Solvated Square-Planar Ternary Copper(II) Complexes: Solvent-Dependent Zipper and Columnar Structures

Two ternary copper(II) complexes having the general formula [Cu(pyp)X] with the tridentate Schiff base
2-N-(picolinylidene)phenol (Hpyp) and halide (X- = Cl-, Br-) as the ancillary ligand have been synthesized and characterized.
Both complexes exhibit solvatomorphism due to cocrystallization with different solvent molecules. Two cases have been
investigated:  (i) the dihydrated species [Cu(pyp)Cl]·2H2O (1) and [Cu(pyp)Br]·2H2O (2), isolated by slow evaporation of aqueous
methanol solution of the complexes, and (ii) the corresponding monomethanolic forms [Cu(pyp)Cl]·CH3OH (3) and [Cu(pyp)Br]·CH3OH (4), obtained by crystallization of 1 and 2 from dry methanol. To investigate the crystal compositions and packing features,
single-crystal X-ray diffraction measurements as well as thermogravimetric and differential scanning calorimetric measurements
have been carried out. In the context of structural features, the hydrated forms and also the monomethanolic forms are isomorphic.
The dihydrated form shows a zipperlike infinite chain structure through hydrogen bonding with the water molecules and π···π
interactions. The parallel zippers are again connected to each other through hydrogen bonding between the water molecules to give
a two-dimensional sheet structure. In contrast, the methanol-containing species form cyclic hydrogen-bonded dimeric host−guest
units which are π-stacked to one-dimensional columnar structures.