On the Structure-Dependent Behavior of Ethylenediaminetetraacetato Complexes of the Rare Earth Ln³⁺ Ions¹

Abstract

type ; displacement, as specified above, of the overlarge La3+ from a central position is responsible for the expansion into the previously unheard of ten-coordination group. (How the substitution of smaller rare ions for La3+ can modify this configuration for the better is discussed in the accompanying communication.6) The nine-coordination group7 of D3h symmetry, the uniquely satisfactory choice8 for La3+ in unconstrained circumstances, is quite unadapted to meet the stereochemical requirements of the chelating agent.Of the four carboxylate oxygen atoms (Ou) which are not complexed by La3+, the one carrying the acid hydrogen can be identified from the bonding data which follow. (Standard deviations for individual bond lengths are 0.0030-0.0035 A. for La-Oc, La-OH2, and La-N; 0.004-0.006 A. for C-Oc and C-Ou.) The averaged length, with mean deviation, for three of the four La-Oc bonds is 2.537 (0.007) A., and the corresponding data for the associated C-Oc and C-Ou bonds are, respectively, 1.261 (0.008) and 1.249 (0.004) A.; this nearly trivial lengthening (0.012 A.

Metal – Aminopolycarboxylic Acid Complexes. I. Studies of Lead(II) and Cadmium(II) Complexes with Diethylenetriaminepentaacetic Acid in Aqueous Solution by Proton Magnetic Resonance Spectroscopy

“…A survey of the coordination chemistry of divalent metal -aminopolycarboxylate complexes revealed evidence for preferred octahedral coordination (17)(18)(19)(20)(21) but the X-ray crystallographic studies of Hoard and co-workers (22)(23)(24)(25)(26)(27)(28)(29)(30) indicate that this is a simplification and some principles for prediction of coordination number were proposed. DTPA is a potentially octadentate ligand.…”

Studies of Oxygen Exchange Between Trivalent Lanthanide – EDTA Complexes and Solvent Water: Evidence for a Structural Change Within the Series

“…Hoard et al (11) found from crystal structure determinations of some hydrated salts that La3+ is coordinated to one EDTA molecule and three water molecules (giving a net coordination number (C.N.) of 9); the entire arrangement is approximately that of two hemispheres, one containing the 3 water molecules and the other, the 6 ethylenediaminetetraacetate donor sites.…”

“…Various authors have expressed the opinion that owing to the "lanthanide contraction" partially hydrated complexes (12)(13)(14) and in particular the EDTA complexes (11,(15)(16)(17) are expected to undergo a change in coordination number somewhere in the middle of the lanthanide series. Such a change is also considered to be revealed in the irregular progression of the enthalpy (AH) and entropy (AS, see Flg.…”

“…1) changes associated with the complex formation reaction (eq. 2) (11,(15)(16)(17). The explanation offered proceeds somewhat as follows.…”

Structure of potassium triaqua(ethylenediaminetetraacetato)neodymate(III) pentahydrate

“…Crystal structures of several lanthanide edta complexes have been reported: K[La(edta)-(H20) 3].5H20 (Hoard, Lee & Lind, 1965), Na[Ln(edta)(HEO)3].5H20, Ln=Tb (Lee, 1967), Dy (Nassimbeni, Wright, van Niekerk & McCallum, 1979), Pr, Gd, Sm (Templeton, Templeton, Zalkin & Ruben, 1982), Sm (Engel, Takusagawa & Koetzle, 1984), Ho (Templeton, Templeton & Zalkin, 1985), and Cs[Yb(edta)(H20)2].3H20 (Nassimbeni, Wright, van Niekerk & McCallum, 1979). It was suggested that there should be a change from a nine-coordinated to an eight-coordinated complex in the lanthanide series La 3+ to Lu 3+ as a result of the decreasing ionic radii.…”