Gas-phase reactions of lanthanum dication with small alkanes and the photodissociation of LaC2H4n+ and LaC3H6n+ (n = 1 and 2)

Abstract

The gas-phase reactivity of La{sup 2+} with C{sub 1}-C{sub 4} linear alkanes is investigated and compared to the analogous reactions of La{sup +}. La{sup 2+} is unreactive with methane and ethane but reacts with propane and butane to give dehydrogenation, alkane loss, and for butane charge-splitting reaction products. Interestingly, charge transfer is not observed in agreement with a simple curve-crossing model. Four ligated species, namely, LaC{sub 2}H{sub 4}{sup +}, LaC{sub 2}H{sub 4}{sup 2+}, LaC{sub 3}H{sub 6}{sup +}, and LaC{sub 3}H{sub 6}{sup 2+}, are photodissociated and the photodissociation thresholds are used directly, or together with information from ligand displacement reactions, to assign thermochemical values for these processes and metal ligand bond energies. The bonding properties of LaC{sub 2}H{sub 2}{sup +} and LaC{sub 2}H{sub 2}{sup 2+} are also investigated. A surprising outcome of this study is that the monocation is in some cases more strongly bound to these ligands than the dication. Theoretical calculations by Bauschlicher and co-workers are in good agreement with these results. 28 refs., 6 figs., 5 tabs.