Vibrational Spectra of [Pd(dmit)2] Dimer (dmit = 1,3-dithiole-2-thione-4,5-dithiolate): Methodology for Examining Charge, Inter-Molecular Interactions, and Orbital

Abstract

We have developed a methodology for analyzing the lattice, charge, and orbital in two-dimensional molecular conductors comprising dimers of [Pd(dimt) 2 ] ([Pd(dimt) 2 ] 2 ) using C=C stretching vibrational modes. After confirming vibrational modes for non-dimerized and loosely dimerized materials, we provide assignments for the four C=C stretching modes – two IR-active modes and two Raman-active modes – for the tight dimer. Of the four modes, the Raman-active and the lowest frequency mode is attributed to redistribution of the molecular orbital due to tight dimerization. By analyzing the vibrational spectra in the charge-ordered (CO) state of Et 2 Me 2 Sb[Pd(dmit) 2 ] 2 , we have found that the four modes are reflect in the intra-dimer interaction, the inter-dimer interaction, molecular charges and orbital levels. The results suggest that the vibrational spectroscopy is a powerful method to investigate electronic correlations, electron–phonon interactions, etc. in [Pd(dimt) 2 ] salts.