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The molecular structures of potassium tetrakis(hexafluoro-acetylacetonato)lanthanate(III) complexes [KLn(hfa) 4 ] (Ln = La, Gd, Lu; hfa = C 5 HF 6 O 2 ,) were studied by synchronous gas-phase electron diffraction / mass spectrometry (GED/MS) supported by quantum-chemical (DFT/PBE0) calculations. The compounds sublimate congruently and the vapors contain single molecular species: the heterobinuclear complex [KLn(hfa) 4 ]. All molecules are of C 1 symmetry with the lanthanide atom in the center of a coordination polyhedron LnO 8 , while the potassium atom is coordinated by three ligands under formation of three K-O and three K-F bonds. Topological analysis of the electron density distributions confirms the existence of ionic-type K-O and K-F bonding. The presence of the potassium ion distorts the coordination polyhedron LnO 8 and takes influence on the structure of the ligands. The structures of the free [KLn(hfa) 4 ] molecules are compared with those of the related compounds [KDy(hfa) 4 ] and [KEr(hfa) 4 ] in their crystalline state. The complex nature of chemical bonding is discussed on the basis of electron density topology analyses. © 2020 Wiley-VCH GmbH.