Cooperative metal–ligand influence on the formation of coordination polymers, and conducting and photophysical properties of Tl(i) β-oxodithioester complexes

Abstract

Eight novel Tl(I) β-oxodithioester complexes, [TlL]_n (1–8), with ligands, L = methyl-3-hydroxy-3-(2-furyl)-2-propenedithioate (L1), methyl-3-hydroxy-3-(2-thienyl)-2-propenedithioate (L2), methyl-3-hydroxy-3-(3-pyridyl)-2-propenedithioate (L3), methyl-3-hydroxy-3-(4-pyridyl)-2-propenedithioate (L4), methyl-3-hydroxy-3-(9-anthracenyl)-2-propenedithioate (L5), methyl-3-hydroxy-3-(4-fluorophenyl)-2-propenedithioate (L6), methyl-3-hydroxy-3-(4-chlorophenyl)-2-propenedithioate (L7) and methyl-3-hydroxy-3-(4-bromophenyl)-2-propenedithioate (L8), were synthesized and thoroughly characterized by elemental analysis, and IR, UV-Vis, ¹H and ¹³C{¹H} NMR spectroscopy, and their structures were ascertained by X-ray crystallography. Complexes 1 and 2 crystallized in P2₁ and P2₁2₁2₁ chiral space groups, respectively, and were studied using Circular Dichroism (CD) spectra. Solid state structural analyses revealed that the β-oxodithioester ligands are bonded to Tl(I) ions in (O, S) chelating and chelating–bridging modes, thereby forming different types of 1D and 2D coordination polymeric structures. By considering the metal-assisted bonding interactions, various coordination numbers of 5–8 and 10 are established around the metal centre. Except for 5 and 7a which have Tl⋯Tl separations at 3.724(1) and 3.767(1), 3.891(1) Å respectively, the remaining complexes have no Tl⋯Tl distances <4.0 Å. This indicates that the majority of structures contain only weak inter- and intramolecular thallophilic interactions. The structures of 1–8 highlight the role played by variations in substituents in the dithioester unit in the structure and properties of the complexes. The multi-dimensional assembly in these complexes rests on important non-covalent C–H⋯π (TlOSC₃, chelate), C–H⋯X (X = F, Cl, O, N), C–H⋯π, H⋯H and rare Tl⋯H–C intermolecular anagostic interactions. The Tl⋯H–C anagostic interactions together with C–O⋯Tl and C–S⋯Tl interactions formed 7-, 11- and 12-membered chelate rings about the metal centers. The anagostic interactions in 1, 2 and 7b were assessed by theoretical calculations. All the complexes showed bright green luminescent emissions in solution and solid phases. Time-resolved emission spectra revealed a triexponential decay curve and short mean lifetime for fluorescence behavior.