Copper(II) carboxylates with 4-aminopyridine: Neutral mononuclear structures, isomerism of aceto compounds and a novel tetranuclear structure

Article abstract of DOI:10.1039/b110051c

Reactions of copper(II) carboxylates with 4-aminopyridine (4-apy) were investigated and their products structurally characterized by single crystal X-ray diffraction. Reaction of copper(II) acetate resulted in two isomers of a monomeric complex of composition Cu(ac)₂(4-apy)₂ with markedly different stabilities: the violet form, 1, unstable in air and the blue, stable form, 2. In both isomers the ligands are arranged around the copper atom in a trans geometry. The 4-apy ligands lie almost in the plane in 1, while they are twisted with respect to each other in 2. Variations were observed also in the coordination of the acetate groups to the copper ion. The energy difference between the two isomers was obtained on the basis of ab initio MO calculations. The result agrees well with the observed relative stabilities in the solid state. Monomeric complexes of the same stoichiometry were obtained also by the reaction of Cu(II) hexanoate and heptanoate with 4-apy. The violet Cu(hex)₂(4-apy)₂, 3, and Cu(hep)₂(4-apy)₂, 4, are isostructural and possess trans geometry of the ligands around the copper centre. Reaction of 4-apy with Cu(II) octanoate lead to formation of a novel, unprecedented basic centrosymmetric tetranuclear compound of composition Cu₄(oct)₆(OH)₂(4-apy)₂, 5. Complex 5 contains bidentate bridging and monoatomic bridging carboxylate groups, triply bridging hydroxyl groups and 4-aminopyridine as a terminal ligand. In all five compounds 4-apy is coordinated through the endocyclic nitrogen atom only.

Full text of DOI:10.1039/b110051c

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Copper(II) carboxylates with 4-aminopyridine: neutral mononuclear
structures, isomerism of aceto compounds and a novel tetranuclear
structure
a
a
b
a
a
Nina Lah,* y Joze Koller, Gerald Giester, Primoz Segedin and Ivan Leban
a
Faculty of Chemistry and Chemical Technology, University of Ljubljana, Askerceva 5,
P.O. Box 537, SI-1001 Ljubljana, Slovenia
Institute of Mineralogy and Crystallography, University of Vienna, Althanstrasse 14,
A-1090 Vienna, Austria
b
Received (in Montpellier, France) 5th November 2001, Accepted 19th December 2001
First published as an Advance Article on the web 18th June 2002
Reactions of copper(II) carboxylates with 4-aminopyridine (4-apy) were investigated and their products
structurally characterized by single crystal X-ray diffraction. Reaction of copper(II) acetate resulted in two
2 2
isomers of a monomeric complex of composition Cu(ac) (4-apy) with markedly different stabilities: the
violet form, 1, unstable in air and the blue, stable form, 2. In both isomers the ligands are arranged around the
copper atom in a trans geometry. The 4-apy ligands lie almost in the plane in 1, while they are twisted with
respect to each other in 2. Variations were observed also in the coordination of the acetate groups to the copper
ion. The energy difference between the two isomers was obtained on the basis of ab initio MO calculations. The
result agrees well with the observed relative stabilities in the solid state. Monomeric complexes of the same
stoichiometry were obtained also by the reaction of Cu(II) hexanoate and heptanoate with 4-apy. The violet
2 2 2 2
Cu(hex) (4-apy) , 3, and Cu(hep) (4-apy) , 4, are isostructural and possess trans geometry of the ligands
around the copper centre. Reaction of 4-apy with Cu(II) octanoate lead to formation of a novel, unprecedented
basic centrosymmetric tetranuclear compound of composition Cu (oct) (OH) (4-apy) , 5. Complex 5 contains
4
6
2
2
bidentate bridging and monoatomic bridging carboxylate groups, triply bridging hydroxyl groups and
-aminopyridine as a terminal ligand. In all five compounds 4-apy is coordinated through the endocyclic
nitrogen atom only.
4
8
wood fungi. We reported recently the synthesis, structures
and study of the dimer-monomer equilibrium of copper(II)
Copper(II) carboxylates are structurally a very diverse group of
coordination compounds due to the various coordination
modes of the carboxylato ligands. In general, most of the
compounds contain a tetracarboxylato Cu (OOCR) core
2 4
having a typical dimeric paddle-wheel structure. A large
number of unligated complexes have been reported, all having
6a
carboxylates with 2-aminopyridine (2-apy). In continuation
of this work, copper(II) carboxylates with 4-aminopyridine
(4-apy) were prepared with attention paid to the influence of
the position of the amino group with respect to the pyridine
nitrogen atom. Reactions of copper(II) carboxylates with 4-apy
resulted in monomeric complexes only, even at low ligand
concentrations, presumably due to higher ligand basicity. In
this paper, we report the structures of two isomers of the
acetate (ac) complex and the structures of the monomeric
hexanoate (hex) and heptanoate (hep) complexes, all having
the polymeric structure [Cu
are linked into chains by the interaction of a Cu ion from one
2 4 n
(OOCR) ] in which dimeric units
1
–3
unit with the carboxylate oxygen of a neighbouring dimer.
Unligated copper(II) carboxylates react with additional (in
most cases nitrogen and oxygen donor) ligands to form com-
plexes that have been shown to have diverse stereochemistries.
By breaking the polymeric structure with the coordination of
an additional ligand to the apical position, distinct dimers of
the acetate hydrate type are obtained [general formula
2 2
Cu(carboxylate) (4-apy) composition. The acetate isomers
exhibit markedly different stability in the solid state. The
energy difference between the two isomers was obtained on the
basis of an ab initio molecular orbital (MO) calculation using
the split shell polarization 6-31G* basis set.
We also report the crystal structure of a novel, basic,
4 6 2 2
tetranuclear complex of Cu (oct) (OH) (4-apy) composition,
with bridging bidentate and monoatomic bridging carboxylate
groups, triply bridging hydroxyl groups and terminal 4-amino-
pyridine ligands.
4
Cu (OOCR) L ]. These have been subject of many magne-
2
4 2
5
tostructural studies. By increasing the ligand concentration,
monomeric complexes of Cu(OOCR) L composition are
often formed with either monodentate or bidentate coordina-
2
2
6
tion modes of the carboxylate ligands. Low-molecular weight
Cu(II) carboxylato compounds have frequently been used to
mimic the active site in metalloenzymes, since many metallo-
protein active sites have been recognized to have carboxylate-
7
rich coordination environments.
Our interest in these compounds arose from ongoing
research on alkyl-chain copper(II) carboxylates with different
N-donor ligands that showed increased activity against some
Experimental
General
Syntheses of the complexes were carried out using commer-
cially available chemicals and solvents. The starting copper(II)
y Present address: Vrije Universiteit Brussel, ULTR, Paardenstraat 65,
1
640 Sint-Genesius-Rode, Belgium. E-mail: nina@ultr.vub.ac.be.
DOI: 10.1039/b110051c
New J. Chem., 2002, 26, 933–938
933
This journal is # The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2002

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carboxylates were prepared by the reaction of the appropriate
sodium carboxylate in an aqueous solution with the required
amount of copper(II) sulfate. So-obtained copper(II) carboxy-
lates were purified by recrystallization from methanol.
C, 52.20; H, 7.95, N, 4.24; C58
52.16; H, 7.85; N, 4.19%).
H
104Cu
4
N
4
O
14 requires: C,
Structure determinations
IR spectra were recorded on a Perkin–Elmer 1720X spec-
ꢀ1
trophotometer in the region between 4000 and 400 cm using
nujol and poli oil techniques. Solid state (Nujol mull) UV-VIS
spectra were recorded on a Perkin–Elmer Lambda 19 spec-
trophotometer. Spectra of compounds 1–4 can be obtained
from the authors upon request. Due to the very low yield, no
spectroscopic data are available for compond 5.
Data were collected on a Nonius Kappa CCD diffractometer
9
10
using COLLECT and reduced using DENZO. All structures
were solved by routine direct methods and refined by least
2
11
squares refinement on F values. All non-hydrogen atoms
were refined anisotropically. Constrained riding hydrogen
atoms were included. Crystal data are summarized in Table 1.
For structure 1 the absolute structure parameter indicated a
racemic twinning of the crystals. Refinement of the racemic
twin model resulted in better R values [Flack parameter
Preparations
Cu(ac) (4-apy)
2
2
, 1. Copper(II) acetate hydrate (0.06 g, 0.15
0.51(6)]. Problems were encountered with the structure of 5.
2
mmol) was dissolved in 30 mL of acetonitrile, with stirring and
heating. 4-Aminopyridine (0.09 g, 1 mmol) was added at the
boiling point. An immediate colour change was followed by
rapid growth of small, violet, block-shaped crystals from the
cooling solution. Maintaining the solution with all the pre-
cipitated violet product at room temperature for a month led
to the qualitative conversion of the violet form to blue plate-
like crystals of Cu(ac)
Found: C, 45.12; H, 4.91; N, 15.15; C14
C, 45.46; H, 4.91; N, 15.15%).
The values of R and wR for least squares refinement on F
1 2
are larger than those normally obtained for small inorganic
molecules. This is presumably a consequence of having dis-
ordered octanoate alkyl chains. The disorder of one of the
three crystallographically independent octanoate groups was
successfully resolved. However, the thermal displacement
parameters of the carbon atoms of the other two octanoate
ligands indicate possible disorder as well. Despite the relatively
poor agreement factors, the crystal structure of 5 is conclusive
as to the general shape of the molecule.
2
(4-apy)
2
, 2. Yield: 72% (0.08 g).
(
H
18CuN requires:
4 4
O
CCDC reference number 181545. See http:==www.rsc.org=
suppdata=nj=b1=b110051c= for crystallographic data in CIF
or other electronic format.
Cu(hex) (4-apy) , 3 and Cu(ac) (4-apy) , 4. The 4-amino-
2
2
2
2
pyridine ligand (0.5 mmol, 0.05 g) was dissolved in the boiling
acetonitrile solution containing 0.1 mmol of the corresponding
copper(II) carboxylate. The resulting intensely blue solution
was filtered to remove any solids and allowed to cool to
ambient temperature. On standing (1–2 days) small violet
crystals formed. Yield: 62% (0.06 g) average for 3, 67% (0.07 g)
for 4. (Found for 3: C, 54.67; H, 7.23; N, 11.80;
C H CuN O requires: C, 54.81; H, 7.11; N, 11.62; found for
Powder diffractogram of compound 1 (after transformation
of the violet crystals into a blue powder) was obtained by the
Guinier de-Wolf camera (Enraf-Nonius) using Cu-Ka radia-
tion. For comparison of the results with the diffractogram of
compound 2, the interplanar spacings and their relative
intensities were calculated using the single-crystal X-ray data
1
2
for compound 2.
2
2
34
4
4
4
5
: C, 56.54; H, 7.68; N, 11.07; C24
6.51; H, 7.51; N, 10.98%).
4 4
H38CuN O requires: C,
Computational
Cu
dissolved in 30 ml of acetonitrile and filtered. The solution of
-aminopyridine (0.05 g) in a mixture of acetonitrile and water
4 ml, 2 ml) was then added. The resulting turquoise solution
was then left at ambient temperature. Blue plate-like single
crystals deposited over a month. Yield: 7% (0.04 g). (Found:
4
(oct)
6
(OH)
2
(4-apy)
2
, 5. Cu(II) octanoate (0.09 g) was
To find the energy difference between the two isomers of the
monomeric acetate complex, ab initio MO calculations at the
HF=6-31G* level were performed. The Gaussian 98 suite of
programs was used. No geometry optimization was applied.
Atomic coordinates were taken as those obtained by the single
crystal X-ray diffraction method.
4
(
1
3
Table 1 Summary of crystal data for compounds 1–5
1
2
3
4
5
Formula
M
T=K
Crystal system
Space group
C
14
H
18CuN
4
O
4
C
14
H
18CuN
4
O
4
C
22
H
34CuN O
4 4
C
24
H
38CuN O
4 4
C
58 4 4 14
H104Cu N O
369.86
200
Tetragonal
I4
8
10.6062(2)
—
31.1002(8)
—
—
369.86
200
Monoclinic
P2
4
9.7290(2)
9.1500(2)
18.4912(2)
—
94.397(1)
—
1643.3(3)
1.355
6111
3239
0.025
2711
0.030
0.087
482.07
200
Triclinic
510.12
200
Triclinic
1335.61
200
Triclinic
-
-
--
--
1
cd
1
=n
P1
1
P1
1
P1
1
Z
+
a=A
+
8.6601(4)
9.2451(4)
9.3080(4)
75.641(3)
69.130(2)
64.620(2)
625.11(5)
0.906
5264
3104
0.031
2184
8.7347(3)
9.3621(3)
9.2479(3)
76.727(2)
73.418(2)
64.590(2)
649.65(4)
0.876
5042
2652
0.020
2464
9.7197(3)
10.3927(3)
19.0069(6)
88.802(1)
84.612(1)
68.313(1)
1776.0(1)
1.238
10 631
6029
0.063
3986
b=A
+
c=A
ꢁ
a=
ꢁ
b=
ꢁ
g=
V=A
—
+
3
3498.5(1)
1.272
3123
1722
0.010
1466
ꢀ
1
m=mm
Coll. reflect.
Indep. reflect.
R
int
Obd. reflect. [I > 2s(I)]
[I > 2s(I)]
[I > 2s(I)]
R
1
0.042
0.129
0.049
0.094
0.031
0.068
0.107
0.284
wR
2
9
34
New J. Chem., 2002, 26, 933–938

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Results and discussion
Although the amino group of the 4-apy ligand is a potential
electron donor, there have been no structures reported with
4
the 4-aminopyridinium cation. Only four structures are
-apy as a bridging ligand. In many structures 4-apy exists as
1
4
2þ
known in which 4-apy is coordinated to Cu ion as a coligand
1
5
16
with carbonate,
phenanthroline,
bis(2-aminoethyl)ox-
amide and formate. The latter includes carboxylate ion
formate) as a bridging ligand. The result is a polymeric
structure with [Cu(formate) (4-apy) ] composition. Analo-
1
7
18
(
2
2 n
gously to these reports, 4-aminopyridine is a terminal ligand in
all five structures reported here.
2 2
Two isomers of Cu(ac) (4-apy) , 1 and 2
The first step of the reaction of copper(II) acetate hydrate with
-apy in various solvents (acetonitrile, methanol, ethanol,
acetone) always produces small violet block-shaped crystals 1,
very unstable when taken from the mother liquor. These
crystals transform into a blue powder in less than a minute.
The crystal structure of the violet compound revealed the
4
Fig. 2 Molecular structure of Cu(ac) (4-apy)
2
numbering scheme.
2
, 2, with the atomic
Cu(ac) (4-apy)2 stoichiometry with the ligands arranged
2
around copper ion in the trans configuration (Fig. 1).
In the blue, staggered form, 2, the arrangement of ligands
around the copper atom remains trans, but the geometry of the
molecule differs from the eclipsed form in many ways. The
pyridine rings are twisted, the dihedral angle between the rings
After storing the solution with the precipitated violet pro-
duct at room temperature for a month, the conversion of the
violet form to blue was completed. The crystals of the blue form
are stable in air. On the basis of the elemental analysis the
same stoichiometry was proposed as in 1. It was first erro-
neously assumed that the blue complex possesses the cis geo-
metry, since the colour of the crystals is similar to the colour of
monomeric cis complexes of copper(II) carboxylates with
ꢁ
being 61.60(7) . In the perpendicular direction two crystal-
lographically independent acetate groups are coordinated to
ꢁ
copper ion with a mutual angle of 23.6(3) . While in the
eclipsed form the coordination is essentially planar with two
acetate oxygen atoms above and below the plane, the coordi-
nation in the staggered form deviates from the planar
arrangement. One of the acetate ligands (O11, O12, C11 and
C12) is coordinated as monodentate with a Cu–O11 distance
6a
2
trans arrangement for the blue compound as well, but with
-aminopyridine. However, the crystal structure showed a
+
+
different orientations of the ligands (Fig. 2). In the violet form,
1, the two 4-apy ligands lie almost in a plane (eclipsed con-
former), while they are twisted with respect to each other in the
blue form, 2 (staggered conformer). In the eclipsed form, 1, the
copper ion lies on a twofold axis passing through atoms of
of 1.9446(14) A . O12 is located at a distance of 3.1274(17) A
from the copper atom, which is even longer than the corre-
sponding distance in the eclipsed form. The second acetate
group is coordinated in a bidentate fashion with the distances
Cu–O21 and Cu–O22 being 2.0102(14) and 2.4845(16) A,
+
0
0
0
the 4-apy ligands (N1, C4, N11 and N1 , C4 and N11 ). The
basic coordination geometry is planar, and the acetate anions
are coordinated in a monodentate fashion [Cu–O11, 1.951(2)
respectively. The resulting coordination is square pyramidal.
The value of the parameter t, introduced to describe the degree
1
9
of trigonality, is in our case 0.049. For a perfectly tetragonal
geometry t is equal to zero, while it becomes unity for a per-
fectly trigonal-bipyramidal geometry. The basal plane is
formed by N atoms of two 4-apy ligands and by O atoms of
the two acetate groups (O11 and O21). The apical position is
occupied by the second oxygen atom of one of the acetate
groups (O22). Thus, the isomerism found for the two forms
could be described as coordinational, rather than simply
rotational. A perspective view of the two isomers is presented
in Fig. 3. Selected geometrical parameters are presented in
Table 2.
+
A]. The remaining acetate oxygen atoms are located above and
below the plane at longer distances [Cu–O12, 2.810(2) A] and
+
thus complete the distorted square bipyramidal coordination,
most typical for related Cu(ac) L complexes. Discrete
2
2
monomeric units of 1 form a three-dimensional network via
hydrogen bonds through amino nitrogen atoms and non-
coordinated acetate oxygen atoms of the neighbouring
molecules.
The two isomers exhibit markedly different stabilities.
Crystals of the violet form, 1, decompose rapidly into a blue
powder after removal from the mother liquor. It was proposed
that the violet form transforms into the blue one, which was
further confirmed by X-ray powder diffraction. The measured
powder diffractogram of the decomposed sample of 1 was
identical to the calculated one of the staggered form, 2, based
on the single crystal X-ray structure.
Since there is a difference in coordination mode of the car-
boxylate ligands to the copper centre, a larger energy difference
between the isomers than that for rotational isomerism was
expected. The calculated energy difference DE is 376.6 kcal
ꢀ
1
mol (Estaggered < Eeclipsed) and corresponds to the formation
of an additional coordination bond between Cu and O22 in the
staggered form. Although the calculated value of the energy
difference is too high (if only the formation of an additional
coordination bond is taken into account), it definitely shows
that one of the isomers is energetically more favoured. The
2 2
Fig. 1 Molecular structure of Cu(ac) (4-apy) , 1, with the atomic
numbering scheme.
New J. Chem., 2002, 26, 933–938
935

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+
ꢁ
Table 3 Selected geometrical parameters (A, ) for compounds 3
and 4
3
4
Cu–N1
1.9890(18)
1.9985(19)
2.628(2)
1.288(4)
1.255(5)
1.9847(14)
1.9717(12)
2.6247(13)
1.271(2)
Cu–O11
Cu–O12
O11–C11
O12–C11
1.247(2)
N1–Cu–O11
N1–Cu–O12
O11–Cu–O12
90.19(8)
94.01(8)
55.60(9)
90.13(5)
94.21(5)
55.33(5)
2 2
Fig. 3 Perspective view of the two isomers of Cu(ac) (4-apy)
showing the orientation of the acetate and 4-aminopyridine ligands.
Eclipsed form, 1, (top) and staggered form, 2, (bottom).
+
ꢁ
Table 2 Selected geometrical parameters (A, ) for compounds 1
and 2
1
2
Cu–N1
Cu–N1
Cu–O11
Cu–O12
Cu–O21
Cu–O22
2.075(15)
1.928(2)
1.951(2)
2.809(2)
—
—
1.9968(16)
1.9846(17)
1.9446(14)
3.1274(17)
2.0102(14)
2.4845(16)
0
O11–Cu–N1
O11–Cu–N1
N1–Cu–N1
O11–Cu–O21
O11–Cu–O22
90.2(3)
89.2(3)
180.0
—
—
87.09(7)
92.36(7)
167.14(7)
164.20(6)
95.74(7)
0
0
change of the coordination number from four to five obviously
stabilizes the complex.
Structures of Cu(hex) (4-apy) , 3, and Cu(hep) (4-apy) , 4
2
2
2
2
Mononuclear copper(II) hexanoate and heptanoate complexes
with 4-apy are isostructural. The geometry of the molecules in
these two complexes is typical and most often observed for
monomeric copper(II) carboxylates. Copper ion occupies a
centre of symmetry and is surrounded by N atoms (N1) from
the two 4-apy ligands and O atoms (O11) from each of the two
carboxylate ligands, resulting in a trans square-planar config-
uration. Similar as in the eclipsed form of the acetate complex,
the remaining two coordination positions above and below the
plane are blocked by carboxylate oxygen atoms (O12), located
at longer distances. The dihedral angle between the planes of
Fig. 4 Molecule of Cu(hex) (4-apy)
2
scheme (top) and perspective view (bottom) of Cu(hep) (4-apy) , 4,
2 2
showing the parallel orientation of the carboxylate alkyl chains to the
pyridine rings.
2
, 3, with the atomic numbering
in a planar trans extended conformation and are oriented
almost parallel to the 4-apy rings (Fig. 4).
the 4-apy ligands and carboxylate groups are 82.6(2) and
ꢁ
As expected, amino groups are involved in a hydrogen bond
formation. The para position of the amino group with respect
to the pyridine N atom precludes any intramolecular hydrogen
bonding. A two-dimensional network, parallel to the ab plane,
is created via intermolecular H bonds to non-coordinated
carboxylate oxygen atoms of the neighbouring monomeric
units.
8
2.72(15) for the hexanoate and heptanoate structures,
respectively. Selected geometrical parameters are quoted in
Table 3. The alkyl chains in both complexes involve a gauche
relation at the C12–C13 bond, giving a torsion angle C11–
ꢁ
ꢁ
C12–C13–C14 of ꢀ65.8(5) for 3 and ꢀ65.1(2) for com-
pound 4. After the gauche relation the hydrocarbon chains are
9
36
New J. Chem., 2002, 26, 933–938

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Structure of Cu(oct)
6
(OH)
2
(4-apy)
2
, 5
copper atom with the apical position of the other. Quinoline
ligands are bound to each of the copper ions, while in the
herein reported structure only one of the two copper atoms is
coordinated by 4-aminopyridine. In both compounds triply
bridging hydroxide groups are observed.
The structural analysis has shown the blue crystals of com-
pound 5 to be composed of discrete centrosymmetric mole-
cules. A view of the structure of a tetranuclear molecule is
presented in Fig. 5 and selected geometrical parameters in
Table 4. The two crystallographically independent copper ions
possess distorted square pyramidal coordination. Three inde-
pendent octanoate groups are present in the molecule; two of
them form bridges from the basal position of one copper ion to
the basal site of the second copper ion. The third octanoate
anion is bound as a monoatomic bridging ligand to the apical
position, shared by both polyhedra. 4-Aminopyridine is
coordinated to Cu1 only and occupies one of the basal posi-
tions. The dihedral angle between the Cu1 and Cu2
Acknowledgements
Financial support of the Ministry of Education, Science and
Sport, Republic of Slovenia through grant PS-511-103 and
Austrian-Slovenian scientific cooperation through grant SLO-A
are gratefully acknowledged.
ꢁ
basal planes is 63.3(2) with the displacement of copper atoms
of 0.122(3) (Cu1) and 0.180(2) A (Cu2) from the basal plane
+
toward the apical position. The distance between the symmetry
related hydroxo-bridged Cu2 atoms is 2.894(2) A, while the
References
+
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¸
˜
+
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3
.0769(16) A. The distance between Cu1 and Cu2 (at ꢀx,
ꢀ
y þ 1, ꢀz þ 1), separated by carboxylate group 1, is
+
3
.3092(15) A. These distances are much longer than the
average Cuꢂ ꢂ ꢂCu separation reported for tetracarboxylato
+
2
F. P. W. Agterberg, H. A. J. Provo Kluit, W. L. Driessen, H.
´
Oevering, W. Buijs, M. T. Lakin, A. L. Spek and J. Reedijk, Inorg.
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4
bridged dimeric compounds (2.676 and 2.625 A for CuO O
4b
4
and CuO N chromophores, respectively.) Basic Cu(II) car-
boxylates are known, but none of the reported examples
showed a stoichiometry resembling this structure. The closest
example is the structure of the basic tetranuclear quinoline
3
4
F. A. Cotton, E. V. Dikarev and M. A. Petrukhina, Inorg. Chem.,
2000, 39, 6072, and references therein.
˘ ˘
(a) M. Melnik, M. Kabesova, M. Koman, L. Macaskova, J.
Garaj, C. Holloway and A. Valent, J. Coord. Chem., 1998, 45, 147;
(b) M. R. Sundberg, R. Uggla and M. Melnik, Polyhedron, 1996,
adduct of copper trifluoroacetate with a Cu
2
4
(tfc)
One molecule contains two crystal-
6 2 4
(OH) (quin)
0
stoichiometry.
1
5, 1157, and references therein.
lographically independent Cu ions, bridged by two indepen-
dent carboxylate ligands. Similarly, the coordination geometry
around each copper atom is square pyramidal. The third car-
boxylate group is monodentate, bound only to one of the
copper atoms at the basal position, while in our case the third
carboxylate group forms a monotomic bridge between the two
copper atoms and thus represent the common edge of the
coordination polyhedra. In the previously reported tetramer,
bridging carboxylate groups connect the basal position of one
5
(a) M. Kato and Y. Muto, Coord. Chem. Rev., 1988, 92, 45; (b) O.
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1
991, 47, 344; (d) T. Kawata, H. Uekusa, S. Ohba, T. Furukawa,
T. Tokii, Y. Muto and M. Kato, Acta Crystallogr., Sect. B, 1992,
8, 253.
4
ˇ
6
7
(a) N. Lah, G. Giester, J. Lah, P. Segedin and I. Leban, New J.
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4
(
1
3; (b) R. H. Holm and E. I. Solomon, Chem. Rev., 1996, 96, 2239;
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998, 37, 1219, and references therein.
ˇ
8
9
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1
999, 18, 755; (b) B. Kozlevcar, N. Lah, I. Leban, I. Turel, P.
ˇ
Segedin, M. Petric, F. Pohleven, A. J. P. White and G. Giester,
Croat. Chim. Acta, 1999, 72, 427.
Collect Data Collection Software, B. V. Nonius, Delft, The
Netherlands, 1999.
1
1
0
1
Z. Otwinowski and V. Minor, Methods Enzymol., 1997, 276, 307.
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¨
Gottingen, Germany, 1997.
1
1
2
3
E. J. Gabe, Y. La Page, J.-P. Charland, F. L. Lee and J. White,
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J. E. Stratmann, J. C. Burant, S. Dapprich, J. M. Millam, A. D.
Daniels, K. N. Kudin, M. C. Strain, O. Farkas, J. Tomasi, V.
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Morokuma, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B.
Foresman, J. Ciolslovski, J. V. Ortiz, B. B. Stefanov, G. Liu, A.
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revision A.5, Gaussian, Inc., Pittsburgh PA, 1998.
Fig. 5 View of the molecular structure of 5. For clarity, carbon
atoms of the octanoate alkyl chains are omitted.
+
ꢁ
Table 4 Selected geometrical parameters (A, ) for compound 5
Cu–O
Cu1–N1
Cu1–O21
Cu1–O11
Cu1–O31
1.977(6)
2.032(8)
1.974(7)
1.937(7)
2.450(7)
Cu2–Oi
Cu2–O
Cu2–O22
Cu2–O12
Cu2–O31
2.021(7)
1.923(7)
1.933(7)
1.951(7)
2.333(7)
i
i
Cu2 –O–Cu1
Cu1–O–Cu2
Cu2 –O–Cu2
100.6(3)
94.4(3)
116.1(4)
i
14 (a) K. E. Halvorson, C. Patterson and R. D. Willett, Acta Crys-
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Willett, Acta Crystallogr., Sect. C, 1994, 50, 862.
Symmetry operator i: ꢀx, ꢀy þ 1, ꢀz þ 1.
New J. Chem., 2002, 26, 933–938
937

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