Study of the complex formation between the [Cu(bpca)]+ secondary building unit and the aromatic N donors 2,3,5,6-tetra(2-pyridyl)pyrazine (tppz) and 1,3-bis(4-pyridyl)propane (bpp)

Article abstract of DOI:10.1039/c7ce01230f

Two new complexes of the formula [{Cu(bpca)}₂(μ-tppz)](NO₃)₂·5H₂O (1) and [Cu(bpca)(H₂O)(ClO₄)(μ-bpp)Cu(bpca)(H₂O)₂]ClO₄·H₂O (2) [tppz = 2,3,5,6-tetra(2-pyridyl)pyrazine and bpp = 1,3-bis(4-pyridyl)propane] have been prepared by the reaction of the [Cu(bpca)]⁺ [Hbpca = bis(2-pyridylcarbonyl)imide] building block and the tppz and bpp N donors. An unusual coordination mode of the tppz ligand was observed in 1, which functions as a bis(bidentate) ligand to two copper(ii) atoms each coordinated to a nitrogen atom of the pyrazine moiety and a pyridyl nitrogen atom. This compound presents a layered structure of alternating anionic (ca. 1.6 ?) and cationic (ca. 10 ?) slices, providing the opportunity to obtain isomorphic structures by exchanging the counterion, the solvent or both of them. As in 1, each bpca group in 2 is the end-cap ligand being coordinated to the copper(ii) ion through its three nitrogen atoms in equatorial positions. The supramolecular layers in 2 are filled by the disordered water molecules and one of the perchlorate groups where the volume occupied by the disordered water can be considered as a void of 91.9 ?³. Additionally, the very weak antiferromagnetic couplings observed in 1 [J = -0.16] and 2 [J = -0.41 cm^-1] can be understood by simple orbital symmetry considerations about the type and orientation of the magnetic orbital at each copper(ii) ion in both compounds which provide a clear picture of the poor ability of the involved bridges in mediating electronic effects between the paramagnetic centers.

Full text of DOI:10.1039/c7ce01230f

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Study of the complex formation between the
+
[
CuIJbpca)] secondary building unit and the
aromatic N donors 2,3,5,6-tetraIJ2-pyridyl)pyrazine
tppz) and 1,3-bisIJ4-pyridyl)propane (bpp)†
Cite this: DOI: 10.1039/c7ce01230f
(
a
a
a
Eloisa O. Ribeiro, Nathália R. de Campos, Antônio C. Doriguetto,
b
c
d
Wdeson P. Barros, Marcos A. Ribeiro,
Humberto O. Stumpf,
fElgte E. B. De Paula,
e
Francesc Lloret,
*
f
a
Miguel Julve
and Maria V. Marinho
Two new complexes of the formula [{CuIJbpca)}
2
IJμ-tppz)]IJNO
3
)
2
·5H
2
O (1) and [CuIJbpca)IJH
2
O)IJClO
1,3-bisIJ4-
bisIJ2-
4
)IJμ-
2 2 4 2
bpp)CuIJbpca)IJH O) ]ClO ·H O
(2) [tppz
=
2,3,5,6-tetraIJ2-pyridyl)pyrazine and bpp
=
+
pyridyl)propane] have been prepared by the reaction of the [CuIJbpca)]
[Hbpca
=
pyridylcarbonyl)imide] building block and the tppz and bpp N donors. An unusual coordination mode of
the tppz ligand was observed in 1, which functions as a bisIJbidentate) ligand to two copperIJII) atoms each
coordinated to a nitrogen atom of the pyrazine moiety and a pyridyl nitrogen atom. This compound pre-
sents a layered structure of alternating anionic (ca. 1.6 Å) and cationic (ca. 10 Å) slices, providing the oppor-
tunity to obtain isomorphic structures by exchanging the counterion, the solvent or both of them. As in 1,
each bpca group in 2 is the end-cap ligand being coordinated to the copperIJII) ion through its three nitro-
gen atoms in equatorial positions. The supramolecular layers in 2 are filled by the disordered water mole-
cules and one of the perchlorate groups where the volume occupied by the disordered water can be con-
3
Received 5th July 2017,
Accepted 12th August 2017
sidered as a void of 91.9 Å . Additionally, the very weak antiferromagnetic couplings observed in 1 [J =
−1
−
0.16] and 2 [J = −0.41 cm ] can be understood by simple orbital symmetry considerations about the type
and orientation of the magnetic orbital at each copperIJII) ion in both compounds which provide a clear pic-
ture of the poor ability of the involved bridges in mediating electronic effects between the paramagnetic
centers.
DOI: 10.1039/c7ce01230f
rsc.li/crystengcomm
in relation to hydrolysis, with drastic conditions being required
for the occurrence of their hydrolytic reaction (temperatures of
Introduction
The organic 2,4,6-trisIJ2-pyridyl)-1,3,5-triazine (tpyt) and 2,4,6-
trisIJ2-pyrimidyl)-1,3,5-triazine (tpymt) molecules are very stable
about 150 °C and the presence of a concentrated mineral
acid). However, in the seventies, Lerner and Lippard found
1
that copperIJII) salts promote the hydrolysis of both triazines in
aqueous solution and under mild conditions to afford the
a
Instituto de Química, Universidade Federal de Alfenas, Alfenas, MG 37130-001,
2
-arylformamide molecule and the [bisIJ2-arylcarbonyl)amido]-
Brazil. E-mail: mvmarinho09@gmail.com
b
2
copperIJII) complex [aryl = pyridyl (tpyt) and pyrimidyl (tpymt)].
Later, only two other metal ions have been found to promote
this hydrolysis, namely rhodiumIJIII) and cobaltIJII) for tpyt and
Instituto de Química, Departamento de Química Inorgânica, Universidade
Estadual de Campinas, Campinas, SP 13083-970, Brazil
c
Departamento de Química, Universidade Federal do Espírito Santo, Vitória, ES
3,4
2
d
9075-910, Brazil
tpymt, respectively.
Remarkably, the crystal structures of
Instituto Federal de Educação, Ciência e Tecnologia do Sul de Minas Gerais,
compounds of the formula [CuIJbpca)IJpca)]X·nH
2
O [pca =
Pouso Alegre, MG 37550-000, Brazil
e
−
−
2-picolinamide and X = CF SO (n = 0) and ClO4 (n = 1)]
3
3
Departamento de Química – ICEx, Universidade Federal de Minas Gerais, Belo
allowed the nature of the two main products of the copperIJII)-
Horizonte, MG 31270-901, Brazil
f
Instituto de Ciencia Molecular/Departament de Química Inorgànica, Universitat
assisted tpyt hydrolysis to be established because both are pres-
5,6
de València, C/Catedrático José Beltrán 2, 46980-Paterna, València, Spain
ent as ligands in them. The structures determined by X-ray
†
Electronic supplementary information (ESI) available: XPRD measurements
diffraction of the mononuclear complexes [CuIJbpca)IJH O) ]-
2
2
(
Fig. S1 and S2), crystallographic tables (Tables S1–S3), TG and DTA curves
Fig. S3), crystallographic drawings (Fig. S4–S9). CCDC 1559171–1559172. For
7
2
NO
3
·2H
2
O, [CuIJbpcam)IJH
2
O)
3
]NO ·2H
3 2
O, and [CuIJbpcam)-
IJH O) ]ClO [bpca = bisIJ2-pyridylcarbonyl)amidate and bpcam
(
8
ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c7ce01230f
2
2
4
=
bisIJ2-pyrimidylcarbonyl)amidate] show that the bisIJ2-
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arylcarbonyl)amidate ligands coordinate to the copperIJII) ion Experimental
as tridentate ligands, the six- or five coordination at the
Materials
copperIJII) ion being achieved by three or two water mole-
cules, respectively. Based on the fact that these coordination
water molecules are easy leaving groups and also the pres-
ence of two peripheral carbonyl groups to be used as do-
nors, they have received great attention as building blocks
CopperIJII) nitrate trihydrate, tpyt, bpp and ethanol were pur-
chased from commercial sources and used as received. The
tppz ligand was prepared according to a previously reported
1
7
procedure with some modifications: α-pyridoin (10 g, 47
mmol) and ammonium acetate (45 g, 580 mmol) were mixed
and slowly heated to 180 °C in an oil-bath with a reflux air
condenser. The mixture soon became molten and a very
intense brown-green colour developed. The heating was
maintained for a further three hours, with occasional shak-
ing. After this time, the mixture was cooled to room tempera-
ture. Ethanol was added and the yellow solid formed was col-
lected by filtration. Its recrystallization from a pyridine/
toluene mixture afforded a colourless crystalline solid. M. p.
8
,9
10
in different synthetic routes to construct di-,
tri- tetra-
10b,11
12
and hexanuclear species as well as one-dimensional
9i,j,l,10b,12,13
compounds,
whose structures and magnetic prop-
erties were thoroughly investigated.
In the context of these studies concerning the use of the
bpca-containing copperIJII) complex as a building block in de-
signing polynuclear systems and having in mind the richness
and variety of the crystal structures based on pyridyl ligands
such as 2,3,5,6-tetraIJ2-pyridyl)pyrazine (tppz) and 1,3-bisIJ4-
1
4–16
−1
pyridyl)propane (bpp),
we have explored the possible
284 °C. Yield: 30%. IR/cm : 3052 [ν(C–H)], 1590, 1568, 1483
+
complex formation between [CuIJbpca)] and these aromatic
N donors (see Scheme 1). The results that we have obtained
are presented herein and they concern the preparation,
thermal study and structural characterization of two com-
pounds of formula [{CuIJbpca)} IJμ-tppz)]IJNO ) ·5H O (1) and
[ν(CC) + ν(CN)], 1288, 1273 [δ(C–H)pyridyl].
[CuIJbpca)IJH O) ]NO ·2H O and [CuIJbpca)]ClO were pre-
2
2
3
2
4
5
,7
pared according to procedures reported elsewhere as fol-
lows: a green coloured suspension was obtained by adding
an aqueous solution of CuIJNO ) ·3H O (0.388 g, 1.6 mmol) or
2
3 2
2
3 2
2
[
CuIJbpca)IJH
2
O)IJClO
4
)IJμ-bpp)CuIJbpca)IJH
2
O)
2
]ClO
4
·H
2
O (2) to-
[CuIJH
sion of tpyt (0.250 g, 0.8 mmol) for [CuIJbpca)IJH
·2H O and [CuIJbpca)]ClO , respectively. Heating at 100 °C
2
O)
6
]IJClO
4
)
2
(0.593 g, 1.6 mmol) to an aqueous suspen-
gether with the study of their magnetic properties as a func-
tion of the temperature.
2
O) ]NO
2
3
2
4
+
Scheme 1 Schematic representation of the [CuIJbpca)] building block and its reaction with the tppz and bpp ligands.
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−
1
with stirring for 30 min yielded a dark blue solution. Evapo-
ration of the solvent at room temperature produced blue
heating rate of 10 °C min . The TG/DTA equipment was cali-
brated using an indium standard for the temperature and an
alumina calibration weight for mass. Powder diffraction data
were obtained on a powder X-ray diffractometer (model Ul-
tima IV, Rigaku, Japan) using a Cu-Kα tube (λ = 1.5418 Å) at a
voltage of 40 kV and a current of 30 mA in the 2θ range 5–
40°. Magnetic susceptibility measurements were carried out
on polycrystalline samples in the temperature range 3.0–300
K using a Quantum Design SQUID susceptometer and using
an applied dc magnetic field of 0.1 T. Corrections for the
diamagnetism of the constituent atoms by using Pascal's
polyhedra of [CuIJbpca)IJH
CuIJbpca)]ClO4.
Warning. Perchlorate salts containing organic ligands are
2 2 3 2
O) ]NO ·2H O and blue needles of
[
potentially explosive. We worked in solution on the mmol
scale and the products were obtained by slow evaporation of
the mother solutions in a hood at room temperature.
Preparation of the complexes
[
{CuIJbpca)}
tion (5 ml) of the tppz ligand (0.016 g, 0.035 mmol) was
poured into a warm solution (70 °C) of [CuIJbpca)IJH O) ]NO
2 3 2 2
IJμ-tppz)]IJNO ) ·5H O (1). An ethanolic solu-
−
6
constants were estimated as −586 × 10 (1) and −505 ×
−
6
3
−1
18
1
0
cm mol (2) [per dicopper(II) unit]. Corrections for
2
2
3
−6
3
the temperature-independent paramagnetism [60 × 10 cm
mol per mol of copperIJII) ions] and the sample holder (a
plastic bag) were also applied.
2
·2H O (0.033 g, 0.070 mmol) in water (10 ml). The resulting
−
1
green mixture was kept under continuous stirring for an hour
and a half. Slow evaporation of the solution at room tempera-
ture gave blue crystals of 1 suitable for single crystal X-ray dif-
fraction experiments. They were collected on filter paper,
washed with a small amount of cold water and dried in the
X-ray data collection and structure refinement
X-ray crystallographic data for 1 and 2 were collected with a
Bruker Apex II Duo diffractometer equipped with a CCD area
detector and using Enhance Source Mo-Kα radiation (λ =
.71073 Å) with a graphite monochromator. The values of the
temperature for the data collection were 293(2) (1) and 150(2)
2) K. Data integration and scaling of the reflections for com-
2 14
open air. Yield ca. 50%. Anal. calc. for C48H42Cu N O15 (1) (%):
C, 48.77; H, 3.58; N, 16.59. Found: C, 48.75; H, 3.54 N, 16.50.
−1
IR/cm : 3406 [ν(O–H)], 3075 [ν(C–H)arom.], 1713 [ν(CO)imide],
0
1
626, 1598, 1476, 1444 [ν(CC/CN)tppz], 1381, 1364 [ν(NO
3
)],
1297, 1251 [δ(C–H)], 1154 [ν(C–C)], 758, 701, 632 [δ(C–H)].
(
[
CuIJbpca)IJH O)IJClO )IJμ-bpp)CuIJbpca)IJH O) ]ClO ·H O (2).
2 4 2 2 4 2
pounds 1 and 2 were performed using the ApexII suite. Final
unit cell parameters were based on the fitting of all reflection
An ethanolic solution (5 ml) of the bpp ligand (0.010 g, 0.035
mmol) was added to a warm aqueous solution (70 °C, 15 ml)
positions. Analytical absorption corrections were performed
of [CuIJbpca)]ClO (0.040 g, 0.070 mmol). The resulting green
4
19,20
using Bruker SADABS
with a multi-scan procedure and
mixture was kept under continuous stirring for an hour and
a half. Slow evaporation of the solution at 19 °C gave single
crystals of 2 as blue-greenish squares. They were collected
on filter paper, washed with a small amount of cold water
and dried in the open air. Yield ca. 75%. Anal. calc. for
C H Cl Cu N O (2) (%): C, 42.37; H, 3.65; N, 10.68. Found:
2
1
the space group identification was done with XPREP. The
structures of compounds 1 and 2 were solved by direct
2
2
methods using the SHELXT program. The positions of all
atoms for each compound could be unambiguously assigned
on consecutive difference Fourier maps. Refinements were
3
7
38
2
2
8
16
23
2
performed using SHELXL based on F through a full-matrix
least-squares routine. All non-hydrogen atoms except those of
the disordered water molecules in 2 were refined with aniso-
tropic atomic displacement parameters. Positional disorder
observed in 2 for the non-coordinated water molecule was re-
liably modelled as follows: the disorder was refined over six
site occupancy factors with 0.334(3), 0.278(3), 0.111(3),
−
1
C, 42.20; H, 3.60; N, 10.60. IR/cm : 3516, 3348 [ν(O–H)],
106, 3075 [ν(C–H)arom.]; 2940, 2864 [ν(C–H)aliph.]; 1709
ν(CO)imide], 1620, 1598, 1572, 1475, 1450 [ν(CC/CN)bpp],
297, 1264 [δ(C–H)], 1159 [ν(C–C)], 1084, 1068, 1049, 1024
ν(ClO )], 755, 706, 618 [δ(C–H)].
3
[
1
[
4
Physical measurements
0
.095(3), 0.131(3), and 0.100(6) occupancy for the O16, O17,
Melting points were determined using a Mettler melting
point apparatus (Mettler-Toledo, Leicester, UK) and are
uncorrected. IR spectra were recorded on a Thermo Scientific
IS50 FT-IR spectrophotometer in the wavenumber range of
O18, O19, O20, and O21 positions, respectively. The occu-
pancy factor of the disordered positions was assigned as free
2
3
variables and a linear restraint (SUMP SHELXL instruction)
was applied to them, restraining the sum of six site occupa-
tion factors to be equal to 1.00. The same isotropic displace-
ment parameters are used for all disordered positions. The
positions of the hydrogen atoms of all the water molecules
(except those of the disordered ones in 2 which were neither
found nor geometrically positioned) were calculated by the
−
1
−1
4
000–400 cm with an average of 144 scans and 4 cm spec-
tral resolution using an attenuated total reflection (ATR) ap-
paratus. Elemental analyses were carried out using a CHNS-O
Elemental Analyzer (model Perkin Elmer 2400) (IQ-USP).
Thermogravimetry (TG) and differential thermal analysis
2
4
(
DTA) were performed and the results were obtained simulta-
neously with the same modulus employing a thermobalance
model EXSTAR SII TG/DTA 7000) in the temperature range
5–1100 °C, using alumina crucibles containing samples of
Nardelli method and they were included as fixed contribu-
2
4
tions according to the riding model. A summary of the crys-
tal data and refinement conditions for 1 and 2 is given in
Table 1. Selected bond lengths and angles are grouped in Ta-
ble S1 (ESI†) (1) and Table S2 (2) (ESI†) whereas the hydrogen
(
3
−
1
approximately 3 mg under a flow of N (100 mL min ) at a
2
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,
a b
Table 2 Hydrogen bonds for 2 (Å, °)
bonds are listed in Tables S3 (ESI†) (1) and Table 2 (2). The
2
5
Mercury software was also used to calculate the X-ray pow-
der diffraction patterns from both the unit cell parameters
and the atomic positions obtained from the single crystal
structure analysis. Anyway, the experimental and calculated
powder X-ray diffraction (PXRD) patterns regarding the two
complexes (see Fig. S1 and S2 in the ESI†), show a good
match, each pattern confirming that the obtained structure
from the single crystal is equal to that of the bulk. CCDC-
D–H⋯A
dIJD–H)
dIJH⋯A)
dIJD⋯A)
<D–H–A
vii
O5–H5a⋯O14
0.88(1)
0.88(1)
0.87(1)
0.87(1)
0.88(1)
0.88(1)
1.91(1)
1.88(1)
1.92(1)
2.14(2)
2.06(1)
2.05(1)
2.782(2)
2.737(2)
2.773(2)
2.830(2)
2.929(4)
2.920(4)
177(3)
166(3)
167(3)
135(2)
175(4)
172(3)
v
O5–H5b⋯O3
ii
i
O14–H14b⋯O2
O14–H14b⋯O4
vi
O15–H15a⋯O12
vi
O15–H15b⋯O9
a
b
D = donor and A = acceptor. Symmetry code as in Fig. 8 and 11:
(
1
i) −x + 1, −y + 1, −z + 1; (ii) −x + 1, −y − 1, −z; (v) −x + 1, −y + 2, −z +
1
559171 and 1559172 contain the supplementary crystallo-
; (vi) x, y − 1, z − 1; (vii) x, y + 1, z.
graphic data for 1 and 2, respectively.
Results and discussion
Synthesis, spectroscopy and thermal characterization
vibration, its presence unambiguously supporting the hydro-
2b,5–7
lysis of the tpyt molecule to afford the bpca ligand.
The
The copperIJII)-assisted hydrolysis of the tpyt molecule in aque-
occurrence of the ν(CC/CN) stretching vibrations in the
+
−1
−1
ous solution affords the mononuclear [CuIJbpca)IJH O) ] spe-
ranges 1638–1450 cm (1) and 1620–1450 cm (2) suggests
the coordination of the aromatic nitrogen donors to the
copperIJII) ion. The broad absorption band in both IR spectra
2
2
cies which has been used as a building block in the preparation
10–13a,b,d,e
of a great variety of polynuclear copperIJII) complexes.
−
1
In fact, the stability of this precursor in solution together with
the easy replacement of the coordinated water molecules by
better donors such as organic linkers are at the origin of this
rewarding synthetic route. Having in mind these characteris-
between 3600 and 3200 cm is due to the presence of water
molecules involved in an extensive network of hydrogen
bonds. Finally, the strong absorptions in the ranges 1389–
−
1
−1
1351 cm (1) and 1090–1025 cm (2) indicate the presence
2
6
tics, we have explored the reactivity of the [CuIJbpca)IJH
2
O)
2
]NO
3
of nitrate and perchlorate groups, respectively.
These
·
2H O and [CuIJbpca)]ClO4 building blocks versus the tppz
spectroscopic features for 1 and 2 were confirmed by their
X-ray structures (see below).
2
and bpp nitrogen donors as spacers, the result being the
dicopperIJII) complexes 1 and 2.
The results of the thermogravimetric/differential thermal
analysis (TG/DTA) studies for compounds 1 and 2 are shown
in Fig. S3a and b (ESI†), respectively. The TG curve of 1 under
The infrared spectra of 1 and 2 exhibit a strong absorption
−
1
around 1710 cm which is characteristic of the ν(CO)imide
2
a N atmosphere shows a first mass loss in the temperature
range of 26–100 °C which has been attributed to the release
of five water molecules (observed 7.48%; calculated 7.61%).
An endothermic peak is observed at 91 °C in the DTA curve
which is attributed to the loss of water molecules. 1 is ther-
mally stable between 100 and 293 °C with three successive
weight losses being observed at higher temperatures which
are most likely due to the release of two nitrate anions plus
the thermal decomposition of the tppz and one mol of the
bpca organic ligand (observed 57.09%; calculated 62.48%).
The exothermic step in the DTA curve at 334 °C corresponds
to them. The heating process continues and an amount of
residue, most likely copperIJII) oxide, was obtained at 1040 °C.
Two consecutive weight losses were observed for 2 in the
temperature range 40–209 °C in good agreement with the
crystal structure of the complex, where solvent molecules are
present. The TG curve shows weight losses in two steps rela-
tive to 6.82% of the total mass which correspond to endother-
mic processes in the DTA curve at 76 and 209 °C. They are
most likely related to the removal of four water molecules
Table 1 Crystallographic details for 1 and 2
Compound
1
2
Formula
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (°)
C
48
H
42Cu
2
N
O
14 15
C
37 2 2 8 16
H38Cl Cu N O
1182.06
Monoclinic
Cc
22.185(4)
18.725(4)
23.730(5)
90
1046.72
Triclinic
P¯1
12.7715(5)
13.2527(5)
14.5883(5)
116.240(1)
101.360(1)
95.472(1)
2124.1(1)
2/1
0.71073
150(2)
1.637
1.209
1068
1.62 to 29.17
101 800
11 053
[Rint = 0.0238]
100.0
11 053/10/617
1.043
0.0392, 0.0995
0.0542, 0.1129
1.200 and −0.733
β (°)
102.68(3)
90
9618(3)
4/2
γ (°)
V (Å )
3
Z/Z′
Wavelength (Å)
0.71073
293(2)
1.633
0.973
4848
T (K)
−3
Dcalc (Mg m
)
−1
Absorp. coef. (mm
FIJ000)
)
Theta range (°)
Reflections collected
1.44 to 25.35
127 033
Independent reflections
17 639
(
calculated 6.88%). An exothermic event associated to the re-
[R
int = 0.0959]
lease of perchlorate anions plus the thermal decomposition
of the bpca and bpp ligands (observed 78.39%; calculated
Completeness to θmax (%)
93.3
Data/restraints/parameters
Goodness of fit on F
17 639/2/1438
1.037
2
81.17%) can be observed at 323 °C. The heating process con-
R, wR [I > 2σ(I)]
R, wR (all data)
0.0438, 0.0834
0.0665, 0.0915
tinues at high temperature where a small amount of residue
can be observed, which was attributed to 2 CuO (observed
15.52%; calculated 15.20%)
Largest diff. peak and
0.557 and −0.493
−3
hole (e Å
)
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Fig. 1 Perspective drawings of the crystallographically independent dicopperIJII) units of 1 with partial atom numbering (the whole numbering
scheme is shown in Fig. S4, ESI†). The hydrogen atoms involved in the intermolecular C–H⋯O type interaction (double dashed lines) are
represented as arbitrary radius spheres whereas the ellipsoids of the non-hydrogen atoms are at the 50% probability level. The remaining hydrogen
atoms, water molecules of crystallization and nitrate counterions were omitted for the sake of clarity.
Fig. 2 (a) An overlaying view of the two dicopperIJII) entities present in the asymmetric unit of 1. (b) A perspective view showing the orientation of
the dinuclear units, nitrate counterions and water molecules in relation to the pseudo-inversion symmetry (black dot) identified in the structure.
Green dashed lines highlight the units related by the pseudo-inversion symmetry.
Description of the structures
crystallographically independent dicopperIJII) entities (Z′ = 2)
in the asymmetric unit. A perspective view of the two discrete
2 3 2 2
[{CuIJbpca)} IJμ-tppz)]IJNO ) ·5H O (1). Compound 1 crystal-
lizes in the non-centrosymmetric space group Cc with two
2+
[
{CuIJbpca)}
metric unit of 1 are shown in Fig. 1. The asymmetric unit of
is completed by four nitrate counterions and ten
uncoordinated water molecules (Fig. S4, ESI†). Overlying the
2
IJμ-tppz)] dinuclear units that built up the asym-
1
2
5
two dinuclear units using Mercury showed them to be very
similar (Fig. 2) and related by an inversion orthogonal trans-
formation with a root mean square deviation of 0.1718 Å be-
tween homologous atoms (maximum distance of 0.3930 Å).
The pseudo-inversion center relating the two dinuclear units
is located at (ca. 0.50, 0.83, 0.53) fractional coordinates (and
at equivalent by symmetry positions of the Cc space group) of
the unit cell. These facts suggest that the crystal could belong
to the centrosymmetric supergroup C2/c (also identified as a
potential space group by systematic extinction analysis), with
just one dinuclear unit per asymmetric unit. However, trial
attempts to solve the structure in C2/c were unsuccessful de-
spite the affine transformation relating the two moieties coin-
ciding with this space group. Closer scrutiny showed this not
Fig. 3 View of 1 showing the packing of the dinuclear units (cationic
layer). The two non-symmetry related dicopperIJII) units are distin-
guished by the colour scheme (blue vs. green). Intermolecular copper–
copper distances are indicated. Hydrogen atoms, water molecules and
nitrate anions were omitted for the sake of clarity.
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Fig. 4 (a) View of the packing of the water molecules and nitrate anions (anionic layer) projected onto the ab plane in 1. The crystallographically
independent water/nitrate molecules/anions are distinguished by the colour scheme and highlighted by a dotted circle. (b) View of 1 showing the
packing onto the ac plane, the cationic (dinuclear units) and anionic (water/nitrate molecules/anions) layers being highlighted. The two
crystallographically independent dinuclear units (blue vs. green) and the water/nitrate molecules/anions are differentiated by the colour scheme.
Least-squares planes through the upper and lower limit of the anionic layer are also shown. The approximate values of the thickness of the cat-
ionic and anionic layers are indicated. Hydrogen atoms were omitted for the sake of clarity.
to be the case because part of the hydration water molecules
and nitrate anions break the crystallographic inversion sym-
metry of the C2/c space group (Fig. 2b). The two dinuclear
units and two [those containing the N27 and N28 nitrogen
atoms (Fig. 2b)] of the four nitrate groups are related by the
pseudo-inversion centers present in the structure. On the
other hand, the two remaining nitrate anions (those
containing the N26 and N29 nitrogen atoms) are not
inversion-related groups breaking the crystallographic inver-
sion symmetry that would result in the whole symmetry be-
ing consistent with C2/c. Interestingly, two of the ten water
molecules present in the structure [those containing the O12
and O16 oxygen atoms (Fig. 2b)] are in the two positions gen-
erated from that of the two non-centrosymmetric nitrate an-
ions operating by the pseudo-inversion center.
Analyzing the intramolecular structure of the dicopperIJII)
units, one can see that tppz adopts the bis-bidentate γ coordi-
nation mode acting as donor at each side through the pyr-
azine and one adjacent pyridyl nitrogen atoms (Fig. 1). The
four crystallographically independent copperIJII) ions (Cu1,
Cu2, Cu3 and Cu4) are five-coordinate in distorted square
pyramidal surroundings. The values of the trigonality param-
eter (τ) are 0.06 (Cu1), 0.11 (Cu2), 0.08 (Cu3) and 0.09 (Cu4)
(τ is equal to 0 or 1 for ideal square pyramidal or trigonal bi-
pyramidal, respectively). A pyridyl nitrogen of the tppz mol-
ecule and three nitrogen atoms from a tridentate bpca ligand
build the basal plane whereas a pyrazine nitrogen of the tppz
fills the apical position in all of them. The basal Cu–N dis-
tances vary in the range 1.894IJ5)–2.013IJ5) Å (Table S1, ESI†),
their values being shorter than the apical Cu–N interactions
2
7
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bon atoms of the tppz molecules (Fig. S5, ESI†). In this way,
a supramolecular chain results along the crystallographic a
axis with alternation of the shortest intermolecular copper–
copper contacts [Cu4⋯Cu1 = 5.000(2) Å and Cu2⋯Cu3 =
4.999(2) Å] (Fig. 1). Additional contributions to the stabiliza-
tion of the pseudo-centrosymmetric entity and consequently
to the supramolecular chain along the [100] direction arise
from weak π-stacking interactions between the pyridyl rings
of the bpca ligands (Fig. S6, ESI†). The separation between
the least-squares planes through neighbouring bpca rings is
ca. 3.3 Å (Fig. S6, ESI†). Parallel supramolecular chains grow-
ing along the [100] direction are connected by van der Waals
forces along the crystallographic b axis generating a supra-
molecular 2D network (Fig. 3). The shortest intermolecular
Cu⋯Cu distances (⋯Cu3⋯Cu1⋯Cu3⋯ or ⋯Cu4⋯Cu2⋯Cu4⋯)
along the b axis are twice longer (ca. 9.6 Å) than those (ca. 6.8
and 5.0 Å for the intra- and inter-dinuclear units, respectively)
along the crystallographic a axis (Fig. 3). Finally, one can see
how the cationic layers containing the dinuclear units (Fig. 3)
and the anionic layers containing water/nitrate molecules/an-
ions (Fig. 4a) are stacked along the c axis (Fig. 4b). Therefore,
a remarkable feature of this structure is the layered structure
alternating anionic (ca. 1.6 Å) and cationic (ca. 10 Å) slices
opening the opportunity to obtain isomorphic structures by
exchanging the counterion, the solvent or both.
Fig. 5 View of 1 projected onto the ab plane showing the hydrogen
bonds between the cationic and the anionic supramolecular layers.
The donor⋯acceptor separations are highlighted by dotted cyan lines.
[2.329(4), 2.360(5), 2.318(5) and 2.330(4) Å for Cu1–N5, Cu2–
N6, Cu3–N17 and Cu4–N19, respectively] as expected due to
the Jahn–Teller effect for the copperIJII) ion. The copperIJII) ions
are shifted by 0.129(3) (Cu1), 0.125(3) (Cu2), 0.114(3) (Cu3) and
0.124(3) Å (Cu4) from the mean basal plane towards the apical
site. The copper–copper separations within each tppz-bridged
dicopperIJII) unit are 6.846(2) [Cu1⋯Cu2] and 6.820IJ2) Å
[Cu3⋯Cu4].
Dealing with the packing of 1, it is also observed in Fig. 1
In spite of the considerable number of water molecules of
crystallization in the structure of 1 (1 : 5 dicopperIJII) unit to
that the crystallographically independent dinuclear units are
connected by two bifurcated C–H⋯O type interactions involv-
ing the O3, O4, O5 and O6 carbonyl oxygens of the peripheral
bpca ligands and the C31 and C56 pyridyl carbon atoms of
the bridging tppz ligands atoms as acceptors and donors, re-
spectively. Indeed, additional supramolecular dimerization
between adjacent dicopperIJII) units occurs along the [100] di-
rection in the same way through O1, O2, O7 and O8 carbonyl
oxygens from the bpca ligands and C13 and C79 pyridyl car-
water molar ratio), just one Oacceptor⋯O
distance involv-
donnor
ing the dinuclear units and the water molecules is expected
to result in a O–H⋯O type hydrogen bond. The expected
interaction would have the O3 carbonyl–oxygen atom from
the bpca as acceptor and the O13 water oxygen atom as do-
nor (O3⋯O13 = 2.890(8) Å) (Fig. 5). However, the final refine-
ment shows that the hydrogen atoms of this water molecule
are not positioned towards O3. Indeed, this water molecule
Fig. 6 View of 1 projected onto the ab plane showing the network of hydrogen bonds involving the water molecules and the nitrate anions
supramolecular anionic layer). The crystallographically independent water/nitrate molecules/anions are differentiated by the colour scheme as in
(
Fig. 4a. The donor⋯acceptor separations are highlighted by dotted cyan lines.
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Fig. 7 Perspective view of the asymmetric units of 2 with partial atom numbering. The hydrogen atoms of the water molecule are represented as
arbitrary radius spheres and the ellipsoids of the non-hydrogen atoms are drawn at the 50% probability level. The longer Cu⋯O interactions are
represented as double dashed lines. The hydrogen atoms attached to the carbon atoms and the disordered water molecule of crystallization were
omitted for the sake of clarity.
could also be involved in two other hydrogen bonds with an-
other water molecule of crystallization (O14) and the O21 ni-
trate oxygen [O13⋯O14 = 2.837(8) Å and O13⋯O21 = 2.997(9)
Å]. A complex network of hydrogen bonds is expected to be
formed among the water molecules of crystallization and the
nitrate counterions, contributing to the stabilization of the
anionic/hydrated layer in the crystal packing (Table S3 (ESI†)
and Fig. 6). However, the hydrogen bond geometries found in
this refinement in terms of donor-H distances and donor-
H⋯acceptor angles could not be the real ones, since it was
not possible to find the positions of the hydrogen atoms of
the water molecules by Fourier-difference procedures. This
limitation is quite probable due to the number of non-
hydrogen atoms in the asymmetric unit in addition to the
presence of metal atoms. In this way, the positions of the hy-
drogen atoms of all the water molecules had to be calculated
bond distances at Cu1 and Cu2 cover the range 1.942IJ2)–
2.033IJ3) Å (Table S2, ESI†). The values of the axial Cu1⋯Ow
interactions which are shown as double dashed lines in
Fig. 7 are 2.522(3) (Cu1⋯O15) and 2.674(2) Å (Cu1⋯O14). In
the case of Cu2, the axial interaction with the perchlorate an-
ion [Cu2⋯O6 = 2.649(2) Å] is somewhat longer than that with
the water molecule [Cu2⋯O5 = 2.369(2) Å] and it could not
be viewed as a coordination bond. This being so, the envi-
ronment at Cu1 could be considered as distorted square pla-
nar (see N–Cu–N and N–Cu–O angles in Table S2, ESI†),
while Cu2 would exhibit a distorted square pyramidal geome-
try (τ = 0.27), the apical position occupied by the O5 water
molecule. This markedly longer apical Cu–O distance was
also observed in the mononuclear complex [CuIJbpca)IJPhpr)-
2
8
IJH
2 2
O)]·3/2H O with Phpr = 3-phenylpropionate [CuIJ1)–OIJ1W)
1
0b
−
= 2.365(2) Å].
The two [CuIJbpca)] units in 2 are connected
24a
by the Nardelli method. Therefore, only the donor⋯acceptor
distances involving oxygen atoms of nitrate (acceptor) and
water (either donor or acceptor) close enough to be consid-
ered a hydrogen bond are included in Table S3 (ESI†).
through the bpp ligand which adopts a TG conformation
(where T = trans and G = gauche) with a value for the N⋯N
distance of 9.071(3) Å in agreement with the definition of
Carlucci et al. about the different conformations that can be
reached by using this ligand in its polymeric structures
[N⋯N values in the ranges 9.1–10.1, 8.6–9.2, 3.9–5.3 and 6.7–
2 4 2 2 4 2
[CuIJbpca)IJH O)IJClO )IJμ-bpp)CuIJbpca)IJH O) ]ClO ·H O (2).
The structure of 2 is constituted by cationic bpp-bridged
dicopperIJII) units with end-cap bpca ligands, non-coordinate
perchlorate and water molecules of crystallization (Fig. 7).
One of the two copperIJII) ions (Cu1) achieves six-coordination
with two weakly coordinated water molecules in the axial po-
sitions. Differently, the six-coordination of Cu2 is completed
by a coordinated water molecule and a semicoordinated per-
chlorate group filling the axial sites. Both basal coordination
planes around the copperIJII) cations on the dinuclear unit are
defined by the three nitrogen donor atoms from each
tridentate bpca ligand and one nitrogen atom from bpp that
adopts the bis-monodentate coordination mode. The basal
1
6b,d
8.6 Å for TT, TG, GG and GG′ conformations, respectively.
The Cu1⋯Cu2 separation across the bpp bridge is
12.396(1) Å.
Looking at the crystal packing of 2, a centrosymmetric su-
pramolecular dimer stabilized by hydrogen bonds involving
one of the water molecules (O14) as donor and two bpca-
ii
i
oxygen atoms (O2 and O4 ) as acceptors (Fig. 8a and Table
S2, ESI†) is present as the main building block. The supramo-
lecular dimers are interconnected by translational symmetry,
once again having O14 as hydrogen donor (O14–H14a) and
the bpca-oxygen O4 as acceptor, generating a supramolecular
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Fig. 8 (a) Perspective view of a fragment of the supramolecular double chain in 2 running parallel to the [021] direction. (b) A view of the
interconnection between the supramolecular double chains in 2 along the crystallographic c axis. The hydrogen atoms involved in the
intermolecular hydrogen bonds (double dashed lines) are represented as arbitrary radius spheres and the thermal ellipsoids of the non-hydrogen
atoms are at the 50% probability level. The remaining hydrogen atoms, the disordered water molecule, and one of the perchlorate counterions
were omitted for the sake of clarity [symmetry code as in Table 2: (i) −x + 1, −y + 1, −z + 1; (ii) −x + 1, −y − 1, −z; (iii) x, y − 2, z − 1; (iv) −x + 1, −y, −z;
(
v) −x + 1, −y + 2, −z + 1; (vi) x, y − 1, z − 1; (vii) x, y + 1, z].
double chain along the [021] direction (Fig. 8a, Table S2,
ESI†). Parallel double chains are also interlinked along the
crystallographic c axis through intermolecular hydrogen
bonds by means of two water molecules (O5 and O15) as do-
ESI†). It is observed that each disordered water molecule
moiety is surrounded by six perchlorate anions in a hexago-
nal arrangement (Fig. S8, ESI†). In fact, the volume occupied
by the disordered water can be considered as a void, which
is defined as empty space in the unit cell that is large
v
vii
nors [O5 has either O3 (bpca-oxygen atom) or O14 (water
vi
25
oxygen) as acceptors, whereas O9 (perchlorate oxygen atom)
enough to hold a spherical “probe” of the given radius.
is the acceptor of O15 (see Fig. 8b and Table S2, ESI†)]. This
leads to a supramolecular 2D network parallel to the (100)
plane depicting a wavy periodicity of the dicopperIJII) cations
within the double chains along the [021] direction (Fig. 9a). It
is important to note that this packing defines the shortest
intermolecular copper–copper separation (values in the range
The void volume occupied by the disordered water mole-
cules is 91.9 Å (about 4.3% of the unit cell of 2 calculated
3
using the contact surface approach with grid spacing and a
probing-sphere radius of 0.7 and 1.1 Å, respectively) (Fig. S9,
ESI†). Fig. 11 shows that the disordered water molecule and
the perchlorate anion contribute to the packing through
intermolecular hydrogen bonds involving hydrogen bond ac-
ceptors/donors (O3, O5 and O15) of the dicopper(II) unit (see
also Table 2).
6
.777–8.388 Å) (Fig. 9b).
The stacking of these supramolecular layers along the
crystallographic a axis gives rise to channels parallel to the
021] direction which are filled by the disordered water mol-
[
ecules and one of the perchlorate groups (C11) [see Fig. 10
and S7 (ESI†)]. These channels are also arranged in a lay-
ered structure parallel to the (100) plane alternating with
the layers of the bpp-bridged dicopperIJII) cations (Fig. S8,
Magnetic properties
The magnetic properties of 1 and 2 in the form of a χMT
product versus T plot [χM being the magnetic susceptibility
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Fig. 9 (a) View of 2 projected onto the bc plane highlighting the wavy-shape of the supramolecular double chains along the [021] direction that
generates the 2D network parallel to the (100) plane. Molecules related by inversion symmetry are differentiated by the colour scheme (magenta
vs. cyan). The hydrogen atoms, disordered water molecules and one of the perchlorate counterions were omitted for the sake of clarity. (b) Intra-
and intermolecular copper–copper distances in 2 where only the copperIJII) ions are shown.
per dicopperIJII) unit] are shown in Fig. 12. At room tempera-
3
−1
ture, χ
which is as expected for two magnetically isolated spin dou-
blets (SCu = 1/2) with g = 2.10. Upon cooling, χ T remains
constant until 40 K and further decreases very slightly to at-
M
T for 1 and 2 is equal to 0.83 cm mol K, a value
M
3
−1
tain values of 0.81 (1) and 0.80 cm mol K (2) at 3.0 K. This
behaviour is typical of a very weak antiferromagnetic interac-
tion between the copperIJII) ions.
Given the dinuclear structure of 1 and 2, we analysed their
magnetic data through a simple Bleaney–Bowers expression
2
9
for a dicopperIJII) unit [eqn (1)]
2
2
χ
M
= (2Nβ g /kT)/[3 + exp(−J/kT)]
the spin Hamiltonian being defined by eqn (2)
H = − JS ·S + gβH(S + S
(1)
1
2
1
2
)
(2)
Fig. 10 View of
2 showing the stacking of layers along the
crystallographic a axis as well as the channel structure filled by the
disordered water molecules (in red) and one of the perchlorate
counterions (in blue). Hydrogen atoms were omitted for the sake of
clarity.
where J is the magnetic coupling parameter, g is the average
Landé factor of the copperIJII) ions and N, β and k have their
usual meanings. Least-squares best-fit parameters are J =
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Fig. 11 A view of 2 projected onto the ab plane showing the hydrogen bond network involving water molecules and perchlorate anions (anionic
layer). The crystallographically independent water/perchlorate molecules/anions are differentiated by the colour scheme as in Fig. S7a (ESI†). The
donor⋯acceptor interactions are highlighted by dotted cyan lines [symmetry code as in Table 2: (vi) x, y − 1, z − 1].
−
1
30
−
0.16 (1) and −0.41 cm (2) and g = 2.10 (1 and 2) with R =
would be negligible. Previous studies of tppz-containing
−
6
−6
6
.7 × 10 (1) and 4.5 × 10 (2), R being the agreement factor
dicopperIJII) complexes, where the tppz adopts the bis-
tridentate coordination mode with the exchange pathway in-
volving equatorial bonds at the copperIJII) ions, showed values
of −J in the range 20–61 cm .
P
P
2
2
defined as
ij(χ T) IJi) − (χ T)
IJi)] / ij(χ T) IJi)] .
i
M
obs
M
calcd
i
M
obs
The very weak antiferromagnetic couplings observed in 1
and 2 can be understood by simple orbital symmetry consid-
erations about the type and orientation of the magnetic or-
bital at each copperIJII) ion in 1 and 2 which provide a clear
picture of the poor ability of the involved bridges in mediating
electronic effects between the paramagnetic centers. In the
case of compound 1, the unpaired electron at each copperIJII)
ion is delocalized in the basal plane of the square pyramid
−1 14a–h
The bis-bidentate bridging
mode of the tppz in 1 connecting apical positions of the
copperIJII) ions through the pyrazine ring accounts for its
poorer ability to mediate magnetic interactions in this com-
pound. As far as compound 2 is concerned, although the pos-
sible intramolecular exchange pathway involves the equatorial
Cu1–N4 and Cu2–N5 bonds (the unpaired electron at each
copperIJII) ion being delocalized in the equatorial plane), the
great distance between the copperIJII) ions through the ex-
tended bpp ligand (ca. 12.4 Å) allows one to predict a very
weak intramolecular magnetic interaction, if any. Finally, the
small magnetic couplings observed for 1 and 2 have to be con-
sidered as the higher ones for the intramolecular magnetic
interaction, the values of the shortest intermolecular copper–
copper separation [ca. 5.0 (1) and 6.8 Å (2)] being shorter than
those of the intramolecular ones [ca. 6.8 (1) and 12.4 Å (2)].
2
2
[
dIJx –y ) type magnetic orbital], the spin density on the apical
position (N5, N6, N17 and N19 at Cu1, Cu2, Cu3 and Cu4, re-
spectively) being very small. Consequently, the overlap be-
tween the two magnetic orbitals of each dicopperIJII) unit by
this axial pathway across the pyrazine ring of the tppz bridge
is expected to be very poor and then the magnetic coupling
Conclusions
In summary, we have reported the synthesis and spectro-
scopic, thermal, structural and magnetic characterization of
two new copperIJII) compounds. Our synthetic strategy
is based on the simultaneous use of the [bisIJ2-
pyridylcarbonyl)amido]copperIJII) metalloligand and tppz and
bpp as spacers to provide the dicopperIJII) compounds
[
{CuIJbpca)} IJμ-tppz)]IJNO ) ·5H O (1) and [CuIJbpca)IJH O)-
2 3 2 2 2
IJClO )IJμ-bpp)CuIJbpca)IJH O) ]ClO ·H O (2). Two crystallo-
4
2
2
4
2
graphically independent tppz-bridged dicopperIJII) units occur
in 1 with values of the copper–copper separation across the
bis-bidentate tppz ligand of 6.846(2) (Cu1/Cu2) and 6.820(2)
Å (Cu3/Cu4). They are interconnected by non-classical hydro-
gen bonds and additional weak π–π type stacking interactions
Fig. 12
M
χ T vs. T plot for 1 (blue circles) and 2 (green squares). Best-fit
curves through eqn (1) (see text) are shown as solid lines.
contributing to the stabilization of the structure.
A
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remarkable feature of the structure of 1 is its supramolecular
layered structure alternating anionic (ca. 1.6 Å) and cationic
4 D. A. Safin, P. M. J. Szell, A. Keller, I. Korobkov, D. L. Bryce
and M. Murugessu, New J. Chem., 2015, 39, 7147.
(
ca. 10 Å) slices opening the opportunity to obtain isomor-
5 A. Cantarero, J. M. Amigó, J. Faus, M. Julve and T.
Debaerdemaeker, J. Chem. Soc., Dalton Trans., 1988, 2033.
6 J. Faus, M. Julve, J. M. Amigó and T. Debaerdemaeker,
J. Chem. Soc., Dalton Trans., 1989, 1681.
7 I. Castro, J. Faus, M. Julve, J. M. Amigó, J. Sletten and T.
Debaerdemaeker, J. Chem. Soc., Dalton Trans., 1990, 891.
8 D. C. de Castro Gomes, H. O. Stumpf, F. Lloret, M. Julve, V.
González, H. Adams and J. A. Thomas, Inorg. Chim. Acta,
2005, 358, 1113.
9 (a) I. Castro, J. Faus, M. Julve, M. Mollar, A. Monge and E.
Gutiérrez-Puebla, Inorg. Chim. Acta, 1989, 161, 97; (b) I.
Castro, J. Faus, M. Julve, Y. Journaux and J. Sletten, J. Chem.
Soc., Dalton Trans., 1991, 2533; (c) I. Castro, J. Sletten, J.
Faus, M. Julve, Y. Journaux, F. Lloret and S. Alvarez, Inorg.
Chem., 1992, 31, 1889; (d) I. Castro, M. L. Calatayud, J.
Sletten, F. Lloret, J. Cano, M. Julve, G. Seitz and K. Mann,
Inorg. Chem., 1999, 38, 4680; (e) M. L. Calatayud, I. Castro, J.
Sletten, F. Lloret and M. Julve, Inorg. Chim. Acta, 2000, 300–
302, 846; ( f ) B. Vangdal, J. Carranza, F. Lloret, M. Julve and
J. Sletten, J. Chem. Soc., Dalton Trans., 2002, 566; (g) R.
Lescouëzec, G. Marinescu, J. Vaissermann, F. Lloret, J. Faus,
M. Andruh and M. Julve, Inorg. Chim. Acta, 2003, 350, 131;
phic structures by exchanging the counterion, the solvent or
both. The structure of 2 consists of bpp-bridged dicopperIJII)
units where the bis-monodentate bpp ligand adopts a TG
conformation (T = trans and G = gauche), the intramolecular
copper–copper distance being 12.3957(6) Å. An extensive net-
work of hydrogen bonds involving the coordinated water and
some of the crystallization water molecules, the carbonyl oxy-
gen atoms of the bpca ligand and one oxygen atom of the co-
ordinated perchlorate leads to a supramolecular 2D network
in 2, with the disordered water molecules and the non-
coordinated perchlorate being located in the interlayer voids.
Thermal studies of 1 revealed the loss of five water molecules
up to 91 °C, the anhydrous phase being stable between 100
and 293 °C, while in 2, the loss of the crystallization and co-
ordinated water molecules occurred in two steps at 40 and
2
09 °C, and the resulting anhydrous phase is stable in the
temperature range 194–255 °C. Very weak antiferromagnetic
couplings are observed in 1 and 2 through the bis-bidentate
tppz and bis-monodentate bpp bridges, these spacers
appearing as very poor mediators of magnetic interactions
between the copperIJII) ions linked by them.
(
h) D. Cangussu, H. O. Stumpf, H. Adams, J. A. Thomas, F.
Conflicts of interest
Lloret and M. Julve, Inorg. Chim. Acta, 2005, 358, 2292; (i) D.
Cangussu, L. M. Toma, H. O. Stumpf, H. Adams, J. A.
Thomas, F. Lloret and M. Julve, Polyhedron, 2008, 27, 559;
There are no conflicts to declare.
(
j) I. Carlucci, G. Ciani, S. Maggini, D. M. Proserpio, R.
Acknowledgements
Sessoli and F. Totti, Inorg. Chim. Acta, 2011, 376, 538; (k) W.
Wu, W.-J. Pan and Y.-Q. Zheng, J. Coord. Chem., 2013, 66,
4
A. P. S. Fontes, W. C. Nunes, F. Lloret, M. Julve and C. L. M.
Pereira, Cryst. Growth Des., 2016, 16, 4094.
The authors thank the Brazilian agencies CAPES (AUXPE -
PNPD 2347/2011), CNPq (48723/2014-0 and 308162/2015-3),
FINEP (Ref. 134/08), and FAPEMIG (Projects APQ-00273-14 and
PPM-00533-16) and the Spanish agencies Ministerio Español
de Economía y Competitividad (Projects CTQ2013-44844P and
CTQ2016-75068P) and Unidad de Excelencia María de Maetzu
415; (l) W. X. C. Oliveira, C. B. Pinheiro, M. M. da Costa,
1
0 (a) J. Sletten, M. Julve, F. Lloret, I. Castro, G. Seitz and K.
Mann, Inorg. Chim. Acta, 1996, 250, 219; (b) T. R. G. Simões,
R. V. Mambrini, D. O. Reis, M. V. Marinho, M. A. Ribeiro,
C. B. Pinheiro, J. Ferrando-Soria, M. Déniz, C. Ruiz-Pérez, D.
Cangussu, H. O. Stumpf, F. Lloret and M. Julve, Dalton
Trans., 2013, 42, 5778.
1 L. M. Toma, R. Lescouëzec, D. Cangussu, R. Llusar, J. Mata,
S. Spey, J. A. Thomas, F. Lloret and M. Julve, Inorg. Chem.
Commun., 2005, 8, 382.
(Project MDM-2015-0538) for financial support. We also thank
CNPq (H. O. S and A. C. D.) and FAPEMIG (N. R. C.) for re-
search fellowships. This work is a collaboration research pro-
ject of members (ACD and MVM) of the Rede Mineira de
Química (RQ-MG) supported by FAPEMIG (Project: CEX – RED-
1
0
0010-14). W. P. B. acknowledges the FAPESP (2015/22379-7).
1
2 W. X. C. Oliveira, M. A. Ribeiro, C. B. Pinheiro, M. M. da
Costa, A. P. S. Fontes, W. C. Nunes, D. Cangussu, M. Julve,
H. O. Stumpf and C. L. M. Pereira, Cryst. Growth Des.,
2015, 15, 1325.
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