Chemistry Reference
In-Depth Information
Figure 4.34
2D framework of [Ag(
µ
-9-allyladenine-
N1
,
N7
)(
µ
-NO
3
)(NH
3
)]
n
compound
and square pyramidal silver atoms bridged by adenine molecules. The adenine
coordinates through N1 to the tetracoordinated metal centre and through N7 to the
pentacoordinated one. This generates a helical strand in which the two metal centres
alternate. The helical coordination chain possesses two adenine residues per turn
with a pitch of
2.5
Å
′
. The crystal structure is completed by the presence of bridging
nitrate counterions binding to the helical strands via silver ions. The authors were
able to deposit this compound on highly oriented pyrolitic graphite retaining the
solid-state structure, as confi rmed by noncontact mode AFM micrographs. Deposi-
tion on alternative substrates such as Si(100), or mica, lacked obvious pattern forma-
tion, suggesting that known adenine- graphite interactions
40
play a role in the
preferential orientation observed on graphite. The authors describe these results in
the context of efforts to functionalize surfaces for advanced nanoscale applications
by means of shape-persistent coordination motifs (Figure 4.34).
41- 42
∼
4.3.3 3 D Coordination Polymers
Nucleobases as Bridging Ligands.
In spite of the great number of potential donor atoms of the nucleobases, especially
in the case of adenine, examples of 3D coordination polymers containing bridging
nucleobases are as of today limited to just two different types of structures: one 3D
porous coordination polymer and a family of isostructural luminiscent 3D polymers.
The fi rst example is the {[Cu
2
( m - ade)
4
(H
2
O)
2
][Cu(ox)(H
2
O)]
2
· 14H
2
O}
n
compound
which shows a 3D coordination network, where the Cu(II) centres are bridged by
tridentate m -
N3,N7,N9
- adeninato ligands (Figure 4.35 ).
43
The crystal structure is
constructed of two distinct types of neutral building blocks: windmill shaped dimeric
[Cu
2
( m - ade)
4
(H
2
O)
2
] units and mononuclear [Cu(ox)(H
2
O)] entities. The deprotona-
tion of the adenine molecules allows the N9 position to act as a donor and in this
