Chelation and bridging of zinc(II) by tetradentate N_2S _2 donor ligands: Similarities and differences to copper(I) and copper(II) systems

摘要

Reaction of zinc(II) triflate with neutral bis(benzimidazolethioether) ligands yielded the complexes [Zn(bmbdb.)(H_2O)(n~1SO _3CF_3)KSO_3CF_3) (1) with tetradentate chelating 1,6-bis(N-methylbenzimidazol-2-yl)-2,5-dithiahexane (bmbdh), and dinuclear {[Zn(μbmdhp)(H_2O)(n~1-SO_3CF _3)]_2}(SO_3CF_3)_2 (2) with bis-bidentate bridging 1,7-bis(N-methylbenzimidazol-2-yl)-2,6-dithiaheptane (bmdhp). In both cases, the oxygen donor ligands aqua and triflate adopt cis positions at the approximately octahedrally configured Zn~(2+) ions. The hexacoordination is facilitated by rather long Zn-S(thioether) distances in contrast to the typically shorter Zn-S(thiolate) bonds from classical zinc finger proteins or their models. With the shorter central (CH_2) _n chain (n = 2) the ligand bmbdh exhibits facial coordination of the two NSS donor sets in 1, similar as in [Cu(bmdhp)]~+ ions with lower coordinate copper(I) but in contrast to the related [Cu~(II)(bmdhp) (H_2O)](Cl0_4)_2 with the longer chain ligand bmdhp. In 2, the bis-bidentate coordination of bmdhp ligands to each Zn ~(2+) ion occurs in an alicis fashion for the pairs of N, S and O donor atoms, in contrast to related [Cu~I(mmb)_2](BF_4). mmb = 1-methyl-2-methylthiomethyl-1Hbenzimidazole.