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New crystal structures of alkali metal tetrakis(pentafluorophenyl)borates

  • Daniel Duvinage , Artem Schröder , Enno Lork and Jens Beckmann EMAIL logo
Published/Copyright: June 21, 2020
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Main Group Metal Chemistry
From the journal Main Group Metal Chemistry Volume 43 Issue 1

Abstract

The crystal structures of the salts [Li(1,2-F2C6H4)] [B(C6F5)4] (1) and Cs[B(C6F5)4] (2) comprise six Li···F contacts (1.965(3) − 2.312(3) Å) and twelve Cs···F contacts (3.0312(1) − 3.7397(2) Å), respectively, which are significantly shorter than the sum of van der Waals radii (3.29 and 4.90 Å).

Keywords: lithium; caesium; boron; borate ion; weakly coordinating anion

Polyfluorinated tetraarylborate ions, such as [B{3,5-(CF3)2C6H3}4]– “BArF” and [B(C6F5)4]– (Scheme 1), have received numerous applications as weakly coordinating anions (Krosssing and Raabe, 2004; Riddlestone et al., 2018), which also stimulated research into their alkali metal salts. Very recently, for the former, the crystal structures of [Li(H2O)][B{3,5-(CF3)2C6H3}4], M[B{3,5-(CF3)2C6H3}4] (M = Na, K) were described (Martínez-Martínez and Weller, 2019). For the latter, the crystal structures of [Li(C6H6)][B(C6F5)4]·benzene (Bolte et al., 2005), [Li(MeC6H5)][B(C6F5)4]·toluene, [Li(Et2O)4][B(C6F5)4], [Li(Et2O)4][B(C6F5)4]·CH2Cl2 (Kuprat et al., 2010; Martin et al., 2010), [Li(MeCN)4][B(C6F5)4] (Zhang et al., 2012) and K[B(C6F5)4] (Protchenko et al., 2016) were reported. In this work we convey two new crystal structures of the same anion.

Crystals of [Li(1,2-F2C6H4)][B(C6F5)4] (1) were obtained by recrystallization of [Li(Et2O)4][B(C6F5)4] from 1,2-difluorobenzene. The key feature of 1 (Figure 1) is the presence of six Li···F contacts (1.965(3) - 2.312(3) Å) that are significantly shorter than the sum of van der Waals radii (3.29 Å) and the absence of π-interactions between cation the electron poor aromatic rings. By contrast, in the crystal structure of [Li(C6H6)][B(C6F5)4]·benzene (Bolte et al., 2005) and [Li(MeC6H5)][B(C6F5)4]·toluene (Kuprat et al., 2010), the cations show also π-interactions with the electron rich solvate molecules. The cesium salt Cs[B(C6F5)4] (2) crystallized in the rare cubic space group I4¯3d(a=19.213(1)Å). It is isostructural with the previously known thallium compound Tl[B(C6F5)4] (a = 19.10(1) Å) (Parvez et al., 2005). The cell volume of 2 (V = 7092(1) Å3) is smaller than that of Tl[B(C6F5)4] (V = 6962(8) Å3), which can be attributed to the smaller ion radius of cesium (1.67 Å) compared to thallium (1.5 Å). The key feature of 2 (Figure 2) is the presence of twelve Cs···F contacts (3.0312(1)-3.7397(2) Å), respectively, which are significantly shorter than the sum of van der Waals radii (4.90 Å). These distances are consistent with those observed for Cs[H2NB2(C6F5)6], which shows even sixteen Cs···F contacts (Pollak et al., 2016).

Figure 1 Crystal structure of [Li(1,2-F2C6H4)][B(C6F5)4] (1) showing 50% probability ellipsoid and the essential atomic numbering. Cation anion contacts [Å]: Li1-F1 2.053(3), Li1-F2 2.090(3), Li1-F11 1.968(3), Li1-F21 1.965(3), Li1-F44a 2.312(3), Li1-F45a 2.018(3).
Figure 1

Crystal structure of [Li(1,2-F2C6H4)][B(C6F5)4] (1) showing 50% probability ellipsoid and the essential atomic numbering. Cation anion contacts [Å]: Li1-F1 2.053(3), Li1-F2 2.090(3), Li1-F11 1.968(3), Li1-F21 1.965(3), Li1-F44a 2.312(3), Li1-F45a 2.018(3).

Figure 2 Crystal structure of Cs[B(C6F5)4] (2) showing 50% probability ellipsoid and the essential atomic numbering. Cation anion contacts [Å]: Cs1-F1 3.0312(1), Cs1-F2 3.7397(2), Cs1-F3 3.1943(1), Cs1-F5 3.3292(1).
Figure 2

Crystal structure of Cs[B(C6F5)4] (2) showing 50% probability ellipsoid and the essential atomic numbering. Cation anion contacts [Å]: Cs1-F1 3.0312(1), Cs1-F2 3.7397(2), Cs1-F3 3.1943(1), Cs1-F5 3.3292(1).

1 X-ray crystallography

Single crystals of 1 were obtained by drying [Li(Et2O)4] [B(C6F5)4] in high vacuum (5·10-3 bar) at 140°C for 24 h and recrystallization from 1,2-difluorobenzene and n-hexane (Romanato et al., 2010). Single crystals of 2 were obtained by ion exchange of 1 in 1,2-difluorobenzene with Cesium fluoride followed by filtration and addition of n-hexane (Mon et al., 2013). Intensity data were collected on a Bruker Venture D8 diffractometer with graphite-monochromated Mo-Kα (0.7107 Å) radiation. The structure was solved by direct methods and difference Fourier synthesis with subsequent Full-matrix least-squares refinements on F2, using all data (Dolomanov, 2009). All non-hydrogen atoms were refined using anisotropic displacement parameters. Hydrogen atoms attached to carbon atoms were included in geometrically calculated positions using a riding model. Crystal and refinement data are collected in Table 1. Figures were created using DIAMOND (Brandenburg and Putz, 2006). Crystallographic data for the structural analysis has been deposited with the Cambridge Crystallographic Data Centre, CCDC numbers 1974618 (1) and 1974619 (2).

Table 1

Crystal data and structure refinement of [Li(1,2-F2C6H4) B(C6F5)4] (1) and [CsB(C6F5)4] (2).

12
FormulaC30H4BF22LiC24BCsF20
Formula weight, g mol–1800.08394.74
Crystal systemmonocliniccubic
Crystal size, mm0.5 × 0.5 × 0.40.3 × 0.3 × 0.3
Space groupP21/nI‾43d
a, Å13.9256(5)19.213(1)
b, Å12.4375(5)19.213(1)
c, Å15.9947(5)19.213(1)
α, °9090
β, °92.016(1)90
γ, °9090
V, Å32768.6(2)7092(1)
Z412
ρcalcd, Mg m–31.9202.281
T, K100100
m (Mo Kα), mm–10.2151.741
F(000)15604608
θ range, deg2.20 to 33.232.60 to 30.43
Index ranges–21 ≤ h ≤ 21–27 ≤ h ≤ 23
–18 ≤ k ≤ 19–27 ≤ k ≤ 23
–24 ≤ l ≤ 24–20 ≤ l ≤ 27
No. of reflns collected10815423264
Completeness to θmax99.9%99.9%
No. indep. Reflns106301805
No. obsd reflns with (I>2σ(I))83911695
No. refined params487105
GooF (F2)1.0371.110
R1 (F) (I > 2σ(I))0.04440.0277
wR2 (F2) (all data)0.12720.0749
(Δ/σ)max< 0.001< 0.001
Largest diff peak/hole, e Å–30.706 / –0.5050.514 / –0.632
Scheme 1 Weakly coordinating polyfluorinated tetraarylborate “BArF” ions.
Scheme 1

Weakly coordinating polyfluorinated tetraarylborate “BArF” ions.

Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: +44-1223-336033; e-mail: deposit@ccdc.cam. ac.uk or http://www.ccdc.cam.ac.uk)

  1. Conflict of interest: One of the authors (Jens Beckmann) is a member of the Editorial Board of Main Group Metal Chemistry.

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Received: 2020-03-01
Accepted: 2020-05-12
Published Online: 2020-06-21

© 2020 Duvinage et al., published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

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https://doi.org/10.1515/mgmc-2020-0011
Keywords for this article
lithium; caesium; boron; borate ion; weakly coordinating anion
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Articles in the same Issue

  1. Research Articles
  2. An accelerated and effective synthesis of zinc borate from zinc sulfate using sonochemistry
  3. A new approach on lithium-induced neurotoxicity using rat neuronal cortical culture: Involvement of oxidative stress and lysosomal/mitochondrial toxic Cross-Talk
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  6. Preparation of skeletally diverse quinazoline-2,4(1H,3H)-diones using Na2SiO3/SnFe2O4 catalytic system through a four-component reaction
  7. Efficient photocatalytic degradation of organic dye from aqueous solutions over zinc oxide incorporated nanocellulose under visible light irradiation
  8. Synthesis of pyrimidines by Fe3O4@SiO2-L-proline nanoparticles
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  10. Organodiphosphines in PtP2X2 (X = As, Ge or Te) derivatives – Structural aspects
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