{Bis[5-methyl-3-(trifluoromethyl)pyrazol-1-yl]borato}{tris[5-methyl-3-(trifluoromethyl)pyrazol-1-yl]borato}cobalt(II): a structure containing a B—H⋯Co agostic interaction

The title compound, [Co(C10H10BF6N4)(C15H13BF9N6)], is a neutral CoII complex which contains one each of the anionic ligands, bis(3-trifluoromethyl-5-methylpyrazol-1-yl)borate (Bp) and tris(3-trifluoromethyl-5-methylpyrazol-1-yl)borate (Tp). A distorted octahedral coordination geometry results from ligation of an H atom, which is part of an agostic B—H⋯Co interaction (H⋯Co = 2.17 Å), and by five imine N atoms, two from a Bp ligand and three from a Tp ligand. In the crystal, molecules form layers parallel to the (10) planes, and the layers are linked along the a axis by C—H⋯F hydrogen bonds. An intramolecular C—H⋯F interaction also occurs.


Crystal data
[Co(C 10 H 10 BF 6 N 4 )(C 15 H 13 BF 9 N 6 )] M r = 829.08 Monoclinic, P2 1 =n a = 10.8195 (16) Table 1 Selected geometric parameters (Å , ).   Siemer et al.., 2001). The H···Co distance in (I), 2.17 Å, lies between these two extremes. Infrared spectral results also support the existence of an agostic 2-electron, 3-center bond in (I). B-H stretching vibrations for BH 2 groups in which one of the H atoms is involved in a 2-electron, 3-center bond with a metal ion typically lie in the range 2100-2500 cm -1 , with the lower value corresponding to the agostic interaction (Ghosh et al., 1998). In (I), IR bands at 2569 and 2483 cm -1 are assigned as free B-H stretching vibrations, while the band at 2223 cm -1 is assigned to the bound B-H group.
In the crystal, the molecules form layers parallel to the (10 -1) planes (Figures 2 and 3), which are linked by intermolecular C-H···F hydrogen bonds (Table 1) in such a way as to form chains along the a cell direction. Platon (Spek, 2009) reveals11 short intermolecular contacts, 10 of which are C-H···F interactions, which, along with the C-H···F hydrogen bonds noted above suggest that the trifluoromethyl groups in (I) contribute substantially to the stability of the structure.

Experimental
Both Tp and Bp ligands were prepared as previously reported (Gorun et al., 2000). To a flask containing 10 ml of acetonitrile,

Refinement
Hydrogen atoms of the methyl groups were located on difference Fourier maps, those of the pyrrole fragments were positioned geometrically. For refinement a riding model was used, with C-H = 0.98 Å for methyl H atoms and 0.95 Å for pyrrole H atoms and U iso (H) = 1.2 U eq (C) and 1.5 U eq (C-methyl). Atom positions and isotropic displacement parameters of B-H hydrogens were refined freely.

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