Trimethylsilyldiazomethane Disassembly at a Three-Fold Symmetric Iron Site.

The reaction of equimolar trimethylsilyldiazomethyllithium (LiTMSD) with high spin ( = 2) PhB(AdIm)FeCl (PhB(AdIm) = tris(3-adamantylimidazol-2-ylidene)phenylborate) affords the corresponding nitrilimido complex PhB(AdIm)Fe-N═N═C(SiMe). This complex can be converted to the thermodynamically more favorable -isocyanoamido isomer PhB(AdIm)Fe-C═N═N(SiMe) by reaction with an additional equivalent of LiTMSD. While the iron(II) complexes are four-coordinate, the diazomethane is bound side-on in the iron(I) congener PhB(AdIm)Fe(,'-κ-NC(H)Si(CH)).

Quantum Mimicry With Inorganic Chemistry.

Quantum objects, such as atoms, spins, and subatomic particles, have important properties due to their unique physical properties that could be useful for many different applications, ranging from quantum information processing to magnetic resonance imaging. Molecular species also exhibit quantum properties, and these properties are fundamentally tunable by synthetic design, unlike ions isolated in a quadrupolar trap, for example. In this comment, we collect multiple, distinct, scientific efforts into an emergent field that is devoted to designing molecules that mimic the quantum properties of objects like trapped atoms or defects in solids.

Asymmetry-enhanced Co NMR thermometry in Co(iii) complexes.

Design strategies for molecular thermometers by magnetic resonance are essential for enabling new noninvasive means of temperature mapping for disease diagnoses and treatments. Herein we demonstrate a new design strategy for thermometry based on chemical control of the vibrational partition function. To do so, we performed variable-temperature Co NMR investigations of four air-stable Co(iii) complexes: Co(accp) (1), Co(bzac) (2), Co(Bu-acac) (3), and Co(acac) (4) (accp = 2-acetylcyclopentanonate; bzac = benzoylacetonate; Bu-acac = 2,2,6,6-tetramethyl-3,5-heptanedionate and acac = acetylacetonate).

Impact of ligand chlorination and counterion tuning on high-field spin relaxation in a series of V(IV) complexes.

Methods of controlling spin coherence by molecular design are essential to efforts to develop molecular qubits for quantum information and sensing applications. In this manuscript, we perform the first studies of how arrangements of Cl nuclear spins in the ligand shell and counterion selection affect the coherent spin dynamics of V(IV) complexes at a high magnetic field. We prepared eight derivatives of the vanadium triscatecholate complex with varying arrangements of Cl substitution on the catechol backbone and RNH counterions (R = Et, -Bu, -Hex) and investigated these species structural and spectroscopic methods.

Geometry-dependent valence tautomerism, magnetism, and electrical conductivity in 1D iron-tetraoxolene chains.

Redox-active tetraoxolene ligands such as 1,4-dihydroxybenzoquinone provide access to a diversity of metal-organic architectures, many of which display interesting magnetic behavior and high electrical conductivity. Here, we take a closer look at how structure dictates physical properties in a series of 1D iron-tetraoxolene chains. Using a diphenyl-derivatized tetraoxolene ligand (HPhdhbq), we show that the steric profile of the coordinating solvent controls whether linear or helical chains are exclusively formed.

Record Chemical-Shift Temperature Sensitivity in a Series of Trinuclear Cobalt Complexes.

Designing spins that exhibit long-lived coherence and strong temperature sensitivity is central to designing effective molecular thermometers and a fundamental challenge in the chemistry/quantum-information space. Herein, we provide a new pathway to both properties in the same molecule by designing a nuclear spin, which possesses a robust spin coherence, to mimic the strong temperature sensitivity of an electronic spin. This design strategy is demonstrated in the group of trinuclear Co(III) spin-crossover compounds [(CpCo(OP(OR)))Co](SbCl) where Cp = cyclopentadienyl and R = Me (), Et (), -Pr (), and -Bu ().

Slowing magnetic relaxation with open-shell diluents.

Strategies for slowing magnetic relaxation via local environmental design are vital for developing next-generation spin-based technologies (e.g., quantum information processing).

Dinitrogen Coordination to a High-Spin Diiron(I/II) Species.

Dinitrogen coordination to iron centers underpins industrial and biological fixation in the Haber-Bosch process and by the FeM cofactors in the nitrogenase enzymes. The latter employ local high-spin metal centers; however, iron-dinitrogen coordination chemistry remains dominated by low-valent states, contrasting the enzyme systems. Here, we report a high-spin mixed-valent cis-(μ-1,2-dinitrogen)diiron(I/II) complex [(FeBr) (μ-N )L ] (2), where [L ] is a bis(β-diketiminate) cyclophane.

Ligand design of zero-field splitting in trigonal prismatic Ni(II) cage complexes.

Complexes of encapsulated metal ions are promising potential metal-based electron paramagnetic resonance imaging (EPRI) agents due to zero-field splitting. Herein, we synthesize and magnetically characterize a series of five new Ni(II) complexes based on a clathrochelate ligand to provide a new design strategy for zero-field splitting in an encaged environment. UV-Vis and X-ray single-crystal diffraction experiments demonstrate slight physical and electronic structure changes as a function of the differing substituents.

Isotopomeric Elucidation of the Mechanism of Temperature Sensitivity in Co NMR Molecular Thermometers.

Understanding the mechanisms governing temperature-dependent magnetic resonance properties is essential for enabling thermometry via magnetic resonance imaging. Herein we harness a new molecular design strategy for thermometry─that of effective mass engineering via deuteration in the first coordination shell─to reveal the mechanistic origin of Co chemical shift thermometry. Exposure of [Co(en)] (; en = ethylenediamine) and [Co(diNOsar)] (; diNOsar = dinitrosarcophagine) to mixtures of HO and DO produces distributions of [Co(en)]- ( = 0-12) and [Co(diNOsar)]- ( = 0-6) isotopomers all resolvable by Co NMR.

Counterion Control of t-BuO-Mediated Single Electron Transfer to Nitrostilbenes to Construct N-Hydroxyindoles or Oxindoles.

tert-Butoxide unlocks new reactivity patterns embedded in nitroarenes. Exposure of nitrostilbenes to sodium tert-butoxide was found to produce N-hydroxyindoles at room temperature without an additive. Changing the counterion to potassium changed the reaction outcome to yield solely oxindoles through an unprecedented dioxygen-transfer reaction followed by a 1,2-phenyl migration.

Ligand Control of Co Nuclear Spin Relaxation Thermometry.

Studying the correlation between temperature-driven molecular structure and nuclear spin dynamics is essential to understanding fundamental design principles for thermometric nuclear magnetic resonance spin-based probes. Herein, we study the impact of progressively encapsulating ligands on temperature-dependent Co (spin-lattice) and (spin-spin) relaxation times in a set of Co(III) complexes: K[Co(CN)] (); [Co(NH)]Cl (); [Co(en)]Cl (), en = ethylenediamine); [Co(tn)]Cl (), tn = trimethylenediamine); [Co(tame)]Cl (), tame = triaminomethylethane); and [Co(dinosar)]Cl (), dinosar = dinitrosarcophagine). Measurements indicate that Co and increase with temperature for - between 10 and 60 °C, with the greatest Δ /Δ and Δ /Δ temperature sensitivities found for and , 5.

A reaction-coordinate perspective of magnetic relaxation.

Understanding and utilizing the dynamic quantum properties of metal ions is the frontier of many next generation technologies. One property in particular, magnetic relaxation, is a complicated physical phenomenon that is scarcely treated in undergraduate coursework. Consequently, principles of magnetic relaxation are nearly impenetrable to starting synthetic chemists, who ultimately design the molecules that fuel new discoveries.

Ligand control of low-frequency electron paramagnetic resonance linewidth in Cr(III) complexes.

Understanding how the ligand shell controls low-frequency electron paramagnetic resonance (EPR) spectroscopic properties of metal ions is essential if they are to be used in EPR-based bioimaging schemes. In this work, we probe how specific variations in the ligand structure impact L-band (ca. 1.

EXAFS investigations of temperature-dependent structure in cobalt-59 molecular NMR thermometers.

Cobalt-59 nuclei are known for extremely thermally sensitive chemical shifts (δ), which in the long term could yield novel magnetic resonance thermometers for bioimaging applications. In this manuscript, we apply extended X-ray absorption fine structure (EXAFS) spectroscopy for the first time to probe the exact variations in physical structure that produce the exceptional thermal sensitivity of the 59Co NMR chemical shift. We apply this spectroscopic technique to five Co(iii) complexes: [Co(NH3)6]Cl3 (1), [Co(en)3]Cl3 (2) (en = ethylenediamine), [Co(tn)3]Cl3 (3) (tn = trimethylenediamine), [Co(tame)2]Cl3 (4) (tame = 1,1,1-tris(aminomethyl)ethane), and [Co(diNOsar)]Cl3 (5) (diNOsar = dinitrosarcophagine).

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

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 H and Br nuclear spins on ligands modulates proton nuclear spin dynamics in the ligand shell of metal complexes.

Nuclear-spin-pattern control of electron-spin dynamics in a series of V(iv) complexes.

Achieving control of phase memory relaxation times ( ) in metal ions is an important goal of molecular spintronics. Herein we provide the first evidence that nuclear-spin patterning in the ligand shell is an important handle to modulate in metal ions. We synthesized and studied a series of five V(iv) complexes with brominated catecholate ligands, [V(CH Br O)] ( = 0, 1, 2, and 4), where the Br and H nuclear spins are arranged in different substitutional patterns.

Influence of ligand encapsulation on cobalt-59 chemical-shift thermometry.

Thermometry magnetic resonance imaging (MRI) would provide a powerful noninvasive window into physiological temperature management. Cobalt-59 nuclear spins demonstrate exceptional temperature dependence of their NMR chemical shifts, yet the insight to control this dependence molecular design is lacking. We present the first systematic evidence that encapsulation of this spin system amplifies the temperature sensitivity.

Metal-ligand covalency enables room temperature molecular qubit candidates.

Harnessing synthetic chemistry to design electronic spin-based qubits, the smallest unit of a quantum information system, enables us to probe fundamental questions regarding spin relaxation dynamics. We sought to probe the influence of metal-ligand covalency on spin-lattice relaxation, which comprises the upper limit of coherence time. Specifically, we studied the impact of the first coordination sphere on spin-lattice relaxation through a series of four molecules featuring V-S, V-Se, Cu-S, and Cu-Se bonds, the PhP salts of the complexes [V(CHS)] (), [Cu(CHS)] (), [V(CHSe)] (), and [Cu(CHSe)] ().

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

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 (EtNH)[V(CHO)] (), (-BuNH)[V(CHO)] (), (-HexNH)[V(CHO)] (), and (-OctNH)[V(CHO)] () were probed by EPR spectroscopy in solid state and solution.

Determination of d-Orbital Populations in a Cobalt(II) Single-Molecule Magnet Using Single-Crystal X-ray Diffraction.

The tetrahedral cobalt(II) compound (PhP)[Co(SPh)] was the first mononuclear transition-metal complex shown to exhibit slow relaxation of the magnetization in zero external magnetic field. Because the relative populations of the d orbitals play a vital role in dictating the magnitude of the magnetic anisotropy, the magnetic behavior of this complex is directly related to its electronic structure, yet the exact role of the soft, thiophenolate ligands in influencing the d-electron configuration has previously only been investigated via theoretical methods. To provide detailed experimental insight into the effect of this ligand field, the electron density distribution in this compound was determined from low-temperature, single-crystal X-ray diffraction data and subsequent multipole modeling.

A Porous Array of Clock Qubits.

Realizing atomic-level spatial control over qubits, the fundamental units of both quantum information processing systems and quantum sensors, constitutes a crucial cross-field challenge. Toward this end, embedding electronic-spin-based qubits within the framework of a crystalline porous material is a promising approach to create precise arrays of qubits. Realizing porous hosts for qubits would also impact the emerging field of quantum sensing, whereby porosity would enable analytes to infuse into a sensor matrix.

Magneto-Structural Correlations in Pseudotetrahedral Forms of the [Co(SPh)] Complex Probed by Magnetometry, MCD Spectroscopy, Advanced EPR Techniques, and ab Initio Electronic Structure Calculations.

The magnetic properties of pseudotetrahedral Co(II) complexes spawned intense interest after (PPh)[Co(SPh)] was shown to be the first mononuclear transition-metal complex displaying slow relaxation of the magnetization in the absence of a direct current magnetic field. However, there are differing reports on its fundamental magnetic spin Hamiltonian (SH) parameters, which arise from inherent experimental challenges in detecting large zero-field splittings. There are also remarkable changes in the SH parameters of [Co(SPh)] upon structural variations, depending on the counterion and crystallization conditions.

Long Coherence Times in Nuclear Spin-Free Vanadyl Qubits.

Quantum information processing (QIP) offers the potential to create new frontiers in fields ranging from quantum biology to cryptography. Two key figures of merit for electronic spin qubits, the smallest units of QIP, are the coherence time (T), the lifetime of the qubit, and the spin-lattice relaxation time (T), the thermally defined upper limit of T. To achieve QIP, processable qubits with long coherence times are required.