Metal-phosphonate chemistry:: Synthesis, crystal structure of calcium-amino-tris-(methylene phosphonate) and inhibition of CaCO3 crystal growth

Organic (poly)phosphonates are additives in water treatment that find broad use as mineral scale and corrosion inhibitors for a plethora of industrial applications. The phenomenon of precipitation of scale inhibitors has been studied intensively. This study reports the synthesis, characterization, and crystal structure of a Ca salt of AMP (AMP = Amino-tris-Methylene Phosphonate). Ca-AMP crystals are monoclinic space group P 2(1)/n with unit cell dimensions, a = 11.3382(5) Angstrom, b = 8.4555(4) Angstrom, c = 15.5254(7) Angstrom, beta = 90.6551degrees, V = 1488.33(12) Angstrom(3) and Z = 4. The structure is polymeric due to chelation of multiple Ca ions by AMP The Ca2+ center is slightly distorted octahedral and is surrounded by five phosphonate oxygens and a water molecule. Ca-O(P) bond lengths range from 2.2924(14) to 2.3356(14) Angstrom. The Ca-O(H2O) bond distance is 2.3693(17). Each phosphonate group is monodeprotonated, and the nitrogen atom is protonated. CaCO3 inhibition and crystal modification by AMP are also reported, together with synergistic effects with polyacrylate-based terpolymers.