Crystal Growth in the Thorium-TEDGA-Oxalate-Nitrate System: Description and Comparison of the Main Structural Features

This paper reports the synthesis and characterization of four new compounds based on thorium and tetraethyl-diglycolamide (TEDGA), Th(TEDGA)₂(C₂O₄)(NO₃)₂)H₂C₂O₄.6H₂O (1), [Th(TEDGA)₂(C₂O₄)₂][H₂C₂O₄]₂.2H₂O (2), [Th(TEDGA)₄][NO₃]₄.4H₂O (3), and [Th₂(C₂O₄)₃(TEDGA)₄][NO₃][HC₂O₄][H₂C₂O₄]4.7H₂O (4). All of them are obtained by successive crystallization from a unique medium containing thorium nitrate and TEDGA, in the presence of oxalic acid. Compound (1) (a = b = 18.7140(12) angstrom, c = 12.9212(9) angstrom, S.G. P42212) crystallized at first from a gel obtained by slow evaporation of the medium. When compound (1) is left in gel for a period of some weeks, it tends to disappear and to be replaced by crystals of (2) (a = 12.246(2) angstrom, b = 32.253(5) angstrom, c = 12.256(2) angstrom, β = 106.741(12)degrees, S.G. P21/n) and (3) (a = 26.5966(13) angstrom, b = 15.4489(7) angstrom, c = 18.5582(9) angstrom, β = 116.528(1)degrees, S.G. C2/c). In their turn, solids (2) and (3) disappear from the gel left for some months, and compound (1) crystallizes in mixture with compound (4) (a = 15.6 611(7) angstrom, b = 17.9082(9) angstrom, c = 18.1814(7) angstrom, α = 89.896(2)degrees, β = 65.549(2)degrees, γ = 87.623(2), S.G. P-1). Solving the crystal structure by single crystal diffraction reveals that TEDGA is always coordinated to thorium through its three oxygen atoms. In the mixed-ligands compounds (1) (2), and (4), Th⁴⁺ is surrounded by two oxalate ligands and two TEDGA, leading to a 10-fold coordination. The dimensionality of the networks changes from linear chains (1D) (1) to isolated entities (0D) (2) or dimeric units (0D) (4). Compound (3) is formed by the assembly of 12-fold coordinated monomeric entities (0D) in which the thorium cation is surrounded by four TEDGA. This compound is the first example of such a coordination number without nitrate anion included in the coordination sphere of Th. (authors)