Solvation of Yttrium with Ammonia: An Experimental and Theoretical Study

The reactivity of the yttrium atom toward ammonia at room temperature has been investigated in a fast-flow reactor. The first step in the reaction is the rapid formation of yttrium imide (YNH) through the oxidative addition of the N-H bond of ammonia and the elimination of molecular hydrogen. The reaction continues with the solvation of yttrium imide with up to three molecules of ammonia. An equilibrium is established between the YNH(NH3)2 and YNH(NH3)3 species. The binding energy of NH3 in the YNH(NH3)3 complex is found to be 19.7 ? 0.3 kcal/mol. Reaction rates have been determined for the solvation processes. Density functional calculations indicate that up to four ammonia molecules can bind to YNH at 0 K. The calculated De is highest for the YNH-NH3 complex and decreases abruptly following the addition of the third ammonia molecule. The calculated binding energy of the YNH(NH3)3 complex is 12 kcal/mol, in fair agreement with experiment. The YNH(NH3)4 complex is too weakly bound to be observed in our experiment. The structures of the complexes have been determined through full geometry optimizations. A molecular orbital analysis indicates that ammonia molecules are ligated to the positive end (Y) of the large dipole of YNH through dipole-dipole interactions and dative bond formation. The singly occupied sp hybrid on Y forces the ammonia molecules to bind side-on to Y.Peer reviewed: YesNRC publication: Ye