The binuclear dual emitter [Br(CO) 3 Re(PN)(NP)Re(CO) 3 Br] (PN): 3-chloro-6-(4-diphenylphosphinyl)butoxypyridazine, a new bridging P,N-bidentate ligand resulting from the ring opening of tetrahydrofuran.

Lithium diphenylphosphide unexpectedly provokes the ring-opening of tetrahydrofuran (THF) and by reaction with 3,6-dichloropyridazine leads to the formation of the ligand 3-chloro-6-(4-diphenylphosphinyl) butoxypyridazine (P center dot center dot center dot N), which was isolated. The reaction of this ligand with the (Re(CO) 3(THF)Br)(2) dimer yields the novel complex [Br(CO) 3Re(mu-3-chloro-6-(4-diphenylphosphinyl) butoxypyridazine)(2)Re (CO)(3)Br] (BrRe(P center dot center dot center dot N)(N center dot center dot center dot P) ReBr), which was crystallized in the form of a chloroform solvate, (C46H40Br2Cl2N4O8P2Re2).(CHCl3). The monoclinic crystal (P2(1)/n) displays a bimetallic cage structure with a symmetry inversion centre in the middle of the rhenium to rhenium line. The molecule shows two oxidation signals occurring at + 1.50 V and + 1.76 V which were assigned to the Re-I/Re-II and Re-II/Re-III metal-centered couples, respectively, while signals observed at -1.38 V and -1.68 V were assigned to ligand centered reductions. Experimental and DFT/TDDFT results indicate that the UV-Vis absorption maximum of BrRe(P center dot center dot center dot N)(N center dot center dot center dot P) ReBr occurring near 380 nm displays a metal to ligand charge transfer (MLCT) character, which is consistent with CV results. Upon excitation at this wavelength, a weak emission (Phi(em) < 1 x 10(-3)) is observed around 580 nm (in dichloromethane) which decays with two distinct lifetimes tau(1) and tau(2) of 24 and 4.7 ns, respectively. The prevalence of non-radiative deactivation pathways is consistent with efficient internal conversion induced by the high conformational flexibility of the P center dot center dot center dot N ligand's long carbon chain. Measurements in a frozen solvent at 77 K, where vibrational deactivation is hindered, show intense emission associated with the (MLCT)-M-3 state. These results demonstrate that BrRe(P center dot center dot center dot N)(N center dot center dot center dot P) ReBr preserves the dual emitting nature previously reported for the mononuclear complex RePNBr, with emission associated with pi(star)(phenyl) and pi(star)(pyridazine) states.