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1. Cu( i )–O ₂ oxidation reactions in a fluorinated all-O-donor ligand environment

   https://doi.org/10.1039/C8DT05028G  

   Brazeau, Sarah E. ; Doerrer, Linda H. ( April 2019 , Dalton Transactions)

   Investigation of Cu–O 2 oxidation reactivity is important in biological and anthropogenic chemistry. Zeolites are one of the most promising Cu/O based oxidation catalysts for development of industrial-scale CH 4 to CH 3 OH conversion. Their oxidation mechanisms are not well understood, however, highlighting the importance of the investigation of molecular Cu( i )–O 2 reactivity with O-donor complexes. Herein, we give an overview of the synthesis, structural properties, and O 2 reactivity of three different series of O-donor fluorinated Cu( i ) alkoxides: K[Cu(OR) 2 ], [(Ph 3 P)Cu(μ-OR) 2 Cu(PPh 3 )], and K[(R 3 P)Cu(pin F )], in which OR = fluorinated monodentate alkoxide ligands and pin F = perfluoropinacolate. This breadth allowed for the exploration of the influence of the denticity of the ligand, coordination number, the presence of phosphine, and K⋯F/O interactions on their O 2 reactivity. K⋯F/O interactions were required to activate O 2 in the monodentate-ligand-only family, whereas these connections did not affect O 2 activation in the bidentate complexes, potentially due to the presence of phosphine. Both families formed trisanionic, trinuclear cores of the form {Cu 3 (μ 3 -O) 2 } 3− . Intramolecular and intermolecular substrate oxidation were also exploredmore »and found to be influenced by the fluorinated ligand. Namely, {Cu 3 (μ 3 -O) 2 } 3− from K[Cu(OR) 2 ] could perform both monooxygenase reactivity and oxidase catalysis, whereas those from K[(R 3 P)Cu(pin F )] could only perform oxidase catalysis.« less
2. Electronic structures and spectroscopic signatures of diiron intermediates generated by O ₂ activation of nonheme iron( ii )–thiolate complexes

   https://doi.org/10.1039/d1dt02286e  

   Ekanayake, Danushka M. ; Pham, Dao ; Probst, Andrew L. ; Miller, Joshua R. ; Popescu, Codrina V. ; Fiedler, Adam T. ( October 2021 , Dalton Transactions)

   The activation of O 2 at thiolate–ligated iron( ii ) sites is essential to the function of numerous metalloenzymes and synthetic catalysts. Iron–thiolate bonds in the active sites of nonheme iron enzymes arise from either coordination of an endogenous cysteinate residue or binding of a deprotonated thiol-containing substrate. Examples of the latter include sulfoxide synthases, such as EgtB and OvoA, that utilize O 2 to catalyze tandem S–C bond formation and S -oxygenation steps in thiohistidine biosyntheses. We recently reported the preparation of two mononuclear nonheme iron–thiolate complexes (1 and 2) that serve as structural active-site models of substrate-bound EgtB and OvoA ( Dalton Trans. 2020, 49 , 17745–17757). These models feature monodentate thiolate ligands and tripodal N 4 ligands with mixed pyridyl/imidazolyl donors. Here, we describe the reactivity of 1 and 2 with O 2 at low temperatures to give metastable intermediates (3 and 4, respectively). Characterization with multiple spectroscopic techniques (UV-vis absorption, NMR, variable-field and -temperature Mössbauer, and resonance Raman) revealed that these intermediates are thiolate-ligated iron( iii ) dimers with a bridging oxo ligand derived from the four-electron reduction of O 2 . Structural models of 3 and 4 consistent with the experimental data were generated viamore »density functional theory (DFT) calculations. The combined experimental and computational results illuminate the geometric and electronic origins of the unique spectral features of diiron( iii )-μ-oxo complexes with thiolate ligands, and the spectroscopic signatures of 3 and 4 are compared to those of closely-related diiron( iii )-μ-peroxo species. Collectively, these results will assist in the identification of intermediates that appear on the O 2 reaction landscapes of iron–thiolate species in both biological and synthetic environments.« less
3. Enabling coherent BaZrO ₃ nanorods/YBa ₂ Cu ₃ O _7−x interface through dynamic lattice enlargement in vertical epitaxy of BaZrO ₃ /YBa ₂ Cu ₃ O _7−x nanocomposites

   https://doi.org/10.1088/1361-6668/ac4aff  

   Wu, Judy Z ; Ogunjimi, Victor ; Sebastian, Mary Ann ; Zhang, Di ; Jian, Jie ; Huang, Jijie ; Zhang, Yifan ; Gautam, Bibek ; Haugan, Timothy ; Wang, Haiyan ( February 2022 , Superconductor Science and Technology)

   Abstract One-dimensional c -axis-aligned BaZrO 3 (BZO) nanorods are regarded as strong one-dimensional artificial pinning centers (1D-APCs) in BZO-doped YaBa 2 Cu 3 O 7− x (BZO/YBCO) nanocomposite films. However, a microstructure analysis has revealed a defective, oxygen-deficient YBCO column around the BZO 1D-APCs due to the large lattice mismatch of ∼7.7% between the BZO (3a = 1.26 nm) and YBCO (c = 1.17 nm), which has been blamed for the reduced pinning efficiency of BZO 1D-APCs. Herein, we report a dynamic lattice enlargement approach on the tensile strained YBCO lattice during the BZO 1D-APCs growth to induce c -axis elongation of the YBCO lattice up to 1.26 nm near the BZO 1D-APC/YBCO interface via Ca/Cu substitution on single Cu-O planes of YBCO, which prevents the interfacial defect formation by reducing the BZO/YBCO lattice mismatch to ∼1.4%. Specifically, this is achieved by inserting thin Ca 0.3 Y 0.7 Ba 2 Cu 3 O 7− x (CaY-123) spacers as the Ca reservoir in 2–6 vol.% BZO/YBCO nanocomposite multilayer (ML) films. A defect-free, coherent BZO 1D-APC/YBCO interface is confirmed in transmission electron microscopy and elemental distribution analyses. Excitingly, up to five-fold enhancement of J c ( B ) at magnetic field Bmore »= 9.0 T// c -axis and 65 K–77 K was obtained in the ML samples as compared to their BZO/YBCO single-layer (SL) counterpart’s. This has led to a record high pinning force density F p together with significantly enhanced B max at which F p reaches its maximum value F p,max for BZO 1D-APCs at B // c -axis. At 65 K, the F p,max ∼158 GN m −3 and B max ∼ 8.0 T for the 6% BZO/YBCO ML samples represent a significant enhancement over F p,max ∼ 36.1 GN m −3 and B max ∼ 5.0 T for the 6% BZO/YBCO SL counterparts. This result not only illustrates the critical importance of a coherent BZO 1D-APC/YBCO interface in the pinning efficiency, but also provides a facile scheme to achieve such an interface to restore the pristine pinning efficiency of the BZO 1D-APCs.« less
4. Thermochemical studies of reactions of Re ⁺ with SO ₂ using guided ion beam experiments and theory

   https://doi.org/10.1039/C9CP06711F  

   Kim, JungSoo ; M Cox, Richard ; Armentrout, P. B. ( February 2020 , Physical Chemistry Chemical Physics)

   The kinetic energy dependent reactions of Re + with SO 2 were studied with guided ion beam tandem mass spectrometry. ReO + , ReO 2 + , and OReS + species were observed as products, all in endothermic reactions. Modeling of the kinetic energy dependent cross sections yields 0 K bond dissociation energies (BDEs, in eV) of 4.78 ± 0.06 (Re + –O), 5.75 ± 0.02 (Re + –O 2 ), and 4.35 ± 0.14 (Re + –SO). The latter two values can be combined with other information to derive the additional values 6.05 ± 0.05 (ORe + –O) and 4.89 ± 0.19 (ORe + –S). BDEs of ReO + and ReO 2 + agree with literature values whereas the values for OReS + are the first measurements. The former result is obtained even though formation of ground state ReO + is spin-forbidden. Quantum mechanical calculations at the B3LYP level of theory with a def2-TZVPPD basis set yield results that agree reasonably well with experimental values. Additional calculations at the BP86 and CCSD(T) levels of theory using def2-QZVPPD and aug-cc-pVxZ (x = T, Q, and 5) basis sets were performed to compare thermochemistry with experiment to determine that ReO 2more »+ rather than the isobaric ReS + is formed. Product ground states are 3 Δ 3 (ReO + ), 3 B 1 (OReO + ), 5 Π −1 (ReS + ), and 3 A′′(OReS + ) after including empirical spin–orbit corrections, which means that formation of ground state products is spin-forbidden for all three product channels. The potential energy surfaces for the ReSO 2 + system were also explored at the B3LYP/def2-TZVPPD level and exhibited no barriers in excess of the endothermicities for all products. BDEs for rhenium oxide and sulfide diatomics and triatomics are compared and discussed. The present result for formation of ReO + is compared to that for formation of ReO + in the reactions of Re + + O 2 and CO, where the former system exhibited interesting dual cross section features. Results are consistent with the hypothesis that the distinction of in-plane and out-of-plane C S symmetry in the triatomic systems might be the explanation for the two endothermic features observed in the Re + + O 2 reaction.« less
5. Synthesis, characterization, and alkoxide transfer reactivity of dimeric Tl ₂ (OR) ₂ complexes

   https://doi.org/10.1039/d0dt03917a  

   Grass, Amanda ; Kulathungage, Lakshani Wathsala ; Wannipurage, Duleeka ; Yousif, Maryam ; Ward, Cassandra L. ; Groysman, Stanislav ( February 2021 , Dalton Transactions)

   Reaction of LiOC t Bu 2 Ph with TlPF 6 forms the dimeric Tl 2 (OC t Bu 2 Ph) 2 complex, a rare example of a homoleptic thallium alkoxide complex demonstrating formally two-coordinate metal centers. Characterization of Tl 2 (OC t Bu 2 Ph) 2 by 1 H and 13 C NMR spectroscopy and X-ray crystallography reveals the presence of two isomers differing by the mutual conformation of the alkoxide ligands, and by the planarity of the central Tl–O–Tl–O plane. Tl 2 (OC t Bu 2 Ph) 2 serves as a convenient precursor to the formation of old and new [M(OC t Bu 2 Ph) n ] complexes (M = Cr, Fe, Cu, Zn), including a rare example of T-shaped Zn(OC t Bu 2 Ph) 2 (THF) complex, which could not be previously synthesized using more conventional LiOR/HOR precursors. The reaction of [Ru(cymene)Cl 2 ] 2 with Tl 2 (OC t Bu 2 Ph) 2 results in the formation of a ruthenium( ii ) alkoxide complex. For ruthenium, the initial coordination of the alkoxide triggers C–H activation at the ortho -H of [OC t Bu 2 Ph] which results in its bidentate coordination. In addition to Tl 2 (OCmore »t Bu 2 Ph) 2 , related Tl 2 (OC t Bu 2 (3,5-Me 2 C 6 H 3 )) 2 was also synthesized, characterized, and shown to exhibit similar reactivity with iron and ruthenium precursors. Synthetic, structural, and spectroscopic characterizations are presented.« less