Metal Tetraphosphonate “Wires” and Their Corrosion Inhibiting Passive Films

Herein, we describe the preparation and characterization of five new divalent metal tetraphosphonates, M-HDTMP [M = Mg2+, Ca2+, Sr2+, Ba2+, and Cu2+; HDTMP = hexamethylenediaminetetrakis(methylenephosphonate) dianion]. Materials {Sr[(HDTMP)(H2O)6]·2H2O}n (1), {Ba[(HDTMP)(H2O)6]·2H2O}n (2), and {Cu[(HDTMP)(H2O)4]·6H2O}n (3), as well as (en)(HDTMP)·2H2O (en = ethylenediammonium cation) have been structurally characterized. Structures depend on the coordination requirements of the M2+ center and waters of crystallization content. The formation and characterization of effective anticorrosion passive films of M-HDTMP (M = Sr2+ and Ba2+) are also reported.