Crystal structure of bis(μ2-4-tert-butyl-2-formylphenolato)-1:2κ3 O 1,O 2:O 1;3:4κ3 O 1,O 2:O 1-bis(4-tert-butyl-2-formylphenolato)-2κ2 O 1,O 2;4κ2 O 1,O 2-di-μ3-methoxido-1:2:3κ3 O;1:3:4κ3 O-di-μ2-methoxido-1:4κ2 O;2:3κ2 O-tetracopper(II)

The dinuclear title compound crystallizes as a dimer forming a tetranuclear copper(II) complex, [Cu4(CH3O)4(C11H13O2)4], in the solid state. In this complex, all CuII atoms have a square-pyramidal coordination sphere, with long axial and short basal Cu—O distances.


Chemical context
The title compound was obtained as a by-product in the synthesis of an unsymmetrically substituted copper(II) salophene complex (Kleij et al., 2005). The latter is of interest with respect to magnetic properties and cooperative effects between the metal(II) atoms (Kahn et al., 1982). In this compound, three types of bridging oxygen ligands are found. The magnetic exchange coupling between the paramagnetic Cu II atoms is considered as strong in this type of bridges since the Cu-O-Cu angles are found to be close to 90 . The distances and coordination modes between Cu II atoms vary and thus, the compound is a suitable study case for investigating different spin-coupling paths. This knowledge is deemed important for the design of tailor-made magnetic compounds.

Structural commentary
The tetranuclear copper(II) title compound consists of two dinuclear complex fragments oriented around a centre of ISSN 2056-9890 inversion. Within each fragment the two Cu II atoms are in a distorted square-planar coordination sphere, thereby bridged by two 2 O methoxido ligands. The terminal bidentate 4-tertbutyl-2-formylphenolate ligand is coordinating each Cu II atom in a manner generating a pseudo-mirror plane perpendicular to the four-membered bis-methoxido dicopper ring in the centre of the fragment. A longer Cu-O bond completes the overall square-pyramidal coordination for each Cu II atom and links the two dinuclear fragments together. The distance between the two copper(II) ions Cu1 and Cu2 within the binuclear fragment is 2.9938 (2) Å ( Fig. 1) which is in the same range as in related complexes (Kahn et al., 1982).

Figure 2
A packing diagram of the title compound. Within the dinuclear fragment, the aromatic rings are tilted by an angle of 24.69 (6) due to repulsion of the tert-butyl groups.

Supramolecular features
In the crystal, the tetranuclear molecules arrange in layers parallel to (101) (Fig. 2). Weak non-classical C-HÁ Á ÁO interactions between the layers (Table 2) help to stabilize the crystal packing.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The positions of all H atoms were calculated according to the geometry of the parent C atom and refined using a riding model with C-H distances of 0.95 Å and U iso (H) = 1.5U eq (C) for sp 2 C atoms and of 0.98 Å and U iso (H) = 1.5U eq (C) for sp 3 C atoms.