Synthesis of a polynuclear complex possessing four spatially arranged rhenium units Bhaskaran Shankar, Palani Elumalai, Malaichamy Sathiyendiran ⁎ Department of Chemistry, University of Delhi, Delhi 110 007, India abstract article info Article history: Received 19 July 2013 Accepted 22 August 2013 Available online 29 August 2013 Keywords: 2-(Benzoxazol-2-yl)phenol Mononuclear Polynuclear complex Pyridyl donor Rhenium The reaction of Re 2 (CO) 10 with 2-(benzoxazol-2-yl)phenol (HL) and 1,2,4,5-tetrakis(4-pyridylvinyl)benzene (L 2 ) gives a heteroleptic tetranuclear complex, [((fac-Re(CO) 3 )L) 4 (L 2 )] 1. The corner of 1 comprises four spatially arranged mononuclear units. © 2013 Elsevier B.V. All rights reserved. Acyclic complexes possessing fac-Re(CO) 3 -NNX (X = Cl, Br, O, N) units have attracted immense research interest due to their photo- physical, photochemical, and electrochemical properties [1–16]. These complexes are applied in a variety of chemistry-related fields for sensing and switching devices [6], probes for thermal and photochemical poly- merizations [7], electroluminescence [8,9], photocatalysis [10], thera- peutic radiopharmaceuticals [11] and emitting materials in organic light-emitting diodes [12–16]. To date, few benzoxazol-based rhenium complexes are known [17]. Previous work in this field focussed on alter- ing the structure of ligands by introducing alkyl or phenyl groups and studying the resultant stability and properties [17–19]. These complexes can be obtained via two synthetic approaches: (1) Reaction of Re(CO) 5 Cl with the appropriate coordination ligands under reflux, and (2) dissocia- tive solvolysis of the dimer by pyridine donors. Due to their potential in materials chemistry, we envision that replacing pyridine with a polytopic nitrogen donor ligand, i.e., L 2 , and using Re 2 (CO) 10 would result in a poly- nuclear cluster possessing spatially arranged metal complexes that may display enhanced properties and functions over those of the mononuclear complex. Herein, we report a tetranuclear complex with four spatially arranged light-emitting complex units. Self-assembly of the complex was achieved by reacting Re 2 (CO) 10 , HL, and 1,2,4,5-tetrakis(4- pyridylvinyl)benzene (L 2 ) in a one-pot approach. Complex 1 was characterized by elemental analysis and FT-IR, UV-vis, and fluorescence spectroscopy. The molecular structure of 1 was further confirmed by single crystal X-ray diffraction analysis. Compound 1 was obtained from the reaction of Re 2 (CO) 10 ,H 2 L, and L 2 in toluene under solvothermal conditions (Scheme 1) [20–30]. The crystalline product was filtered and air-dried. The product is air- and moisture-stable [31] and is moderately soluble in organic polar sol- vents. The elemental analysis results of 1 match with a mixed ligand tetranuclear complex with a formula of [((fac-Re(CO) 3 ) L) 4 (L 2 )] •0.5C 7 H 8 (1•0.5C 7 H 8 ). The FT-IR spectrum of 1 showed three distinct and strong bands at 2015, 1905, and 1877 cm -1 , which are characteris- tic of a pseudo-octahedral fac-Re(CO) 3 core. A similar stretching pattern was observed for a mononuclear rhenium complex containing fac- Re(CO) 3 , deprotonated 2-(benzoxazol-2-yl)phenol (L), and a pyridine unit [17]. This stretching pattern further supports that the Re-O and C–O bond lengths are all different. The 1 H NMR spectrum of 1 differed from the spectra of free H 2 L and L 2 . Interpretation of the 1 H NMR spec- trum of 1 is difficult due to the overlapping signals in the aromatic region; this overlap is likely due to different chemical environments for the L units in the complex. The molecular structure of 1 consists of one L 2 , four anionic L moieties, and four fac-Re(CO) 3 cores (Fig. 1). The coordination sphere around the rhenium centres has a fac-C 3 N 2 O distorted octahedral geometry. The Re ions form a rectangle with Re · · · Re distances of 12.2450 and 12.2847 Å. The L moiety chelates the rhenium centre through the benoxazolyl nitrogen atom and phenolate oxygen atom. The four L moieties in the molecule are arranged in a syn,anti,syn,anti fashion. The Re–O and Re–N bond distances indicate the ionic and covalent character, respectively. The Re–O chel and Re–N chel bond lengths are similar to those of the previously reported mononuclear complexes [17]. The L units are arranged perpendicular to the plane of the pyridyl units (dihedral angles = 81° and 60°). The dihedral angles between the best planes passing through the four rhenium Inorganic Chemistry Communications 36 (2013) 109–112 ⁎ Corresponding author. Tel.: +91 9871497211. E-mail addresses: mvdiran@yahoo.com, msathi@chemistry.du.ac.in (M. Sathiyendiran). 1387-7003/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.inoche.2013.08.026 Contents lists available at ScienceDirect Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche