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  1. Free, publicly-accessible full text available November 13, 2024
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  3. Solid-state photoreactions are generally controlled by the rigid and ordered nature of crystals. Herein, the solution and solid-state photoreactivities of carbonylbis(4,1-phenylene)dicarbonazidate (1) were investigated to elucidate the solid-state reaction mechanism. Irradiation of 1 in methanol yielded primarily the corresponding amine, whereas irradiation in the solid state gave a mixture of photoproducts. Laser flash photolysis in methanol showed the formation of the triplet ketone (TK) of 1 (τ ∼ 99 ns), which decayed to triplet nitrene 31N (τ ∼ 464 ns), as assigned by comparison to its calculated spectrum. Laser flash photolysis of a nanocrystalline suspension and diffuse reflectance laser flash photolysis also revealed the formation of TK of 1 (τ ∼ 106 ns) and 31N (τ ∼ 806 ns). Electron spin resonance spectroscopy and phosphorescence measurements further verified the formation of 31N and the TK of 1, respectively. In methanol, 31N decays by H atom abstraction. However, in the solid state, 31N is sufficiently long lived to thermally populate its singlet configuration (11N). Insertion of 11N into the phenyl ring to produce oxazolone competes with 31N cleavage to form a radical pair. Notably, 1 did not exhibit photodynamic behavior, likely because the photoreaction occurs only on the crystal surfaces. 
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    Free, publicly-accessible full text available November 8, 2024
  4. This work centers around the nickel complexes derived from two tetrahydrosalen-type proligands: N , N ′-bis(2-hydroxybenzyl)- o -phenylenediamine (H 2 salophan) and N , N ′-bis(2-hydroxy-3-methylbenzyl)- o -phenylenediamine (H 2 salophan_Me). The reaction of H 2 salophan with Ni(OAc) 2 ·4H 2 O generates a dinuclear complex Ni 2 (Hsalophan) 2 (OAc) 2 or Na[Ni 2 (salophan) 2 (OAc)] when NaOH is added to assist ligand deprotonation. The reaction of H 2 salophan_Me with Ni(OAc) 2 ·4H 2 O, however, yields a mononuclear complex Ni(Hsalophan_Me) 2 . Unlike the corresponding salen-type nickel complexes, these tetrahydrosalen-type complexes are paramagentic and air sensitive (in solution). Oxidation by O 2 or peroxides results in dehydrogenation of the ligand backbone to form the salen-type complexes. 
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    Free, publicly-accessible full text available August 22, 2024
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  8. Ethylene cross-bridged tetraazamacrocycles are known to produce kinetically stable transition metal complexes that can act as robust oxidation catalysts under harsh aqueous conditions. We have synthesized ligand analogs with single acetate pendant arms that act as pentadentate ligands to Mn, Fe, Co, Ni, Cu, and Zn. These complexes have been synthesized and characterized, including the structural characterization of four Co and Cu complexes. Cyclic voltammetry demonstrates that multiple oxidation states are stabilized by these rigid, bicyclic ligands. Yet, redox potentials of the metal complexes are modified compared to the “parent” ligands due to the pendant acetate arm. Similarly, gains in kinetic stability under harsh acidic conditions, compared to parent complexes without the pendant acetate arm, were demonstrated by a half-life seven times longer for the cyclam copper complex. Due to the reversible, high oxidation states available for the Mn and Fe complexes, the Mn and Fe complexes were examined as catalysts for the bleaching of three commonly used pollutant model dyes (methylene blue, methyl orange, and Rhodamine B) in water with hydrogen peroxide as oxidant. The efficient bleaching of these dyes was observed. 
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