Synthesis and characterization of the complexes [Cu(II)(Et4todit)X2]n•nTHF (Et4todit = 4,5,6,7,-tetrathiocino[1,2-b:3,4-b']diimidazolyl-1,3,8,10-tetraethyl-2,9-dithione; X = Cl, Br). Crystal and molecular structure of [Cu(II)(Et4todit)Cl2]n•nTHF