6,6′-Dimethoxy-2,2′-{[(E,E)-hydrazine-1,2-diylidene]bis(methanylylidene)}diphenol methanol disolvate

The title compound, C16H16N2O4·2CH3OH, is a hydrazone in an E geometric arrangement, with an inversion centre at the mid-point of the N—N bond. A symmetry-related pair of six-membered hydrogen-bonded rings [graph-set motif S 1 1(6)] are present for the terminal vanillin–imine moieties. Two lattice methanol solvent molecules are present per formula unit (Z′ = 1/2), which form hydrogen-bonded chains along [010] with two orientations due to disorder of the methanol H-atom.


D-HÁ
Data collection: CrystalClear-SM Expert (Rigaku, 2009); cell refinement: CrystalClear-SM Expert; data reduction: CrystalClear-SM Expert; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2. The synthesis of this compound was performed because of its intriguing interactions with both transition and lanthanide metals. The ability for the vanillin moieties to bridge multiple metal centers to form polymetallic clusters has potential applications in the fields of molecular magnetics and supramolecular chemistry.
While the previously reported solventless structure (Lu et al. 2011) and the title compound are comprised of two vanillin-imine moieties, in the title compound, these are related by an inversion centre about the N1 i -N1 bond (i = 1 - x,2 -y,1 -z). There are two available geometries for the hydrazone functional group, the E and Z isomers. Both this report, and the previously reported structure, feature the E isomer ( Figure 1).
There are multiple hydrogen bonding interactions, one intramolecular for the main molecule and one intermolecular hydrogen bonding chain, however, there are no discernable hydrogen bonding interaction between the main molecule and the solvent methanol molecules. The intramolecular hydrogen bond between N1 and H1 forms a stable six-membered hydrogen bound ring with graph set notation S 1 1 (6) (one hydrogen bond donor, and one acceptor enclosed in a sixmembered ring; Figure 1) (Bernstein et al. 1995, Etter et al. 1990). This interaction was also present in the previous report (Lu et al. 2011). This structural motif would likely provide an energetic barrier to rotation about the C2-C3 bond, which would be required to maximize the number of metals that could be incorporated into a cluster for further study.
A second hydrogen bond interaction is present as a one-dimensional chain of solvent methanol molecules, with graph set notation of C 1 1 (2) (Figure 2.) The methanolic protons, H3A and H3B, are disordered, with occupancy of 1/2, and when extended packing diagrams are examined, it can be seen that the hydrogen bonded chains propagate along [0 1 0] (i.e. run parallel to the b axis), with the disorder representing a reversal in the D-H···A orientation.

Refinement
With the exception of H3A, H3B and H2, all hydrogen positions were calculated after each cycle of refinement using a riding model, with C-H = 0.93 Å and U iso (H) = 1.2U eq (C) for aromatic H atoms, and with C-H = 0.96 Å and U iso (H) = 1.5U eq (C) for methyl H atoms. H2 was allowed to refine positionally, with U iso (H) = 1.5U eq (O2). The disordered H atoms, H3A and H3B were refined with distance (O3-H) and angle (C5-O3-H) restraints of 0.87 Å and 110° respectively, and with U iso (H) = 1.5U eq (O3). H3A and H3B were both assigned an occupancy of 0.5 based on similar residual peak program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

Figure 1
Molecular structure of the title compound at 50% probability ellipsoid level. Symmetry operator i = 1 -x, 2 -y, 1 -z; iv = 1 -x, 1 -y, 1 -z.  Packed unit cell of the title compound, highlighting the hydrogen bonding chains which propagate along [0 1 0]. One of the disordered H-atoms is omitted from each methanol molecule.

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.