jp502667k_si_001.pdf (488.07 kB)
Pnicogen-Bonded Anionic Complexes
journal contribution
posted on 2014-05-08, 00:00 authored by Janet E. Del Bene, Ibon Alkorta, José ElgueroAb initio MP2/aug′-cc-pVTZ
calculations have been carried
out to investigate the pnicogen-bonded complexes H2YP:X–, for X,Y = Cl, NC, F, CCH, and CH3. Of
the 36 possible complexes, only 21 are unique equilibrium structures.
All substituents form (H2XPX)− complexes
with symmetric X–P–X bonds. The P–A ion–molecule
pnicogen bonds in these and some additional complexes have partial
covalent character, while some P–A′ covalent bonds have
partial ion–molecule character. A and A′ are the atoms
of X and Y, respectively, which are directly bonded to P. Complexes
with these types of bonds include the symmetric complexes (H2XPX)−, H2(CH3)P:F–, H2(CCH)P:F–, H2FP:NC–, H2FP:Cl–, H2FP:CN–, and H2(NC)P:Cl–. Charge transfer from A to the P–A′ σ* orbital
stabilizes H2YP:X– complexes and leads
to a reduction of the negative charge on X. For fixed X, the smallest
negative charge occurs in the symmetric complex. Then, for a given
X, the order of decreasing negative charge with respect to Y is CH3 > CCH > CN (bonded through C) > F > NC (bonded
through N)
> Cl, which is also the order of decreasing P–A distance.
EOM-CCSD
spin–spin coupling constants 1pJ(P–A) differentiate between shorter ion–molecule pnicogen
bonds with partial covalent character and longer P···A
ion–molecule pnicogen bonds. Similarly, coupling constants 1J(P–A′) differentiate between
longer covalent P–A′ bonds with partial ion–molecule
character and shorter P–A′ covalent bonds.