Self-assembly of a new class of rhenium(i)-based double stranded dinuclear monohelicates with their photophysical and electrochemical studies

Abstract

A new class of double stranded dinuclear monohelicates, fac-[{Re(CO)₃-(μ-L)-Re(CO)₃}Lⁿ] (1–4), were self-assembled from Re₂(CO)₁₀, a rigid bischelating donor (H₂-L: 1,4-dihydroxybenzoquinone (H₂-dhbq) for 1 and 3; 2,5-pyrazine dicarboxylic acid (H₂-pydc) for 2 and 4) and a flexible bis(monodentate) pyrazolyl N donor Lⁿ (L¹ = bis(4-((pyrazolyl)methyl)phenyl)methane for 1 and 2; L² = bis(4-((pyrazolyl)methyl)phenyl)methanone for 3 and 4) in mesitylene. Metallomacrocycle 1 was confirmed by single crystal X-ray crystallography. Although these helicates contain two organic ligand strands, only one strand is arranged in a helical fashion, which is an unprecedented form in the helicate architecture. The molecular structures of 1–4 as helicates and mesocates were optimized using DFT methods. The dynamic interconversion of the metallomacrocycles in solution was studied by ¹H NMR studies. The photophysical properties of 1–4 were studied experimentally and the nature of electronic transitions was determined by TD-DFT analysis. Quinonoid motif-based complexes 1 and 3 displayed strong visible light absorption. The redox properties of 1–4 were studied using cyclic voltammetry.