Thermally Controlled Synthesis of Octahedral Rhenium Clusters with 4,4′-Bipyridine and CN− Apical Ligands

Anton A Ulantikov,Konstantin A Brylev,Natalia V Maltseva,Yuri V Mironov,Taisiya S Sukhikh,Yakov M Gayfulin,Evgeniy N Gribov

doi:10.3390/sym13112187

Abstract

The selective preparation, structural and spectroscopic study of two new rhenium cluster complexes trans-[Re6S8(bpy)4(CN)2] and trans-[Re6S8(bpy)2(CN)4]2− (bpy = 4,4′-bipyridine) obtained by reactions of corresponding hexarhenium cyanohalides with molten bpy are reported. The complexes were crystallized as solvates, displaying supramolecular structures based on cluster units linked by numerous weak interactions with bpy molecules. The molecular compound trans-[Re6S8(bpy)4(CN)2] (1) is insoluble in water and common organic solvents, while the ionic compound trans-Cs1.7K0.3[Re6S8(bpy)2(CN)4] (2) is somewhat soluble in DMSO, DMF and N-methylpyrrolidone. The presence of the redox-active ligand bpy leads to the occurrence of multi-electron reduction transitions in a solution of 2 at moderate potential values. The ambidentate CN− ligand is the secondary functional group, which has potential for the synthesis of coordination polymers based on the new cluster complexes. In addition, both new compounds show a weak red luminescence, which is characteristic of complexes with a {Re6S8}2+ cluster core.

Highlights

The synthesis of molecular complexes of transition metals with redox-active ligands is one of the current major directions of inorganic chemistry
Understanding the mutual influence of the transition metal cation and ligand composition on the electronic structure of the complex, the number and position of electrochemical transitions plays a crucial role in the study of the properties of redox-active complexes
Each rhenium atom can be coordinated by an apical ligand of an organic or inorganic nature

Summary

Introduction

The synthesis of molecular complexes of transition metals with redox-active ligands is one of the current major directions of inorganic chemistry. The physical and chemical properties of complexes based on octahedral cluster cores {Re6Q8}2+ (Q = S or Se) have attracted a lot of attention [5] These clusters are composed of an octahedral metallocluster ReIII6 consisting of rhenium atoms linked by covalent bonds. The cluster core is redox-active and capable of one-electron oxidation, with the formation of a 23-electron metal center ReIII5ReIV [6,7,8] The position of this transition is determined mainly by the type of chalcogenide ligands and weakly depends on the type of apical ligands. The potentials of the corresponding electrochemical transitions, as a rule, display a significant anodic shift [10] This feature motivated us to study the mutual influence of the {Re6Q8}2+ cluster core and coordinated redox-active ligands on the electrochemical properties of the resulting complexes. An unusual finding in this work is the discovered ability of bpy molecules to replace the CN− ligands of the precursor cluster [Re6S8(CN)4Cl2]4− during the melt synthesis, which is one of very few reports of the lability of CN− ligands in the chemistry of octahedral rhenium clusters

Materials and methods

Synthesis

Luminescence