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

High-purity syntheses are reported for a series of first, second, and third row transition metal and actinide hexahalide compounds with equivalent, noncoordinating countercations: (Ph4P)2TiF6 (1) and (Ph4P)2MCl6 (M = Ti, Zr, Hf, Th, U, Np, Pu; 2–8). While a reaction between MCl4 (M = Zr, Hf, U) and 2 equiv of Ph4PCl provided 3, 4, and 6, syntheses for 1, 2, 5, 7, and 8 required multistep procedures. For example, a cation exchange reaction with Ph4PCl and (NH4)2TiF6 produced 1, which was used in a subsequent anion exchange reaction with Me3SiCl 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 ThCl62–, NpCl62–, and PuCl62– 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 MCl62– 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 (Ph4P)2MCl6 complexes.