Stijn Schaltin

Copper(I)‐Containing Ionic Liquids for High‐Rate Electrodeposition

New metal-containing ionic liquids [Cu(CH(3)CN)(n)][Tf(2)N] (n=2, 4; Tf(2)N=bis(trifluoromethylsulfonyl)- amide) have been synthesised and used as a non-aqueous electrolyte for the electrodeposition of copper at current densities greater than 25 A dm(-2). The tetrahedral copper(I)-containing cation in [Cu(CH(3)CN)(4)][Tf(2)N] is structurally analogous to quaternary ammonium and phosphonium ionic liquids and overcomes problems of metal solubility and mass transport. Two CH(3)CN ligands are removed at elevated temperatures to give [Cu(CH(3)CN)(2)][Tf(2)N], which can be used as a concentrated non-aqueous electrolyte. The structural and electrochemical characterisation of these compounds is described herein.

Cobalt(II) complexes of nitrile-functionalized ionic liquids.

A series of nitrile-functionalized ionic liquids were found to exhibit temperature-dependent miscibility (thermomorphism) with the lower alcohols. Their coordinating abilities toward cobalt(II) ions were investigated through the dissolution process of cobalt(II) bis(trifluoromethylsulfonyl)imide and were found to depend on the donor abilities of the nitrile group. The crystal structures of the cobalt(II) solvates [Co(C(1)C(1CN)Pyr)(2)(Tf(2)N)(4)] and [Co(C(1)C(2CN)Pyr)(6)][Tf(2)N](8), which were isolated from ionic-liquid solutions, gave an insight into the coordination chemistry of functionalized ionic liquids. Smooth layers of cobalt metal could be obtained by electrodeposition of the cobalt-containing ionic liquids.

Influence of the Anion on the Electrodeposition of Cobalt from Imidazolium Ionic Liquids

Cyclic voltammetry and absorption spectrophotometry were used to examine the complex formation of cobalt(II) in the ionic liquids 1-butyl-3-methylimidazolium chloride ([C 4 mim]Cl) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C 4 mim][Tf 2 N]). In [C 4 mim]Cl, cobalt(II) is complexed as [CoCl 4 ] 2- at CoCl 2 concentrations less than 33 mol %. Cyclic voltammograms show that cobalt cannot be electrodeposited at these concentrations. However, cobalt metal can be electrodeposited at CoCl 2 concentrations above the threshold concentration of 33 mol %. In the ionic liquid [C 4 mim][Tf 2 N] there is no threshold CoCl 2 concentration for electrodeposition due to the absence of [CoCl 4 ] 2- .

Electrodeposition from Cationic Cuprous Organic Complexes: Ionic Liquids for High Current Density Electroplating

The electrochemical behavior of the low-melting copper salts CuMeCNxTf2N and CuPhCNxTf2Nx = 2–4, where MeCN is acetonitrile and PhCN is benzonitrile, is presented. In these compounds, the copperI ion is a main component of the ionic liquid cation. Consequently, the copper concentration is the highest achievable for an ionic liquid and this permits to obtain a good mass transport and high current densities for electrodeposition. The cathodic limit of the ionic liquid is the reduction of copperI to copper metal instead of the breakdown of the cation as in conventional ionic liquids. It is shown that pure, crack-free copper layers can be deposited from these copper-containing ionic liquids in unstirred solutions at current densities up to 25 A dm �2

Heteroleptic silver-containing ionic liquids

The first examples of structurally characterised mixed-ligand metal-containing ionic liquids (ILs) are presented, synthesised by the use of different N-alkylimidazoles. The cations consist of two-coordinate silver(i) centres ligated by two different N-alkylimidazole ligands. It is shown that the resulting ionic liquids have lower melting points than the single ligand ILs.

Electrodeposition of germanium from the ionic liquid 1-butyl-1-methylpyrrolidinium dicyanamide

The electrodeposition of germanium from the ionic liquid 1-butyl-1-methylpyrrolidinium dicyanamide ([BMP][DCA]) and a mixture of [BMP][DCA] and 1-butyl-1-methylpyrrolidinium chloride ([BMP]Cl) was studied using cyclic voltammetry and using an electrochemical quartz crystal microbalance (EQCM). [GeCl4(BuIm)2] (BuIm = N-butylimidazole) was used as germanium source as it has a solubility of 0.47 M, up to 13 times the solubility of GeCl4 in [BMP][DCA]. Cyclic voltammograms show an irreversible electrochemical behavior and two reduction waves were observed. The wave at the more positive potential was assigned to the reduction of Ge(4+) to Ge(2+). The wave at the more negative potential was attributed to the formation of Ge(0). The diffusion coefficient of Ge(4+) in [BMP][DCA] containing 0.1 M [GeCl4(BuIm)2] is 1.1 × 10(-12) m(2) s(-1), and the exchange current density is 2 × 10(-4) A m(-2) at 50 °C. Polymerization of dicyanamide anions took place at the anode in the solution of [BMP][DCA]. The polymerization reaction could be avoided by using an equimolar [BMP]Cl-[BMP][DCA] mixture as electrolyte. Smooth, porous germanium films were electrodeposited on both copper and silicon substrates.

Continuous Synthesis of Peralkylated Imidazoles and their Transformation into Ionic Liquids with Improved (Electro)Chemical Stabilities

A versatile and efficient method to synthesize tetrasubstituted imidazoles via a one-pot modified Debus-Radziszewski reaction and their subsequent transformation into the corresponding imidazolium ionic liquids is reported. The tetrasubstituted imidazoles were also synthesized by means of a continuous flow process. This straightforward synthetic procedure allows for a fast and selective synthesis of tetrasubstituted imidazoles on a large scale. The completely substituted imidazolium dicyanamide and bis(trifluoromethylsulfonyl)imide salts were obtained via a metathesis reaction of the imidazolium iodide salts. The melting points and viscosities are of the same order of magnitude as for their non-substituted analogues. In addition to the superior chemical stability of these novel ionic liquids, which allows them to be applied in strong alkaline media, the improved thermal and electrochemical stabilities of these compounds compared with conventional imidazolium ionic liquids is also demonstrated by thermogravimetrical analysis (TGA) and cyclic voltammetry (CV). Although increased substitution of the ionic liquids does not further increase thermal stability, a definite increase in cathodic stability is observable.

Modeling of Aluminium Deposition from Chloroaluminate Ionic Liquids

A finite-element model of the electrodeposition of aluminium from chloroaluminate ionic liquids is introduced. The purpose of this model is to give an explanation for the reasonable current densities that can be achieved in chloroaluminate ionic liquids despite the fact that the electrochemically active Al2Cl 7 complexes are transformed into inactive AlCl 4 complexes during the electrodeposition of aluminium. The obtainable current density in the electrodeposition from chloroaluminate ionic liquids strongly depends on the chemical rate constants for establishing the equilibrium Al2Cl 7 þ Cl 2AlCl 4 . A high current (up to 3000 A m ) was found for both high and low rate constants whereas a minimum current (200 A m ) was found for intermediate rate constants due to kinetics and thermodynamics. The model is compared to experiments conducted in the ionic liquid AlCl3 [C2mim]Cl (60/40 mol%) where [C2mim]Cl is 1-ethyl-3-methylimidazolium chloride. VC 2011 The Electrochemical Society. [DOI: 10.1149/1.3623781] All rights reserved.

Liquid Nickel Salts: Synthesis, Crystal Structure Determination, and Electrochemical Synthesis of Nickel Nanoparticles

New nickel-containing ionic liquids were synthesized, characterized and their electrochemistry was investigated. In addition, a mechanism for the electrochemical synthesis of nanoparticles from these compounds is proposed. In these so-called liquid metal salts, the nickel(II) cation is octahedrally coordinated by six N-alkylimidazole ligands. The different counter anions that were used are bis(trifluoromethanesulfonyl)imide (Tf2 N(-) ), trifluoromethanesulfonate (OTf(-) ) and methanesulfonate (OMs(-) ). Several different N-alkylimidazoles were considered, with the alkyl sidechain ranging in length from methyl to dodecyl. The newly synthesized liquid metal salts were characterized by CHN analysis, FTIR, DSC, TGA and viscosity measurements. An odd-even effect was observed for the melting temperatures and viscosities of the ionic liquids, with the complexes with an even number of carbon atoms in the alkyl chain of the imidazole having a higher melting temperature and a lower viscosity than the complexes with an odd number of carbons. The crystal structures of several of the nickel(II) complexes that are not liquid at room temperature were determined. The electrochemistry of the compounds with the lowest viscosities was investigated. The nickel(II) cation could be reduced but surprisingly no nickel deposits were obtained on the electrode. Instead, nickel nanoparticles were formed at 100 % selectivity, as confirmed by TEM. The magnetic properties of these nanoparticles were investigated by SQUID measurements.

Direct Cu-on-Ta electroplating from ionic liquids in high vacuum

Jan.Fransaer@mtm.kuleuven.be, Tel.: +32 16 32 12 86, Fax: +32 16 32 19 91 Smooth layers of 20 nm of copper have been deposited on a tantalum substrate from ionic liquids under high vacuum conditions. By electrochemical vacuum deposition (EVD) it is possible to achieve extremely low concentrations of oxygen and water, so that the tantalum electrode does not oxidize. Due to the low vapor pressure of ionic liquids, no evaporation of the electrolyte was observed in high vacuum. The wide electrochemical windows of the ionic liquids are advantageous to obtain nucleation densities up to 8 10