Introduction of an aromatic phenyl ring at the N9 position of
adenine leads to 9-benzyladenine (5), exhibiting a monodentate
coordination mode via N1 alone resulting in a dimeric silver
complex. Such an arrangement is rarely observed for adenine thus,
there are very few reports depicting the N1–M–N1 coordination
mode for the adenine moiety.8
The asymmetric unit consists of silver ion coordinated to N1
nitrogens of two adenine moieties while the other two coordination
sites were occupied by a nitrate oxygen and an acetonitrile
molecule, thus acquiring a distorted tetrahedral geometry around
the silver ion. N6-hydrogen atoms of the adenine moiety are
involved in the hydrogen bonding with nitrate oxygen as well as the
N7 nitrogen of the adjacent adenine. Additionally, intermolecular
hydrogen bonding interactions between the oxygen atoms of the
nitrate anion and the C8-H of the adjacent adenine molecules
further stabilizes the crystal lattice (Fig. 5).
the coordination mode to afford either linear chain via N1
and N7 coordination or a dimeric species with rare N1–Ag–N1
coordination. These results may be helpful in understanding the
binding of silver ion with nucleic acids, leading to conformational
transitions.
X-Ray crystal data were collected on a Bruker SMART APEX
CCD diffractometer instrument using graphite-monochromated
Mo KR radiation (l = 0.71073). The hexyl and nonyl chains in
3 and 4 are disordered and solved by using various restraints,
like DFIX, ISOR etc. All non-hydrogen atoms are refined
anisotropically and hydrogen atoms are placed at geometrically
idealized position. Crystal data for 1: C10H12Ag2N14O14, M =
˚
768.08, Monoclinic, a = 6.5283(17), b = 8.175(2), c = 20.896(5) A,
3
˚
b = 95.687(4), U = 1109.7(5) A , T = 100(2) K, space group =
P21/c (no. 14), Z = 2, 6942 reflections measured, 2727 unique
(Rint = 0.0390) which were used in all calculations. R1 = 0.0440 (I >
2s(I)], The final wR(F2) was 0.1870 (all data). Crystal data for
2: C8H11AgClN5O4.5, M = 392.54, Orthorhombic, a = 25.146(5),
3
˚
b = 25.516(4), c = 7.849(3), U = 5036(2) A , T = 100(2) K, space
group = Fdd2 (no. 43), Z = 16, Flack parameter = -0.18(11),
7959 reflections measured, 2683 unique (Rint = 0.0533) which were
used in all calculations. R1 = 0.0498(I > 2s(I)), The final wR(F2)
was 0.1987 (all data). Crystal data for 3: C39H57Ag4N24O16, M =
1549.57, Monoclinic, a = 18.577(4), b = 7.346(5), c = 25.747(3),
3
˚
b = 103.013(5), U = 3423(3) A , T = 100(2) K, space group =
P21/c (no. 14), Z = 2, 21565 reflections measured, 8482 unique
(Rint = 0.1001) which were used in all calculations. R1 = 0.0997(I >
2s(I)), The final wR(F2) was 0.3383 (all data). Crystal data for
4: C55H91Ag4N24O16, M = 1776.00, Monoclinic, a = 20.600(3),
Fig. 5 Part of the crystal lattice showing hydrogen bonding interactions
(dotted lines) between N6-H and C8-H of the adenine moiety with
nitrate oxygen along with N6-H with N7 nitrogen of the adenine moiety.
Highlighted portion reveals monodentate coordination mode for the
adenine moiety resulting in mononuclear dimeric species.
3
˚
b = 7.1530(11), c = 25.954(4), b = 93.326(5), U = 3817.9(10) A ,
T = 100(2) K, space group = P21/c (no. 14), Z = 2, 23423
reflections measured, 9349 unique (Rint = 0.0692) which were used
in all calculations. R1 = 0.0749(I > 2s(I)),The final wR(F2) was
0.2242 (all data). Crystal data for 5: C26H25AgN12O3, M = 661.45,
Orthorhombic, a = 23.072(4), b = 19.976(5), c = 6.025(4), U =
3
˚
Part of the crystal lattice when viewed along the c-axis reveals
extensive p–p stacking interactions between the adjacent adenine
moieties where the distance between the centroids of the ade-
2777(2) A , T = 100(2) K, space group = Pnma (no. 62), Z = 4,
14489 reflections measured, 2818 unique (Rint = 0.0690) which were
used in all calculations. R1 = 0.0404(I > 2s(I)), The final wR(F2)
was 0.1197 (all data).
˚
nine units is found to be 3.56(6) A (Fig. S5, ESI†). Significant
stacking interaction has also been observed between adjacent
benzyl substituents, thereby stabilizing the crystal lattice.
Caution! Perchlorate salts are potentially hazardous, and should
be handled with care.
In conclusion, we have systematically explored the silver-
adenine coordination mode with varying substituents at the
N9 position. Scheme 2 represents the variation in coordination
sites resulting in different structural patterns, in N9-substituted
adenine-silver complexes. While smaller substituents at the N9
position results in a unique m-N1,N3,N7 coordination mode
leading to metallaquartet formation, larger substituents affect
Notes and references
1 (a) B. Pan, Y. Xiong, K. Shi, J. Deng and M. Sundaralingam, Structure,
2003, 11, 815; (b) B. Pan, Y. Xiong, K. Shi and M. Sundaralingam,
Structure, 2003, 11, 825.
2 (a) V. Esposito, A. Randazzo, A. Galeone, M. Varra and L. Mayol,
Bioorg. Med. Chem., 2004, 12, 1191; (b) E. Gavathiotis and M. S. Searle,
Org. Biomol. Chem., 2003, 1, 1650; (c) P. K. Patel, A. S. Koti and R. V.
Hosur, Nucleic Acids Res., 1999, 27, 3836; (d) J. Suhnel, Biopolymers,
2001, 61, 32; (e) J. Gu and J. Leszczynski, Chem. Phys. Lett., 2001, 335,
465.
3 (a) P. Amo-Ochoa, P. J. S. Miguel, P. Lax, I. Alonso, M. Roitzsch, F.
Zamora and B. Lippert, Angew. Chem., Int. Ed., 2005, 44, 5670; (b) B.
Knobloch, R. K. O. Sigel, B. Lippert and H. Sigel, Angew. Chem., Int.
Ed., 2004, 43, 3793.
4 (a) C. S. Purohit, A. K. Mishra and S. Verma, Inorg. Chem., 2007, 46,
8493; (b) C. S. Purohit and S. Verma, J. Am. Chem. Soc., 2006, 128,
400.
5 (a) A. K. Mishra, C. S. Purohit and S. Verma, CrystEngComm,
2008, 10, 1296; (b) J. Kumar and S. Verma, Inorg. Chem., 2009, 48,
6350.
Scheme 2 Pictorial representation of the varying complexity of silver
adenine complexes as a result of N9 substitution.
10036 | Dalton Trans., 2010, 39, 10034–10037
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