizes in the triclinic space group P ˉ1 and presents a between the pyridine ring H and acetato O atoms of neigh-
2
2
6
4
linear trinuclear complex, with the syn-rotamer of ligand L bouring complex molecules form polymeric chains extending
k
(
Fig. 8). The complex molecule is centrosymmetric. All atoms along the a axis; hydrogen bonds C14–H14B⋯O4 between the
of the asymmetric unit occupy general sites except for the acetato anions, belonging to different complex molecules, link
manganese atom lying on the inversion centre. In the complex the chains into polymeric layers parallel with the ab plane
molecule, the copper and manganese atoms are separated by (Fig. 9) [symmetry codes: ( j) x + 1, y, z; (k) 2 − x, 1 − y, 1 − z;
j
ca. 3.42 Å, being linked together via three acetato bridges.
hydrogen bonds geometry: C10⋯O5 = 3.412(2) Å, C10–
j
k
k
The manganese atom adopts slightly elongated octahedral H10⋯O5 = 150°; C14⋯O4 = 3.384(2) Å, C14–H14B⋯O4
=
coordination of six oxygen atoms of six acetato anions, with 179°]. In the layer, each complex molecule is hydrogen-bonded
i
equatorial bond lengths Mn1–O2(O2 ) = 2.1434(11) and Mn1– to four others. Intramolecular hydrogen bonds C8–H8⋯O3
i
i
O3(O3 ) = 2.1559(11) Å, and with axial ones Mn1–O6(O6 ) = [hydrogen bond geometry: C8⋯O3 = 3.108(2) Å, C8–H8⋯O3 =
.2028(11) Å [symmetry code: (i) 1 − x, 2 − y, 1 − z]. In the octa- 118°] between the pyridine H and acetato O atoms of a
hedron, the angles between neighbouring Mn–O bonds lie in complex molecule are additional within the layer.
the range of 84.94(4)–95.06(4)°.
[Cu MnL (OAc) ]·2DMSO (complex 5). Compound 5 crystal-
2
2
2
6
The Cu1 atom is surrounded by one chelating ligand L and lizes in the triclinic space group P ˉ1 and presents a hetero-
three acetato anions. It would be considered as five-coordi- bimetallic trinuclear complex, co-crystallized with solvate
nated, with a square pyramidal environment, when taking into DMSO molecules (Fig. 10). The ligand L exists as the anti
account the tetrazole ring N1 atom [Cu1–N1 = 2.4267(13) Å] rotamer, in contrast to complex 4. The manganese atom lies
lying in the apical position of the pyramid, and the pyridine on the inversion centre, providing C symmetry of the complex
i
N7, acetato O1, O4, and O5 atoms being in basal sites, with molecule. All remaining atoms of the asymmetric unit occupy
distances Cu1–N7 = 2.0458(13), Cu1–O1 = 1.9299(11), Cu1–O4 = general positions. As in complex 4, the copper and manganese
1
.9521(11) and Cu1–O5 = 1.9652(11) Å. However, there are two atoms are linked together via three acetato bridges and sepa-
long bonds with two acetato anions, Cu1–O3 = 2.8319(12) Å and rated by ca. 3.44 Å. Coordination features of the manganese
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bond Cu1–N4 = 2.3486(11) Å, and two semi-coordinated long
bonds Cu1–O3 = 2.7756(9) and Cu1–O6 = 2.7790(10) Å. These
bonds form a distorted octahedron around the copper atom
with a bifurcated vertex (O3, O6). In the copper polyhedron, N4–
Cu1–N7 = 77.04(4)°, O1–Cu1–N4 = 101.74(4)°, O4–Cu1–O5 =
175.58(4)°, O1–Cu1–N7 = 177.31(4)°, and all remaining coordi-
nation angles lie in the range of 88.16(4)–93.79(4)° (the angles
including the atoms O3 and O6 are excluded from the list).
In ligand L of complex 5, the tetrazole and pyridine rings
are inclined at 6.03(7)°. The bonds lengths and valence angles
in both heterocycles are usual. In solvate DMSO molecule, the
sulphur and methyl H atoms are disordered over two posi-
tions, with occupancies 0.9789(14) and 0.0211(14).
In the crystal structure of complex 5, there are no direct
hydrogen bonds between the complex molecules. They are
linked together only by DMSO molecules, which play the role
of bridges between the complex molecules due to hydrogen
m
n
bonds. These are C18–H18B⋯O1 , C19–H19A⋯O5 , and C19–
m
Fig. 9 Crystal packing of complex 4, viewed along the c axis. Dashed lines indi-
cate hydrogen bonds. Hydrogen atoms not participating in hydrogen bonds and
the tert-butyl groups are omitted for clarity.
H19E⋯O4 between solvate H and acetato O atoms, as well as
the bond C10–H10⋯O7 between the pyridine H and solvate
o
O atoms [symmetry codes: (m) 1 − x, 2 − y, 1 − z; (n) 1 − x,
1
− y, 1 − z; (o) 2 − x, 1 − y, 1 − z; hydrogen bonds geometry:
m
m
n
C18⋯O1 = 3.338(2) Å, C18–H18B⋯O1 = 151°, C19⋯O5
3
C19–H19E⋯O4 = 156°, C10⋯O7 = 3.2926(18) Å, C10–
H10⋯O7 = 136°]. These non-classic hydrogen bonds form
=
n
m
.449(2) Å, C19–H19A⋯O5 = 168°, C19⋯O4 = 3.375(2) Å,
m
o
o
polymeric layers parallel with the ab plane. Intramolecular
hydrogen bonds C8–H8⋯O6 [hydrogen bond geometry:
C8⋯O6 = 3.1590(17) Å, C8–H8⋯O6 = 123°] between the pyri-
dine H and acetato O atoms are additional in the layers.
FT-IR spectra of compound L and complexes 1–4
Vibrational spectra of free ligand L and complexes 1–4 were
interpreted in accordance with the literature data on related
compounds, in particular chelating pyridyl-containing
5
6
57
azoles,
N-alkyltetrazoles and their metal complexes.
According to these data, coordination with metal ion leads to
significant changes in the frequencies of the ν(CvN) bands of
the pyridine and tetrazole rings, typically located in the region
−
1
1
500–1450 cm in spectra of N-containing heterocyclic com-
5
7,58
Fig. 10 Complex molecule of 5 and solvate DMSO molecule. The atom-num- pounds.
These vibrational bands of both heterocycles,
found at 1471 cm in the spectrum of L, are shifted to 1445,
440, 1463 and 1410 cm in the spectra of complexes 1, 2, 3
and 4, respectively. This is in accordance with chelating coordi-
nation of ligand molecules L in the complexes. It should be
noted that in the spectrum of complex 4, the heterocyclic
ν(CvN) band and the band of symmetric ν(CO) stretching
bering scheme is given for the asymmetric unit. Displacement ellipsoids are
−1
drawn at the 50% probability level, and the hydrogen atoms are shown as
spheres of arbitrary radii. Dashed lines show semi-coordinated Cu–O bonds. For
disordered DMSO molecule, only the atoms being in sites of higher occupancy
are shown.
−1
1
and copper atoms are close to those in complex 4. A distorted vibrations of the carboxylato group of bridging acetato ligands
octahedral coordination of the manganese atom shows the (typically located at 1410 cm−
1 59
)
are overlapping, and, as a
l
l
−1
bond lengths Mn1–O2(O2 ) = 2.1252(9), Mn1–O3(O3 ) = 2.1731(9), result, only one broad intense band at 1410 cm is registered.
and Mn1–O6(O6 ) = 2.1920(9) Å [symmetry code: (l) 2 − x, 2 − This is responsible for a seeming considerable shift of
l
y, 1 − z]. The angles between neighbouring Mn–O bonds in the the heterocyclic ν(CvN) band for complex 4 in comparison
octahedron lie in the range of 85.30(4)–94.70(4)°. As in the with 1–3.
case of complex 4, the copper atom is seven-coordinated, with
In general, the spectra of complexes 1–4 in the region of
usual bonds Cu1–O4 = 1.9639(10), Cu1–O5 = 1.9526(10), Cu1– stretching and stretching-deformation vibrations of the tetra-
O1 = 1.9480(10), Cu1–N7 = 2.0652(11) Å, somewhat elongated zole and pyridine rings and the C–H bonds of the tert-butyl
2
992 | Dalton Trans., 2013, 42, 2985–2997
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substituent are almost identical with the spectrum of L. The
shifts of C–H stretching bands of the pyridine ring by
−
1
1
3
0–20 cm
to lower values on going from L (3090 and
055 cm− ) to its complexes can be attributed to involving the
1
pyridine ring H atoms in hydrogen bonding.
The thiocyanate groups in complex 2 are revealed in the
spectrum due to intense absorption at 2086 and 821 cm−
attributed to the asymmetric vibrations ν(C–N) and ν(C–S),
respectively. The coordination of the thiocyanate groups in
complex 2 is responsible for a strong band ν(Cu–NNCS) at
1
05 cm− in the far-IR region. The uncoordinated perchlorate
1
58
3
anions in complex 3 are identified by the strong bands at 1110
and 1040 cm−
1 58
.
The very strong band ν(OH) at 3390 cm as
−1
−
1
well as the very weak band ν(Cu–O) at 460 cm found in the
spectrum of complex 3 are typical of coordination of water
5
8
molecules to a copper(II) atom. In complex 4, weak bands
ν(Mn–Oacetate) and ν(Cu–Oacetate) appear at 489 and 457 cm−
1
,
respectively.
The far-IR spectra of complexes 1–4 show low-frequency
vibrations of ligand molecules L, as well as vibrations ν(Cu–N)
−
1
at 232, 235, 321 and 332 cm
for 1–4, respectively, and
ν(Cu–Cl) at 353 cm− in the case of complex 1.
1
Thermal properties
Thermal behaviour of L and complexes 1–4 is shown in
Fig. 11. Compound L forms a stable melt at 141 °C. After
heating up to 600 °C, it reveals mass loss of 58.8% and an
exothermic peak at 262 °C. According to data on thermolysis
of 2,5-disubstituted tetrazoles, decomposition of L proceeds
probably through elimination of tert-butyl azide and formation
6
0
of 2-cyanopyridine.
Decomposition of complexes 1 and 2 starts as an endo-
thermic process at 236 and 215 °C, respectively, accompanied
by a mass loss of 58.8 (1) and 69.8% (2), caused by partial (1)
or total (2) desorption of ligand L. For complex 1, exothermic
peak at 329 °C (mass loss 20.8%) indicates the transformation
of intermediate destruction products of L. The solids, remain-
ing after decomposition of complexes 1 and 2, revealed the
compounds CuCl and CuS
powder patterns.
2
, respectively, as follows from XRD
Complex 3 shows an endothermic peak at 89 °C, with mass
loss of 3.8%, which can be attributed to the removal of water
molecules. After melting at 213 °C, a desolvate form of 3
decomposes explosively in an exothermic process (peaks at
2
56 and 295 °C, total mass loss 70.8%), corresponding to the
destruction of ligands L, reduction of perchlorate anions and
formation of CuO residue (confirmed by XRD powder data).
For complex 4, desorption of a molecular form of ligand L
occurs as an endothermic process at 212 °C (mass loss 44.7%),
analogous to the thermolysis of the heterobimetallic Cu(II)/
6
1
Mn(II) acetato complex with 2,2′-bipyridine. The desorption
is followed by destruction of acetato fragments of Cu Mn-
2
(
OAc) , passing through a three-step loss of acetato residues at
6
3
08, 344, and 385 °C, with mass loss of 12.6, 10.2 and 5.1%,
respectively. According to XRD powder data, crystalline CuO
and a spinel-like solid solution (Cu,Mn)Mn O4 are solid
2
Fig. 11 TG/DSC/DTG curves of L and complexes 1–4.
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was possible over the full temperature range, yielding J =
2.5 cm− , gCu = 2.25 and gMn = 2.01. Thus, each of the term-
1
−
inal copper(II) ions is weakly antiferromagnetic exchange-
coupled to the central manganese(II) ion of the trinuclear
complex 4.
Discussion
The synthesized monometallic complexes 1–3 are mono-
nuclear, whereas heterobimetallic 4 and 5 show a trinuclear
structure. In all the complexes, the ligand L is coordinated in a
bidentate chelating mode via the pyridine nitrogen atom and
the tetrazole ring N4 (complexes 1–3, 5) or N1 atom (complex
4
). Coordination of ligand molecules L by metal atoms results
M
Fig. 12 Temperature dependence of χ T for complex 4. The solid line rep-
in more planar geometry of the pyridine-tetrazole skeleton. So,
the dihedral angle between two heterorings of 21.30(5)° in
compound L decreases to 4.97(15)/3.56(15), 0.12(8), 1.80(1),
−
1
resents the best theoretical fits. The insert shows χ
M
vs. T.
products of thermal degradation of the complex. This shows 10.86(11), and 6.03(7)° in complexes 1–5, respectively. More
that complex 4 might be suggested as a precursor of mixed- planar geometry of the skeletons can be attributed to an influ-
6
2
metal oxides systems for dedicated catalytic applications.
ence of chelating coordination mode in the complexes.
In complexes 1–5, the ligands L are chelating ones relative
to the copper atoms. Analysis of the chelate geometry (Table 2)
shows that the bonds Cu–NPy (Py = pyridine) with the pyridine
Magnetic properties of heterobimetallic complex 4
Fig. 12 shows the temperature dependence of the molar χ T nitrogen atoms are usual in all the complexes, with bond
M
−
1
product and the reverse magnetic susceptibility χ
M
for lengths lying in the range 1.993(2)–2.0652(11) Å; the exocyclic
complex [Cu MnL (OAc) ] over the 2–330 K temperature range, angles ∠5 and ∠6 do not differ to a great extent from an
2
2
6
with an applied magnetic field of 500 G.
The value of χ T at 330 K of 5.36 cm K mol (6.55 µ
expected average value of 120°. However, another situation
), occurs for the coordinated tetrazole ring nitrogen atoms.
3
−1
−1
M
B
3
being close to the spin only value of 5.12 cm K mol (6.40 µB) Firstly, for all complexes 1–5, there is considerable deviation of
is expected for two magnetically isolated Cu(II) ions (S = S = exocyclic angles ∠1 and ∠2 from an expected average value of
1
3
1
2
/2) and one high-spin Mn(II) ion (S = 5/2) with g = 2.00.
During cooling, χ T decreases until near 60 K; below this
M
3
−1
temperature, the χ T value decreases sharply to 1.65 cm K mol
a
M
Table 2 Chelate geometry (Å, °) in complexes 1–5
B
(3.63 µ ) at 2 K, suggesting a net intramolecular antiferromag-
netic exchange interaction. The magnetic susceptibility data in
the temperature range 30–330 K obey the Curie–Weiss law
6
3
3
−1
expression with a Curie constant of C = 5.32 cm K mol
and a Weiss constant of θ = −10.3 K, which further confirms
an overall antiferromagnetic interaction between the acetato-
bridged Cu(II) and Mn(II) ions.
Complex 1 Complex 2 Complex 3 Complex 4 Complex 5
Cu–NPy
Cu–NTz
1.993(2),
2.005(2)
2.422(2),
2.0540(12) 2.0377(18) 2.0458(13) 2.0652(11)
2.3944(12) 1.9928(19) 2.4267(13) 2.3486(11)
To estimate the magnitude of the exchange coupling in the
trinuclear complex 4, an isotropic Heisenberg–Hamiltonian
with the addition of a Zeeman term (eqn (1)) was employed by
2
.493(2)
N
Py–Cu–NTz 77.72(8),
76.60(4)
80.78(7)
76.76(5)
77.04(4)
6
3,64
76.52(8)
using a full-matrix diagonalization approach.
∠
∠
∠
∠
1
150.55(18), 148.04(10) 139.16(15) 152.39(10) 147.04(9)
51.82(19)
103.31(15), 105.52(9) 113.40(15) 104.36(10) 106.52(8)
01.85(16)
1
Ĥ ¼ ꢀJðŜ1 ꢁ Ŝ2 þ Ŝ2 ꢁ Ŝ3Þ þ μBB½gCuðŜ1 þ Ŝ3Þ þ gMnŜ2ꢂ
ð1Þ
2
3
4
1
In the model, the exchange coupling interaction between
the terminal Cu(II) ions and the central Mn(II) ion were
assumed to be predominant, therefore coupling between the
b
b
123.02(2),
123.4(2)
122.47(13) 118.4(2)
122.72(14) 121.88(11)
115.2(2),
115.11(13) 111.85(19) 116.35(14) 115.29(11)
1
16.7(2)
120.67(17), 120.30(10) 115.13(14) 119.16(11) 118.81(9)
21.4(17)
two copper ions was neglected. Since the molecular structure ∠5
1
2
revealed that the Mn(II) (S = 5/2) ion lies on the inversion
∠
6
120.89(18), 121.39(10) 127.14(15) 122.59(11) 122.61(9)
119.91(18)
centre, the two Cu(II) ions (S = S = 1/2) can be considered
1
3
identical. Hence, the magnetic exchange coupling constants
12 = J23 = J were also assumed to be equivalent. A satisfactory
fit of the experimental data, shown in Fig. 12 as solid lines, the angles ∠3 and ∠4 are 126.10(9) and 117.02(9)°, respectively.
a
The schematic picture shows correspondence between the angle-
J
b
numbering (∠1–∠6) and the angles in the chelate ring. For compound L,
2
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ca. 127° (the angles ∠1 and ∠2 lie in the ranges ca. 139–152
and 102–113°, respectively). Secondly, all complexes, except for
complex 3, have elongated bonds Cu–NTz (Tz = tetrazole) lying
in the range 2.3486(11)–2.493(2) Å, and high values of the
angle ∠1 and low values of the angle ∠2. Thirdly, complex 3
reveals usual Cu–NTz bonds; the angles ∠1 and ∠2, having,
respectively, lower and higher values in comparison with other
complexes, differ to a lesser extent from the expected average
Scheme 3 Carboxylato binding modes in [M
3
(μ-RCOO)
6
] type complexes (M =
Mn, Cu).
6
5
value; the angles ∠3 and ∠4 have the lowest values among most preferable coordination center in the tetrazole ring.
compounds 1–5, L. It should be noted that all complexes 1–5 Moreover, in ligand molecules relatively bulk tert-butyl and
reveal rather low values of coordination angles N –Cu–N , 2-pyridyl substituents can hinder binding of the N1 atom
Py
Tz
(the nitrogen atoms belong to the same ligand molecule), lying with the copper atom. Notably, the Cu–N1 bond length of
in the range 76.52(8)–80.78(7)°.
2.4267(13) Å in complex 4 is shorter than those in copper(II)
Based on these facts, the following conclusions can be complexes of 2-monosubstituted tetrazoles, showing a rare
made concerning the chelating coordination mode in the (N1,N4)-bridging coordination mode [Cu–N1 bond lengths of
6
5–67
investigated compounds: (a) in molecular complexes 1, 2, 4, 2.50–2.85 Å].
and 5, coordination bonds Cu–NTz are weaker than the bonds
The analysis of crystal structures of complex 4 and analo-
Cu–NPy, and considerable deviation of exocyclic angles ∠1 and gous homometallic compounds with
[Mn (μ-RCOO) ]
2 from expected values takes place; (b) in complex 3, consist- core68–70 reveals the existence of two superexchange pathways
ing of complex cations and perchlorate anions, the bonds Cu– controlling the overall magnetic behavior: (i) through a bi-
Tz are stronger as compared with complexes 1, 2, 4, and 5, atomic acetato O,O bridge (Scheme 3, syn–syn mode D), or (ii)
a
3
6
∠
N
and some deformation of ligand L (via the angles ∠3 and ∠4) via a monoatomic acetato O bridge (mode E). Moreover, a com-
and some change in the exocyclic angles ∠1, ∠2, ∠5 and ∠6 bined mode F can also contribute to the magnetic coupling.
occur. Probably, more information on chelate complexes with
ligand L should be accumulated to explain specific coordi- netic coupling with J values lying in the range from −6.3 to
[Mn (μ-RCOO) ] type compounds show weak antiferromag-
3
6
−
1
nation in complex 3 compared to others.
−1.2 cm
depending on the geometry of carboxylato
In heterobimetallic complexes 4 and 5, complex molecules bridges.68–70 In particular, the presence of a monoatomic
show similar trinuclear structures, with acetato bridges bridge (mode E) reduces the M⋯M distance and increases the
between the copper and manganese atoms, and chelate |J| value. Complex 4, being the first magnetically characterized
ligands L coordinated only by the copper atoms. Another linear trinuclear complex with two different 3d metal ions
common feature of the complexes is that the copper atoms are bridged by carboxylato moieties, also shows antiferromagnetic
seven-coordinated, with two long semi-coordinated Cu–O coupling. In contrast to monometallic trinuclear complexes, a
bonds completing a square pyramidal copper environment to significant shift of acetato bridged oxygen atoms away from
distorted octahedron with
a bifurcated vertex. In both the terminal copper(II) atom, which is accompanied by the for-
compounds, the manganese atoms adopt the usual slightly mation of long semi-coordinated Cu–O bonds in complex 4,
distorted octahedral coordination, formed by the acetato results in the asymmetric character of monoatomic acetato
O atoms.
bridge and, therefore, in non-coupling between the Cu(II) and
Despite the similarity of complex molecules in compounds Mn(II) ions across the acetato binding modes E and F. By
4
and 5, they reveal considerable structural differences, con- taking into account these facts, weak exchange coupling (J =
sisting in different rotameric forms of ligand L in the com- −2.5 cm− ) in complex 4 could be explained by acetato bridges
pounds, namely syn in 4 and anti in 5. These forms in syn–syn coordination mode D only.
correspond to different nitrogen atoms coordinated by the
1
copper atoms in the chelate mode, namely N1 in complex 4
and N4 in complex 5. There is a difference in crystal packing
of complexes 4 and 5, which takes place because of the pres-
Conclusions
ence of solvate DMSO molecules in crystals of complex 5. In The first representative of the 2,5-disubstituted tetrazoles,
this compound, in contrast to 4, there are no hydrogen bonds 2-tert-butyl-5-(2-pyridyl)-2H-tetrazole, was involved in direct
between the complex molecules, which are linked together synthesis of coordination compounds using oxidative dissolu-
only via the hydrogen bonds with DMSO molecules.
tion of copper powder in a non-aqueous solution of
It should be noted that complex 4 presents the first ammonium salts in open air. In accordance with our expec-
example of coordination of 2,5-disubstituted tetrazole via the tations, direct synthesis provided a facile and convenient tool
N1 tetrazole ring atom. The observed N1 coordination mode is toward novel Cu(II) and heterobimetallic Cu(II)/Mn(II) com-
rather unexpected, since quantum-chemical calculations of plexes with different nuclearity. Moreover, this approach has
molecular electrostatic potential, charge distribution and allowed us to realize the expected bidentate chelating mode of
energies of hydronation of nitrogen atoms in the molecule of the ligand via the pyridine nitrogen atom and the tetrazole
2
-monosubstituted tetrazoles indicate that the N4 atom is the ring N4 atom, as well as unexpected one through the pyridine
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nitrogen atom and the tetrazole ring N1 atom. The finding of 16 R.-J. Xu, D.-W. Fu, J. Dai, Y. Zhang, J.-Z. Ge and H.-Y. Ye,
monodentate coordination of the tetrazole ring through the Inorg. Chem. Commun., 2011, 14, 1093–1096.
N1 atom opens new routes in design of complexes based on 17 A. D. Bond, A. Fleming, J. Gaire, F. Kelleher, J. McGinley,
2
-mono- and 2,5-disubstituted tetrazoles. Structural, thermal
V. McKee and U. Sheridan, Polyhedron, 2012, 33, 289–
and magnetic properties of complexes reported here are
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0 C. Femoni, S. Muzzioli, A. Palazzi, S. Stagni, S. Zacchini,
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Acknowledgements
We are grateful to Dr. Vitaly Matulis (Belarusian State Univer-
sity) for quantum chemical calculations. J. Lach thanks the
SAB for an ESF grant.
10.1039/C2DT32056H.
21 Q.-Y. Li, G.-W. Yang, X.-Y. Tang, Y.-S. Ma, F. Zhou, W. Liu,
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