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Protonation constants of methyliminobis(methylenephosphonic) acid and the stability-constants of its complexes

I. Lukeš and I. Dominák

Department of Inorganic Chemistry, Charles University, CS-128 40 Prague


Abstract: The protonation constants of methyliminobis(methylenephosphonic) acid (H4mibmp) and the stability constants of its complexes with nine cat­ions have been determined at 25 °C and the ionic strength I(NaCl04) = 0.1 mol dm-3 by Potentiometrie titrations (pK1 < 2, pK2 = 5.00, pK3 = 6.22, pK4 = 11.94). The data were treated using the MINIQUAD statistical pro­ gram. It has been verified that Mg2+, Ca2+, Sr2+, and Ba2+ form only the complexes of the type [Mmibmp]2- (log{ß}=5.00 (Mg2+)-4.21 (Ba2+)). With the transition metal cations, Co2+, Ni2+, Zn2+, and Cd2+, the existence of the complexes of the types [Mmibmp]2- , [Mmibmp2]6- and their protonated forms, [MHmibmp]- and [M(Hmibmp)2]4- , has been confir­ med. The [Mmibmp2]6- complex has not been found in the systems contain­ ing copper. On the basis of the results, coordination through N-atoms is assumed only for the complexes with Cu2+ and Cd2+ . The other cations are probably coordinated only through the oxygen atoms.

Full paper in Portable Document Format: 423a311.pdf


Chemical Papers 42 (3) 311–317 (1988)

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