198083-48-6Relevant articles and documents
Five-coordinate complexes [FeX(depe)2]BPh4, X = Cl, Br: Electronic structure and spin-forbidden reaction with N2
Franke, Oliver,Wiesler, Beatrix E.,Lehnert, Nicolai,Naether, Christian,Ksenofontov, Vadim,Neuhausen, Joerg,Tuczek, Felix
, p. 3491 - 3499 (2002)
The bonding of N2 to the five-coordinate complexes [FeX(depe)2]+, X = Cl (1a) and Br (1b), has been investigated with the help of X-ray crystallography, spectroscopy, and quantum-chemical calculations. Complexes 1a and 1b are found to have an XP4 coordination that is intermediate between square-pyramidal and trigonal-bipyramidal. Moessbauer and optical absorption spectroscopy coupled with angular overlap model (AOM) calculations reveal that 1a and 1b have 3B1 ground states deriving from a (xz)1(Z2)1 configuration. The zero-field splitting for this state is found to be 30-35 cm-1. In contrast, the analogous dinitrogen complexes [FeX(N2)(depe)2]+, X = Cl (2a) and Br (2b), characterized earlier are low-spin (S = 0; Wiesler, B. E.; Lehnert, N.; Tuczek, F.; Neuhausen, J.; Tremel, W. Angew. Chem, Int. Ed. 1998, 37, 815-817). N2 bonding and release in these systems are thus spin-forbidden. It is shown by density functional theory (DFT) calculations of the chloro complex that the crossing from the singlet state (ground state of 2a) to the triplet state (ground state of la) along the Fe-N coordinate occurs at rc = 2.4 A. Importantly, this intersystem crossing lowers the enthalpy calculated for N2 release by 10-18 kcal/mol. The free reaction enthalpy ΔG° for this process is calculated to be 4.7 kcal/mol, which explains the thermal instability of N2 complex 2a with respect to the loss of N2. The differences in reactivity of analogous trans hydrido systems are discussed.
