cis-[Aqua/methanol(0.45/1.55)](1,1,1-trifluoro-5,5-dimethylhexane-2,4-dionato)nickel(II)–cis-[aqua/methanol(1.49/0.51)](1,1,1-trifluoro-5,5-dimethylhexane-2,4-dionato)nickel(II) (1/1)

The title compound, [Ni(C8H10F3O2)2(CH4O)1.55(H2O)0.45][Ni(C8H10F3O2)2(CH4O)0.51(H2O)1.49], is an octahedral nickel(II) complex with two acetylacetonate-like 1,1,1-trifluoro-5,5-dimethylhexane-2,4-dionate ligands. The two chelating ligands are in cis positions with respect to each other and the remaining two adjacent coordination sites are taken up by water and methanol donor molecules. In both crystallographically independent molecules, each donor site shows disorder of methanol and water with occupancies of 0.51 (1) and 0.55 (1) in favor of methanol. The remaining two donor sites are not disordered and are water for the first and methanol for the second independent molecule. Rotational disorder is observed for one of the tert-butyl groups, the occupancy rate for the major component here is 0.687 (9). O—H⋯O hydrogen bonds connect the two independent molecules with each other and, across a crystallographic inversion center, they are combined with two neighboring molecules to form a centrosymmetric hydrogen-bonded tetramer.


Comment
The research of metal β-diketonate compounds can be traced back to the early to mid 1950's. Since then extensive research has been conducted in order to gain a better understanding of these compounds for a wide variety of scientific applications.
Some of the more recent applications are catalysis (Burtoloso, 2005), carbon-nanotube structures (Katok et al., 2006), and the deposition of metallic or ceramic then films (Condorelli et al., 2007). Our own research group is most interested in investigating gas-phase rearrangements of selected metal β-diketonate complexes via mass spectrometry. Our overall goal is to examine stability through fragmentation and to better understand ligand exchange reactions in the gas phase. Several acetylacetonate and substituted acetylacetonate species were already observed to undergo various ligand exchange reactions and association reactions (Schildcrout, 1976;Lerach & Leskiw, 2008). To completely characterize the complexes prior to their use in mass spectrometry, several solid state structures of such complexes have been determined including those of the Co-, Zn and Ni-complexes with the ligand 1,1,1-trifluoro-5,5-dimethylhexane-2,4-dionate. The Ni complex is the title complex of this report, the structures of the Co-and Zn complexes were reported recently (Lerach et al., 2007;Hunter et al., 2009).
The two chelating ligands are in cis position to each other and the remaining two adjacent coordination sites are taken up by water and methanol donor molecules ( Figure 1). In both crystallographically independent molecules each one donor site shows disorder of methanol and water with occupancies of 0.51 (1) and 0.55 (1) in favor of methanol. The remaining two donor sites are not disordered and are water for the first and methanol for the second independent molecule. Rotational disorder is observed for one of the tert-butyl groups, the occupancy rate for the major component here is 0.687 (9).
Hydrogen bonds connect the two independent molecules with each other. Across a crystallographic inversion center, they are combined with two neighboring molecules to form a centrosymmetric hydrogen bonded [Ni(O 2 C 8 F 3 ) 2 L 2 ] tetramer ( Figure 2).

Experimental
The synthesis of the title compound was adapted from Watson & Lin (1966). 0.40 ml (2.5 mmol) of the ligand were added to a stirring solution of 0.25 g NiCl 2 (1.97 mmol) and 50 ml of de-ionized water. Diluted 1:1 (v/v) NH 4 OH was added dropwise to the mixture until no more visible precipitate formed. The mixture was stirred overnight at room temperature, and the precipitate was isolated via vacuum filtration resulting in a pale blue powder. The powder was dried at room temperature overnight resulting in a blue-green product which was re-crystallized overnight by vapor diffusion of hexanes into a solution in diethyl ether.

Refinement
Disorder is observed for one hydroxyl group and two of the methanol ligands are only partially present with the remainder taken up by water molecules. The occupancy ratio for the two tert-butyl moieties is 0.687 (9) to 0.313 (9). The rate of presence for the methanol molecules is 0.51 (1) and 0.55 (1), respectively.
OH hydrogen atoms were located in difference density Fourier maps and were refined with an O-H distance restraint of 0.84 (2) Å. H···H distances within disordered water molecules were restrained to 1.35 Å. All other H atoms were placed in calculated positions with C-H distances of 0.98 (methyl) and 0.95 Å (CH). The methyl and hydroxyl H's were refined with an isotropic displacement parameter U iso of 1.5 times U eq of the adjacent carbon or oxygen atom, and the C-H hydrogen atom with U iso = 1.2 U eq (C). Methyl hydrogen atoms were allowed to rotate to best fit the experimental electron density. Fig. 1. Thermal ellipsoid respresentation of the two crystallograpically independent molecules. The probability level for the anisotropic displacement parameters is at 50%. Minor moieties of disordered sections are omitted for clarity.

Special details
Experimental. Disorder is observed for one hydroxyl group and two of the methanol ligands are only partially present with the remainder taken up by water molecules. The occupancy ratio for the two tert-butyl moieties is 0.687 (9) to 0.313 (9). The rate of presence for the methanol molecules is 0.51 (1) and 0.55 (1), respectively.
OH hydrogen atoms were located in difference denisty Fourier maps and were refined with an O-H distance restraint of 0.84 (2) Å. The second hydrogen atoms in disordered water molecules were restrained to have a distance of 1.35 (2) Å from the position of the first H atom. All other H atoms were placed in calculated positions with C-H distances of 0.98 (methyl) and 0.95 Å (CH). The methyl and hydroxyl H's were refined with an isotropic displacement parameter U iso of 1.5 times U eq of the adjacent carbon or oxygen atom, and the C-H hydrogen atom with U iso = 1.2 U eq (C). Methyl hydrogen atoms were allowed to rotate to best fit the experimental electron density. 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 Rfactors(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.