PREPARATION, VIBRATIONAL-SPECTRA, AND NORMAL-COORDINATE ANALYSIS OF HEXACHLORORHENATE(V) AND CRYSTAL-STRUCTURE OF [P(C6H5)4][RECL6]

By oxidation of A2[ReCl6], A = [(n-C4H9)4N]+, [P(C6H5)4]+, with Cl2 in dichloromethane/trifluoracetic acid A[ReCI6] is formed. [P(C6H5)4][ReCl6] crystallizes with tetragonal symmetry, space group P4/n-C4h3, a = 12.967(4), c = 7.6992(8) angstrom, Z = 2. The octahedral complexion [ReCl6]- is compressed (C4v) with the bond lengths, axial Re-Cl1 = 2.28 and Re-Cl3 = 2.24 angstrom, equatorial Re-Cl2 = 2.31 angstrom. The infrared active antisymmetric Re-Cl stretching vibration is split into nu2' = 346 an nu3'' = 326 cm-1. The assignment of all IR and Raman modes is confirmed by a normal coordinate analysis. The different valence force constants, f(d)(ReCl1) = 2.09, f(d)(ReCl3) = 2.10, f(d)(ReCl2) = 1.88 mdyn/angstrom result from the distortion of the octahedron. On excitation with the Ar laser line 514.5 nm a resonance Raman spectrum is observed, showing 8 overtones of nu'(A1) = 382 cm-1, from which the harmonic frequency omega1 = 382.1 cm-1, the anharmonicity constant X11 = -0.76 cm-1 and the maximum bond dissociation energy of the [ReCl6]- ion to be 138 kcal/mol, are calculated. The vibrational fine structure of the intraconfigurational transitions in the near infrared has been resolved by measuring the absorption spectrum of [(n-C4H9)4N][ReCl6] at low temperature (10 K), resulting in the assignment of the following electronic origins: GAMMA3(3T1g) --> GAMMA4(3T1g): 7512, GAMMA3(3T1g) --> GAMMA1(3T1g): 7624 and GAMMA3(3T1g) --> GAMMA5(1T2g), GAMMA3(1E(g)): 8368 cm-1.