Abstract
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.
Highlights
In a recent study [1], we reported the structures, binding energies, and bonding properties of two series of binary complexes represented as N-base:PH2F and PH2F:BeX2, and the corresponding ternary complexes N-base:PH2F:BeX2, with NH3, HN = CH2, and NCH as the nitrogen bases, the phosphorous molecule fluorophosphane PH2F, and five beryllium derivatives BeH2, BeF2, BeCl2, BeCO3, and BeSO4
The P-N stretching frequencies range from 107 cm–1 at a P-N distance of 2.77 Å in the binary complex HCN:PH2F, to 310 cm–1 at a P-N distance of 2.10 Å in the ternary complex H3N:PH2F:BeCl2 A
The P-N distances are longest in the binary complexes and the ternary complexes HCN:PH2F:BeX2, and these complexes have the smallest P-N stretching frequencies
Summary
In a recent study [1], we reported the structures, binding energies, and bonding properties of two series of binary complexes represented as N-base:PH2F and PH2F:BeX2, and the corresponding ternary complexes N-base:PH2F:BeX2, with NH3, HN = CH2, and NCH as the nitrogen bases, the phosphorous molecule fluorophosphane PH2F, and five beryllium derivatives BeH2, BeF2, BeCl2, BeCO3, and BeSO4. Two equilibrium isomers labelled A and B were found on the potential surfaces having BeH2, BeF2, and BeCl2 as the acids, and these are illustrated in Figure 1 for NH3:PH2F:BeH2. In isomer A, the BeH2 molecule lies in the symmetry plane of the complex, with the F. Be bond cis to the bisector of the H-P-H angle with respect to the P-F bond. Isomer B has no symmetry in point group C1, since BeH2 assumes
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