Two new supramolecular metal diphosphonates: Synthesis, characterization, crystal structure and inhibiting effects on metallic corrosion.

Two new divalent metal(II) aminodiphosphonates with layered structure, namely, Cu(H 3 L 1 ) 2 ·2H 2 O ( 1 ), [H4L 1 =methyl-N(CH 2 PO 3 H 2 ) 2 ] and Cd 2 (H 2 L 2 ) 4 ( 2 ), [H 4 L 2 =n-propyl-N(CH 2 PO 3 H 2 ) 2 ] were synthesized and characterized. The Cu(II) ions in complex 1 are octahedrally coordinated by four oxygen atoms from two chelating ligands and two phosphonate oxygen atoms from two neighboring Cu(H 3 L 1 ) 2 units. The Cu(H 3 L 1 ) 2 units are interconnected by bridging phosphonate groups, forming a 2-D metal phosphonate layer. The structure of complex 2 contains two unique Cd(II) ions octahedrally-coordinated by six phosphonate oxygen atoms from four H 2 L 2 diphosphonate anions. Corrosion inhibition performances of 1 and 2 were also compared with each other in order to study the effect of combinations of externally added Cd/H 4 L 2 and Cu/H 4 L 1 (1:1 ratio) on corrosion rates of carbon steel. It was found that at pH 3.0, Cd/H 4 L 2 or Cu/H 4 L 1 combinations do not have noticeable corrosion inhibition efficiency for carbon steel. In contrast, at pH 7.0, higher corrosion inhibition efficiency was achieved for Cd/H 4 L 2 . Physical characterizations such as scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) were applied to study the corrosion specimens and film material. [ABSTRACT FROM AUTHOR]