The monoadduct of dirhodium tetra(trifluoroacetate) with THF has been obtained by deposition from the vapor phase. The compound Rh-2(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 P (1) over bar with a = 9.557(2) Angstrom, b = 10.126(2) Angstrom, c = 11.840(4) Angstrom, alpha = 95.97(2)degrees, beta = 90.40(2)degrees, gamma = 115.58(1)degrees, and Z = 2; for 2, triclinic space group (P) over bar 1 with a 8.6347(3) Angstrom, b = 9.678(1) Angstrom, c = 13.773(4) Angstrom, alpha = 73.182(5)degrees, beta = 74.622(5)degrees, gamma = 89.76(1)degrees, 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 Rh-2 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) Angstrom, and the Rh-O(THF)Ph angle is 111.8(3)degrees. The crystal structure of 2 is not polymeric. Pairs of Rh-2(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) Angstrom, respectively.