| Abstract
| - Ab initio equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) calculations have been carriedout to investigate the effect of a third polar near-neighbor on one-bond (1JX-H and 1hJH-Y) and two-bond(2hJX-Y) spin−spin coupling constants in AH:XH:YH3 complexes, where A and X are 19F and 35Cl and Y iseither 15N or 31P. The changes in both one- and two-bond spin−spin coupling constants upon trimer formationindicate that the presence of a third molecule promotes proton transfer across the X−H−Y hydrogen bond.The proton-shared character of the X−H−Y hydrogen bond increases in the order XH:YH3< ClH:XH:YH3< FH:XH:YH3. This order is also the order of decreasing shielding of the hydrogen-bonded proton anddecreasing X−Y distance, and is consistent with the greater hydrogen-bonding ability of HF compared toHCl as the third molecule. For all complexes, the reduced X−H and X−Y spin−spin coupling constants(1KX-H and 2hKX-Y) are positive, consistent with previous studies of complexes in which X and Y are second-period elements in hydrogen-bonded dimers. 1hKH-Y is, as expected, negative in these complexes which havetraditional hydrogen bonds, except for ClH:FH:NH3 and FH:FH:NH3. In these two complexes, the F−H−Nhydrogen bond has sufficient proton-shared character to induce a change of sign in 1hKH-Y. The effects oftrimer formation on spin−spin coupling constants are markedly greater in complexes in which NH3 ratherthan PH3 is the proton acceptor.
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