We employed temperature-controlled Raman spectroscopy to obtain the vibrational structures of the linear tricobalt metal-string complex Co 3 (dpa) 4 Cl 2 (dpa = di(2-pyridyl) amide) and to identify its low-lying electronic states. The density functional theory (DFT) method B3LYP*-D3 was used to obtain the molecular structures, vibrational frequencies, and electronic levels of varied spin states. Co 3 (dpa) 4 Cl 2 has sym-and unsym-forms of Co-Co metal bonding. The Raman intensities of pyridyl breathing bands appeared to be sensitive to the coordinated Co atom and hence could be used to identify both forms. In s-Co 3 crystal, the split pyridyl Raman breathing bands indicated both symmetric and unsymmetric forms. This is explained that the molecule populated both the 2 A 2 (the ground state) and possibly 2 B (reduced symmetry of 2 E) states even at 77 K. The 2 B state is coupled to the 4 B state, which has an unsymmetric Co-Co bond. As the temperature increased to 423 K, the intensity of the low-wavenumber pyridyl breathing band further increased and was attributed to the 4 B state. At 77-323 K, the Raman spectra of u-Co 3 crystal populated mostly in the 4 B state. From the SERS measurements, the samples were prepared in solution phase, and u-Co 3 displayed spectral behavior similar to that of s-Co 3 , implying that the global minimal geometry is a symmetric form.

The vibrational and electronic structures of diruthenium nickel and copper complexes [Ru2Ni(dpa)4Cl2]0,1+ and [Ru2Cu(dpa)4Cl2]0,1+ were studied by using temperature‐controlled Raman spectroscopy and density functional theory (DFT) calculations. In the neutral species, the Ru−Ru stretching mode νRu−Ru was assigned to the 333/325 cm−1 band for the diruthenium Ni/Cu complexes, and this band greatly red shifted to 317/321 cm−1 at high temperatures. In contrast, this νRu−Ru band showed no shift in the oxidized forms. The time‐dependent DFT (TD‐DFT) calculations yielded that these complexes in the neutral form, have [Ru2]5+[M]1+ cores with [Ru2] moiety configuration (π*)2(δ*)1 and two low‐lying electronic excited states with [Ru2]4+[M]2+ cores and [Ru2] configurations of (π*)2(δ*)2 and (π*)3(δ*)1, respectively. The significant red shift of νRu−Ru band was explained to thermally access to these two excited states which have [Ru2]4+ cores and weak Ru−Ru bonding. These two states were resulted from metal‐to‐metal intramolecular charge transfer processes from [Ru2]5+[Ni/Cu]1+ to [Ru2]4+[Ni/Cu]2+. This charge transfer reaction is prohibited in the oxidized form.