OHO]− and +[NHO]− hydrogen bonds in the 2:1 adduct of pentachlorophenol with 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene [(PCP)2·MTBD

Abstract

The results of X-ray diffraction and IR spectroscopic studies for 2:1 pentachlorophenol-7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene [(PCP)2·MTBD] adduct are reported. The geometry of MTBD cations reflects the equal distribution of the positive charge among three nitrogen atoms. Short asymmetric [OHO]− hydrogen bonds with O⋯O distance of 2.508(2)Å and NH+⋯O− hydrogen bonds with N⋯O distance of 2.802(2)Å are formed showing broad IR absorption with two maxima located at ∼1200 and ∼2400cm−1. The second maximum is interpreted as due to the 0→2 transition between split levels in an asymmetric double minimum potential. One of the oxygen atoms forms an additional O⋯H–N+ hydrogen bonding with an MTBD cation. The situation is somewhat different in acetonitrile solution whose IR spectrum shows continuous absorption extended over whole the IR region. In acetonitrile, dissociation to free OHO− and +NH ions takes place and the OHO− bridges become dynamically symmetric. The broadening is interpreted in terms of a stochastic distribution of the geometry and the Zundel polarizability theory.