Lewis Acid Behavior of ReO<sub>2</sub>F<sub>3</sub>: Synthesis of (ReO<sub>2</sub>F<sub>3</sub>)<sub>∞</sub>, ReO<sub>2</sub>F<sub>4</sub><sup>-</sup>, Re<sub>2</sub>O<sub>4</sub>F<sub>7</sub><sup>-</sup>, Re<sub>3</sub>O<sub>6</sub>F<sub>10</sub><sup>-</sup>, and ReO<sub>2</sub>F<sub>3</sub>(CH<sub>3</sub>CN) and Study by NMR Spectroscopy, Raman Spectroscopy, and Density Functional Theory Calculations; and X-ray Structures of [Li][ReO<sub>2</sub>F<sub>4</sub>], [K][Re<sub>2</sub>O<sub>4</sub>F<sub>7</sub>], [K][Re<sub>2</sub>O<sub>4</sub>F<sub>7</sub>]·2ReO<sub>2</sub>F<sub>3</sub>, [Cs][Re<sub>3</sub>O<sub>6</sub>F<sub>10</sub>], and ReO<sub>3</sub>F(CH<sub>3</sub>CN)<sub>2</sub>·CH<sub>3</sub>CN