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; XCl, Br). Crystal and molecular structure of [Cu(II)(Et4todit)Cl2]n·nTHF