Tetrakis(μ3-2-{[1,1-bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-6-nitrophenolato)tetracopper(II)

The title cluster, [Cu4(C11H12N2O6)4], was obtained from the Cu0–FeCl2·4H2O–H4 L–Et3N–DMF reaction system (in air), where H4 L is 2-hydroxymethyl-2{[(2-hydroxy-3-nitrophenyl)methylidene]amino}propane-1,3-diol and DMF is dimethylformamide. The asymmetric unit consists of one Cu2+ ion and one dianionic ligand; a -4 symmetry element generates the cluster, which contains a {Cu4O4} cubane-like core. The metal ion has an elongated square-based pyramidal CuNO4 coordination geometry with the N atom in a basal site. An intramolecular O—H⋯O hydrogen bond is observed. The solvent molecules were found to be highly disordered and their contribution to the scattering was removed with the SQUEEZE procedure in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148–155], which indicated a solvent cavity of volume 3131 Å3 containing approximately 749 electrons. These solvent molecules are not considered in the given chemical formula.


Related literature
For general background to direct synthesis (DS), see: Kokozay & Shevchenko (2005). For related structures, see: Dey et al.

Experimental
Crystal data [Cu 4 (C 11 Table 1 Selected bond lengths (Å ).  The reaction of copper powder with iron(II) chloride in dmf solution of the tetrapodal Schiff base ligand, formed in situ, in basic medium with free access of air leads to the isolation of the homometallic cuban complex [Cu 4 (C 11 H 12 O 6 N 2 ) 4 ]. The Schiff base ligand H 4 L was obtained by condensation of 3-nitro-salicylaldehyde and tris(hydroxymethyl)aminomethane ( Fig. 1). The molar ratio of starting materials (Cu 0 : FeCl 2 : Schiff base ligand) was taken 1:1:2. The reaction was carried out in air with heating and stirring till total dissolution of metal powder was observed.

Refinement
All H atoms were placed in idealized positions (C-H = 0.95 -0.99 Å, O-H = 0.84 Å) and constrained to ride on their parent atoms, with U iso = 1.2Ueq (except U iso = 1.5Ueq for hydroxyl groups). Hydrogen atom of the hydroxyl group O4-H4 was disordered over two sites with equal occupancy factors of 0.50 in order to fit the intramolecular hydrogen bond O4-H4A···O4′. Several isolated electron density peaks were located during the refinement, whose were believe to be a solvent molecules. Large displacement parameters were observed modeling the disordered oxygen, carbon, and sulfur atoms. SQUEEZE procedure of PLATON indicated a solvent cavity of volume 3131 Å 3 centered at (0,0,0), containing approximately 749 electrons. In the final refinement, this contribution was removed from the intensity data that produced better refinement results. The hydroxyl group O5-H5A located near the void was believed to be H-bonded with one of the removed solvent molecules. Several reflections with great differences between calculated and observed F 2 were omitted during the refinement. These reflections were believed to arise because of little impurities of the crystal under study.

Computing details
Data   The crystal-packing diagram along the (001) direction.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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 R-factors(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.