Dibromidooxido[(Z)-N′-(propan-2-ylidene)benzohydrazidato](triphenylphosphane)rhenium(V)

The asymmetric unit of the title neutral rhenium(V) coordination compound, [ReBr2(C10H11N2O)O(C18H15P)], contains two molecules. In each of the two molecules the metal atom is octahedrally coordinated, the bromido ligands being cis-orientated. The chelate ligand is present in its imine-tautomeric form. In the crystal, C—H⋯Br contacts connect the molecules into chains along [101]. The shortest intercentroid distance between two aromatic rings was found to be 3.906 (2) Å.

The asymmetric unit of the title neutral rhenium(V) coordination compound, [ReBr 2 (C 10 H 11 N 2 O)O(C 18 H 15 P)], contains two molecules. In each of the two molecules the metal atom is octahedrally coordinated, the bromido ligands being cis-orientated. The chelate ligand is present in its iminetautomeric form. In the crystal, C-HÁ Á ÁBr contacts connect the molecules into chains along [101]. The shortest intercentroid distance between two aromatic rings was found to be 3.906 (2) Å .

Related literature
For the crystal structures of rhenium(I), rhenium(III) and rhenium(V) metal complexes featuring tridentate ONX (X = O, N, S)-donor Schiff bases, see: Potgieter et al. (2010). For graph-set analysis of hydrogen bonds, see: Etter et al. (1990); Bernstein et al. (1995). For puckering analysis, see: Cremer & Pople (1975). For general information about radiopharmaceuticals, see: Gerber et al. 649 parameters H-atom parameters constrained Á max = 1.11 e Å À3 Á min = À1.33 e Å À3 Table 1 Hydrogen-bond geometry (Å , ). of radiopharmaceuticals -combining the advantages of chemotherapy as well as radiation methods while at the same time avoiding their unique respective undesired side-effects -has been a topic of research (Gerber et al., 2011). Tailoring and fine-tuning of the envisioned radiopharmaceuticals' properties such as lipophilicity and, in particular, inertness is of paramount importance with respect to possible future in vivo applications in contemporary medicine and requires sound knowledge about structural parameters of the ligands applied if a more heuristic approach in the synthesis is to triumph over pure trial-and-error as it is encountered in this specific field of coordination chemistry up to the present day. In continuation of our interest in rhenium-based coordination compounds that might serve as radiopharmaceuticals, we determined the molecular and crystal structure of the title compound. Information about the crystal structures of rhenium coordination compounds with the central atom in different oxidation states is apparent in the literature (Potgieter et al., 2010).
The central atom in both molecules of the asymmetric unit is hexacoordinate. The ligand sphere features one chelate ligand which is present in its tautomeric imine form. Both oxygen atoms are in trans-position, the bromido ligands are cisorientated. While the small puckering amplitude of one of the five-membered chelate rings (τ = 4.3 °) precludes a conformational analysis (Cremer & Pople, 1975) in the first molecule of the asymmetric unite, the corresponding five-membered ring in the second molecule adopts an envelope conformation on the rhenium atom ( Re2 E, Q 2 = 0.076 (3) Å, π 2 = 358 (3) °).
The central atom is displaced by 0.184 (1) Å and 0.188 (1) Å, respectively, from the plane defined by the bromido ligands as well as the coordinating nitrogen atom and phosphorus atom (Fig. 1).
In the crystal, C-H···Br contacts can be observed whose range falls by more than 0.1 Å below the sum of van-der-Waals radii of the respective atoms. These are supported exclusively by hydrogen atoms of phenyl groups on the triphenylphosphane ligand and involve hydrogen atoms in ortho as well as in meta position as donors and the bromido ligand in transposition to the coordinating phosphorus atom as acceptors. In terms of graph-set analysis (Etter et al., 1990;Bernstein et al., 1995), the descriptor for these contacts is DD on the unitary level. In total, the molecules are connected to chains along [1 0 1] (Fig. 2). The shortest intercentroid distance between two centers of gravity was found at 3.906 (2) Å.

Experimental
Benzhydrazide and trans-[ReOBr 3 (PPh 3 ) 2 ] were refluxed in acetone for 5 h. After cooling to room temperature and filtration the filtrate was stored at room temperature upon which crystals formed in the course of a couple of days.
supplementary materials sup-2 Refinement Carbon-bound H atoms were placed in calculated positions (C-H 0.95 Å for aromatic C atoms, C-H 0.98 Å for methyl groups) and were included in the refinement in the riding model approximation, with U(H) set to 1.2U eq (C) for aromatic carbon atoms and U(H) set to 1.5U eq (C) for methyl groups. Fig. 1. The molecular structure of the title compound, with atom labels and anisotropic displacement ellipsoids (drawn at 50% probability level).