Complexes of copper(II) formate with 2-(phenylamino)pyridine and 2-(methylamino)pyridine: New copper formato paddle-wheel compounds

Article abstract of DOI:10.1016/j.ica.2006.02.031

The derivatives of Cu(HCOO)₂ · 4H₂O with 2-(phenylamino)pyridine and 2-(methylamino)pyridine, [Cu₂(μ-HCOO)₄(PhNHpy)₂] (1), [Cu₂(μ-HCOO)₄(MeNHpy)₂] (2) and Cu(HCOO)₂(MeNHpy)₂ (3), have been synthesized and characterized. Compounds 1 and 2 show the paddle-wheel structure of [Cu₂(μ-HCOO)₄L₂], with four syn-syn bridging formato groups and two molecules of PhNHpy or MeNHpy coordinated to the axial positions, respectively. Intramolecular hydrogen bonds are formed in both cases: two in each dimer of 1 and four in the dimer of compound 2. The dimer units are oriented in two different directions. Dimers with the same orientation form rows along the c and the a axis in compounds 1 and 2, respectively, with a π-π stacking of the pyridine rings. In compound 1, an intercalation of the phenyl rings of contiguous rows of dimers gives rise to a succession of phenyl rings at a distance of 4.38 A? and an angle of 30.44° between alternate rings. They are antiferromagnetic. Signals of the triplet state are observed in their EPR spectra and the zero-field splitting parameter has been determined. Compound 3 obeys the Curie-Weiss law and the magnetic results indicate the absence of magnetic interaction between Cu(II) atoms.

Full text of DOI:10.1016/j.ica.2006.02.031

Inorganica Chimica Acta 359 (2006) 2424–2430
www.elsevier.com/locate/ica
Complexes of copper(II) formate with 2-(phenylamino)pyridine and
2-(methylamino)pyridine: New copper formato
paddle-wheel compounds
a
a,
a
*
´
´
´
´
Montserrat Barquın , Marıa J. Gonzalez Garmendia , Liher Larrınaga ,
b,c
b
´
Elena Pinilla , Marıa R. Torres
a
Grupo de Quı´mica Inorga´nica, Facultad de Ciencias Quı´micas, Universidad del Paı´s Vasco, UPV/EHU, Apartado 1072, 20080 San Sebastia´n, Spain
b
Laboratorio de Difraccio´n de Rayos-X, Facultad de Ciencias Quı´micas, Universidad Complutense, 28040 Madrid, Spain
Departamento de Quı´mica Inorga´nica, Facultad de Ciencias Quı´micas, Universidad Complutense, 28040 Madrid, Spain
c
Received 1 December 2005; received in revised form 15 February 2006; accepted 23 February 2006
Available online 3 March 2006
Abstract
The derivatives of Cu(HCOO)2 Æ 4H2O with 2-(phenylamino)pyridine and 2-(methylamino)pyridine, [Cu2(l-HCOO)4(PhNHpy)2] (1),
[Cu2(l-HCOO)4(MeNHpy)2] (2) and Cu(HCOO)2(MeNHpy)2 (3), have been synthesized and characterized. Compounds 1 and 2 show
the paddle-wheel structure of [Cu2(l-HCOO)4L2], with four syn–syn bridging formato groups and two molecules of PhNHpy or MeNHpy
coordinated to the axial positions, respectively. Intramolecular hydrogen bonds are formed in both cases: two in each dimer of 1 and four
in the dimer of compound 2. The dimer units are oriented in two different directions. Dimers with the same orientation form rows along
the ‘‘c’’ and the ‘‘a’’ axis in compounds 1 and 2, respectively, with a p–p stacking of the pyridine rings. In compound 1, an intercalation of
˚
the phenyl rings of contiguous rows of dimers gives rise to a succession of phenyl rings at a distance of 4.38 A and an angle of 30.44ꢀ
between alternate rings. They are antiferromagnetic. Signals of the triplet state are observed in their EPR spectra and the zero-field split-
ting parameter has been determined. Compound 3 obeys the Curie–Weiss law and the magnetic results indicate the absence of magnetic
interaction between Cu(II) atoms.
ꢁ 2006 Elsevier B.V. All rights reserved.
Keywords: Copper; Hydrogen bonds; Dimers; Formate; Antiferromagnetism; EPR
1. Introduction
(dmso)2] [8] and [Cu2(l-HCOO)4(dmf)2] [9], chains of
dimers as . . .dioxane–[Cu2(l-HCOO)4]–dioxane–[Cu2-
(l-HCOO)4]–. . . [10] and dimers or chains of dimers with
pyrazine and different isomers of dimethylpyrazine [11].
The copper(II) formate tetrahydrate, Cu(HCOO)2 Æ
4H2O, does not have the dinuclear unit [Cu2(l-HCOO)4],
similar to that of the copper(II) acetate. It consists of
chains . . .–Cu(H2O)2–(l-HCOO)2–Cu(H2O)2–(l-HCOO)2–
. . ., with anti–anti bridging HCOOꢀ, linked by hydrogen
bonds through additional water molecules [12].
The dinuclear copper acetate dihydrate [Cu2(l-OAc)4-
(H2O)2] and the adducts [Cu2(l-OAc)4L2] with different
ligands in the axial positions are among the most studied
dinuclear compounds of Cu(II) in their structural and
magnetic aspects [1–6]. On the contrary, few compounds
containing the paddle-wheel dinuclear group [Cu2-
(l-HCOO)4], with four syn–syn formate groups are known.
This structure is present in some complexes: molecular
dimers as [Cu2(l-HCOO)4(urea)2] [7], [Cu2(l-HCOO)4-
In previous papers, we reported the study of the
complexes with 2-(phenylamino)pyridine and 2-(methyl-
amino)pyridine, [Cu2(l-OAc)4(PhNHpy)2] [13] and [Cu2-
(l-OAc)4(MeNHpy)2] [14], respectively. In both cases, the
*
Corresponding author. Tel.: +34 43 018208; fax: +34 43 015270.
´
E-mail address: mariaj.gonzalez@ehu.es (M.J. Gonzalez Garmendia).
0020-1693/$ - see front matter ꢁ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.02.031

M. Barquı´n et al. / Inorganica Chimica Acta 359 (2006) 2424–2430
2425
structural and magnetic results were similar to those of the
2.4. Measurements
copper acetate hydrate. The ligands are coordinated in the
axial positions of the dimer through the pyridinic nitrogen
atom. Two intramolecular hydrogen bonds are formed
between each ligand and an oxygen atom of one acetate
group.
In this paper, we describe the interaction between Cu-
(HCOO)2 Æ 4H2O and the ligands 2-(phenylamino)pyridine
(PhNHpy), and 2-(methylamino)pyridine (MeNHpy), with
the purpose of observing the difference between OAcꢀ and
HCOOꢀ and the influence of the substitution of Ph for Me
in the molecule of the additional ligand. Magnetic and
EPR results are also described.
C, H and N were analysed in a Leco 932-CHNS Elemen-
tal Analyser. IR spectra were recorded on a Nicolet FT-IR
510 spectrometer in the range 4000–400 cmꢀ1 using KBr
pellets. Electronic spectra were recorded on a Shimadzu
UV-265 FW spectrophotometer. Magnetic measurements
were carried out with a magnetometer SQUID MPMSXL
of Quantum Design. Diamagnetic corrections were applied
[2]. The EPR spectra were recorded on a Bruker ESP 300
spectrometer with a Bruker ER 035 M gaussmeter and
HP 5325 frequency counter.
2.5. X-ray crystallographic study
2. Experimental
Data collection was carried out at room temperature on
a Bruker Smart CCD diffractometer using graphite-mono-
chromated Mo Ka radiation (k = 0.71073 A), operating at
2.1. Synthesis of [Cu2(l-HCOO)4(PhNHpy)2] (1)
˚
A solution of Cu(HCOO)2 Æ 4H2O (225.6 mg, 1 mmol)
in MeOH (20 ml) was added to a solution of PhNHpy
(851 mg, 5 mmol) in MeOH (10 ml). The green solution
was stirred during 24 h. The formed precipitate was
filtered off, washed with MeOH/Et2O (1:1) and Et2O
and dried by air suction and in vacuo over CaCl2. Yield:
184 mg (56%). Anal. Calc. for C26Cu2H24N4O8 (647.59):
C, 48.22; H, 3.74; N, 8.65. Found: C, 47.91; H, 3.65; N,
8.70%. Crystals suitable for X-ray diffraction were
obtained by slow evaporation of a solution of the com-
plex in CH2Cl2.
50 kV and 30 mA, in the u and x scanning mode. The data
were collected over a hemisphere of the reciprocal space by
a combination of three exposure sets. Each exposure cov-
ered 0.3 in x. The cell parameters were determined and
refined by a least-squares fit of all reflections. The first 50
frames were recollected at the end of the data collection
to monitor crystal decay, and no appreciable decay was
observed. A summary of the fundamental crystal and
refinement data are given in Table 1.
Table 1
Crystallographic and structure refinement data for compounds 1 and 2
2.2. Synthesis of [Cu2(l-HCOO)4(MeNHpy)2] (2)
Compound
[Cu2(l-HCOO)4-
(PhNHpy)2] (1)
[Cu2(l-HCOO)4-
(MeNHpy)2] (2)
To a solution of 2-(methylylamino)pyridine (0.216 ml,
2 mmol) in MeCN (20 ml), solid Cu(HCOO)2 Æ 4H2O
(450 mg, 2 mmol) was added. The mixture was stirred dur-
ing 15 h and the remaining solid filtered off. The solution
was carried next to dryness in the rotavapour. The residue
was collected with CCl4. The solid was filtered off, washed
with Et2O and dried by air suction and in vacuo over
CaCl2. Yield: 260 mg (49%). Anal. Calc. for C16Cu2-
H20N4O8 (523.44): C, 36.71; H, 3.85; N, 10.70. Found: C,
36.87; H, 3.83; N, 10.75%. Crystals suitable for X-ray dif-
fraction were obtained by slow evaporation of a solution of
the complex in CH2Cl2.
Empirical formula
Formula weight
T (K)
Crystal system
Space group
Unit cell dimensions
C
323.79
293(2)
monoclinic
P21/c
13H12N2O4Cu
C8H10N2O4Cu
261.72
293(2)
monoclinic
P21/n
˚
a (A)
15.154(2)
11.156(2)
7.888(1)
92.970(3)
1331.8(3)
4
1.615
1.654
660
1.35–25.00
(ꢀ17,ꢀ13,ꢀ9)
to (17,11,9)
6773
2332 (0.0721)
99.7
7.772(1)
13.408(2)
10.279(2)
107.806(3)
1019.8(3)
4
1.705
2.137
532
2.58–25.00
(ꢀ9,ꢀ10,ꢀ12)
to (9,15,11)
5248
1796 (0.0672)
99.8
1796/0/137
0.900
R1 = 0.0426
(1043)
˚
b (A)
˚
c (A)
b (ꢀ)
3
˚
V (A )
Z
Dcalc (g cmꢀ3
)
Absorption coefficient l (mmꢀ1
F(000)
)
2.3. Synthesis of Cu(HCOO)2(MeNHpy)2 (3)
h Range for data collection (ꢀ)
Index ranges
To a solution of 2-(methylylamino)pyridine (1 ml,
10 mmol) in MeCN (25 ml), solid Cu(HCOO)2 Æ 4H2O
(450 mg, 2 mmol) was added. The mixture was stirred dur-
ing 4 h and the solution was carried next to dryness in the
rotavapour. The residue was collected with CCl4. The solid
was filtered off, washed with a minimum volume of MeCN
and with Et2O, and dried by air suction and in vacuo over
CaCl2. Yield: 441 mg (60%). Anal. Calc. for C14CuH18-
N4O4 (369.87): C, 45.46; H, 4.91; N, 15.15. Found: C,
45.33; H, 4.89; N, 15.20%.
Reflections collected
Independent reflections (Rint
)
Completeness to h = 25.00ꢀ (%)
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
(observed reflections)
2332/0/181
0.928
R1a = 0.0453
(1414)
R indices (all data)
wR2b = 0.1158
wR2 = 0.1088
P
P
a
[|Fo| ꢀ |Fc|]/ |Fo|.
P
P
2
2
1=2
b
f
½wðF 2o ꢀ F c2Þ ꢁ= ½wðF 2oÞ ꢁg
.

2426
M. Barquı´n et al. / Inorganica Chimica Acta 359 (2006) 2424–2430
Table 2
Both structures were solved by direct methods and
˚
refined by full-matrix least-square procedures on F2 [15].
All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were included in calculated positions
and refined riding on the respective carbon atoms, except
H2, bonded to the nitrogen atom, which has been located
in a Fourier synthesis included and their coordinates fixed.
The largest peaks andꢀh3oles in the final difference mꢀa3p were
Selected interatomic distances (A) and angles (ꢀ) for compounds 1 and 2
Compound
[Cu2(l-HCOO)4-
(PhNHpy)2] (1)
[Cu2(l-HCOO)4-
(MeNHpy)2] (2)
˚
Interatomic distances (A)
Cu(1)–O(1)
Cu(1)–O(2)
Cu(1)–O(3)
Cu(1)–O(4)
1.984(3)
1.963(4)
1.969(3)
1.971(4)
2.226(4)
2.710(1)
0.987
1.980(4)
1.979(4)
1.981(4)
1.971(4)
2.177(4)
2.710(1)
0.977
˚
˚
0.626 and ꢀ0.457 e A and 0.480 and ꢀ0.394 e A for 1
and 2, respectively.
Cu(1)–N(1)
Cu(1)ꢂ ꢂ ꢂCu(1)*
N(2)–H(2)
Bond angles (ꢀ)
O(4)–Cu(1)–O(2)
O(4)–Cu(1)–O(1)
O(2)–Cu(1)–O(1)
O(4)–Cu(1)–O(3)
O(2)–Cu(1)–O(3)
O(1)–Cu(1)–O(3)
O(4)–Cu(1)–N(1)
O(2)–Cu(1)–N(1)
O(1)–Cu(1)–N(1)
O(3)–Cu(1)–N(1)
N(1)–Cu(1)–Cu(1)*
3. Results and discussion
166.2(2)
90.2(2)
88.7(2)
88.5(2)
89.2(2)
166.3(2)
99.2(2)
94.6(2)
98.3(1)
95.4(1)
177.7(1)
166.4(2)
89.1(2)
89.7(2)
89.5(2)
88.5(2)
166.4(1)
96.9(2)
96.7(2)
99.5(2)
94.2(2)
177.3(1)
By the reaction of Cu(HCOO)2 Æ 4H2O with 2-(phenyl-
amino)pyridine in 1:5 proportion, the dimer [Cu2-
(l-HCOO)4(PhNHpy)2] (1) was obtained and with
2-(methylylamino)pyridine the dimer [Cu2(l-HCOO)4-
(MeNHpy)2] (2) and the complex of composition Cu-
(HCOO)2(PhNHpy)2 (3) were obtained using 1:1 and 1:5
proportions, respectively.
3.1. Characterization
Torsion angles (ꢀ)
O(1)–Cu(1)–N(1)–C(7)
O(2)–Cu(1)–N(1)–C(7)
O(3)–Cu(1)–N(1)–C(7)
O(4-)Cu(1)–N(1)–C(7)
ꢀ7.5(4)
ꢀ97.0(4)
173.3(4)
84.0(4)
ꢀ41.1(4)
ꢀ131.9(4)
139.1(4)
49.2(4)
The molar conductivity values for 1, 2 and 3 in methanol
correspond to non-ionic compounds. The most significant
bands in the IR spectra are those assigned to the stretching
m(N–H) at 3409, 3317 and 3300 cmꢀ1 for 1, 2, and 3,
respectively.
Symmetry transformations used to generate equivalent atoms: *, ꢀx + 1,
ꢀy + 1, ꢀz + 1.
The diffuse reflectance spectra show a broad d ! d band
centred at 730, 740 and 640 nm for 1, 2, and 3, respectively.
The wavelength of the absorption increases with the pres-
ence of the dimeric unit.
Each copper atom lies in a square-planar pyramidal
coordination, with four oxygen atoms in a plane, at an
average distance of 1.971 A; the fifth coordination position
˚
is occupied by the pyridine nitrogen, N(1), of a molecule of
˚
˚
3.2. Crystal structure of [Cu2(l-HCOO)4(PhNHpy)2] (1)
ligand, at 2.226(4) A. The Cuꢂ ꢂ ꢂCu distance is 2.710(1) A.
The trigonality index, s < 0.002, corresponds clearly to a
square pyramidal coordination [16]. The angle between
phenyl and pyridine rings of each ligand is of 53.7ꢀ.
The hydrogen atom, H(2), bonded to the anilinic nitro-
gen, N(2), is involved in an hydrogen bond to the oxygen,
O(1), of a formato group (Table 3). Only two of the four
formato groups are involved in the intramolecular hydro-
gen bonds.
Compound 1 consists of centrosymmetric dinuclear pad-
dle-wheel units in which four formato groups are bridging
the two copper atoms, in a syn–syn disposition, and a
PhNHpy ligand occupies the axial position of each copper
atom, coordinated to them through the pyridine nitrogen
atom. Fig. 1 shows the ORTEP view of dimer 1, showing
the atomic numbering scheme (35% probability ellipsoids).
Some carbon atoms and hydrogen atoms have been ommit-
ted for clarity; only H(2), involved in an hydrogen bond, is
included. The selected interatomic distances and angles are
listed in Table 2.
The dimers are oriented in the crystal in two different
directions, which form between them an angle of 17ꢀ, as
is observed in Fig. 2. In each row of dimers along the c-axis
˚
the pyridine rings are stacked with a distance of 7.888 A
Fig. 1. ORTEP view of the dimer [Cu2(l-HCOO)4(PhNHpy)2] (1).

M. Barquı´n et al. / Inorganica Chimica Acta 359 (2006) 2424–2430
2427
Table 3
Hydrogen bonds data for compounds 1 and 2
˚
˚
˚
Compound
N–Hꢂ ꢂ ꢂO
d(N–H) (A)
d(Hꢂ ꢂ ꢂO) (A)
d(Nꢂ ꢂ ꢂO) (A)
\NHO (ꢀ)
[Cu2(l–HCOO)4(PhNHpy)2] (1)
[Cu2(l-HCOO)4(MeNHpy)2] (2)
N(2)–H(2)ꢂ ꢂ ꢂO(1)
N(2)–H(2)ꢂ ꢂ ꢂO(1)
N(2)–H(2)ꢂ ꢂ ꢂO(4)
0.99
0.98
0.98
1.87
2.18
2.56
2.856(5)
3.078(6)
3.263(6)
172.6
152.8
128.9
(c). There is an intercalation of phenyl rings of ligands of
contiguous dimers rows, so that the phenyl ring centroids
define a zig-zag line along the ‘‘c’’-direction. The distance
atomic distances and angles are listed in Tables 2 and 3.
The trigonality index is practically zero, s < 0.0002, and cor-
responds clearly to a square pyramidal coordination [16].
The hydrogen atom, H(2), bonded to the anilinic nitro-
gen, N(2), is involved in this case in two hydrogen bonds to
the oxygen atoms O(1) and O(4) of two formato groups
(Table 3). The formato groups in the dimer are involved
in four intramolecular hydrogen bonds and not only in
two, as in complex 1. According to this fact, the values
of the torsion angles around the N–Cu bond (Table 2)
make clear that the pyridine plane bisects the
O(1)Cu(1)O(4) and O(2)Cu(1)O(3) angles in complex 2,
whilst it is coplanar with the plane defined by
O(1)Cu(1)O(3) in complex 1.
˚
between phenyl rings centroids is 4.38 A and the angle
between alternate phenyl rings is 30.44ꢀ. The intercalation
of phenyl rings makes possible a bidimensional interaction
which gives rise to the formation of a sort of sheets parallel
to the ‘‘bc’’-plane (Fig. 2). These intercalations were not
observed in the structure of [Cu2(l-OAc)4(PhNHpy)2]
[13]. In this case, the dimers adopt a unique orientation
in the crystal and are arranged in rows along the ‘‘b’’-axis.
3.3. Crystal structure of [Cu2(l-HCOO)4(MeNHpy)2] (2)
Similar to compound 1, compound 2 consists of centro-
symmetric dinuclear paddle-wheel units in which four
formato groups are bridging the two copper atoms, in a
syn–syn disposition. A molecule of MeNHpy occupies the
axial position of each copper atom, coordinated to them
through the pyridine nitrogen atom. Fig. 3 shows the
ORTEP view of the dimer showing the atomic numbering
scheme (35% probability ellipsoids). The hydrogen atoms,
except H2, have been ommitted for clarity. Selected inter-
The dimers are oriented in the crystal in two different
modes as is observed in Fig. 4. They form rows of dimers
along the a-axis with the pyridine rings stacked at a dis-
˚
tance of 7.772 A (a). The disposition of these rows gives
rise to the formation of a sort of sheets parallel to ‘‘bc’’-
plane. All the dimers in a sheet have the same orientation.
In the acetate complex, [Cu2(l-OAc)4(MeNHpy)2], similar
rows of dimers along the ‘‘a’’-axis are observed, but all the
dimers in the crystal present the same orientation [14].
Fig. 2. View of compound 1 along the ‘‘c’’-axis.

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M. Barquı´n et al. / Inorganica Chimica Acta 359 (2006) 2424–2430
Fig. 3. ORTEP view of the dimer [Cu2(l-HCOO)4(MeNHpy)2] (2).
Fig. 4. Crystal structure of 2 viewed along the a-axis.
3.4. Magnetic and EPR results
The results for the best fit for g = 2.14 (EPR result) and
Na = 60 · 10ꢀ6 cm3 molꢀ1 are collected in Table 4.
Compounds 1 and 2 show a strong antiferromagnetism.
The magnetic moments decrease from 1.12 lB and 1.25 lB
at 300 K, to 0.16 lB and 0.17 lB at 5 K, for complexes 1
and 2, respectively. The plot of vMT, per mole of dimer,
versus temperature (T) for compound 1 is shown in
Fig. 5. The plot is similar for compound 2.
The data, from 50 to 300 K, were fitted to the Bleaney–
Bowers equation for a dimer with S1 = S2 = 1/2, modified
by the inclusion of the fraction of monomeric impurity [17]:
The antiferromagnetic parameter, 2J, is similar to those
found for other complexes with the group [Cu2(l-HCOO)4]
and higher than those found for the analogous compounds
of acetate. These results agree with the conclusions of
´
Rodrıguez-Fortea et al. in a density functional study of
the exchange coupling in carboxylato-bridged dinuclear
copper(II) compounds [18]: in [Cu2(l-RCOO)4] groups,
the antiferromagnetic interaction strength decreases with
the presence of electron-with-drawing R groups. This
explains the difference between 2J values for acetato and
formato derivatives.
The powder EPR spectra of 1 and 2, at Q band and
room temperature, are similar and show the signals of
the triplet state (S = 1) for D ¼ 0 and E ꢃ 0. Fig. 6 corre-
sponds to the spectrum of compound 2. The spectra were
vMð2CuÞ ¼ 2f½C exð1 ꢀ qÞ=ð1 þ 3exÞꢁ þ Cq=4 þ Nag
where C = Ng2b2/kT, x = 2 J/kT, 2J = separation between
singlet and triplet states, q is the fraction of monomeric
impurity and Na is the temperature independent paramag-
netism (TIP).

M. Barquı´n et al. / Inorganica Chimica Acta 359 (2006) 2424–2430
2429
0.35
0.3
For DM = 1:
H ¼ ðg =g ÞðHo ꢀ D0Þ
k
e
k
1=2
1=2
H
¼ ðg =g Þ½HoðHo ꢀ D0Þꢁ
?1
e
?
0.25
0.2
H
¼ ðg =g Þ½HoðHo þ D0Þꢁ
?2
e
?
For DM = 2:
1=2
Hmin ¼ ðge=gminÞ½ðH2o=4Þ ꢀ ðD02=3Þꢁ
0.15
0.1
1=2
Hdq ¼ ðge=gavÞ½H2o ꢀ D02=3ꢁ
Ho ¼ hm=geb; D0 ¼ D=geb
0.05
0
The experimental values of H and the calculated param-
eters: gi, g^, gav and D are collected in Table 5. The zero-
field splitting parameter is, in both cases, higher than that
found for the acetate complexes, [Cu2(l-OAc)4(PhNHpy)2]
0
50
100
150
200
250
300
350
T (K)
Fig. 5. Plot of XMT vs. T, per mole of dimer, for 1.
(0.33 cmꢀ1) [13] and [Cu2(l-OAc)4(MeNHpy)2] (0.36 cmꢀ1
)
[14], and similar to that of formate derivatives with pyra-
zine and dimethylpyrazines (0.42–0.43 cmꢀ1) [11].
Table 4
Magnetic results for compounds 1 and 2
For compound 3 the magnetic moment value is practi-
cally constant, from 1.84 lB at room temperature to
1.83 lB at 5 K. The fit of the experimental data to the
Curie–Weiss law leads to h = 0.054 K, indicating the
absence of magnetic interaction between the copper atoms.
Even though the structure of 3 is unknown, the magnetic
results allow to conclude that it does not include the anti-
ferromagnetic [Cu2(l-HCOO)4] group.
The powder Q band spectrum for 3 (Fig. 7), at room
temperature, shows four signals. H = 10758, 11225,
11502 and 11800. They could be compatible with the exis-
tence in the structure of two different copper atoms,
responsible for a triple signal (g = 2.26; 2.16; 2.06) and
an isotropic signal (g = 2.11), respectively.
Compound
2J (cmꢀ1
)
q
R
Reference
1
2
ꢀ455
ꢀ403
0.024 5.31 · 10ꢀ4
0.048 4.83 · 10ꢀ4
[Cu2(l-OAc)4(PhNHpy)2] ꢀ288
[Cu2(l-OAc)4(MeNHpy)2] ꢀ285
0.054 1.16 · 10ꢀ3 [13]
0.06
[14]
[7]
[8]
[9]
[Cu2(l-HCOO)4(urea)2]
[Cu2(l-HCOO)4(dmso)2]
ꢀ408
ꢀ434
ꢀ470
[Cu2(l-HCOO)4(dmf)2]
R = (vMTiexp ꢀ vMTical)2/ (vMTiexp)2.
P
P
2000
4000
6000
8000
10000
H(G)
12000
14000
16000
Fig. 6. EPR Q band (m = 33.9645 GHz) spectrum of powdered compound
2, at room temperature.
10000
10500
11000
11500
12000
12500
H(G)
interpreted according to the Wasserman, Snyder and Yager
equations [19,20], based on the Hamiltonian H ¼ gHSbþ
D½S2z ꢀ 2=3ꢁ þ E½Sx2 ꢀ S2y ꢁ, with D ¼ 0 and E = 0.
Fig. 7. EPR Q band spectrum (m = 33.9708 GHz) of powdered 3, at room
temperature.
Table 5
EPR results for 1 and 2
Compound
Hmin (G)
Hi (G)
H^1 (G)
H^2 (G)
Hdq (G)
gi
g^
gav
D (cmꢀ1
)
1
2
5000
4970
6850
6550
9200
9160
13870
13850
10980
10990
2.27
2.26
2.06
2.07
2.14
2.14
0.44
0.44

2430
M. Barquı´n et al. / Inorganica Chimica Acta 359 (2006) 2424–2430
[6] M. Nakagawa, Y. Inomata, F.S. Howell, Inorg. Chim. Acta 295
4. Supplementary material
(1999) 121.
[7] D.B.W. Yawney, R.J. Doedens, Inorg. Chem. 9 (1970) 1626.
CCDC No. 289007 and CCDC No. 289008 contain the
supplementary crystallographic data for 1 and 2, respec-
tively. These data can be obtained free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html [or from the
Cambridge Crystallographic Data Centre, 12, Union
Road, Cambridge CB2 1EZ, UK; fax: (internat.) +44
1223 336 033; e-mail: deposit@ccdc.cam.ac.uk].
´
[8] F. Sapina, M. Burgos, E. Escriva, J.V. Folgado, P. Gomez Romero,
˜
Inorg. Chim. Acta 216 (1994) 185.
´
´
[9] R. Cejudo, G. Alzuet, J. Borras, M. Liu-Gonzalez, F. Sanz-Ruiz,
Polyhedron 21 (2002) 1057.
[10] M. Bukowska-Strzyzewska, Rocz. Chem. 40 (1966) 567.
´
´
´
[11] M. Barquın, M.J. Gonzalez Garmendia, L. Larrınaga, E. Pinilla,
M.R. Torres, Z. Anorg. Allg. Chem. 631 (2005) 2210.
[12] R. Kiriyama, H. Ibamoto, K. Matsuo, Acta Crystallogr. 7 (1954)
482.
´
[13] J.M. Seco, M.J. Gonzalez Garmendia, E. Pinilla, M.R. Torres,
Acknowledgements
Polyhedron 21 (2002) 457.
´
´
[14] M. Barquın, M.J. Gonzalez Garmendia, S. Pacheco, E. Pinilla, S.
Quintela, J.M. Seco, M.R. Torres, Inorg. Chim. Acta 357 (2004)
3230.
´
Financial support from the ‘‘Diputacion Foral de
´
Guipu´zcoa’’ and the Ministerio de Ciencia y Tecnologıa
[15] G.M. Sheldrick, SHELXL-97:
A Program for Refinement of
(Project BQU2002-00129) is gratefully acknowledged.
Crystal Structure, University of Go¨ttingen, Go¨ttingen, Germany,
1997.
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