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]}_<i>n</i> (<b>1</b>), {[Cu­(μ-iso)­(μ-9Meade)]}_<i>n</i> (<b>2</b>), {[Cu₂(μ₄-iso)₂­(9Meade)₂]­·2H₂iso}_<i>n</i> (<b>3</b>), {[Cu₂(μ₃-iso)₂­(μ-9Meade)­(H₂O)]·H₂O}_<i>n</i> (<b>4</b>), and {[Cu₂(μ₃-iso)₂­(μ-9Meade)­(H₂O)₂]­·1.5H₂O}_<i>n</i> (<b>5</b>) (where iso = isophthalato and 9Meade = 9-methyladenine) are reported. Compound <b>1</b> contains neutral chains in which the isophthalato dianion acts as a bridging ligand, while the methylated nucleobase behaves as N7-coordinated terminal ligand. Compound <b>2</b> exhibits a two-dimensional network in which the aromatic dicarboxylate ligand and the nucleobase act as bidentate bridging ligands. Compound <b>3</b> 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 <b>4</b> and <b>5</b> 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