Crystallographic and computational investigation of nitrate salts of nickel(II) ethylenediamine complexes

Two nitrate salts of Ni(II) and ethylenediamine (en), trans-diaquabis(ethylenediamine)nickel(II) nitrate (1) and Λ-δδδ-tris(ethylenediamine)nickel(II) nitrate (2), were investigated crystallographically and the nature of the intermolecular interactions in 2 were explored using the quantum theory of atoms in molecules (QTAIM) of Bader from a X3LYP/6–31 + G(d) single point calculation on a portion of the crystal structure. In 1 the two chelate rings, related by inversion, are in the λ and δ conformations, respectively. The metal complex cations are hydrogen bonded to the axial H2O ligands and the amino protons and pack in ribbons along the crystallographic a axis. In 2, which is the enantiometric form of the known Δ-λλλ-tris(ethylenediamine)nickel(II) nitrate, each nitrate is in a distorted tetrahedral site defined by [Ni(en)3]2+ cations. QTAIM analysis indicates that NO3− forms O····HN hydrogen bonds to amino groups of en, as well as a O····HC hydrogen bond to one of the methylene groups of the ligand. In addition, neighbouring [Ni(en)3]2+ ions are connected by a weak H–H bond between en methylene groups.