Halogenaustausch an Re3-Clustern: Ein neuer Syntheseweg für binäre und ternäre Rhenium(III)-bromide. Kristallstrukturen von Cs2[Re3Br11] und Cs3[Re3Br3Cl9]

Halogen Exchange at Re₃-Clusters: A New Synthetic Route to Binary and Ternary Rhenium(III) Bromides. Crystal Structures of Cs₂Re₃Br₁₁] and Cs₃Re₃Br₃Cl₉] The substitution of “inner” ligands in transition metal clusters in aqueous HX solutions is hitherto unknown. For the first time the substitution of bridging and terminal chloride for bromide ions was observed at rhenium clusters, Re₃(μ-Cl^i,b)₃(Cl)(Cl^i,t)_(3?x)(H₂O^i,t)_x]^(3?x)? (x = 0–3), via the reaction of “ReCl₃ · 2 H₂O” in hot hydrobromic acid solution under an inert gas atmosphere. This establishes a new synthetic route to ternary Re(III) bromides as well as to ReBr₃. However, ternary Re(IV) bromides, A₂ReBr₆ (A = Rb, Cs), are dominating in the presence of oxygen, rhenium(III) bromides are only by-products. Dark brown rods of Cs₂Re₃Br₁₁] are obtained from argon saturated, hot hydrobromic acid solutions of “ReCl₃ · 2 H₂O” and CsBr. The crystal structure (orthorhombic, Pnma (Nr. 62); a = 955.51(5); b = 1 610.29(10); c = 1 372.70(9); Z = 4; V_m = 318.0(2) cm³mol^?1; R = 0.084, R_w = 0.058) consists of defect clusters Re₃BrBrBr□^i,t]^2? in which one in plane, terminal position is not occupied. The substitution of “inner” ligands has been observed in the case of chloride for bromide only, the Br^i,b and I^i,b ligands in ReBr₃ and ReI₃, respectively, are not substituted in hydrochloric acid even at temperatures as high as 100°C. Bordeaux red square pyramids of CsReBrCl₃ = Cs₃Re₃(μ-Br^i,b)₃ClCl] are obtained from hot hydrochloric acid solutions of ReBr₃ · 2/3 H₂O upon evaporation. CsReBrCl₃ (orthorhombic, C2cm (Nr. 40); a = 1 419.0(1); b = 1 419.2(1); c = 1 080.30(8) pm; Z = 4; V_m = 327.6(3) cm³mol^?1; R = 0.033, R_w = 0.028) is isostructural to the corresponding chloride CsReCl₄.