Synthesis, pH-Dependent Structural Characterization, and Solution Behavior of Aqueous Aluminum and Gallium Citrate Complexes

Reactions of Al(III) and Ga(III) with citric acid in aqueous solutions, yielded the complexes (NH4)5{M(C6H4O7)2}·2H2O (M(III) = Al (1), Ga (2)) at alkaline pH, and the complexes (Cat)4{M(C6H5O7)(C6H4O7)}·nH2O (M(III) = Al (3), Ga (4), Cat. = NH4 +, n = 3; M(III) = Al (5), Ga (6), Cat. = K+, n = 4) a...

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Published in:Inorganic chemistry 2001-04, Vol.40 (8), p.1734-1744
Main Authors: Matzapetakis, M, Kourgiantakis, M, Dakanali, M, Raptopoulou, C. P, Terzis, A, Lakatos, A, Kiss, T, Banyai, I, Iordanidis, L, Mavromoustakos, T, Salifoglou, A
Format: Article
Language:English
Subjects:
Aluminum - pharmacokinetics
Aluminum Compounds - chemical synthesis
Aluminum Compounds - chemistry
Citrates - chemical synthesis
Citrates - chemistry
Crystallography, X-Ray
Gallium - chemistry
Gallium - pharmacokinetics
Hydrogen-Ion Concentration
Kinetics
Magnetic Resonance Spectroscopy
Molecular Structure
Molecular Weight
Solutions
Spectroscopy, Fourier Transform Infrared
Water - chemistry
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Summary:Reactions of Al(III) and Ga(III) with citric acid in aqueous solutions, yielded the complexes (NH4)5{M(C6H4O7)2}·2H2O (M(III) = Al (1), Ga (2)) at alkaline pH, and the complexes (Cat)4{M(C6H5O7)(C6H4O7)}·nH2O (M(III) = Al (3), Ga (4), Cat. = NH4 +, n = 3; M(III) = Al (5), Ga (6), Cat. = K+, n = 4) at acidic pH. All compounds were characterized by spectroscopic (FT-IR, 1H, 13C, and 27Al NMR, 13C-MAS NMR) and X-ray techniques. Complex 1 crystallizes in space group P1̄, with a = 9.638(5) Å, b = 9.715(5) Å, c = 7.237(4) Å, α = 90.96(1)°, β = 105.72(1)°, γ = 119.74(1)°, V = 557.1(3) Å3, and Z = 1. Complex 2 crystallizes in space group P1̄, with a = 9.659(6) Å, b = 9.762(7) Å, c = 7.258(5) Å, α = 90.95(2)°, β = 105.86(2)°, γ = 119.28(1)°, V = 564.9(7) Å3, and Z = 1. Complex 3 crystallizes in space group I2/a, with a = 19.347(3) Å, b = 9.857(1) Å, c = 23.412(4) Å, β = 100.549(5)°, V = 4389(1) Å3, and Z = 8. Complex 4 crystallizes in space group I2/a, with a = 19.275(1) Å, b = 9.9697(6) Å, c = 23.476(1) Å, β = 100.694(2)°, V = 4432.8(5) Å3, and Z = 8. Complex 5 crystallizes in space group P1̄, with a = 7.316(1) Å, b = 9.454(2) Å, c = 9.569(2) Å, α = 64.218(4)°, β = 69.872(3)°, γ = 69.985(4)°, V = 544.9(2) Å3, and Z = 1. Complex 6 crystallizes in space group P1̄, with a = 7.3242(2) Å, b = 9.4363(5) Å, c = 9.6435(5) Å, α = 63.751(2)°, β = 70.091(2)°, γ = 69.941(2)°, V = 547.22(4) Å3, and Z = 1. The crystal structures of 1−6 reveal mononuclear octahedral complexes of Al(III) (or Ga(III)) bound to two citrates. Solution NMR, on both 4− and 5− species, reveals rapid intramolecular exchange of the bound and unbound terminal carboxylates. Upon dissolution in water, the complexes, through a complicated reaction cascade, transform to oligonuclear 1:1 species that, in agreement with previous studies, represent the thermodynamically stable state in solution. The data provide, for the first time, structural details of low MW, mononuclear complexes of Al(III) (or Ga(III)) with citrate that are dictated, among other factors, by pH. The properties of 1−6 may provide clues relevant to their biological association with humans.
ISSN:0020-1669
1520-510X
DOI:10.1021/ic000461l