Studies of Dirhodium Tetra(trifluoroacetate). 3. Solid State Isomers of the Compound Rh2(O2CCF3)4(THF) Prepared by Sublimation

Abstract

The monoadduct of dirhodium tetra(trifluoroacetate) with THF has been obtained by deposition from the vapor phase. The compound Rh₂(O₂CCF₃)₄(THF) crystallizes in two isomeric forms, 1 and 2, whose structures have been determined by X-ray crystallography. The crystallographic parameters are as follows: for 1, triclinic space group P1̄ with a = 9.557(2) Å, b = 10.126(2) Å, c = 11.840(4) Å, α = 95.97(2)°, β = 90.40(2)°, γ = 115.58(1)°, and Z = 2; for 2, triclinic space group P1̄ with a = 8.6347(3) Å, b = 9.678(1) Å, c = 13.773(4) Å, α = 73.182(5)°, β = 74.622(5)°, γ = 89.76(1)°, and Z = 2. Compound 1 is unique as the only extended structure where dirhodium carboxylate molecules are bridged by a single exogenous atom. The oxygen atom of the THF ligand coordinates to the axial positions of two Rh₂ units so that a one-dimensional zigzag chain is formed. The bridging is slightly asymmetric with Rh−O(THF) distances of 2.363(6) and 2.407(6) Å, and the Rh−O(THF)−Rh angle is 111.8(3)°. The crystal structure of 2 is not polymeric. Pairs of Rh₂(O₂CCF₃)₄(THF) units are associated through O atoms of carboxylate groups to produce a dimer of dimers. The lengths of the terminal Rh−O(THF) and axial bridging Rh···O(Ac) interactions are 2.214(7) and 2.406(6) Å, respectively.