Conversions of monomeric, dimeric and tetrameric lanthanum and samarium citrates with ethylenediaminetetraacetates in aqueous solutions. (1st October 2018) - Chen, Mao-Long
Graphical abstract: The successful isolations of high soluble monomeric, dimeric and tetrameric lanthanide citrates with ethylenediaminetetraacetates which obtained from aqueous solutions provide a valuable approach for the construction of water soluble citrato rare-earth complexes and understanding the detail species in modified Pechini method for the syntheses of composite lanthanide oxides. Abstract: Our continued research on lanthanide citrate with ethylenediaminetetraacetate results in an isolation of a monomeric samarium complex K4 [Sm(Hcit)(EDTA)]·10H2 O (1 ) (H4 cit = citric acid and H4 EDTA = ethylenediaminetetraacetic acid) from the reaction of lanthanide ethylenediaminetetraacetate trihydrates with citric acid at pH ∼6.5, where the three coordinated water molecules of K[Sm(EDTA)(H2 O)3 ]·5H2 O (4 ) were substituted by the α-hydroxy, α-carboxy and β-carboxy groups of citrate. When involving lanthanum element, the reaction of lanthanum ethylenediaminetetraacetate trihydrates with dimeric lanthanum complex K4 (NH4 )4 [La2 (Hcit)2 (EDTA)2 ]·17H2 O (2 ) gives a novel tetrameric lanthanum citrate with ethylenediaminetetraacetate K2 (NH4 )8 [[La(EDTA)(H2 O)2 ]2 [La2 (Hcit)2 (EDTA)2 ]]·22H2 O (3 ). The main structural feature of 2 consists of a dinuclear unit deca-coordinated by citrate and EDTA, while tetramer 3 is a dinuclear unit bridged with two lanthanum ethylenediaminetetraacetates through pendent β-carboxy groups. It is interesting to note that 1 –3 contain strong intramolecular hydrogen bonds between α-hydroxy and β-carboxy groups with very good solubilities in water. The relationships between the isolations of mixed EDTA–citrate lanthanides and modified Pechini method are discussed.