First N-allyl-aminothiadiazole copper(I) pi-complexes : synthesis and structural peculiarities of Cu(L)CFsub3SOsub3 and Cusub2(L)sub2(Hsub2O)sub2(SiFsub6)times2.5Hsub2O compounds (L = 2-(allyl)-amino-5-methyl-1,3,4-thiadiazole)