First homo- and hetero-nuclear complexes of a chemical messenger-histamine: Cu(II) complex being a supramolecular assembly based on hydrogen bond, Ni(II)⋯π and C–H⋯π non-covalent interactions

In this study, the first homo- and hetero-nuclear cyanocomplexes of histamine (His), namely, [Cu(His)2][Ni(CN)4], [Ni(His)2Ni(CN)4]n and [Cd(His)Ni(CN)4]n are investigated by X-ray diffraction (XRD) technique, electron paramagnetic resonance (EPR) and infrared (IR) spectroscopy. Besides being the first hetero-nuclear complex of histamine, [Cu(His)2][Ni(CN)4] complex has an interesting property as being a supramolecular structure constructed by three different non-covalent interactions as hydrogen bond, Ni(II)⋯π and C–H⋯π interactions. In [Cu(His)2][Ni(CN)4] complex histamine exists in gauche conformation and Nτ–H tautomeric form, and plays an important role in supramolecular structure formation by participating in non-covalent interactions through its aminoethyl side chain and imidazole group. The shifts and splittings in the stretching vibrations of cyano groups show that [Ni(His)2Ni(CN)4]n and [Cd(His)Ni(CN)4]n complexes are one-dimensional and three-dimensional coordination polymers, respectively. In [Ni(His)2Ni(CN)4]n complex, histamine acts as a chelating ligand by adopting gauche conformation. In [Cd(His)Ni(CN)4]n complex, Cd(II) ions and [Ni(CN)4]2− anions form two-dimensional layered structure and histamine has a novel bonding mode as a bridging ligand between these layered structures. It is concluded that histamine may have trans conformation and Nπ–H tautomer as a bridging ligand in [Cd(His)Ni(CN)4]n complex, which has not been reported so far for the solid structures of bidentate histamine. EPR studies on [Cu(His)2][Ni(CN)4] and Cu2+-doped [Cd(His)Ni(CN)4]n   complexes show that the ground state of the unpaired electron in both complexes is dominantly dx2-y2dx2-y2.

The adjacent supramolecular layers are linked by the imidazole groups of histamine.Figure optionsDownload as PowerPoint slideHighlights
► The first homo- and hetero-nuclear complexes of histamine are investigated.
► Histamine may have Nπ–H tautomeric form which has not been observed so far for bidendate histamine in solid state.
► Three noncovalent interactions emphasize the importance of noncovalent interactions in supramolecular complex formation.
► Study presents first coordination polymers of histamine as one-dimensional and three-dimensional structures.