Luminescent gold–thallium derivatives with a pyridine-containing 12-membered aza-thioether macrocycle

Abstract

The coordination modes of the ligand 2,5,8-trithia[9](2,6)pyridinophane (L) to thallium(I), gold(III) and gold(I) have been studied. Thallium(I) is coordinated by the macrocyclic ligand in [Tl(L)](PF₆) (1) through all the sulfur and nitrogen atoms, in a distorted square-pyramidal geometry with the thallium(I) ion in the apical position and with the presence of an inert lone pair. Gold(III) is bonded by the ligand only through the nitrogen of the pyridine group in [AuCl₃(L)] (2), whereas two Au^I–C₆F₅ fragments coordinate the sulfur atoms next to the pyridine moiety of the ligand in [{Au(C₆F₅)}₂(μ-L)] (3), which form a linear polymer through intermolecular aurophilic contacts. The heterometallic Tl^I/Au^I complex {[Au(C₆F₅)₂Tl]₂(L)}_n (4) features a polymeric structural nature with a metallic pseudo-rhombic Au₂Tl₂ core, which repeats itself forming a zig-zag polymer. In each Au₂Tl₂ unit only one thallium atom is bonded by the NS₃ donor set of the macrocyclic ligand and also forms two unsupported Au–Tl bonds with two [Au(C₆F₅)₂]⁻ units in an overall pseudo-octahedral geometry. The other thallium atom similarly bridges the same [Au(C₆F₅)₂]⁻ units and links a neighbouring Au₂Tl₂ moiety, thus exhibiting a distorted trigonal planar geometry being bonded only to three gold atoms with unsupported Au–Tl interactions. This complex displays an interesting thermochromic behaviour showing emissions mainly resulting from MM′CT transitions at room temperature. At 77 K a dual emission appears, probably arising from the two different thallium environments. DFT calculations have been carried out in the attempt to investigate the origin of the emissions of complex 4.