THE FIRST X-RAY CRYSTALLOGRAPHIC CHARACTERIZATION OF A DIALKYLAMINOMETHYLENEPHOSPHONIC ACID - SYNTHESIS OF CRYSTALLINE N,N'DIETHYLAMINOMETHYLENEPHOSPHONIC ACID, ITS PROTONATION EQUILIBRIA, AND THE STABILITIES OF ITS COMPLEXES WITH LEAD(II)

The X-ray crystal structure of N,N'-diethylaminomethlenephosphonic aci d (LH(2)) shows the molecule to be present as the N-protonated zwitter ion. The unusually large P-C-N angle [120.1(3)degrees] is apparently o wing to steric factors arising from the ''eclipsed'' conformation of t he ethyl methylene carbon atoms and phosphonate oxygen atoms. Potentio metric titration and determination of the pH dependence of delta(13) ( P) were used to elucidate the protonation equilibria for LH(2). Stoich iometric stability constants for complexes of LH(2) with lead(II) prov ide evidence that LH(2) is selective for lead(II) over most transition metal ions [log beta(PbLH)(PbLH) : 11.55 +/- 0.12(011); 16.92 +/- 0.1 5(012); 18.3 +/- 0.5(013); 7.45 +/- 0.18(110); 14.81 +/- 0.35(111); -0 .49 +/- 0.33(01-1)]. Copyright (C) 1996 Elsevier Science Ltd