A step closer to the binary: the (1)(∞)[Bi6I20](2-) anion

Area of Science:

• Inorganic Chemistry
• Materials Science
• Coordination Chemistry

Background:

• Crown ethers are macrocyclic compounds known for their ability to selectively bind cations.
• Iodidobismuthates are a class of inorganic compounds containing bismuth and iodide ions, often exhibiting interesting structural and optical properties.
• The synthesis of novel bismuth-iodide complexes can lead to materials with tunable electronic and optical characteristics.

Purpose of the Study:

• To synthesize and characterize novel crown ether-based iodidobismuthates.
• To investigate the templating effect of different crown ether-based cations on the resulting structures.
• To explore the influence of the iodine-to-bismuth (I/Bi) ratio and inter-iodine (I···I) interactions on the optical properties of these compounds.

Main Methods:

• Synthesis of iodidobismuthate compounds using dibenzo-18-crown-6 (DB18C6), bismuth(III) iodide (BiI3), and alkali metal iodides (NaI or KI) in acetonitrile (MeCN).
• Structural characterization of the resulting compounds, including X-ray crystallography.
• Analysis of optical properties, correlating them with structural features and I/Bi ratios.

Main Results:

• Four new iodidobismuthate compounds were successfully prepared: [(DB18C6)Na(MeCN)2]4[Bi6I22]·2MeCN (1), [(DB18C6)Na(MeCN)2]4[Bi8I28]·6MeCN (2), [(DB18C6)Na(MeCN)2]2[Bi6I20]·3MeCN (3), and [(DB18C6)K(MeCN)]4[Bi6I22]·2MeCN (4).
• Compound 3 contains a novel strand-like anion, [Bi6I20]2-, with an I/Bi ratio of 3.33, which is the closest to that of binary BiI3 among the studied iodidobismuthates.
• The study explored how cation templating and variations in the I/Bi ratio affect the optical properties of these bismuth-iodide complexes.

Conclusions:

• Crown ether cations effectively template the formation of diverse iodidobismuthate structures.
• The I/Bi ratio and inter-iodine interactions significantly influence the optical properties of iodidobismuthates.
• Compound 3 represents a significant structural finding, offering a unique anion with an I/Bi ratio approaching that of the parent binary compound.