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 3 , H 2 O, and HF and Their Protonated and Deprotonated Ions and Hydrogen-Bonded Complexes