CO ₂ and C ₃ O Puthiyavalappil K. Arathi, Mini Bharati Ahirwar, Cherumuttathu H. Suresh

ABSTRACT

A density functional theory study of CO ₂ and the cyclic trimer 1,3,5‐trioxanetrione (C ₃ O ₆ ) coordination to Ni ²⁺ , Cu ²⁺ , and Zn ²⁺ is presented to elucidate how metal identity, ligand topology, and coordination environment govern multiligand binding thermodynamics. In the absence of coordinating anions, both CO ₂ and C ₃ O ₆ follow an intrinsic affinity order of Ni ²⁺  > Cu ²⁺  > Zn ²⁺ . Successive ligand addition leads to cumulative stabilization for all metals, while decreasing per‐ligand interaction and free energies indicate progressive electronic saturation and coordination‐sphere crowding. Coordination of C ₃ O ₆ induces localized structural activation, reflected in characteristic C–O bond distortions that follow the same metal‐dependent trend. The ligand environment significantly modulates binding: weakly coordinating BF ₄ ⁻ counterions reduce interaction strengths and alter relative affinities, whereas coordinating Cl ⁻ ligands occupy metal coordination sites and limit ligand accessibility. Despite these effects, Ni ²⁺ retains favorable binding across coordination numbers, while Cu ²⁺ and Zn ²⁺ show more limited coordination. Comparison with equivalent monomeric CO ₂ assemblies reveals that the C ₃ O ₆ binding mode provides enhanced metal–ligand stabilization per CO ₂ equivalent, arising from its cyclic, multidentate nature. Although this stabilization partially compensates the intrinsic endothermicity associated with C ₃ O ₆ formation, the process remains thermodynamically uphill with respect to CO ₂ . Overall, the results highlight the interplay of metal electronic structure, coordination‐sphere crowding, counterion effects, and ligand preorganization in governing multiligand CO ₂ binding.