A Combined Experimental and Theoretical Study on the Formation of a Cyclic Tetrameric Water Cluster and a Similar Type of Cyclic Cluster in Copper(II) Schiff Base Complexes

Two copper(II) complexes, [CuL 1 ]⋅2H 2 O ( 1 ) and [CuL 2 ]⋅H 2 O ( 2 ) [where H 2 L 1 {= N,N′‐bis(3‐methoxysalicylidene)propane‐1,3‐diamine} and H 2 L 2 {=N,N′‐bis(3‐ethoxysalicylidene)propane‐1,3‐diamine} are potential hexadentate N 2 O 4 donor compartmental Schiff bases], were synthesized and characterized. In each complex, copper(II) was placed in the inner N 2 O 2 environment, with a four‐coordinate distorted square planar environment keeping the outer O 4 compartment pendant. Lattice water molecules were hydrogen bonded with the pendant O 4 compartments of the Schiff base ligands. Both complexes formed self‐assembled dimers via chelate ring⋅⋅⋅chelate ring and C–H⋅⋅⋅π interactions. A cyclic tetrameric water cluster was stabilized by the oxygen rich region of the Schiff‐base ligand in complex 1 . A similar type of cyclic cluster involving two water molecules was also observed in complex 2 . These supramolecular assemblies were analysed via a DFT study at the M06‐2X/def2‐TZVP level of theory.