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.