(KF)₄·4GaMe₃

In the structure of tetra­kis(potassium fluoridotrimethyl­gallium), or tetra-μ₄-fluorido-dodeca­methyl­tetra­potassium­tetra­gallium, (KF)₄·4Ga(CH₃)₃ or [K₄Ga₄(CH₃)₁₂F₄], the F atoms of the K₄F₄ cube coordinate to the Ga(CH₃)₃ groups. The crystallographic site symmetry of the tetra­mer is 23 (T).

Key indicators

• Single-crystal X-ray study
• T = 295 K
• Mean [sigma](K-F) = 0.001 Å
• R factor = 0.014
• wR factor = 0.035
• Data-to-parameter ratio = 21.6

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT042_ALERT_1_C Calc. and Rep. MoietyFormula Strings Differ ....          ?
PLAT180_ALERT_3_C Check Cell Rounding: # of Values Ending with 0 =          3
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for        Ga1
PLAT732_ALERT_1_C Angle   Calc    35.41(3), Rep    35.41(1) ......       2.73 su-Ra
              F1   -GA1  -K1      1.555   1.555   1.555
PLAT764_ALERT_4_C Overcomplete CIF Bond List Detected (Rep/Expd) .       2.86 Ratio

Alert level G
FORMU01_ALERT_1_G  There is a discrepancy between the atom counts in the
            _chemical_formula_sum and _chemical_formula_moiety. This is
            usually due to the moiety formula being in the wrong format.
            Atom count from _chemical_formula_sum:   C12 H36 F4 Ga4 K4
            Atom count from _chemical_formula_moiety:C12 H36 F4 K4
ABSTM02_ALERT_3_G  The ratio of expected to reported Tmax/Tmin(RR) is > 1.10
            Tmin and Tmax reported:      0.225     0.292
            Tmin and Tmax expected:      0.133     0.195
            RR =      1.128
            Please check that your absorption correction is appropriate.
REFLT03_ALERT_1_G ALERT: Expected hkl max differ from CIF values
           From the CIF: _diffrn_reflns_theta_max           25.85
           From the CIF: _reflns_number_total                453
           From the CIF: _diffrn_reflns_limit_ max hkl   21.   19.   20.
           From the CIF: _diffrn_reflns_limit_ min hkl  -21.   -5.  -21.
           TEST1: Expected hkl limits for theta max
           Calculated maximum hkl   21.   21.   21.
           Calculated minimum hkl  -21.  -21.  -21.
REFLT03_ALERT_4_G 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.
           From the CIF: _diffrn_reflns_theta_max           25.85
           From the CIF: _reflns_number_total                453
           Count of symmetry unique reflns          258
           Completeness (_total/calc)            175.58%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured       195
           Fraction of Friedel pairs measured     0.756
           Are heavy atom types Z>Si present        yes

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   5 ALERT level C = Check and explain
   4 ALERT level G = General alerts; check

   4 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   1 ALERT type 2 Indicator that the structure model may be wrong or deficient
   2 ALERT type 3 Indicator that the structure quality may be low
   2 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

The potassium fluoride adduct (KF)₄·4GaMe₃, (1), is a suitable intermediate in the purification of GaMe₃, since this reactive compound can be liberated by simply heating (1) in vacuum (Starowieyski et al., 2000). (1) crystallizes in space group F43c, z = 8. The K and F atoms in (1) form a heterocubane structure with the fluorine atoms coordinating to the gallium atoms of the Ga(CH₃)₃ groups. This extends the number of valence electrons of the gallium atoms from six to a complete octet and increases the stability significantly (Elschenbroich, 2003). The first report on the synthesis of the KF–Ga(CH₃)₃ complex appeared in 1974 (Wilson & Dehnicke, 1974). Originally the structure of (1) was reported in space group P43m, z = 1 (Starowieyski et al., 2000). However, then the carbon atom of the refined methyl group occupies a general position resulting in disorder with half occupancy. Isostructural with (1) is the potassium silanolate [KOSi(CH₃)₃]₄, which also has originally been characterized by powder diffraction and described in space group P43m (Weiss et al., 1970); the structure analysis has been corrected after refinement in space group F43c (Pauer & Sheldrick, 1993).

We observed reflections with non-integer Miller indices in (1), if indexing is based on the cubic primitive cell, and succeeded in refinement in space group F43c with twice the lattice parameter a and without disorder of the methyl group. Similar to the isostructural potassium silanolate, these reflections were obviously not recognized in the original structure analysis. This is understandable, since only few reflections hkl with odd indices are allowed at low diffraction angles because of the zonal extinctions in F43c, that allow Miller indices hhl only for h,l = 2n. Therefore only two reflections with odd indices at 2Θ angles below 20° can be observed. A data set collected at 180 K gives the same results with lattice parameter a = 17.608 (2) Å and smaller thermal ellipsoids.

The unit cell of (1) contains eight formula units (KF)₄·4Ga(CH₃)₃ with the K, F and Ga atoms on the threefold axes. The K₄F₄ heterocubane shows K–F–K angles of 98.07 (5) °. The main difference to the description in P43m is the well ordered arrangement of the methyl groups. Important geometric parameters of (1) are summerized in table 2.

Related literature

For related literature, see: Elschenbroich (2003); Pauer & Sheldrick (1993); Sheldrick (1997); Starowieyski et al. (2000); Weiss et al. (1970); Wilson & Dehnicke (1974).

S2. Experimental

Ga(CH₃)₃ has been synthesized by reaction of GaCl₃ with methyl lithium in diethylether. (KF)₄·4Ga(CH₃)₃ was prepared by complexation with potassium fluoride in toluene similar to the procedure described by Starowieyski et al. (Starowieyski et al., 2000).

S3. Refinement

Structure solution and refinement: SHELX97 (Sheldrick, 1997)

Computing details

Data collection: X-AREA (Stoe & Cie, 2005); cell refinement: X-AREA (Stoe & Cie, 2005); data reduction: X-AREA (Stoe & Cie, 2005) and X-RED (Stoe & Cie, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND2 (Brandenburg, 1998); software used to prepare material for publication: SHELXL97 (Sheldrick, 1997).

Figures

Fig. 1. Structure of (KF)4·4Ga(CH3)3 showing 50% probability ellipsoids (hydrogen atoms omitted).

tetra-µ₄-fluorido-dodecamethyltetrapotassiumtetragallium

Crystal data

[K4Ga4(CH3)12F4]	Dx = 1.640 Mg m^−3
Mr = 691.69	Mo Kα radiation, λ = 0.71073 Å
Cubic, F43c	Cell parameters from 4321 reflections
Hall symbol: F -4c 2 3	θ = 2.0–29.6°
a = 17.760 (2) Å	µ = 4.42 mm^−1
V = 5601.8 (11) Å^3	T = 295 K
Z = 8	Block, colorless
F(000) = 2752	0.48 × 0.40 × 0.37 mm

Data collection

Stoe IPDS 2T diffractometer	453 independent reflections
Radiation source: fine-focus sealed tube	376 reflections with I > 2σ(I)
Plane graphite monochromator	Rint = 0.045
Detector resolution: 6.67 pixels mm^-1	θmax = 25.9°, θmin = 2.3°
rotation method, ω scans	h = −21→21
Absorption correction: numerical (X-RED; Stoe & Cie, 2001)	k = −5→19
Tmin = 0.225, Tmax = 0.292	l = −21→20
2577 measured reflections

Refinement

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.014	w = 1/[σ^2(Fo^2) + (0.013P)^2 + 2.0232P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.035	(Δ/σ)max = 0.002
S = 1.10	Δρmax = 0.13 e Å^−3
453 reflections	Δρmin = −0.18 e Å^−3
21 parameters	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.00081 (6)
Primary atom site location: structure-invariant direct methods	Absolute structure: Flack (1983), 195 Friedel pairs
Secondary atom site location: difference Fourier map	Absolute structure parameter: 0.02 (2)

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	0.57967 (2)	0.57967 (2)	0.42033 (2)	0.0535 (2)
F1	0.56874 (6)	0.56874 (6)	0.56874 (6)	0.0508 (5)
Ga1	0.632228 (10)	0.632228 (10)	0.632228 (10)	0.03593 (14)
C1	0.62937 (17)	0.58083 (14)	0.73121 (12)	0.0619 (6)
H1A	0.5784	0.5672	0.7430	0.093*
H1B	0.6484	0.6141	0.7693	0.093*
H1C	0.6599	0.5363	0.7293	0.093*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
K1	0.0535 (2)	0.0535 (2)	0.0535 (2)	−0.00930 (18)	0.00930 (18)	0.00930 (18)
F1	0.0508 (5)	0.0508 (5)	0.0508 (5)	−0.0086 (5)	−0.0086 (5)	−0.0086 (5)
Ga1	0.03593 (14)	0.03593 (14)	0.03593 (14)	−0.00040 (7)	−0.00040 (7)	−0.00040 (7)
C1	0.0710 (17)	0.0682 (15)	0.0465 (13)	0.0086 (14)	0.0009 (13)	0.0141 (11)

Geometric parameters (Å, º)

K1—F1	2.6501 (10)	F1—Ga1	1.9528 (18)
K1—F1^i	2.6502 (10)	F1—K1^i	2.6502 (10)
K1—F1^ii	2.6502 (10)	F1—K1^ii	2.6502 (10)
K1—C1^iii	3.473 (2)	Ga1—C1^vii	1.982 (2)
K1—C1^iv	3.473 (2)	Ga1—C1^viii	1.982 (2)
K1—C1^v	3.473 (2)	Ga1—C1	1.982 (2)
K1—Ga1^i	3.9881 (6)	Ga1—K1^ii	3.9882 (6)
K1—Ga1^ii	3.9881 (5)	Ga1—K1^i	3.9882 (5)
K1—Ga1	3.9881 (5)	C1—H1A	0.96
K1—K1^i	4.0023 (13)	C1—H1B	0.96
K1—K1^ii	4.0023 (13)	C1—H1C	0.96
K1—K1^vi	4.0023 (13)
F1—K1—F1^i	81.31 (6)	C1^iii—K1—K1^ii	100.60 (5)
F1—K1—F1^ii	81.31 (6)	C1^iv—K1—K1^ii	149.72 (5)
F1^i—K1—F1^ii	81.31 (6)	C1^v—K1—K1^ii	133.47 (4)
F1—K1—C1^iii	95.47 (5)	Ga1^i—K1—K1^ii	109.327 (10)
F1^i—K1—C1^iii	168.81 (5)	Ga1^ii—K1—K1^ii	59.882 (9)
F1^ii—K1—C1^iii	108.91 (6)	Ga1—K1—K1^ii	59.884 (9)
F1—K1—C1^iv	108.91 (6)	K1^i—K1—K1^ii	60.0
F1^i—K1—C1^iv	95.47 (5)	F1—K1—K1^vi	84.06 (4)
F1^ii—K1—C1^iv	168.81 (5)	F1^i—K1—K1^vi	40.97 (2)
C1^iii—K1—C1^iv	75.35 (7)	F1^ii—K1—K1^vi	40.97 (2)
F1—K1—C1^v	168.81 (5)	C1^iii—K1—K1^vi	149.72 (5)
F1^i—K1—C1^v	108.91 (6)	C1^iv—K1—K1^vi	133.47 (4)
F1^ii—K1—C1^v	95.47 (5)	C1^v—K1—K1^vi	100.60 (5)
C1^iii—K1—C1^v	75.35 (7)	Ga1^i—K1—K1^vi	59.882 (9)
C1^iv—K1—C1^v	75.34 (7)	Ga1^ii—K1—K1^vi	59.882 (9)
F1—K1—Ga1^i	100.42 (2)	Ga1—K1—K1^vi	109.329 (11)
F1^i—K1—Ga1^i	25.27 (3)	K1^i—K1—K1^vi	60.0
F1^ii—K1—Ga1^i	100.42 (2)	K1^ii—K1—K1^vi	60.0
C1^iii—K1—Ga1^i	148.41 (5)	Ga1—F1—K1	119.32 (4)
C1^iv—K1—Ga1^i	73.72 (4)	Ga1—F1—K1^i	119.32 (4)
C1^v—K1—Ga1^i	90.69 (5)	K1—F1—K1^i	98.07 (5)
F1—K1—Ga1^ii	100.42 (2)	Ga1—F1—K1^ii	119.32 (4)
F1^i—K1—Ga1^ii	100.42 (2)	K1—F1—K1^ii	98.07 (5)
F1^ii—K1—Ga1^ii	25.27 (3)	K1^i—F1—K1^ii	98.06 (5)
C1^iii—K1—Ga1^ii	90.69 (5)	F1—Ga1—C1^vii	103.38 (8)
C1^iv—K1—Ga1^ii	148.41 (5)	F1—Ga1—C1^viii	103.38 (8)
C1^v—K1—Ga1^ii	73.72 (4)	C1^vii—Ga1—C1^viii	114.82 (6)
Ga1^i—K1—Ga1^ii	112.761 (9)	F1—Ga1—C1	103.38 (8)
F1—K1—Ga1	25.27 (3)	C1^vii—Ga1—C1	114.81 (6)
F1^i—K1—Ga1	100.42 (2)	C1^viii—Ga1—C1	114.81 (6)
F1^ii—K1—Ga1	100.42 (2)	F1—Ga1—K1	35.407 (11)
C1^iii—K1—Ga1	73.72 (4)	C1^vii—Ga1—K1	76.52 (8)
C1^iv—K1—Ga1	90.69 (5)	C1^viii—Ga1—K1	94.34 (9)
C1^v—K1—Ga1	148.40 (5)	C1—Ga1—K1	136.33 (8)
Ga1^i—K1—Ga1	112.763 (9)	F1—Ga1—K1^ii	35.408 (11)
Ga1^ii—K1—Ga1	112.763 (9)	C1^vii—Ga1—K1^ii	136.33 (8)
F1—K1—K1^i	40.97 (2)	C1^viii—Ga1—K1^ii	76.52 (8)
F1^i—K1—K1^i	40.97 (2)	C1—Ga1—K1^ii	94.34 (9)
F1^ii—K1—K1^i	84.06 (4)	K1—Ga1—K1^ii	60.234 (17)
C1^iii—K1—K1^i	133.48 (4)	F1—Ga1—K1^i	35.408 (11)
C1^iv—K1—K1^i	100.60 (5)	C1^vii—Ga1—K1^i	94.34 (9)
C1^v—K1—K1^i	149.72 (5)	C1^viii—Ga1—K1^i	136.33 (8)
Ga1^i—K1—K1^i	59.882 (9)	C1—Ga1—K1^i	76.52 (8)
Ga1^ii—K1—K1^i	109.327 (10)	K1—Ga1—K1^i	60.234 (17)
Ga1—K1—K1^i	59.884 (9)	K1^ii—Ga1—K1^i	60.233 (17)
F1—K1—K1^ii	40.97 (2)	Ga1—C1—H1A	109.5
F1^i—K1—K1^ii	84.06 (4)	Ga1—C1—H1B	109.5
F1^ii—K1—K1^ii	40.97 (2)	Ga1—C1—H1B	109.5

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