A new MoVI Schiff base complex: methanol[N′-(3-methoxy-2-oxidobenzylidene)benzohydrazidato]dioxidomolybdenum(VI)

In the title benzilidene Schiff base molybdenum(VI) complex, [Mo(C15H12N2O3)O2(CH3OH)], the MoVI ion is coordinated by two oxide O atoms and by two O atoms and one N atom of the tridentate N′-(3-methoxy-2-oxidobenzylidene)benzohydrazidate (L) Schiff base ligand. The methanol O atom completes the distorted octahedral configuration of the MoVI atom. Strong O—H⋯N hydrogen bonds form a C(5) chain around a 21 screw axis. Weak C—H—O hydrogen bonds are also present.


Comment
The condensation products of primary amines and aldehydes or ketones (RCH=NR'), where R and R' represent alkyl and /or aryl constituents), are called Schiff bases (Dhar & Taploo, 1982); they play an important role in inorganic chemistry (Blake et al., 1995;Johnson et al.,1996;Alizadeh et al., 1999) as they easily form stable complexes with most transition metal ions.
Transition metal compounds containing the Schiff base ligands have been of interest for many years (Yamada, 1999;Chang et al., 1998;Archer & Wang, 1990;Sheikhshoaie & Fabian, 2009;Jalali-Heravi et al., 1999). Many complexes play an important role in the developing of coordination chemistry related to catalytic (Holm, 1990;Rao et al., 1999;Bagherzadeh et al., 2008;Ambroziak et al., 2004;Bagherzadeh & Amini, 2009;Hatefi et al., 2009) and enzymatic reactions (Bindlish et al., 1978;Bhatia et al., 1981;Costamagna et al., 1992). High valent metal oxo species have demonstrated the ability to catalyze the oxidation of a variety of organic substrates, via homogeneous as well as heterogeneous routes (Holm, 1990;Maurya et al., 1997). In particular, the Mo-catalyzed alkene to epoxide conversion has received most attention. In the course of our studies on transition metal Schiff base complexes Monadi et al., 2009), we have synthesized a dioxo molybdenium complex with a tridentate ligand (L) and the crystal structure of the title complex (I) is presented here.
There are strong hydrogen bonds present between the hydroxy group of methanol and N2 i atom in an adjacent complex [symmetry code: (i):-x + 1/2,y + 1/2,-z + 1/2] forming thus a C(5) chain around 2 1 screw axis, see Fig.2. There are also weak hydrogen bonds of the type in the C-H-O hydrogen bonds present, see Table 2. Fig. 3 shows the packing of the complexes in the unit cell, but there are no π-π interactions present.
Comparison with other similar structures is presented in Table 3. In all complexes molybdenum atom is coordinated by two oxo oxygen atoms, one nitrogen atom of C=N group and one oxygen atom from solvent (methanol or ethanol). In all these complexes, the longest bond from the solvent coordination indicates the most labile site available for substitution. In  Table 4 provides a comparison of important frequencies in the IR spectra of (I) and some dioxo-molybdenum(VI) complexes.

Experimental
All reagents were used assupplied by Fluka and Merck without further purification. Solvents used for the reaction were purified and dried by conventional methods (Perrin et al., 1990).
NMR spectra were obtained on a BRUKER AVANCE DRX500 (500 MHz

Refinement
Aromatic hydrogen atoms were refined isotropically with U iso (H) = 1.2U eq (C), and their positions were constrained to an ideal geometry using an appropriate riding model, (C-H = 0.95 Å). For methyl groups, O-C-H angles (109.5°) were kept fixed, while the torsion angle was allowed to refine with the starting positions based on the circular Fourier synthesis averaged using the local 3-fold axis with U iso (H)= 1.5U eq (C) and a constrained C-H distance of 0.98Å was applied. For hydroxy group, the O-H distance (0.84 Å) and C-O-H angle (109.5°) were kept fixed, while the torsion angle was allowed to refine with the starting position based on the maximum on the circular Fourier synthesis, U iso (H)= 1.5U eq (O). Fig. 1. The atom numbering scheme for (I), with atomic displacement ellipsoids drawn at the 50% probability level.

Special details
Experimental. Data were collected at 173 K using a Siemens SMART CCD diffractometer equipped with LT-2 A cooling device. A full sphere of reciprocal space was scanned by 0.3° steps in ω with a crystal-to-detector distance of 3.97 cm, 1 second per frame. Preliminary orientation matrix was obtained from the first 100 frames using SMART (Bruker, 2003). The collected frames were integrated using the preliminary orientation matrix which was updated every 100 frames. Final cell parameters were obtained by refinement on the position of 5066 reflections with I>10σ(I) after integration of all the frames data using SAINT (Bruker, 2003 (1)