Structural and new spectroscopic properties of neutral [M(dmit)(2)](dmit = (CS52-)-S-3, 1,3-dithiole-2-thione-4,5-dithiolate) and [M(H(2)timdt)(2)](H(2)timdt = H2C3N2S31-, monoanion of imidazolidine-2,4,5-trithione) complexes within the density functional

We give a detailed description of the structural, electronic and optical properties of the [M(dmit)(2)] (M = Ni, Pd, Pt) neutral dithiolenes by calculating their geometries, their bonding energies, their vibrational spectra, their ground and exited electronic states within the density functional approach. The dominant relativistic effects are treated by using the zeroth-order regular approximation. We compare their properties with those of the similar [M(H(2)tmidt)(2)] (M = Ni, Pd, Pt) series of dithiolenes and we find, in particular, that the LUMOs in the [M(dmit)(2)] compounds lay at energy very close to those of the HOMOs in the corresponding [M(H(2)tmidt)(2)] compounds, which indicates the mixed-ligand complexes as possible non-linear optical materials. The analysis of the UV-vis-NIR spectrum of the [Ni(dmit)(2)] complex shows that the intense NIR absorption is redshifted with respect to that in [Ni(H(2)tmidt)(2)], which may candidate this compound as dyes for Q-switching and/or mode locking the NdYAG and Nd:YLF lasers.