Complexes of lanthanoid salts with macrocyclic ligands. Part 17. Synthesis and crystal and molecular structure of a hydroxide-bridged praseodymium trifluoroacetate complex with 15-crown-5-ether, [Pr2(CF3CO2)3(OH)(C10H20O5)2][Pr2(CF3CO2)8]

Abstract

The reaction of praseodymium trifluoroacetate with 15-crown-5 ether in acetonitrile-methanol (3 : 1) gave a complex formulated as [ Pr(CF₃CO₂)₃]₂(C₁₀H₂₀O₅). This compound was recrystallised and the X-ray crystal structure determined by the heavy-atom method and refined by least-squares methods to a final R value of 0.075. The recrystaliised complex turned out to have a different formula, as indicated in the title. It crystallises in the monoclinic space group P2₁/m, with lattice parameters a= 9.124(1), b= 31.607(4), c= 13.006(2)Å, β= 99.55(1)°, and Z= 2. There are two praseodymium sites. One metal ion is nine-co-ordinate and is bonded to the macrocycle [mean Pr–O(crown) 2.58(2)Å], three bridging trifluoroacetate groups [mean Pr–0 2.45(2)Å], and a bridging hydroxide ion [ Pr–OH 2.31(1)Å] which lies in the mirror plane y=¼ This gives rise to dimeric cations [Pr₂(CF₃CO₂)₃(OH)(C₁₀H₂₀O₅)₂]²⁺, the co-ordination polyhedron of which may be regarded as arising from distortion of a square antiprism by addition of a ninth ligand. The second praseodymium is eight-co-ordinate with a fairly regular square-antiprismatic co-ordination polyhedron consisting of one bidentate trifluoroacetate and three bridging bidentate trifluoroacetates [mean Pr–O 2.46(2)Å] that give rise to infinite polymeric zigzag chains parallel to a.