Metal Complexes of 1,4-Bis(2-Hydroxyethyl) Piperazine: Thermodynamic and Theoretical Approach

In the present study, the acid-base equilibria of 1,4-bis(2- hydroxyethyl)piperazine (BHEB) and the formation equilibria of complexes with the metal ions Cu(II), Ni(II), Co(II),and Zn(II) are investigated using the potentiometric technique. The aciddissociation constants of BHEP in the protonated form and the formation constants of the complexes are determined using the Miniquad-75 program in the temperature range (of15oC - 35oC). The thermodynamic parameters were determined and discussed. The concentration distribution diagrams of the complexes are evaluated. The effect of metal ion properties such as atomic number, ionic radius, electronegativity, and ionization potential are investigated. The complexes were synthesized and characterized by elemental analysis and mass spectra. Density Functional Theory (DFT) calculations have been performed to study the equilibrium geometry of 1,4-bis(2-hydroxyethyl)piperazine and its complexes. The optimization of the structure of the complexes reveals that CuIIand CoIIcomplexes have distorted octahedral geometry. NiIIcomplex has a distorted square planar geometry.ZnIIcomplex has a distorted tetrahedral geometry. The calculated total energies, energies of the highest occupied molecular orbital ( HOMO), energies of the lowest unoccupied molecular orbital (LUMO), and dipole moments are reported. The N---N distance for uncoordinated 1,4-bis(2- hydroxyethyl)piperazine is calculated to be 2.870 angstrom and decreased to 2.588 angstrom, 2.491 angstrom, 2.502 angstrom, 2.479 angstrom, and 2.552 angstrom for Cu(II), Co(II), Ni(II) and Zn(II) complexes respectively. Also, bonds connected to N atoms are elongated upon complex formation. The interactions with the receptors as breast cancer oxidoreductase were feasible as evidencedby Docking analysis.