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Lanthanide Complexes Formed with the Tri- and Tetraacetate Derivatives of Bis(aminomethyl)phosphinic Acid: Equilibrium, Kinetic and NMR Spectroscopic Studies

Tircsó, Gyula and Kálmán, Ferenc Krisztián and Pál, Róbert and Bányai, István and Varga, Tamás Róbert and Király, Róbert and Lázár, István and Québatte, Laurent and Merbach, André E. and Tóth, Éva and Brücher, Ernő (2012) Lanthanide Complexes Formed with the Tri- and Tetraacetate Derivatives of Bis(aminomethyl)phosphinic Acid: Equilibrium, Kinetic and NMR Spectroscopic Studies. EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 2012 (12). pp. 2062-2073. ISSN 1434-1948

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Abstract

The lanthanide(III) complexes formed with the tri- (TCAP, L1) and tetra-acetate derivatives of the bis(aminomethyl)phosphinic acid (BIMP, L2) have been studied by pH-potentiometry, spectrophotometry, 1H-, and 17O-NMR spectroscopy. The ligand L1 forms LnL, LnL2 and protonated LnLH, LnLH2 and LnL(OH) hydroxo complexes. The heptadentate L2 forms LnL, protonated LnLH and LnLH2 complexes in solution and it shows a strong propensity to form Ln2L dinuclear complexes which was not detected earlier. The stability constants (log KLnL) of the complexes increase in the order LnL1 < LnL2 following the order of increasing number of acetate pendants attached to the bis(aminomethyl)phosphinic acid (BAP) backbone. Within the LnIII series, the log KLnL values increase from La3+ to Gd3+ and remain practically constant for the heavier lanthanides. Despite the lower basicity, the ligands containing a phosphinate group generally form similar (L1) or more stable Ln3+ complexes than the diamino-polycarboxylates of similar structure (ED3APh, L3). This result indicates that the hard linker phosphinate group may be coordinated to the Ln3+ ions in the complexes, while the larger negative charge of the BAP derivatives may also have an extra stabilizing effect. The kinetic inertness of the LnL1 and LnL2 complexes is lower than that of the similar Ln(EDTA), but the rate constants characterizing the dissociation of the LnL2 complexes are at least two orders of magnitude lower than those obtained for the Ln(PDTA) (LnL4) complexes. Variable temperature 17O transverse and longitudinal relaxation rates and chemical shifts have been measured to assess water exchange and rotational dynamics on GdL2. The chemical shifts evidenced monohydration of the complex. The water exchange rate, kex298 = (2.70.4)107 s-1 is about ten times higher than that of Gd(DTPA)2. The rotational correlation time, RO298 = 27030 ps is very long considering the small size of the chelate and it points to an aggregation phenomenon in aqueous solution, in accordance with the high value of the proton relaxivity measured.

Item Type: Article
Subjects: Q Science / természettudomány > QD Chemistry / kémia > QD01 Analytical chemistry / analitikai kémia
Q Science / természettudomány > QD Chemistry / kémia > QD02 Physical chemistry / fizikai kémia
Q Science / természettudomány > QD Chemistry / kémia > QD03 Inorganic chemistry / szervetlen kémia
Depositing User: Dr Tircsó Gyula
Date Deposited: 20 Sep 2014 18:09
Last Modified: 20 Sep 2014 18:10
URI: http://real.mtak.hu/id/eprint/15653

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