Magnetic circularly polarized luminescence from spin-flip transitions in a molecular ruby.

Magnetic circularly polarized luminescence (MCPL), the possibility of generating circularly polarized luminescence in the presence of a magnetic field in achiral or racemic compounds, is a technique of rising interest. Here we show that the far-red spin-flip (SF) transitions of a molecular Cr(iii) complex give intense MCD (magnetic circular dichroism) and in particular MCPL ( up to 6.3 × 10 T) even at magnetic fields as low as 0.

Cobalt(II) Single-Ion Magnet Coordinated by Double Deprotonation of 2,2'-Bipyridine-6,6'-diol Ligands.

In this study, we synthesized a new Co(II) complex, [NMe][Co(bpyO)] (), using deprotonated 2,2'-bipyridine-6,6'-diol ligands (bpyO ). This compound exhibits a significant zero-field splitting () value. The far-infrared magneto spectroscopy and high-frequency and field electron paramagnetic resonance (HFEPR) measurements indicated that compound possesses = -54.

Control of the geometry and anisotropy driven by the combination of steric and anion coordination effects in Co complexes with N-tripodal ligands: the impact of the size of the ligand on the magnetization relaxation time.

Four mononuclear Co complexes of formula [Co(L)(SCN)(CHOH)(HO)]·1.5HO·0.75CHOH (1), [Co(L1)Cl]·HO·2CHCN (2), [Co(L1)(SCN)]·1.

Divalent Titanium via Reductive N-C Coupling of a Ti Nitrido with π-Acids.

The nitrido-ate complex [(PN)Ti(N){μ-K(OEt)}] (1) (PN=(N-(2-PPr-4-methylphenyl)-2,4,6-MeCH) reductively couples CO and isocyanides in the presence of DME or cryptand (Kryptofix222), to form rare, five-coordinate Ti complexes having a linear cumulene motif, [K(L)][(PN)Ti(NCE)] (E=O, L=Kryptofix222, (2); E=NAd, L=3 DME, (3); E=NBu, L=3 DME, (4); E=NAd, L=Kryptofix222, (5)). Oxidation of 2-5 with [Fc][OTf] afforded an isostructural Ti center containing a neutral cumulene, [(PN)Ti(NCE)] (E=O, (6); E=NAd (7), NBu (8)) and characterization by CW X-band EPR spectroscopy, revealed unpaired electron to be metal centric. Moreover, 1e reduction of 6 and 7 in the presence of Kryptofix222cleanly reformed corresponding discrete Ti complexes 2 and 5, which were further characterized by solution magnetization measurements and high-frequency and -field EPR (HFEPR) spectroscopy.

Electronic Structure of Three-Coordinate Fe and Co β-Diketiminate Complexes.

The β-diketiminate supporting group, [ArNCRCHCRNAr], stabilizes low coordination number complexes. Four such complexes, where R = -butyl, Ar = 2,6-diisopropylphenyl, are studied: (nacnac)ML, where M = Fe, Co and L = Cl, CH. These are denoted , , , and and have been previously reported and structurally characterized.

Softer Is Better for Titanium: Molecular Titanium Arsenido Anions Featuring Ti≡As Bonding and a Terminal Parent Arsinidene.

We introduce the arsenido ligand onto the Ti ion, yielding a remarkably covalent Ti≡As bond and the parent arsinidene Ti═AsH moiety. An anionic arsenido ligand is assembled via reductive decarbonylation involving the discrete Ti salt [K(cryptand)][(PN)TiCl] () (cryptand = 222-Kryptofix) and Na(OCAs)(dioxane) in thf/toluene to produce the mixed alkali ate-complex [(PN)Ti(As)](μ-KNa(thf)) () and the discrete salt [K(cryptand)][(PN)Ti≡As] () featuring a terminal Ti≡As ligand. Protonation of or with various weak acids cleanly forms the parent arsinidene [(PN)Ti═AsH] (), which upon deprotonation with KCHPh in thf generates the more symmetric anionic arsenido [(PN)Ti(As){μ-K(thf)}] ().

Zero-Field SMM Behavior Triggered by Magnetic Exchange Interactions and a Collinear Arrangement of Local Anisotropy Axes in a Linear Co Complex.

A new linear trinuclear Co(II) complex with a formula of [{Co(μ-L)}Co] has been prepared by self-assembly of Co(II) ions and the NO-tripodal Schiff base ligand HL, which is obtained from the condensation of 1,1,1-tris(aminomethyl)ethane and salicylaldehyde. Single X-ray diffraction shows that this compound is centrosymmetric with triple-phenolate bridging groups connecting neighboring Co(II) ions, leading to a paddle-wheel-like structure with a pseudo- axis lying in the Co-Co-Co direction. The Co(II) ions at both ends of the Co(II) molecule exhibit distorted trigonal prismatic CoNO geometry, whereas the Co(II) at the middle presents an elongated trigonal antiprismatic CoO geometry.

Haldane topological spin-1 chains in a planar metal-organic framework.

Haldane topological materials contain unique antiferromagnetic chains with symmetry-protected energy gaps. Such materials have potential applications in spintronics and future quantum computers. Haldane topological solids typically consist of spin-1 chains embedded in extended three-dimensional (3D) crystal structures.

Terahertz EPR spectroscopy using a 36-tesla high-homogeneity series-connected hybrid magnet.

Electron Paramagnetic Resonance (EPR) is a powerful technique to study materials and biological samples on an atomic scale. High-field EPR in particular enables extracting very small g-anisotropies in organic radicals and half-filled 3d and 4f metal ions such as Mn (3d) or Gd (4f), and resolving EPR signals from unpaired spins with very close g-values, both of which provide high-resolution details of the local atomic environment. Before the recent commissioning of the high-homogeneity Series Connected Hybrid magnet (SCH, superconducting + resistive) at the National High Magnetic Field Laboratory (NHMFL), the highest-field, high-resolution EPR spectrometer available was limited to 25 T using a purely resistive "Keck" magnet at the NHMFL.

Spectroscopic and Magnetic Studies of Co(II) Scorpionate Complexes: Is There a Halide Effect on Magnetic Anisotropy?

The observation of single-molecule magnetism in transition-metal complexes relies on the phenomenon of zero-field splitting (ZFS), which arises from the interplay of spin-orbit coupling (SOC) with ligand-field-induced symmetry lowering. Previous studies have demonstrated that the magnitude of ZFS in complexes with 3d metal ions is sometimes enhanced through coordination with heavy halide ligands (Br and I) that possess large free-atom SOC constants. In this study, we systematically probe this "heavy-atom effect" in high-spin cobalt(II)-halide complexes supported by substituted hydrotris(pyrazol-1-yl)borate ligands (Tp and Tp).

Magnetic anisotropy and structural flexibility in the field-induced single ion magnets [Co{(OPPh)(EPPh)N}], E = S, Se, explored by experimental and computational methods.

During the last few years, a large number of mononuclear Co(II) complexes of various coordination geometries have been explored as potential single ion magnets (SIMs). In the work presented herein, the Co(II) S = 3/2 tetrahedral [Co{(OPPh)(EPPh)N}], E = S, Se, complexes (abbreviated as CoO2E2), bearing chalcogenated mixed donor-atom imidodiphosphinato ligands, were studied by both experimental and computational techniques. Specifically, direct current (DC) magnetometry provided estimations of their zero-field splitting (zfs) axial () and rhombic () parameter values, which were more accurately determined by a combination of far-infrared magnetic spectroscopy and high-frequency and -field EPR spectroscopy studies.

Pushing up the easy-axis magnetic anisotropy and relaxation times in trigonal prismatic Co mononuclear SMMs by molecular structure design.

The replacement of pyridine by 1-methyl-imidazol in the arms of a N-tripodal ligand allows preparing two new Co complexes with quasi-ideal triangular prismatic geometry, which behave as SIMs (Single Ion Magnets) at zero dc field with enhanced axial magnetic anisotropy, magnetic relaxation times and magnetic hysteresis.

Tale of Three Molecular Nitrides: Mononuclear Vanadium (V) and (IV) Nitrides As Well As a Mixed-Valence Trivanadium Nitride Having a VN Double-Diamond Core.

Transmetallation of [VCl(THF)] and [TlTp] afforded [(Tp)VCl] (, Tp = hydro-tris(3-butyl-5-methylpyrazol-1-yl)borate), which was reduced with KC to form a symmetric V complex, [(Tp)VCl] (). Complex has a high-spin ( = 1) ground state and displays rhombic high-frequency and -field electron paramagnetic resonance (HFEPR) spectra, while complex has an = 3/2 A ground state observable by conventional EPR spectroscopy. Complex reacts with NaN to form the V nitride-azide complex [(Tp)V≡N(N)] ().

Electronic Structure and Magnetic Properties of a Low-Spin Cr Complex: -[CrCl(dmpe)] (dmpe = 1,2-Bis(dimethylphosphino)ethane).

Octahedral coordination complexes of the general formula -[MX(RECHCHER)] (M = Ti, V, Cr, Mn; E = N, P; R = alkyl, aryl) are a cornerstone of both coordination and organometallic chemistry, and many of these complexes are known to have unique electronic structures that have been incompletely examined. The -[CrCl(dmpe)] complex (dmpe = MePCHCHPMe), originally reported by Girolami and co-workers in 1985, is a rare example of a six-coordinate d system with an = 1 (spin triplet) ground state, as opposed to the high-spin ( = 2, spin quintet) state. The ground-state properties of = 1 systems are challenging to study using conventional spectroscopic methods, and consequently, the electronic structure of -[CrCl(dmpe)] has remained largely unexplored.

Electronic Structure of Tetrahedral, = 2, [Fe{(EPPr)N}], E = S, Se, Complexes: Investigation by High-Frequency and -Field Electron Paramagnetic Resonance, Fe Mössbauer Spectroscopy, and Quantum Chemical Studies.

In this work, we assessed the electronic structures of two pseudotetrahedral complexes of Fe, [Fe{(SPPr)N}] ) and [Fe{(SePPr)N}] (), using high-frequency and -field EPR (HFEPR) and field-dependent Fe Mössbauer spectroscopies. This investigation revealed = 2 ground states characterized by moderate, negative zero-field splitting (zfs) parameters . The crystal-field (CF) theory analysis of the spin Hamiltonian (sH) and hyperfine structure parameters revealed that the orbital ground states of and have a predominant d character, which is admixed with d (∼10%).

Applying Unconventional Spectroscopies to the Single-Molecule Magnets, Co(PPh ) X (X=Cl, Br, I): Unveiling Magnetic Transitions and Spin-Phonon Coupling.

Large separation of magnetic levels and slow relaxation in metal complexes are desirable properties of single-molecule magnets (SMMs). Spin-phonon coupling (interactions of magnetic levels with phonons) is ubiquitous, leading to magnetic relaxation and loss of memory in SMMs and quantum coherence in qubits. Direct observation of magnetic transitions and spin-phonon coupling in molecules is challenging.

Spectroscopic Investigation of a Metal-Metal-Bonded Fe Single-Molecule Magnet with an Isolated = / Giant-Spin Ground State.

The metal-metal-bonded molecule [BuN][(L)Fe(dmf)] (Fe) was previously shown to possess a thermally isolated spin = / ground state and found to exhibit slow magnetization relaxation below a blocking temperature of ∼5 K [ , , 13949-13956]. Here, we present a comprehensive spectroscopic investigation of this unique single-molecule magnet (SMM), combining ultrawideband field-swept high-field electron paramagnetic resonance (EPR) with frequency-domain Fourier-transform terahertz EPR to accurately quantify the spin Hamiltonian parameters of Fe. Of particular importance is the near absence of a 4th-order axial zero-field splitting term, which is known to arise because of quantum mechanical mixing of spin states on account of the relatively weak spin-spin (superexchange) interactions in traditional polynuclear SMMs such as the celebrated Mn-acetate.

Positive zero-field splitting and unexpected slow magnetic relaxation in the magneto-chemical calibrant HgCo(NCS).

DC magnetization data for HgCo(NCS)4 confirm positive value of the zero-field splitting D-parameter. High-frequency and -field EPR gave gz = 2.05, gx = 2.

A Mononuclear and High-Spin Tetrahedral Ti Complex.

A high-spin, mononuclear Ti complex, [(Tp)TiCl] [Tp = hydridotris(3--butyl-5-methylpyrazol-1-yl)borate], confined to a tetrahedral ligand-field environment, has been prepared by reduction of the precursor [(Tp)TiCl] with KC. Complex [(Tp)TiCl] has a A ground state (assuming symmetry based on structural studies), established a combination of high-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy, solution and solid-state magnetic studies, Ti K-edge X-ray absorption spectroscopy (XAS), and both density functional theory and ab initio (complete-active-space self-consistent-field, CASSCF) calculations. The formally and physically defined Ti complex readily binds tetrahydrofuran (THF) to form the paramagnetic adduct [(Tp)TiCl(THF)], which is impervious to N binding.

Probing the Magnetic Anisotropy of Co(II) Complexes Featuring Redox-Active Ligands.

Coordination complexes that possess large magnetic anisotropy (otherwise known as zero-field splitting, ZFS) have possible applications in the field of magnetic materials, including single molecule magnets (SMMs). Previous studies have explored the role of coordination number and geometry in controlling the magnetic anisotropy and SMM behavior of high-spin ( = 3/2) Co(II) complexes. Building upon these efforts, the present work examines the impact of ligand oxidation state and structural distortions on the spin states and ZFS parameters of pentacoordinate Co(II) complexes.

Magnetic Properties and Electronic Structure of the = 2 Complex [Mn{(OPPh)N}] Showing Field-Induced Slow Magnetization Relaxation.

The high-spin = 2 Mn(III) complex [Mn{(OPPh)N}] () exhibits field-induced slow relaxation of magnetization ( , , 12869). Magnetic susceptibility and dual-mode X-band electron paramagnetic resonance (EPR) studies revealed a negative value of the zero-field-splitting (zfs) parameter . In order to explore the magnetic and electronic properties of in detail, a combination of experimental and computational studies is presented herein.

Homoleptic mono-, di-, and tetra-iron complexes featuring phosphido ligands: a synthetic, structural, and spectroscopic study.

We report the first series of homoleptic phosphido iron complexes synthesized by treating either the β-diketiminato complex [(Dippnacnac)FeClLi(dme)] (Dippnacnac = HC[(CMe)N(CH-2,6-iPr)]) or [FeBr(thf)] with an excess of phosphides RPLi (R = tBu, tBuPh, Cy, iPr). Reaction outcomes depend strongly on the bulkiness of the phosphido ligands. The use of tBuPLi precursor led to an anionic diiron complex 1 encompassing a planar FeP core with two bridging and two terminal phosphido ligands.

Single-Ion Magnetic Behaviour in an Iron(III) Porphyrin Complex: A Dichotomy Between High Spin and 5/2-3/2 Spin Admixture.

A mononuclear iron(III) porphyrin compound exhibiting unexpectedly slow magnetic relaxation, which is a characteristic of single-ion magnet behaviour, is reported. This behaviour originates from the close proximity (≈550 cm ) of the intermediate-spin S=3/2 excited states to the high-spin S=5/2 ground state. More quantitatively, although the ground state is mostly S=5/2, a spin-admixture model evidences a sizable contribution (≈15 %) of S=3/2 to the ground state, which as a consequence experiences large and positive axial anisotropy (D=+19.

Electronic Structure and Magnetic Properties of a Titanium(II) Coordination Complex.

Stable coordination complexes of Ti (3d) are relatively uncommon, but are of interest as synthons for low oxidation state titanium complexes for application as potential catalysts and reagents for organic synthesis. Specifically, high-spin Ti ions supported by redox-inactive ligands are still quite rare due to the reducing power of this soft ion. Among such Ti complexes is -[TiCl(tmeda)], where tmeda = ,,','-tetramethylethane-1,2-diamine.