Silver Coordination Chemistry of the Weakly Basic Cage As 4 S 4

By reacting As 4 S 4 (realgar) with Ag[Al(OR F ) 4 ] [R F = C(CF 3 ) 3 ] in SO 2 or ortho ‐difluorobenzene ( o ‐dfb) at room temperature, the compounds Ag(As 4 S 4 )(SO 2 ) 2 [Al(OR F ) 4 ] ( 1 ) and Ag 3 (As 4 S 4 ) 4 ( o ‐dfb)[Al(OR F ) 4 ] 3 ( 2 ) were obtained and characterized by single‐crystal X‐ray structure determinations, Raman spectroscopy, as well as solution NMR spectroscopy and mass spectrometry. Compound 1 aggregates to form a one‐dimensional polymer including SO 2 ligands binding to the metal cation. Compound 2 forms a two‐dimensional polymer displaying an unprecedented coordination mode of the ligand through one of the arsenic atoms. As a side reaction in o ‐dfb, small amounts of the oxidation product As 3 S 4 [Al(OR F ) 4 ] ( 3 ) form. This result indicates that coordination to arsenic is energetically near to the degradation and oxidation of the cluster. Experiments, as well as orienting DFT calculations suggest that the As 4 S 4 cage is an inferior ligand, compared to the nortricyclane cages P 4 E 3 (E = S, Se) and As 4 S 3 . Electronegativity arguments, as well as population analyses with three independent methods suggest that the sulfur atoms in realgar always bear a negative partial charge. Thus, if the coordination of the ligand is a charge‐controlled reaction, coordination of realgar should proceed through the sulfur atoms. However, the close energetic proximity of HOMO and HOMO–1 indicates that frontier orbital control could either proceed through an η 2 (S; S), or η 1 (As) coordination, as observed in one case.