Reversible Redox Transformations of Bridging Sulfide Ligands within Bioctahedral Rhenium Cluster Anions

Abstract

The present study provides new experimental data on the reactivity of sulfur‐based ligands connected to Re atoms. It was recently discovered that oxidation of µ‐S ligands within the bioctahedral [Re12CS14(µ‐S)3(CN)6]6– cluster anion using H2O2 led to the formation of µ‐SO2 and µ‐SO3 products. This work is focused on the investigation of the opposite process – reduction of the [Re12CS14(µ‐SO2)3(CN)6]6– anion to [Re12CS14(µ‐S)3(CN)6]6– by sulfide ions in an aqueous medium under mild conditions. The reduction results in a slow change of the solution colour, making it possible to investigate in detail the intermediate products. Analysis of the reaction mixture by ESI mass spectrometry revealed that a series of cluster anions [Re12CS17On(CN)6]6– (n = 0–5) was generated during the process. This indicates stepwise chemical reduction of bridging SO2 ligands proceeding through the formation of µ‐SO ligands. In this way, twelve‐nuclear rhenium clusters demonstrate a unique, fully reversible redox cycle of their µ‐bridging ligands, keeping the cluster core unchanged. Two mixed‐ligand cluster anions, [Re12CS14(µ‐SO2)2(µ‐S)(CN)6]6– and [Re12CS14(µ‐SO2)(µ‐S)2(CN)6]6–, were found to be the major reaction intermediates. The former was crystallised with [Cu(NH3)5]2+ and [Cd(NH3)n]2+ ammine cations and investigated by single‐crystal X‐ray diffraction. To understand the electronic structure and charge distribution in [Re12CS17On(CN)6]6– cluster anions, DFT calculations were also carried out.

Facile Substitution of Bridging SO22– Ligands in Re12 Bioctahedral Cluster Complexes

“…According to the previous study, the μ-SO 2 2– groups are easily converted to μ-SO 3 2– groups (with the formation of Re–O–S–Re bridges) by atmospheric oxygen in aqueous and CH 3 CN solutions at room temperature. , Moreover, there was a mass-spectrometric evidence for formation of a small amount of SO 4 2– -containing clusters. Combining these data with the current observations, one can suppose that heating of the K 6 [Re 12 CS 14 (μ-SO 2 ) 3 (CN) 6 ] salt in the presence of oxygen causes oxidation of μ-SO 2 2– groups to μ-SO 3 2– , both in solution and in the solid state.…”

“…Therefore, in order to structurally investigate the [Re 12 CS 14 (μ-O) 3 (CN) 6 ] 6– anion, we employed a different approach. As was shown earlier, the bioctahedral Re cluster anions can often be isolated by crystallization from aqueous ammonia solutions containing the d -metal cations, such as Cu 2+ , Cd 2+ , and Ni 2+ . Following this idea, we used compound 1 in the reaction with Cu­(II) ammine complexes, which allowed us to successfully crystallize compound 2 .…”

“…The resulting anion, [Re 12 CS 14 (μ-SO 2 ) 3 (CN) 6 ] 6– , belongs to a narrow group of Re clusters containing bridging sulfur oxide ligands . Further investigations revealed that μ-SO 2 2– ligands can be oxidized by air oxygen or reduced by sulfide and selenide ions to form μ-SO 3 2– or μ-SO 2– ligands, respectively, without undesirable destruction of the cluster core . It is noteworthy that, during these transformations, the μ-bridging groups retain their formal oxidation state (2−), which causes the resulting anions to be of the same total charge (6−) and the same CVE number (46).…”

“…DOI:10.1021/acs.inorgchem.7b01889 Inorg.Chem. 2017, 56, 12389−12400 T h i s c o n t e n t i s o n l y l i c e n s e d f o r c o n s u m p t i o n b y A u t h o r i z e d i n d i v i d u a l n o t d i r e c t l y a s s o c i a t e d w i t h s c i t e i s p r o h i b i t e d .…”