Bis(4-aminopyridinium) and bis(2-amino-6-methylpyridinium) cations stabilised by [MS4]2− anions: Synthesis, crystal structures, Hirshfeld surface analysis and sulfur transfer reactions

Four new organic ammonium tetrasulfidometallates: (4-aminopyridinium)₂[MoS₄]·H₂O 1, (4-aminopyridinium)₂[WS₄]·H₂O 2, (2-amino-6-methylpyridinium)₂[MoS₄] 3, and (2-amino-6-methylpyridinium)₂[WS₄] 4 have been synthesized by a well-known base promoted cation exchange method. All compounds were characterized by elemental analysis, IR/Raman/UV–Vis spectroscopy, thermogravimetric analysis, and X-ray crystallography. The structures of 1 and 2 consist of unique tetrahedral [MoS₄]²⁻ and [WS₄]²⁻ dianions, which are charge-balanced by crystallographically independent 4-aminopyridinium monocations. Additionally, both have a lattice water molecule, which contributes to the overall stability of their structures. In compounds 3 and 4, 4-aminopyridinium of 1 and 2 are replaced by 2-amino-6-methylpyridinium cation and lack lattice water. The different H-bonding interactions viz NH⋯S, CH⋯S, NH⋯O and OH⋯O are observed in 1 and 2, which are reduced to two viz. NH⋯S and CH⋯S in 3 and 4. The weak interactions (NH⋯O and OH⋯O) originating from lattice water further interlink cations with [MoS₄]²⁻ and [WS₄]²⁻ anions forming extended networks in 1 and 2. To understand the importance of intermolecular interactions in the structures of 1–4, the Hirshfeld surface analyses were performed. The enrichment ratio (E) in the structures of compounds 1–4 was obtained. Compounds 1–4 were tested for their sulfur transfer ability. Only compound 1 showed a predominant disulfide product formation in reaction with 1,3-dibromopropane.