Metal-Organotetraphosphonate Inorganic-Organic Hybrids: Crystal Structure and Anticorrosion Effects of Zinc Hexamethylenediaminetetrakis(methylenephosphonate) on Carbon Steels

The synthesis and structural characterization of the first polymeric M-HDTMP organic-inorganic hybrids are described [M = Zn2+, Ca2+; HDTMP = hexamethylenediaminetetrakis(methylenephosphonate)]. The 3D crystal structure of the Zn2+ analogue [Zn(HDTMP)·H2O] is described. The Zn center is found in a distorted octahedral environment of phosphonate oxygens. There is a long Zn···O interaction (2.622 (angstrom)) originating from a protonated -P-OH group. Synergistic combinations of Zn2+ and the tetraphosphonate are found to form films that protect against the corrosion of carbon steels.