Isomeric icosaboranes B₂₀H₂₆: the synchrotron structure of 1,1'-bis(nido-decaboranyl)

An isomer of B₂₀H₂₆, isolated from the autolysis of nido-B₁₀H₁₄ in a silent electrical discharge, is shown to be the title compound 1,1'-bis(nido-decaboranyl). The mol­ecule has crystallographic inversion symmetry and a long intercage B-B bond of 1.704 (3) Å.

S1. Comment

Some time ago, the synthesis of the globular macropolyhedral megaloborane B₂₀H₂₆, from the passage of B₁₀H₁₄ through a silent electrical discharge, was reported, although precise reaction conditions were unspecified (Friedman et al., 1963). An alternative Me₂BNHMe-catalysed thermolytic preparation was also reported (Miller & Muetterties, 1963; Miller et al., 1964). Since then (Miller & Muetterties, 1963, Enemark et al., 1966), this very interesting compound has been essentially unexamined. We have now developed an interest in B₂₀H₂₆ and in the possibilities of synthesizing other globular boranes (Kaur et al., 1997; Bould et al., 1999, 2000, Yao et al., 1999), and have consequently sought to duplicate the original synthesis that used a silent electrical discharge. A 1500 V AC silent discharge through a glass tube containing decaborane(14) yielded predominantly a yellow material which is a main focus of our investigations and which we have yet to identify. However, dichloromethane extraction of the material followed by high-performance liquid chromatographic (HPLC) separation yielded very small quantities of several substances, shown by NMR spectroscopy to be a variety of boron hydride species. Predominant among these was a series of compounds identified by NMR spectroscopy (compare with Boocock et al., 1980) as being in the bis(nido-decaboranyl) family, (B₁₀H₁₃)₂. Two of these were identified as the known compounds, i.e. 2,2'- and 1,2'-(nido-B₁₀H₁₃)₂ (after Boocock et al., 1981). A further previously unobserved bis(nido-decaboronyl) isomer was isolated and crystallized by slow sublimation in an evacuated tube. We report here its structure determination as the 1,1'-(nido-B₁₀H₁₃)₂ isomer, i.e. the title compound. Crystals were small (0.03 mm micron cubes) and the single-crystal work required synchrotron-generated X-irradiation for sufficient diffraction intensity (Cernik et al., 1997, 2000; Clegg et al., 1998).

There are 15 possible isomers of (nido-B₁₀H₁₃)₂, of which eight are four enantiomeric pairs (Boocock et al., 1980). Those previously characterized structurally by single-crystal X-ray work are the 1,2'- (Barrett et al., 1985), the 1,5'- (Brown et al., 1979), the 2,2'- and the 2,6'- species (Boocock et al., 1980). The 6,6'- (Boocock et al., 1979), 2,5'- and 5,5'-isomers (Boocock et al., 1981) have been characterized by NMR spectroscopy. The 1,1'-isomer (Fig. 1) contains an inversion centre in the midpoint of the intercage B—B linkage. The B—B linkage distance [B1—B1ⁱ; symmetry code: (i) 1 - x, 1 - y, 1 - z] of 1.704 (3) Å is at the top end of the range of values for reported bis(decaboranyl) isomers, which range from 1.698 (2) (1,5'-isomer; Brown et al., 1979) to 1.679 (3) Å (2,2'-isomer; Barrett et al., 1985). The basal intracluster B—B distances associated with the linkage B1 atom show small but significant lengthenings of ca 0.017 (2) Å compared to those around the unsubstituted B3 atom and are similar in magnitude to those noted previously (0.015 Å; Boocock et al., 1980). Other distances on the substituted side of the decaborane subcluster do not differ significantly from those on the unsubstituted side with the exception of the long B5—B10 `gunwale' interboron vector in the nido-decaboronyl `boat', which, at 1.955 (2) Å, is 0.016 (2) Å shorter than the opposing B7—B8 distance.

Related literature

For related literature, see: Barrett et al. (1985); Boocock et al. (1979, 1980, 1981); Bould et al. (1999, 2000); Brown et al. (1979); Cernik et al. (1997, 2000); Clegg et al. (1998); Enemark et al. (1966); Friedman et al. (1963); Kaur et al. (1997); Miller & Muetterties (1963); Miller et al. (1964); Yao et al. (1999).

S2. Experimental

Decaborane(14) (0.472 g), contained in a small sample vial, was placed in a glass high-voltage silent-discharge reaction tube [constructed in a similar manner to the one used by Friedman et al. (1963)]. Silent electrical discharge under dynamic vacuum (1500 V AC, ca 10^-3 mm Hg) for 90 min resulted in a substantial amount of yellow material being deposited on the sides of the tube. The reaction vessel was opened to air and the material extracted with dichloromethane. The extract was filtered through silica gel and the filtrate subjected to preparative high-performance liquid chromatograpic (HPLC) separation (25 × 2.12 cm column, Lichosorb SI 60, 15:85 CH₂Cl₂/n-hexane, 20 ml min^-1) giving three products with R_T 6.9 (component A), 7.3 (component B) and 7.7 m (component C). Components A and B were identified by ¹¹B NMR spectroscopy as 2,2' and 1,2'-(nido-B₁₀H₁₃)₂, respectively, by comparison with previously characterized samples (Boocock et al., 1981). The ¹¹B NMR spectroscopic characterization of component C suggested the previously unreported 1,1'-bis-decaboranyl isomer; CDCl₃ solution 300 K, cluster resonances ordered as, assignment δ(¹¹B)/p.p.m. [²J(¹¹B–¹H)/Hz in brackets]: B2,4 - 34.5 [156]; B5,7,8,10 + 0.8 [148]; B6,9 + 9.5 [165]; B3 + 12.8 [151]; B1 + 19.8 [site of conjuncto linkage]. Single crystals were grown over a period of 2 months by sublimation in a sealed evacuated glass tube placed on a warm oven.

S3. Refinement

Data collection procedures are described by Clegg et al. (1998). The data set, derived from several series of exposures, is complete to θ = 26°. Corrections were applied for the decay in the synchrotron primary beam intensity. All H atoms were refined freely [B—H range 1.051 (16)–1.329 (17) Å].

Computing details

Data collection: SMART (Siemens, 1997); cell refinement: SAINT (Siemens, 1997); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 1998); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and local programs.

Figures

Fig. 1. The crystallographically determined molecular structure of 1,1'-(nido-B10H13)2 drawn with 40% probability ellipsoids and with H atoms shown as small circles of arbitrary radii.

1,1'-bis(nido-decaboranyl)

Crystal data

B20H26	Dx = 0.983 Mg m^−3
Mr = 242.41	Synchrotron radiation, λ = 0.6890 Å
Orthorhombic, Pbca	Cell parameters from 5421 reflections
a = 10.6601 (5) Å	θ = 2.7–29.4°
b = 10.5515 (5) Å	µ = 0.04 mm^−1
c = 14.5604 (6) Å	T = 150 K
V = 1637.75 (13) Å^3	Cuboid, colourless
Z = 4	0.03 × 0.03 × 0.03 mm
F(000) = 504

Data collection

Siemens SMART CCD diffractometer	1746 reflections with I > 2σ(I)
Radiation source: Daresbury SRS station 9.8	Rint = 0.056
Silicon 111 monochromator	θmax = 29.4°, θmin = 2.7°
ω rotation with narrow frames scans	h = −14→14
10589 measured reflections	k = −14→7
2301 independent reflections	l = −20→20

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.056	Hydrogen site location: difference Fourier map
wR(F^2) = 0.150	All H-atom parameters refined
S = 1.09	w = 1/[σ^2(Fo^2) + (0.074P)^2 + 0.3725P] where P = (Fo^2 + 2Fc^2)/3
2301 reflections	(Δ/σ)max < 0.001
143 parameters	Δρmax = 0.38 e Å^−3
0 restraints	Δρmin = −0.18 e Å^−3

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

	x	y	z	Uiso*/Ueq
B1	0.46647 (12)	0.55218 (12)	0.46270 (9)	0.0164 (3)
B2	0.55859 (14)	0.67977 (13)	0.41826 (10)	0.0202 (3)
H2	0.6587 (16)	0.6820 (15)	0.4308 (11)	0.031 (4)*
B3	0.49222 (14)	0.56719 (14)	0.34216 (9)	0.0203 (3)
H3	0.5547 (17)	0.5096 (18)	0.3019 (11)	0.038 (5)*
B4	0.35058 (13)	0.49886 (13)	0.38247 (9)	0.0187 (3)
H4	0.3340 (15)	0.3996 (15)	0.3736 (10)	0.023 (4)*
B5	0.44334 (14)	0.70690 (14)	0.50513 (10)	0.0216 (3)
H5	0.4615 (15)	0.7348 (16)	0.5758 (11)	0.028 (4)*
B6	0.47698 (15)	0.81984 (15)	0.41677 (12)	0.0271 (3)
H6	0.5098 (16)	0.9159 (16)	0.4290 (12)	0.035 (5)*
B7	0.48766 (15)	0.72877 (15)	0.31286 (11)	0.0258 (3)
H7	0.5337 (16)	0.7655 (16)	0.2549 (12)	0.033 (4)*
B8	0.34977 (16)	0.60858 (15)	0.28909 (11)	0.0269 (3)
H8	0.3291 (16)	0.5832 (15)	0.2190 (12)	0.036 (5)*
B9	0.22848 (14)	0.60423 (15)	0.37348 (11)	0.0257 (3)
H9	0.1329 (15)	0.5890 (15)	0.3596 (11)	0.030 (4)*
B10	0.30692 (13)	0.58756 (14)	0.48119 (10)	0.0210 (3)
H10	0.2541 (14)	0.5530 (14)	0.5389 (10)	0.023 (4)*
H11	0.3832 (18)	0.7963 (17)	0.4698 (13)	0.044 (5)*
H12	0.4106 (16)	0.8139 (16)	0.3396 (12)	0.035 (5)*
H13	0.2693 (17)	0.6912 (16)	0.3154 (11)	0.038 (5)*
H14	0.2419 (18)	0.6740 (16)	0.4456 (12)	0.043 (5)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
B1	0.0164 (6)	0.0165 (6)	0.0164 (6)	0.0014 (5)	0.0010 (4)	−0.0013 (5)
B2	0.0209 (7)	0.0161 (6)	0.0235 (7)	−0.0002 (5)	−0.0003 (5)	0.0009 (5)
B3	0.0240 (7)	0.0198 (7)	0.0170 (6)	0.0006 (5)	0.0017 (5)	0.0004 (5)
B4	0.0201 (6)	0.0168 (6)	0.0192 (6)	0.0008 (5)	−0.0027 (5)	−0.0008 (5)
B5	0.0236 (7)	0.0190 (7)	0.0224 (7)	0.0047 (5)	−0.0022 (5)	−0.0042 (5)
B6	0.0267 (7)	0.0194 (7)	0.0351 (8)	0.0013 (6)	−0.0033 (6)	0.0002 (6)
B7	0.0272 (7)	0.0227 (8)	0.0275 (7)	0.0002 (6)	0.0012 (6)	0.0075 (6)
B8	0.0315 (8)	0.0261 (8)	0.0232 (7)	−0.0015 (6)	−0.0077 (6)	0.0036 (6)
B9	0.0219 (7)	0.0221 (7)	0.0333 (8)	0.0021 (5)	−0.0073 (6)	0.0001 (6)
B10	0.0190 (6)	0.0219 (7)	0.0221 (6)	0.0031 (5)	0.0005 (5)	0.0004 (5)

Geometric parameters (Å, º)

B1—B1^i	1.704 (3)	B5—B10	1.955 (2)
B1—B10	1.7620 (19)	B5—H5	1.088 (16)
B1—B5	1.7628 (19)	B5—H11	1.251 (18)
B1—B3	1.7836 (19)	B6—B7	1.796 (2)
B1—B2	1.788 (2)	B6—H6	1.087 (17)
B1—B4	1.7910 (19)	B6—H11	1.288 (19)
B2—B6	1.715 (2)	B6—H12	1.329 (17)
B2—B3	1.772 (2)	B7—B8	1.972 (2)
B2—B5	1.787 (2)	B7—H7	1.051 (18)
B2—B7	1.787 (2)	B7—H12	1.278 (17)
B2—H2	1.083 (17)	B8—B9	1.784 (2)
B3—B7	1.758 (2)	B8—H8	1.077 (17)
B3—B8	1.759 (2)	B8—H13	1.282 (17)
B3—B4	1.773 (2)	B9—B10	1.786 (2)
B3—H3	1.075 (18)	B9—H9	1.051 (16)
B4—B9	1.717 (2)	B9—H13	1.321 (17)
B4—B10	1.777 (2)	B9—H14	1.290 (17)
B4—B8	1.786 (2)	B10—H10	1.075 (15)
B4—H4	1.070 (15)	B10—H14	1.258 (18)
B5—B6	1.790 (2)
B1^i—B1—B10	116.40 (12)	B2—B6—B5	61.24 (8)
B1^i—B1—B5	115.71 (12)	B2—B6—B7	61.15 (9)
B10—B1—B5	67.37 (8)	B5—B6—B7	105.19 (10)
B1^i—B1—B3	128.32 (12)	B2—B6—H6	129.6 (9)
B10—B1—B3	106.26 (9)	B5—B6—H6	124.6 (9)
B5—B1—B3	106.51 (10)	B7—B6—H6	128.1 (9)
B1^i—B1—B2	119.14 (13)	B2—B6—H11	102.7 (8)
B10—B1—B2	115.21 (10)	B5—B6—H11	44.3 (8)
B5—B1—B2	60.42 (8)	B7—B6—H11	116.8 (8)
B3—B1—B2	59.49 (8)	H6—B6—H11	109.4 (12)
B1^i—B1—B4	120.14 (13)	B2—B6—H12	103.9 (7)
B10—B1—B4	60.02 (8)	B5—B6—H12	118.0 (7)
B5—B1—B4	115.02 (10)	B7—B6—H12	45.3 (7)
B3—B1—B4	59.48 (8)	H6—B6—H12	110.8 (11)
B2—B1—B4	112.29 (9)	H11—B6—H12	94.8 (11)
B6—B2—B3	111.54 (11)	B3—B7—B2	59.96 (8)
B6—B2—B5	61.45 (9)	B3—B7—B6	108.43 (11)
B3—B2—B5	106.00 (10)	B2—B7—B6	57.20 (8)
B6—B2—B7	61.65 (9)	B3—B7—B8	55.91 (8)
B3—B2—B7	59.21 (8)	B2—B7—B8	106.26 (10)
B5—B2—B7	105.70 (10)	B6—B7—B8	116.40 (11)
B6—B2—B1	112.02 (11)	B3—B7—H7	122.6 (9)
B3—B2—B1	60.14 (8)	B2—B7—H7	126.8 (9)
B5—B2—B1	59.10 (8)	B6—B7—H7	120.6 (9)
B7—B2—B1	107.24 (10)	B8—B7—H7	116.4 (9)
B6—B2—H2	118.9 (8)	B3—B7—H12	128.7 (8)
B3—B2—H2	120.9 (8)	B2—B7—H12	102.3 (8)
B5—B2—H2	123.7 (8)	B6—B7—H12	47.7 (8)
B7—B2—H2	123.7 (8)	B8—B7—H12	91.5 (8)
B1—B2—H2	119.8 (8)	H7—B7—H12	106.6 (12)
B7—B3—B8	68.21 (9)	B3—B8—B9	108.47 (10)
B7—B3—B2	60.83 (8)	B3—B8—B4	60.03 (8)
B8—B3—B2	116.94 (11)	B9—B8—B4	57.49 (8)
B7—B3—B4	116.81 (11)	B3—B8—B7	55.88 (8)
B8—B3—B4	60.74 (8)	B9—B8—B7	115.84 (11)
B2—B3—B4	113.93 (10)	B4—B8—B7	106.24 (10)
B7—B3—B1	108.70 (10)	B3—B8—H8	122.1 (9)
B8—B3—B1	108.75 (10)	B9—B8—H8	119.8 (9)
B2—B3—B1	60.37 (8)	B4—B8—H8	124.1 (9)
B4—B3—B1	60.47 (7)	B7—B8—H8	118.6 (9)
B7—B3—H3	115.6 (10)	B3—B8—H13	128.0 (8)
B8—B3—H3	115.8 (9)	B9—B8—H13	47.7 (8)
B2—B3—H3	118.2 (10)	B4—B8—H13	102.5 (7)
B4—B3—H3	118.6 (10)	B7—B8—H13	90.5 (8)
B1—B3—H3	125.6 (9)	H8—B8—H13	108.4 (12)
B9—B4—B3	110.92 (10)	B4—B9—B8	61.30 (9)
B9—B4—B10	61.45 (8)	B4—B9—B10	60.94 (8)
B3—B4—B10	106.06 (10)	B8—B9—B10	105.54 (10)
B9—B4—B8	61.21 (9)	B4—B9—H9	130.6 (9)
B3—B4—B8	59.23 (8)	B8—B9—H9	125.0 (9)
B10—B4—B8	105.85 (10)	B10—B9—H9	127.4 (9)
B9—B4—B1	111.67 (10)	B4—B9—H13	104.4 (8)
B3—B4—B1	60.05 (8)	B8—B9—H13	45.8 (8)
B10—B4—B1	59.18 (7)	B10—B9—H13	118.4 (8)
B8—B4—B1	107.23 (10)	H9—B9—H13	107.6 (12)
B9—B4—H4	120.0 (8)	B4—B9—H14	102.9 (8)
B3—B4—H4	119.9 (8)	B8—B9—H14	117.7 (9)
B10—B4—H4	124.7 (8)	B10—B9—H14	44.7 (8)
B8—B4—H4	122.8 (8)	H9—B9—H14	110.6 (13)
B1—B4—H4	120.0 (8)	H13—B9—H14	95.0 (11)
B1—B5—B2	60.48 (8)	B1—B10—B4	60.80 (8)
B1—B5—B6	109.67 (10)	B1—B10—B9	109.80 (10)
B2—B5—B6	57.31 (8)	B4—B10—B9	57.61 (8)
B1—B5—B10	56.29 (7)	B1—B10—B5	56.34 (7)
B2—B5—B10	106.38 (9)	B4—B10—B5	106.78 (9)
B6—B5—B10	116.72 (10)	B9—B10—B5	116.20 (10)
B1—B5—H5	123.9 (9)	B1—B10—H10	123.6 (8)
B2—B5—H5	126.2 (9)	B4—B10—H10	126.2 (8)
B6—B5—H5	117.7 (9)	B9—B10—H10	118.3 (8)
B10—B5—H5	118.4 (9)	B5—B10—H10	118.0 (8)
B1—B5—H11	128.7 (9)	B1—B10—H14	128.5 (9)
B2—B5—H11	100.5 (9)	B4—B10—H14	101.1 (8)
B6—B5—H11	46.0 (9)	B9—B10—H14	46.2 (8)
B10—B5—H11	91.8 (9)	B5—B10—H14	90.9 (8)
H5—B5—H11	106.0 (12)	H10—B10—H14	106.3 (12)

Symmetry code: (i) −x+1, −y+1, −z+1.