[Ni(bpy)(mal)(H2O)3]·H2O and [Ni(4,4′-dmbpy)(mal)(H2O)3]·1.5H2O: syntheses, crystal structures, magnetic properties, and computational study of stacking interactions

[Ni(bpy)(mal)(H2O)3]·H2O and [Ni(4,4′-dmbpy)(mal)(H2O)3]·1.5H2O (mal = maleato; bpy = 2,2′-bipyridine; 4,4′-dmbpy = 4,4′-dimethyl-2,2′-bipyridine) exhibit molecular crystal structures. The Ni(II) central ions in both complexes are six-coordinate by one chelate bonded L–L ligand, three aqua ligands, and one position is occupied by a maleato oxygen donor atom. Hydrogen bonded ribbon-like supramolecular structural motifs are present in both studied complexes; these are linked by weaker C–H⋯O hydrogen bonds in [Ni(bpy)(mal)(H2O)3]·H2O, whereas in [Ni(4,4′-dmbpy)(mal)(H2O)3]·1,5H2O the hydrogen bonded ribbons are linked by O⋯H-O-H⋯O hydrogen bonds with the participation of the additional water solvate molecule positioned on the twofold axis. In both structures, π–π stacking interactions with different patterns in respective structures were found. The role of dispersion energy and many-body effects in the stabilization of bpy and 4,4′-dmbpy stacking interactions were investigated using methods of comput...