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

Abstract

Two copper(II) complexes, [CuL1]⋅2H2O (1) and [CuL2]⋅H2O (2) [where H2L1 {= N,N′-bis(3-methoxysalicylidene)propane-1,3-diamine} and H2L2 {=N,N′-bis(3-ethoxysalicylidene)propane-1,3-diamine} are potential hexadentate N2O4 donor compartmental Schiff bases], were synthesized and characterized. In each complex, copper(II) was placed in the inner N2O2 environment, with a four-coordinate distorted square planar environment keeping the outer O4 compartment pendant. Lattice water molecules were hydrogen bonded with the pendant O4 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.