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A novel Cr II -dimeric complex, [Cr II N(Si i Pr 3 ) 2 (μ-Cl)(THF)] 2 ( 1 ), has been successfully constructed using a bulky silyl-amide ligand. Single-crystal structure analysis reveals that complex 1 exhibits a binuclear motif, with a Cr 2 Cl 2 rhombus core, where two equivalent tetra-coordinate Cr II centers in the centrosymmetric unit display quasi-square planar geometry. The crystal structure has been well simulated and explored by density functional theory calculations. The axial zero-field splitting parameter ( D < 0) with a small rhombic ( E ) value is unambiguously determined by systematic investigations of magnetic measurements, high-frequency electron paramagnetic resonance spectroscopy, and ab initio calculations. Remarkably, ac magnetic susceptibility data unveil that 1 features slow dynamic magnetic relaxation typical of single-molecule magnet behavior with U eff = 22 K in the absence of a dc field. This increases up to 35 K under a corresponding static field. Moreover, magnetic studies and theoretical calculations point out that a non-negligible ferromagnetic coupling (FMC) exists in the dimeric Cr-Cr units of 1 . The coexistence of magnetic anisotropy and FMC contributes to the first case of Cr II -based single-molecule magnets (SMMs) under zero dc field.

The hydrolysis of CH 2 OO is not only a dominant sink for the CH 2 OO intermediate in the atmosphere but also a key process in the formation of aerosols. Herein, the reaction mechanism and kinetics for the hydrolysis of CH 2 OO catalyzed by the precursors of atmospheric aerosols, including H 2 SO 4 , H 2 SO 4 ···H 2 O, and (H 2 SO 4 ) 2 , have been studied theoretically at the CCSD(T)-F12a/cc-pVDZ-F12//B3LYP/6-311+G(2 df ,2 pd ) level. The calculated results show that the three catalysts decrease the energy barrier by over 10.3 kcal·mol -1 ; at the same time, the product formation of HOCH 2 OOH is more strongly bonded to the three catalysts than to the reactants CH 2 OO and H 2 O, revealing that small clusters of sulfuric acid promote the hydrolysis of CH 2 OO both kinetically and thermodynamically. Kinetic simulations show that the H 2 SO 4 -assisted reaction is more favorable than the H 2 SO 4 ···H 2 O- (the pseudo-first-order rate constant being 27.9-11.5 times larger) and (H 2 SO 4 ) 2 - (between 2.8 × 10 4 and 3.4 × 10 5 times larger) catalyzed reactions. Additionally, due to relatively lower concentration of H 2 SO 4 , the hydrolysis of CH 2 OO with H 2 SO 4 cannot compete with the CH 2 OO + H 2 O or (H 2 O) 2 reaction within the temperature range of 280-320 K, since its pseudo-first-order rate ratio is smaller by 4-7 or 6-8 orders of magnitude, respectively. However, the present results provide a good example of how small clusters of sulfuric acid catalyze the hydrolysis of an important atmospheric species.

The H 2 O 2 + HO → HO 2 + H 2 O reaction is an important reservoir for both radicals of HO and HO 2 catalyzing the destruction of O 3 . Here, this reaction assisted by NH 3 and HCOOH catalysts was explored using the CCSD(T)-F12a/cc-pVDZ-F12//M06-2X/aug-cc-pVTZ method and canonical variational transition state theory with small curvature tunneling. Two possible sets of mechanisms, (i) one-step routes and (ii) stepwise processes, are possible. Our results show that in the presence of both NH 3 and HCOOH catalysts under relevant atmospheric temperature, mechanism (i) is favored both energetically and kinetically than the corresponding mechanism (ii). At 298 K, the relative rate for mechanism (i) in the presence of NH 3 (10, 2900 ppbv) and HCOOH (10 ppbv) is respectively 3-5 and 2-4 orders of magnitude lower than that of the water-catalyzed reaction. This is due to a comparatively lower concentration of NH 3 and HCOOH than H 2 O which indicates the positive water effect under atmospheric conditions. Although NH 3 and HCOOH catalysts play a negligible role in the reservoir for both radicals of HO and HO 2 catalyzing the destruction of O 3 , the current study provides a comprehensive example of how acidic and basic catalysts assisted the gas-phase reactions., Competing Interests: The authors declare no competing financial interest., (This journal is © The Royal Society of Chemistry.)

This paper determined the delta 13C annual series of three Cryptomeria fortunei tree rings at West Tianmu Mountain, and analyzed their similarities and differences. In the period of 1837 to approximately 1982, the correlations among the three delta 13C series were significant, with r12 = 0.47, r13 = 0.65 and r23 = 0.52 (P < 0.001, n = 146), respectively. After removing the high-frequencies from the original delta 13C series by using polynomial function model, a significant correlation was observed among three low-frequencies, with the correlation coefficient varied from 0. 95 to 0.998. A significant correlation was also observed between original low-frequencies and simulated high-frequencies, with the correlation coefficient being 0.79 to approximately 0.84. The three delta 13C annual series had similar high-frequency and low-frequency variations. High-frequency variation recorded similar climate variation information, while low-frequency reflected the information of atmospheric CO2 changes. It was the common case for different individuals of trees that in the three delta 13C annual series, climatic factors caused high-frequency change, while atmospheric CO2 concentration caused low-frequency variation. The differences among the three delta 13C annual series were mainly caused by the local environmental conditions at the growth sites of trees, while the individual difference among the three delta 13C series caused by local environmental conditions had very small effects on the changes of the three delta 13C series. It could be concluded that the differences among the three delta 13C series did not affect the suitability of using tree ring's delta 13C annual series as the indirect evidence in climatic variation study, and the reliability and coherence of reconstructing historical climate changes.