Crystal structure of tris(ortho-phenylenediamide-N,N’)-rhenium(VII) bromide, C18H18BrN6Re

Abstract

C 18 H 18 BrN 6 Re, monoclinic, P2 1 /n (no. 14), a =11.0894 ( Source of materialThe title compound was prepared upon reacting ReBr 3 (dab)(PPh 3 ) 2 (dab =1 ,2-diaminobenzene) with the symmetric two-fold Schiff-base derived from 1,3-diamino-propan-2-ol and 2-hydroxy-benzaldehyde in ethanol. Crystals suitable for the diffraction study were obtained upon free evaporation of the solvent at ambient conditions. Experimental detailsCarbon-bound Hatomswere placed in calculated positions (C-H 0.95 Å) and were included in the refinementinthe riding model approximation, with U iso (H) setto1.2U eq (C). All nitrogen-bound Ha toms were locatedo nad ifferenceF ourier mapa nd refined freely using DFIX instructions, the N-H distances set to 0.88 Å. DiscussionNext to cardiovascular diseases, cancer has become one of the main fatal diseases in industrialized countries. Apart fromclassical 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 chemotherapy as well as radiation methods while at the sametimeavoiding their unique respectivendesiredside-effects -has been atopic of research [1,2]. 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 addition, the spatial requirements of pharmaceuticalsa re of importance as this factor influences on their interaction with enzymatic systems and, as a consequence, thep athway and rateo fc onjugation, functionalization and secretion from the body. In continuation of our ongoing research on the field of rhenium coordination compounds, the coordination of amultidentate ligand towards arhenium(V) startingm aterial was attempted [3].As tructural analysis of the crystalline reaction product showed the formation of an unexpected product. The crystal structures of two other comparable rhenium coordination compounds as found in the current reaction product are apparent in the literature [4].T he compound is ahomoleptic rhenium(VII) coordination compound featuringt hree chelating ortho-phenylenediamine ligands that are invariably two-folddeprotonated. The positive charge of the coordination unit is balanced by ab romide anionpresent in the crystal structure. Ac onformational analysis of the fivemembered chelate rings according to Cremer &Pople [5]shows the latter to invariably adopt E 1 conformations on the rhenium atom [6].R e-N bond lengthsc over an arrowr ange of 1.991(2)-2.0106(19) Åonly.The least-squares planes as defined by...