Complexing Properties of Pyridine-4-methylene Derivatives: Diethyl(pyridine-4-ylmethyl)phosphate, 4-Pyridylmethylphosphonic Acid and 4-Hydroxymethylpyridine with Cu(II) in Aqueous Solution

The coordinating properties in aqueous solution of two novel pyridine-4-methylene derivatives, diethyl(pyridine-4-ylmethyl)phosphate (4-PO(Oet) 2 CH 2 -py = 4-pmOpe) and 4-pyridylmethylphos phonic acid (4-PO(OH) 2 CH 2 -py = 4-pmpa), towards Cu(II) are compared with those of 4-hydroxymethyl-pyridine (4-OHCH 2 -py = 4-pmOH). The two new derivatives were chosen due to their expected interesting biological activity that is observed for related solid complexes of several metals with various pyridine-methylene derivatives. The studies were carried out using pH potentiometry, UV–Vis spectrophotometry and EPR spectroscopy. The results show that 4-pmOpe and 4-pmpa, similarly to 4-OHCH 2 -py, form mononuclear L:M = 1:1 and 2:1 complexes with Cu(II). However, in the case of 4-pmpa, complexation occurs both via oxygen atoms of the R- PO_3^2 - group (ML and ML 2 species) and the N( 1 ) nitrogen (protonated MLH and ML 2 H 2 complexes). The possible attendance of the third ligand in the coordination sphere was indicated for 4-OHCH 2 -py by EPR spectroscopy.