Bis(ethanol-κO)bis(1-ferrocenyl-4,4,4-trifluorobutane-1,3-dionato-κ2 O,O′)nickel(II)

In this novel trimetallic complex, the central NiII ion is six-coordinate, forming an octahedral [NiO6] core.


Structure description
The introduction of the lipophilic organometallic moiety ferrocene, a compound with a sandwich-like structure, in an existing bioactive molecule, is a promising tool for the development of new more efficient drugs with innovative mechanisms of action (Ludwig et al., 2019). As a result of their lipophilic character, ferrocene derivatives can be transferred across cell membranes (Lai et al., 2019). Ferrocene is not only an excellent chromophore group, it also performs as an excellent intermolecular electron and energytransfer group. The introduction of trifluoromethyl into the compound is conducive to intermolecular charge transfer, and thus potentially gives the molecule better non-linear optical properties. The -diketonate ligands form stable six-membered metallacycles with transition metals such as Ru, and their terminal groups can be easily modified to change the electronic character of the ligand (Baird et al., 2003).
The molecular structure of the trimetallic title compound is shown in Fig. 1. The Ni II centre shows an octahedral coordination environment built up by the coordination of two chelating -diketonate ligands and two ethanol molecules in a cis arrangement. The nickel is placed in general position in the triclinic cell, and the Ni-O coordination bond lengths are in the range 2.003 (2) to 2.149 (2) Å . The cis bond angles describing the octahedral coordination geometry around Ni II are in the range 85.60 (10) to 93.52 (10) .

data reports
The ferrocene moieties substituting the -diketonate ligands have the expected geometry, with eclipsed cyclopentadiene rings.
There are interactions between molecules in the crystal structure, through hydrogen bonds involving both coordinated ethanol molecules (Table 1). Other secondary contacts are C16-H16Á Á ÁF5 ii and C13-H13Á Á ÁC13 iii . The crystal is further stabilized by C-HÁ Á Á contacts involving cyclopentadiene rings of neighbouring molecules (Fig. 2), giving rise to a threedimensional architecture.

Synthesis and crystallization
4,4,4-Trifluoro-1-ferrocenebutane-1,3-dione (1.6 mmol, 0.518 g) and triethylamine (2.45 mmol, 0.248 g) were dissolved in ethanol (10 ml). Nickel acetate tetrahydrate (0.5 mmol, 0.122 g) was dissolved in 15 ml of ethanol, added to the previous solution, and stirred at room temperature for 10 min. The mixture was then refluxed for 4 h. After the reaction was complete, the mixture was cooled to room temperature and filtered. The residue was washed twice with 30 ml of ethanol, yielding a red solid (yield: 370 mg, 92%). Single crystals for X-ray analysis were obtained by recrystallization from cyclohexane.

Figure 2
Part of the crystal structure of the title compound, showing some intermolecular interactions.

Figure 1
The molecular structure of the title compound, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level; H atoms were omitted for clarity.

Special details
Refinement. H atoms for the hydroxy groups of ethanol molecules, H2 and H3, were found in a difference map, and refined with free coordinates and U iso (H) = 1.5×U eq (O). Other H atoms were refined using a riding model.