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Article

Tetrabromidocuprates(II)—Synthesis, Structure and EPR

1
Institute of Chemistry, University of Potsdam, Karl-Liebknechtstr.-Str. 24-25, Potsdam D-14476, Germany
2
Engineering Education Research Group, Hamburg University of Technology (TUHH), Am Schwarzberg-Campus 3 (E), Hamburg D-21073, Germany
*
Author to whom correspondence should be addressed.
Int. J. Mol. Sci. 2016, 17(4), 596; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms17040596
Submission received: 16 March 2016 / Revised: 11 April 2016 / Accepted: 14 April 2016 / Published: 20 April 2016
(This article belongs to the Special Issue Ionic Liquids 2016 and Selected Papers from ILMAT III)

Abstract

:
Metal-containing ionic liquids (ILs) are of interest for a variety of technical applications, e.g., particle synthesis and materials with magnetic or thermochromic properties. In this paper we report the synthesis of, and two structures for, some new tetrabromidocuprates(II) with several “onium” cations in comparison to the results of electron paramagnetic resonance (EPR) spectroscopic analyses. The sterically demanding cations were used to separate the paramagnetic Cu(II) ions for EPR measurements. The EPR hyperfine structure in the spectra of these new compounds is not resolved, due to the line broadening resulting from magnetic exchange between the still-incomplete separated paramagnetic Cu(II) centres. For the majority of compounds, the principal g values (g and g) of the tensors could be determined and information on the structural changes in the [CuBr4]2− anions can be obtained. The complexes have high potential, e.g., as ionic liquids, as precursors for the synthesis of copper bromide particles, as catalytically active or paramagnetic ionic liquids.

Graphical Abstract

1. Introduction

Metal-containing ionic liquids (ILs) or ionic liquid crystals (ILCs) are of interest for a variety of technical applications, e.g., as precursors for the synthesis of (nano)particles, magnetic or thermochromic materials [1,2,3] or as extraction agents [4] and catalysts [5,6,7,8]. Tetrahalidometalate complexes exhibit many of these interesting properties. Also liquid-crystalline ILs based on tetrahalidometalates have been reported [9,10,11,12,13]. Some ILs and ILCs combining tetrahalidocuprate dianions with alkylpyridinium cations can serve as precursors for inorganic materials [2,14,15,16,17]. A variety of these metal-containing ionic liquids show interesting electrochemical properties as electrochromy and/or magnetic behaviour [18,19]. The properties of ionic liquid materials such as tuneable acidity, polarity, amphiphilic character, coordinating ability, and miscibility with many compounds might be combined with the unique properties introduced by the metal ions. ILs of this type are also of interest as catalysts, as alternative solvents and even morphology templates for inorganic materials simultaneously. Reports on tetrahalidometalate-based ILs/ILCs and their applications as well as their structural characterization are still relatively rare [2,10,11,12,13,20,21,22,23,24,25,26,27,28,29,30,31,32]. We present the syntheses, electron paramagnetic resonance (EPR) spectra and two X-ray structures of some new tetrabromidocuprate(II) compounds. The following cations with different steric demand were used to separate the paramagnetic Cu(II) ions for the EPR measurements (see Scheme 1): the homogenously substituted tetraalkyl onium cations with varying chain lengths tetraethylammonium, (Et4N+), tetrabutylphosphonium, (Bu4P+), tetrahexylammonium, (Hex4N+), the benzyl/alkyl substituted ammonium cations benzyltrimethylammonium, (BzlMe3N+), benzyltriethylammonium, (BzlEt3N+), benzyltributylammonium, (BzlBu3N+), the alkyltriphenylphosphonium cations ethyltriphenylphosphonium, (EtPh3P+), hexyltriphenylphosphonium, (HexPh3P+) and the long chain cations dodecyltrimethylammonium, (C12H25Me3N+), hexadecylpyridinium, (C16H33-py+), hexadecyldimethylammonium, (C16H33)2Me2N+), giving raise to lamellar structures [33]. It is known that tetrahalidocuprate(II)-ions present a high structural flexibility. Thus, the complex anion adopts coordination geometries between square-planar and tetrahedral. Recently we have shown that there is a correlation of EPR parameters and the isotropic or averaged g-values with the degree of geometrical distortion in the coordination sphere of tetrahalidocuprates expressed by the cis-angle, the average of the four smallest X-Cu-X angles of the tetrahalidocuprate dianion [33,34,35].

2. Results and Discussion

2.1. X-ray Crystallography

Table 1 summarizes the crystallographic data and refinement parameters for the structures of (BzlEt3N)2[CuBr4] (5) and (HexPh3P)2[CuBr4] (8).

2.2. Bis(benzyltriethylammonium)tetrabromidocuprate(II) (5)

(BzlEt3N)2[CuBr4] (5) crystallizes in the monoclinic space group P21/c with four formula units per unit cell. The corresponding lattice parameters are a = 15.1019(5) Å, b = 11.6664(5) Å, c = 17.5517(6) Å, and β = 99,166(3)°. The complex dianion has a distorted tetrahedral geometry with Br–Cu–Br angles between 98.2° and 131.8° (see Table 2), the resulting cis-angle, the average of the four smallest angles, is 99.8°. The shortest Cu···Cu distances are 9.12 and 9.44 Å. Figure 1 shows the molecular structure of (BzlEt3N)2[CuBr4] (5). The structure is stabilized by a series of hydrogen bonds (see Table 3).

2.3. Bis(hexyltriphenylphosphonium)tetrabromidocuprate(II) (8)

(HexPh3P)2[CuBr4] (8) crystallizes in the monoclinic space group P21/n with Z = 4. The corresponding lattice parameters are a = 10.7410(3) Å, b = 22.4775(9) Å, c = 19.6455(6) Å, and β = 99,807(2)°. This complex dianion has also a distorted tetrahedral geometry with Br–Cu–Br angles between 100.4° and 124.8° (Table 4), with a resulting cis-angle of 103.3°. The shortest Cu···Cu distances are 10.62 and 10.74 Å. Figure 2 shows the molecular structure of (HexPh3P)2[CuBr4] (8). The structure is stabilized by a variety of hydrogen contacts (Table 5).

2.4. Electron Paramagnetic Resonance (EPR) Spectroscopy

Figure 3 shows a spectrum of (EtPh3P)2[CuBr4] (7) at 150 K, characteristic for most of the recorded spectra. In general the spectra are of poor resolution, due to the magnetic interactions between the paramagnetic centers and no hyperfine structure can be observed. Some of the spectra are of axial symmetry and g as well as g can be determined; for a few samples only an isotropic signal (giso) could be extracted. The EPR data are shown in Table 6. The gav-values correspond to the isotropic giso-value of liquid systems as long as strong solvents are excluded (e.g., solutions or ionic liquids).
The averaged g-values gav for axial symmetry are calculated by the following expression:
g a v = g I I + 2 × g 3
For rhombic symmetry the averaged g-values gav are calculated as follows:
g a v = g 1   +   g 2 + g 3 3
The variation of the structural parameter (ϕav) reflects the degree of structural flexibility of the tetrahalidocuprate(II) moiety. With a series of known X-ray structures combined with EPR parameters of tetrabromidocuprates(II) it could be possible to classify the degree of distortion between square planar and tetrahedral geometries, as well as those of complexes with unknown structures as was recently shown for tetrabromidocuprates(II) [34]. With larger the cis-angles the gav or the isotropic giso-values have a tendency to increase (see Figure 4). This is also supported by calculated values from DFT calculations.
Figure 5 shows the temperature-dependent EPR spectra of (EtPh3P)2[CuBr4] (7) recorded in a temperature range from 300 to 430 K. The signal intensity decreases with rising temperature until it is fully distinct, due to spin saturation effects. This thermal cycle is completely reversible without any signs of decomposition. Interestingly, after cooling to room temperature, only an isotropic EPR signal remains (Figure 6), which returned to the starting axial symmetric spectrum after a couple of days (Figure 7). Obviously the re-crystallization process is kinetically enhanced. Compounds of this type might be useful as ionic liquids for higher temperatures.
The EPR spectrum of (C12H25Me3N)2[CuBr4] (9) at 110 K (Figure 7) reflects a rhombic symmetry of the g-tensor with three different g-values and indicates a change in coordination geometry or a possible lamellar structure.

2.5. Differential Scanning Calorimetry (DSC)

(EtPh3P)2[CuBr4] (7) shows a glass transitions at 306 K, a melting point at 432 K and a cold crystallization by 369 K. Figure 8 shows the second heat run of the compound. The third measurement comes to the same result as the second. It can be concluded that the compound has a temperature reversibility at least up to 443 K. The results of the differential scanning calorimetry of (7) are in good agreement with the data from EPR-spectroscopy.

3. Materials and Methods

3.1. Methods

The melting points were determined using a Mikroheiztisch Boetius (VEB Wägetechnik, Radebeul, DDR). Elemental analyses were carried out on an Elementar Vario EL III analyzer (elementar Analysensysteme GmbH, Hanau, Germany). Infrared spectra were recorded on a Perkin-Elmer type 16PC FT-IR spectrophotometer (Perkin-Elmer GmbH, Überlingen, GErmany) between 4000 and 400 cm−1 as KBr-pellets (reference KBr). The measurements of the magnetic susceptibility were performed with a Magnetic Susceptibility Balance-Auto from Johnson Matthey GmbH (Matthey GmbH, Cambridge, UK) at room temperature, for diamagnetic correction the increment system of Pascal and Pacault [38] was applied. EPR spectra were recorded at 9.4 GHz (X-band) using a Bruker CW Elexsys E 500 spectrometer (Bruker BioSpin GmbH, Rheinstetten, Germany)
For X-ray structure determinations, the crystals were embedded in perfluoropolyalkylether oil and mounted on a glass fibre (5) or within a MicroGripper (8). For structure analysis of (5), the intensity data were collected at 210 K using an Imaging Plate Diffraction System IPDS-2 (Stoe, Darmstadt, Germany) with graphite monochromatized Mo-Kα radiation (λ = 0.71073 Å) at 50 kV and 40 mA. The data collection for (8) was performed on a StadiVari diffractometer (Stoe, Darmstadt, Germany) equipped with a four-circle goniometer (open Eulerian cradle), a Genix Microfocus X-ray source (Mo) with a graded multilayer mirror and a Pilatus 200 K detector (Dectris, Baden-Daettwil, Switzerland). The data were corrected for absorption as well as for Lorentz polarization and extinction effects using the program X-Area (Stoe, 2004) [39]. The structures were solved by direct methods using SHELXS-2013/1 [40] and refined by full-matrix least squares on F2 using the program SHELXL-2014/7 [41]. All non-hydrogen atoms were refined anisotropically. The hydrogen atoms were calculated in their expected positions and refined with a riding model. CCDC 1459578 (5) and CCDC 1459612 (8) contain the supplementary crystallographic data for this paper. These data are provided free of charge by The Cambridge Crystallographic Centre (Cambridge, UK).
Differential scanning calorimetry (DSC) measurements were performed with a DSC 214 Polyma (Netzsch GmbH & Co. KG, Selb, Germany) by NETZSCH operating with a scan rate of 5–10 °C·min−1 under a nitrogen flow.

3.2. Chemicals

The following chemicals were used without further purification. Copper(II) bromide (99%), ethanol anhydrous (99%), n-hexane (96%), potassium bromide (Uvasol, Merk KGaA, Darmstadt, Germany, for IR spectroscopy) tetraethylammonium bromide (98%), tetrabutylphosphonium bromide (99%), tetrahexylammonium bromide (99%), benzyltrimethylammonium bromide (98%), benzyltriethylammonium bromide (98%), benzyltributylammonium bromide (99%), ethyltriphenylphosphonium bromide (98%), hexyltriphenylphosphonium bromide (>99%), dodecyltrimethylammonium bromide (>98%), hexadecylpyridinium bromide (98%), and dihexadecyldimethylammonium bromide (99%).

3.3. Syntheses

3.3.1. General Preparation

In general, tetrabromidocuprate(II) complexes can be achieved by different procedures [42,43,44]. In the current work, the [CuBr4]2− moiety was synthesized according to a protocol by N. S. Gill and R. S. Nyholm [44]: an ethanolic solution of a stoichiometric amount of CuBr2 was added to the respective bromide salt of the cation dissolved in a minimum volume of ethanol. The reaction mixture was stirred for one hour at room temperature. The product was precipitated by evaporating the solvent.

3.3.2. Bis(tetraethylammonium)tetrabromidocuprate(II), (Et4N)2[CuBr4] (1)

Compound (1) was synthesized according to an already published protocol [36].
A solution of 1.5 mmol (0.32 g) of tetraethylammonium bromide in 3 mL of ethanol was mixed with a solution of 0.5 mmol (0.11 g) of copper(II) bromide in 10 mL ethanol. The solution was stirred one hour at room temperature. The solvent was removed and a violet powder was received, filtered off and dried.
Melting point: 241–242 °C. Yield: 0.22 g (67%). Elemental analysis calculated for C16H40N2CuBr4 (643.66): C 29.85, H 6.26, N 4.35 (%); found: C 29.80, H 6.20, N 4.34 (%). IR (KBr, cm−1): 3443 s, 2976 m, 2921 m, 2852 wm, 1628 wm, 1478 s, 1402 m, 1307 w, 1183 m, 1032 m, 1006 m, 793 m.
(IR: s = strong, ms = medium strong, m = medium, wm = weak medium, w = weak).

3.3.3. Bis(tetrabutylphosphonium)tetrabromidocuprate(II), (Bu4P)2[CuBr4] (2)

Solutions of 0.5 mmol (0.11 g) copper(II) bromide and 1.0 mmol (0.32 g) tetrabutylphosphonium bromide, each dissolved in 2 mL ethanol, were combined and stirred at room temperature for 1 h. The resulting violet precipitate is filtered off and dried.
Melting point: 49–52 °C. Yield: 0.38 g (84%). Elemental analysis calculated for C32H72P2CuBr4 (902.13): C 42.60, H 8.04 (%), found: C 42.08, H 8.16 (%). IR (KBr, cm−1): 2928 s, 2891 ms, 2870 ms, 1463 ms, 1407 m, 1375 m, 1237 w, 1098 m, 968 w, 920 m, 722 m. μeff = 1.5 B.M.

3.3.4. Bis(tetrahexylammonium)tetrabromidocuprate(II), (Hex4N)2[CuBr4] (3)

A solution of 1.0 mmol (0.22 g) CuBr2 in 5 mL ethanol was added to a solution of 2.0 mmol (0.87 g) tetrahexylammonium bromide in 5 mL ethanol. The mixed solution was stirred at room temperature for 1 h. The resulting violet precipitate was filtered off and dried.
Melting point: 93–95 °C. Yield: 0.58 g (53%). Elemental analysis calculated for C48H104N2CuBr4 (1092.51): C 52.77, H 9.60, N 2.56 (%), found: C 53.06, H 9.70, N 2.67 (%). IR (KBr, cm−1): 2928 s, 2553 m, 1634 w, 1480 m, 1383 mw, 1050 w, 728 w. μeff = 1.5 B.M.

3.3.5. Bis(benzyltrimethylammonium)tetrabromidocuprate(II), (BzlMe3N)2[CuBr4] (4)

Compound (4) was also synthesized according to an already published procedure [37].
To a solution of 0.5 mmol (0.11 g) of CuBr2 in 3.5 mL methanol a solution of 1.0 mmol (0.23 g) benzyltrimethylammonium bromide, dissolved in 1.5 mL methanol, was added. The mixture was stirred for one hour at room temperature. After a short while the complex precipitated as purple crystals.
Melting point: 173–175 °C. Yield: 0.35 g (72%). Elemental analysis calculated for C20H32N2CuBr4 (969.51): C 35.16, H 4.72, N 4.10 (%); found: C 35.09, H 4.71, N 4.17 (%). IR (KBr, cm−1): 3017 m, 1585 w, 1485 s, 1476 s, 1411 m, 1218 m, 989 m, 974 m, 887 s, 780 s, 703 s. μeff = 1.4 B.M.

3.3.6. Bis(benzyltriethylammonium)tetrabromidocuprate(II), (BzlEt3N)2[CuBr4] (5)

0.5 mmol (0.11 g) of CuBr2 dissolved in 3 mL HBr was heated under reflux for 0.5 h. To this copper solution a solution of 1.0 mmol (0.27 g) BzlEt3NBr and 2 mL methanol was slowly added. The mixture was stirred for one hour at room temperature. The solvent was reduced and purple crystals were obtained by covering the remaining solution with N-hexane.
Melting point: 110–112 °C. Yield: 0.21 g (54%). Elemental analysis calculated for C26H44N2CuBr4 (767.7): C 40.67, H 5.78, N 3.65 (%); found: C 40.56, H 5.76, N 3.69 (%). IR (KBr, cm−1): 2983 m, 1583 w, 1450 s, 1402 ms, 1372 w, 1171 w, 1154 m, 1027 m, 1005 m, 787 m,756 s, 705 s. μeff = 1.6 B.M.

3.3.7. Bis(benzyltributylammonium)tetrabromidocuprate(II), (BzlBu3N)2[CuBr4] (6)

A solution of 1.0 mmol (0.22 g) CuBr2 in 5 mL ethanol was added to a solution of 2.0 mmol (0.71 g) benzyltributylammonium bromide in 5 mL ethanol. The mixed solution was stirred at room temperature for 1 h. The resulting violet precipitate was filtered off and dried.
Melting point: 58–60 °C. Yield: 0.59 g (63%). Elemental analysis calculated for C38H68N2CuBr4 (936.12): C 48.75, H 7.32, N 2.99 (%), found: C 48.90, H 7.48, N 3.12 (%). IR (KBr, cm−1): 2959 s, 2871 m, 1654 w, 1561 w, 1474 m, 1458 m, 1380 mw, 1212 w, 869 mw, 725 m, 704 m. μeff = 1.5 B.M.

3.3.8. Bis(ethyltriphenylphosphonium)tetrabromidocuprate(II), (EtPh3P)2[CuBr4] (7)

The synthesis of (EtPh3P)2[CuBr4] as follows: 0.5 mmol (0.11 g) copper(II) bromide and 1.0 mmol (0.37 g) EtPh3PBr solved even in 2 mL ethanol. The combined solutions are stirred for one hour at room temperature. A violet powder was obtained.
Melting point: 135–137 °C. Yield: 0.23 g (48%). Elemental analysis calculated for C40H40P2CuBr4 (964.90): C 49.74, H 4.17 (%), found: C 49.74, H 4.19 (%). IR (KBr, cm−1): 2922 m, 1586 m, 1483 m, 1438 s, 1113 s, 996 m, 780 w, 739 s, 691 s, 531 s, 510 s, 482 m. μeff = 1.6 B.M.

3.3.9. Bis(hexyltriphenylphosphonium)tetrabromidocuprate(II), (HexPh3P)2[CuBr4] (8)

A solution of 1.0 mmol (0.22 g) copper(II) bromide in 5 mL ethanol is added to 2.0 mmol (0.85 g) hexyltriphenylphosphonium bromide dissolved in 5 mL ethanol. The solution was stirred for 1 h at room temperature. The formed violet precipitate was filtered off and dried. Purple crystals were obtained by covering the remaining solution with n-hexane for slowly interdiffusion.
Melting point: 102–103 °C. Yield: 0.65 g (60%). Elemental analysis calculated for C48H56P2CuBr4 (1078.04): C 53.47, H 5.24 (%), found: C 53.05, H 4.97 (%). IR (KBr, cm−1): 2956 m, 2923 m, 2758 m, 1585 w, 1485 w, 1436 s, 1113 s, 724 s, 689 s, 533s, 498 ms. μeff = 1.6 B.M.

3.3.10. Bis(dodecyltrimethylammonium)tetrabromidocuprate(II), (C12H25Me3N)2[CuBr4] (9)

A solution of 1.0 mmol (0.22 g) of CuBr2 in 5 mL ethanol and a solution of 2.0 mmol (0.62 g) C12H25Me3NBr in 5 mL ethanol were combined and stirred at room temperature for 1 h. The resulting violet precipitate was filtered off and dried.
Melting point: 94–95 °C. Yield: 0.56 g (85%). Elemental analysis calculated for C30H48N2CuBr4 (662.23): C 42.89, H 8.16, N 3.34 (%), found: C 43.19, H 8.23, N 3.37 (%). IR (KBr, cm−1): 2922 ms, 2851 m, 1632 w, 1469 s, 966 ms, 909 m, 722 m. μeff = 1.5 B.M.

3.3.11. Bis(hexadecylpyridinium)tetrabromidocuprate(II), (C16-py)2[CuBr4] (10)

A solution of 0.5 mmol (0.11 g) copper(II) bromide in 10 mL ethanol is added to 1.0 mmol (0.40 g) hexadecylpyridinium bromide dissolved in 3 mL ethanol. The solution was stirred for 1 h at room temperature. The obtained violet precipitate was filtered off and dried.
Melting point: 73–74 °C. Yield: 0.15 g (30%). Elemental analysis calculated for C42H76N2CuBr4 (992.23): C 50.84, H 7.72, N 2.82 (%), found: C 47.67, H 7.20, N 2.95 (%). IR (KBr, cm−1): 3446 wm, 3053 w, 2918 s, 2850 m, 1633 wm, 1485 m, 1468 wm, 1175 w, 768 w, 721 w, 679 w. μeff = 1.6 B.M.

3.3.12. Bis(dihexadecyldimethylammonium)tetrabromidocuprate(II), (C16H33)2Me2N)2[CuBr4] (11)

A solution of 1.0 mmol (0.58 g) dihexadecyldimethylammonium bromide in 3 mL ethanol was slowly added to a solution of 0.5 mmol (0.11 g) copper(II) bromide in 3 mL ethanol. The mixture was stirred at room temperature for 1 h. The formed violet precipitate was filtered off and dried.
Melting point: 36–38 °C. Yield: 0.67 g (98%). Elemental analysis calculated for C68H144N2CuBr4 (1373.05): C 59.48, H 10.57, N 2.04 (%), found: C 59.11, H 10.89, N 2.15 (%). IR (KBr, cm−1): 2919 m, 2851 m, 1628 w, 1469 s, 1376 w, 1054 w, 990 w, 968 w, 878 w, 718 m.

4. Conclusions

Some of the compounds in this series are real ionic liquids—(2), (3), (6), (10) and (11)—with melting points below 100 °C, or very close to it—(5) and (8). All the reported compounds are thermally stable up to at least 430 K. This thermal cycle is completely reversible without any signs of decomposition. Interestingly, after cooling to room temperature, for (7) only an isotropic EPR signal remains, which returned to the axial symmetric spectrum after a couple of days. That means the re-crystallizing process is kinetically enhanced. Compounds of this type might be useful as ionic liquids for higher temperatures.
Two compounds, (5) and (8), could be structurally characterized by X-ray structure analysis. The structures are stabilized by a variety of hydrogen contacts between the [CuBr4]2− anions and corresponding onium cations, responsible for the coordination geometry of the tetrahalidocuprates. The EPR parameters also reflect the degree of structural flexibility of the tetrahalidocuprate(II) moiety. With a series available data sets of known X-ray structures combined with EPR parameters of tetrabromidocuprates(II) it is possible to classify the degree of the distortion coordination sphere between square planar and tetrahedral geometries, as was recently shown for tetrabromidocuprates(II) [34].

Acknowledgments

We acknowledge Ulf Steinhoff and Ahed Abouserie for DSC measurements and Anne Nitschke for recording the IR-spectra.

Author Contributions

André Zabel, Peter Strauch: writing of manuscript, analytical interpretation, literature search; André Zabel, Alette Winter: syntheses; Peter Strauch, Alette Winter: EPR spectroscopy; Alexandra Kelling, Uwe Schilde: X-ray crystallography.

Conflicts of Interest

The authors declare no conflict of interest.

Abbreviations

DFTDiscrete Fourier Transform
EPRElectron Paramagnetic Resonance
DSCDifferential Scanning Calorimetry

References

  1. Taubert, A. Heavy elements in ionic liquids. Top. Curr. Chem. 2009, 290, 127–159. [Google Scholar]
  2. Taubert, A. CuCl Nanoplatelets from an ionic liquid-crystal precursor. Angew. Chem. Int. Ed. 2004, 43, 5380–5382. [Google Scholar] [CrossRef] [PubMed]
  3. Saito, G. Electric conductivity and magnetic ionic liquids. In Electrochemical Aspects of Ionic Liquids, 2nd ed.; Ohno, H., Ed.; John Wiley & Sons, Inc.: New York, NY, USA, 2011; pp. 337–346. [Google Scholar]
  4. Kalb, R. Use of Magnetic, Ionic Liquids as an Extraction Agent. PCT Int. Pat. WO 2009080648 A1, 2 July 2009. [Google Scholar]
  5. Dengler, J.E.; Doroodian, A.; Rieger, B. Protic metal-containing ionic liquids as catalysts: Cooperative effects between anion and cation. J. Organomet. Chem. 2011, 696, 3831–3835. [Google Scholar] [CrossRef]
  6. Bica, K.; Gaertner, P. Metal-containing ionic liquids as efficient catalysts for hydroxymethylation in water. Eur. J. Org. Chem. 2008, 3453–3456. [Google Scholar] [CrossRef]
  7. Bica, K.; Gaertner, P. An iron-containing ionic liquid as recyclable catalyst for aryl grignard cross-coupling of aryl halides. Org. Lett. 2006, 8, 733–735. [Google Scholar] [CrossRef] [PubMed]
  8. Lin, I.J.B.; Vasam, C.S. Metal-containing ionic liquids and ionic liquid crystals based on imidazolium moiety. J. Organomet. Chem. 2005, 690, 3498–3512. [Google Scholar] [CrossRef]
  9. Bowlas, C.J.; Bruce, D.W.; Seddon, K.R. Liquid-crystalline ionic liquids. Chem. Commun. 1996, 1625–1626. [Google Scholar] [CrossRef]
  10. Neve, F.; Francescangeli, O.; Crispini, A.; Charmant, J. A2[MX4] Copper(II) pyridinium salts. From ionic liquids to layered solids to liquid crystals. Chem. Mater. 2001, 13, 2032–2041. [Google Scholar] [CrossRef]
  11. Neve, F.; Francescangeli, O.; Crispini, A. Crystal architecture and mesophase structure of long-chain N-alkylpyridinium tetrachlorometallates. Inorg. Chim. Acta 2002, 338, 51–58. [Google Scholar] [CrossRef]
  12. Neve, F.; Crispini, A. C–H···Br–M Interactions at Work: Tetrabromometalates of the bolaamphiphilic N,N′-dodecamethylenedipyridinium cation. Cryst. Growth Des. 2001, 1, 387–393. [Google Scholar] [CrossRef]
  13. Neve, F.; Crispini, A. C-H···Br-M Interactions at work: Tetrabromometalates of the bolaamphiphilic N,N′-dodecamethylenedipyridinium cation. Cryst. Growth Des. 2001, 1, 519. [Google Scholar] [CrossRef]
  14. Taubert, A.; Palivan, C.; Casse, O.; Gozzo, F.; Schmitt, B. Ionic liquid-crystal precursors (ILCPs) for CuCl platelets: The origin of the exothermic peak in the DSC curves. J. Phys. Chem. C 2007, 111, 4077–4082. [Google Scholar] [CrossRef]
  15. Taubert, A.; Steiner, P.; Mantion, A. Ionic liquid crystal precursors for inorganic particles: Phase diagram and thermal properties of a CuCl nanoplatelet precursor. J. Phys. Chem. B 2005, 109, 15542–15547. [Google Scholar] [CrossRef] [PubMed]
  16. Willett, R.D.; Haugen, J.A.; Lebsack, J.; Morrey, J. Thermochromism in copper(II) chlorides. Coordination geometry changes in CuCl42− anions. Inorg. Chem. 1974, 13, 2510–2513. [Google Scholar] [CrossRef]
  17. Thiel, K.; Klamroth, T.; Strauch, P.; Taubert, A. On the interaction of ascorbic acid and the tetrachloridocuprate ion [CuCl4]2− in CuCl nanoplatelet formation from an ionic liquid precursor (ILP). Phys. Chem. Chem. Phys. 2011, 13, 13537–13543. [Google Scholar] [CrossRef] [PubMed]
  18. Zhuravlev, O.E.; Verolainen, N.V.; Voronchikhina, L.I. Thermal stability of 1,3-disubstituted imidazolium tetrachloroferrates, magnetic ionic liquids. Russ. J. Appl. Chem. 2011, 84, 1158–1164. [Google Scholar] [CrossRef]
  19. Branco, A.; Branco, L.C.; Pina, F. Electrochromic and magnetic ionic liquids. Chem. Commun. 2011, 47, 2300–2302. [Google Scholar] [CrossRef] [PubMed]
  20. Neve, F.; Crispini, A.; Armentano, S. Synthesis, structure, and thermotropic mesomorphism of layered N-alkylpyridinium tetrahalopalladate(II) salts. Chem. Mater. 1998, 10, 1904–1913. [Google Scholar] [CrossRef]
  21. Neve, F.; Francescangeli, O. Layered ω-substituted alkylpyridinium salts with inorganic anions: Effects of H-bonding patterns on the layer thickness. Cryst. Growth Des. 2005, 5, 163–166. [Google Scholar] [CrossRef]
  22. Neve, F.; Crispini, A. Competitive interactions in carboxy-functionalized pyridinium salts: Crossover from O–H···O to O–H···X–M contacts. Cryst. Eng. Commun. 2007, 9, 698–703. [Google Scholar] [CrossRef]
  23. Neve, F.; Crispini, A. N,N′-Dodecamethylene-bis(pyridinium) goes lamellar. Role of C–H···I, C–H···M, and I···I interactions in the crystal structure of its hexaiododipalladate(II) derivative. Cryst. Eng. Commun. 2003, 5, 265–268. [Google Scholar] [CrossRef]
  24. Neve, F.; Crispini, A.; Francescangeli, O. Structural studies on layered alkylpyridinium iodopalladate networks. Inorg. Chem. 2000, 39, 1187–1194. [Google Scholar] [CrossRef] [PubMed]
  25. Binnemans, K. Ionic liquid crystals. Chem. Rev. 2005, 105, 4148–4204. [Google Scholar] [CrossRef] [PubMed]
  26. Goossens, K.; Lava, K.; Nockemann, P.; van Hecke, K.; van Meervelt, L.; Driesen, K.; Görller-Walrand, C.; Binnemans, K.; Cardinaels, C. Pyrrolidinium ionic liquid crystals. Chem. Eur. J. 2009, 15, 656–674. [Google Scholar] [CrossRef] [PubMed]
  27. Suisse, J.-M.; Douce, L.; Bellemin-Laponnaz, S.; Maisse-Francois, A.; Welter, R.; Miyake, Y.; Shimizu, Y. Liquid crystal imidazolium salts: Towards materials for catalysis and molecular electronics. Eur. J. Inorg. Chem. 2007, 2007, 3899–3905. [Google Scholar] [CrossRef]
  28. Dobbs, W.; Suisse, J.-M.; Douce, L.; Welter, R. Electrodeposition of silver particles and gold nanoparticles from ionic liquid-crystal precursors. Angew. Chem. Int. Ed. 2006, 45, 4179–4182. [Google Scholar] [CrossRef] [PubMed]
  29. Lee, C.K.; Peng, H.H.; Lin, I.J.B. Liquid crystals of N,N′-dialkylimidazolium salts comprising palladium(II) and copper(II) ions. Chem. Mater. 2004, 16, 530–536. [Google Scholar] [CrossRef]
  30. Herber, R.H.; Nowik, I.; Kostner, M.E.; Kahlenberg, V.; Kreutz, C.; Laus, G.; Schottenberger, H. Mössbauer spectroscopy and X-ray diffraction study of 57Fe-labeled tetrachloroferrate(III)-based magnetic ionic liquids. Int. J. Mol. Sci. 2011, 12, 6397–6406. [Google Scholar] [CrossRef] [PubMed]
  31. De Pedro, I.; Rojas, D.P.; Albo, J.; Luis, P.; Irabien, A.; Blanco, J.A.; Fernandez, J.R. Long-range magnetic ordering in magnetic ionic liquid: Emim[FeCl4]. J. Phys. Condens. Matter 2010, 22, 296006. [Google Scholar] [CrossRef] [PubMed]
  32. Sasaki, T.; Zhong, C.; Tada, M.; Iwasawa, Y. Immobilized metal ion-containing ionic liquids: Preparation, structure and catalytic performance in Kharasch addition reaction. Chem. Commun. 2005, 2506–2508. [Google Scholar] [CrossRef] [PubMed]
  33. Winter, A.; Zabel, A.; Strauch, P. Tetrachloridocuprates(II)-synthesis and electron paramagnetic resonance (EPR) spectroscopy. Int. J. Mol. Sci. 2012, 13, 1612–1619. [Google Scholar] [CrossRef] [PubMed]
  34. Farra, R.; Thiel, K.; Winter, A.; Klamroth, T.; Pöppl, A.; Kelling, A.; Schilde, U.; Taubert, A.; Strauch, P. Tetrahalidocuprates(II)—Structure and EPR spectroscopy. Part 1: Tetrabromidocuprates(II). New J. Chem. 2011, 35, 2793–2803. [Google Scholar] [CrossRef]
  35. Winter, A.; Thiel, K.; Zabel, A.; Klamroth, T.; Pöppl, A.; Kelling, A.; Schilde, U.; Taubert, A.; Strauch, P. Tetrahalidocuprates(II)—Structure and EPR spectroscopy. Part 2: Tetrachloridocuprates(II). New J. Chem. 2014, 38, 1019–1030. [Google Scholar] [CrossRef]
  36. Starova, G.L.; Skripkin, M.Y.; Gusev, I.M. Structure of complex bromides crystallizing in MBr2—NEt4Br—H2O systems (M = Cd, Cu, Co) at 25 °C. Russ. J. Gen. Chem. 2010, 80, 1236–1241. [Google Scholar] [CrossRef]
  37. Jin, L.; Liu, N.; Li, Y.-J.; Wu, D.-H. Bis(benzyltrimethylammonium)tetrabromidocuprates(II). Acta Crystallogr. Sect. E 2011, E67, m1325. [Google Scholar] [CrossRef] [PubMed]
  38. Hellwege, K.-H.; Hellwege, A.M. (Eds.) Magnetic Properties of Coordination and Organo-Metallic Transition Metal Compounds. Landolt-Börnstein—Group II, Atomic and Molecular Radicals; Springer: New York, NY, USA, 1966; Volume 2.
  39. X-Area Vers. 1.26; Stoe & Cie: Darmstadt, Germany, 2004.
  40. Sheldrick, G.M. SHELXS-2013/1, Program for the Crystal Structure Solution; University Göttingen: Göttingen, Germany, 2013. [Google Scholar]
  41. Sheldrick, G.M. SHELXL-2014/7, Program for the Refinement of Crystal Structures; University Göttingen: Göttingen, Germany, 2014. [Google Scholar]
  42. Furlani, C.; Morpurgo, G. Properties and electron structure of tetrahalogenocuprate (II)-complexes. Theor. Chim. Acta 1963, 1, 102–115. [Google Scholar] [CrossRef]
  43. Liu, H.; Wang, X.; Hu, W.; Guo, L.; Ouyang, S. Preparation and characterization of (C4H9NH3)2CuX4 (X = Cl, Br). Chem. J. Intern. 2004, 6, 066039ne. [Google Scholar]
  44. Gill, N.S.; Nyholm, R.S. Complex halides of the transition metals. Part I tetrahedral nickel complexes. J. Chem. Soc. 1959, 3997–4007. [Google Scholar] [CrossRef]
Scheme 1. Cations of the [CuBr4]2− salts.
Scheme 1. Cations of the [CuBr4]2− salts.
Ijms 17 00596 sch001
Figure 1. Molecular structure of (BzlEt3N)2[CuBr4] (5), hydrogen contacts are presented as fragmented lines.
Figure 1. Molecular structure of (BzlEt3N)2[CuBr4] (5), hydrogen contacts are presented as fragmented lines.
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Figure 2. Molecular structure of (HexPh3P)2[CuBr4] (8), hydrogen contacts are presented as fragmented lines.
Figure 2. Molecular structure of (HexPh3P)2[CuBr4] (8), hydrogen contacts are presented as fragmented lines.
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Figure 3. Electron paramagnetic resonance (EPR) spectrum of (EtPh3P)2[CuBr4] (7) at 150 K.
Figure 3. Electron paramagnetic resonance (EPR) spectrum of (EtPh3P)2[CuBr4] (7) at 150 K.
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Figure 4. Correlation of EPR parameter (gav/giso) with the coordination geometry (averaged cis-angle) including the four new data sets from Table 6 (squares); the circles represent the calculated data (DFT).
Figure 4. Correlation of EPR parameter (gav/giso) with the coordination geometry (averaged cis-angle) including the four new data sets from Table 6 (squares); the circles represent the calculated data (DFT).
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Figure 5. Temperature dependent EPR spectra of (EtPh3P)2[CuBr4] (7) recorded in the temperature range from 300 to 430 K (10 K steps).
Figure 5. Temperature dependent EPR spectra of (EtPh3P)2[CuBr4] (7) recorded in the temperature range from 300 to 430 K (10 K steps).
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Figure 6. EPR spectrum of (EtPh3P)2[CuBr4] (7) at 150 K directly after the thermal treatment; only an isotropic signal remains.
Figure 6. EPR spectrum of (EtPh3P)2[CuBr4] (7) at 150 K directly after the thermal treatment; only an isotropic signal remains.
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Figure 7. EPR spectrum of (C12H25Me3N)2[CuBr4] (9) at 110 K.
Figure 7. EPR spectrum of (C12H25Me3N)2[CuBr4] (9) at 110 K.
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Figure 8. Second DSC scan from (EtPh3P)2[CuBr4] (7).
Figure 8. Second DSC scan from (EtPh3P)2[CuBr4] (7).
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Table 1. Crystallographic data and refinement parameters for (5) and (8).
Table 1. Crystallographic data and refinement parameters for (5) and (8).
Compound(BzlEt3N)2[CuBr4] (5)(HexPh3P)2[CuBr4] (8)
Empirical formulaC26H44N2CuBr4C48H56P2CuBr4
MW/g·mol−1767.811078.04
Crystal descriptionpurple platepurple needle
Crystal size/mm0.7 × 0.5 × 0.10.8 × 0.2 × 0.1
Crystal systemmonoclinicmonoclinic
Space groupP21/cP21/n
a15.1019(5)10.7410(3)
b11.6664(5)22.4775(9)
c17.5517(6)19.6455(6)
α9090
β99.166(3)99.807(2)
γ9090
V33052.9(2)4673.7(3)
Z44
F(000)15322172
Density/mg·m−31.671.532
μ/mm−15.973.987
Θ range/°2.10–25.002.15–24.998
Rint0.13380.0740
Reflections measured38,76773,469
Reflections independent53728223
Parameters299496
R1/wR2 (I > 2σ(I))0.0370/0.08930.0480/0.1183
R1/wR2 (all data)0.0529/0.09750.0711/0.1293
Goodness of fit1.0151.031
Max. difference peak/hole/e Å−30.71/−0.832.231/−1.220
Table 2. Selected bond lengths and bond angles of (BzlEt3N)2[CuBr4] (5).
Table 2. Selected bond lengths and bond angles of (BzlEt3N)2[CuBr4] (5).
Bond Lengths/ÅBond Angles/°
Cu1–Br12.3981(7)Br1–Cu1–Br299.73(2)
Br1–Cu1–Br398.38(2)
Br1–Cu1–Br4130.80(3)
Cu1–Br22.3747(7)Br2–Cu1–Br3131.84(3)
Cu1–Br32.3918(7)Br2–Cu1–Br498.19(2)
Cu1–Br42.3984(7)Br3–Cu1–Br4102.80(2)
Table 3. Hydrogen contacts for (BzlEt3N)2[CuBr4] (5).
Table 3. Hydrogen contacts for (BzlEt3N)2[CuBr4] (5).
C–H∙∙∙BrH∙∙∙Br/ÅC∙∙∙Br/ÅAngles C–H∙∙∙Br/°
C1–H1A···Br2 i2.933.568(4)124.2
C2–H2A···Br23.093.955(6)151.1
C6–H6A···Br2 ii2.823.742(6)161.1
C6–H6A···Br1 ii3.013.621(6)132.2
C7–H7A···Br2 ii2.993.935(4)164.6
C7–H7B···Br33.043.982(5)165.4
C14–H14A···Br1 iii3.083.564(4)112.3
C14–H14B···Br32.923.720(5)140.3
C16–H16A···Br43.023.849(5)144.6
C16–H16B···Br12.963.868(5)156.9
C20–H20A···Br1 ii3.083.982(4)154.6
Symmetry codes: (i) 1 − x, 2 − y, 1 − z; (ii) 1 − x, 0.5 + y, 0.5 − z; (iii) −x, −0.5 + y, 0.5 − z.
Table 4. Selected bond lengths and bond angles for (HexPh3P)2[CuBr4] (8).
Table 4. Selected bond lengths and bond angles for (HexPh3P)2[CuBr4] (8).
Bond Lengths/ÅBond Angles/°
Cu1–Br12.4500(9)Br1–Cu1–Br2120.66(4)
Br1–Cu1–Br3103.25(3)
Br1–Cu1–Br4104.45(3)
Cu1–Br22.3867(9)Br2–Cu1–Br3104.95(3)
Cu1–Br32.4207(9)Br2–Cu1–Br4100.39(3)
Cu1–Br42.3677(9)Br3–Cu1–Br4124.76(4)
Table 5. Hydrogen bond geometry for (HexPh3P)2[CuBr4] (8).
Table 5. Hydrogen bond geometry for (HexPh3P)2[CuBr4] (8).
C–H∙∙∙BrH∙∙∙Br/ÅC∙∙∙Br/ÅAngles C–H∙∙∙Br/°
C12–H12∙∙∙Br22.823.744(6)166.4
C19–H19B∙∙∙Br3 iii3.104.064(5)166.4
C26–H26∙∙∙Br13.133.840(5)133.8
C26–H26∙∙∙Br33.073.718(6)127.2
C32–H32∙∙∙Br4 ii2.903.673(5)140.8
C36–H36∙∙∙Br2 i2.843.776(5)176.7
C43–H43B∙∙∙Br12.883.834(5)165.9
C43–H43A∙∙∙Br2 i3.064.000(6)161.1
Symmetry codes: (i) 0,5 + x, 0.5 − y, 0.5 + z; (ii) 1 + x, y, z; (iii) 1 − x, y, z.
Table 6. Experimental g-values (g, g and giso), calculated values gav and known cis-angles (ϕav) for this series of tetrabromidocuprates(II).
Table 6. Experimental g-values (g, g and giso), calculated values gav and known cis-angles (ϕav) for this series of tetrabromidocuprates(II).
Cation/CompoundgggisogavϕavReference (ϕav)
Et4N+/(1)--2.18 a-108.06 *[36]
Bu4P+/(2)--2.089--
Hex4P+/(3)2.34 a2.0792.11 a2.166-
BzlMe3N+/(4)2.2212.0582.1012.10999.64 *[37]
BzlEt3N+/(5)--2.11 a-99.77 *
BzlBu3P+/(6)--2.108--
EtPh3P+/(7)2.2172.062-2.114-
BuPh3P+/(8)2.2802.069-2.139-
HexPh3P+/(9)--2.13 a-103.26 *
(C12H25)Me3N+/(10)2.26 a, 2.124, 2.0402.141-
(C16H33)py+/(11)--2.15 a--
(C16H33)2Me2N+/(12)2.28 a2.079-2.146-
Experimental errors: g-values: ±0.005; a g: ±0.01; *: new added EPR/structure data sets.

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Zabel, A.; Winter, A.; Kelling, A.; Schilde, U.; Strauch, P. Tetrabromidocuprates(II)—Synthesis, Structure and EPR. Int. J. Mol. Sci. 2016, 17, 596. https://0-doi-org.brum.beds.ac.uk/10.3390/ijms17040596

AMA Style

Zabel A, Winter A, Kelling A, Schilde U, Strauch P. Tetrabromidocuprates(II)—Synthesis, Structure and EPR. International Journal of Molecular Sciences. 2016; 17(4):596. https://0-doi-org.brum.beds.ac.uk/10.3390/ijms17040596

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Zabel, André, Alette Winter, Alexandra Kelling, Uwe Schilde, and Peter Strauch. 2016. "Tetrabromidocuprates(II)—Synthesis, Structure and EPR" International Journal of Molecular Sciences 17, no. 4: 596. https://0-doi-org.brum.beds.ac.uk/10.3390/ijms17040596

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