Cooperativity and Anticooperativity Effects in a Cadmium-Based Metal-Organic Framework: Structural Characterization,...

Two polynuclear cadmium(II)-based metal-organic framework complexes, [CdL¹bpy]_n·nH₂L¹(1) (H₂L¹ = 4-hydroxy-7-(trifluoromethyl)quinoline-3-carboxylic acid, bpy = 4,4'-bipyridine) and [CdL²ClH₂O]_n(2) (HL² = 3-(5-phenyl-1,3,4-oxadiazol-2-yl)propanoic acid), were successfully synthesized, and their structures and properties were thoroughly characterized by single crystal elemental analysis, X-ray diffraction, thermogravimetric analysis, and density functional theory (DFT) studies. The metal centers are found to be six-coordinated with a distorted octahedral geometry around them. Both the complexes show few significant hydrogen bonding interactions to produce supramolecular networks. Complexes 1 and 2 are observed to produce three-dimensional and two-dimensional polymeric network architectures, respectively. Furthermore, a computational analysis was performed using DFT to quantitatively and qualitatively gain insight into the role of the noncovalent interactions (NCIs) that stabilize the three-dimensional architecture of complex 1. Specifically, molecular electrostatic potential surfaces, quantum theory of atoms in molecules, and NCI plot index analysis were employed to characterize H-bonding, π-stacking, and weak CH···π interactions involving the discrete H₂L¹ cocrystallized units. Energy calculations were utilized to compare the strength of the H-bonding and π-stacking motifs and to assess cooperativity effects in the overall supramolecular assembly. Moreover, complex 1 exhibited higher catalytic efficacy for the Knoevenagel condensation reaction at room temperature, reflecting the structural advantages of its three-dimensional architecture. It also showed high stability and could be recycled for up to four catalytic cycles with comparable catalytic activity.