Acetonitrilebis(2,9-dimethylphenanthroline)copper(II) bis(tetrafluoridoborate) acetonitrile disolvate

In the title compound, [Cu(CH3CN)(C14H12N2)2](BF4)2·2CH3CN, the CuII atom shows a distorted CuN5 square-pyramidal geometry with the acetonitrile N atom in an equatorial site, which differs substantially from the distorted trigonal-bipyramidal arrangement usually observed for five-coordinate complexes of CuII with two phenanthroline-type ligands and one other ligand. The B atom of one of the BF4 − anions is disordered over two sites in a 0.825 (2):0.175 (2) ratio. In the crystal, C—H⋯F hydrogen bonds help to establish the packing.

In the title compound, [Cu(CH 3 CN)(C 14 H 12 N 2 ) 2 ](BF 4 ) 2 Á-2CH 3 CN, the Cu II atom shows a distorted CuN 5 squarepyramidal geometry with the acetonitrile N atom in an equatorial site, which differs substantially from the distorted trigonal-bipyramidal arrangement usually observed for fivecoordinate complexes of Cu II with two phenanthroline-type ligands and one other ligand. The B atom of one of the BF 4 À anions is disordered over two sites in a 0.825 (2):0.175 (2) ratio. In the crystal, C-HÁ Á ÁF hydrogen bonds help to establish the packing.

S1. Comment
The copper-containing cation ( Fig. 1) of the title compound, (I), consists of a 5-coordinate Cu center, with the geometry about copper being best described (Kepert, 1973) as distorted square pyramidal, rather than as a distorted TBP structure, which is most commonly observed for five-coordinate copper bis-phenanthroline complexes (Bush, et al., 2001). Most of the distortion from idealized square pyramidal can be explained in terms of the restricted bite angles of the rigid phenanthroline rings. It is assumed that steric strain associated with the presence of the 2,9-dimethyl groups on the ligand overrides electronic considerations (Rossi and Hoffman, 1975), resulting in formation of the disfavored square pyramidal geometry for the d 9 complex. The steric strain inherent in the structure is also reflected in the copper being located considerably outside of the normal coordination plane of the phenanthroline [0.470 (1) and 0.636 (1)Å from the least squares planes of the two rings], and in a clear bowing of the phenanthroline ligand itself.
The observation of an electronically high-energy structure is fully consistent with electrochemical data (James and Williams, 1961) which show the 2,9-disubstituted phenanthroline complex to be significantly easier to reduce than the analogous complexes lacking the 2,9-substituents. Reduction of the [Cu(neocuproine) 2 (solv)] 2+ complexes affords the air-stable [Cu(neocuproine) 2 ] + species, which adopt pseudo-tetrahedral geometries that alleviate the steric strain between the substituents.
In the structure of (I), close contact of the disordered BF 4and the coordinated CH 3 CN suggest that a C-H hydrogen bonding interaction exists (see, for example: Vega, et al., 1985). Similar interactions between BF 4ions and Cu-bound acetonitrile ligands have been observed previously (Aligo, et al., 2005). The packing of (I) is shown in Fig. 2 and the H bonds are listed in Table 2.

S3. Refinement
All H atoms were included at calculated positions and were allowed to ride with their C atoms during refinement. The structure exhibits disorder of one of the two BF 4counterions. The disorder was modeled using two identical constrained fragments which shared a common F atom. Occupancy refinement indicated a relative population of 0.175 (2) to 0.825 (2) for the two positions.  View of the cation in (I) with H atoms omitted for clarity. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
The packing for (I): H atoms are omitted for clarity and displacement ellipsoids are drawn at the 50% probability level.  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.009 Δρ max = 0.54 e Å −3 Δρ min = −0.35 e Å −3 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 F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.