Intra- and inter-molecular hydrogen bonding in some cobaltacarboranes

Article abstract of DOI:10.1016/S0022-2860(03)00346-6

Two novel and unsymmetrical commo-cobaltacarboranes which contain an intramolecular hydrogen bond between the dicarbollyl C-H and the nitrogen atom of a piperidine or pyrollidine substituent and two additional external hydrogen bond interactions. Each of the two dicarbollide ligands is monosubstituted at carbon, leaving one acidic carboranyl C-H in each dicarbollide ligand available for hydrogen bonding interactions. One of these interacts with the substituent on the other dicarbollide ligand while the other interacts more weakly with a solvent molecule. One of the two amine substituents is protonated, making the cobaltacarborane neutral, and the resulting ammonium hydrogen interacts with a solvent molecule. The mono-N-protonated piperidine and pyrollidine cobalt carborane derivatives 1 and 2, respectively, were characterized by X-ray diffraction studies.

Full text of DOI:10.1016/S0022-2860(03)00346-6

Journal of Molecular Structure 656 (2003) 239–247
www.elsevier.com/locate/molstruc
Intra- and inter-molecular hydrogen bonding
in some cobaltacarboranes
*
M. Frederick Hawthorne , Cynthia L. Beno, David E. Harwell, Satish S. Jalisatgi,
Carolyn B. Knobler
Department of Chemistry and Biochemistry, University of California at Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90095-1569, USA
¨
Dedicated to professor Achim Muller on the occasion of his 65th birthday
Abstract
Two novel and unsymmetrical commo-cobaltacarboranes which contain an intramolecular hydrogen bond between the
dicarbollyl C–H and the nitrogen atom of a piperidine or pyrollidine substituent and two additional external hydrogen bond
interactions. Each of the two dicarbollide ligands is monosubstituted at carbon, leaving one acidic carboranyl C–H in each
dicarbollide ligand available for hydrogen bonding interactions. One of these interacts with the substituent on the other
dicarbollide ligand while the other interacts more weakly with a solvent molecule. One of the two amine substituents is
protonated, making the cobaltacarborane neutral, and the resulting ammonium hydrogen interacts with a solvent molecule. The
mono-N-protonated piperidine and pyrollidine cobalt carborane derivatives 1 and 2, respectively, were characterized by X-ray
diffraction studies.
q 2003 Elsevier B.V. All rights reserved.
Keywords: Cobaltacarboranes; Hydrogen bond; Crystal structure; X-ray diffraction
1. Introduction
and skepticism [3]. Nearly every type of hydrogen
atom bonded to carbon, ranging from those in weakly
acidic methyl groups to strongly acidic alkynes [4]
and cyclopropanes [5] forms C–H· · ·O hydrogen
bonds [6]. Although the acidic nature of the
carboranyl C–H would lead one to believe that its
hydrogen bonding interactions would be common,
and the ability of carborane C–H vertices to serve as
proton donors in hydrogen bonding was investigated
by IR spectroscopy in the 1970s and reviewed in 1992
[7], there are relatively few examples of such
interaction in the literature. Wade has described
such an interaction in the ortho-carborane 1:1 adduct
with hexamethylphosphoramidite [8]. An aza-crown
ether: ortho-carborane adduct contains a carboranyl
C–H interaction with an oxygen of the crown ether
A hydrogen bond, X–H· · ·Y, is an interaction of a
hydrogen atom attracted to two (or more) atoms, X
and one or more Y atoms [1]. This attraction increases
with the increasing electronegativity of X and Y [2].
Thus O–H and N–H donor groups are known to form
strong hydrogen bonds in crystals. The existence of
the C–H· · ·O hydrogen bond, an interaction involving
a weak donor and a strong acceptor, is now well
established, although the original concept, when
introduced in the early sixties, was met with doubt
*
Corresponding author. Tel.: þ1-310-825-7378; fax: þ1-310-
825-5490.
E-mail address: mfh@chem.ucla.edu (M.F. Hawthorne).
0022-2860/03/$ - see front matter q 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0022-2860(03)00346-6

240
M.F. Hawthorne et al. / Journal of Molecular Structure 656 (2003) 239–247
[9]. Evidence has been presented for intramolecular
carboranyl C–H· · ·O interactions in a solution of
ortho-carboranyl b-lactoside [10]. We have reported a
self-assembly involving intermolecular carboranyl
C–H hydrogen bonding between functionalized
ortho-carborane molecules [11], carboranyl C–H
p-bonding to phenyl ligands and CH bonding to F
[12]. Fewer carboranyl C–H· · ·N interactions have
been reported. Such an interaction is found between
molecules of 9-cyano-ortho-carborane [13]. The
majority of cited examples involve intermolecular
hydrogen bonding. In contrast, we report here two
new unsymmetrical commo-cobaltacarboranes which
display both intramolecular and intermolecular hydro-
gen bond interactions.
spectra were obtained on a VG ZAB-SE reverse-
geometry magnetic sector mass spectrometer.
2.3. Synthesis of ethyl-3,4-dipropargyloxylbenzoate, 3
A mixture of potassium carbonate (5.4 g.,
0.041 mol), ethyl-3,4-dihydroxybenzoate (3.4 g,
0.019 mol), and 4.6 ml (0.041 mol) of propargyl
bromide (20% toluene) was stirred together in acetone
overnight. Solvent was removed from the resulting
brown solution by rotary evaporation. The brown
solid was dissolved in 200 ml benzene and washed
with 2 £ 100 ml brine solution. The organic layer was
dried over anhydrous magnesium sulfate, filtered and
concentrated in vacuo. The product, 3 was obtained as
a white solid in 75% yield (3.6 g). 1H NMR
(200 MHz, acetone-d6): d 7.69 (2H, m), 7.20 (1H,
d), 4.87 (4H, m), 4.32 (2H, q), 1.33 (3H, t).
2. Experimental
2.4. Synthesis of 1-ethyl-3,4-di-(10,20-dicarba-closo-
dodecahydrododecaboran-10-ylmethoxy)benzoate, 4
2.1. Starting materials
All operations were performed under a nitrogen
atmosphere using standard Schlenk line and glovebox
techniques. Prior to use, THF was dried over sodium
benzophenone ketal and freshly distilled under a
nitrogen atmosphere, toluene was dried over sodium
and freshly distilled under a nitrogen atmosphere, and
diethyl sulfide was distilled from lithium aluminum
hydride under a nitrogen atmosphere. All other
reagents were obtained from commercial sources
and used without further purification. All glassware
was previously dried in an oven and cooled under
nitrogen flow.
Decaborane (5.2 g, 0.043 mol) and diethyl sulfide
(10.1 ml, 0.094 mol) were heated together in 50 ml
dry toluene at reflux temperature under a nitrogen
atmosphere with stirring overnight. The resulting
bright yellow solution was cooled and a solution of
5.0 g (0.019 mol) ethyl-3,4-dipropargyloxybenzoate
in 25 ml dry toluene was added via syringe. The
reaction product was heated again at reflux tempera-
ture under a nitrogen atmosphere with stirring over-
night. The solution was then cooled and the solvent
was removed in vacuo. The resulting yellow solid was
dissolved in 200 ml CH2Cl2 and washed with
2 £ 100 ml of a saturated solution of aqueous sodium
bicarbonate and then washed with 1 £ 100 ml brine.
The organic layer was dried over anhydrous mag-
nesium sulfate, filtered and concentrated by rotary
evaporation. The product, 4, was purified by column
chromatography (silica gel, hexanes: ethyl acetate 8:
2). 1H NMR (200 MHz, acetone-d6): d 7.64 (3H, m),
7.13 (2H, d), 4.86 (2H, s), 4.79 (2H, d), 4.28 (3H, q),
1.22 (2H, t); 11B NMR (methylene chloride): 22.4
(1B, d), 23.4 (1B, d), 28.6 (3B, d), 211.1 (2B, d),
212.5 (3B, d); HRMS (EI): for C15H34B20O4 (m/z)
calcd. 495.4440, 495.4442 obs (Mþ).
2.2. Physical measurements
1
The H NMR spectra were recorded on a Bruker
AF 200 spectrometer at 200.13 HMz. 11B NMR
spectra were recorded on a Bruker AC 500 MHz
spectrometer at 160.46 MHz referenced to an external
BF3zOEt2 (0.0 ppm with negative values upfield).
Electron impact (EI) mass spectrometry spectra were
obtained on a VG Autospec computer-controlled
magnetic sector mass spectrometer. Negative ion
fast atom bombardment (FAB) mass spectrometry

M.F. Hawthorne et al. / Journal of Molecular Structure 656 (2003) 239–247
241
2.5. Deboronation of ethyl-3,4-di-(10,20-dicarba-
closo-dodecahydrododecaboran-10-ylmethoxy)
benzoate with pyrrolidine forming 5
2.7. Metal complexation, formation of 1
A mixture of 1.0 g (0.0016 mol) of 6, 50 ml
tetrahydrofuran, and 0.32 g (0.0080 mol) of sodium
hydride (60% oil dispersion) was stirred at reflux
temperature overnight and then 0.313 g (0.002 mol)
of cobaltous chloride was added neat. The reaction
mixture turned light blue and then deepened to
midnight blue. The mixture was then heated to reflux
with stirring overnight and then cooled, filtered, and
the solvent was removed by rotary evaporation,
leaving a red solid with a yellow impurity. The
product, 1, was dissolved in methylene chloride and
the impurity was separated by filtration. The product
was recrystallized from acetone.
To a solution of 4 (1.4 g, 0.0029 mol) in 50 ml
ethanol was added 2.4 ml (0.028 mol) pyrrolidine.
The reaction mixture was stirred at reflux temperature
overnight. The mixture was cooled to room tempera-
ture and the solvents were removed in vacuo. The
resulting oil was dissolved in 100 ml methylene
chloride, washed with 2 £ 100 ml of a saturated
solution of aqueous sodium bicarbonate and then
1 £ 100 ml brine. The organic layer was dried over
anhydrous magnesium sulfate, filtered and concen-
trated by rotary evaporation. The product, 5, an off-
white solid, was purified by column chromatography
(silica gel, 5% acetonitrile in methylene chloride,
followed by an ethanol wash).
2.8. Metal complexation, formation of 2
A mixture of 0.9 g (0.0015 mol) of 5, 50 ml of
tetrahydrofuran, 0.29 g (0.0073 mol) of sodium
hydride (60% oil dispersion) was stirred at reflux
temperature overnight and then 0.28 g (0.0220 mol)
of cobaltous chloride was added neat, yielding a light
blue mixture which deepened to midnight blue. The
reaction mixture was then heated to reflux with
stirring overnight and then cooled, filtered, and the
solvent was removed by rotary evaporation to yield a
red solid. The solid was partially purified by column
chromatography (silica gel, ethyl acetate). The
solvent was removed by rotary evaporation, leaving
a red solid with a yellow impurity. The product, 2, was
dissolved in methylene chloride and the impurity was
separated by filtration. The product was recrystallized
from acetone.
1H NMR (200 MHz, acetone-d6): d 7.54 (m), 6.96
(m), 4.20 (m), 4.12 (m), 3.96 (dd), 3.62 (m), 2.08 (m),
1.93 (s), 1.35 (m), 1.29 (t); 11B NMR (160 MHz,
CH2Cl2): d 210.2 (1B, d), 211.4 (1B, d), 215.2 (1B,
d), 216.5 (1B, d), 218.6 (2B, s), 223.1 (1B, d),
233.4 (1B, d), 238.0 (1B, d); HRMS (neg-FAB) for
[C19H44B18O4N]2: (m/z) [M22 þ C4H10Nþ]2
545.5054 calcd., 545.5076 obs.
2.6. Deboronation of ethyl-3,4-di-(10,20-dicarba-
closo-dodecahydrododecaboran-10-ylmethoxy)
benzoate with piperidine forming 6
To a solution of 4 (1.35 g, 0.0027 mol) in 50 ml
ethanol was added 2.7 ml (0.0273 mol) piperidine.
The reaction mixture was stirred at reflux temperature
overnight. The solution was cooled to room tempera-
ture and the solvents were removed in vacuo.The
resulting oil was dissolved in 100 ml methylene
chloride, washed with 2 £ 100 ml of a saturated
solution of aqueous sodium bicarbonate and then
washed with 1 £ 100 ml brine. The organic layer was
dried over anhydrous magnesium sulfate, filtered and
concentrated by rotary evaporation. The product, 6, an
off-white solid, was purified by column chromatog-
raphy (silica gel, 5% acetonitrile in methylene
chloride, followed by an ethanol wash).
2.9. Crystallographic studies
All data were collected at 25 8C in the u–2u scan
mode and were corrected for Lorentz and polarization
effects and for secondary extinction and absorption
(and decay for 2·2(CH3CN)). Atoms were located by
use of heavy atom methods. Programs used in this
work include locally modified versions of the
following programs: CARESS (Broach, Coppens,
Becker and Blessing), peak profile analysis, Lorentz
and polarization corrections; SHELX 76 (Sheldrick), a
crystal structure package, SHELX 86 (Sheldrick), a
crystal structure solution package, and ABSCOR,

242
M.F. Hawthorne et al. / Journal of Molecular Structure 656 (2003) 239–247
a locally written absorption correction program based
on psi scans. These programs are all part of the UCLA
Crystallographic Package. In addition, SHELXTL and
other programs furnished by Bruker have been used in
final calculations. Scattering factors for H were
obtained from Stewart et al. [14]. Anomalous
dispersion terms were included [15].
a Syntex P-1 diffractometer. Systematic absences
were found for 0k0 reflections for which k ¼ 2n þ 1
and for ho1 reflections for which h ¼ 2n þ 1: Unit cell
parameters were determined from a least-squares fit of
21 reflections (16.48 , 2u , 32.18). Intensities of the
three standard reflections did not decay during the
course of the experiment (48.4 h). Of the 4755 unique
reflections measured, 2053 had I . 2sðIÞ.
A summary of crystallographic data for 1·2(CH3-
COCH3), 1·(CH3CN) (C2H5OH), and 2·2(CH3CN) is
presented in Table 1.
2.9.4. Solution and refinement of the structure
of 1·(CH3CN)(C2H5OH)
2.9.1. Collection and reduction of X-ray data
for 1·2(CH3COCH3)
The unit cell contains 4 molecules of cobaltacar-
borane, 4 molecules of acetonitrile, and 4 molecules
of ethanol. The ethanol molecules are disordered in
two half-occupancy orientations. The cobalt atom and
all non-hydrogen atoms of the piperidine ligands and
the acetonitrile solvent molecule were refined with
anisotropic parameters. All other non-hydrogen atoms
were refined isotropically. Carboranyl hydrogen
atoms were located and were included in the structure
factor calculations, but position parameters were
refined only for the carboranyl C–H hydrogen atom
involved in an interaction with a nitrogen atom. All
other hydrogen atoms were placed in calculated
positions. Hydrogen atoms were assigned isotropic
displacement values based on the value for the
attached atom.
A red crystal, obtained from an acetone solution,
was coated with epoxy cement, placed on a fiber, and
mounted on a Syntex P-1 diffractometer. Systematic
absences were found for 0k0 reflections for which k ¼
2n þ 1 and for hol reflections for which l ¼ 2n þ 1:
Unit cell parameters were determined from a least-
squares fit of 66 reflections (19.98 , 2u , 38.48).
Intensities of the 3 standard reflections decayed 4%
during the course of the experiment (93.6 h). Of the
7170 unique reflections measured, 3074 had I .
2sðIÞ:
2.9.2. Solution and refinement of the structure
of 1· 2(CH3COCH3)
The unit cell contains 8 molecules of the
cobaltacarborane and 16 molecules of acetone.
Cobalt, piperidine carbon and nitrogen and solvent
oxygen atoms were refined with anisotropic par-
ameters. All other nonhydrogen atoms were refined
isotropically. Carboranyl hydrogen atoms were
located and were included in structure factor calcu-
lations, but, with the exception of the carboranyl C–H
hydrogen atoms, positional parameters were not
refined. Positional parameters for hydrogen atoms
bonded to nitrogen were refined. All other hydrogen
atoms were placed in calculated positions. Hydrogen
atoms were assigned isotropic displacement values
based on the value for the attached atom.
2.9.5. Collection and reduction of X-ray data
for 2·2(CH3CN)
A red crystal, obtained from an acetonitrile
solution, was placed on a fiber and mounted on a
Huber (Crystal Logic) diffractometer. Unit cell
parameters were determined from a least-squares fit
of 16 reflections (9.48 , 2u , 18.08). The intensities
of the three standard reflections decayed 37% during
the course of the experiment (93.4 h). Of the 13553
unique reflections measured, 7567 had I . 2sðIÞ.
2.9.6. Solution and refinement of the structure
of 2·2(CH3CN)
The unit cell contains 4 molecules of the
cobaltacarborane and 8 molecules of acetonitrile.
All non-hydrogen atoms were refined with aniso-
tropic parameters. Carboranyl hydrogen atoms were
located and were included in structure factor
2.9.3. Collection and Reduction of X-ray data
for 1· (CH3CN)(C2H5OH)
A red crystal, obtained from an acetonitrile/ethanol
solution, was placed on a fiber and mounted on

M.F. Hawthorne et al. / Journal of Molecular Structure 656 (2003) 239–247
243
Table 1 (continued)
Table 1
Crystal data and structure refinement
˚
Unit cell dimensions
a ¼ 17:236ð12Þ A
a ¼ 908
1·2(CH3COCH3)
˚
b ¼ 9:937ð8Þ A
b ¼ 111:25ð2Þ8
g ¼ 908
Identification code
Empirical formula
Formula weight
Temperature (K)
cbco3sm
˚
c ¼ 21:729ð15Þ A
C22 H57 B18 Co N2 O2
635.21
3
˚
Volume
3469(4) A
293(2)
Z
4
˚
Wavelength (A)
1.54180
Density (calculated)
(Mg/m3)
1.159
Crystal system
Space group
Monoclinic
P21=c
Absorption coefficient 4.013
(mm 2 1)
˚
Unit cell dimensions
a ¼ 10:291ð4Þ A
a ¼ 908
˚
Fð000Þ
1276
b ¼ 41:273(17) A
b ¼ 91:050ð10Þ8
g ¼ 908
Crystal size ( mm3)
Theta range for data
collection (8)
0.15 £ 0.05 £ 0.35
2.18–57.49
˚
c ¼ 17:158ð7Þ A
3
˚
Volume (A )
7286(5)
8
Z
Index ranges
0 ,¼ h ,¼ 18;
0 ,¼ k ,¼ 10;
223 ,¼ l ,¼ 22
4755
Density (calculated)
(Mg/m3)
1.158
Absorption coefficient 3.856
(mm21
Reflections collected
)
Independent reflections 4755
Fð000Þ
2688
½RðintÞ ¼ 0:0000ꢀ
Crystal size (mm3)
Theta range for data
collection (8)
0.40 £ 0.22 £ 0.12
2.14–50.00
Completeness to
theta ¼ 57:498
100.0%
Refinement method
Full-matrix least-
squares on F2
4755/0/304
Index ranges
0 ,¼ h ,¼ 10;
0 ,¼ k ,¼ 40;
217 ,¼ l ,¼ 17
7672
Data/restraints/
parameters
Goodness-of-fit on F2 0.964
Reflections collected
Independent reflections 7170
Final R indices
R1 ¼ 0:0715;
½RðintÞ ¼ 0:0732ꢀ
95.9%
½I . 2sigmaðIÞꢀ
R indices (all data)
wR2 ¼ 0:1490
R1 ¼ 0:1967;
wR2 ¼ 0:1823
0.00064(11)
Completeness to
theta ¼ 50:00 (8)
Max. and min.
transmission
0.6548 and 0.3077
Extinction coefficient
Largest diff. peak and 0.286 and 20.214
23
Refinement method
Full-matrix least-
squares on F2
7170/0/565
˚
hole (e A
)
2·2(CH3CN)
Data/restraints/
parameters
Goodness-of-fit on F2 1.054
Identification code
Empirical formula
Formula weight
Temperature (K)
cbcohm
C36 H94 B36 Co2 N8
1146.21
Final R indices
R1 ¼ 0:0756;
½I . 2sigmaðIÞꢀ
R indices (all data)
wR2 ¼ 0:1678
R1 ¼ 0:1953;
wR2 ¼ 0:1986
0.00022(4)
293(2)
˚
Wavelength (A)
0.71073
Crystal system
Space group
Triclinic
P-1
Extinction coefficient
Largest diff. peak
0.514 and 20.286
23
)
˚
and hole (e A
˚
Unit cell dimensions
a ¼ 9:319ð5Þ A
a ¼ 86:85ð2Þ8
b ¼ 87:83(2)8
g ¼ 72:696ð15Þ8
˚
b ¼ 9:388ð5Þ A
1·(CH3CN)(C2H5OH)
˚
c ¼ 38:46ð2Þ A
Identification code
Empirical formula
Formula weight
Temperature (K)
cbcoep
3
˚
C40 H106 B36 Co2 N6 O2
1210.33
Volume
3207(3) A
Z
4
293(2)
Density (calculated)
(Mg/m3)
1.187
˚
Wavelength (A)
1.54180
Crystal system
Space group
Monoclinic
P21=a
Absorption coefficient 0.554
(mm 2 1)
(continued on next page)

244
M.F. Hawthorne et al. / Journal of Molecular Structure 656 (2003) 239–247
Table 1 (continued)
cage and effectively forms a bridge between the two
cages of the commo-molecule. The remaining carbor-
anyl C–H, from the cage containing the non-
protonated ligand, bonds more weakly to a solvent
molecule. A third, and strongest, hydrogen bond is
formed between N–H of the protonated ligand, LHþ,
and a solvent molecule. These hydrogen bonds are
summarized in Table 2.
Fð000Þ
1200
Crystal size (mm3)
Theta range for data
collection (8)
0.35 £ 0.25 £ 0.3
0.53–27.50
Index ranges
0 ,¼ h ,¼ 12;
211 ,¼ k ,¼ 12;
249 ,¼ l ,¼ 49
13553
Reflections collected
Independent reflections 13553
½RðintÞ ¼ 0:0000ꢀ
91.9%
3.1.1. Synthesis of cobaltacarboranes 1 and 2
Completeness to
theta ¼ 27:50 (8)
Refinement method
In accord with Scheme 1, the precursor, 3,4-
dihydroxyethylbenzoate, was converted to the
3,4-dipropargyloxyethylbenzoate by reaction with
propargyl bromide in the presence of potassium
carbonate. The resulting alkyne was reacted with the
diethyl sulfide adduct of decaborane, arachno-
B10H12(SEt2)2, to yield the closo-carborane.
Attempted degradation of this closo-carborane with
tetrabutylammonium fluoride and with alcoholic
ethoxide yielded an inseparable mixture of products.
Treatment with either piperidine or pyrrolidine
successfully produced the desired di-nido-carborane
dianion as the piperidinium or pyrrolidinium salt.
During the routine metal complexation to yield the
expected bridged commo-cobaltacarborane, sodium
hydride was used to remove the bridging hydrogen
of the nido-carborane and react with the piperidi-
nium or pyrrolidinium counterion, liberating piper-
idine or pyrrolidine, respectively. The base was now
free to attack the methylene carbon a to the
dicarbollide, adding to this carbon atom with
the concurrent loss of the ether linkage and the
formation of commo-cobaltacarboranes 1 and 2,
respectively, following the addition of cobaltous
chloride. The mechanism of this overall transform-
ation is under investigation and will be reported
elsewhere.
Full-matrix least-
squares on F2
13553/0/805
Data/restraints/
parameters
Goodness-of-fit on F2 1.192
Final R indices
R1 ¼ 0:0673;
½I . 2sigmaðIÞꢀ
R indices (all data)
wR2 ¼ 0:1975
R1 ¼ 0:1415;
wR2 ¼ 0:2162
Largest diff. peak and 0.455 and 20.367
23
)
˚
hole (e A
calculations, but, with the exception of the four CH
hydrogen atoms involved in close approaches to a
nitrogen atom, positional parameters were not
refined. Other hydrogen atoms were placed in
calculated positions. Hydrogen atoms were assigned
isotropic displacement values based on the value for
the attached atom.
3. Results and discussion
3.1. Two new charge-compensated cobaltacarboranes
1 and 2
Each of the neutral charge-compensated commo-
metallacarboranes 1 and 2 is monosubstituted at a
carboranyl carbon of each 7,8-dicarbollide cage,
leaving one acidic carboranyl C–H per cage available
for hydrogen bonding interaction. One of the two
ligands is protonated resulting in a neutral molecule.
An intramolecular hydrogen bond links a carboranyl
carbon atom, from the cage containing the protonated
ligand, LHþ, and the nitrogen atom of a piperidine or
pyrrolidine ligand, L, on a second 7,8-dicarbollide
3.1.2. Molecular structures
3.1.2.1. Molecular structure of 1·2(CH3COCH3). The
structure, shown in Fig. 1, was confirmed by X-ray
crystallography.
3.1.2.2. Molecular structure of 1·(CH3CN)(C2H5OH).
The structure, shown in Fig. 2, was confirmed by X-
ray crystallography.

M.F. Hawthorne et al. / Journal of Molecular Structure 656 (2003) 239–247
245
Table 2
Hydrogen bonds
D–H· · ·A
d(D–H)
d(H· · ·A)
d(D· · ·A)
,(DHA)
˚
cbco3sm [A and 8]
C(2A)–H(2A) · · ·O(1S)
C(2B)–H(2B) · · ·N(14A)
N(14B)–H(14B) · · ·O(1T)
C(2C)–H(2C) · · ·N(14D)
N(14C)–H(14C) · · ·O(1V)
C(2D)–H(2D) · · ·O(1U)
0.96(7)
1.09(5)
0.97(7)
1.10
2.43(7)
2.13(6)
2.05(7)
2.12
3.280(11)
3.023(10)
2.955(9)
148(5)
137(4)
153(6)
141.9
3.063(10)
2.927(11)
3.292(12)
1.10(7)
0.87(7)
1.95(7)
2.57(7)
146(6)
140(6)
˚
cbcoep [A and 8]
C(2A)–H(2A) · · ·O(3Y)#1
C(2B)–H(2B) · · ·N(3A)
N(3B)–H(3B) · · ·N(1S)
1.10
2.98
3.665(18)
3.055(8)
2.986(10)
120.7
138(4)
148(5)
0.94(5)
0.95(5)
2.29(5)
2.14(6)
˚
cbcohm [A and 8]
N(4A)–H(4AN) · · ·N(9S)
C(2A)–H(2A) · · ·N(4B)
C(2B)–H(2B) · · ·N(3S)
C(2C)–H(2C) · · ·N(6S)#5
C(2D)–H(2D) · · ·N(4C)
N(4D)–H(4DN) · · ·N(12S)
0.79(6)
0.96(6)
0.91(6)
0.94(6)
1.02(6)
0.85(6)
2.14(6)
2.25(6)
2.63(6)
2.60(6)
2.19(6)
2.08(6)
2.891(8)
3.021(8)
3.404(9)
3.413(9)
3.090(8)
2.904(9)
159(6)
137(5)
143(5)
146(5)
146(5)
164(6)
Symmetry transformations used to generate equivalent atoms: #1 2x þ 1=2; y þ 1=2; 2z þ 1; #5 x 2 1; y; z
3.1.2.3. Molecular structure of 2·2(CH3CN). The
structure, shown in Fig. 3, was confirmed by X-ray
crystallography.
the 7,8-dicarbollide ion ligand, carbon atoms of
the two 7,8-dicarbollide ligands are on the same side
and the two C2B3 faces bonding to Co are not parallel.
The angle between normals to these planes is 8.7(5)
and 10.0(5)8 for the two molecules of 1·2(CH3-
COCH3), 8.6(4)8 for 1·(CH3CN)(C2H5OH), and
3.1.2.4. A comparison of the three structures. Unlike
many other commo-cobaltacarboranes derived from
Scheme 1. Synthesis of 1 and 2.

246
M.F. Hawthorne et al. / Journal of Molecular Structure 656 (2003) 239–247
Fig. 1. Structure of 1·2(CH3COCH3) with 30% probability thermal
ellipsoids. For clarity, the hydrogen atoms have been omitted with
the exception of those participating in hydrogen bonding. The two
crystallographically unrelated cobaltacarboranes are very similar.
Fig. 3. Structure of 2·2(CH3CN) with 30% probability thermal
ellipsoids. For clarity the hydrogen atoms have been omitted with
the exception of those participating in hydrogen bonding.
8.2(4)8 for the two molecules of 2·2(CH3CN), all tilted
open on the side where the carboranyl carbon atoms
are located. The five atoms of the C2B3 faces bonding
to Co in each molecule are coplanar with a maximum
deviation of 0.028(6), 0.019(6), 0.026(6), 0.024(6),
0.024(4), 0.024(4), 0.016(4), 0.022(4), 0.020(4), and
˚
0.020(4) A from a plane. Co is 1.499(4), 1.500(4),
1.499(4), 1.497(4), 1.494(3), 1.499(3), 1.502(3),
˚
1.500(3), 1.502(3), and 1.506(3) A from these planes.
The protonated ligand CH2NHC5Hþ10 (1) or CH2-
NHC4Hþ8 (2) is always bent away from the center of
the molecule and interacts with a solvent molecule,
NH· · · acetone or acetonitrile. These are the strongest
hydrogen bonds in each molecule. The N· · ·O distance
˚
ranges from 2.927(11) to 2.955(9) A and the N· · ·N
˚
distance ranges from 2.892(8) to 2.986(10) A.
The unprotonated ligand bends toward the center
of the molecule and its nitrogen atom interacts with
the acidic hydrogen of the unsubstituted carbon atom
of the icosahedron bearing the protonated ligand.
Fig. 2. Structure of 1·(CH3CN)(C2H5OH) with 30% probability
thermal ellipsoids. For clarity, the hydrogen atoms have been
omitted with the exception of those participating in hydrogen
bonding.

M.F. Hawthorne et al. / Journal of Molecular Structure 656 (2003) 239–247
247
The C· · ·N distance ranges from 3.021(8) to
˚
3.090(8) A. The remaining unsubstituted carboranyl
obtained free of charge from: The Director, CCDC, 12
Union Road, Cambridge CB2 1EZ, UK (fax: þ44-
1223-336-033; e-mail: deposit@ccdc.cam.ac.uk or
http://www.ccdc.cam.ac.uk). These may be obtained
on quoting the depository numbers CCDC 203795,
CCDC 203796, and CCDC 203797, respectively.
carbon atom is weakly hydrogen bonded to acetone,
ethanol, or acetonitrile. These C· · ·O distances range
˚
from 3.280(11) to 3.66(2) A and C· · ·N distances
˚
range from 3.404(9) to 3.412(9) A. The C· · ·O
distances are much longer than the shortest carboranyl
C· · ·O distance found in 9,12-bis-(4-acetylphenyl)-
˚
1,2-dicarbadodecaborane(12) of 3.015(7) A [11]. and
Acknowledgements
˚
in 9-acetyl-ortho-carborane of 3.059(2) and 3.296 A.
The C· · ·N (solvent) distances are longer than that
˚
found in 9-cyano-ortho-carborane of 3.3225(17) A
The authors gratefully acknowledge the support of
this research by the grant CHE-0111718 from
National Science Foundation.
[13]. but the intramolecular C· · ·N distance is
significantly shorter. In 1·2(CH3COCH3) and in
2·2(CH3CN) the two crystallographically unrelated
cobaltacarboranes are very similar.
References
[1] G.R. Desiraju, Acc. Chem. Res. 35 (2002) 565.
[2] L. Pauling, The Nature of the Chemical Bond, Cornell
University Press, Ithaca, New York, 1939.
4. Conclusion
[3] A. Allerhand, P.V.R. Schleyer, J. Am. Chem. Soc. 85 (1963)
1715. D.J. Sutor, Nature 68 (1962) 195. D.J. Sutor, J. Chem.
Soc. (1963) 1105. J. Donohue, A. Rich, N. Davidson,
Structural Chemistry and Molecular Biology, W.H. Free-
manSan Francisco (1968) 459–463. R. Taylor, O. Kennard,
J. Am. Chem. Soc. 104 (1982) 5063. J.A.R. Sarma, G.R.
Desiraju, Acc. Chem. Res. 19 (1986) 222. G.R. Desiraju, Acc.
Chem. Res. 24 (1991) 290. G.R. Desiraju, Acc. Chem. Res. 29
(1996) 441.
In this paper, the syntheses and crystal structures of
two new charge-compensated and unsymmetrical
commo-cobaltacarboranes have been presented. In
each molecule three types of hydrogen bonds are
present, two of which involve carboranyl CH hydro-
gen. One of these is intramolecular, linking one
unsubstituted carboranyl carbon to the ligand, piper-
idine or pyrrolidine, of the other C2B9 moiety. The
other bond is weaker and links the other carboranyl
CH hydrogen to solvent O or N. The strongest
hydrogen bond in these crystal structures links the
charged ligand having a piperidinium or pyrrolidi-
nium NH substituent to a solvent O or N.
[4] G.R. Desiraju, J. Chem. Soc, Chem. Commun. (1990) 454.
[5] F.H. Allen, J.P.M. Lommerse, V.J. Hoy, J.A.K. Howard, G.R.
Desiraju, Acta Crystallogr. Section B 53 (6) (1997) 1006.
[6] R. Taylor, O. Kennard, J. Am. Chem. Soc. 104 (1982) 5063.
[7] L.A. Leites, Chem. Rev. 92 (1992) 279.
[8] M.G. Davidson, T.G. Hibbert, J.A.K. Howard, A. Mackinnon,
K. Wade, J. Chem. Soc. Chem Commun. (1996) 2285.
[9] P.D. Godfrey, W.J. Grigsby, P.J. Nichols, C.L. Raston, J. Am.
Chem. Soc. 119 (1997) 9283–9284.
[10] A. Donati, S. Ristori, C. Bonechi, L. Panza, G. Martini, C.
Rossi, J. Am. Chem. Soc. 124 (2002) 8778.
5. Supplementary material
[11] G. Harakas, T. Vu, C.B. Knobler, M.F. Hawthorne, J. Am.
Chem. Soc. 120 (1998) 6405.
Crystallographic details (excluding structure fac-
tors) on the structure analyses of compounds 1·2(CH3-
COCH3), CCDC deposition no. 203795;
1·(CH3CN)(C2H5OH), CCDC deposition no. 203796
and 2·2(CH3CN), CCDC deposition no. 203797 have
been deposited with the Cambridge Crystallographic
Data Center. Copies of this information may be
[12] H. Lee, C.B. Knobler, M.F. Hawthorne, Chem. Commun.
(2000) 2485.
[13] L. Cra˜ciun, R. Custelcean, Inorg. Chem. 38 (1999) 4916.
[14] R.F. Stewart, E.R. Davidson, W.T. Simpson, J. Chem. Phys.
42 (1965) 3175.
[15] International Tables for X-ray Crystallography, vol. IV,
Kynoch Press, Birmingham, England, 1974.