More Like this

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. 

   more » « less
2. Gd 3+ –Gd 3+ distances exceeding 3 nm determined by very high frequency continuous wave electron paramagnetic resonance

   https://doi.org/10.1039/c6cp07119h  

   Clayton, Jessica A. ; Qi, Mian ; Godt, Adelheid ; Goldfarb, Daniella ; Han, Songi ; Sherwin, Mark S. ( January 2017 , Physical Chemistry Chemical Physics)

   Electron paramagnetic resonance spectroscopy in combination with site-directed spin labeling is a very powerful tool for elucidating the structure and organization of biomolecules. Gd 3+ complexes have recently emerged as a new class of spin labels for distance determination by pulsed EPR spectroscopy at Q- and W-band. We present CW EPR measurements at 240 GHz (8.6 Tesla) on a series of Gd-rulers of the type Gd-PyMTA–spacer–Gd-PyMTA, with Gd–Gd distances ranging from 1.2 nm to 4.3 nm. CW EPR measurements of these Gd-rulers show that significant dipolar broadening of the central |−1/2〉 → |1/2〉 transition occurs at 30 K for Gd–Gd distances up to ∼3.4 nm with Gd-PyMTA as the spin label. This represents a significant extension for distances accessible by CW EPR, as nitroxide-based spin labels at X-band frequencies can typically only access distances up to ∼2 nm. We show that this broadening persists at biologically relevant temperatures above 200 K, and that this method is further extendable up to room temperature by immobilizing the sample in glassy trehalose. We show that the peak-to-peak broadening of the central transition follows the expected 1/ r 3 dependence for the electron–electron dipolar interaction, from cryogenic temperatures up to room temperature. A simple procedure for simulating the dependence of the lineshape on interspin distance is presented, in which the broadening of the central transition is modeled as an S = 1/2 spin whose CW EPR lineshape is broadened through electron–electron dipolar interactions with a neighboring S = 7/2 spin. 

   more » « less
3. Anisotropic magnetic and transport properties of orthorhombic o-Pr 2 Co 3 Ge 5

   https://doi.org/10.1088/2515-7639/ac9ad9  

   Kyrk, Trent M. ; Kennedy, Ellis R. ; Galeano-Cabral, Jorge ; Wei, Kaya ; McCandless, Gregory T. ; Scott, Mary C. ; Baumbach, Ryan E. ; Chan, Julia Y. ( October 2022 , Journal of Physics: Materials)

   The crystal structure, electron energy-loss spectroscopy (EELS), heat capacity, and anisotropic magnetic and resistivity measurements are reported for Sn flux grown single crystals of orthorhombic Pr₂Co₃Ge₅(U₂Co₃Si₅-type,Ibam). Our findings show thato-Pr₂Co₃Ge₅hosts nearly trivalent Pr ions, as evidenced by EELS and fits to temperature dependent magnetic susceptibility measurements. Complex magnetic ordering with a partially spin-polarized state emerges nearT_sp= 32 K, with a spin reconfiguration transition nearT_M= 15 K. Heat capacity measurements show that the phase transitions appear as broad peaks in the vicinity ofT_spandT_M. The magnetic entropy further reveals that crystal electric field splitting lifts the Hund’s rule degeneracy at low temperatures. Taken together, these measurements show that Pr₂Co₃Ge₅is an environment for complexfstate magnetism with potential strongly correlated electron states.

    

   more » « less
4. A Clock Transition in the Cr7Mn Molecular Nanomagnet

   https://doi.org/10.3390/magnetochemistry5010004  

   Collett, Charles ; Ellers, Kai-Isaak ; Russo, Nicholas ; Kittilstved, Kevin ; Timco, Grigore ; Winpenny, Richard ; Friedman, Jonathan ( March 2019 , Magnetochemistry)

   A viable qubit must have a long coherence time T 2 . In molecular nanomagnets, T 2 is often limited at low temperatures by the presence of dipole and hyperfine interactions, which are often mitigated through sample dilution, chemical engineering and isotope substitution in synthesis. Atomic-clock transitions offer another route to reducing decoherence from environmental fields by reducing the effective susceptibility of the working transition to field fluctuations. The Cr7Mn molecular nanomagnet, a heterometallic ring, features a clock transition at zero field. Both continuous-wave and spin-echo electron-spin resonance experiments on Cr7Mn samples, diluted via co-crystallization, show evidence of the effects of the clock transition with a maximum T 2 ∼ 390 ns at 1.8 K. We discuss improvements to the experiment that may increase T 2 further. 

   more » « less
5. CaMn 3 IV O 4 Cubane Models of the Oxygen‐Evolving Complex: Spin Ground States S <9/2 and the Effect of Oxo Protonation

   https://doi.org/10.1002/ange.202105303  

   Lee, Heui Beom ; Shiau, Angela A. ; Marchiori, David A. ; Oyala, Paul H. ; Yoo, Byung‐Kuk ; Kaiser, Jens T. ; Rees, Douglas C. ; Britt, R. David ; Agapie, Theodor ( August 2021 , Angewandte Chemie)

   We report the single crystal XRD and MicroED structure, magnetic susceptibility, and EPR data of a series of CaMn₃^IVO₄and YMn₃^IVO₄complexes as structural and spectroscopic models of the cuboidal subunit of the oxygen‐evolving complex (OEC). The effect of changes in heterometal identity, cluster geometry, and bridging oxo protonation on the spin‐state structure was investigated. In contrast to previous computational models, we show that the spin ground state of CaMn₃^IVO₄complexes and variants with protonated oxo moieties need not beS=9/2. Desymmetrization of thepseudo‐C₃‐symmetric Ca(Y)Mn₃^IVO₄core leads to a lowerS=5/2 spin ground state. The magnitude of the magnetic exchange coupling is attenuated upon oxo protonation, and anS=3/2 spin ground state is observed in CaMn₃^IVO₃(OH). Our studies complement the observation that the interconversion between the low‐spin and high‐spin forms of the S₂state is pH‐dependent, suggesting that the (de)protonation of bridging or terminal oxygen atoms in the OEC may be connected to spin‐state changes.

    

   more » « less