[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)]1.5H(2)O (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-HO hydrogen bonds in [Ni(bpy)(mal)(H2O)(3)]H2O, whereas in [Ni(4,4-dmbpy)(mal)(H2O)(3)]1,5H(2)O the hydrogen bonded ribbons are linked by OH-O-HO hydrogen bonds with the participation of the additional water solvate molecule positioned on the twofold axis. In both structures, - 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 computational chemistry. Those confirm the dispersion-dominated stabilization of the 4,4-dmbpy supramolecular chain-like structure, with only marginal impact of cooperativity effects. Thermal decompositions of both complexes start with dehydration. Magnetic susceptibility studies performed from 2 to 300K revealed a dominant effect of the zero-field splitting of the Ni(II) ion, governing the low-temperature magnetic properties of both compounds. [GRAPHICS] .