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2 Polish Journal of Chemistry

2 2009

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Diazene, a Potential New Hydrogen Bond Donor and Acceptor with Blue-Shifted N-H Stretching Modes: A Theoretical Study

Karpfen A., Liedl E., Wolschann P.

Polish Journal of Chemistry

2009

Vol. 83, nr 5

933-942

The structure and vibrational spectra of hydrogen-bonded complexes formed between trans-HNNH (diazene or diimide) and the fluoromethanes CH3F, CH2F2, and CHF3 are stud ied at the MP2/6-311++G(2d,2p) level. For each fluoromethane, complex structures were detected in which diazene plays either the role of a hydrogen bond do nor or a hydrogen bond acceptor. In addition to the well-known blue shifts of the fluoromethane C–H stretch ing frequencies, blue-shifted N–H stretching frequencies are predicted for the diazene molecule, irrespective of whether HNNH acts as do nor or acceptor. It is shown that this finding can be interpreted as a consequence of the negative intramolecular coupling (NIC) between N–N and N–H stretching degrees of free domin the isolated HNNH molecule which, upon complex formation, leads to a negative intramolecular response (NIR)

Blue and Red Frequency Shift Effects Related with XA–H...B-Y Complex Formation

Rutkowski K. S., Karpfen A., Melikova S. M., Rodziewicz P.

Polish Journal of Chemistry

2009

Vol. 83, nr 5

965-980

Results of FTIR spectroscopic measurements in cryosolutions and ab initio calculations performed for a set of complexes stabilized by conventional and “im proper” H-bonds have been presented and analyzed. The main attention is paid to the blue and red frequency shift effects on the stretching vibrations which were ob served/or predicted for complexes of a weak to medium strength, formed between so called CH acids and various electron donor counter parts. It has been shown that the features of the dipole moment function and the type of intramolecular coupling between the vicinal bonds of the inter acting counter parts predefine in the most extent the sign of the frequency shift of respective stretching vibrations.