A systematic comparison of second-order polarization propagator approximation (SOPPA) and equation-of-motion coupled cluster singles and doubles (EOM#CCSD) spin#spin coupling constants for selected singly bonded molecules, and the hydrides NH, HO, and HF and their protonated and deprotonated ions and hydrogen-bonded complexes

Abstract

Second-order polarization propagator approximation (SOPPA) and equation-of-motion coupled cluster singles and doubles (EOM-CCSD) methods have been employed for the calculation of one-bond spin-spin coupling constants in series of small molecules and ions, and of one- and two-bond coupling constants across X-H⋯Y hydrogen bonds. For isolated molecules, one-bond SOPPA coupling constants 1J(X-Y) involving 13C, 15N, 17O, and 19F have larger absolute values than corresponding EOM-CCSD coupling constants, with the EOM-CCSD values being in significantly better agreement with available experimental data. The difference between SOPPA and EOM-CCSD tends to increase as the number of nonbonding electrons on the coupled atoms increases, and the SOPPA values for O-F coupling are significantly in error. Similarly, the absolute values of SOPPA one-bond coupling constants 1J(X-H) for the hydrides NH3, H 2O, and FH and their protonated and deprotonated ions are greater than EOM-CCSD values, with the largest differences occurring for F-H coupling. One- and two-bond coupling constants 1J(X-H), 1hJ(H-Y), and 2hJ(X-Y) across X-H⋯;Y hydrogen bonds in neutral, protonated, and deprotonated complexes formed from the hydrides are similar at SOPPA and EOM-CCSD, with the largest differences again found for 1J(F-H) in complexes with F-H as the proton donor, and 2hJ(F-F) for (FHF)-. The signs of 1J(X-H), 1hV(H-Y), and 2hJ(X-Y) are the same at both levels of theory, as is their variation across the proton-transfer coordinate in F-H⋯;NH3. SOPPA would appear to provide a reliable and more cost-effective alternative approach for computing coupling constants across hydrogen bonds, although couplings involving F may be problematic. © 2008 American Chemical Society.