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].