Synthesis, structure and magnetic properties of tetrakis-μ-carboxylato-bis(dodecylnicotinato)dicopper(II) complexes; crystal and molecular structure of the decyl carboxylate derivative

Article abstract of DOI:10.1107/S0108768100002056

Dodecylnicotinate bis-adducts of binuclear copper carboxylates, of the general formula Cu₂(O₂CC_n-1H_2n-1)₄(C ₅H₄NCOOC₁₂H₂₅)₂, were synthesized for n = 10, 12, 14, 16, 18 and 20, and their crystal structure, thermal behavior and magnetic properties studied. The molecular structure of the decyl derivative has been determined from single-crystal X-ray diffraction data. The dimer is centrosymmetric with the Cu^II ions in a square-pyramidal coordination with four O-alkyl O atoms [average d(Cu - O) 1.960 (6) A] in the basal plane and the nicotine N atom at apical positions [d(Cu - N) 2.183 (3) A]. The copper ions, 2.615 (1) A apart, are bridged by four O-alkyl carboxylate groups. Both the n = 20 and n = 18 homologues exhibit lamellar phases, which can be related to the supramolecular arrangement found in the n = 10 derivative. The magnetic behavior of the decyl and octadecyl dimers was studied in the 2-300 K temperature range. They exhibit a strong intramolecular antiferromagnetic interaction (Cu-Cu superexchange coupling constant J = -347 cm^-1 for the decyl derivative), which can be attributed to a large overlap of the metal 3d orbitals and the oxygen lone pair orbitals of the linking carboxylate groups.

Full text of DOI:10.1107/S0108768100002056

research papers
Acta Crystallographica Section B
Structural
Science
Synthesis, structure and magnetic properties of
tetrakis-l-carboxylato-bis(dodecylnicotinato)dicop-
per(II) complexes; crystal and molecular structure
of the decyl carboxylate derivative
ISSN 0108-7681
Marcia Rusjan,a,b Zulema Chaia,a
Oscar E. Piro,c Daniel Guillond
Dodecylnicotinate bis-adducts of binuclear copper carboxy-
lates, of the general formula Cu2(O2CCn 1H2n 1)4(C5H4N-
Received 8 November 1999
Accepted 4 February 2000
and Fabio D. Cukiernika,b
*
COOC12H25)2, were synthesized for n = 10, 12, 14, 16, 18 and
20, and their crystal structure, thermal behavior and magnetic
properties studied. The molecular structure of the decyl
derivative has been determined from single-crystal X-ray
diffraction data. The dimer is centrosymmetric with the CuII
ions in a square-pyramidal coordination with four O-alkyl O
a
Â
INQUIMAE, Departamento de Quõmica Inor-
Â
Â
Â
Â
ganica, Analõtica y Quõmica Fõsica, Facultad de
Ciencias Exactas y Naturales, Universidad de
Â
Buenos Aires, Pabellon II, Ciudad Universitaria,
1428 Buenos Aires, Argentina, bInstituto de
atoms [average d(CuÐO) 1.960 (6) A] in the basal plane and
the nicotine N atom at apical positions [d(CuÐN)
Ê
Ciencias, Universidad Nacional de General
Sarmiento, Roca 850, 1663 San Miguel, Buenos
Ê
Ê
2.183 (3) A]. The copper ions, 2.615 (1) A apart, are bridged
by four O-alkyl carboxylate groups. Both the n = 20 and n =
18 homologues exhibit lamellar phases, which can be related
to the supramolecular arrangement found in the n = 10
derivative. The magnetic behavior of the decyl and octadecyl
dimers was studied in the 2±300 K temperature range. They
exhibit a strong intramolecular antiferromagnetic interaction
(Cu±Cu superexchange coupling constant J = 347 cm 1 for
the decyl derivative), which can be attributed to a large
overlap of the metal 3d orbitals and the oxygen lone pair
orbitals of the linking carboxylate groups.
c
Â
Aires, Argentina, Departamento de Fõsica,
Facultad de Ciencias Exactas, Universidad
Nacional de La Plata and IFLP (CONICET), CC
67, 1900 La Plata, Argentina, and dInstitut de
Â
Physique et Chimie des Materiaux de Strasbourg,
Â
Groupe des Materiaux Organiques, 23 rue du
Loess, 67037 Strasbourg CEDEX, France
Correspondence e-mail:
fabioc@cuca.q1.fcen.uba.ar
1. Introduction
Investigations on dicopper carboxylates exhibiting the lantern
structure have been directed for a variety of interests
(Mehrotra & Bohra, 1983; Kato & Muto, 1988). The structural
and magnetic properties of the acetate derivative in the past
were considered to be very important in the understanding of
magnetic exchange in dinuclear compounds, relevant topics in
inorganic and physical chemistry, and in the development of
appropriate models to describe the magnetic coupling
between metal centers (Bleaney & Bowers, 1952; Kahn, 1993).
More recent studies on long-chain derivatives showed their
potential application as advanced materials, as they exhibit
thermotropic columnar mesophases (Abied et al., 1987; Ibn-
Elhaj et al., 1992; Marchon et al., 1992), and also as biologically
active substances and antifungal agents, for which bis(nicotin-
amide derivatives) adducts are examples (Mehrotra & Bohra,
1983; Kozlevcar et al., 1996).
All the copper carboxylate liquid crystals reported thus far
are polymeric, the axial position of each Cu2+ ion being
occupied, in the Cu2(O2CR)4 series, by an O atom of a
neighbor dimer. To break this polymeric structure into distinct
dimers we decided to `block' the axial positions of the long-
chain dicopper carboxylates by forming bis(pyridine deriva-
tive) adducts (like in the nicotinamide antifungals). As in the
equatorial carboxylate, the axial ligand we used also bears a
long chain.
# 2000 International Union of Crystallography
Printed in Great Britain ± all rights reserved
ꢀ
666 Rusjan et al. Tetrakis-ꢀ-carboxylato-bis(dodecylnicotinato)dicopper(II)
Acta Cryst. (2000). B56, 666±672

research papers
We report here the synthesis, spectroscopic and structural
characterization, phase transitions and magnetic properties of
tetrakis-ꢀ-carboxylato-bis(dodecylnicotinato)-dicopper(II)
complexes Cu2(O2CCn 1H2n 1)4(C5H4NCOOC12H25)2 for
n = 10, 12, 14, 16, 18 and 20, including the crystal and mole-
cular structure of the decyl derivative.
69.59 (70.35), N 1.49 (1.51), H 10.76 (10.82), yield 70%; for n =
20: C 71.12 (71.23), N 1.49 (1.43), H 10.94 (11.03), yield 75%.
2.3. Physicochemical methods
IR spectroscopy was carried out on a Nicolet FTIR 510P
with KBr pellets and UV±vis measurements on a HP8453
spectrometer. 1H NMR spectra were run on a Bruker AC200
in CDCl3. Differential scanning calorimetry (DSC) was
performed on a Shimadzu DSC-50 calorimeter. For optical
microscopy observations,
a Leitz DMRX microscope
equipped with a Leitz 1350 heating stage device was used.
Elemental analyses were performed on a Carlo Erba CHNS-O
EA1108 instrument.
Magnetic measurements between 2 K and room tempera-
ture were performed on a Quantum Design MPMS-XL
susceptometer in a 5000 G magnetic ®eld. The powdered
samples, typically 5±15 mg, were placed in a cellophane bag.
Raw magnetic data were corrected for the sample holder
contribution and for the sample diamagnetism, which was
evaluated using Pascal's constants (Selwood, 1956).
Variable-temperature powder X-ray diffraction (XRD)
patterns were recorded using an INEL CPS-120 curved posi-
tion-sensitive detector and Cu Kꢂ radiation from an INEL
X-ray generator; room-temperature data were collected on
Siemens D5000 equipment.
2. Experimental
2.1. Synthesis of dodecyl nicotinate (C5H4NCOOC12H25
)
Nicotinic acid (2.53 g, 20.5 mmol) was re¯uxed with a large
excess of SOCl2 for 4 h under an N2 atmosphere in an anhy-
drous toluene and DMF (10:1) mixture. Excess thionyl
chloride was removed after reaction by vacuum distillation.
Dodecanol (14 ml, 62 mmol) dissolved in toluene was added
to the nicotinyl chloride and the mixture was stirred for 4 h at
353 K under an N2 atmosphere. The reaction mixture was then
poured into water and NaOH 10% was added to alkalinity.
The product was extracted with diethyl ether, the organic
fraction washed with water and the solvents removed in
vacuum. The oily product was puri®ed by silica gel chroma-
tography in cyclohexane: diethyl ether gradient. Yield: 83%.
1H NMR: ꢁ 9.23 (d, 1H, pyridine ring), 8.77 (dd, 1H, pyridine
ring), 8.29 (m, 1H, pyridine ring), 7.39 (m, 1H, pyridine ring),
4.35 (t, 2H, CH2), 1.78 (q, 2H, CH2), 1.26 (m, 18H, CH2), 0.88
(t, 3H, CH3).
2.4. Single-crystal diffraction data and structure solution and
refinement of Cu2(O2CC9H19)4(C5H4NCOOC12H25 2
)
Crystal data, data collection procedure, structure determi-
nation methods and re®nement results are summarized in
Table 1.1 As expected for a complex with extended organic
ligands, the samples turned out to diffract poorly. Only about
Ê
59% of the X-ray intensity data up to 0.841 A resolution were
above two standard deviations of measurement errors.
Several H atoms were detected at approximate locations in
a difference Fourier map. They, however, were positioned
stereochemically and re®ned with the riding model. During
the re®nement, the CH3 H atoms were allowed to rotate as a
rigid group around the CÐCH3 bond so as to maximize the
sum of the electron density at the three calculated hydrogen
positions.
2.2. Synthesis of Cu2(O2CCn 1H2n 1)4(C5H4NCOO-
C H25)2 compounds
12
Dodecyl nicotinate (2 mmol) was dissolved in 10 ml of
boiling n-heptane. The corresponding copper carboxylate
(0.5 mmol in 10 ml of boiling n-heptane), synthesized as
described by Ibn-Elhaj et al. (1992), was added dropwise. The
mixture was re¯uxed for 30 min and then cooled to 255 K
overnight. A green solid was recovered by ®ltration at low
temperature. The solid was dried in vacuum over silica. The
compound with n = 10 crystallized as green platelet crystals,
from which single-crystal samples were selected for crystal-
lographic studies.
3. Results and discussion
3.1. Synthesis and characterization
The formation of the expected complexes was ®rst studied
in solution. Experiments carried out with Cu2(O2CC9H19)4
dissolved in toluene showed a progressive conversion of the
678 nm absorption band of the starting complex into a new
band centered at ca 702 nm, as the dodecyl nicotinate
1 Supplementary data for this paper, including listings of atomic anisotropic
displacement parameters, full bond distances and angles, H-atom positions,
calculated and observed structure factor amplitudes for the n = 10 compound
are available from the IUCr electronic archives (Reference: CA0004). Services
for accessing these data are described at the back of the journal. Powder XRD
patterns for n = 12, 14, 16, 18 and 20 derivatives are available from the authors.
Anal.: exp. (calc.) for n = 10: C 65.57 (65.43), N 2.08 (2.01),
H 9.39 (9.68), yield 49%; for n = 12: C 66.65 (66.94), N 1.85
(1.85), H 9.91 (10.03), yield 54%; for n = 14: C 67.99 (68.23), N
1.79 (1.73), H 9.19 (10.33), yield 84%; for n = 16: C 69.59
(69.36), N 1.61 (1.61), H 10.68 (10.59), yield 91%; for n = 18: C
ꢀ
Acta Cryst. (2000). B56, 666±672
Rusjan et al. Tetrakis-ꢀ-carboxylato-bis(dodecylnicotinato)dicopper(II) 667

research papers
Table 1
Experimental details.
Table 1 (continued)
Structure solution
Structure re®nement
Preparation of material for
publication
SHELXS86 (Sheldrick, 1990)
SHELXL93 (Sheldrick, 1993)
SHELXL93 (Sheldrick, 1993)
Crystal data
Chemical formula
Chemical formula weight
Cell setting
[Cu(C10H19O2)4(C18H29NO2)2]
1394.93
Triclinic
P1
Space group
Ê
a (A)
Ê
10.231 (3)
12.878 (4)
16.804 (2)
92.39 (2)
104.31 (2)
106.17 (3)
2045.8 (9)
1
1.132
1.12
Immersion
Mo Kꢂ
0.71073
758
b (A)
Ê
c (A)
ꢂ ꢂꢁ†
ꢄ ꢂꢁ†
ꢅ ꢂꢁ†
concentration increased. This shift is consistent with a change
in the coordination number around Cu2+from four to ®ve. For
example, the pyridine adduct band shifts down in energy to
713 nm owing to its strong interaction with copper. Job's
method (Reilley & Sawyer, 1961) clearly indicated a 1:2
complex-to-nicotinate ligand ratio, as expected for a bis-
adduct, but also showed that the stability constant for this
Cu2(O2CR)4(nicotinate)2 compound is not very high. To
overcome this we performed the synthesis of the compounds
in excess dodecyl nicotinate ligand; their high solubility in
non-polar solvents indicated that a low-temperature crystal-
lization process was necessary.
3
Ê
V (A )
Z
3
Dx (Mg m
Dm (Mg m
)
)
3
Density measured by
Radiation type
Ê
Wavelength (A)
F(000)
No. of re¯ections for cell
parameters
23
ꢆ range (ꢁ)
9.8±15.71
0.574
293 (2)
1
ꢀ (mm
)
Temperature (K)
Crystal form
Crystal size (mm)
Crystal colour
Plate
0.44 Â 0.40 Â 0.16
The characterization of the solid product was completed by
the crystal structure determination of the decyl derivative by
XRD methods (see below) and IR spectroscopy. The main IR
bands are, in addition to the ꢃCH , ꢃCH stretching vibrations
Blue±green
Data collection
Diffractometer
Data collection method
Absorption correction
3
2
Enraf±Nonius CAD-4
!±2ꢆ scans
Numerical (Busing & Levy,
1957)
0.793
0.916
characteristic of long-chain organic compounds, the ꢃCO
2
vibration of the ester at 1725±1740 cm 1, the ꢃpy symmetric
1
stretching mode of the pyridine ring (1591 cm in the free
Tmin
Tmax
ligand) shifted by coordination to 1616±1618 cm 1, as well as
the ꢃ symmetric and asymmetric stretching modes of the
CO2
No. of measured re¯ections
No. of independent re¯ections
No. of observed re¯ections
Criterion for observed re¯ections
Rint
7627
6369
4529
I > 2ꢇ(I)
0.036
24.97
12 ! h ! 11
15 ! k ! 15
0 ! l ! 19
1
1
bridging carboxylates at 1424±1437 cm (depending on the
carboxylate chain length) and 1599±1588 cm 1, respectively.
These values agree with those found for bis-nicotinamide
copper carboxylates (Kozlevcar et al., 1996).
ꢆmax (ꢁ)
Range of h, k, l
No. of standard re¯ections
Frequency of standard re¯ections
Intensity decay (%)
Every 30 min
1.5
3.2. Crystallographic structural results and discussion for the
n = 10 derivative
Re®nement
Re®nement on
R‰F2>2ꢇꢂF2†Š
wRꢂF2†
F2
Atomic fractional coordinates and equivalent isotropic
displacement parameters are given in Table 2. Selected bond
distances and angles are listed in Table 3. Fig. 1 is an ORTEP
(Johnson, 1965) drawing of the dimeric complex.
0.0504
0.1295
1.086
6369
S
No. of re¯ections used in
re®nement
The Cu2(O2C(CH2)8CH3)4(C5H4NCO2(CH2)11CH3)2 com-
plex is located on a crystallographic inversion center. The pair
of CuII ions in a dimer are bridged through the carboxylate
groups of four CH3(CH2)8CO2 ligands. Each Cu atom is in an
elongated octahedral environment, coordinated equatorially
No. of parameters used
H-atom treatment
Weighting scheme
423
H-atom parameters constrained
w = 1/[ꢇ2(Fo2) + (0.0878P)2
+ 0.2591P],
where P = (Fo + 2Fc2)/3
2
ꢂÁ=ꢇ†
0.006
max
3
Ê
Ê
Áꢈmax (e A
)
0.393
0.288
None
to four carboxylate
CH3(CH2)8CO2 moieties [CuÐO bond distances vary from
O
atoms of two independent
3
Áꢈmin (e A
)
Extinction method
Source of atomic scattering
factors
Ê
1.950 (3) to 1.966 (2) A] and axially by the pyridine nitrogen
International Tables for
Crystallography (1992, Vol. C,
Tables 4.2.6.8 and 6.1.1.4)
of
2.183 (3) A] and by the other inversion-related Cu atom
a
C5H4NCO2(CH2)11CH3 molecule [d(CuÐN)
Ê
=
Ê
located at 2.615 (1) A. The local molecular symmetry is close
Computer programs
Data collection
Cell re®nement
Data reduction
Enraf±Nonius CAD-4
Enraf±Nonius CAD-4
SDP (B. A. Frenz & Associates,
1983)
to D4h. The nicotinate ring plane is approximately coplanar to
one of the CÐOÐCuÐOÐC bonds, but slightly bent by 11ꢁ
with respect to the CuÐCu direction.
ꢀ
668 Rusjan et al. Tetrakis-ꢀ-carboxylato-bis(dodecylnicotinato)dicopper(II)
Acta Cryst. (2000). B56, 666±672

research papers
3.3. Phase transitions and thermal behavior of the
Cu2(O2CCn 1H2n 1)4(C5H4NCO2C12H25)2 series
The CuÐCu distance is the second shortest CuÐCu
distance found for Cu2(O2CnH2n 1)4L2 compounds. This can
be related to the moderate basicity of the axial pyridinic ligand
Â
Â
The compound in which n = 20 exhibits a lamellar phase
from room temperature up to 377 K, where it melts to the
Ê
isotropic liquid. The interlamellar distance, d100, is 49.4 A at
Ê
298 K, but it sharply changes to 49.1 A at 325 K and then to
Ê
52.8 A at 339 K. This contraction±expansion sequence corre-
(Melnõk et al., 1985; Melnõk, 1982); in fact, the only compound
which exhibits a shorter CuÐCu distance is the pyrazine
derivative, the least basic axial ligand (pKa = 0.65) for which
the bis-adduct has been structurally characterized. The CuÐO
distances are also slightly shorter than the corresponding
Ê
Â
lates with phase transitions detected in DSC measurements.
Table 4 contains the thermodynamic parameters of these
transitions. The experimental interlamellar distance is in good
agreement with the molecular length in an elongated confor-
values reported previously in the range 1.96±1.98 A (Melnõk et
al., 1985). The observed CuÐOeq/CuÐNax distances rela-
tionship is as expected on the basis of the local electro-
neutrality principle (Kato & Muto, 1988; Pauling, 1960) for
such a weak basic ligand.
Ê
mation, estimated as 52 A by extrapolation from the solved
structure for the n = 10 derivative. The n = 18 homologue
One of the two independent alkyl chains of the equatorial
carboxylates is completely elongated, in a fully extended
zigzag trans arrangement, whereas the other aligns parallel to
the ®rst one after a gauche conformation at the C(12)ÐC(13)
bond. The alkyl chain of the nicotinate ligand is also in an
extended conformation, after turning at the C(37) atom,
rotated from the nicotinate plane to align with the carboxylate
chains (see Fig. 1). Both the equatorial ligands and the nico-
tinate alkyl chain are straight and tilt slightly with respect to
the plane perpendicular to the NÐCuÐCuÐN axis. Three
crystallographycally non-equivalent alkyl chains converge in a
plane: that belonging to the elongated carboxylate is posi-
tioned between the alkyl chain of the other non-equivalent
carboxylate from the same dimer and a third one belonging to
a nicotinate of a neighboring molecule. These alkyl chains are
completely interdigitated (see Fig. 2), leading to the formation
of two different layers along the crystal: one is de®ned by the
polar copper carboxylate cores and the second, non-polar one
contains the alkyl chains. This type of polar±nonpolar layer
arrangement is typically found in mesomorphic systems.
Ê
showed a transition to a lamellar phase at 333 K (d100 = 46.7 A,
Ê
consistent with an estimated length of 47 A). During the phase
transitions of both compounds some differences in the high
diffraction angle region have been observed, revealing
changes in the crystalline order at the aliphatic chain packing
level. The powder XRD patterns of the n = 12, 14 and 16
derivatives are much more complicated, precluding any
straightforward assignment. As mentioned above, the crystal
structure of the decyl derivative can also be interpreted as a
layered arrangement of polar cores on the ab plane separated
by aliphatic chains, but now the interlamellar separation is
about half that expected for a segregated bilayer. This is due to
the intercalation of the alkyl chains belonging to neighboring
dimers related to each other by a unit cell translation along the
c axis.
Interestingly, the differences in the supramolecular features
between long-chain and short-chain derivatives can be
correlated with molecular characteristics. Indeed, the IR
spectra showed that the position of the ꢃCO symmetric
2
stretching band depends on the
chain length: it appears at
1
1599 cm for the n = 10, 12, 14
and 16 compounds, and at
1
1588 cm for the n = 18 and 20
derivatives.
The
difference
between the ꢃCO asymmetric and
symmetric stretching mode wave-
2
1
numbers decreases from 176 cm
1
for n = 10 to 150 cm for n = 20,
thus re¯ecting a more symmetric
coordination (Deacon & Phillips,
1980) of the equatorial ligands as
the chain length increases.
No liquid crystal phases have
been found for these compounds,
despite the presence of the long
alkyl chains and the rich poly-
morphism they exhibited before
melting to the isotropic liquid. All
the studied compounds decom-
pose between 493 and 513 K. The
thermal stability is higher than
those of nicotinamide adducts of
Figure 1
ORTEP (Johnson, 1965) drawing of Cu2(O2CC9H19)4(C5H4NCOOC12H25)2 showing the numbering
scheme of the non-H atoms.
ꢀ
Acta Cryst. (2000). B56, 666±672
Rusjan et al. Tetrakis-ꢀ-carboxylato-bis(dodecylnicotinato)dicopper(II) 669

research papers
Table 2
Fractional atomic coordinates and equivalent isotropic displacement
copper carboxylates (Kozlevcar et al., 1996).
2
parameters (A ).
Ê
3.4. Magnetic behavior
Ueq ˆ ꢂ1=3†ÆiÆjUijaiajai:aj:
Fig. 3 shows the molar magnetic susceptibility (ꢉ) of the
Cu2(O2CC9H19)4(C5H4NCOOC12H25)2 dimer measured as a
function of temperature. As for the other lantern-structured
copper carboxylates, these data correspond to a system with
two antiferromagnetically coupled S = 12 centers (the increase
of ꢉ at low temperature is due to a very small amount of a
paramagnetic impurity, very likely being a monomeric Cu2+
species). The octadecyl derivative, Cu2(O2CC17H35)4(C5H4N-
COOC12H25)2, exhibits essentially the same ꢉ versus T varia-
tion.
x
y
z
Ueq
0.0564 (2)
Cu
0.10395 (4)
0.2103 (2)
0.0340 (3)
0.1594 (4)
0.2546 (5)
0.3620 (6)
0.3002 (5)
0.4061 (8)
0.3615 (7)
0.4698 (9)
0.4390 (8)
0.5486 (11)
0.5294 (12)
0.1358 (2)
0.0400 (3)
0.0622 (4)
0.1020 (5)
0.0062 (4)
0.0357 (5)
0.0698 (5)
0.0331 (6)
0.1412 (7)
0.1105 (7)
0.2204 (9)
0.1972 (10)
0.2843 (3)
0.2706 (4)
0.3890 (4)
0.5196 (4)
0.5326 (4)
0.4130 (4)
0.3746 (5)
0.4702 (4)
0.2456 (4)
0.2233 (7)
0.0733 (8)
0.0347 (7)
0.0369 (8)
0.1377 (7)
0.1397 (8)
0.2330 (8)
0.2346 (8)
0.3294 (8)
0.3324 (8)
0.4337 (11)
0.4441 (11)
0.45719 (3)
0.6037 (2)
0.6753 (2)
0.6801 (3)
0.7861 (3)
0.7753 (4)
0.7241 (4)
0.7233 (5)
0.6762 (5)
0.6783 (6)
0.6327 (6)
0.6364 (7)
0.5972 (8)
0.5074 (2)
0.5803 (2)
0.5559 (3)
0.5869 (5)
0.6012 (4)
0.6294 (4)
0.6432 (5)
0.6702 (4)
0.6847 (6)
0.7088 (5)
0.7217 (8)
0.7449 (7)
0.3929 (3)
0.2926 (3)
0.2567 (3)
0.3283 (4)
0.4298 (4)
0.4599 (4)
0.1470 (4)
0.1206 (3)
0.0796 (2)
0.0308 (4)
0.0924 (4)
0.0551 (5)
0.0738 (5)
0.0354 (6)
0.0449 (6)
0.0001 (6)
0.0035 (5)
0.0446 (6)
0.0469 (5)
0.0948 (8)
0.1012 (7)
0.01842 (2)
0.0749 (2)
0.0450 (2)
0.0795 (2)
0.1286 (3)
0.2037 (3)
0.2708 (3)
0.3483 (4)
0.4168 (4)
0.4930 (4)
0.5634 (4)
0.6368 (5)
0.7081 (6)
0.08604 (14)
0.1173 (2)
0.1319 (2)
0.2092 (3)
0.2789 (2)
0.3555 (2)
0.4265 (3)
0.5030 (3)
0.5740 (3)
0.6513 (3)
0.7215 (4)
0.7960 (4)
0.0471 (2)
0.0172 (2)
0.0207 (2)
0.0548 (3)
0.0875 (3)
0.0821 (2)
0.0151 (3)
0.0311 (3)
0.0285 (2)
0.0645 (4)
0.0752 (4)
0.1366 (4)
0.2247 (5)
0.2844 (5)
0.3740 (5)
0.4301 (5)
0.5189 (5)
0.5730 (5)
0.6608 (5)
0.7127 (6)
0.7969 (6)
O11
O12
C11
C12
C13
C14
C15
C16
C17
C18
C19
C110
O21
O22
C21
C22
C23
C24
C25
C26
C27
C28
C29
C210
N3
C31
C32
C33
C34
C35
C36
O31
O32
C37
C38
C39
C310
C311
C312
C313
C314
C315
C316
C317
C318
0.0755 (7)
0.0738 (7)
0.0635 (9)
0.0900 (13)
0.119 (2)
0.1032 (15)
0.149 (3)
0.125 (2)
0.156 (3)
0.150 (2)
0.193 (4)
0.243 (5)
0.0690 (6)
0.0776 (7)
0.0652 (9)
0.107 (2)
0.0834 (12)
0.0963 (14)
0.111 (2)
0.1043 (15)
0.136 (2)
0.132 (2)
0.195 (4)
0.206 (4)
0.0620 (7)
0.0650 (9)
0.0731 (10)
0.0857 (13)
0.0880 (13)
0.0749 (11)
0.0896 (13)
0.1292 (13)
0.0933 (9)
0.123 (2)
0.132 (2)
0.128 (2)
0.144 (2)
0.149 (2)
0.145 (2)
0.157 (3)
0.144 (2)
0.161 (3)
0.139 (2)
0.201 (4)
0.198 (4)
The magnetic behavior of the copper unpaired electrons
(S1 = S2 = 1/2) in the dimeric complex can be described by the
following Hamiltonian (Bleaney & Bowers, 1952)
H ˆ ꢂV1 ‡ V2† JS1:S2 ‡ ꢅꢂL1:S1 ‡ L2:S2†
‡ ꢄHꢂL1 ‡ 2S1 ‡ L2 ‡ 2S2†;
ꢂ1†
where the ®rst term describes ligand ®eld effects, the second is
the exchange coupling between the electrons, and the third
and fourth contributions are the spin-orbit and Zeeman
interactions. The crystal ®eld effects lead to a mainly metal
d(x2 y2) ground state orbital with its lobes along the CuÐO
bonds, energetically well separated from the electronic excited
states. The exchange interaction produces the largest (®rst-
order) perturbation to the spin fourfold-degenerated ground
state by splitting it into diamagnetic singlet (total spin S = 0)
and paramagnetic triplet (S = 1) levels, energy separated in |J|.
Perturbation theory up to second-order including exchange
spin-orbit and Zeeman interactions shows that the triplet state
can be described by the effective spin (S = 1) Hamiltonian
Heff ˆ S:D:S ‡ ꢄS:g:H;
ꢂ2†
where D and g are the ®ne and gyromagnetic tensors,
respectively. The ®ne interaction splits the triplet state in the
absence of an external magnetic ®eld into a singlet and a
doublet. It arises from the combined effect of ligand ®eld,
exchange and spin-orbit interactions and vanishes for uncou-
pled (J = 0) electrons. The symmetric D and g tensors share
the same principal (x,y,z) axes, where the spin Hamiltonian
adopts the form
ground and excited states. This warrants the description of the
powder molar magnetic susceptibility by the Van Vleck
expression, which to second-order approximation leads to the
Bleaney±Bowers equation
Heff ˆ DS2z ‡ EꢂSx2 S2y† ‡ ꢄꢂgxHxSx ‡ gyHySy ‡ gzHzSz†:
ꢂ3†
Single-crystal EPR measurements in the closely related
system of Cu2(CH3COO)4(H2O)2 shows that the dimer exhi-
bits approximate axial symmetry and therefore E ' 0, gx ' gy
ꢀ
ꢁ
Ng2pꢄ2
2kT
2Ng2ꢄ2
ꢉꢂT† ˆ
‡ TIP ꢂ1 ꢈ† ‡
ꢈ: ꢂ5†
j=kT
kTꢂ3 ‡ e
†
' g and gz = g|| (Bleaney & Bowers, 1952). Assuming the
?
same holds for our system, (3) further simpli®es to
The TIP contribution to ꢉ corresponds to temperature-inde-
pendent paramagnetic effects and the last term in (5) accounts
for the presence of small amounts of paramagnetic impurities
in a proportion ꢈ. g2 is an isotropic average of the squared g-
tensor, the gp value can be taken to be equal to 2 and the other
parameters have their usual meaning.
Heff ˆ DS2z ‡ ꢄ‰g ꢂHxSx ‡ HySy† ‡ g HzSzŠ:
The ®ne and Zeeman interactions (a fraction of 1 cm 1) are
much smaller than the exchange interaction (in the present
case, a few hundredths of a cm 1). This interaction, in turn, is
much less than the energy separation between electronic
ꢂ4†
?
jj
ꢀ
670 Rusjan et al. Tetrakis-ꢀ-carboxylato-bis(dodecylnicotinato)dicopper(II)
Acta Cryst. (2000). B56, 666±672

research papers
Table 3
Selected geometric parameters (A, ).
Table 4
Transition temperature (K) and enthalpy (in kJ mol within parenth-
eses) for Cu2(O2CCn 1H2n 1)4(C5H4NCOOC12H25)2 derivatives.
1
ꢁ
Ê
CuÐO12i
CuÐO11
CuÐO22i
CuÐO21
CuÐN3
1.950 (3)
1.960 (3)
1.962 (2)
1.966 (2)
2.183 (3)
2.6146 (10)
O11ÐC11
O12ÐC11
C11ÐC12
O21ÐC21
O22ÐC21
C21ÐC22
1.242 (4)
1.254 (4)
1.504 (5)
1.252 (4)
1.247 (4)
1.493 (5)
C1, C2, C3 refer to crystalline phases; I refers to the isotropic phase.
n = 10
n = 12
C ! I
315 (97)
318 (< 2)
328 (90)
316 (3)
334 (162)
310 (14)
337 (153)
364 (29)
333 (73)
370 (70)
325 (13)
339 (121)
377 (32)
C1 ! C2
C2 ! I
CuÐCui
n = 14
n = 16
C1 ! C2
C2 ! I
N3ÐC31
N3ÐC35
C31ÐC32
C32ÐC33
C32ÐC36
1.323 (4)
1.329 (4)
1.401 (5)
1.362 (6)
1.466 (6)
C33ÐC34
C34ÐC35
C36ÐO31
C36ÐO32
1.356 (6)
1.366 (5)
1.206 (5)
1.321 (5)
C1 ! C2
C2 ! C3
C3 ! I
n = 18
n = 20
C1 ! C2
C2 ! I
O12iÐCuÐO22i
O11ÐCuÐO22i
O12iÐCuÐO21
O11ÐCuÐO21
O22iÐCuÐO21
O12iÐCuÐN3
O11ÐCuÐN3
O22iÐCuÐN3
O21ÐCuÐN3
O12iÐCuÐCui
90.31 (12)
89.42 (12)
88.59 (11)
89.27 (11)
168.33 (9)
96.76 (11)
95.15 (11)
97.00 (10)
94.66 (10)
85.15 (8)
O11ÐCuÐCui
O22iÐCuÐCui
O21ÐCuÐCui
N3ÐCuÐCui
C11ÐO11ÐCu
C11ÐO12ÐCui
O11ÐC11ÐO12
O11ÐC11ÐC12
O12ÐC11ÐC12
C21ÐO21ÐCu
82.90 (8)
85.18 (7)
83.16 (7)
177.08 (8)
125.0 (2)
122.5 (2)
124.4 (3)
118.1 (3)
117.5 (3)
124.4 (2)
C1 ! C2
C2 ! C3
C3 ! I
The compound shows a strong intramolecular anti-
ferromagnetic interaction, which can be attributed to CuÐCu
superexchange through the carboxylate groups. In order to
correlate these magnetic results with structural characteristics,
we veri®ed that the diffraction pattern of the bulk powdered
sample used for magnetic experiments effectively agrees with
that calculated from the crystallographic data. In general, the
values of the magnetic parameters agree with those already
published for Cu2(O2CnH2n 1)4L2 compounds, where L
coordinates via N atoms. The more relevant parameter, |J|, is
near the upper limit of the thus far reported values
(308±353 cm 1; Kato & Muto, 1988; Kawata et al., 1992;
C21ÐO22ÐCui
O22ÐC21ÐO21
O22ÐC21ÐC22
O21ÐC21ÐC22
C31ÐN3ÐC35
C31ÐN3ÐCu
122.3 (2)
124.9 (3)
118.4 (3)
116.7 (3)
119.0 (3)
120.2 (2)
119.7 (3)
121.2 (4)
118.3 (4)
120.2 (4)
C31ÐC32ÐC36
C34ÐC33ÐC32
C33ÐC34ÐC35
N3ÐC35ÐC34
O31ÐC36ÐO32
O31ÐC36ÐC32
O32ÐC36ÐC32
C36ÐO32ÐC37
O32ÐC37ÐC38
121.4 (4)
120.0 (3)
118.7 (4)
122.6 (4)
123.2 (5)
123.7 (5)
113.1 (4)
116.1 (4)
107.7 (4)
C35ÐN3ÐCu
N3ÐC31ÐC32
C33ÐC32ÐC31
C33ÐC32ÐC36
Symmetry code: (i) x; 1 y; z.
Â
Melnõk et al., 1985), which seems in agreement with the short
CuÐO bond distances. The correlation of |J| with the basicity
of the ligand has been the subject of some controversy in the
literature. Indeed, some authors invoked an increase of the
exchange parameter as the axial ligand becomes a stronger
Least-squares ®t of (5) to the susceptibility data leads to the
following parameters: J = 347 (1) cm 1, g = 2.037 (4) and ꢈ =
0.65 (1)%; the value of the TIP is not meaningful because of
uncertainties in the diamagnetic correction of such a large
molecule. The corresponding ꢉ(T) curve is compared in Fig. 3
with the experimental susceptibility.
Â
Â
electron donor (Melnõk et al., 1985; Melnõk, 1982); contrarily,
others claimed (Kato & Muto, 1988) that the AF super-
exchange increases as the axial ligand basicity decreases, a fact
that has been interpreted as a consequence of the strong CuÐ
O
bonds (shorter distances)
present in order to maintain the
local electroneutrality of
copper(II) ions, which enhance
the overlap between magnetic
orbitals through the bridge's
HOMO, resulting in a stronger
AF interaction. Our results seem
to support the conclusion drawn
by Kato and Muto. However, the
magnetic coupling described by
J depends simultaneously on
several factors and it cannot be
assigned only to the ligand
basicity. For example, it has been
found that there is no correla-
tion between J and the CuÐCu
distance (as expected for a
Figure 2
ORTEP (Johnson, 1965) drawing showing two dimeric units of Cu2(O2CC9H19)4(C5H4NCOOC12H25)2
symmetry related by a unit-cell translation along c.
bridged-mediated
coupling
ꢀ
Acta Cryst. (2000). B56, 666±672
Rusjan et al. Tetrakis-ꢀ-carboxylato-bis(dodecylnicotinato)dicopper(II) 671

research papers
Â
Ã
measurements, Benoõt Heinrich (GMO, Strasbourg) for his
help and advice on the variable-temperature XRD experi-
mechanism; Melnõk, 1982), but a marked one with the bend
angle de®ned by the OÐCuÐCuÐO and OÐCÐO planes
(Kawata et al., 1992): the smaller the bend angle, the stronger
the superexchange coupling through the carboxylates, due to a
good overlap between magnetic orbitals in the CuÐOÐCÐ
OÐCu fragment. In the present compound the very small
bend angle (0.8ꢁ) agrees with the high |J| value.
Â
Â
ments as well as Elsa Sileo and Matõas Jobbagy
(INQUIMAE) for their acquisition and simulation of some
of the XRD patterns. Single-crystal X-ray experiments were
carried out at the National Diffraction Laboratory
(LANADI), La Plata, Argentina. Elemental analyses and
room-temperature powder X-ray diffraction determinations
were performed at INQUIMAE, Buenos Aires, Argentina.
Variable-temperature powder X-ray diffraction data were
4. Conclusions
Â
collected at the Groupe des Materiaux Organiques and
magnetic susceptibility data at Groupe des Materiaux Inor-
The use of long-chain nicotinate derivatives as axial ligands
was successful in order to break out the polymeric structure of
dicopper carboxylates.
Â
ganiques (IPCMS, Strasbourg, France). This work was
Â
supported by CONICET, Fundacion Antorchas, ANPCyT
Even if they did not present liquid crystal phases, there is
evidence in the crystal structure of the decylcarboxylate
adduct of a microsegregation of the alkyl chains from the
remaining, and more polar, part of the molecule. In fact, the
compounds with the longest alkyl chains exhibit a lamellar
crystalline structure whose interlamellar distance was related
to the largest dimension of one molecule. Those results indi-
cate that this system could be slightly modi®ed to induce the
appearance of liquid crystal smectic phases.
and CICPBA of Argentina and by a Secyt-Ecos grant
(A97E08) for international cooperation. CONICET is also
acknowledged for research fellowships to ZC and MR. FDC
and OEP are members of CONICET.
References
The structural analysis of the decyl derivative allowed the
interpretation of the magnetic behavior of this compound,
which exhibits one of the strongest antiferromagnetic inter-
actions among this type of dinuclear copper compounds. The
short CuÐO distance, in addition to the coplanarity of the
CuÐOÐCÐOÐCu group, warrant a large overlap between
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Figure 3
Temperature dependence of the measured molar magnetic susceptibility
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*
ꢉ ( ) for the complex Cu2(O2CC9H19)4(C5H4NCOOC12H25)2. The solid
È
line corresponds to the value calculated with the model described in the
text.
ꢀ
672 Rusjan et al. Tetrakis-ꢀ-carboxylato-bis(dodecylnicotinato)dicopper(II)
Acta Cryst. (2000). B56, 666±672