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Synthesis and Crystal Structure of Ordered, Orthorhombic α-NbBr5
Wolfgang Hönle (Max Planck Institute for Solid State Research), Sigrid Furuseth (Max Planck Institute for Solid State Research), Hans Georg̀ von Schnering (Max Planck Institute for Solid State Research)
Résumé : Niobium pentabromide, NbBr5, is prepared in the orthorhombic ordered (α)-form from the elements in sealed quartz ampoules (Nb powder, Br2, l) at 973 K. The structure has been determined from single crystal data (a = 1288.8(2), b = 1869.0(3), c = 614.9(1) pm; Pnma (No. 62); Z = 8; R = 0.055). α-NbBr5_ forms dimeric Nb2Br10 molecules with d̄(Nb–Brb) = 271.5 pm, d̄(Nb–Bre) = 240.8 pm and d̄(Nb– Bra) = 246.1 pm. α-NbBr5 is a diamagnetic semiconductor with cgsχmol dia(300 K) = –72 × 10-6 cm3/mol. The band gaps of NbCl5, α-NbBr5 and NbI5 have been determined by diffuse reflection to be Eg(NbCl5) = 2.74 eV, Eg(α-NbBr5) = 1.99 eV, and Eg(NbI5) = 0.99 eV.