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-9H-purin-9-yl) propanoic acid (L). 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 1 [C16H18Ag2N10O5] affords formation of coordination framework with embedded dimeric, tetrameric, and pentameric metallacycles, corresponding copper complexation results in a discrete dimer 2 [C32H46Cl2Cu2N20O14]. Changing the counteranion from strongly coordinating chloride ion to weakly coordinating perchlorate anion resulted in the formation of a 1D coordination polymer 3 [C18H26Cl2CuN10O14]. Cobalt complexes 4 [C16H32CoN10O12] and 5 [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 6 [C8H12CdCl2N6O6] and 7 [C16H24Cd2N12O14], while basic conditions yielded an unusual porous metal organic framework 8 [C9H15CdN5O5.5].