Two New Adenine-Based Co(II) Coordination Polymers: Synthesis, Crystal Structure, Coordination Modes, and Reversible Hydrochromic Behavior

We report the synthesis of two new
three-dimensional coordination
polymers (CPs) based on Co­(II), adenine, and aromatic tetracarboxylate
linkers. Adenine exhibits bidentate binding modes in both CPs, coordinating
through the N3 and N9 sites in a first compact
CP and through the more rare N3 and N7 sites
in a second open, flexible, and H2O-responsive CP. These
differences together with an analysis of the extended coordination
structures made of adenine reported in the Cambridge Structural Database
illustrate the rich coordination versatility of adenine as a building
block for CPs. Although the latter CP is nonporous to N2 or CO2, it shows a reversible and detectable color change
from pink to purple, and vice versa, upon hydration
and dehydration, respectively.