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.

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)}] ().

Ligand field design enables quantum manipulation of spins in Ni complexes.

Creating the next generation of quantum systems requires control and tunability, which are key features of molecules. To design these systems, one must consider the ground-state and excited-state manifolds. One class of systems with promise for quantum sensing applications, which require water solubility, are d Ni ions in octahedral symmetry.

Spectroscopic and Theoretical Investigation of High-Spin Square-Planar and Trigonal Fe(II) Complexes Supported by Fluorinated Alkoxides.

The electronic structures and spectroscopic behavior of three high-spin Fe complexes of fluorinated alkoxides were studied: square-planar {K(DME)}[Fe(pin)] () and quasi square-planar {K(222)}[Fe(pin)] () and trigonal-planar {K(18C6)}[Fe(OCF)] () where pin = perfluoropinacolate and OCF = -perfluoro--butoxide. The zero-field splitting (ZFS) and hyperfine structure parameters of the = 2 ground states were determined using field-dependent Fe Mössbauer and high-field and -frequency electron paramagnetic resonance (HFEPR) spectroscopies. The spin Hamiltonian parameters were analyzed with crystal field theory and corroborated by density functional theory (DFT) and complete active space self-consistent field (CASSCF) calculations.

Large Magnetic Anisotropy in Mono- and Binuclear cobalt(II) Complexes: The Role of the Distortion of the Coordination Sphere in Validity of the Spin-Hamiltonian Formalism.

To get a better insight into understanding the factors affecting the enhancement of the magnetic anisotropy in single molecule (single ion) magnets, two cobalt(II) complexes based on a tridentate ligand 2,6-di(thiazol-2-yl)pyridine substituted at the 4-position with -methyl-pyrrol-2-yl have been synthesized and studied by X-ray crystallography, AC and DC magnetic data, FIRMS and HFEPR spectra, and theoretical calculations. The change of the counteranion in starting Co(II) salts results in the formation of pentacoordinated mononuclear [Co(mpyr-dtpy)Cl]·2MeCN () complex and binuclear [Co(mpyr-dtpy)][Co(NCS)] () compound. The observed marked distortion of trigonal bipyramid geometry in and cationic octahedral and anionic tetrahedral units in brings up a question about the validity of the spin-Hamiltonian formalism and the possibility of determining the value and sign of the zero-field splitting parameter.

Disorder-Enriched Magnetic Excitations in a Heisenberg-Kitaev Quantum Magnet Na_{2}Co_{2}TeO_{6}.

Using optical magnetospectroscopy, we investigate the magnetic excitations of Na_{2}Co_{2}TeO_{6} in a broad magnetic field range (0  T≤B≤17.5  T) at low temperature. Our measurements reveal rich spectra of in-plane magnetic excitations with a surprisingly large number of modes, even in the high-field spin-polarized state.

Metal-Free Biomass-Derived Environmentally Persistent Free Radicals (Bio-EPFRs) from Lignin Pyrolysis.

To assess contribution of the radicals formed from biomass burning, our recent findings toward the formation of resonantly stabilized persistent radicals from hydrolytic lignin pyrolysis in a metal-free environment are presented in detail. Such radicals have particularly been identified during fast pyrolysis of lignin dispersed into the gas phase in a flow reactor. The trapped radicals were analyzed by X-band electron paramagnetic resonance (EPR) and high-frequency (HF) EPR spectroscopy.

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)] ().

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).

Tuning of Cr-Cr Magnetic Exchange through Chalcogenide Linkers in Cr Molecular Dimers.

A set of three Cr-dimer compounds, Cr(en) (: S, Se; : Br, Cl; : ethylenediamine), with monoatomic chalcogenide bridges have been synthesized via a single-step solvothermal route. Chalcogenide linkers mediate magnetic exchange between Cr centers, while bidentate ethylenediamine ligands complete the distorted octahedral coordination of Cr centers. Unlike the compounds previously reported, none of the chalcogenide atoms are connected to extra ligands.

Homochiral Mn Spin-Crossover Complexes: A Structural and Spectroscopic Study.

Structural, magnetic, and spectroscopic data on a Mn spin-crossover complex with Schiff base ligand 4-OMe-Sal323, isolated in crystal lattices with five different counteranions, are reported. Complexes of [Mn(4-OMe-Sal323)]X where X = ClO (), BF (), NO (), Br (), and I () crystallize isotypically in the chiral orthorhombic space group 222 with a range of spin state preferences for the [Mn(4-OMe-Sal323)] complex cation over the temperature range 5-300 K. Complexes and are high-spin, complex undergoes a gradual and complete thermal spin crossover, while complexes and show stepped crossovers with different ratios of spin triplet and quintet forms in the intermediate temperature range.

The Ising triangular-lattice antiferromagnet neodymium heptatantalate as a quantum spin liquid candidate.

Disordered magnetic states known as spin liquids are of paramount importance in both fundamental and applied science. A classical state of this kind was predicted for the Ising antiferromagnetic triangular model, while additional non-commuting exchange terms were proposed to induce its quantum version-a quantum spin liquid. However, these predictions have not yet been confirmed experimentally.

Magneto-structural Correlations in Ni-Halide···Halide-Ni Chains.

We present the magnetic properties of a new family of = 1 molecule-based magnets, NiF(3,5-lut)·2HO and NiX(3,5-lut), where X = HF, Cl, Br, or I (lut = lutidine CHN). Upon creation of isolated Ni-X···X-Ni and Ni-F-H-F···F-H-F-Ni chains separated by bulky and nonbridging lutidine ligands, the effect that halogen substitution has on the magnetic properties of transition-metal-ion complexes can be investigated directly and in isolation from competing processes such as Jahn-Teller distortions. We find that substitution of the larger halide ions turns on increasingly strong antiferromagnetic interactions between adjacent Ni ions via a novel through-space two-halide exchange.

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.

Nitrene Photochemistry of Manganese N-Haloamides*.

Manganese complexes supported by macrocyclic tetrapyrrole ligands represent an important platform for nitrene transfer catalysis and have been applied to both C-H amination and olefin aziridination catalysis. The reactivity of the transient high-valent Mn nitrenoids that mediate these processes renders characterization of these species challenging. Here we report the synthesis and nitrene transfer photochemistry of a family of Mn N-haloamide complexes.

o-Semiquinone radical anion isolated as an amorphous porous solid.

The use of metal cations is a commonly applied strategy to create S > 1/2 stable molecular systems containing semiquinone radicals. Persistent mono-semiquinonato complexes of diamagnetic metal ions (S = 1/2) have been hitherto less common and mostly limited to the complexes of heavy metal ions. In this work, a mono-semiquinonato complex of aluminum, derived from 1,2-dihydroxybenzene, is obtained using a surprisingly short and uncomplicated procedure.

High-Frequency and -Field Electron Paramagnetic Resonance Spectroscopic Analysis of Metal-Ligand Covalency in a 4f Valence Series (Eu, Gd, and Tb).

The recent isolation of molecular tetravalent lanthanide complexes has enabled renewed exploration of the effect of oxidation state on the single-ion properties of the lanthanide ions. Despite the isotropic nature of the S ground state in a tetravalent terbium complex, [Tb(NP(1,2-bis-Bu-diamidoethane)(NEt))], preliminary X-band electron paramagnetic resonance (EPR) measurements on tetravalent terbium complexes show rich spectra with broad resonances. The complexity of these spectra highlights the limits of conventional X-band EPR for even qualitative determination of zero-field splitting (ZFS) in these complexes.

Investigation of vanadium(III) and vanadium(IV) compounds supported by the linear diaminebis(phenolate) ligands: correlation between structures and magnetic properties.

A family of oxidovanadium(iv) compounds containing linear diaminebis(phenolate (salans) L1-5 ligands (L1 = [MeNCH2CH2NMe(CH2-4-CMe2CH2CMe3-C6H3O)2]2-; L2 = [MeNCH2CH2NMe(CH2-4-CH3-C6H3O)2]2-; L3 = [MeNCH2CH2NMe(CH2-4-Cl-C6H3O)2]2-; L4 = {MeNCH2CH2NMe[CH2-4,6-(CH3)2-C6H2O]2}2-; and L5 = {MeNCH2CH2NMe[CH2-4,6-(Br)2-C6H2O]2}2-) and non-oxidovanadium(iii) with L2,4 and acac ligands has been prepared and characterized by chemical and physical techniques. Reactions of [VO(acac)2] with ligand precursors H2L2,4 in toluene or hexane afforded vanadium(iii) compounds [V(L-κ4ONNO)(acac)] (1, L2; 2, L4), while the use of acetonitrile or ethanol led to the formation of dimeric oxidovanadium(iv) [(VO)2(μ-L-κ4ONNO)2] (3, L1; 4, L2; 5, L3) and monomeric [VO(L-κ4ONNO)] (6, L4, 7, L5) compounds. As shown by X-ray crystallography, compounds 1 and 2 are monomeric, in which the chelating ligands afford octahedral cis-α geometry at the vanadium center.

Controlling Magnetic Anisotropy in a Zero-Dimensional = 1 Magnet Using Isotropic Cation Substitution.

The [ZnNi(HF)(pyz)]SbF ( = 0.2; pyz = pyrazine) solid solution exhibits a zero-field splitting () that is 22% larger [ = 16.2(2) K (11.

Ferro- antiferromagnetic exchange between two Ni(II) ions in a series of Schiff base heterometallic complexes: what makes the difference?

Three new NiII/ZnII heterometallics, [NiZnL'2(OMe)Cl]2 (1), [NiZnL''(Dea)Cl]2·2DMF (2) and [Ni2(H3L''')2(o-Van)(MeOH)2]Cl·[ZnCl2(H4L''')(MeOH)]·2MeOH (3), containing three-dentate Schiff bases as well as methanol or diethanolamine (H2Dea) or o-vanillin (o-VanH), all deprotonated, as bridging ligands were synthesized and structurally characterized. The Schiff base ligands were produced in situ from o-VanH and CH3NH2 (HL'), or NH2OH (HL"), or 2-amino-2-hydroxymethyl-propane-1,3-diol (H4L'''); a zerovalent metal (Ni and Zn in 1, Zn only in 2 and 3) was employed as a source of metal ions. The first two complexes are dimers with a Ni2Zn2O6 central core, while the third compound is a novel heterometallic cocrystal salt solvate built of a neutral zwitterionic ZnII Schiff base complex and of ionic salt containing dinuclear NiII complex cations.

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.

Origin of Magnetic Ordering in a Structurally Perfect Quantum Kagome Antiferromagnet.

The ground state of the simple Heisenberg nearest-neighbor quantum kagome antiferromagnetic model is a magnetically disordered spin liquid, yet various perturbations may lead to fundamentally different states. Here we disclose the origin of magnetic ordering in the structurally perfect kagome material YCu_{3}(OH)_{6}Cl_{3}, which is free of the widespread impurity problem. Ab initio calculations and modeling of its magnetic susceptibility reveal that, similar to the archetypal case of herbertsmithite, the nearest-neighbor exchange is by far the dominant isotropic interaction.