Early atomic transition metal cations reacting with ammonia at room temperature: H2 elimination and NH3 ligation kinetics across and down the periodic table

The kinetics of H-2 elimination and ligation of ammonia reacting with early atomic transition metal cations and ensuing ammonia ligation reactions were measured across (Groups 3-9) and down (the three rows) the periodic table. The atomic cations were produced in an Inductively Coupled Plasma (ICP) source at ca. 5500 K and allowed to decay radiatively and to thermalize by collisions with argon and helium atoms prior to reaction. Kinetic measurements were performed using an ICP/Selected-Ion Flow Tube (ICP/SIFT) tandem mass spectrometer with helium bath gas at 0.35 Torr and 295 +/- 2 K. Our survey showed that bimolecular H-2 elimination to produce MNH+ predominated with very early atomic transition metal cations: M+ = Sc+ and Ti+ in the first row, Y+, Zr+ and Nb+ in the second row, and La+, Hf+,Ta+, W+, Os+ and Ir+ in the third row. The remaining atomic transition metal cations were observed to ligate ammonia (with He acting as a third body): M+ =V+, Cr+, Mn+, Fe+ and Co+ in the first row, Mo+, Ru+ and Rh+ in the second row, and Re+ and Ir+ in the third row. Higher order ligation reactions were observed with M+ to form M+(NH3)(n) with n up to 6 and MNH+(NH3)(n) with n up to 3. Experiments with three of the 3rd row MNH+ cations (M =Ta+, W+, and Os+) revealed the rapid formation of a second imido bond to produce M(NH)(2)(+) followed by ammonia ligation. Variations in the occurrence of imido bond formation and the extent of ligation and trends in measured rate coefficients are scrutinized across and down the periodic table in terms of available theoretical computations of potential energy surfaces as well as atomic orbital filling effects. (C) 2018 Elsevier B.V. All rights reserved.