Design, synthesis, characterization, and preliminary complexation studies of chromogenic vanadophiles: 1,3-alternate thiacalix[4]arene tetrahydroxamic acids

Synthesis, Structure, and Characterization of Thiacalix[4]-2,8-thianthrene

Sulfur-containing macrocycles have attracted substantial interest because they exhibit unique characteristics due to their polygonal ring-shaped skeleton. In this study, a thianthrene-based cyclic tetramer with the sulfur linker, thiacalix[4]-2,8-thianthrene (TC[4]TT), was successfully prepared from a cyclo-p-phenylenesulfide derivative using acid-induced intramolecular condensation. Single crystal X-ray diffraction revealed that TC[4]TT adopts an alternative octagonal form recessed to the inner side. Its internal cavity included small solvents, such as chloroform and carbon disulfide. Due to its polygonal geometry, TC[4]TT laminated in a honeycomb-like pattern with a porous channel. Furthermore, TC[4]TT showed fluorescence and phosphorescence emission in a CH₂Cl₂ solution at ambient and liquid nitrogen temperatures. Both emission bands were slightly redshifted compared with those of the reference compounds (di(thanthren-2-yl)sulfane (TT₂S) and thianthrene (TT)). This work describes a sulfur-containing thiacalixheterocycle-based macrocyclic system with intriguing supramolecular chemistry based on molecular tiling and photophysical properties in solution.

Binding of a TlCl Entity by a Tetragold Tetramercaptothiacalixarene Metalloligand via Metallophilic Interactions

The successive auration of p-tert-butyltetramercaptotetrathiacalix[4]arene, H₄ (MTC[4]), with gold(I) phosphine units was investigated. Through deprotonation with NaOMe, followed by salt metathesis reactions with (PR₃ )AuCl (R=Me, Ph) complexes with two and three [(PR₃ )Au]⁺ moieties could be prepared and isolated, namely [(Ph₃ PAu)₂ H₂ (MTC[4])] and [(Me₃ PAu)₃ H(MTC[4])]. In [(Me₃ PAu)₃ H(MTC[4])] two gold atoms already come close enough to undergo aurophilic interactions. To introduce a fourth [(PR₃ )Au]⁺ entity TlOEt had to be used for the deprotonation, which led to the finding that four gold atoms organised by the (MTC[4])^4- coordination platform are able to bind and stabilize a TlCl entity, yielding [(Me₃ PAu)₄ TlCl(MTC[4])]. As evidenced by structural and theoretical investigations the binding occurs through strong metallophilic interactions, which lead to photoluminescence at low temperatures.