TY - JOUR
T1 - Synthesis, pH-dependent structural characterization, and solution behavior of aqueous aluminum and gallium citrate complexes
AU - Matzapetakis, M.
AU - Kourgiantakis, M.
AU - Dakanali, M.
AU - Raptopoulou, C. P.
AU - Terzis, A.
AU - Lakatos, A.
AU - Kiss, T.
AU - Banyai, I.
AU - Iordanidis, L.
AU - Mavromoustakos, T.
AU - Salifoglou, A.
PY - 2001/4/9
Y1 - 2001/4/9
N2 - 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.
AB - 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.
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U2 - 10.1021/ic000461l
DO - 10.1021/ic000461l
M3 - Article
C2 - 11312727
AN - SCOPUS:0035831570
SN - 0020-1669
VL - 40
SP - 1734
EP - 1744
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 8
ER -