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1. Counterion influence on dynamic spin properties in a V( iv ) complex

   https://doi.org/10.1039/C8SC04122A  

   Lin, Chun-Yi ; Ngendahimana, Thacien ; Eaton, Gareth R. ; Eaton, Sandra S. ; Zadrozny, Joseph M. ( January 2019 , Chemical Science)

   Using transition metal ions for spin-based applications, such as electron paramagnetic resonance imaging (EPRI) or quantum computation, requires a clear understanding of how local chemistry influences spin properties. Herein we report a series of four ionic complexes to provide the first systematic study of one aspect of local chemistry on the V( iv ) spin – the counterion. To do so, the four complexes (Et 3 NH) 2 [V(C 6 H 4 O 2 ) 3 ] ( 1 ), ( n -Bu 3 NH) 2 [V(C 6 H 4 O 2 ) 3 ] ( 2 ), ( n -Hex 3 NH) 2 [V(C 6 H 4 O 2 ) 3 ] ( 3 ), and ( n -Oct 3 NH) 2 [V(C 6 H 4 O 2 ) 3 ] ( 4 ) were probed by EPR spectroscopy in solid state and solution. Room temperature, solution X-band ( ca. 9.8 GHz) continuous-wave electron paramagnetic resonance (CW-EPR) spectroscopy revealed an increasing linewidth with larger cations, likely a counterion-controlled tumbling in solution via ion pairing. In the solid state, variable-temperature (5–180 K) X-band ( ca. 9.4 GHz) pulsed EPR studies of 1–4 in o -terphenyl glass demonstrated no effect on spin–lattice relaxation times ( T 1 ), indicating little role for the counterion on this parameter. However, the phase memory time ( T m ) of 1 below 100 K is markedly smaller than those of 2–4 . This result is counterintuitive, as 2–4 are relatively richer in 1 H nuclear spin, hence, expected to have shorter T m . Thus, these data suggest an important role for counterion methyl groups on T m , and moreover provide the first instance of a lengthening T m with increasing nuclear spin quantity on a molecule. 

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2. Programmable Nuclear-Spin Dynamics in Ti(IV) Coordination Complexes

   https://doi.org/10.1021/acs.inorgchem.0c00244  

   Johnson, Spencer H. ; Jackson, Cassidy E. ; Zadrozny, Joseph M. ( April 2020 , Inorganic Chemistry)

   Interstitial patterning of nuclear spins is a nascent design principle for controlling electron spin superposition lifetimes in open-shell complexes and solid-state defects. Herein we report the first test of the impact of the patterning principle on ligand-based nuclear spin dynamics. We test how substitutional patterning of 1H and 79/81Br nuclear spins on ligands modulates proton nuclear spin dynamics in the ligand shell of metal complexes. To do so, we studied the 1H nuclear magnetic resonance relaxation times (T1 and T2) of a series of eight polybrominated catechol ligands and six complexes formed by coordination of the ligands to a Ti(IV) ion. These studies reveal that 1H T1 values can be enhanced in the individual ligands by a factor of 4 (from 10.8(3) to 43(5) s) as a function of substitution pattern, reaching the maximum value for 3,4,6-tribromocatechol. The T2 for 1H is also enhanced by a factor of 4, varying by ∼14 s across the series. When complexed, the impact of the patterning design strategy on nuclear spin dynamics is amplified and 1H T1 and T2 values vary by over an order of magnitude. Importantly, the general trends observed in the ligands also match those when complexed. Hence, these results demonstrate a new design principle to control 1H spin dynamics in metal complexes through pattern-based design strategies in the ligand shell. 

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3. Metal‐Templated, Tight Loop Conformation of a Cys‐X‐Cys Biomimetic Assembles a Dimanganese Complex

   https://doi.org/10.1002/ange.201913259  

   Le, Trung ; Nguyen, Hao ; Perez, Lisa M. ; Darensbourg, Donald J. ; Darensbourg, Marcetta Y. ( January 2020 , Angewandte Chemie)

   With the goal of generating anionic analogues to MN₂S₂⋅Mn(CO)₃Br we introduced metallodithiolate ligands, MN₂S₂²⁻prepared from the Cys‐X‐Cys biomimetic, ema⁴⁻ligand (ema=N,N′‐ethylenebis(mercaptoacetamide); M=Ni^II, [V^IV≡O]²⁺and Fe^III) to Mn(CO)₅Br. An unexpected, remarkably stable dimanganese product, (H₂N₂(CH₂C=O(μ‐S))₂)[Mn(CO)₃]₂resulted from loss of M originally residing in the N₂S₂⁴⁻pocket, replaced by protonation at the amido nitrogens, generating H₂ema²⁻. Accordingly, the ema ligand has switched its coordination mode from an N₂S₂⁴⁻cavity holding a single metal, to a binucleating H₂ema²⁻with bridging sulfurs and carboxamide oxygens within Mn‐μ‐S‐CH₂‐C‐O, 5‐membered rings. In situ metal‐templating by zinc ions gives quantitative yields of the Mn₂product. By computational studies we compared the conformations of “linear” ema⁴⁻to ema⁴⁻frozen in the “tight‐loop” around single metals, and to the “looser” fold possible for H₂ema²⁻that is the optimal arrangement for binucleation. XRD molecular structures show extensive H‐bonding at the amido‐nitrogen protons in the solid state.

    

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4. Metal‐Templated, Tight Loop Conformation of a Cys‐X‐Cys Biomimetic Assembles a Dimanganese Complex

   https://doi.org/10.1002/anie.201913259  

   Le, Trung ; Nguyen, Hao ; Perez, Lisa M. ; Darensbourg, Donald J. ; Darensbourg, Marcetta Y. ( January 2020 , Angewandte Chemie International Edition)

   With the goal of generating anionic analogues to MN₂S₂⋅Mn(CO)₃Br we introduced metallodithiolate ligands, MN₂S₂²⁻prepared from the Cys‐X‐Cys biomimetic, ema⁴⁻ligand (ema=N,N′‐ethylenebis(mercaptoacetamide); M=Ni^II, [V^IV≡O]²⁺and Fe^III) to Mn(CO)₅Br. An unexpected, remarkably stable dimanganese product, (H₂N₂(CH₂C=O(μ‐S))₂)[Mn(CO)₃]₂resulted from loss of M originally residing in the N₂S₂⁴⁻pocket, replaced by protonation at the amido nitrogens, generating H₂ema²⁻. Accordingly, the ema ligand has switched its coordination mode from an N₂S₂⁴⁻cavity holding a single metal, to a binucleating H₂ema²⁻with bridging sulfurs and carboxamide oxygens within Mn‐μ‐S‐CH₂‐C‐O, 5‐membered rings. In situ metal‐templating by zinc ions gives quantitative yields of the Mn₂product. By computational studies we compared the conformations of “linear” ema⁴⁻to ema⁴⁻frozen in the “tight‐loop” around single metals, and to the “looser” fold possible for H₂ema²⁻that is the optimal arrangement for binucleation. XRD molecular structures show extensive H‐bonding at the amido‐nitrogen protons in the solid state.

    

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5. A maximally preorganized tetra‐pyridyl ligand. Rigid five‐membered chelate rings enhance selectivity for large metal ions, such as Th(IV), UO 2 2+ and Lanthanides. A DFT and Thermodynamic study

   https://doi.org/10.1002/ejic.202300633  

   Uritis, Stuart ; Thummel, Randolph P. ; Jones, S. Bart ; Lee, Hee‐Seung ; Hancock, Robert D. ( February 2024 , European Journal of Inorganic Chemistry)

   Size‐based selectivity for metal ions based on highly preorganized five‐membered chelate rings is discussed. Metal ion complexation by the tetra‐pyridyl ligand EBIP ((8,9‐dihydro‐diquino[8,7‐b:7′,8′‐j][1,10]phenanthroline) is investigated, Formation constants (log K₁) are reported for EBIP with 28 metal ions in 50 % CH₃OH/H₂O (v/v). The shift in size‐selectivity toward large metal ions and against small metal is demonstrated. Log K₁for the EBIP complexes shows a steady increase from La(III) to Lu(III), with a strong local maximum at Sm(III), and strong local minimum at Gd(III). This difference in log K₁between Sm(III) and Gd(III) for the tetra‐pyridyls is shown to depend largely on the level of preorganization of the ligand, being at a maximum for EBIP and a minimum for quaterpyridine. Log K₁for the Y(III) complex is invariably lower than for the similarly‐sized Ho(III) for all ligands that contain any nitrogen donors. Lower log K values for Y(III) are due to stabilization of the Ln(III) complexes with nitrogen donors by participation of the 5d orbitals, and to a lesser extent the 4 f orbitals, of the Ln(III) ions in M−L bonding. A DFT analysis of selectivity of tetra‐pyridyls for metal ions shows that Y(III) complexes should be less stable than similarly‐sized Ho(III) complexes.

    

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