μ-1,6-Dioxo-1,6-diphenylhexane-3,4-diolato-bis[(2,2′-bipyridine)chloridocopper(II)] dihydrate

The title complex sits astride an inversion center with each CuII atom having an N2O2Cl coordination sphere. Charge balance is achieved via the tetronediate and one coordinated chloride ion per CuII. Hydrogen bonding to a solvent water molecule links the molecules into a chain parallel to the bc-face diagonal.

The reaction of CuCl 2 with 1,6-diphenyl-1,3,5,6-hexanetetrone and 2,2 0 -bipyridine (bipy) in ethanol gave crystals of the corresponding bimetallic complex, [Cu 2 (C 18 H 12 O 4 )Cl 2 (C 10 H 8 N 2 ) 2 ]•2H 2 O.The molecule is centrosymmetric with each Cu II ion coordinated to two oxygen atoms from the tetronediate, two nitrogen atoms from a bipy ligand and one coordinated chloride ion.A water molecule of crystallization forms hydrogen bonds to the chloride ions, linking the molecules into a chain parallel to the bc-face diagonal.

Structure description
1,6-Diphenyl-1,3,4,6-hexanetetrone has been known for over 100 years (Widman & Virgin, 1909) and its structure has been reported (Kaitner et al., 1992).Both its synthesis by oxidation (Balenovic ´et al., 1954) and its reactions with oxidizing agents have been studied (Balenovic ´, 1948;Bird & Thorley, 1977;Poje et al., 1978), as well as its use as a starting material for the preparation of a variety of aminated products (Lacan et al., 1973;Unterhalt & Pindur, 1977;Kaitner et al., 1992;Waring et al., 2002;Kobelev et al., 2019).The backbone core resembles a bis-acac structure and and as such it has been used in the preparation of transition-metal complexes (Boucher & Bailar, 1964;Saalfrank et al., 1998;Nawar, 1994).However, we were surprised to find that there are no reported structures of transition-metal complexes containing this ligand (Groom et al., 2016).We investigated its coordination chemistry with Cu II as part of our studies on potential magnetic ladders (Monroe et al., 2022).
The molecule sits astride a crystallographic inversion center (Fig. 1).Each Cu II ion is five-coordinate, including two oxygen atoms from the tetronediate ligand, two nitrogen atoms from a bipy molecule and one coordinated chloride ion.The CuN 2 O 2 equatorial plane is nearly planar (mean deviation of the N 2 O 2 donor set = 0.0219 A ˚) with the Cu II ion displaced [0.2219 (15) A ˚] toward the chloride ion.The 1,3-dionato motif chelates a copper ion and generates a six-membered metallocyclic ring that is only slightly less planar (mean deviation of constituent atoms = 0.1207 A ˚).The two heterocyclic rings are co-planar as required by symmetry.The pyridyl rings are canted 0.67 (13) � from each other.
�-Stacking is observed between molecules.The Cu1dionato ring sits above the N11-containing bpy ring with an interplanar distance of 3.33 (2) A ˚; the rings are canted 4.4 (2) � with respect to each other.The distance between the ring centroids is 3.73 (2) A ˚with a slip angle of 25.1 (3) � .This effectively blocks the vacant coordination site on Cu1, preventing the addition of a sixth ligand.�-Stacking is also observed between the phenyl rings of the tetrone ligand.Adjacent phenyl rings are parallel with an interplanar distance of 3.33 (2) A ˚with a slip angle of 22.8 (3) � .The bimetallic units are linked into chains via hydrogen bonds between the solvent water molecules and chloride ions (Table 1 and Fig. 2).

Synthesis and crystallization
CuCl 2 (0.403 g, 2.99 mmol) was dissolved in 50 ml of absolute ethanol to generate a green solution.2,2 0 -Bipyridine (0.469 g, 3.01 mmol) was added to the solution with stirring to make a light-blue slurry.Addition of 1,6-diphenyl-1,3,4,6-hexanetetrone (0.438 g, 1.49 mmol) generated a lime green slurry, which was stirred for 1 h.The precipitate was recovered by vacuum filtration, washed with ethanol and dried in air to yield 0.973 g of lime green powder (77%).Crystals suitable for X-ray diffraction were grown by recrystallization from DMF.

Figure 1
The molecular structure of the title compound.

Special details
Geometry.All esds (except the esd in the dihedral angle between two l.s.planes) are estimated using the full covariance matrix.The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry.An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s.planes.Refinement.Hydrogen atoms bonded to carbon atoms were placed geometrically and refined with fixed isotropic thermal parameters.Hydrogen atoms bonded to O2 were located in the difference map and their positions refined with fixed isotropic thermal parameters (O-H = 0.82 (5) & 0.98 (4) Å).

Table 2
Experimental details.