Aqua{4,4′,6,6′-tetrafluoro-2,2′-[(piperazine-1,4-diyl)dimethylene]diphenolato}copper(II)

In the title compound, [Cu(C18H16F4N2O2)(H2O)], the CuII atom shows a distorted square-pyramidal coordination geometry with the N,N′,O,O′-tetradentate piperazine–diphenolate ligand forming the basal plane. The apical site is occupied by the O atom of a coordinated water molecule. Neighbouring complexes are associated through intermolecular O—H⋯O and O—H⋯F hydrogen bonds between the water molecule and a phenolate O atom or an F atom from an adjacent ligand, respectively, forming a centrosymmetric dimer. Dimers are linked by additional intermolecular C—H⋯O and C—H⋯F hydrogen bonds, giving infinite chains propagating along the a axis.

In the title compound, [Cu(C 18 H 16 F 4 N 2 O 2 )(H 2 O)], the Cu II atom shows a distorted square-pyramidal coordination geometry with the N,N 0 ,O,O 0 -tetradentate piperazine-diphenolate ligand forming the basal plane. The apical site is occupied by the O atom of a coordinated water molecule. Neighbouring complexes are associated through intermolecular O-HÁ Á ÁO and O-HÁ Á ÁF hydrogen bonds between the water molecule and a phenolate O atom or an F atom from an adjacent ligand, respectively, forming a centrosymmetric dimer. Dimers are linked by additional intermolecular C-HÁ Á ÁO and C-HÁ Á ÁF hydrogen bonds, giving infinite chains propagating along the a axis.

Comment
Piperazine adopts chair and boat conformations by complexing various metal ions, showing several coordination modes and geometries (Kubono et al., 2003;Loukiala et al. 1997;Mukhopadhyay et al. 2004;Weinberger et al. 2000). Therefore, metal complexes with piperazine based ligands have been of great interest in coordination and supramolecular chemistry (Tsai et al., 2008;Zhao et al., 2004). Recently, we have reported the crystal structure of a Cu II complex with tetrachloro-2,2'-(piperazine-1,4-diyldimethylene)diphenolate, Cu 2 (Cl 2 bpi) 2 , (Kubono et al., 2009), which is a centrosymmetric dinuclear complex. As a continuation of this work on the structural characterization of piperazine-diphenolato compounds, the title mononuclear Cu(II) complex with difluorophenol derivative of the Cl 2 bpi ligand is reported here (Fig. 1).
The Cu(II) atom shows a distorted square-pyramidal coordination geometry with the basal plane comprised of two phenolate O and two tertiary alkyl N atoms from a piperazine-diphenolato ligand. The apical site is occupied by the O atom of a water molecule. The orientaion of two benzene rings in the title complex is anti-parallel, different from that in the dichlorophenol derivative, Cu 2 (Cl 2 bpi) 2 (Kubono et al., 2009). The difference is reflected in the torsion angles C10-N2-C12-C13 [-69.9 (3) ° in the title complex and -171.8 (4) ° in Cu 2 (Cl 2 bpi) 2 ]. Bond lengths and angles involving copper are comparable to those observed in related complexes (Kubono et al., 2009;Loukiala et al. 1997;Mukhopadhyay et al. 2004;Weinberger et al. 2000).

Neighbouring mononuclear complexs are associated through O-H···O and O-H···F intermolecular hydrogen bonds
between the H atoms in the water ligand and a phenolate O atom or a F atom from an adjacent ligand generated by inversion operation, forming a centrosymmetric dimer (Fig. 2). The dimeric structure of the title complex is different from those of Cu 2 (Cl 2 bpi) 2 and the dimethylphenolato derivative (Mukhopadhyay et al., 2004), which are µ-type complexes bridged by a phenolate O atom from an adjacent ligand. The Cu1···Cu1 i distance within the dimer of the title compound is 5.5646 (6) Å [symmetry code: (i) -x, -y, -z + 1.]. The dimeric structure of the complex is additionally stabilized by intermolecular C12-H13···F1 i hydrogen bonds (Table 1).

Experimental
The ligand, H 2 F 2 bpi, was prepared by heating 2,4-difluorophenol (190 mmol), piperazine (95 mmol) and paraformaldehyde (190 mmol) under reflux in methanol for 6 h. The mixture was cooled to room temperature, then the solvent was evaporated under vacuum. The product was recrystallized from chloroform-methanol to give colorless ligand crystals (yield 36%).
supplementary materials sup-2 H 2 F 2 bpi (0.1 mmol) was dissolved in 60 ml hot methanol. Then 1 ml of a aqueous solution of copper acetate monohydrate (0.15 mmol) was added to this solution. The mixture was stirred for 30 min at 340 K. After a few weeks at room temperature, green crystals of (I) were obtained (yield 30%). Analysis calculated for C 18 H 18 CuF 4 N 2 O 3 : C 48.05, H 4.03, N 6.23%; found: C 47.92, H 4.08, N 6.18%.

Refinement
All H atoms bound to carbon were placed at idealized positions and refined using a riding model, with C-H = 0.93-0.97Å and U iso (H) = 1.2 U eq (C). H atoms bound to the water O atom were found in a difference Fourier map, and then refined isotropically.   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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq supplementary materials sup-9