Unusual O-coordination of caffeine in tetrakis(μ-3,5-dinitrobenzoato- k2O:O′)bis[(caffeine-kO)copper(II)]

Article abstract of DOI:10.1107/S0108270106025467

The title compound (systematic name: tetrakis(μ-3,5-dinitro-benzoato- k²O:O′)bis[(3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione- kO²)copper(II)]}, [Cu₂(C₇H₃N ₂O₆)₄(C₈H₁₀N ₄O₂)₂], consists of paddle-wheel dimeric tetrakis(μ-3,5-dinitro-benzoato-k²O:O′)dicopper(II) units with O-coordinated caffeine molecules in both apical positions. The entire dimeric molecule lies on a tetragonal inversion 4 axis, and thus one nitrobenzoate anion with one Cu atom in a special position belong to the independent part of the molecule. The caffeine ligand bonded to the Cu atom is disordered on a local twofold non-crystallographic axis coincident with the 4 axis. A π-π stacking interaction is observed between the caffeine rings and adjacent symmetry-related benzene rings of the 3,5-dinitro-benzoate anions.

Full text of DOI:10.1107/S0108270106025467

metal-organic compounds
Ê
slightly displaced from the basal plane by 0.200 (1) A toward
the apical O7 atom, and the ꢃ parameter (Addison et al., 1984)
of 0.16 implies tetragonal geometry.
Acta Crystallographica Section C
Crystal Structure
Communications
ISSN 0108-2701
Unusual O-coordination of caffeine in
tetrakis(l-3,5-dinitrobenzoato-
j2O:O0)bis[(caffeine-jO)copper(II)]
a
a
a
Ï
Â
Petra Stachova, Jan Moncol, * Dusan Valigura and
Tadeusz Lisb
a
Â
Department of Inorganic Chemistry, Slovak Technical University, Radlinskeho 9,
SK-812 37, Bratislava, Slovakia, and bFaculty of Chemistry, University of Wrocøaw,
14 Joliot-Curie St, 50-383 Wrocøaw, Poland
Correspondence e-mail: jan.moncol@stuba.sk
Received 9 June 2006
Accepted 3 July 2006
Online 29 July 2006
The caffeine molecules are signi®cantly planar; the dihedral
angle between the pyrimidine and imidazole rings is 0ꢀ. These
dihedral angles in other complexes with caffeine are in the
range 0±5ꢀ. The dihedral angle is 0ꢀ only for [Cu2(ꢀ-¯ufena-
The title compound {systematic name: tetrakis(ꢀ-3,5-dinitro-
benzoato-ꢁ2O:O0)bis[(3,7-dihydro-1,3,7-trimethyl-1H-purine-
2,6-dione-ꢁO2)copper(II)]}, [Cu2(C7H3N2O6)4(C8H10N4O2)2],
consists of paddle-wheel dimeric tetrakis(ꢀ-3,5-dinitro-
benzoato-ꢁ2O:O0)dicopper(II) units with O-coordinated
caffeine molecules in both apical positions. The entire dimeric
molecule lies on a tetragonal inversion 4 axis, and thus one
nitrobenzoate anion with one Cu atom in a special position
belong to the independent part of the molecule. The caffeine
ligand bonded to the Cu atom is disordered on a local twofold
non-crystallographic axis coincident with the 4 axis. A ꢂ±ꢂ
stacking interaction is observed between the caffeine rings and
adjacent symmetry-related benzene rings of the 3,5-dinitro-
benzoate anions.
2
0
Â
mato-ꢁ O:O )4(caffeine-ꢁN)(H2O)] (Melnõk et al., 1998) and
[Cu2(ꢀ-CCl3CO2-ꢁ2O:O0)4(caffeine-ꢁN)2]ÁC6H6 (Horie et al.,
1986).
There are ꢂ±ꢂ stacking interactions (Fig. 2) (Janiak, 2000)
between the caffeine rings and adjacent symmetry-related
benzene rings of the 3,5-dinitrobenzoate anions at ( x, y,
1
2
z + 1) and (x, y + , z + 1); the distances between the
Ê
caffeine and benzene planes are in the range 3.28±3.52 A.
Comment
Benzoates, especially salicylates and fenamates, are known to
play an important role in human medicine. The preparation of
new nitro-substituted benzoato±copper complexes with
different biologically active ligands, the study of their
composition, stereochemistry, structure and spectroscopic
properties, and of course the study of their biological activity,
are the basis of our approach to analyzing these compounds.
The complex molecule of the title compound, (I) (Fig. 1), is
located on a 4 inversion axis, with both Cu atoms and atoms
O7, C8 and C10 of the caffeine ligand on a twofold axis. Each
Cu atom in the dimeric structure has a tetragonal±pyramidal
coordination, with four carboxylate O atoms (O1, O2 and
their symmetry equivalents) in equatorial positions [CuÐO1 =
Ê
Ê
1.933 (2) A and CuÐO2 = 1.983 (2) A] and caffeine atom O7
ii
Ê
Figure 1
in the apical position [CuÐO7 = 2.180 (3) A]. The CuÁ Á ÁCu
A perspective view of (I), showing the atom-numbering scheme.
Displacement ellipsoids are drawn at the 30% probability level. For
disorder information, see Experimental. [Symmetry codes: (i) x, 12 y, z;
1
4
1
4
Ê
separation is 2.661 (3) A [symmetry code: (ii) y
,
x,
5
z], which is close to the CuÁ Á ÁCu distance in [Cu3(C7H3-
4
È
N2O6)6(CH3OH)2]n (Hokelek et al., 1998). The Cu atoms are
1
4
1
(ii) y
,
4
x, 54 z.]
Acta Cryst. (2006). C62, m375±m377
DOI: 10.1107/S0108270106025467
# 2006 International Union of Crystallography m375

metal-organic compounds
Crystal data
3
[Cu2(C7H3N2O6)4(C8H10N4O2)2]
Mr = 1359.96
Dx = 1.790 Mg m
Mo Kꢄ radiation
ꢀ = 0.96 mm
T = 100 (2) K
1
Tetragonal, I41=a
Ê
a = 12.900 (5) A
Ê
c = 30.33 (3) A
Ê
V = 5047 (3) A
Z = 4
Tetragonal plate, blue
0.24 Â 0.12 Â 0.11 mm
3
Data collection
Kuma KM-4-CCD area-detector
diffractometer
! scans
Absorption correction: analytical
(CrysAlis RED; Oxford
Diffraction, 2003)
19901 measured re¯ections
5131 independent re¯ections
2721 re¯ections with I > 2ꢄ(I)
Rint = 0.067
ꢅmax = 35.0ꢀ
Tmin = 0.826, Tmax = 0.908
Re®nement
Figure 2
Re®nement on F2
R[F2 > 2ꢆ(F2)] = 0.054
wR(F2) = 0.078
S = 1.01
5131 re¯ections
216 parameters
H-atom parameters constrained
w = 1/[ꢆ2(Fo2) + (0.0207P)2]
The ꢂ±ꢂ stacking interactions (dashed lines) in the crystal structure of (I).
2
where P = (Fo + 2Fc2)/3
(Á/ꢆ)max < 0.001
3
Ê
Áꢇmax = 0.91 e A
As a ligand, caffeine usually prefers an N atom as the donor
atom, e.g. in the copper(II) carboxylate complexes [Cu2(ꢀ-
3
Ê
0.61 e A
Áꢇmin
=
2
¯ufenamato-ꢁ O:O0)4(caffeine-ꢁN)(H2O)] (Melnõk et al.,
Â
Table 1
Selected geometric parameters (A, ).
1998) or [Cu2(ꢀ-RCO2-ꢁ2O:O0)4(caffeine-ꢁN)2], where
RCO2 is the benzoate anion (Kawata et al., 1992), the
naproxenate anion (Koman et al., 2000), the chloroacetate
ꢀ
Ê
CuÐO1i
CuÐO1
CuÐO2
1.933 (2)
1.933 (2)
1.983 (2)
CuÐO2i
CuÐO7
CuÁ Á ÁCuii
1.983 (2)
2.180 (3)
2.661 (3)
Ï
anion (Koren et al., 1985), the o-iodobenzoate anion (Valach et
al., 2001), the benzoylformate anion (Harada et al., 1997) or
the trichloroacetate anion (Horie et al., 1986). The CuÁ Á ÁCu
separations and CuÐNap(caffeine) bond distances in these
O1iÐCuÐO1
O1iÐCuÐO2
O1ÐCuÐO2
O1ÐCuÐO2i
O2ÐCuÐO2i
173.16 (8)
88.75 (6)
90.27 (6)
88.75 (6)
163.57 (8)
O1iÐCuÐO7
O1ÐCuÐO7
O2ÐCuÐO7
O2iÐCuÐO7
93.42 (4)
93.42 (4)
98.21 (4)
98.21 (4)
Ê
complexes are in the ranges 2.633±2.852 and 2.239±2.116 A,
respectively. The O atom was found to participate in co-
ordination only in {[Cu2(ꢀ-CCl3CO2-ꢁ2O:O0)4(ꢀ-caffeine-
ꢁ2N:O)]Á2PhCH3}n, which contains caffeine as a bridging
ligand (Uekusa et al., 1992). It is interesting that the bonding
of caffeine via an O atom in the title compound results in a
smaller distance from the Cu atom to the basal plane
compared with those compounds with caffeine as an N-donor
Symmetry codes: (i) x; y ‡ 12; z; (ii) y
;
x ‡ 14; z ‡ 54.
1
4
Discrete positional disorder of the caffeine ligands is observed.
Molecules of (I) lie around a 4 inversion axis. Atoms Cu, O7, C8 and
C10 lie on special positions on the twofold rotation axis and have
occupancy factors of 0.5 in the asymmetric unit. In Fig. 1, atoms which
have full occupancy in complete molecules are drawn with solid lines.
Atoms which have 0.5 occupancy in parts A or B alongside the
twofold rotation axis are drawn with open or open dashed lines.
Atom N5 from the caffeine ligand in part A and atom O8 from the
caffeine ligand in mirror part B lie in the same positions and were
constrained by EXYZ and EADP (SHELXL97; Sheldrick, 1997)
with occupancy factors of 0.5. In part A, the full caffeine ligand
consists of atoms O7, C8, C9, N3, N4, N5, C11 and C13, atoms in
inversion C9i, N3i, C13i, C12i and O8i [symmetry code: (i)
x; y ‡ 12 ; z], and their parent H atoms. In part B, the full molecule
consists of atoms O7, C8, C9, N3, C12, O8 and C13, atoms in inver-
sion C9i, N3i, C13i, N4i, N5i and C11i, and their parent H atoms. The
remaining H atoms were positioned geometically, with CÐH = 0.95
Â
ligand [0.223 (Melnõk et al., 1998), 0.204 (Kawata et al., 1992),
0.217 (Koman et al., 2000), 0.236 (Koren et al., 1985), 0.236
Ï
Ê
(Valach et al., 2001), 0.259 (Harada et al., 1997) or 0.315 A
(Horie et al., 1986)].
Complex (I) is also unusual for the manner of bonding
adopted by the 3,5-dinitrobenzoate anion. This anion prefers a
monodentate or ionic bonding manner, and there is only one
example of a bidentate bridging mode forming copper(II)
acetate-like dimers, viz. [Cu3(C7H3N2O6)6(CH3OH)2]n
È
(Hokelek et al., 1998), and in this case (O-donor apical ligand),
the Cu atom is displaced from the basal plane by 0.195 A.
Ê
Ê
and 0.98 A for aromatic and methyl H atoms, respectively, and
constrained to ride on their parent atoms, with Uiso(H) = 1.2Ueq(C).
Data collection: CrysAlis CCD (Oxford Diffraction, 2003); cell
re®nement: CrysAlis RED (Oxford Diffraction, 2003); data reduc-
tion: CrysAlis RED; program(s) used to solve structure: SIR97
(Altomare et al., 1999); program(s) used to re®ne structure:
SHELXL97 (Sheldrick, 1997); molecular graphics: XP in SHELXTL
(Sheldrick, 1998); software used to prepare material for publication:
enCIFer (Allen et al., 2004).
Experimental
Caffeine (0.5 mmol) was added to copper(II) acetate (1 mmol) in an
aqueous solution (50 ml). 3,5-Dinitrobenzoic acid (2 mmol) was then
added. The powdery blue product was ®ltered off, washed with water
and dried at room temperature. Blue crystals of (I) suitable for X-ray
analysis were obtained from the mother liquor after a few weeks by
slow room-temperature crystallization.
ꢁ
Â
m376 Stachova et al. [Cu2(C7H3N2O6)4(C8H10N4O2)2]
Acta Cryst. (2006). C62, m375±m377

metal-organic compounds
Harada, A., Tsuchimoto, M., Ohba, S., Iwasawa, K. & Tokii, T. (1997). Acta
Cryst. B53, 654±661.
The authors thank the Scienti®c Grant Agency of the
Ministry of Education of the Slovak Republic and the Slovak
Academy of Sciences for ®nancial support under grant No.
1/2452/05, and the Research and Development Support
Agency for ®nancial support under grant No. APVT-20-
005504.
È
È
Æ
Hokelek, T., Mert, Y. & Unaleroglu, C. (1998). Acta Cryst. C54, 310±313.
Horie, H., Husebye, S., Kato, M., Meyers, E. A., Muto, Y., Suzuki, I., Tokii, T.
& Zingaro, R. A. (1986). Acta Chem. Scand. Ser. A, 40, 579±589.
Janiak, C. (2000). J. Chem. Soc. Dalton Trans. pp. 3885±3896.
Kawata, T., Uekusa, H., Ohba, S., Furukawa, T., Tokii, T., Muto, Y. & Kato, M.
(1992). Acta Cryst. B48, 253±261.
Â
Koman, M., Melnõk, M., Moncol, J. & Gøowiak, T. (2000). Inorg. Chem.
Commun. 3, 489±492.
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: SF3010). Services for accessing these data are
described at the back of the journal.
Ï
 Â
Koren, B., Valach, F., Sivy, P. & Melnõk, M. (1985). Acta Cryst. C41, 1160±
1162.
Â
Melnõk, M., Koman, M. & Gøowiak, T. (1998). Polyhedron, 17, 1767±
1771.
Oxford Diffraction (2003). CrysAlis CCD and CrysAlis RED. Versions 1.171.
Oxford Diffraction Poland, Wrocøaw, Poland.
Sheldrick, G. M. (1997). SHELXL97. University of GoÈttingen, Germany.
Sheldrick, G. M. (1998). SHELXTL. Version 5.10. Bruker AXS Inc., Madison,
Wisconsin, USA.
References
Addison, A. W., Rao, T. N., Reedijk, J., van Rijn, J. & Verschoor, G. C. (1984).
J. Chem. Soc. Dalton Trans. pp. 1349±1356.
Allen, F. H., Johnson, O., Shields, G. P., Smith, B. R. & Towler, M. (2004). J.
Appl. Cryst. 37, 335±338.
Altomare, A., Burla, M. C., Camalli, M., Cascarano, G. L., Giacovazzo, C.,
Guagliardi, A., Moliterni, A. G. G., Polidori, G. & Spagna, R. (1999). J.
Appl. Cryst. 32, 115±119.
Uekusa, H., Ohba, S., Tokii, T., Muto, Y., Kato, M., Husebye, S., Steward,
O. W., Chang, S.-C., Rose, J. P., Pletcher, J. F. & Suzuki, I. (1992). Acta Cryst.
B48, 650±667.
ÏÂ
Valach, F., Tokarcõk, M., Maris, T., Watkin, D. J. & Prout, C. K. (2001). J.
Organomet. Chem. 622, 166±171.
ꢁ
Â
Acta Cryst. (2006). C62, m375±m377
Stachova et al.
[Cu2(C7H3N2O6)4(C8H10N4O2)2] m377