<scp> CO ₂ </scp> and <scp> C ₃ O ₆ </scp> Coordination to Ni ²⁺ , Cu ²⁺ , and Zn ²⁺ : Metal‐Dependent Multiligand Binding and Counterion Effects

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+ &gt; Cu 2+ &gt; 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.