Potassium tri­fluoro­[(E)-2-phenyl-1-ethenyl]­borate

In the title compound, K⁺·C₈H₇BF₃⁻, the closest distance between the K⁺ and C₈H₇BF₃⁻ moieties is a K...F distance of 2.1619 (17) Å. The overall structure consists of two-dimensional sheets in which C₈H₇BF₃⁻ moieties coordinate to both sides of layers of K⁺ ions.

Key indicators

• Single-crystal X-ray study
• T = 100 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.026
• wR factor = 0.067
• Data-to-parameter ratio = 13.2

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



STRVAL_01
         From the CIF: _refine_ls_abs_structure_Flack    0.500
         From the CIF: _refine_ls_abs_structure_Flack_su    0.040
           Alert C Flack test results are ambiguous.

General Notes



REFLT_03
         From the CIF: _diffrn_reflns_theta_max           25.02
         From the CIF: _reflns_number_total               1576
         Count of symmetry unique reflns          919
         Completeness (_total/calc)            171.49%
         TEST3: Check Friedels for noncentro structure
         Estimate of Friedel pairs measured       657
         Fraction of Friedel pairs measured     0.715
         Are heavy atom types Z>Si present          yes
          Please check that the estimate of the number of Friedel pairs is
          correct. If it is not, please give the correct count in the
          _publ_section_exptl_refinement section of the submitted CIF.


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 1 Alert Level C = Please check

---

S1. Comment

While (E)-2-phenyl-1-ethenylboronic acid, along with other aryl- and alkenylboronic acids, has been successfully employed in rhodium(I)-catalyzed 1,4-additions to α,β-unsaturated carbonyl compounds (Sakai et al., 1997) and additions to aldehydes (Sakai et al., 1998), the title compound, (I), has shown greater reactivity in analogous processes (Batey et al., 1999). The potassium trifluoroborate salt, (I), is also considerably more stable towards air and water than the corresponding boronic acid, and consequently facile to prepare, isolate, store, and handle.

Compound (I) crystallizes as discrete K⁺ and C₈H₇BF₃^- moieties (Fig. 1). The closest distance between a cation and an anion is 2.1619 (17) Å, which is between K1 and F1. In the structure, each K⁺ is surrounded by five anions making close contacts with seven F atoms (Fig. 2) with distances ranging between 2.6169 (17) and 2.8924 (16) Å (see Table 1). The overall structure consists of two-dimensional sheets in which the –BF₃ groups of C₈H₇BF₃^- are coordinated above and below layers of K⁺, and the terminal phenyl groups point away from the center on either side of the layers. Hence, each two-dimensional sheet is separated by normal van der Waals interactions between terminal phenyl groups (Fig. 3).

A search of the April 2001 release of the Cambridge Structural Database (Allen & Kennard, 1993) revealed only three other structures of potassium trifluoroborate salts, namely potassium methyltrifluoroborate (Brauer et al., 1982), potassium trifluoromethyltrifluoroborate (Brauer et al., 1977), and potassium phenyltrifluoroborate (Conole et al., 1995).

S2. Experimental

Crystals of (I) were obtained by treatment of (E)-2-phenyl-1-ethenylboronic acid in a minimal amount of methanol with aqueous potassium hydrogen fluoride. The precipitate was subsequently collected by filtration, and recrystallized from acetonitrile.

S3. Refinement

H atoms were included in calculated positions with C—H distances of 0.95 Å. 668 Friedel pairs were used to determine the absolute stereochemistry and the Flack parameter refined to 0.50 (4) indicating the crystal was a racemic twin (Flack, 1983).

Computing details

Data collection: COLLECT (Nonius, 1997-2001); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN; program(s) used to solve structure: SHELXTL (Sheldrick, 1999); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. View of (I) showing the atom-labelling scheme. Ellipsoids are at the 50% probability level.
	Fig. 2. View of K^+ cation environment with the five closest anions. Only F atoms involved in close contacts are labelled. Ellipsoids are at the 50% probability level.
	Fig. 3. Diagram viewed approximately perependicular to the ab plane showing the packing of two-dimensional sheets.

Potassium (E)-2-Phenyl-1-ethenyltrifluoroborate

Crystal data

K^+·C8H7BF3^−	Dx = 1.471 Mg m^−3
Mr = 210.05	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pca21	Cell parameters from 5135 reflections
a = 7.0265 (4) Å	θ = 4.2–25.0°
b = 18.9749 (10) Å	µ = 0.55 mm^−1
c = 7.1157 (4) Å	T = 100 K
V = 948.72 (9) Å^3	Plate, colourless
Z = 4	0.30 × 0.30 × 0.05 mm
F(000) = 424

Data collection

Nonius KappaCCD diffractometer	1576 independent reflections
Radiation source: fine-focus sealed tube	1488 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.048
Detector resolution: 9 pixels mm^-1	θmax = 25.0°, θmin = 4.2°
ϕ scans, and ω scans with κ offsets	h = −8→8
Absorption correction: multi-scan (DENZO-SMN; Otwinowski & Minor, 1997)	k = −22→22
Tmin = 0.852, Tmax = 0.973	l = −8→8
5135 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.026	H-atom parameters constrained
wR(F^2) = 0.067	w = 1/[σ^2(Fo^2) + (0.0117P)^2 + 0.3254P] where P = (Fo^2 + 2Fc^2)/3
S = 1.06	(Δ/σ)max = 0.001
1576 reflections	Δρmax = 0.20 e Å^−3
119 parameters	Δρmin = −0.27 e Å^−3
1 restraint	Absolute structure: Flack (1983)
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.50 (4)

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
K1	0.43167 (7)	0.07292 (3)	−0.80398 (7)	0.01951 (16)
F1	0.40771 (19)	0.11045 (9)	−0.4509 (2)	0.0209 (4)
F2	0.44468 (19)	0.05323 (9)	−0.1735 (2)	0.0201 (4)
F3	0.7002 (2)	0.06972 (8)	−0.3648 (2)	0.0231 (4)
B1	0.5347 (4)	0.10411 (15)	−0.2950 (5)	0.0177 (5)
C1	0.5722 (3)	0.17718 (15)	−0.1942 (4)	0.0195 (6)
H1A	0.6730	0.1802	−0.1055	0.023*
C2	0.4691 (4)	0.23458 (15)	−0.2279 (4)	0.0225 (6)
H2A	0.3715	0.2292	−0.3192	0.027*
C3	0.4847 (4)	0.30522 (15)	−0.1439 (4)	0.0211 (6)
C4	0.6188 (4)	0.32289 (15)	−0.0041 (5)	0.0266 (6)
H4A	0.7036	0.2879	0.0415	0.032*
C5	0.6284 (4)	0.39051 (16)	0.0672 (4)	0.0281 (6)
H5A	0.7207	0.4017	0.1601	0.034*
C6	0.5045 (4)	0.44212 (15)	0.0044 (5)	0.0256 (6)
H6A	0.5115	0.4885	0.0542	0.031*
C7	0.3691 (4)	0.42573 (16)	−0.1324 (4)	0.0255 (6)
H7A	0.2829	0.4608	−0.1751	0.031*
C8	0.3607 (4)	0.35829 (15)	−0.2057 (4)	0.0233 (6)
H8A	0.2692	0.3477	−0.2998	0.028*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
K1	0.0150 (2)	0.0296 (3)	0.0139 (2)	0.0017 (2)	0.0002 (3)	−0.0010 (3)
F1	0.0196 (7)	0.0293 (9)	0.0138 (8)	0.0007 (6)	−0.0036 (6)	−0.0011 (7)
F2	0.0188 (7)	0.0265 (9)	0.0151 (7)	−0.0026 (6)	0.0020 (6)	0.0007 (7)
F3	0.0139 (7)	0.0288 (8)	0.0267 (8)	0.0011 (6)	0.0037 (6)	−0.0003 (7)
B1	0.0135 (12)	0.0264 (13)	0.0133 (11)	−0.0009 (10)	−0.0011 (13)	0.0020 (15)
C1	0.0156 (11)	0.0296 (15)	0.0133 (13)	−0.0028 (10)	−0.0028 (11)	0.0029 (11)
C2	0.0193 (12)	0.0290 (15)	0.0193 (12)	−0.0030 (11)	−0.0033 (11)	−0.0027 (12)
C3	0.0202 (11)	0.0265 (15)	0.0167 (13)	−0.0018 (12)	−0.0011 (12)	−0.0013 (11)
C4	0.0250 (12)	0.0296 (15)	0.0251 (14)	−0.0001 (12)	−0.0043 (13)	−0.0028 (14)
C5	0.0283 (14)	0.0310 (16)	0.0251 (13)	−0.0053 (13)	−0.0046 (14)	−0.0044 (13)
C6	0.0290 (13)	0.0264 (14)	0.0215 (13)	−0.0051 (12)	0.0059 (15)	−0.0038 (11)
C7	0.0275 (15)	0.0293 (16)	0.0198 (14)	0.0019 (12)	0.0038 (14)	0.0015 (12)
C8	0.0220 (13)	0.0299 (14)	0.0179 (12)	0.0002 (12)	−0.0009 (12)	0.0012 (12)

Geometric parameters (Å, º)

K1—F1	2.6169 (17)	C2—C3	1.472 (4)
K1—F3^i	2.6235 (15)	C2—H2A	0.950
K1—F2^ii	2.6573 (16)	C3—C8	1.403 (4)
K1—F1^iii	2.6993 (15)	C3—C4	1.410 (4)
K1—F2^iv	2.7106 (17)	C4—C5	1.382 (4)
K1—F2^iii	2.8275 (14)	C4—H4A	0.950
K1—F3^iv	2.8934 (16)	C5—C6	1.385 (4)
F1—B1	1.429 (4)	C5—H5A	0.950
F2—B1	1.442 (3)	C6—C7	1.396 (5)
F3—B1	1.423 (3)	C6—H6A	0.950
B1—C1	1.583 (4)	C7—C8	1.383 (4)
C1—C2	1.330 (4)	C7—H7A	0.950
C1—H1A	0.950	C8—H8A	0.950
F1—K1—F3^i	103.18 (5)	F3—B1—C1	115.1 (2)
F1—K1—F2^ii	172.09 (5)	F1—B1—C1	112.5 (2)
F3^i—K1—F2^ii	78.44 (5)	F2—B1—C1	112.8 (3)
F1—K1—F1^iii	104.08 (4)	F3—B1—K1^v	135.71 (17)
F3^i—K1—F1^iii	144.43 (5)	F1—B1—K1^v	52.08 (10)
F2^ii—K1—F1^iii	71.60 (5)	F2—B1—K1^v	57.38 (10)
F1—K1—F2^iv	86.10 (5)	C1—B1—K1^v	109.15 (15)
F3^i—K1—F2^iv	73.74 (5)	F3—B1—K1^vii	58.58 (12)
F2^ii—K1—F2^iv	101.76 (4)	F1—B1—K1^vii	96.48 (15)
F1^iii—K1—F2^iv	130.45 (5)	F2—B1—K1^vii	51.28 (12)
F1—K1—F2^iii	70.15 (5)	C1—B1—K1^vii	150.5 (2)
F3^i—K1—F2^iii	166.73 (5)	K1^v—B1—K1^vii	83.77 (6)
F2^ii—K1—F2^iii	109.79 (4)	C2—C1—B1	123.0 (2)
F1^iii—K1—F2^iii	48.38 (4)	C2—C1—H1A	118.5
F2^iv—K1—F2^iii	94.05 (4)	B1—C1—H1A	118.5
F1—K1—F3^iv	112.18 (5)	C1—C2—C3	129.2 (2)
F3^i—K1—F3^iv	105.63 (4)	C1—C2—H2A	115.4
F2^ii—K1—F3^iv	74.43 (5)	C3—C2—H2A	115.4
F1^iii—K1—F3^iv	84.61 (5)	C8—C3—C4	117.8 (3)
F2^iv—K1—F3^iv	47.75 (4)	C8—C3—C2	118.7 (2)
F2^iii—K1—F3^iv	68.04 (4)	C4—C3—C2	123.6 (3)
B1—F1—K1	133.03 (14)	C5—C4—C3	120.8 (3)
B1—F1—K1^v	103.23 (14)	C5—C4—H4A	119.6
K1—F1—K1^v	110.91 (5)	C3—C4—H4A	119.6
B1—F2—K1^vi	120.93 (16)	C4—C5—C6	120.5 (3)
B1—F2—K1^vii	104.20 (14)	C4—C5—H5A	119.7
K1^vi—F2—K1^vii	118.30 (6)	C6—C5—H5A	119.7
B1—F2—K1^v	97.19 (13)	C5—C6—C7	119.7 (3)
K1^vi—F2—K1^v	105.91 (5)	C5—C6—H6A	120.1
K1^vii—F2—K1^v	107.70 (5)	C7—C6—H6A	120.1
B1—F3—K1^viii	137.52 (15)	C8—C7—C6	119.9 (3)
B1—F3—K1^vii	96.62 (13)	C8—C7—H7A	120.1
K1^viii—F3—K1^vii	108.22 (5)	C6—C7—H7A	120.1
F3—B1—F1	106.1 (2)	C7—C8—C3	121.3 (3)
F3—B1—F2	105.1 (2)	C7—C8—H8A	119.4
F1—B1—F2	104.34 (18)	C3—C8—H8A	119.4

Symmetry codes: (i) −x+3/2, y, z−1/2; (ii) x, y, z−1; (iii) −x+1/2, y, z−1/2; (iv) −x+1, −y, z−1/2; (v) −x+1/2, y, z+1/2; (vi) x, y, z+1; (vii) −x+1, −y, z+1/2; (viii) −x+3/2, y, z+1/2.