A 2:1 cocrystal of the cis and trans isomers of bis[1,1,1,5,5,5-hexafluoropentane-2,4-dionato(1−)-κ2 O,O′]bis(4-phenylpyridine N-oxide-κO)copper(II)

The title compound is a co-crystal of the cis and trans isomers, namely cis-bis[1,1,1,5,5,5-hexafluoropentane-2,4-dionato(1−)-κ2 O,O′]bis(4-phenylpyridine N-oxide-κO)copper(II)–trans-bis[1,1,1,5,5,5-hexafluoropentane-2,4-dionato(1−)-κ2 O,O′]bis(4-phenylpyridine N-oxide-κO)copper(II) (2/1), [Cu(C5HF6O2)2(C11H9NO)2]. In both isomers, the coordination geometry of the Cu2+ atom is octahedral, exhibiting typical Jahn–Teller distortion. The metal atom of the trans isomer is located on an inversion centre. In the cis isomer, the phenyl ring in one 4-phenylpyridine N-oxide ligand is disordered over two orientations in a 1:1 ratio. In the crystal, weak intermolecular C—H⋯F and C—H⋯O contacts establish connections between the cis and trans isomers.


Related literature
; Braga et al. (2006). For a description of the Cambridge Structural Database, see: Allen (2002). For a description of the graph-set notation for hydrogen-bonded aggregates, see: Grell et al. (1999).
The title compound (see Scheme) results from a co-crystallization of the cis and trans isomers of [Cu(hfac) 2 (PPNO) 2 ] ( Figure 1). For each isomer, the Cu 2+ centre is coordinated to two hfacand two PPNO ligands, with the {CuO 6 } coordination polyhedra resembling the typical Jahn-Teller distorted octahedral geometry.
In the trans isomer (Figure 1 -top) the metal centre is situated at an inversion point. The Cu1-O distances are 1.966 (2) and 2.331 (2) Å for the hfacanion, and 1.968 (2) Å for the PPNO ligand. The cis octahedral angles fall within a short range of the ideal value being found in the 86.25 (9)-93.75 (9)° range. In the cis isomer (Figure 1 - 2.365 (2) Å (Cu-O6 with hfac -). As in the other isomer, the cis and trans octahedral angles in this complex also approach those of an ideal octahedron being found in the 80.26 (9)-98.43 (9)° and 165.15 (8)-176.63 (9)° ranges, respectively. In addition, the terminal phenyl ring of one coordinated PPNO was found to be disordered over two positions (see Experimental Section). This crystallographic feature seems to be driven by the need to form a short C-H···F contact (see below). An interesting feature common to both isomers concerns the 〈(Cu-O-N) angles of the coordinated PPNO ligands which approach ca 120°. Indeed, while the 〈(Cu1-O3-N1) angle for the trans isomer is 117.82 (18)°, for the cis isomer the analogues 〈(Cu1-O9-N3) and 〈(Cu1-O8-N2) angles are 131.12 (17) and 122.39 (16)°, respectively.
Besides the need to effectively fill the available space, the crystal packing of the two isomers ( Figure 2) is also mediated by a number of C-H···F and C-H···O short contacts ( supplementary materials sup-2 Experimental All chemicals and solvents were purchased from commercial sources and were used without further purification. 4-Phenylpyridine-N-oxide (PPNO, Aldrich, 71.1 mg, 0.415 mmol) was slowly added to a previously prepared 10 ml solution of [Cu(hfac) 2 ] (99.6 mg, 0.208 mmol) in acetone (hfac -= hexafluoroacetylacetonate). The resulting solution was allowed to homogenize with magnetic stirring at 30 °C for 60 minutes, after which time the solvent was evaporated. Diffusion of an ethanolic solution of the extract into water afforded two crystalline solids at different crystallization times. The first compound to crystallize, and obtained in smaller quantity as small light-green single crystals, was identified as identical to the binuclear species [Cu(C 5 HF 6 O 2 ) 2 (C 11 H 9 NO)] 2 recently described by us (Ramos et al., 2010). The second material, obtained at a later stage, was solely composed of large deep-green block crystals of the title compound.

Refinement
Hydrogen atoms bound to aromatic carbon atoms were placed in their idealized positions and were included in the final structural model in riding-motion approximation with C-H = 0.95 Å. The isotropic thermal displacement parameters for these atoms were fixed at 1.2×U eq/iso of the respective parent carbon atom.
The phenyl ring of one coordinated PPNO ligand in the cis isomer was treated as disordered over two orientations with occupancies fixed to 0.5. The carbon atoms were included in the final structural model and allowed to refine unrestrained.
An independent and refineable U iso value was modelled for each position of this phenyl ring. Fig. 1. Schematic representation of the two distinct cis and trans isomers present in the title compound. All non-hydrogen atoms are represented as thermal ellipsoids drawn at the 50% probability level and hydrogen atoms as small spheres with arbitrary radius. The labeling scheme is provided for all atoms composing the first coordination sphere of Cu1 and Cu2. Symmetry transformation used to generate equivalent atoms: (i) 2 -x, 1 -y, 1 -z.