Gravar-mail: catena-Poly[[[bis­[2,2′-(propane-1,3-diyl­dithio)bis­(1,3,4-thia­diazole)-κN (4)]copper(II)]-bis­[μ-2,2′-(propane-1,3-diyldithio)bis­(1,3,4-thia­diazole)-κ(2) N (4):N (4′)]] bis­(perchlorate)]