Three Azamacrocycle-Based Coordination Complexes Bearing a New Triazine Derived Carboxylic Ligand Via In Situ Ligand Hydrolysis: The Trap of Resonance Structure

The in situ ligand hydrolysis reaction of 2,4,6-tris-(4-carboxyphenoxy)-1,3,5-triazine and macrocyclic complexes yields three coordination complexes bearing new triazine derived carboxylic ligands, namely, {(NiL₁)(L₀)·DMF}_n (1), {(NiL₂)(L₀)·DMF·H₂O}_n (2), and [NiL₃][(NiL₃)(L₀)₂]·2H₂O (3) (L_o = 4-(6-Hydroxy-4-oxo-4,5-dihydro-[1,3,5]triazine-2-yloxy)-benzoic acid, L₁ = 1,4,8,11-tetraazacyclotetradecane, L₂ = 1,8-dimethyl-1,3,6,8,10,13-hexaazacyclotetradeca and L₃ = 1,3,6,9,11,14-hexaazatricyclooctadecane). Single-crystal X-ray diffraction analyses reveal that 1 and 2 exhibit a one-dimensional (1D) chain structure, which is further connected into a three-dimensional (3D) supramolecular structure by hydrogen bonds. In complex 2, π···π stacking interaction is observed. In contrast, 3 shows a ion-pair structure, which is connected into a 2D 4⁴ hydrogen bonded supramolecular structure. The results indicate the subtle difference of azamacrocycle may lead to diverse structures. Importantly, in complexes 1–3, the resonance structure is trapped in crystals 1–3.