Magnetic, structural and computational studies on transition metal complexes of a neurotransmitter, histamine

In this study, the transition metal complexes of histamine (His) prepared with oxalate (Ox), that is, [Cu(His)(Ox)(H2O)], [Zn(His)(Ox)(H2O)] (or [Zn(His)(Ox)]·(H2O)), [Cd(His)(Ox)(H2O)2] and [Co(His)(Ox)(H2O)], are investigated experimentally and computationally as part of ongoing studies on the mode of complexation, the tautomeric form and non-covalent interactions of histamine in supramolecular structures. The structural properties of prepared complexes are experimentally studied by X-ray diffraction (XRD) technique and Fourier transform infrared (FT-IR) spectroscopy and computationally by density functional theory (DFT). The magnetic properties of the complexes are investigated by electron paramagnetic resonance (EPR) technique. The [Cu(His)(Ox)(H2O)] complex has a supramolecular structure constructed by two different non-covalent interactions as hydrogen bond and C–H⋯π interactions. EPR studies on [Cu(His)(Ox)(H2O)], Cu2+-doped [Zn(His)(Ox)(H2O)] and [Cd(His)(Ox)(H2O)2] complexes show that the paramagnetic centers have axially symmetric g values. It is also found that the ground state of the unpaired electrons in the complexes is dominantly d x 2 - y 2 and unpaired electrons’ life time is spent over this orbital.