Emitting-State Displacements in Ligand-Centered Vibrational Modes in the trans-[OsO2(NCS)4]²-….

Low-temperature luminescence spectra from three salts of the trans-[OsO2(NCS)4]2- complex exhibit highly resolved vibronic structure in both metal-ligand high-frequency O=Os=O (885 cm-1) and lower-frequency Os-N(CS) (255 cm-1) symmetric stretching modes as well as in a ligand-centered CS stretching mode (858 cm-1). Band maxima range from 10000 to 12000 cm-1, and spectra contain irregular frequency intervals that correspond to transitions from more than one origin and phonon sidebands. Experimental band shapes are distinctly different for all three compounds and are calculated assuming harmonic potential energy surfaces for both the ground and emitting states. Normal-coordinate offsets along all displaced vibrational modes are determined and compared for the three compounds. The analyses reveal emitting-state displacement of high-frequency ligand-centered (CS) and metal-ligand (O=Os=O) symmetric stretching modes, leading to observed high-frequency intervals (855–880 cm-1) that do not match any frequencies determined from ground-state Raman spectra. The values for the high-frequency normal-coordinate offsets, ΔQO=Os=O and AQCS, were found to be on the order of 0.06 Å. Offsets along the 255 cm-1 Os-N mode varied noticeably between the three compounds and were largest for the compound with the largest value of ΔQCS. [ABSTRACT FROM AUTHOR]