Crystal Engineering with 2‑Aminopurine Containing a Carboxylic Acid Pendant

This article reports synthesis, design, and luminescent properties of a series of structurally interesting coordination frameworks prepared from a modified purine ligand, 3-(2-amino-9<i>H</i>-purin-9-yl) propanoic acid (<b>L</b>). Corresponding transition metal complexes reported in this study were unambiguously characterized by X-ray crystallography to reveal an array of diverse crystallographic signatures reflecting crystal design around varying coordination geometries of a central metal ion. While silver complex <b>1</b> [C₁₆H₁₈Ag₂N₁₀O₅] affords formation of coordination framework with embedded dimeric, tetrameric, and pentameric metallacycles, corresponding copper complexation results in a discrete dimer <b>2</b> [C₃₂H₄₆Cl₂Cu₂N₂₀O₁₄]. Changing the counteranion from strongly coordinating chloride ion to weakly coordinating perchlorate anion resulted in the formation of a 1D coordination polymer <b>3</b> [C₁₈H₂₆Cl₂CuN₁₀O₁₄]. Cobalt complexes <b>4</b> [C₁₆H₃₂CoN₁₀O₁₂] and <b>5</b> [C₁₆H₃₀CoN₁₂O₁₆] yielded 2D grid-type assembly and a discrete dimer, respectively. Change in pH offered an interesting effect on the structural outcome of cadmium complexes: acidic and neutral conditions lead to the formation of 1D coordination polymer <b>6</b> [C₈H₁₂CdCl₂N₆O₆] and <b>7</b> [C₁₆H₂₄Cd₂N₁₂O₁₄], while basic conditions yielded an unusual porous metal organic framework <b>8</b> [C₉H₁₅CdN₅O_5.5]