Crystal structure of μ6-chlorido-nonakis(μ-4-chloropyrazolato)bis-μ3-methoxo-hexacopper(II)

The hexanuclear copper pyrazolato complex has a trigonal prismatic shape and contains an encapsulated chloride ligand.


Chemical context
Multinuclear transition metal ion complexes often have interesting properties, such as magnetic, electrochemical, and catalytic functions. N-donor ligands have coordination plasticity and large affinity for transition metals, and their employment has provided structures of various nuclearities and dimensionalities, which have been shown to be of interest in catalysis, bio-inorganic chemistry and molecular magnetism. There have been several reports concerning multinuclear copper(II) complexes supported by pyrazolato (pz À ) bridging ligands. In this context, we have investigated a family of redoxactive Cu 6 -pyrazolato complexes with trigonal prismatic shapes (Mezei et al., 2007;Zueva et al., 2009), including one with a 6 -F central ligand (Mathivathanan et al., 2015). In connection with our earlier work, the title compound, [{Cu 3 ( 3 -OCH 3 )(-C 3 H 2 N 2 Cl) 3 } 2 ((-C 3 H 2 N 2 Cl) 3 ( 6 -Cl)], has been prepared recently; it contains an encapsulated 6 -Cl ligand at the center of the hexanuclear complex. ISSN 2056-9890
Differences in structural parameters between the four known {Cu 6 -pyrazolato} complexes with trigonal prismatic shape are compiled in Table 1. The inter-trimer and intratrimer CuÁ Á ÁCu distances are shorter in the title compound than those in the [Cu 6 Cl] compound reported earlier with 4-Hpz as a ligand (Kamiyama et al., 2002), indicating the effect of electron-withdrawing Cl-substitution of the pyrazolato ligands. The Cu-N distances of the pyrazolato ligands connecting the two trimers are longer compared to those in {Cu 6 -6 -F} (Mathivathanan et al., 2015) or {Cu 6 -6 -Cl} (Kamiyama et al., 2002). However, the Cu-N distances are similar to those in the empty Cu 6 -pyrazolato cage (Mezei et al., 2007).

Figure 1
The molecular structure of the title compound, showing the atom-labeling scheme. H atoms are not shown for clarity. Displacement ellipsoids are drawn at the 40% probability level. Non-labeled atoms are related to the labeled atoms by the symmetry operation (Àx, y, Àz + 1 2 ).

Synthesis and crystallization
The complex was formed in an one-pot reaction when CuCl 2 Á2H 2 O (0.06 mmol, 10.2 mg), 4-Cl-pzH (0.09 mmol, 8.9 mg) and ethylamine (0.08 mmol, 11.3 ml) were stirred in 10 ml CH 2 Cl 2 for 24 h at ambient temperature. The green solution was transferred to a test tube after filtration. A 4 ml 1:1 mixture of CH 2 Cl 2 :MeOH (v/v) was layered over the CH 2 Cl 2 layer, 1,2-di(4-pyridyl)ethylene (1,2-bpe) (0.01mmol, 1.9 mg) in 4 ml MeOH was added as the third layer on top of the lower two. Suitable crystals for X-ray diffraction were obtained one week later.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. Hydrogen atoms were placed in geometrically calculated positions and refined with a riding model. Structure refinement indicates a minimum (À1.56 e Å À3 ) near the 6 -Cl atom (Cl6), which decreases if the structure is refined with a free site-occupation factor for this atom. This can be explained if some of the Cu 6 -cages (< 10%) are vacant. Such a discrepancy is within the experimental error of the CHN elemental analysis, and we decided to refine the model with full occupancy for this Cl atom. In the final cycles, restraints were applied to obtain acceptable U ij parameters for Cl6. Crystal structure of µ 6 -chlorido-nonakis(µ-4-chloropyrazolato)bis-µ 3 -methoxo-

µ 6 -Chlorido-nonakis(µ-4-chloropyrazolato)bis-µ 3 -methoxo-hexacopper(II)
Crystal data 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.