Abstract
Four geminal bis(phosphinic acids), namely, aminomethyl-bis(H-phosphinic acid) (H2L1) and 4-aminobutyl-1-hydroxy-1,1-bis(R-phosphinic acid) with R = H (H2L2), Me (H2L3) and CH2CH2COOH (H4L4), were studied. Their acid-base properties and coordination ability towards Cu(2+), Ni(2+) and Zn(2+) ions were studied by potentiometry, UV/Vis spectroscopy and NMR spectroscopy.
The amine group in H2L1 has a lower protonation constant (log K(a) = 6.79) than those found for other studied bisphosphinates (logK(a) = 10.75-11.05) with distant amine groups. The structure of [Ca(H2L2-O,O')(HL2-O,O')]Cl revealed an octahedral arrangement of the metal coordination sphere and a linear polymeric structure, which forms through eight-membered Ca(-O-P-O-)(2)Ca rings.
The structure of [Cu(HL3-O,O')(2)(H2O)] . 5H2O shows two chelating bisphosphinate groups in an equatorial O(4) environment. The structure of [Cu(H(0.5)L3-O,O')(NO3)(0.5)] . 2.25H2O shows two different coordination environments, one is an elongated tetragonal pyramid, and the other is a trigonal bipyramid with a bidentate nitrate ion.