Metal Complexes of Dithiolate Ligands: 5,6-Dihydro-1,4-dithiin-2,3-dithiolato (dddt2-), 5,7-Dihydro-1,4,6-trithiin-2,3-dithiolato (dtdt2-), and 2-Thioxo-1,3-dithiole-4,5-dithiolato (dmit2-). Synthesis, Electrochemical Studies, Crystal and Electronic Structures, and Conducting Properties