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Concept: Jahn–Teller effect

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This tutorial review discusses the structural and electronic consequences of the Jahn-Teller effect in transition metal complexes, focussing on copper(ii) compounds which tend to be the most studied. The nature of a Jahn-Teller distortion in molecular complexes and extended lattices can be manipulated by application of pressure or temperature, by doping a molecule into a host lattice, or simply by molecular design. Many of these results have been achieved using compounds with a trans-[CuX(4)Y(2)] coordination sphere, which seems to afford copper centres that are particularly sensitive to their environment. Jahn-Teller distortions lead to some unusual phenomena in molecular magnetism, and are important to the functionality of important classes of conducting and superconducting ceramics.

Concepts: Electron, Jahn–Teller effect, Silver, Chemical bonding, Oxygen, Zinc, Inorganic chemistry, Coordination chemistry

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Natural goethite (a-FeOOH) commonly accommodates various metal elements by substituting for Fe, which greatly alters the surface reactivity of goethite. This study discloses the enhancement of Mn-substitution for the Pb2+ adsorption capacity of goethite. The incorporated Mn in the synthesized goethite presents as Mn(III) and causes a slight decrease in the a and c of the unit cell parameters and an observable increase in the b direction due to the Jahn-Teller effect of the Mn(III)O6 octahedra. With the Mn content increasing, the particle size decreases gradually, and the surface clearly becomes roughened. The Pb2+ adsorption capacity of goethite is observably enhanced by Mn substitution due to the modified surface complexes. And the increased surface-area-normalized adsorption capacity for Mn-substituted goethite indicated that the enhancement of Pb adsorption is not only attributed to the increase of surface area but also to the change of binding complexes. Extended X-ray Absorption Fine Structure (EXAFS) analysis indicates that the binding structures of Pb2+ on goethite presents as edge-sharing complexes with a regular R Pb-Fe=3.31 Å. In the case of Mn-goethite, Pb2+ is also bound with the Mn surface site on the edge-sharing complex with a larger R Pb-Mn=3.47 Å. The mechanism for enhancing Pb2+ adsorption on Mn-goethite can be interpreted as the preferred Pb2+ binding on the Mn site of Mn-goethite surface. In summary, the Mn-goethite has great potential for material development in environmental remediation.

Concepts: X-ray absorption fine structure, Observable, Hilbert space, Jahn–Teller effect, Electron, Metal, Knitting, Structure

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The first free cyclobutadiene (CBD) germanium analogue was obtained as room-temperature stable dark red crystals via the reaction of the bulky EMind-substituted 1,2-dichlorodigermene with lithium naphthalenide. The cyclic 4π-electron antiaromaticity is essentially stabilized by the polar Jahn-Teller distortion in the germanium CBD producing a planar rhombic-shaped charge-separated structure.

Concepts: Edward Teller, Jahn–Teller effect

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The local distortions and electron paramagnetic resonance (EPR) parameters for Cu(2+) in the mixed alkali borate glasses xNa2 O-(30-x)K2 O-70B2 O3 (5 ≤ x ≤ 25 mol%) are theoretically studied with distinct modifier Na2 O compositions x. Owing to the Jahn-Teller effect, the octahedral [CuO6 ](10-) clusters show significant tetragonal elongation ratios p ~ 19% along the C4 axis. With the increase of composition x, the cubic field parameter Dq and the orbital reduction factor k exhibit linearly and quasi-linearly decreasing tendencies, respectively, while the relative tetragonal elongation ratio p has quasi-linearly increasing rule with some fluctuations, leading to the minima of g factors at x = 10 mol %. The composition dependences of the optical spectra and the EPR parameters are suitably reproduced by the linear or quasi-linear relationships of the relevant quantities (i.e., Dq, k and p) with x. The above composition dependences are analyzed from mixed alkali effect, which brings forward the modifications of the local crystal-fields and the electronic cloud distribution around Cu(2+) with the variation of the composition of Na2 O.

Concepts: Jahn–Teller effect, Order theory, Magnetic moment, Inorganic chemistry, C, Electron paramagnetic resonance, Function, Fundamental physics concepts

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The structure of free manganese(III) tris(acetylacetonate) [Mn(acac)3] was determined by mass-spectrometrically controlled gas-phase electron diffraction. The vapor of Mn(acac)3 at 125(5)°C is composed of a single conformer of Mn(acac)3 in C2 symmetry with the central structural motif of a tetragonal elongated MnO6 octahedron and 47(2) Mol% of acetylacetone (Hacac) formed by partial thermal decomposition of tris(acetylacetonate). Three types of Mn-O distances have been refined (rh1 = 2.157(16), 1.946(5) and 1.932(5) Å. We have found no indication of significant deviations of the -C-C-C-O-Mn-O- six-membered rings from planarity, which is observed in the solid state.

Concepts: Fundamental physics concepts, The Central, Acetylacetone, Structure, Jahn–Teller effect, Temperature, Gas, Electron

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Vibronic-coupling effects play a key role in excited-state charge- and energy-transfer processes of organic molecular systems. Here, we demonstrate how Jahn-Teller effect in triplet excited states of highly symmetric cycloparaphenylenes triggers an indirect intersystem crossing deactivation pathway. Strong Jahn-Teller distortion in the doubly- degenerate second excited triplet state (T2) brings the molecular system close to the lower excited state (T1), thereby opening the possibility for an extremely rapid internal conversion. Quantum dynamics simulations reveal an initial T2→T1 population decay within 50 fs. Experimental observation of size-dependent intersystem crossing rates is explained based on the proposed S1→T3/T2→T1 mechanism.

Concepts: Edward Teller, Excited state, Jahn–Teller effect, Chemical bonding, Atom, Quantum mechanics

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The occupied and unoccupied electronic structures of three high spin TM(acac)3 (TM = Cr, Mn, and Fe) complexes (I, II, and III, respectively) were studied by revisiting their literature vapour-phase He(i) and, when available, He(ii) photoemission (PE) spectra and by means of original near-edge X-ray absorption fine structure (NEXAFS) spectroscopic data recorded at the O K-edge ((O)K-edge) and TM L2,3-edges (™L2,3-edges). The assignments of the vapour-phase He(i)/He(ii) PE spectra were guided by the results of spin-unrestricted non-relativistic Slater transition state calculations, while the (O)K-edge and ™L2,3-edge spectroscopic pieces of evidence were analysed by exploiting the results of spin-unrestricted scalar-relativistic time-dependent density functional theory (DFT) and DFT/ROCIS calculations, respectively. Although the actual symmetry (D3, in the absence of any Jahn-Teller distortion) of the title molecules allowed an extensive mixing between TM t2g-like and eg-like atomic orbitals, the use of the Nalewajski-Mrozek TM-O bond multiplicity index combined with a thorough analysis of the ground state (GS) outcomes allowed the assessment of the TM-O bond weakening associated with the progressive TM 3d-based eg-like orbital filling. The experimental information provided by (O)K-edge spectra was rather poor; nevertheless, the combined use of symmetry, orbitals and spectra allowed us (i) to rationalise minor differences characterizing spectral features along the series, (ii) to quantify the contribution provided by the ligand-to-metal-charge-transfer (LMCT) excitations to the different spectral features, and (iii) to recognize the t2g-/eg-like nature of the TM 3d-based orbitals involved in LMCT transitions. As far as the ™L2,3-edge spectra and the DFT/ROCIS results were concerned, the lowest lying I(,)IIL3 spectral features included states having either the GS spin multiplicity (S(I) = 3/2, S(II) = 2) or, at higher excitation energies (EEs), states with ΔS = ±1. In contrast to that, only states with ΔS = 0, -1 significantly contributed to the IIIL3 spectral pattern. Along the whole series, the L3 higher EE side was systematically characterized by states involving ™2p → π4 MLCT excitations; as such, coupled-single excitations with ΔS = 0 were involved in I and II, while single MLCT ™2p → π4 transitions with ΔS = -1 were involved in III.

Concepts: Chemical bonding, Jahn–Teller effect, Quantum mechanics, Edward Teller, Quantum chemistry, Density functional theory, Spin, Electron

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M-MOF-74s were examined for potential applications in ethylene abatement and/or storage/delivery. Due to labile binding resulting from a Jahn-Teller distortion, Cu-MOF-74 exhibits a gradual initial uptake that, in turn, translates into the highest deliverable capacity among the MOFs examined (3.6 mmol g(-1)). In contrast, Co-MOF-74 is the most promising candidate for ethylene abatement due to the sharp uptake at low pressure.

Concepts: Weather map, Heavy metal music, Adsorption, Atom, Gas, Ethylene, Jahn–Teller effect, Ideal gas law

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MSb2O6 compounds (M = Mg, Co, Ni, Cu, Zn) are known in the tetragonal trirutile forms, slightly distorted monoclinically with M = Cu due to the Jahn-Teller effect. In this study, using a low-temperature exchange reaction between ilmenite-type NaSbO3 and molten MSO4-KCl (or MgCl2-KCl) mixtures, these five compositions were prepared for the first time as trigonal layered rosiaite (PbSb2O6)-type phases. Upon heating, they irreversibly transform to the known phases via amorphous intermediates, in contrast to previously studied isostructural MnSb2O6, where the stable phase is structurally related to the metastable phase. The same method was found to be applicable for preparing stable rosiaite-type CdSb2O6. The formula volumes of the new phases show an excellent correlation with the ionic radii (except for M = Cu, for which a Jahn-Teller distortion is suspected) and are 2-3% larger than those for the known forms although all coordination numbers are the same. The crystal structure of CoSb2O6 was refined via the Rietveld method: P3[combining macron]1m, a = 5.1318(3) Å, and c = 4.5520(3) Å. Compounds with M = Co and Ni antiferromagnetically order at 11 and 15 K, respectively, whereas the copper compound does not show long-range magnetic order down to 1.5 K. A comparison between the magnetic behavior of the metastable and stable polymorphs was carried out. FeSb2O6 could not be prepared because of the 2Fe(2+) + Sb(5+) = 2Fe(3+) + Sb(3+) redox reaction. This electron transfer produces an additional 5s(2) shell for Sb and results in a volume increase. A comparison of the formula volume for the stable mixture FeSbO4 + 0.5Sb2O4 with that extrapolated for FeSb2O6 predicted that the trirutile-type FeSb2O6 can be stabilized at high pressures.

Concepts: Edward Teller, Redox, Chemical compound, Coordination chemistry, Jahn–Teller effect, Chemical bonding, Copper, Volume

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The effective Debye temperatures ([Formula: see text]) of the surface region of UO2 single crystals, prepared by the hydrothermal synthesis technique, were obtained from temperature-dependent x-ray photoemission in the temperature range of 300 K-623 K. A lattice stiffening transition, characterized by different regions of different effective Debye temperature, 500  ±  59 K below 475 K and 165  ±  21 K above 475 K is identified. A comparison of the temperature dependence of the effective UO2 Debye temperature, with the changes in the lattice expansion coefficient for UO2, support strong lattice-phonon interaction arising from the Jahn-Teller distortion.

Concepts: Jahn–Teller effect, Chemical reaction, Crystallography, Heat transfer, Fundamental physics concepts, Temperature, Solid, Thermodynamics