Structural Flexibilities and Gas Adsorption Properties of One-Dimensional Copper(II) Polymers with Paddle-Wheel Units by Modification of Benzoate Ligands

CO2 and N2 gas adsorption/desorption properties of
one-dimensional copper­(II) polymers with paddle-wheel units [CuII2(p-XBA)4(pyrazine)]∞ were successfully controlled through
the tuning of interchain interactions by modification of para-substituent
X groups on the benzoate (BA) ligands (X = Cl, Br, I, and OCH3). Although none of the four crystals had sufficient void
space to integrate the crystallization solvents, gate-opening gas
adsorption and desorption behaviors coupled with structural phase
transitions were observed for CO2 (T =
195 K) and N2 (T = 77 K), with differences
depending on the precise substituent. van der Waals interchain interactions,
specifically π···π, halogen···π,
and C–H···π contacts, were dominant in
forming the crystal lattice; their magnitude was associated with gate-opening
pressure and hysteresis behaviors. Both the type and magnitude of
the interactions were evaluated by Hirshfeld surface analysis, which
indicated that structural flexibility decreased as larger halogen
atoms were included. Overall, weak interchain interaction and structural
flexibility generated new void spaces to adsorb CO2 and
N2 gases.