An investigation of the electron density of a Jahn–Teller‐distorted CrII cation: the crystal structure and charge density of hexakis(acetonitrile‐κN)chromium(II) bis(tetraphenylborate) acetonitrile disolvate

In the crystal structure of the title homoleptic Cr^II complex, [Cr(CH₃CN)₆](C₂₄H₂₀B)₂·CH₃CN, the [Cr(CH₃CN)₆]²⁺ cation is a high‐spin d⁴ complex with strong static, rather than dynamic, Jahn–Teller distortion. The electron density of the cation was determined by single‐crystal X‐ray refinements using aspherical structure factors from wavefunction calculations. The detailed picture of the electronic density allowed us to assess the extent and directionality of the Jahn–Teller distortion of the Cr^II cation away from idealized octahedral symmetry. The topological analysis of the aspherical d‐electron density about the Cr^II cation showed that there are significant valence charge concentrations along the axial Cr—N axes. Likewise, there were significant valence charge depletions about the Cr^II cation along the equatorial Cr—N bonds. These charge concentrations are in accordance with a Jahn–Teller‐distorted six‐coordinate complex.     

Studies on the local structures for the trigonal Ni3+ centers in cathode materials LiAlyCo1–yO2 (y = 0, 0.1, 0.5, and 0.8)

The local angular distortions Δθ are theoretically studied for the various Ni³⁺ centers in LiAl_yCo_1–yO₂ at different Al concentrations (y = 0, 0.1, 0.5, and 0.8) based on the perturbation calculations of electron paramagnetic resonance g factors for a trigonally distorted octahedral 3d⁷ cluster with low spin (S = 1/2). Due to the Jahn–Teller effect, the [NiO₆]^9– clusters are found to experience the local angular distortions (Δθ ≈ 5°–9°) along the C₃ axis. The variation trend of Δθ with y is in accordance with that of anisotropy (Δg = g_|| − g_⊥). As the substitutions can weaken bond strengths between transition metal and oxygen and the structural stability plays an important role in cathode performances, detailed investigations on the structural properties of the cathode materials LiAl_yCo_1–yO₂ can be practically helpful to understand the performances of these materials. The oxy‐redox properties of LiAl_yCo_1–yO₂ systems are comprehensible in the framework of Ni³⁺/Ni⁴⁺ couples, and the trigonally compressed octahedral [NiO₆]^9– clusters are applicable to the clarification of the electrochemical properties of lithium nickel oxide batteries. It appears that LiAl_0.8Co_0.2O₂ with the largest Al concentration may correspond to the smallest distortion among the mixing systems.     

Enhanced Pseudocapacitance in Multicomponent Transition‐Metal Oxides by Local Distortion of Oxygen Octahedra

Anomalously high pseudocapacitance of a metal oxide was observed when Ni, Co, and Mn were mixed in a solid solution. Analysis by X‐ray absorption near‐edge spectroscopy (XANES) identified a wider redox swing of Ni as the origin of the enlarged pseudocapacitance. Ab initio DFT calculations revealed that aliovalent species resulting from the copresence of multiple transition metals can generate permanent local distortions of [NiO₆] octahedra. As this type of distortion breaks the degenerate e_g level of Ni²⁺, the Jahn–Teller lattice instability necessary for the Ni^2+/3+ redox flip can be effectively diminished during charge–discharge, thus resulting in the significantly increased capacitance. Our findings highlight the importance of understanding structure–property correlation related to local structural distortions in improving the performance of pseudocapacitors.     

Nonadiabatic theory of triatomics: Formalism for 1Πu/1Φg interaction,for electronic spin,and for 2Λ Renner–Teller effect

A recent theory of nonadiabatic effects in triatomic molecules is specialized to the four-state Renner–Teller and Jahn–Teller ¹Π_u/¹Φ_g interactions and is then generalized by including the electronic spin and by considering the ²Λ Renner–Teller effect.     

Mononuclear vs. binuclear carboxylates of copper(II) with 2,2′‐bipyridine: Synthesis,characterization, structural description,and properties

Two new copper(II) carboxylate complexes with 2,2′‐bipyridine and para‐nitrophenyl acetate (complex 1 ) and phenyl acetate (complex 2 ) have been synthesized; isolated in quantitative yield; and characterized using fourier‐transform infrared spectroscopy (FT‐IR), electron paramagnetic resonance, absorption spectroscopy, electrochemistry, and powder and single crystal X‐ray diffraction (XRD) techniques. Being mononuclear, the geometry around copper in complex 1 is a Jahn–Teller distorted octahedral, while complex 2 is binuclear with slightly distorted square pyramidal geometry around both copper ions. Powder XRD indicated several peaks in spectra of both complexes, which coincided with their theoretical spectra. FT‐IR results of the carboxylate stretching frequency were in accordance with the single crystal structure data. Electron paramagnetic resonance spectra of complexes 1 and 2 yielded g_┴ values of 2.06161 and 2.24623 and 1.94959, respectively, indicating a localized electron in b₁ (d _x²_–y²‐orbital). Ultra‐violet (UV)–visible spectroscopy and electrochemistry helped in characterization, as well as in deoxyribonucleic acid (DNA)‐binding ability of the complexes, yielding DNA‐binding constant values = 1.351 × 10⁴ and 1.361 × 10⁴ and 1.820 × 10⁴ and 2.426 × 10⁴ M^?1, respectively, for complexes 1 and 2 . The complexes demonstrate good biological potential.     

Microporous La–Metal–Organic Framework (MOF) with Large Surface Area

A microporous La–metal‐organic framework (MOF) has been synthesized by the reaction of La(NO₃)₃ ? 6 H₂O with a ligand 4,4′,4′′‐s‐triazine‐1,3,5‐triyltri‐p‐aminobenzoate (TATAB) featuring three carboxylate groups. Crystal structure analysis confirms the formation of 3D MOF with hexagonal micropores, a Brunauer–Emmett—Teller (BET) surface area of 1074 m² g^?1 and high thermal and chemical stability. The CO₂ adsorption capacities are 76.8 cm³ g^?1 at 273 K and 34.6 cm³ g^?1 at 293 K, a highest measured CO₂ uptake for a Ln–MOFs.     

Sodium and Manganese Stoichiometry of P2‐Type Na2/3MnO2

To realize a reversible solid‐state Mn^III/IV redox couple in layered oxides, co‐operative Jahn–Teller distortion (CJTD) of six‐coordinate Mn^III (t_2g³–e_g¹) is a key factor in terms of structural and physical properties. We develop a single‐phase synthesis route for two polymorphs, namely distorted and undistorted P2‐type Na_2/3MnO₂ having different Mn stoichiometry, and investigate how the structural and stoichiometric difference influences electrochemical reaction. The distorted Na_2/3MnO₂ delivers 216 mAh g^?1 as a 3 V class positive electrode, reaching 590 Wh (kg oxide)^?1 with excellent cycle stability in a non‐aqueous Na cell and demonstrates better electrochemical behavior compared to undistorted Na_2/3MnO₂. Furthermore, reversible phase transitions correlated with CJTD are found upon (de)sodiation for distorted Na_2/3MnO₂, providing a new insight into utilization of the Mn^III/IV redox couple for positive electrodes of Na‐ion batteries.     

Water‐Stable Zirconium‐Based Metal–Organic Framework Material with High‐Surface Area and Gas‐Storage Capacities

We designed, synthesized, and characterized a new Zr‐based metal–organic framework material, NU‐1100 , with a pore volume of 1.53 ccg^?1 and Brunauer–Emmett–Teller (BET) surface area of 4020 m²g^?1; to our knowledge, currently the highest published for Zr‐based MOFs. CH₄/CO₂/H₂ adsorption isotherms were obtained over a broad range of pressures and temperatures and are in excellent agreement with the computational predictions. The total hydrogen adsorption at 65 bar and 77 K is 0.092 g g^?1, which corresponds to 43 g L^?1. The volumetric and gravimetric methane‐storage capacities at 65 bar and 298 K are approximately 180 v_STP/v and 0.27 g g^?1, respectively.     

ESR STUDY OF IRRADIATED PENTACYANONITROSYL COBALTATE (II)

Abstract

An ESR study of γ-irradiated pentacyanonitrosyl cobaltate (II) shows the presence of two paramagnetic species. One, with g∥ =2.005, g∥ =2.172, A∥ 81.3 and A∥ =-26.2 × 10^?4 cm^?1, is the well-known d ⁷ species Co(CN)₅ ^3-. The second shows g∥<g∥ and much lower ⁵⁹Co hyperfine interactions. The ESR parameters are shown to be consistent with those predicted for the species [Co(CN)₅ NO]^4- with C _S symmetry, a bent Co–N–O bond, and a d ₇ configuration with the odd electron in an a' orbital formed by mixing the cobalt d _x –y ² and d _z ² orbitals. Theoretical arguments are advanced to show that, in general, small metal hyperfine splittings in low symmetry ions do not necessarily establish that the unpaired electron is in a ligand-dominated orbital.     

P2‐Na0.67AlxMn1−xO2: Cost‐Effective,Stable and High‐Rate Sodium Electrodes by Suppressing Phase Transitions and Enhancing Sodium Cation Mobility

Sodium layered P2‐stacking Na_0.67MnO₂ materials have shown great promise for sodium‐ion batteries. However, the undesired Jahn–Teller effect of the Mn⁴⁺/Mn³⁺ redox couple and multiple biphasic structural transitions during charge/discharge of the materials lead to anisotropic structure expansion and rapid capacity decay. Herein, by introducing abundant Al into the transition‐metal layers to decrease the number of Mn³⁺, we obtain the low cost pure P2‐type Na_0.67Al_xMn_1?xO₂ (x=0.05, 0.1 and 0.2) materials with high structural stability and promising performance. The Al‐doping effect on the long/short range structural evolutions and electrochemical performances is further investigated by combining in situ synchrotron XRD and solid‐state NMR techniques. Our results reveal that Al‐doping alleviates the phase transformations thus giving rise to better cycling life, and leads to a larger spacing of Na⁺ layer thus producing a remarkable rate capability of 96 mAh g^‐1 at 1200 mA g^‐1.     

C–C bridged Ni(II) complexes bearing β‐keto‐9‐fluorenyliminato ligands prepared by different in situ bonding mechanisms and their use in catalytic (co)polymerization of norbornene and styrene

Two C–C bridged Ni(II) complexes bearing β‐keto‐9‐fluorenyliminato ligands with electron‐withdrawing groups (─CF₃), Ni{PhC(O)CHC[N(9‐fluorenyl)]CF₂}₂ (Ni 1 ) and Ni{CF₃C(O)CHC[N(9‐fluorenyl)]Ph}₂ (Ni 2 ), were synthesized by metal coordination reaction and different in situ bonding mechanisms. The C–C bridged bonds of Ni 1 were formed by in situ intramolecular trifluoromethyl and 9‐fluorenyl carbon–carbon cross‐coupling reaction and those of Ni 2 were formed by in situ intramolecular 9‐fluorenyl carbon–carbon radical coupling reaction mechanism. The obtained complexes were characterized using ¹H NMR spectroscopy and elemental analyses. The crystal and molecular structures of Ni 1 and Ni 2 with C–C bridged configuration were determined using X‐ray diffraction. Ni 1 and Ni 2 were used as catalysts for norbornene (NB) polymerization after activation with B(C₆F₅)₃ and the catalytic activities reached 10⁶ g_polymer mol_Ni^?1 h^?1. The copolymerization of NB and styrene catalyzed by the Ni 1 /B(C₆F₅)₃ system showed high activity (10⁵ g_polymer mol_Ni^?1 h^?1) and the catalytic activities decreased with increasing feed content of styrene. All vinyl‐type copolymers exhibited high molecular weight (10⁴ g mol^?1), narrow molecular weight distribution (M_w/M_n = 1.71–2.80), high styrene insertion ratios (11.13–50.81%) and high thermal stability (T_d > 380°C) and could be made into thin films with high transparency in the visible region (400–800 nm).     

Jahn‐Teller‐Ordnung in Mangan(III)‐fluoridsulfaten. II. Phasenübergang und Verzwillingung bei K2[MnF3(SO4)] und 1D Magnetismus in Verbindungen A2[MnF3(SO4)] (A = K,NH4, Rb,Cs)

Jahn‐Teller Ordering in Manganese(III) Fluoride Sulfates. II. Phase Transition and Twinning of K₂[MnF₃(SO₄)] and 1D Magnetism in Compounds A₂[MnF₃(SO₄)] (A = K, NH₄, Rb, Cs) According to single‐crystal X‐ray investigations, K₂[MnF₃(SO₄)] crystallizes at low temperature, like the isostructural Rb, NH₄, and Cs analogues in space group P2₁/c, Z = 4, e.g. at 100 K with a = 7.197, b = 10.704, c = 8.427Å, β = 91.84°. Below about 300 K, the crystals are found to be [001] axis twins. Using a new integration method for area detector records, nearly complete intensity data could be gained allowing for structure refinements of similar quality as for untwinned crystals (e.g. at 100 K: wR₂ = 0.050, R = 0.020 for all reflections). With rising temperature, the monoclinic angle approaches continuously 90°. For an ordering parameter Δβ = β?90° a 2^nd‐order phase transition is observed with an exponent λ = 0.17. At the transition temperature of 280 K resulting from the fit, the monoclinic structure changes – with delay – to orthorhombic with the minimum super‐group Pnca, a = 7.243, b = 10.763, c = 8.457Å, R = 0.024, as found in an early structure determination at room temperature by Edwards 1971. In the chain‐like [MnF₃(SO₄)]^2? anions, manganese(III) is octahedrally coordinated by two trans‐terminal and two trans‐bridging fluorine ligands as well as by the O atoms of two trans‐bridging sulfate ligands. At low temperature, the octahedral elongation by the Jahn‐Teller effect alternates between a F–Mn–F and an O–Mn–O axis (antiferrodistortive ordering). All bridges are asymmetric. From about 320 K on they become symmetric. Due to 2D dynamical Jahn‐Teller effect all octahedra appear compressed. All compounds A₂[MnF₃(SO₄)] show 1D antiferromagnetism. The antiferrodistortive Jahn‐Teller order at low temperatures and the small bridge angles explain the much lower magnetic exchange energies and their inverse relation to the bridge angles as compared with other fluoromanganate(III) chain compounds with the usual ferrodistortive ordering.     

Conducting π Columns of Highly Symmetric Coronene,The Smallest Fragment of Graphene

Coronene, which is the smallest D_6h‐symmetric polycyclic aromatic hydrocarbon, attracts particular attention as a basic component of electronic materials because it is the smallest fragment of graphene. However, carrier generation by physical methods, such as photo‐ or electric field‐effect, has barely been studied, primarily because of the poor π‐conduction pathway in pristine coronene solid. In this work we have developed unprecedented π‐stacking columns of cationic coronene molecules by electrochemical hole‐doping with polyoxometallate dianions. The face‐to‐face π–π interactions as well as the partially charged state lead to electrical conductivity at room temperature of up to 3 S cm^?1, which is more than 10 orders of magnitude higher than that of pristine coronene solid. Additionally, the robust π–π interactions strongly suppress the in‐plane rotation of the coronene molecules, which has allowed the first direct observation of the static Jahn–Teller distortion of cationic coronene molecules.     

An alternative interpretation of the “anomalous” positive g∥-shift observed for NH4I: Cu2+

It is shown that the positive g_∥-shift observed for two centers in NH₄I : Cu²⁺ with compressed octahedral geometry can be reasonably understood within a molecular orbital picture for a true C_4v complex. Following this explanation, which discards the vibronic admixture mechanism proposed by Chand and Upreti, the positive g_∥ - g₀ value arises from a charge-transfer contribution to g_∥ - g₀ similar to that of d⁷ ions in strong-field situations.     

Jahn–Teller Effect in Circulenes: X‐ray Diffraction Study of Coronene and Corannulene Radical Anions

Single‐crystal X‐ray diffraction studies of two polyaromatic radical anions crystallized as sodium salts, namely [Na(DME)₃]⁺[C₂₀H₁₀^?] ( 1 ) and [Na(DME)₃]⁺[C₂₄H₁₂^?] ( 2 ) are reported. This allowed the first structural evaluation of Jahn–Teller (JT) effects for monoreduced circulenes and a comparison between bowl‐shaped corannulene and planar coronene. The C_s and D_2h symmetrical distortions are found to fit the experimental data for C₂₀H₁₀^.? and C₂₄H₁₂^.?, respectively. The continuous symmetry measure (CSM) analysis was carried out to provide a quantitative measure of the JT distortions in 1 and 2 . In addition, the X‐ray crystallographic results were fully supported by DFT calculations.     

Role of Magnetic Exchange Interactions in the Magnetization Relaxation of {3d–4f} Single‐Molecule Magnets: A Theoretical Perspective

Combined density functional and ab initio calculations are performed on two isomorphous tetranuclear {Ni₃^IIILn^III} star‐type complexes [Ln=Gd ( 1 ), Dy ( 2 )] to shed light on the mechanism of magnetic exchange in 1 and the origin of the slow magnetization relaxation in complex 2 . DFT calculations correctly reproduce the sign and magnitude of the J values compared to the experiments for complex 1 . Acute ?Ni?O?Gd bond angles present in 1 instigate a significant interaction between the 4f_xyz orbital of the Gd^III ion and 3d orbital of the Ni^II ions, leading to rare and strong antiferromagnetic Ni???Gd interactions. Calculations reveal the presence of a strong next‐nearest‐neighbour Ni???Ni antiferromagnetic interaction in complex 1 leading to spin frustration behavior. CASSCF+RASSI‐SO calculations performed on complex 2 suggest that the octahedral environment around the Dy^III ion is neither strong enough to stabilize the m_J |±15/2〉 as the ground state nor able to achieve a large ground‐state–first‐excited‐state gap. The ground‐state Kramers doublet for the Dy^III ion is found to be the m_J |±13/2〉 state with a significant transverse anisotropy, leading to very strong quantum tunneling of magnetization (QTM). Using the POLY_ANISO program, we have extracted the J_NiDy interaction as ?1.45 cm^?1. The strong Ni???Dy and next‐nearest‐neighbour Ni???Ni interactions are found to quench the QTM to a certain extent, resulting in zero‐field SMM behavior for complex 2 . The absence of any ac signals at zero field for the structurally similar [Dy(AlMe₄)₃] highlights the importance of both the Ni???Dy and the Ni???Ni interactions in the magnetization relaxation of complex 2 . To the best of our knowledge, this is the first time that the roles of both the Ni???Dy and Ni???Ni interactions in magnetization relaxation of a {3d–4f} molecular magnet have been established.     

[CH3NH3]4Ga4SbS9S0.28O0.72H: A Three‐Dimensionally Open‐Framework Heterometallic Chalcogenidoantimonate Exhibiting Ni2+ Ion‐Exchange Property

An open‐framework chalcogenidoantimonate, namely, [CH₃NH₃]₄Ga₄SbS₉S_0.28O_0.72H ( 1 ), has been solvothermally synthesized and structurally characterized. Interestingly, 1 showed Ni²⁺ ion‐exchange properties and wide pH resistance, with a maximum exchange capacity of 76.9 mg g^?1. To the best of our knowledge, this is the first example of amine‐directed three‐dimensional (3D) heterometallic chalcogenidometalates for highly selective Ni²⁺ ion capture with a high distribution coefficient (K_d=1.65×10⁵ mL g^?1).     

A comparison of ground- and excited-state properties of [Ru(bz)2]2+ and bis(η6-benzene)ruthenium(II) p-toluenesulfonate using the density functional theory

The ground- and excited-state properties of both [Ru(bz)₂]²⁺ and crystalline bis(η⁶-benzene)ruthenium(II) p-toluenesulfonate are investigated using the density functional theory. A symmetry-based technique is employed to calculate the energies of the multiplet structure splitting of the singly excited triplet states. For the crystalline system, a Buckingham potential is introduced to describe the intermolecular interactions between the [Ru(bz)₂]²⁺ system and its first shell of neighbor molecules. The overall agreement between experimental and calculated ground- and excited-state properties is good, as far as the absolute transition energies, the Stokes shift, and the geometry of the excited states are concerned. The calculated d-d excitation energies of the isolated cluster are typically 1000–2000 cm⁻¹ too low. An energy lowering is obtained in a_1g→e_1g(³E_1g) excited state when the geometry of [Ru(bz)₂]²⁺ is bent along the e_1u Renner–Teller active coordinate. It vanishes as the crystal packing is taken into account. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1343–1353, 1999     

Green Luminescence of Divalent Europium in the Hydride Chloride EuHCl

Luminescence properties of divalent europium in the mixed‐anion hydride chloride EuHCl were studied for the first time. Olive‐green single crystals of EuHCl (PbFCl‐type structure: tetragonal, P4/nmm, a = 406.58(3) pm, c = 693.12(5) pm, c/a = 1.705, Z = 2) resulted from the reaction of elemental europium (Eu), sodium hydride (NaH) and sodium chloride (NaCl), while powder samples were prepared from the binary components europium dihydride (EuH₂) and dichloride (EuCl₂). Low temperature X‐ray powder diffraction proved the absence of phase transitions for 12(2) K ≤ T ≤ 295(2) K. Bright green emission was observed under UV‐excitation and assigned to the 4f⁶5d¹–4f⁷ transition of divalent europium. Temperature‐dependent luminescence absorption and emission, as well as lifetime measurements were carried out on single crystal and powder samples. Surprisingly, only limited concentration quenching was found. Additionally, two emission bands (485 and 510 nm) are observed, whose intensity ratio depends strongly on temperature. In order to explain this behavior for a single Eu²⁺ site, we suggest either a dynamical Jahn–Teller effect in the excited 5d¹ state or emission from both a 4f⁶5d¹ state and a trapped exciton state.     

P2‐Na0.67AlxMn1−xO2: Cost‐Effective,Stable and High‐Rate Sodium Electrodes by Suppressing Phase Transitions and Enhancing Sodium Cation Mobility

Sodium layered P2‐stacking Na_0.67MnO₂ materials have shown great promise for sodium‐ion batteries. However, the undesired Jahn–Teller effect of the Mn⁴⁺/Mn³⁺ redox couple and multiple biphasic structural transitions during charge/discharge of the materials lead to anisotropic structure expansion and rapid capacity decay. Herein, by introducing abundant Al into the transition‐metal layers to decrease the number of Mn³⁺, we obtain the low cost pure P2‐type Na_0.67Al_xMn_1?xO₂ (x=0.05, 0.1 and 0.2) materials with high structural stability and promising performance. The Al‐doping effect on the long/short range structural evolutions and electrochemical performances is further investigated by combining in situ synchrotron XRD and solid‐state NMR techniques. Our results reveal that Al‐doping alleviates the phase transformations thus giving rise to better cycling life, and leads to a larger spacing of Na⁺ layer thus producing a remarkable rate capability of 96 mAh g^‐1 at 1200 mA g^‐1.