Synthesis, structural, Hirshfeld surfaces, Infrared-Raman spectroscopy, and DFT-Monte Carlo-DM quantum studies of monocalcium dihydrogenomonophosphate monohydrate Ca(H2PO4)2•H2O intended for corrosion inhibition of mild steel in 1 M HCl solution

The present study reports structural, vibrational, surface interactions analyses and (DFT-M-DM) computational results of the monocalcium dihydrogenomonophosphate monohydrate Ca(H2PO4)2.H2O synthetized using slow evaporation of solution containing stoichiometric amounts of H3PO4 and CaCO3 reagents. The obtained material crystallized in triclinic centrosymmetric space group P-1 (Z=2) with unit cell parametres: a=5.6770(7) & Aring;, b=6.3070(11) & Aring;, c=11.9940(17) & Aring;, alpha=92.670(10)degrees, beta=96.610(10)degrees, gamma=114.170(10)degrees. The crystal structure, determined at (R=0.0431, wR2=0.0401), consists of layers of corner-connected CaO7(Ow) and [H2PO4]- phosphate polyhedra, involving divers O center dot center dot center dot O bonds varying from 2.561 to 2.937 & Aring;, with an average of 2.718 & Aring;. Infrared Raman vibrational study is made based on factor group analysis and compared with phosphate materials, which identified the H2PO4-groups and water molecules, linked by hydrogen bonding. Hirshfeld surface analysis showed the crystal packing surface dominated by O...H/H...O intercontacts (48.9%), in agreement with structural and vibrational results. Density functional theory B3LYP/6-311+G(2d,p), and Monte Carlo/Molecular Dynamics (MC/MD) methods are used at atomic and molecular scales to correlate electronic donor-acceptor interactions properties with adsorption and inhibitory actions of the studied material. HOMO-LUMO band gap estimated at 5.113 eV indicate good stability and promising semi-conducting behavior of Ca(H2PO4)2.H2O. The good adsorption on the steel substrate Fe (110) in 1 M HCl solution suggest this crystal as an effectiveness inhibitor for corrosion applications.