LIGAND EFFECTS IN ORGANOMETALLIC THERMOCHEMISTRY - THE SEQUENTIAL BOND-ENERGIES OF NI(CO)(X)(+) AND NI(N-2)(X)(+) (X=1-4) AND NI(NO)(X)(+) (X=1-3)

The sequential bond energies of Ni(CO)(x)(+) and Ni(N-2)(x)(+) (X = 1-4) and Ni(NO)(x)(+) (x = 1-3) are determined by collision-induced dissociation in a guided ion beam tandem mass spectrometer. Values for the 0 K (CONi+-CO bond energies (in eV) are found to be 1.81 +/- 0.11, 1.74 +/- 0.11, 0.95 +/- 0.06, and 0.75 +/- 0.03 for x = 1-4, respectively. The sum of these bond energies, 5.25 +/- 0.17 eV, is in excellent agreement with literature thermochemistry, but individual BDEs disagree with values obtained in photoionization and electron impact ionization experiments. We also observe electronically excited Ni(CO)(2)(+) and NiCO+. We also report the following gas-phase bond energies (in eV at 0 K): 1.15 +/- 0.11, 1.15 +/- 0.11, 0.58 +/- 0.04, and 0.44 +/- 0.10 for (N-2Ni+-N-2 (X = 1-4), respectively, and 2.36 +/- 0.08, 1.27 +/- 0.07, and 1.19 +/- 0.05 for (NONi+-NO (x = 1-3), respectively. The trends in these bond energies are discussed in terms of sigma-donor and pi-acceptor capabilities of the ligands.