The microwave-induced decomposition of bis{N,N'-diisopropylacetamidinate}nickel(II) [Ni{MeC(NiPr) } ] or bis(1,5-cyclooctadiene)nickel(0) [Ni(COD) ] in imidazolium-, pyridinium-, or thiophenium-based ionic liquids (ILs) with different anions (tetrafluoroborate, [BF ] , hexafluorophosphate, [PF ] , and bis(trifluoromethylsulfonyl)imide, [NTf ] ) yields small, uniform nickel nanoparticles (Ni NPs), which are stable in the absence of capping ligands (surfactants) for more than eight weeks. The soft, wet-chemical synthesis yields the metastable Ni hexagonal close-packed (hcp) and not the stable Ni face-centered cubic (fcc) phase. The size of the nickel nanoparticles increases with the molecular volume of the used anions from about 5 nm for [BF ] to ≈10 nm for [NTf ] (with 1-alkyl-3-methyl-imidazolium cations). The n-butyl-pyridinium, [BPy] , cation ILs reproducibly yield very small nickel nanoparticles of 2(±1) nm average diameter. The Ni NPs were characterized by high-resolution transmission electron microscopy (HR-TEM) and powder X-ray diffraction. An X-ray photoelectron spectroscopic (XPS) analysis shows an increase of the binding energy (E ) of the electron from the Ni 2p orbital of the very small 2(±1) nm diameter Ni particles by about 0.3 eV to E =853.2 eV compared with bulk Ni , which is traced to the small cluster size. The Ni nanoparticles show superparamagnetic behavior from 150 K up to room temperature. The saturation magnetization of a Ni (2±1 nm) sample from [BPy][NTf ] is 2.08 A m kg and of a Ni (10±4 nm) sample from [LMIm][NTf ] it is 0.99 A m kg , ([LMIm]=1-lauryl-3-methyl- imidazolium). The Ni NPs were active catalysts in IL dispersions for 1-hexene or benzene hydrogenation. Over 90 % conversion was reached under 5 bar H in 1 h at 100 °C for 1-hexene and a turnover frequency (TOF) up to 1330 mol (mol ) h or in 60 h at 100 °C for benzene hydrogenation and TOF=23 mol (mol ) h .

The simultaneous determination of halide impurities (fluoride, chloride, bromide, and iodide) and ionic liquid (IL) anions (tetrafluoroborate, hexafluorophosphate, and triflimide) using ion chromatography was developed with a basic, non‐gradient ion chromatography system. The non‐gradient method uses the eluent Na2CO3/NaHCO3 in water/acetonitrile (70:30 v:v) on the AS 22 column to enable a rapid and simultaneous analysis of different IL and halide anions within an acceptable run‐time (22 min) and with good resolution R of larger than 2.4, a capacity k′ between 0.4 and 5.1, selectivities α between 1.3 and 2.1, and peak asymmetries As of less than 1.5. Halide impurities below 1 ppm (1 mg·L–1 of prepared sample solution) could be quantified. A range of ionic liquids with tetrafluoroborate [BF4]–, hexafluorophosphate [PF6]–, and bis(trifluoromethylsulfonyl)imide (triflimide) [NTf2]– anions combined with cations based on imidazole, pyridine, and tetrahydrothiophene could be analyzed for their anion purity. The IL‐cations do not influence the chromatographic results. With the analysis of 18 ILs differing in their cation‐anion combination we could prove the general applicability of the described method for the anion purity analysis of ionic liquids with respect to halide ions. The IL‐anion purity of most ILs was above 98 wt %. The highest IL‐anion purity was 99.8 wt %, implying anion impurities of only 0.2 wt %. The used halide anion from the synthesis route was the major anion impurity, yet with chloride also bromide and fluoride (potentially from hydrolysis of [BF4]–) were often detected. When iodide was used, at least chloride but sometimes also bromide and fluoride was present. However, even if the IL‐anion content is above 99 wt %, it does not necessarily indicate an ionic liquid devoid of other impurities. From the IC analysis, one can also deduce a possible cation impurity if one takes into account the expected (calculated) IL‐anion content. A matching experimental and theoretical IL‐anion content excludes, a higher experimental content indicates the presence of residual KBF4, NH4PF6, or LiNTf2 salt from the halide to IL‐anion exchange.