Formation of van der Waals complexes between allene and HCl in cryosolutions. An IR and ab initio study

The mid-IR spectra of mixtures of allene (C3H4) and hydrogen chloride, diss olved in liquid argon (LAr) and in liquid nitrogen (LN2), have been investi gated between 98 and 120 K. They show that a 1 : 1 complex C3H4 . HCl and a 1 : 2 complex C3H4 . (HCl)(2) are formed in LAr, while only the 1 : 1 comp lex was detected in LN2. The complexation enthalpies for the 1 : 1 complex were determined to be - 6.4(3) kJ mol(-1) (LAr) and -5.1(4) kJ mol(-1) (LN2 ), while for the 1 : 2 complex a value of -14.6(6) kJ mol(-1) (LAr) was der ived. Ab initio calculations, at the MP2/6-31 + G(d,p) level, of structures and IR spectra of monomers and complexes were made. Comparison with the ex perimental spectra shows that the 1 : 2 complex has a chain structure, in w hich the second HCl molecule is bonded to the chlorine atom of the first.