Cost-effective new Mannich bases 1-(pyridin-4-yl­(pyrrolidin-1-yl)­methyl)­urea (UPyP), 1-(morpholino­(pyridin-4-yl)­methyl)­urea (UMP), and 1-(piperidin-1-yl­(pyridin-4-yl)­methyl)­urea (UPP) were synthesized, characterized, and examined as corrosion inhibitors for the corrosion of a mild steel surface in 1.0 M hydrochloric acid (HCl) solution using weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) measurements. The X-ray structures of UMP and UPP are reported. The inhibition efficiency increases with increasing inhibitor concentration and decreases with increasing solution temperature. Potentiodynamic polarization measurements showed that all inhibitors are mixed type. The values of thermodynamic and activation parameters were calculated and discussed. Adsorption of inhibitors on the mild steel surface in the presence of HCl follows Langmuir’s adsorption isotherm. The relationship between molecular structure and their inhibition efficiencies has been studied using density functional theory (DFT) calculations. Experimental and theoretical results are in good agreement.

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We are reporting structural characterization of two new hexanuclear cages (H3O)2[Cu3(μ3-OH)(μ3-NH3)(0.5)(L)3]2·8H2O (1) and (H3O)2[Cu3(μ3-OH)(μ3-H2O)(0.5)(L)3]2·8H2O (1a) where L(2-) is the dianionic form of the Schiff base of L-alanine and salicylaldehyde. The complex 1 has two C3 symmetric hydroxo bridged trinuclear halves joined by an ammonia or water molecule at the center through H-bonding. Each of the trinuclear halves is enantiopure but of opposite chirality to the other half, making the hexanuclear unit a meso isomer. Temperature dependent magnetic measurements showed the presence of ferromagnetic interactions among trinuclear Cu(II) units, a rare occurrence among trinuclear Cu(II) complexes. Characterization of the LiHL showed it to be enantiopure. Addition of a base, monitored using optical rotation, showed that racemization occurs as a result of base addition. The racemization depends on the base as well as the temperature. Base or Cu(II) induced racemization of amino acid derivatives has been indicated in a number of cases in the past but structural characterization of the products or formation of this type of chiral hexanuclear architecture was never reported. Structures of the complex and the ligand have a number of interesting H-bonding situations.