(1,4,7,10,13,16-Hexaoxacyclooctadecane-κ6 O)bis(tetrahydrofuran-κO)potassium bis[(1,2,3,4-η)-anthracene]cobalt(−I) tetrahydrofuran monosolvate

The asymmetric unit of the title compound, [K(C12H24O6)(C4H8O)2][Co(C14H10)2]·C4H8O, consists of one cationic potassium complex, one anionic cobalt dianthracene complex and one tetrahydrofuran solvent molecule. The potassium cation is situated at the centre of an 18-crown-6 molecule and between two tetrahydrofuran molecules, the latter coordinating above and below the mean plane formed by the O atoms of the crown ether molecule. The Co atom is coordinated by eight C atoms of two anthracene molecules in an η4 manner. The third free tetrahydrofuran molecule shows orientational disorder on two partially occupied positions [occupancy ratio 0.561 (8):0.439 (8)].

The asymmetric unit of the title compound, [K(C 12 H 24 O 6 )-(C 4 H 8 O) 2 ][Co(C 14 H 10 ) 2 ]ÁC 4 H 8 O, consists of one cationic potassium complex, one anionic cobalt dianthracene complex and one tetrahydrofuran solvent molecule. The potassium cation is situated at the centre of an 18-crown-6 molecule and between two tetrahydrofuran molecules, the latter coordinating above and below the mean plane formed by the O atoms of the crown ether molecule. The Co atom is coordinated by eight C atoms of two anthracene molecules in an 4 manner.
The third free tetrahydrofuran molecule shows orientational disorder on two partially occupied positions [occupancy ratio 0.561 (8)
This work was supported by the Deutsche Forschungsgemeinschaft. HH thanks the Chinese Scholarship Council for support.
The title compound was obtained via reduction of CoBr 2 by potassium anthracene in THF. Although the reaction conditions were very similar to those described by Brennessel, Young & Ellis (2002), we found the compound to crystallize including an additional free solvent molecule (Fig.1). Consequently different from the literature, our indexation resulted in the orthorhombic, but acentric space group P2 1 2 1 2 1 instead of P1. Besides these differences, those structural entities, which are present in both compounds, show almost the same shape (Fig.2).
The Co atom is sandwiched by two anthracene molecules in 1,2,3,4-η 4 coordination, respectively, with a slight tilt of 10.2° for the two planes formed by the respective coordinating atoms C1-C4. The C 6 rings, which are directly bond to the Co atom, are in eclipsed position, but the main molecule axes form an angle of about 65°. The anthracene molecules are folded at an axis running through the C1 and C4 atoms, the angles between the planes formed by C1, C2, C3, and C4 and by C1, and C4-C14 are almost identical (29.18° and 28.99° for both molecules).

Experimental
To a deep-blue solution of K[C 14 H 10 ] (3.43 mmol) in tetrahydrofuran (THF) (30 ml, -78°C) was added a bright-blue solution of CoBr 2 (0.25 g, 1.15 mmol) in THF (30 ml, -78°C). The reaction was stirred overnight and warmed slowly to room temperature, the colour of the solution gradually changed to deep-pinkish-red. It was filtered to remove KBr, and 18-crown-6 (0.302 g, 1.15 mmol) in THF (10 ml) was added to the filtrate. Hexane (20 ml) was added and the volume was reduced to about 20 ml in vacuum. The brown-black needle-like product was crystallized at -40°C by diffusion of diethyl ether (50 ml) which yields the title compound (Yield: 41% based on CoBr 2 ). The energy-dispersive X-ray analysis (EDX) shows an atomic ratio of Co/K close to 1:1 in all the analysed crystals of [K(C 12

Refinement
The H atoms were included in calculated positions and treated as riding atoms: C-H = 0.93 Å with U iso (H) = 1.2 U eq (parent C atom) for the aromatic, C-H = 0.97 Å with U iso (H) = 1.2 U eq (parent C atom) for the crown ether, and C-H = 0.97 Å with U iso (H) = 1.5 U eq (parent C atom) for the tetrahydrofuran H atoms. The free solvent molecule shows disorder and was refined at two positions with partial occupations of 56% and 44%, respectively. Two C atoms of the THF molecule with lower occupation have been refined with isotropic thermal displacement parameters.    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.