Bis(2-hydroxyiminomethyl-6-methoxyphenolato-κ2 N,O 1)copper(II)

In the title compound, [Cu(C8H8NO3)2], the nearly planar molecule (r.m.s. deviation = 0.037 Å) is centrosymmetric with the CuII atom lying on an inversion center. The CuII atom is tetracoordinated, displaying a slightly distorted square-planar geometry. The main deviation from the ideal geometry is seen in the differences in the Cu—O [1.8833 (10) Å] and Cu—N [1.9405 (13) Å] bond lengths, while angular deviations are less than 3°. Intramolecular O—H⋯O and intermolecular Csp2—H⋯O hydrogen bonds form S(5) and R 2 2(8) ring motifs, respectively. The latter interaction results in chains of molecules along [100].

In the title compound, [Cu(C 8 H 8 NO 3 ) 2 ], the nearly planar molecule (r.m.s. deviation = 0.037 Å ) is centrosymmetric with the Cu II atom lying on an inversion center. The Cu II atom is tetracoordinated, displaying a slightly distorted square-planar geometry. The main deviation from the ideal geometry is seen in the differences in the Cu-O [1.8833 (10) Å ] and Cu-N [1.9405 (13) Å ] bond lengths, while angular deviations are less than 3 . Intramolecular O-HÁ Á ÁO and intermolecular Csp 2 -HÁ Á ÁO hydrogen bonds form S(5) and R 2 2 (8) ring motifs, respectively. The latter interaction results in chains of molecules along [100].
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: LR2071). In all cases the total dissolution of copper and manganese powders was observed within 5 -6 h resulting into intensive dark green solutions. X-ray quality crystalls were obtained from the systems with NH 4 Br in dmso and NH 4 Cl in dmf, but in the former one the yield was some better.
The asymmetric unit of [Cu(HL) 2 ] includes one-half of the molecule with Cu atom occupying the (1/2 1/2 1/2) special position of multiplicity 2. The coordination geometry of the metal atom is square-planar, with the CuN 2 O 2 chromophore, formed by means of two imine nitrogen atoms and two phenolate oxygen atoms of the two monodeptotonated Schiff base ligands realising their bidentate chelate function, [1.1 1 1 1 0] by Harris notation (Coxall et al., 2000) (Fig. 1). Difference between Cu-O and Cu-N bond lengths (Table 1) causes significant linear distortion of the square. Deviations in bond angles at the Cu atom are less than 3°. The bond valence sum analysis applied to the appropriate bond lengths supports the +2 oxidation state for copper, BVS(Cu) = 2.003 (Brown & Altermatt, 1985).  Table 2). As a result, two ligands being coordinated to the Cu II ion form some analogue of a macrocyclic ligand [R14] based on HBs which binds to the copper center generating two 6-membered (with only covalent bonds) and two 5membered (with covalent and hydrogen bonds) rings (Fig. 1). It is worth noting that all known structures with H 2 L, namely Co(HL) 2 (Zhang et al., 2008), Ni(HL) 2 (Li et al., 2009) and VO(HL) 2 (Li et al., 2004), are built in the same manner demonstrating high thermodynamic stability of such structure.

Refinement
Structure was solved by direct method and refined against F 2 within anisotropic approximation for all non-hydrogen atoms. All hydrogen atoms were located from difference Fourier map and refined isotropically, except phenyl (H(3) -H(5)) and hydroxyl (H(3O)) H atoms that were allowed to ride on their attached atoms with C-H = 0.93 (1) Å and U iso (H)= 1.2Ueq(C) for phenyl, and C-H = 0.82 (1) Å and U iso (H)= 1.5Ueq(C) for hydroxyl H atoms. Coordinates of Cu(1) were constrained to special position (x=0.5000, y=0.5000, z=0.5000).

Bis(2-hydroxyiminomethyl-6-methoxyphenolato-κ 2 N,O 1 )copper(II)
Crystal data Special details Experimental. CrysAlis RED, Oxford Diffraction Ltd., 2010. Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm. 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.