2-Azaniumylcarba-closo-dodecaborate ethanol monosolvate

Two formula units of the title compound, 2-H3N-closo-1-CB11H11·CH3CH2OH or CH14B11N·C2H5OH, form a ring motif of R 4 2(8) type in the solid state that surrounds a crystallographic center of symmetry. The ring motif is a result of N—H⋯O hydrogen bonds. In contrast to many structures of {closo-1-CB11} clusters, the assignment of the position of the cluster C atom in the structure of the title compound is unambigious. The relatively long B—N bond length [1.5396 (10) Å] documents the absence of any B—N π-interaction in the title compound although this was observed for a related 2-aminocarba-closo-dodecaborate.

Two formula units of the title compound, 2-H 3 N-closo-1-CB 11 H 11 ÁCH 3 CH 2 OH or CH 14 B 11 NÁC 2 H 5 OH, form a ring motif of R 4 2 (8) type in the solid state that surrounds a crystallographic center of symmetry. The ring motif is a result of N-HÁ Á ÁO hydrogen bonds. In contrast to many structures of {closo-1-CB 11 } clusters, the assignment of the position of the cluster C atom in the structure of the title compound is unambigious. The relatively long B-N bond length [1.5396 (10) Å ] documents the absence of any B-Ninteraction in the title compound although this was observed for a related 2-aminocarba-closo-dodecaborate.

Comment
Icosahedral monocarba-closo-dodecaborates with functional groups, for example amino or ammonio that are bonded to the cluster atoms are building blocks for a broad range of applications (Körbe et al., 2006). The properties and the reactivity of the amino groups depend on (i) the further substituents of the {closo-1-CB 11 } cluster and (ii) the type of the cluster atom, either carbon or boron that it is bonded to. The influence of the substituents is evident from a comparison of the properties of [1-H 2 N-closo-1-CB 11 X 11 ]with X equal to either H or F. The non-fluorinated anion is indefinitely stable in concentrated aqueous bases and acids whereas the fluorinated anion decomposes in acidic aqueous solutions and undergoes substituent exchange reactions in basic aqueous solutions (Finze et al., 2007). Furthermore, [1-H 2 N-closo-1-CB 11 F 11 ]reacts with strong non-nucleophilic bases under aprotic conditions to result in a cluster rearrangement that so far was observed for highly fluorinated aminocarba-closo-dodecaborates only (Finze, 2007). The difference in the properties of amino groups that are either bonded to the cluster carbon atom or to one of the boron atoms is demonstrated by a comparison of the pK a value of 1-H 3 N-closo-CB 11 H 11 6.0 (Jelínek et al., 1986) and of 2-H 3 N-closo-CB 11 H 11 >10.5 (Finze, 2009).
The inner salt 2-H 3 N-closo-1-CB 11 H 11 crystallizes as ethanol solvate in the monoclinic space group P2 1 /c with one complete molecule and one ethanol molecule in the asymmetric unit. The cluster carbon atom is unambiguously assigned as evident from comparative refinements ( Figure 1). Furthermore, the experimental inner cluster carbon-boron and boronboron bond lengths are in excellent agreement to values derived from DFT calculations at the B3LYP/6-311++G(d,p) and at the MP2/6-311++G(d,p) level of theory, which were reported earlier (Finze, 2009). In this earlier contribution it was concluded on the basis of experimental inner-cluster d(C-B) and d(B-B) of the related {closo-1-CB 11 } species [1-Ph-2-H 2 N-closo-1-CB 11 H 10 ]and 1-Ph-2-Me 3 N-closo-1-CB 11 H 10 in conjunction with theoretical bond lengths of [2-H 2 N-closo-1-CB 11 H 11 ]and 2-H 3 N-closo-1-CB 11 H 11 that there is a small amount of B-N π-interaction for the amino derivatives whereas for the ammonio derivatives this π-interaction was not observed. The d(B2-N1) of 1.5396 (10) Å in the structure of the title compound supports these previous results. As a consequence of this weakened B2-N1 bond the inner-cluster C1-B2 bond is strengthened as documented by d(C1-B2) of 1.6872 (11) Å.
supplementary materials sup-2 Experimental 2-H 3 N-closo-1-CB 11 H 11 was synthesized according to a published procedure that also includes the spectroscopic data (Finze, 2009). The title compound was dissolved in a minimum amount of diethyl ether, ethanol, and chloroform (20:1:1). The clear colorless solution was stored at 3 °C in a refrigerator resulting in colorless crystals within two days.
A single crystal suitable for structure determination was harvested under a dry nitrogen atmosphere and was directly transferred into the cooling stream of an Oxford-Xcalibur diffractometer equipped with an EOS-CCD detector.

Refinement
All hydrogen atoms were located from difference Fourier synthesis. The H atoms of the 2-aminocarba-closo-dodecaborane and the H atom of the hydroxy group of the ethanol molecule were refined without any restraints. For the H atoms of the CH 2 and CH 3 group a riding model was employed and for each group a common U iso value was refined. Fig. 1. In the carborane 2-H 3 N-closo-1-CB 11 H 11 the hydrogen atoms are drawn with an arbitrary radius and the displacement ellipsoids are shown at the 50% probability level. Fig. 2. Hydrogen-bonded motif formed by 2-H 3 N-closo-1-CB 11 H 11 .CH 3 CH 2 OH (Symmetry code: ' = -x + 2, -y + 2, -z + 2; hydrogen atoms are drawn with an arbitrary radius and the displacement ellipsoids are shown at the 50% probability level).