The crystal and molecular structures of the title complexes are described. Crystals of Rh(C 5H 7O)(C 4F 6)(C 2H 4) are triclinic, a 7.89(2), b 12.64(3), c 8.57(2) Å, α 95.9(2), β 121.1(2), γ 94.8(2)°, Z 2, space group P 1 . Full matrix least-squares refinement has returned the residual, R, as 0.053. Crystals of Rh(C 5H 7O)(C 4F 6)(C 8H 14) are monoclinic, a 14.16(3), b 17.89(3), c 15.71(3) Å, β 97.5(2)°, Z 8, space group B2 1/ c. Block-diagonal least-squares refinement has returned R as 0.048. Both complexes are monomeric with square planar inner coordinations. The olefin and acetylene groups are approximately perpendicular to the square coordination planes. The RhC and RhO distances are (i) ethylene; olefin 2.142(14), 2.171(17) Å, acetylene 2.016(10), 2.042(11) Å, acetylacetone 2.015(6), 2.033(7) Å; (ii) cyclooctene; olefin 2.163(13), 2.196(11) Å, acetylene 2.034, 2.059(10) Å, acetylacetone 2.017(8), 2.038(7) Å. The average ‘;bend-back’; angle of the substituted acetylenes is 30.1° for both complexes, which is low compared with most other hexafluorobut-2-yne complexes.