Structural Diversity in a Copper(II)/Isophthalato/9-Methyladenine System. From One- to Three-Dimensional Metal-Biomolecule Frameworks

The synthesis, X-ray single crystal
structure analyses, and physicochemical
characterization of copper­(II)-isophthalato coordination polymers
containing the 9-methyladenine nucleobase {[Cu­(μ-iso)­(9Meade)­(H2O)2]}n (1), {[Cu­(μ-iso)­(μ-9Meade)]}n (2), {[Cu2(μ4-iso)2­(9Meade)2]­·2H2iso}n (3), {[Cu2(μ3-iso)2­(μ-9Meade)­(H2O)]·H2O}n (4), and {[Cu2(μ3-iso)2­(μ-9Meade)­(H2O)2]­·1.5H2O}n (5) (where iso = isophthalato and
9Meade = 9-methyladenine) are reported. Compound 1 contains
neutral chains in which the isophthalato dianion acts as a bridging
ligand, while the methylated nucleobase behaves as N7-coordinated
terminal ligand. Compound 2 exhibits a two-dimensional
network in which the aromatic dicarboxylate ligand and the nucleobase
act as bidentate bridging ligands. Compound 3 is based
on dimeric paddle-wheel shaped entities in which the copper­(II) atoms
are bridged by means of four isophthalato ligands to give a NO4 chromophore with the N7 nitrogen atom of the 9-methyladenine
filling the axial position. The linkage of the dimeric entities through
the second carboxylate group of the dianions leads to covalent layers
that are further connected to give a supramolecular three-dimensional
pillared structure by means of hydrogen bonding and π–π
interactions involving noncoordinated isophthalic acid molecules.
Compounds 4 and 5 contain paddle-wheel [Cu2(μ-iso)4­(9Meade)2] entities
and [Cu­(H2O)] or [Cu­(H2O)2] units
connected by means of the isophthalate and 9-methyladenine bidentate
bridging ligands.