Long‐range π‐type hydrogen bond in dimers CH 2 HF, CH 2 OH 2 O, and CH 2 ONH 3

Using four basis bets, (6‐311G( d , p ), 6‐31+G( d , p ), 6‐31++G(2 d ,2 p ), and 6‐311++G(3 df ,3 pd ), the optimized structures with all real frequencies were obtained at the MP2 level for the dimers CH 2 OHF, CH 2 OH 2 O, CH 2 ONH 3 , and CH 2 OCH 4 . The structures of CH 2 OHF, CH 2 OH 2 O, and CH 2 ONH 3 are cycle‐shaped, which result from the larger bend of σ‐type hydrogen bonds. The bend of σ‐type H‐bond O…HY (YF, O, N) is illustrated and interpreted by an attractive interaction of a chemically intuitive π‐type hydrogen bond. The π‐type hydrogen bond is the interaction between one of the H atoms of CH 2 O and lone pair(s) on the F atom in HF, the O atom in H 2 O, or the N atom in NH 3 . In contrast with the above three dimers, for CH 2 OCH 4 , because there is not a π‐type hydrogen bond to bend its linear hydrogen bond, the structure of CH 2 OCH 4 is noncyclic shaped. The interaction energy of hydrogen bonds and the π‐type H‐bond are calculated and discussed at the CCSD (T)/6‐311++G(3 df ,3 pd ) level. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005