Source of materialThe compound was obtained upon reacting ReCl 3 (MeCN)(PPh 3 ) 2 with the chelating ligandinacetonitrile.
Experimental detailsCarbon-boundHatoms were placed in calculated positions(C-H 0.95 Å) andwereincludedinthe refinement in the riding model approximation, with U iso (H) setto1.2U eq (C). The Hatoms of the methyl groups were allowed to rotate with afixed angle around the C-C bond to best fit the experimental electron density (HFIX 137 in the SHELX program suite[ 6]),w ith U iso (H)s et to 1.5U eq (C).
DiscussionNext to cardiovascular diseases, cancer has become one of the main fatal diseases in industrializedcountries. Apart from classical surgery,chemo-and radiotherapeutic treatments have entered the arsenal of possible cures for certain types of cancer. All methods, however, suffer from theirown setofproblematic side-effects and, as ac onsequence, the development of radiopharmaceuticals -combining the advantages of chemotherapyaswellasradiation methods while at the same timeavoiding theiruniquerespectiveundesired side-effects -has been atopic of research [1]. Tailoring andf ine-tuningo ft he 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 amore 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, the title compound was synthesized. As imilar compound featuring bromido instead of chlorido ligands has recently been described in the literature [2]. The compound is acentrosymmetric dinuclear rhenium(V) coordination compound. The asymmetric unit contains half of the coordination compound as well as am olecule of acetonitrile. The latter is disordered over two positions at aratio of nearly 0.5:0.5. The two rhenium atomsa re connected by means of an oxido bridge.The central Re atoms are hexacoordinate. Therespective octahedral coordinationsphereiscompleted by means of achelating molecule of 4,5-diaza-fluoren-9-one as well as an oxido and two chlorido ligands in cis configuration. The two Re-O bond lengths of 1.699(3) Åand 1.9019(2) Åfor the double as well as the single bond, respectively, areingood agreement with values found for other compounds containing the O=Re-O-Re moiety whose structural data has been deposited with the Cambridge Structural Database [3].The twoRe-N bonds are nearlyidentical with respecttotheir length,afinding that also holdstruefor the twoRe-Cl bonds. TheRe-O-Re angleismeasured at 180°. The least-squares planes as defined by the non-hydrogen atomsofthe the two individual pyridine subunits present on the 4,5-diazafluoren-9-one ligand intersect at an angle of 0.6(3)°only.Inthe crystal, amultitude of C-H×××O, C-H×××Nand C...