Dependence of Transition-Metal Telluride Phases on Metal Precursor Reactivity and Mechanistic Implications

Abstract

Modern bottom-up synthesis to nanocrystalline solid-state materials often lacks the reasoned product control that molecular chemistry boasts from having over a century of research and development. In this study, six transition metals including iron, cobalt, nickel, ruthenium, palladium, and platinum were reacted with the mild reagent didodecyl ditelluride in their acetylacetonate, chloride, bromide, iodide, and triflate salts. This systematic analysis demonstrates how rationally matching the reactivity of metal salts to the telluride precursor is necessary for the successful production of metal tellurides. The trends in reactivity suggest that radical stability is the better predictor of metal salt reactivity than hard–soft acid–base theory. Of the six transition-metal tellurides, the first colloidal syntheses of iron and ruthenium tellurides (FeTe2 and RuTe2) are reported.

Controlling Phase in Colloidal Synthesis

“…While halides can do one- or two-electron chemistry, trifoliate can only do two-electron chemistry; thus, it was inferred that one-electron chemistry is underpinning the formation of metal tellurides from didodecylditelluride. The reactivity of all the metal centers correlated with the radical stability of the counter-species, with metal iodides being the most reactive . More recently, the group of Hernández-Pagán similarly found the phase control of the MnS and MnSe systems was sensitive to the halide (F – , Cl – , Br – , I – ) counterion of the manganese precursor employed during synthesis …”

“…Tellurium reagents include didodecylditelluride, elemental tellurium, and TeO 2 in reducing environments . Being so low on the periodic table, tellurium’s soft nature and highly negative reduction potential makes it unlikely to react with a metal at high temperatures common to nanocrystalline syntheses . In these conditions, tellurium precursors will often decompose into Te(0) particles.…”

“… 8 Common selenium precursors include elemental selenium in octadecene or amines, selenourea, 24 aromatic and dialkyl diselenides. 25 Tellurium reagents include didodecylditelluride, 26 elemental tellurium, 27 and TeO 2 in reducing environments. 28 Being so low on the periodic table, tellurium’s soft nature and highly negative reduction potential makes it unlikely to react with a metal at high temperatures common to nanocrystalline syntheses.…”

“…The reactivity of all the metal centers correlated with the radical stability of the counter-species, with metal iodides being the most reactive. 26 More recently, the group of Hernández-Pagán similarly found the phase control of the MnS and MnSe systems was sensitive to the halide (F – , Cl – , Br – , I – ) counterion of the manganese precursor employed during synthesis. 49 …”

“…This trend has been seen for sulfides, 42 selenides, 42 , 43 , 108 and tellurides. 26 , 109 The chemistry of these precursors lends them to reactivity at moderate temperatures, hindering thermal activation of transformations from metastable to thermodynamic phases. Second, as hypothesized in the case of Cu 2 Se, 108 their decomposition may give slow, careful deposition of monomers on growing nuclei through their particular reaction mechanisms.…”