Synthesis, pH-dependent structural characterization, and solution behavior of aqueous aluminum and gallium citrate complexes

M. Matzapetakis, M. Kourgiantakis, M. Dakanali, C. P. Raptopoulou, A. Terzis, A. Lakatos, T. Kiss, I. Banyai, L. Iordanidis, T. Mavromoustakos, A. Salifoglou

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Abstract

Reactions of Al(III) and Ga(III) with citric acid in aqueous solutions, yielded the complexes (NH4)5{M(C6H4 O7)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.

Original languageEnglish (US)
Pages (from-to)1734-1744
Number of pages11
JournalInorganic Chemistry
Volume40
Issue number8
DOIs
StatePublished - Apr 9 2001

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ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

Cite this

Matzapetakis, M., Kourgiantakis, M., Dakanali, M., Raptopoulou, C. P., Terzis, A., Lakatos, A., Kiss, T., Banyai, I., Iordanidis, L., Mavromoustakos, T., & Salifoglou, A. (2001). Synthesis, pH-dependent structural characterization, and solution behavior of aqueous aluminum and gallium citrate complexes. Inorganic Chemistry, 40(8), 1734-1744. https://doi.org/10.1021/ic000461l