Structural and new spectroscopic properties of neutral $$[\hbox{M(dmit)}_{\bf 2}] (\hbox{dmit} = \hbox{C}_{\bf 3} \hbox{S}_{\bf 5}^{\bf 2-}$$ , 1,3-dithiole-2-thione-4,5-dithiolate) and $$[\hbox{M}(\hbox{H}_{\bf 2}\hbox{timdt})_{\bf 2}](\hbox{H}_{\bf 2}\hbox{timdt} = \hbox{H}_{\bf 2} \hbox{C}_{\bf 3} \hbox{N}_{\bf 2} \hbox{S}_{\bf 3}^{\bf 1-}$$ , monoanion of imidazolidine-2,4,5-trithione) complexes within the density functional approach