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High-resolution X-ray diffraction experiments, theoretical calculations and atom-specific X-ray absorption experiments were used to investigate two nickel complexes, (MePh 3 P) 2 [Ni II (bdtCl 2 ) 2 ]·2(CH 3 ) 2 SO [complex (1)] and (MePh 3 P)[Ni III (bdtCl 2 ) 2 ] [complex (2)]. Combining the techniques of nickel K - and sulfur K -edge X-ray absorption spectroscopy with high-resolution X-ray charge density modeling, together with theoretical calculations, the actual oxidation states of the central Ni atoms in these two complexes are investigated. Ni ions in two complexes are clearly in different oxidation states: the Ni ion of complex (1) is formally Ni II ; that of complex (2) should be formally Ni III , yet it is best described as a combination of Ni 2+ and Ni 3+ , due to the involvement of the non-innocent ligand in the Ni— L bond. A detailed description of Ni—S bond character (σ,π) is presented. 

Abstract A porous molecular crystal (PMC) assembled by macrocyclic cyclotetrabenzoin acetate is an efficient adsorbent for CO₂separations. The 7.1×7.1 Å square pore of PMC and its ester C=O groups play important roles in improving its affinity for CO₂molecules. The benzene walls of macrocycle engage in an apparent [π⋅⋅⋅π] interaction with the molecule of CO₂at low pressure. In addition, the polar carbonyl groups pointing inward the square channels reduce the size of aperture to a 5.0×5.0 Å square, which offers kinetic selectivity for CO₂capture. The PMC features water tolerance and high structural stability under vacuum and various gas adsorption conditions, which are rare among intrinsically porous organic molecules. Most importantly, the moderate adsorbate‐adsorbent interaction allows the PMC to be readily regenerated, and therefore applied to pressure swing adsorption processes. The eluted N₂and CH₄are obtained with over 99.9 % and 99.8 % purity, respectively, and the separation performance is stable for 30 cycles. Coupled with its easy synthesis, cyclotetrabenzoin acetate is a promising adsorbent for CO₂separations from flue and natural gases.