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 tetraethyldiglycolamide (TEDGA), [Th(TEDGA)(2)(C2O4)][NO3](2)[H2C2O4] 6H(2)O (1), [Th(TEDGA)(2)(C2O4)(2)][H2C2O4](2) 2H(2)O (2), [Th(TEDGA)(4)][NO3](4) 4H(2)O (3), and [Th-2(C2O4)(3)(TEDGA)(4)][NO3][HC2O4][H2C2O4](4)7H(2)O (<bold>4</bold>). 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, beta = 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, beta = 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 (<bold>4</bold>) (a = 15.6611(7) angstrom, b = 17.9082(9) angstrom, c = 18.1814(7) angstrom, alpha = 89.896(2)degrees, beta = 65.549(2)degrees, gamma = 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 (<bold>4</bold>), 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) (<bold>4</bold>). 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.