Featuring the Role of Coordination Geometry in Effective CO2 Fixation in Lower-Dimensional Hybrid Copper Phosphonate Frameworks.

The rising atmospheric CO2 concentrations and their role in climate change necessitate the formulation of effective techniques for CO2 capture and utilization. The catalytic conversion of CO2 into valuable compounds offers a possible method for reducing its environmentally harmful effects. The present study explores the investigation of two amine-templated one-dimensional copper phosphonate frameworks: [C3N6H6][Cu2(H2hedp)]·H2O (I) and [C4N2H12][Cu3(hedp)2]·4H2O (II) via a hydrothermal synthetic strategy using H4hedp (1-hydroxyethane-1,1-diphosphonic acid) as the primary ligand and two different amines as templating agents under similar reaction conditions. The introduction of a neutral aromatic amine (melamine) and a protonated aliphatic amine (piperazine) plays a vital role in structural stabilization of lower-dimensional structures through hydrogen bonding interactions. Their catalytic efficiency was evaluated in the solvent-free cycloaddition of CO2 with epoxides under mild conditions. Compound I exhibited enhanced catalytic activity, attaining virtually complete conversion (∼99% yield), due to its four-coordinated unsaturated active Cu center and nitrogen-rich composition that improves hydrogen bonding interactions with substrates. Screening of the substrate scope with variable sizes confirms the proposed plausible mechanism. Both catalysts demonstrated exceptional recyclability, preserving structural integrity and catalytic efficacy throughout several catalytic cycles. This study highlights the potential of amine-templated metal phosphonate low-dimensional frameworks as robust, effective, and recyclable catalysts for CO2 fixation, aiding sustainable catalytic processes.