Effect of pyridyl substituents leading to the formation of green luminescent mercury(ii) coordination polymers, zinc(ii) dimers and a monomer

Abstract

Pyridine-2, -3 and -4 functionalized dithiocarbamate ligands yielded the coordination polymers with mercury, namely [{Hg(L)₂}_n] (L = L1, C₅H₄NCH₂NCS₂CH₂C₇H₅O₂ (1); L2, C₅H₄NCH₂NCS₂CH₃ (2); L3, C₅H₄NCH₂NCS₂CH₂C₄H₃O (3); and L4, C₅H₄NCH₂NCS₂CH₂CH₂C₆H₅ (4)), [PhHg(L3)] (5), and mononuclear [Hg(L5)₂], L5 = C₅H₄NCH₂NCS₂CH₂C₆H₅ (6). Unexpectedly, the pyridine-2-functionalized ligand, L6, C₅H₄NCH₂NCS₂CH₂C₆H₅ gave a cyclized product, benzyl-2H-imidazo[1,5-a]pyridine-3-thione (7), C₁₄H₁₃N₂S, instead of a mercury complex. Complexes with zinc were also characterized, namely dinuclear [Zn₂(L5)₄] (8) and [Zn₂(L7)₄], L7 = CH₃CH₂O₂C₅H₉NCS₂ (9) and a mononuclear complex [Zn(L8)₂], L8 = C₄H₃NCH₃CH₂NCS₂CH₂C₆H₅ (10). These ten compounds have been characterized by microanalysis and X-ray crystallography. Complexes (1, 2) and 3 are 1-D and 2-D coordination polymers in which the ligands are uniquely bonded in the bridging-chelating mode in a μ², κ³-N, S, S fashion establishing square pyramidal five-coordinate and octahedral six-coordinate geometries about the Hg atom respectively. The structure of 4 is also a 1-D coordination polymer formed via bridging sulphur bonds with a five-coordinate distorted geometry about the mercury atom. 6 is a mononuclear mercury(II) complex forming an interesting polymeric 1-D architecture through intermolecular Hg⋯S interactions. 8 is the first example of a homoleptic dinuclear zinc(II) dithiocarbamate complex bridged through ligand L5 in a μ², κ³-N, S(11), S(13) bridging-chelating manner. L7 and L8 form a typical S, S-bridged dimer 9 and a mononuclear complex 10. The nature of the Hg–N and Zn–N bonds in the coordination polymers 1, 2 and 3 and in the dinuclear 8 has been assessed by DFT calculations. Complexes 1–9 are luminescent in both solution and solid phases; especially, significant red shifted green emission in the solid phase for the coordination polymers 1, 2 and 3 shows good structure–property correlations.