trans-Dichloridobis(3,5-dimethylpyridine-κN)(ethanolato-κO)oxidorhenium(V)

The title compound, [Re(C2H5O)Cl2O(C7H9N)2], was crystallized from ethanol. The crystal structure of this complex contains a Re(V) atom in a slightly distorted octahedral coordination geometry with pairs of equivalent ligands in trans positions. Adjacent complex molecules are linked by weak C—H⋯Cl hydrogen bonds. The crystal structure is additionally stabilized by π–π stacking interactions between the aromatic rings with centroid–centroid distances of 3.546 (4) Å.

The title compound, [Re(C 2 H 5 O)Cl 2 O(C 7 H 9 N) 2 ], was crystallized from ethanol. The crystal structure of this complex contains a Re(V) atom in a slightly distorted octahedral coordination geometry with pairs of equivalent ligands in trans positions. Adjacent complex molecules are linked by weak C-HÁ Á ÁCl hydrogen bonds. The crystal structure is additionally stabilized bystacking interactions between the aromatic rings with centroid-centroid distances of 3.546 (4) Å .

Comment
Complexes of the ReO(OR)X 2 L 2 type (where R is an alkyl group, X is a halogen and L is an N-donor ligand or monodendate phosphine) are commonly used as precursors for other Re(V) species, such as dioxo mononuclear and dinuclear compounds (Fortin & Beauchamp, 1998). When L is a diaza ligand, they might also be applied for the construction of multi-metal supramolecular assemblies (Iengo et al., 2001). Normally, these complexes are obtained as the all trans isomers (Lock & Turner, 1977). In this paper we report the synthesis procedure and crystal structure of an oxorhenium(V) complex with 3,5-dimethylpyridine ligands, the title compound.
The environment around the metal center is a slightly distorted octahedron with two chloro ligands, two 3,5-dimethylpyridine ligands, ethoxo and oxo ligands, all in trans positions to each other ( Fig. 1). The observed Re-ligand bond distances (Table 1) are similar to the reported for analogous complexes of the ReO(OR)X 2 L 2 type. However, the distortion of the angles in the coordination sphere of the Re atom is more significant than in similar compounds. Especially, the O1-Re-O2 and Cl1-Re-Cl2 angles differ from the expected value of 180°.
In the crystal structure, the molecules of the title complex are linked by a few weak hydrogen interactions of the C-H···Cl type (Desiraju & Steiner, 1999). The C13 and C121 atoms act as hydrogen-bond donors to Cl1 i [symmetry code: (i) x -1, y, z] as an acceptor ( Table 2). The observed C-H···Cl distances are similar to the values of the N-H···Cl hydrogen bonds identified for Cl bonded to a transition metal (Aullón et al., 1998). Each of the molecules accepts two hydrogen bonds and also donates two hydrogen bonds (Fig. 2), thus forming a C(7)C(7)[R 2 1 (6)] chain of rings motif (Bernstein et al., 1995).
Additionally, the N1/C11-C15 and N2/C21-C25 rings are engaged in π-π stacking contacts (Fig. 2), which further assist in the stabilization of the crystal structure by assembling chains running parallel to the [100] direction. The distance of the centroids and the offset of the pyridine rings (Table 3) are typical for energetically favorable non-bonded aromatic interactions (McGaughey et al., 1998).

Experimental
The title compound was prepared similarly to the previously reported rhenium(V) complex with pyrazine ligands (Iengo et al., 2001). 3,5-dimethylpyridine (0.55 ml, 4.77 mmol) was added to the suspension of ReOCl 3 (OPPh 3 )(SMe 2 ) (1.0 g, 1.54 mmol) in absolute ethanol (10 ml All H atoms were positioned geometrically and refined using a riding model with aromatic C-H = 0.95Å and U iso (H) = 1.2U eq (C). The methyl groups were refined with C-H = 0.98Å and U iso (H) = 1.5U eq (C). The highest residual peak and the deepest hole in the final difference map are located 0.97 and 1.24Å from the Re atom, respectively. Fig. 1. The molecular structure and atom numbering scheme of the title compound. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii.

Special details
Experimental. The crystal was placed in the cold stream of an open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 90 K.
Analytical numeric absorption correction was carried out with CrysAlis RED (Oxford Diffraction, 2010) using a multifaceted crystal model (Clark & Reid, 1995