Synthesis and Structure of (Ph₄P)₂MCl₆(M = Ti, Zr, Hf, Th, U, Np, Pu)

Abstract

High-purity syntheses are reported for a series of first, second, and third row transition metal and actinide hexahalide compounds with equivalent, noncoordinating countercations: (Ph(4)P)(2)TiF(6) (1) and (Ph(4)P)(2)MCl(6) (M = Ti, Zr, Hf, Th, U, Np, Pu; 2-8). While a reaction between MCl(4) (M = Zr, Hf, U) and 2 equiv of Ph(4)PCl provided 3, 4, and 6, syntheses for 1, 2, 5, 7, and 8 required multistep procedures. For example, a cation exchange reaction with Ph(4)PCl and (NH(4))(2)TiF(6) produced 1, which was used in a subsequent anion exchange reaction with Me(3)SiCl to synthesize 2. For 5, 7, and 8, synthetic routes starting with aqueous actinide precursors were developed that circumvented any need for anhydrous Th, Np, or Pu starting materials. The solid-state geometries, bond distances and angles for isolated ThCl(6)(2-), NpCl(6)(2-), and PuCl(6)(2-) anions with noncoordinating counter cations were determined for the first time in the X-ray crystal structures of 5, 7, and 8. Solution phase and solid-state diffuse reflectance spectra were also used to characterize 7 and 8. Transition metal MCl(6)(2-) anions showed the anticipated increase in M-Cl bond distances when changing from M = Ti to Zr, and then a decrease from Zr to Hf. The M-Cl bond distances also decreased from M = Th to U, Np, and Pu. Ionic radii can be used to predict average M-Cl bond distances with reasonable accuracy, which supports a principally ionic model of bonding for each of the (Ph(4)P)(2)MCl(6) complexes.

Structure, Phase Transitions, and Isotope Effects in [(CH3)4N]2PuCl6

“…Although this is on the shorter side of the range of bond distances reported, the Pu−Cl distance is consistent with those previously reported for other hexachloroplutonate salts. 14,15,17,54 A projection down an axis of the unit cell highlights the rotation of the plutonium octahedra as well the tetramethyammonium cations with respect to each other, as shown in Figure 2. The torsion angle, as measured between Cl−Pu−Pu−Cl, between two octahedra down a face in the protonated structure is 9.48°at 300 K, and it changes with temperature and isotopic substitution, as will be discussed later, Figure 3.…”

Probing the Electronic Structure and Chemical Bonding in Tricoordinate Uranyl Complexes UO2X3– (X = F, Cl, Br, I): Competition between Coulomb Repulsion and U–X Bonding

“…34−36 Recently, Groenewold et al measured the infrared multiphoton dissociation spectroscopy (IRMPD) of UO 2 X 3 − (X = F, Cl, Br, I) in the gas phase. 13 We observed stable UO 2 F 4 2− and UO 2 Cl 4 2− dianions and their solvation complexes with water and acetonitrile molecules in the gas phase using electrospray ionization (ESI), 37,38 but UO 2 Br 4 2− and UO 2 I 4 2− were not observed in these experiments.…”

“…For example, an F − ligand in the UO 2 F 5 3− trianion is substituted by a neutral solvent molecule (water or acetonitrile) to form the UO 2 F 4 (solvent) 2− dianions. 30,31 EXAFS and UV− Vis absorption experiments show that the UO 2 Cl 4 2− dianion exists in organic solutions with high concentrations of Cl − . 32 The UO 2 Br 4 2− dianion has been observed to be stable in ionic liquids, 33 whereas high-energy X-ray scattering (HEXS) data have revealed an average U−Br CN eq of 1.9 in concentrated aqueous hydrobromic acid solutions.…”

“…30,31 EXAFS and UV− Vis absorption experiments show that the UO 2 Cl 4 2− dianion exists in organic solutions with high concentrations of Cl − . 32 The UO 2 Br 4 2− dianion has been observed to be stable in ionic liquids, 33 whereas high-energy X-ray scattering (HEXS) data have revealed an average U−Br CN eq of 1.9 in concentrated aqueous hydrobromic acid solutions. 25 Uranyl species tend to retain low CN eq in the gas phase due to increased Coulomb repulsion between the ligands.…”

Organometallic neptunium(III) complexes

“…(L Ar ) 2-, can support a range of organometallic neptunium(III) complexes, and explore their redox chemistry and molecular and electronic structure and bonding. 21 , and longer than in Np IV complexes 22,23 . Figure 2c shows the molecular structure of complex 3, described below, which represents the first structural characterisation of a metallocene-type geometry for a Np III centre.…”