DOI: 10.1080/00268976.2021.1905191  (OpenAccess)

IR and NMR properties of N-base:PH2F:BeX2 ternary and corresponding binary complexes stabilised by pnicogen and beryllium bonds

Ab initio MP2/aug’-cc-pVTZ calculations have been performed to determine selected stretching frequencies and chemical shieldings for ternary complexes N-base:PH2F:BeX2 and the corresponding binary complexes, with NH3, H2C=NH, and HCN as the nitrogen bases and H, F, and Cl as the substituents X. Be-F and P-F stretching frequencies depend on the Be-F and P-F distances, respectively, while P and F chemical shieldings depend on the N-P and P-F distances, respectively. The graph of the P chemical shieldings versus the P-F distance bears a remarkable resemblance to the graph of the P-F stretching frequencies versus that same distance. EOM-CCSD spin–spin coupling constants have also been evaluated for binary and ternary complexes. 1pJ(N-P) is negative at the longer N-P distances found in ternary complexes with HCN in which the N···P bond is a traditional pnicogen bond with some phosphorous-shared character, gains phosphorus-shared character as the N-P distance continues to decrease, and then becomes a phosphorous-transferred bond with ion-pair character at the shorter distances in the complexes with NH3 and H2C=NH. 1J(P-F) values are large and negative in complexes with HCN, but increase and become positive in complexes with H2C=NH and NH3 as the P-F distance increases.