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1. Electronic structure of cobalt valence tautomeric molecules in different environments

   https://doi.org/10.1039/d2nr06834f  

   Mishra, Esha ; Ekanayaka, Thilini K. ; Panagiotakopoulos, Theodoros ; Le, Duy ; Rahman, Talat S. ; Wang, Ping ; McElveen, Kayleigh A. ; Phillips, Jared P. ; Zaid Zaz, M. ; Yazdani, Saeed ; et al ( January 2022 , Nanoscale)

   Future molecular microelectronics require the electronic conductivity of the device to be tunable without impairing the voltage control of the molecular electronic properties. This work reports the influence of an interface between a semiconducting polyaniline polymer or a polar poly-D-lysine molecular film and one of two valence tautomeric complexes, i.e. , [Co III (SQ)(Cat)(4-CN-py) 2 ] ↔ [Co II (SQ) 2 (4-CN-py) 2 ] and [Co III (SQ)(Cat)(3-tpp) 2 ] ↔ [Co II (SQ) 2 (3-tpp) 2 ]. The electronic transitions and orbitals are identified using X-ray photoemission, X-ray absorption, inverse photoemission, and optical absorption spectroscopy measurements that are guided by density functional theory. Except for slightly modified binding energies and shifted orbital levels, the choice of the underlying substrate layer has little effect on the electronic structure. A prominent unoccupied ligand-to-metal charge transfer state exists in [Co III (SQ)(Cat)(3-tpp) 2 ] ↔ [Co II (SQ) 2 (3-tpp) 2 ] that is virtually insensitive to the interface between the polymer and tautomeric complexes in the Co II high-spin state.
2. Magnetic anisotropy and slow magnetic relaxation processes of cobalt( ii )-pseudohalide complexes

   https://doi.org/10.1039/C9DT00644C  

   Cui, Hui-Hui ; Zhang, Yi-Quan ; Chen, Xue-Tai ; Wang, Zhenxing ; Xue, Zi-Ling ( January 2019 , Dalton Transactions)

   Three mononuclear six-coordinate Co( ii )-pseudohalide complexes [Co(L)X 2 ] with two N-donor pseudohalido coligands occupying the cis -positions (X = NCS − ( 1 ), NCSe − ( 2 ) or N(CN) 2 − ( 3 )), and a five-coordinate complex [Co(L)(NCO)][B(C 6 H 5 ) 4 ] ( 4 ) [L = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane (12-TMC)] have been prepared and structurally characterized. Easy-plane magnetic anisotropy for 1–3 and easy-axis anisotropy for 4 were revealed via the analyses of the direct-current magnetic data, high-frequency and -field EPR (HFEPR) spectra and ab initio theoretical calculations. They display slow magnetic relaxations under an external applied dc field. Typically, two slow relaxation processes were found in 1 and 2 while only one relaxation process occurs in 3 and 4 . The Raman-like mechanism is found to be dominant in the studied temperature range in 1 . For 2–4 , the Raman process is dominant in the low temperature region, while the Orbach mechanism dominates in the high temperature range.
3. Geometrical control of the magnetic anisotropy in six coordinate cobalt complexes

   https://doi.org/10.1039/D0CC03238G  

   Saber, Mohamed R. ; Singh, Mukesh K. ; Dunbar, Kim R. ( July 2020 , Chemical Communications)

   The geometry of cobalt( ii ) ions in the axially distorted octahedral cation in [Co(MeCN) 6 ](BF 4 ) 2 ( 1 ) was compared to the trigonal prismatic cation in [CoTp py ]PF 6 ( 2 ) which revealed significant differences in magnetic anisotropy. Combined experimental and ab initio CASSCF/NEVPT2 calculations support the observed zero field SMM behaviour for 2 , with easy axis anisotropy, attributed to the rigidity of the trigonal prismatic ligand. Strong transverse anisotropy for 1 leads to significant quantum tunnelling processes.
4. Exchange-biased quantum tunnelling of magnetization in a [Mn ₃ ] ₂ dimer of single-molecule magnets with rare ferromagnetic inter-Mn ₃ coupling

   https://doi.org/10.1039/d0cp06611g  

   Ghosh, Tuhin ; Marbey, Jonathan ; Wernsdorfer, Wolfgang ; Hill, Stephen ; Abboud, Khalil A. ; Christou, George ( April 2021 , Physical Chemistry Chemical Physics)

   A covalently-linked dimer of two single-molecule magnets (SMMs), [Mn 6 O(O 2 CMe) 6 (1,3-ppmd) 3 ](ClO 4 ) 2 , has been synthesized from the reaction of [Mn 3 O(O 2 CMe) 6 (py) 3 ](ClO 4 ) with 1,3-phenylene- bis (pyridin-2-ylmethanone) dioxime (1,3-ppmdH 2 ). It contains two [Mn III 3 O] +7 triangular units linked by three 1,3-ppmd 2− groups into an [Mn 3 ] 2 dimer with D 3 symmetry. Solid-state dc and ac magnetic susceptibility measurements showed that each Mn 3 subunit retains its properties as an SMM with an S = 6 ground state. Magnetization vs. dc field sweeps on a single crystal reveal hysteresis loops below 1.3 K exhibiting exchange-biased quantum tunnelling of magnetization (QTM) steps with a bias field of +0.06 T. This is the first example of a dimer of SMMs showing a positive exchange bias of the QTM steps in the hysteresis loops, and it has therefore been subjected to a detailed analysis. Simulation of the loops determines that each Mn 3 unit is exchange-coupled with its neighbour primarily through the 1,3-ppmd 2− linkers, confirming a weak ferromagnetic inter-Mn 3 interaction of J 12 ≈ +6.5 mK ( Ĥ =more »−2 JŜ i · Ŝ j convention). High-frequency EPR studies of a microcrystalline powder sample enable accurate determination of the zero-field splitting parameters of the uncoupled Mn 3 SMMs, while also confirming the weak exchange interaction between the two SMMs within each [Mn 3 ] 2 dimer. The combined results emphasize the ability of designed covalent linkers to generate inter-SMM coupling of a particular sign and relative magnitude, and thus the ability of such linkers to modulate the quantum physics. As such, this work supports the feasibility of using designed covalent linkers to develop molecular oligomers of SMMs, or other magnetic molecules, as multi-qubit systems and/or other components of new quantum technologies.« less
5. Determining the coordination environment and electronic structure of polymer-encapsulated cobalt phthalocyanine under electrocatalytic CO ₂ reduction conditions using in situ X-Ray absorption spectroscopy

   https://doi.org/10.1039/D0DT01288B  

   Liu, Yingshuo ; Deb, Aniruddha ; Leung, Kwan Yee ; Nie, Weixuan ; Dean, William S. ; Penner-Hahn, James E. ; McCrory, Charles C. ( January 2020 , Dalton Transactions)

   Encapsulating cobalt phthalocyanine (CoPc) within the coordinating polymer poly-4-vinylpyridine (P4VP) results in a catalyst–polymer composite (CoPc–P4VP) that selectively reduces CO 2 to CO at fast rates at low overpotential. In previous studies, we postulated that the enhanced selectively for CO over H 2 production within CoPc–P4VP compared to the parent CoPc complex is due to a combination of primary, secondary, and outer-coordination sphere effects imbued by the encapsulating polymer. In this work, we perform in situ electrochemical X-ray absorption spectroscopy measurements to study the oxidation state and coordination environment of Co as a function of applied potential for CoPc, CoPc–P4VP, and CoPc with an axially-coordinated py, CoPc(py). Using in situ X-ray absorption near edge structure (XANES) we provide experimental support for our previous hypothesis that Co changes from a 4-coordinate square-planar geometry in CoPc to a mostly 5-coordinate species in CoPc(py) and CoPc–P4VP. The coordination environment of CoPc–P4VP is potential-independent but pH-dependent, suggesting that the axial coordination of pyridyl groups in P4VP to CoPc is modulated by the protonation of the polymer. Finally, we show that at low potential the oxidation state of Co in the 4-coordinate CoPc is different from that in the 5-coordinate CoPc(py), suggesting that the primarymore »coordination sphere modulates the site of reduction (metal-centered vs. ligand centered) under catalytically-relevant conditions.« less