capitalize on the delocalization of the positive charge into neighboring heteroatoms. Hence, a genuine π-allyl cation analogue based on heavier elements still remains elusive. Due to its privileged place in the periodic table as the last stable element, we envisaged that the heaviest analogue of this cationic structure should be within reach using bismuth. A direct comparison of the frontier orbitals involved in bonding leads to the realization that a cationic triatomic complex of bismuth with formal oxidation state +1 for the three contiguous Bi atoms (Bi)3 + would be analogous to that of the carbon-based allyl cation (Figure , right). This seemingly simple analogy presents an enormous synthetic challenge: examples of unsupported neutral or cationic di-coordinated bismuth(I) compounds are rare. Siddiqui et al. developed a cationic Bi(I) supported by two sterically encumbered CAAC which resembled the heaviest analogue of a carbone. Recently, the group of Driess and Frenking developed a similar structure with germylenes as supporting ligands. For many years, overlapping of large and diffused orbitals leading to chemical bonding between 5p and 6p orbitals was regarded as a challenge in organometallic chemistry. However, this canonical notion has recently been challenged with several examples of heavy main group elements (HMGE) that form double and triple bonds akin the lightest main group elements. Based on our recent findings on mono-coordinated bismuthinidene 1, here we present the synthesis, structure, characterization and reactivity of a unique cationic complex featuring three contiguously bonded Bi atoms in a low oxidation state. The electronic structure calculations reveal the delocalization of two electrons through the nonhybridized 6p orbitals of the trimetallic (Bi3) + core -due to the low energy of the buried 6s 2 orbitalscharacteristic of the classical π-allyl cation. When 1 was mixed with mono-hydrated tris(pentafluorophenyl)borane (BCF) in PhMe-d8 at 25 °C, 2 precipitated from the mixture as an air-sensitive dark brown solid. As by-product, the protonated organic framework was obtained. The structure of 2 was unambiguously determined by single crystal X-ray diffraction (SC-XRD) which revealed its ionic nature. While the cation is constituted by a triatomic bismuth core connected in a linear zig-zag fashion with the bulky organic backbone, a [(BCF)2OH] -serves as counter anion. Whereas the distance between BiI-BiII [2.93361(12) Å] is 2% shorter (∆d = 0.0571 Å) than the Bi-Bi single bond [2.990(2) Å] in 3 (Fig. ), it is 3% longer (∆d = 0.08721 Å) than the Bi=Bi double bond distance in dibismuthene 4 [2.8464(4) Å]. Together with previously described bond lengths, the distances in 2 falls in the range between a single and a double bond. At the same time, the BiII-C(sp 2 ) distance in 2 suggests a single bond [2.2851(16) Å in 2 vs 2.2783 (10) in 1] which implies an inexistent delocalization of the charge on the aryl system in the ground state (vide infra). The observed C-BiI-BiII and BiII-BiI-BiII bond angles [(101.29(4)° and 80.637(3)°, respectively] are indicative of the limited ability of Bi to form hybridized sp 2 orbitals, primarily due to the contraction of the 6s orbital as a consequence of relativistic effects. In solution, compound 2 is stable in dicholoromethane-d2 and could be fully characterized at 25 °C by NMR. At this temperature, 2 shows C2v symmetry; however, this symmetry is lost at -100°C, in line with the crystal structure (see Supplementary Materials). A single set of ArF signals can also be observed at 25 °C, arising from the polyfluorinated anion in 2. At lower temperatures, this equivalence is broken and three distinct Ar groups appear, in agreement with previous observations for this anion. Compound 2 appears diamagnetic, and no signal was observed by EPR. One the basis of the crystal structure, the geometric structure of 2 was optimized without constraints using the ORCA 5.0 , program suite together with the B3LYP functional, the D3(BJ) dispersion correction and the def2-TZVP basis set with associated effective core potentials. The obtained stationary point was confirmed to be a minimum through the calculation of harmonics frequencies. The calculated BiI-BiII distance of 2.912 Å and the Bi-C distance of 2.295 Å (average) are in overall agreement with the SC-XRD data of 2.93361(12) Å and 2.2851(16) Å, respectively. Given the strong sensitivity of the Bi-Bi distance to the bond order between the two atoms, these results provide evidence for the notion that the electronic situation in the (Bi)3 + core is properly represented by the calculations. A closer analysis of the electronic structure of the cationic core in 2 confirms that the two BiII are nearly equivalent and distinct from the bridging BiI. As deduced from the analysis of the occupied orbitals, all Bi atoms feature a non-bonding lone pair of electrons corresponding to the inert 6s 2 (Figure ). At the same time, the terminal BiII atoms further engage in two-electron-two center single bonds with the ligand framework as well as with BiI respectively.