Infrared multiphoton chemistry of transition metal/ethanol ion complexes

A detailed study has been undertaken of the infrared multiphoton chemistry of complexes of the general form M+(C2H5OH)(n), where M is chromium, mangan ese, iron, cobalt, or nickel and n is either 1 or 2. The ions have been pre pared via ligand stripping from volatile metal-carbonyl compounds and held in an ion trap, where photofragment intensities have been recorded as a fun ction of CO2 laser frequency by using radiation from a line-tuneable laser. All the metal complexes exhibit structured photofragmentation patterns as a function of laser frequency, and the results are consistent with the abso rber being an adduct of M+ bonded to ethanol via ion-dipole and -induced di pole interactions. For the metals Fe, Ni, and Co, photoexcitation of the co mplex promotes a dehydration reaction, whereas for Mn and Cr, the metal ion -ethanol bond is broken upon photoexcitation. In association with iron, the efficiency of the photoexcitation process is very dependent upon isotopic substitution, and the relative intensities of H2O, DHO, and D2O from comple xes composed of mixtures of isotopomers show evidence of both primary and s econdary isotope effects. Overall, the results show a strong correlation be tween the reaction pathway of an ion complex and the electronic spin config uration of the metal ions concerned. Those metal ions that are in low spin states with no 4s electrons are found to exhibit the dehydration reaction.