Influence of temperature on the crystallization of Cu^II complex with tetradentate Schiff base

The complex of copper(II) with N₂O₂ Schiff base, 2,2′-[1,3-propanediyl)bis(nitriloeth-1-yl-1-ylidene)]diphenol (H₂L), has been synthesized from methanol. Crystallization of the complex was conducted at room temperature (20 °C) and at 4 °C. Carrying out the crystallization process at various temperatures leads to the formation of two different complexes CuL·MeOH (1) and [{Cu₂L₂}{CuL}₂]·2MeOH (2). The Schiff base and its complexes were characterized by elemental analysis, X-ray crystallographic techniques, spectroscopic (UV–Vis, IR), and thermal (TG\DSC) methods. Complex 1 crystallizes in the monoclinic space group P2₁/c. The N₂O₂ core forms a tetrahedrally distorted square-planar geometry around the metal center. Crystallization of 2 took place in the centrosymmetric triclinic space group (P). In the structure of 2 there are two crystallographically different Cu^II ions, one is four-coordinate in a square planar geometry, whereas the second has a five-coordinate square pyramidal geometry. The complexes are stable at ambient temperature. After heating at first they lose methanol molecules, then the organic part undergoes gradual fragmentation and combustion.