Single-Crystal Polarized Electronic Spectra of the Compounds Dichlorotetrakis( Mu -Pivalato)Dirhenium(III), Tetra-N-Butylammonium Octachlorodirhenate(III), Tetra-N-Butylammonium Octabromodirhenate(III), Dimolybdenum(II) Tetrapival

摘要

(N(C sub 4 H sub 9 ) sub 4 ) sub 2 Re sub 2 Br sub 8 crystallizes in the monoclinic space group P2 sub 1 /n. It has a disordered form, such that 62.1% of the Re-Re bonds are aligned in one direction while 37.9% are aligned in a direction perpendicular to this. For both the octabromo and octachloro salts, highly resolved vibrational structures for the first observed electronic band at about 14,000 cm exp -1 were recorded by the spectrophotometer. It was possible to resolve the Franck-Condon progressions for both the major and minor site components of each compound with intensities consistent with the delta implies delta* ( exp 1 A/sub 1g/ implies exp 1 A/sub 2u/) assignment. However, additional absorption features were observed that have been attributed to further disorder components that have not been revealed by the x-ray diffraction structures. Polarized electronic spectra in the 15,000 to 35,000 cm exp -1 region are reported for Re sub 2 (O sub 2 CC(CH sub 3 ) sub 3 ) sub 4 Cl sub 2 . A peak at 20,200 cm exp -1 is assigned as the electric-dipole-allowed exp 1 A/sub 1g/ implies exp 1 A/sub 2u/ (delta implies delta*) transition with z-polarization. Weak transitions are observed at 21,600, 24,700, 29,000, and 32,000 cm exp -1 . The first three weak transitions appear to be electric-dipole-forbidden vibronically allowed transitions with x, y-polarization. The beta - and gamma -Mo sub 2 (O sub 2 CC(CH sub 3 ) sub 3 ) sub 4 form one-dimensional chains along the c-axis of the unit cell. Polarized spectra are reported for these two polymorphs at 300 and 6 K. The evidence available from earlier studies in this research group with Mo sub 2 (O sub 2 CCH sub 3 ) sub 4 and Mo sub 2 (O sub 2 CCF sub 3 ) sub 4 provides a justification for assigning the lowest energy bands as weak electric-dipole-allowed transitions with molecular z-polarization under the local D/sub 4h/ symmetry. 65 refs., 26 figs., 17 tabs. (ERA citation 11:001063)