Recent discoveries involving the roles of nitric oxide in humans have stimulated intense interest in transition metal nitrosyl complexes. A series of dinitrosyl iron complexes with the formula [(DPPX)Fe(NO)2], {DPPX = 1,2-bis(diphenylphosphino)benzene (1), 1,3-bis(diphenylphosphino)propane (2), and cis-1,2-bis(diphenylphosphino)ethylene (3)} has been prepared and characterized through a combination of FT-IR, NMR, UV-vis, X-ray crystallography, and electrochemical techniques. Infrared spectroscopy showed NO shifts to the region of 1723 and 1674 cm−1 for complexes 1 and 3, and 1708 and 1660 cm−1 for 2, indicating that ligand 2 acts as a stronger σ–donor. The X-ray crystallographic data showed that 1 and 3 possess the rare repulso conformation while 2 has the attracto conformation. CV studies on compounds 1, 2 and 3 display two quasi-reversible oxidations with the E°1/2 values at 0.101 and 0.186 V, 0.121 and 0.184 V, and 0.019 and 0.342 V, respectively. The larger ΔE value for compound 2 compared with that of 1 and 3 is attributed to the lack of π-bonds between the two phosphorus atoms. Theoretical calculations using density functional theory were carried out on the synthesized compounds and model compounds and the results are consistent with the experimental data. The calculated HOMO-LUMO gaps for compounds 1, 2 and 3 are 3.736, 4.060, and 3.669 eV, respectively, which supports the stronger back-donation for compound 2 than that of compounds 1 and 3.

A new potential energy surface (PES) for the atmospheric formation of sulfuric acid from OH+SO 2 is investigated using density functional theory and high-level ab initio molecular orbital theory. A pathway focused on the new PES assumes the reaction to take place between the radical complex SO 3 ·HO 2 and H 2 O. The unusual stability of SO 3 ·HO 2 is the principal basis of the new pathway, which has the same final outcome as the current reaction mechanism in the literature but it avoids the production and complete release of SO 3 . The entire reaction pathway is composed of three consecutive elementary steps: (1) HOSO 2 +O 2 →SO 3 ·HO 2 , (2) SO 3 ·HO 2 +H 2 O→SO 3 ·H 2 O·HO 2 , (3) SO 3 ·H 2 O·HO 2 →H 2 SO 4 +HO 2 . All three steps have small energy barriers, under 10 kcal/mol, and are exothermic, and the new pathway is therefore favorable both kinetically and thermodynamically. As a key step of the reactions, step (3), HO 2 serves as a bridge molecule for low-barrier hydrogen transfer in the hydrolysis of SO 3 . Two significant atmospheric implications are expected from the present study. First, SO 3 is not released from the oxidation of SO 2 by OH radical in the atmosphere. Second, the conversion of SO 2 into sulfuric acid is weakly dependent on the humidity of air.