Anhydrous Actinide Starting Materials: Synthesis and Structural Characterization of [UCl<sub>4</sub>(Et<sub>2</sub>O)<sub>2</sub>], an Alternative Route to [UO<sub>2</sub>Cl<sub>2</sub>(THF)<sub>2</sub>]<sub>2</sub>, and Comments on the Synthesis of [ThCl<sub>4</sub>(dme)<sub>2</sub>]