In this work, various transition and main group metals were heated in a low temperature molten sulfur/iodine flux to produce metal sulfides and metal sulfide iodides, in a one-pot synthesis method that eliminates the use of toxic or costly precursors. The lower reaction temperatures of a S/I2 flux, enables the synthesis of metastable (Bi13S18I2 and PbSnS3) and kinetically driven phases. Variables such as reaction temperature and iodine content were explored to determine their effects on reactivity, phase yield, crystallinity, and morphology. All metals were reactive within the temperature range studied (300-600 °C). Reactions containing transition metals formed a variety of metal sulfide phases. Ternary metal sulfide iodides were only observed for reactions with main group metals. Bismuth reactions produced three different products (Bi2S3, BiSI, and Bi13S18I2). The latter compound, formerly reported as “Bi19I3S27,” grew as well formed needles from the flux. This enabled extensive crystallographic studies by single crystal XRD and powder synchrotron XRD. These data allow a more accurate assignment of the disordered bismuth sites in the structure, indicating formation of subvalent Bi24+ dimers. Thermal decomposition studies and Raman spectroscopy support this structural model, and electronic structure calculations and optical reflectance studies indicate this compound is an indirect band gap semiconductor with band gap of 0.3 eV. Additionally, this work studied reactions of mixed metal systems of bismuth/antimony, bismuth/indium, and lead/tin in S/I2 flux. It was determined that Bi13-xSbxS18I2 can only reach a substitution limit of 25% for antimony on the bismuth sites. The complete solid solution range was observed for the phase Bi1-xSbxSI. Two-mode behavior was seen in Raman spectra, indicating localized covalent bonding. UV/Vis/NIR diffuse reflectance measurements for Bi1-xSbxSI were unable to indicate how antimony substitution affects absorption edge shifts due to the variation in substitution between crystals within the same product matrix. Single crystals of InBiS3 could be synthesized from reactions of bismuth and indium in sulfur/iodine flux, but it was not able to be synthesized phase pure. Bi2In4S9 was always present as a byproduct, preventing UV/Vis/NIR diffuse reflectance measurements. Similarly, single crystals of PbSnS3 were synthesized, but were produced with byproducts of SnS2 and PbI2 preventing additional characterization. PbSnS3 is an analogue of the mixed valent tin sulfide (Sn2S3), where lead is in the 2+ oxidation state and tin in the 4+ state. Microwave-assisted heating, an alternative and inductive heating process, was explored and products were compared to those synthesized from traditional furnace heating. The use of low temperatures (<500 °C) and mild iodine contents (<0.5 mmol per 10 mmol S) for reactions lead to the formation of many compounds at much lower bulk reaction temperatures and shorter reaction times than seen in the traditional furnace reactions. Some of these materials include metastable and mixed valent phases.
