Complexing properties of phosphinic analogues of glycine

A series of aminomethylphosphinic acids H(2)NCH(2)PRO(2)H (R = H, Me, Bu(t) or Ph) was synthesized and the acid-base and complexing properties with Co-II, Ni-II and Cu-II were determined pH-metrically (25 degrees C, 0.1 mol dm(-3) KNO3). The pK(a) values were found to increase from R = H to Ph, Me and Bu(t), as the -I effect decreases. The complex stability constants lie in the same order, except for R = H. The compound H2NCH2PHO2H (HL(1)) exhibits higher values than the ligands with methyl or phenyl substituents, probably due to better deformability of the PHO2- group and its better ability to form chelate rings. The complexes of H2NCH2P(Ph)O2H (HL(4)), H2NCH2P(Me)O2H (HL(2)) and H2NCH2P(Bu(t))O2H (HL(3)) with several transition metals were prepared and the crystal structures of [CuL(2)(4)] 1 and [Cu(3)L(4)(2)][ClO4](2) 2 were determined. The formation of chelate rings was observed in both structures; 1 forms dimers and 2 polymeric layers via the phosphinates.