Inorganic Chemistry Communications 8 (2005) 1056–1059
www.elsevier.com/locate/inoche
Metal–nucleobase interactions: Interplay of coordination and hydrogen
bonding in cadmium (II) complexes of N6-substituted adenines q
N. Stanley a, P. Thomas Muthiah
a
a,*
, P. Luger b, M. Weber b, S.J. Geib
c
School of Chemistry, Bharathidasan University, Palkalaiperur, Tiruchirappalli, Tamilnadu 620024, India
b
Institute for Chemistry/Crystallography, Free University of Berlin, D-14195, Berlin, Germany
c
Department of Chemistry, University of Pittsburgh, PA 15260, USA
Received 16 May 2005; accepted 13 August 2005
Available online 28 September 2005
Abstract
The X-ray crystal structures of 1 [Cd2(BAD+)2(l-Cl)4Cl2]n (BAD+ = N3 protonated N6-benzyladenine)] and 2 [Cd2(FAD+)2
(l-Cl)4Cl2]n (FAD+ = N3 protonated N6-furfuryladenine) reveal an one-dimensional polymer. In both the structures, the interplay of
coordination and hydrogen bonding results in the formation of almost the same type of supramolecular architectures via N–H Cl,
C–H Cl and C–H N hydrogen bonds.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Cadmium (II) complexes; Metal–adenine interactions; Crystal structures; Hydrogen bonds
The design and construction of specific supramolecular
architectures, particularly one-, two- and three-dimensional extended frameworks are of great current interest
because of their abilities for functional materials [1,2], such
as non-linear opticals (NLO), electrical switches, etc. The
interplay of coordination and hydrogen bonding of the
complexes have recently been reported [3,4]. The recurring
packing patterns adopted by certain functional groups and
the robustness of the same type of supramolecular motifs
can create new solid state structures [5]. By assembling of
molecules or ions into architectures with desirable structure, functional materials with desirable properties would
be built up [6]. Our recent investigations are devoted to
hydrogen bonding patterns and metal coordination exhibited by some biologically important ligands [3,4,7]. Many
N6-substituted adenine derivatives function as plant
growth stimulants [8], example, N6-benzyladenine and
N6-furfuryladenine. The interactions between Cd2+ ions
q
The work has been presented briefly at First Asian Meeting of
Bioinorganic Chemistry, Okazaki National Research Institutes, Okazaki,
Japan, March 7–10, 2003, P-74.
*
Corresponding author. Fax: +91 431 2407045.
E-mail address: [email protected] (P.T. Muthiah).
1387-7003/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2005.08.012
and DNA have recently been reported by Hossain and
Huq [9]. They believed that Cd2+ ions covalently bind into
adenine and guanine in DNA. Some crystal structures of
mononuclear complexes of N6-benzyladenine derivatives
have been reported [10–14]. The design of supramolecular
architectures using nucleobases as building motifs has been
recently reviewed [20]. The present study is aimed at gaining further understanding of the interplay of the coordination and hydrogen bonding to form a supramolecular
architectures involving cadmium chloride and N6-benzyladenine (1)/N6-furfuryladenine (2). Both compounds have
been synthesized [21] and characterized by X-ray crystallography [22].
In both the crystal structures, the Cd2+ ions have a distorted octahedral geometry. The coordination polyhedron
of the cadmium atom is made up of five chloride ions
and a nitrogen atom (N9) from the purine ring of N6-benzyladenine in 1 and N6-furfuryladenine in 2. They are significant from the crystal engineering point of view, in
that both the structures are made up of linear polymeric
chains, each chain consisting of the Cd octahedra. Two
adjacent octahedra share their edges. Thus, the two edge
chloride ions bridge the two successive Cd2+ ions. The
N. Stanley et al. / Inorganic Chemistry Communications 8 (2005) 1056–1059
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Fig. 1a. Linear polymeric chains (hydrogen atoms are omitted for clarity and labeled atoms are in the asymmetric unit) observed in 1: The distances (Å)
and angles (°) around cadmium in 1 are Cd1–Cl1 = 2.638(1), Cd1–Cl2 = 2.611(2), Cd1–Cl3 = 2.651(1), Cd1–N9 = 2.347(2), Cd1–Cl2a = 2.582(1), Cd1–
Cl3b = 2.681(2), Cl1–Cd1–Cl1 = 99.5(1), Cl1–Cd1–Cl3 = 163.7(1), Cl1–Cd1–N9 = 84.2(1), Cl2–Cd1–N9 = 85.5(1), Cl2a–Cd1–N9 = 171.0(1), Cl2a–Cd1–
Cl3b = 92.3(1).
adjacent chloride bridges have been found to be perpendicular to one another. The linear polymeric chain (onedimensional) in the structures of 1 and 2 are shown in Figs.
1a and 1b.
In the crystal structure of neutral N6-benzyladenine [15],
the hydrogen atom remains in the N9 position and the
compound exists as N9–H tautomer. In monoprotonated
adenine systems, N1 is the protonation site [16,17]. However, in the crystal structure of 1, the adenine moiety exists
as the N7–H tautomer with the proton at N3 (these hydrogen atoms being located from the difference Fourier map
and refined isotropically from the data collected at very
low temperature) and coordination is at N9 position. The
internal angles at N3 and N7 are 117.0(2)° and 107.6(2)°.
The corresponding angles in neutral N6-benzyladenine
[15] moieties are 110.7(2) and 103.9(2)°. This type of protonation and N7–H tautomeric forms have already been
observed in many mononuclear metal complexes of N6substituted adenines [11–14]. But in the crystal structure
of 2, the corresponding hydrogen atoms were not located
from the difference Fourier map and two N6-furfuryladenine moieties (A and B) are present in the asymmetric unit.
The ring angles at N3 and N7 are 117.6(5) and 108.3(5)° in
moiety A and 117.9(5) and 107.2(5)° in moiety B. These
Fig. 1b. Linear polymeric chains (hydrogen atoms are omitted for clarity and labeled atoms are in the asymmetric unit) observed in 2: The distances (Å)
and angles (°) around cadmium in 2 are Cd1–Cl1 = 2.622(2), Cd1–Cl2 = 2.625(2), Cd1–Cl3 = 2.660(2), Cd1–Cl4 = 2.728(2), Cd1–N9 = 2.338(5), Cd2–
Cl3 = 2.710(2), Cd2–Cl4 = 2.667(3), Cd2–Cl5 = 2.634(2), Cd2–Cl6 = 2.600(2), Cd2–N9A = 2.361(5), Cl1–Cd1–Cl2 = 99.5(1), Cl1–Cd1–Cl3 = 160.4(1),
Cl1–Cd1–N9 = 84.9(2), Cl2–Cd1–Cl4 = 175.0(2), Cl2–Cd1–N9 = 85.1(2), Cl3–Cd1–N9 = 84.8(2), Cl3–Cd2–Cl4 = 80.8(1), Cl3–Cd2–Cl6 = 175.6(1), Cl3–
Cd2–N9A = 96.5(2), Cl5–Cd2–Cl6 = 99.1(1), Cl4–Cd2–Cl6 = 95.6(2), Cl6–Cd2–N9A = 86.0(2).
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N. Stanley et al. / Inorganic Chemistry Communications 8 (2005) 1056–1059
values are very close to those observed in the N3-protonated N7–H tautomeric adenine complexes [11,13,16,17].
The corresponding angles in neutral N6-furfuryladenine
[18] moieties are 110.9(3) and 102.8(3)°.
In both the crystal systems, the orientations of the benzyl and furfuryl groups are distal to the imidazole ring of
the adenine base. The dihedral angle between benzyl and
adenine planes is 88.5(2)° in 1. In 2, the dihedral angle between furfuryl and adenine planes is 63.6(4)° in moiety A
and 68.9(4)° in moiety B. In both the crystal systems, the
protons at N7 and N6 are hydrogen-bonded with one of
the chloride anions (Cl1 for 1 and C16 for 2) through N–
H Cl hydrogen bonds to form a seven-membered ring.
This can be designated by the graph-set notation [19],
R21(7) and it has also been observed in the crystal structure
of N6-furfuryladenine hydrochloride [16]. This ring motif is
self-organized through metal coordination and C–H O
hydrogen bonds leading to the formation of a supramolecular 2D-sheet like pattern. The supramolecular 2D-sheet
has been observed in both the crystal systems, which is significant for crystal engineering. In both the crystal systems,
the packing arrangements are very close to one another. In
structure 2, the furfuryl moieties (moiety A) are symmetrically (1 x, 1/2 + y, z) paired through a pair of C–H O
hydrogen bonds to form an eight-membered ring [with
graph-set notation, R22(8)]. Furfuryl pairs interconnect
two such supramolecular sheets, whose view along b axis
is shown in Fig. 2b. But two such sheets are not connected
in 1. Its hydrogen bonding pattern is shown in Fig. 2a,
which is viewed along b axis. In both the crystal systems,
the interplay of coordination and hydrogen bonds (N–
H Cl, C–H Cl and C–H N in 1 and N–H Cl, C–
H Cl, C–H N and C–H O in 2) results in the formation of a same kind of supramolecular patterns. Recently,
Trávniček and co-workers have analysed the cytotoxic
activity of Cu(II) complexes with N6-substituted adenines
(N3 protonated with N7–H tautomer and N9 coordina-
Fig. 2b. Supramolecular architecture in compound 2.
tion). Also in the present crystal structures, the adenine
moiety exists as the N7–H tautomer with the proton at
N3 and coordination is at N9 position. Hence, it is believed
that the two polymeric structures reported here which
interestingly have the same types coordinations and supramolecular architectures are worthy of study for similarities
in their properties, which may eventually lead to their use
as functional materials.
Acknowledgement
N.S. thanks the Council of Scientific and Industrial
Research, New Delhi, India for the award of a Senior
Research Fellowship [Reference No. 9/475(111)/2002EMR-I].
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.inoche.2005.
08.012.
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[21] Synthesis: The polymeric cadmium complexes of N6-benzyladenine
[Cd2(BAD+)2(l-Cl)4Cl2]n (BAD+=N3-protonated N6-benzyladenine)
and N6-furfuryladenine [Cd2(FAD+)2(l-Cl)4Cl2]n (FAD+) = N3protonated N6-furfuryladenine) were prepared by mixing hot methanolic solutions of cadmium chloride tetrahydrate (LOBA Chemicals
PVT., LTD., India) and N6-benzyladenine (s.d.Fine Chemicals, India)
or N6-furfuryladenine (s.d.Fine Chemicals, India) in 1:1 molar ratio
and the resultant solutions were acidified with a few drops of dilute
1059
hydrochloric acid to keep the pH maintained at 4.5. After few hours
colourless fine crystals of complex 1 were collected from water bath
itself and after a few days colourless crystals of complex 2 were
obtained from the respective solutions. Spectroscopy. For 1: IR (KBr
pallet, cm 1): 1574m, 1619s m(C@C), 1639s m(C@N), 2370–2680w
m(N7–H), 3126w m(C–H) and 3230w m(N–H); 1H NMR (CD3SOCD3,
300 MHz, 25 °C); d = 4.02 (2H; CH2) and d = 3.85(1H; N6–H); For 2:
IR (KBr pallet, cm 1): 1560m, 1610s m(C@C), 1644s m(C@N), 2400–
2700w m(N7–H), 3135w m(C–H) and 3235w m(N–H); 1H NMR
(CD3SOCD3, 300 MHz, 25 °C); d = 4.15(2H; CH2) and
d = 3.92(1H; N6–H).
[22] X-ray crystallography for compound 1, the data were collected at
100 K on a Bruker Smart Apex CCD diffractometer provided with
a graphite monochromated Mo Ka radiation. Whereas in compound 2, the data were collected at room temperature on STOE
four circle diffractometer provided with a graphite monochromated
Mo Ka radiation. Both the structures were solved by direct
method using the program SHELXS97 and refined by full-matrix
least-squares with SHELXL97. All the non-hydrogen atoms were
refined anisotropically. In compound 1, all the hydrogen atoms
were located from the difference Fourier map and refined
isotropically. In compound 2, few hydrogen atoms (H2, H6,
H6A, H7A, H8A and H12) were located from the difference
Fourier map and refined isotropically. All other hydrogen atoms
were fixed geometrically and refined using riding model. Crystal
data. For 1: C12H12CdCl3N5, FW = 445.03, Monoclinic, P21/c,
a = 15.4237(6), b = 6.8772(2), c = 15.6463(6)Å, b = 109.4920(10)°,
V = 1564.52(10)Å3, Z = 4, Dc = 1.889 g cm 3, T = 100 K, l(Mo
Ka) = 1.907 mm 1, 238 parameters, F2 refinement, R1 = 0.0339 for
4482 data with I > 2s (I), wR2 = 0.0979 (all data); for 2:
FW = 869.98,
Monoclinic,
P21,
C20H20Cd2Cl6N10O2,
a = 15.583(2), b = 7.0050(10), c = 13.796(2)Å, b=103.390(10)°,
V = 1465.0(4)Å3, Z = 2, Dc = 1.907 g cm 3, T = 293 K, l(Mo
Ka) = 2.038 mm 1, R1 = 0.0402 for 3317 data with I > 2s (I),
wR2 = 0.1030 (all data); (CCDC No. 204505 for 1 and CCDC No.
204506 for 2).