Aminoalkyl-1,1-bis(phosphinic acids): Stability, Acid-Base, and Coordination Properties

摘要

Four geminal bis(phosphinic acids), namely, aminomethylbis(H-phosphinic acid) (H_2L~1) and 4-aminobutyl-1-hydroxy-1,1-bis(R-phosphinic acid) with R = H (H_2L~2), Me (H_2L~3) and CH_2CH_2COOH (H_4L~4), 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 H_2L~1 has a lower protonation constant (log K_a = 6.79) than those found for other studied bisphosphinates (log K_a = 10.75-11.05) with distant amine groups. The structure of [Ca(H_2L~2-O,O′)(HL~2-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-)_2Ca rings. The structure of [Cu(HL~3-O,O′)_2(H_2O)]·5H_2O shows two chelating bisphosphinate groups in an equatorial O_4 environment. The structure of [Cu(H_(0.5)L~3-O,O′)(NO_3)_(0.5)]· 2.25H_2O shows two different coordination environments, one is an elongated tetragonal pyramid, and the other is a trigonal bipyramid with a bidentate nitrate ion.