198 Topics in Current Chemistry Editorial Board: A. de Meijere KN ...

Functional Organic Zeolite Analogues 137
ty of the cavities, the channels can be designed in a more straightforward
manner by letting porous 2D nets stack sheet by sheet. Pillared clays and
graphite, in contrast to zeolites and diamond, represent typical layer structures.
Porous 2D nets are obtained by assembling planar tri- or tetratopic building
blocks directly or via connectors. Layered 2D nets may be classified according to
the types of intersheet interactions.
When assembled with Cd II (Cd(NO 3 – )2◊ 2H 2O) as a linear (trans) or bent (cis)
2-connector, the above-mentioned tetra(4-pyridyl)porphyrin (3; X=N and
M=Pd II ) forms a (4,2)-connected 2D net 17 (Fig. 4) [43].
The same Cd II ion in Cd(NO 3 – )2 acting in this case as a square planar
4-connector is used to assemble 4,4¢-bipyridine 18 as a bidentate linear ligand to
afford a (2,4)-connected 2D net 19 (Fig. 5) [44].
Tritopic tricyano derivative 20 [41] or 22 [45] and the Ag I ion (AgOTf) in the
trigonal-bipyramidal geometry form a (3,3)-connected 2D net composed of a
hexagonal 21 or 12-annulene-like cyclic motif 23, respectively (Figs. 6 and 7).
The resulting molecular sheets stack vertically to form channels incorporating
solvent molecules and counter anions; the intersheet distances depend on
the extent of coplanarity of the in-sheet aromatic moieties and are 4.68, 6.30,
17
Fig. 4. 2D net formed by 3◊ Cd(OH 2) 2(NO 3) 2 (X=N and M=Pd II ). The sheets (17) are layered
to give intersheet channels