Nanocluster Formation and Stabilization Fundamental Studies: Investigating “Solvent-Only” Stabilization En Route to Discovering Stabilization by the Traditionally Weakly Coordinating Anion BF₄^- Plus High Dielectric Constant Solvents

Abstract

The nanocluster literature contains a wide variety of nanocluster stabilizing agents. In addition to the plethora of putative stabilizing additives, 12 claims appear of "solvent-only" stabilization of transition-metal nanoclusters-a hypothesis that is tested for the first time as part of the present studies. When the two main modes of nanocluster stabilization, electrostatic and steric are considered, "solvent-only" stabilization can only be steric (i.e., is not electrostatic). Solvent-only stabilization would, therefore, require that a strongly coordinated, perhaps even kinetically nonlabile, solvent be present on the nanocluster surface. Hence, an investigation has been conducted into potential sources for the stabilization of prototype Ir(0)n transition-metal nanoclusters prepared from [(1,5-COD)Ir(CH3CN)2][BF4] in five different solvents, with a special focus on the formulation and testing of alternative hypotheses regarding the true source of the nanocluster stabilization in putative solvent-only stabilization conditions. Seven total hypotheses are tested with five being initially ruled out; they are, namely, stabilization by (i) trace chloride (ii), surface hydrides, (iii) scavenged charge, (iv) solvent oxidative addition reactions with the nanocluster surface, or (v) polymerized solvent. This led in turn to two additional main alternative hypotheses: (vi) nanocluster surface ligation by high-donor number solvents (i.e., in the absence of anions) and (vii) nanocluster stabilization by surface-coordination of the traditionally weakly coordinating anion BF(4-). Our results reveal a significant contribution to nanocluster stability from the traditionally weakly coordinating BF(4-) in high dielectric constant solvents, such as propylene carbonate. Literature claims of solvent-only nanocluster stabilization are not supported by our findings. Overall, DLVO (Derjaugin-Landau-Verwey-Overbeek) theory of colloidal stability is supported and found to apply to even traditionally weakly coordinating anions.

Imidazolium ionic liquids as promoters and stabilising agents for the preparation of metal(0) nanoparticles by reduction and decomposition of organometallic complexes

“…Interestingly, the formation of an ethyl substituted IL BMEI$NTf 2 (BMEI ¼ 1-n-butyl-2-ethyl-3-methylimidazolium) was also observed by NMR spectroscopies (COSY, HETCOR and DOSY) and confirmed by electrospray mass spectrometry where cations at m/z ¼ 139 and 167 were observed with similar abundances, corresponding to [ (B 2 MI ¼ 1,2-di-n-butyl-3-methylimidazolium) was also observed by mass spectrometry, m/z ¼ 195, probably a result of oligomerisation of ethylene to 1-butene before reaction with the imidazolium cycle. The evidence gathered suggests that the observed decomposition could be due to the cleavage of the very acidic C2-H bond and the consequent in situ generation of NHC species, as already reported in the case of Ir(0)-NP preparation in ILs, [36][37][38][39][40] and with homogeneous complexes of Ni, 41 Pd,…”

Ruthenium Nanoparticles in Ionic Liquids – A Saga

“…The idea of NP stabilisation in ILs by a combination of surface hydrides and confinement in non-polar domains of the IL is similar to that previously reported in organic media (see Fig. 3), and in stark contrast to the often described "electrosteric stabilisation" model in ionic liquids, whereby the electropositive NP surface is surrounded by a double-layer of anions and cations forming a protective shell through electrostatic and DVLO type forces [67][68][69][70][71][72]. Fig.…”

Catalytic Applications of Metal Nanoparticles in Imidazolium Ionic Liquids

“…Moreover, XPS experiments indicate that the MNP surface is more susceptible to oxidation in air than the bulk metal and that this oxide layer may also be a significant source of stability of the metal nanoparticles. [34] It is noticea- Figure 2. A three-dimensional simplified schematic view of the arrangements of 1-ethyl-3-methylimidazolium cation associated with a tetrahedral anion showing the channels formed.…”