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

Abstract

In this study, the first homo- and hetero-nuclear cyanocomplexes of histamine (His), namely, [Cu(His)<inf>2</inf>][Ni(CN)<inf>4</inf>], [Ni(His)<inf>2</inf>Ni(CN)<inf>4</inf>]<inf>n</inf> and [Cd(His)Ni(CN) <inf>4</inf>]<inf>n</inf> 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) <inf>2</inf>][Ni(CN)<inf>4</inf>] 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)<inf>2</inf>][Ni(CN)<inf>4</inf>] 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)<inf>2</inf>Ni(CN)<inf>4</inf>]<inf>n</inf> and [Cd(His)Ni(CN) <inf>4</inf>]<inf>n</inf> complexes are one-dimensional and three-dimensional coordination polymers, respectively. In [Ni(His)<inf>2</inf>Ni(CN) <inf>4</inf>]<inf>n</inf> complex, histamine acts as a chelating ligand by adopting gauche conformation. In [Cd(His)Ni(CN)<inf>4</inf>]<inf>n</inf> complex, Cd(II) ions and [Ni(CN)<inf>4</inf>]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)<inf>4</inf>]<inf>n</inf> complex, which has not been reported so far for the solid structures of bidentate histamine. EPR studies on [Cu(His)<inf>2</inf>][Ni(CN)<inf>4</inf>] and Cu2+-doped [Cd(His)Ni(CN)<inf>4</inf>]<inf>n</inf> complexes show that the ground state of the unpaired electron in both complexes is dominantly dx2. © 2011 Elsevier Ltd. All rights reserved.