Gas-phase properties and fragmentation behavior of cationic, dinuclear iron chloride clusters Fe(2)Cl(n)()(+) (n = 1-6).

Sector-field mass spectrometry is used to probe the fragmentation patterns of cationic dinuclear iron chloride clusters Fe(2)Cl(n)()(+) (n = 1-6). For the chlorine-rich, high-valent Fe(2)Cl(n)()(+) ions (n = 4-6), losses of atomic and molecular chlorine prevail in the unimolecular and collision-induced dissociation patterns. Instead, the chlorine deficient, formally low-valent Fe(2)Cl(n)()(+) clusters (n = 1-3) preferentially undergo unimolecular degradation to mononuclear FeCl(m)()(+) ions. In addition, photoionization is used to determine IE(Fe(2)Cl(6)) = 10.85 +/- 0.05 eV along with appearance energy measurements for the production of Fe(2)Cl(5)(+) and Fe(2)Cl(4)(+) cations from iron(III) chloride vapor. The combination of the experimental results allows an evaluation of some of the thermochemical properties of the dinuclear Fe(2)Cl(n)()(+) cations: e.g., Delta(f)H(Fe(2)Cl(+)) = 232 +/- 15 kcal/mol, Delta(f)H(Fe(2)Cl(2)(+)) = 167 +/- 4 kcal/mol, Delta(f)H(Fe(2)Cl(3)(+)) = 139 +/- 4 kcal/mol, Delta(f)H(Fe(2)Cl(4)(+)) = 113 +/- 4 kcal/mol, Delta(f)H(Fe(2)Cl(5)(+)) = 79 +/- 5 kcal/mol, and Delta(f)H(Fe(2)Cl(6)(+)) = 93 +/- 2 kcal/mol. The analysis of the data suggests that structural effects are more important than the formal valency of iron as far as the Fe-Cl bond strengths in the Fe(2)Cl(n)()(+) ions are concerned.