To study pnictogen bonding involving bismuth, flexible accordion‐like molecular complexes of the composition [P(C 6 H 4 ‐ o ‐CH 2 SCH 3 ) 3 BiX 3 ], (X=Cl, Br, I) have been synthesised and characterised. The strength of the weak and mainly electrostatic interaction between the Bi and P centres strongly depends on the character of the halogen substituent on bismuth, which is confirmed by single‐crystal X‐ray diffraction analyses, DFT and ab initio computations. Significantly, 209 Bi– 31 P through‐space coupling ( J =2560 Hz) is observed in solid‐state 31 P NMR spectra, which is so far unprecedented in the literature, delivering direct information on the magnitude of this pnictogen interaction.

To account for the charge transfer and covalent character in bonding between P and Bi centers, the electronic structures of [P(C 6 H 4 - o -CH 2 SCH 3 ) 3 BiCl n ] (3– n )+ ( n = 0–3) model species have been investigated computationally. On the basis of this survey a synthetic target compound with a dative P→Bi bond has been selected. Consecutively, the highly reactive bismuth cage [P(C 6 H 4 - o -CH 2 SCH 3 ) 3 Bi] 3+ has been accessed experimentally and characterized. Importantly, our experiments (single-crystal X-ray diffraction and solid-state NMR spectroscopy) and computations (NBO and AIM analysis) reveal that the P···Bi bonding in this trication can be described as a dative bond. Here we have shown that our accordion-like molecular framework allows for tuning of the interaction between P and Bi centers.

Adducts of bismuth trihalides BiX 3 (X = Cl, Br, I) and the PS 3 ligand ( PS 3 = P(C 6 H 4 - o -CH 2 SCH 3 ) 3 ) react with HCl to form inorganic/organic hybrids with the general formula [H PS 3 BiX 4 ] 2 . On the basis of their solid-state structures determined by single-crystal X-ray diffraction, these compounds exhibit discrete bis-zwitterionic assemblies consisting of two phosphonium units [H PS 3 ] + linked to a central dibismuthate core [Bi 2 X 8 ] 2– via S→Bi dative interactions. Remarkably, the phosphorus center of the PS 3 ligand undergoes protonation with hydrochloric acid. This is in stark contrast to the protonation of phosphines commonly observed with hydrogen halides resulting in equilibrium. To understand the important factors in this protonation reaction, 31 P NMR experiments and DFT computations have been performed. Furthermore, the dibismuthate linker was utilized to obtain the coordination polymer {[Ag PS 3 BiCl 3 (OTf)] 2 (CH 3 CN) 2 } ∞ , in which dicationic [Ag( PS 3 )] 2 2+ macrocycles containing five-coordinate silver centers connect the dianionic [Bi 2 Cl 6 (OTf) 2 ] 2– dibismuthate fragments. The bonding situation in these dibismuthates has been investigated by single-crystal X-ray diffraction and DFT calculations (NBO analysis, AIM analysis, charge distribution).

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Pnictogen bond with bismuth: The flexibility of accordion‐like molecular skeletons paves the way for tunable pnictogen bonding between phosphorus and bismuth centres. The strength of this weak and mainly electrostatic interaction between the Bi and P centres strongly depends on the halogen substituent on bismuth. The first‐ever observation of a coupling between the two nuclei 209Bi and 31P (and the first through‐space coupling involving bismuth) by solid‐state 31P NMR spectroscopy, reported in the Communication by Z. Benkő, D. Heift et al. on page 4017 ff., is a direct measure for the strength of the pnictogen bonding.