Solid-State Coexistence of Neutral and Ionic Cadmium Complexes: A Lattice-Stabilized Mixed-Crystal System

We report a rare case of solid-state cocrystallization involving both neutral and ionic Cd(II) complexes, [CdL(NO3)2] (2a) and [CdL(H2O)(NO3)]NO3 (2b), within a single lattice-stabilized mixed-crystal system, where L is a flexible morpholine-based ligand. The neutral species adopts an unusual staggered cis-κ1-nitrate coordination stabilized by intramolecular hydrogen bonding, while the ionic component incorporates outer-sphere nitrate ions that participate in complementary lattice interactions. Single-crystal X-ray diffraction reveals that cooperative hydrogen-bonding and packing effects enable the coexistence of these chemically distinct species within a common asymmetric unit. Density functional theory calculations indicate that, although the ionic form is thermodynamically disfavored in solution, it is preferentially stabilized in the solid state. Collectively, these results demonstrate how ligand flexibility and secondary supramolecular interactions can dictate crystal growth outcomes by stabilizing mixed-crystal lattices composed of structurally divergent coordination species.