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

Abstract

In this study, the first homo- and hetero-nuclear cyanocomplexes of histamine (His), namely, [Cu(His)(2)] [Ni(CN)(4)], [Ni(His)(2)Ni(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 heteronuclear 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). and C-H center dot center dot center dot pi interactions. In [Cu(His)(2)][Ni(CN)(4)] complex histamine exists in gauche conformation and 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)(2)Ni(CN)(4)](n) and [Cd(His)Ni(CN)(4)](n) complexes are one-dimensional and three-dimensional coordination polymers, respectively. In [Ni(His)(2)Ni(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 N pi-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 d(x2-y2). (C) 2011 Elsevier Ltd. All rights reserved.