Spectroscopy and bonding in ternary metal hydride complexes—Potential hydrogen storage media

Parker, Stewart F.

doi:10.1016/j.ccr.2009.06.016

Cited by 86 publications

(38 citation statements)

References 153 publications

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“…Hydride species bound to transition-metal sites 1 play important roles in numerous areas of biological [2][3][4] and chemical [5][6][7] catalyses, H 2 -storage technologies, [8][9][10] and present and future renewable energy applications for a hydrogen economy. [11][12][13] An improved understanding of the structural and, in particular, the electronic properties of hydride-binding in transition-metal compounds, therefore is expected to impact the development of improved tailored materials.…”

Section: Introductionmentioning

confidence: 99%

Bridging-hydride influence on the electronic structure of an [FeFe] hydrogenase active-site model complex revealed by XAES-DFT

et al. 2013

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Two crystallized [FeFe] hydrogenase model complexes, 1 = (μ-pdt)[Fe(CO)(2)(PMe(3))](2) (pdt = SC1H2C2H2C3H2S), and their bridging-hydride (Hy) derivative, [1Hy](+) = [(μ-H)(μ-pdt)[Fe(CO)(2) (PMe(3))](2)](+) (BF(4)(−)), were studied by Fe K-edge X-ray absorption and emission spectroscopy, supported by density functional theory. Structural changes in [1Hy](+) compared to 1 involved small bond elongations (<0.03 Å) and more octahedral Fe geometries; the Fe–H bond at Fe1 (closer to pdt-C2) was ~0.03 Å longer than that at Fe2. Analyses of (1) pre-edge absorption spectra (core-to-valence transitions), (2) Kβ(1,3), Kβ', and Kβ(2,5) emission spectra (valence-to-core transitions), and (3) resonant inelastic X-ray scattering data (valence-to-valence transitions) for resonant and non-resonant excitation and respective spectral simulations indicated the following: (1) the mean Fe oxidation state was similar in both complexes, due to electron density transfer from the ligands to Hy in [1Hy](+). Fe 1s→3d transitions remained at similar energies whereas delocalization of carbonyl AOs onto Fe and significant Hy-contributions to MOs caused an ~0.7 eV up-shift of Fe1s→(CO)s,p transitions in [1Hy](+). Fed-levels were delocalized over Fe1 and Fe2 and degeneracies biased to O(h)–Fe1 and C(4v)–Fe2 states for 1, but to O(h)–Fe1,2 states for [1Hy](+). (2) Electron-pairing of formal Fe(d(7)) ions in low-spin states in both complexes and a higher effective spin count for [1Hy](+) were suggested by comparison with iron reference compounds. Electronic decays from Fe d and ligand s,p MOs and spectral contributions from Hys,p→1s transitions even revealed limited site-selectivity for detection of Fe1 or Fe2 in [1Hy](+). The HOMO/LUMO energy gap for 1 was estimated as 3.0 ± 0.5 eV. (3) For [1Hy](+) compared to 1, increased Fed (x(2) − y(2)) − (z(2)) energy differences (~0.5 eV to ~0.9 eV) and Fed→d transition energies (~2.9 eV to ~3.7 eV) were assigned. These results reveal the specific impact of Hy-binding on the electronic structure of diiron compounds and provide guidelines for a directed search of hydride species in hydrogenases.

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Section: Introductionmentioning

confidence: 99%

Bridging-hydride influence on the electronic structure of an [FeFe] hydrogenase active-site model complex revealed by XAES-DFT

et al. 2013

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“…B-H vibrations are readily studied by vibrational spectroscopy while the much lower energy transfers of stochastic reorientations are investigated by means of quasi-elastic neutron scattering. The structural dynamics of monometallic borohydrides have been extensively investigated by vibrational spectroscopy [28][29][30], solid state NMR spectroscopy [31][32][33][34][35], inelastic x-ray scattering IXS [36], inelastic neutron scattering INS [37], QENS [38][39][40] and recently by molecular dynamics assisted density functional theory (MD-DFT) [41,42]. The importance of the vibrational density of states for the stabilities of different polymorphs has also been discussed [43].…”

Section: Structural Dynamicsmentioning

confidence: 99%

Di-hydrogen contact induced lattice instabilities and structural dynamics in complex hydride perovskites

Schouwink

Hagemann

Embs

et al. 2015

J. Phys.: Condens. Matter

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attempt to consider the question as to whether homopolar dihydrogen contacts may also be exploited, i.e. those between atoms of the same sign charge, for instance to geometrically engineer lattice instabilities in crystal lattices, alluding to other geometrical schemes applied to generate low symmetries in solids [2][3][4][5]. To investigate this, we choose one of the simplest and best known structure types known to solid state science, the ABX 3 perovskite. Perovskite functionalities are known to be extremely sensitive to small structural distortions, and many properties adopt critical values across phase transitions, which hence play a crucial role in perovskite engineering. This concerns, for instance, electronic and magnetic transitions,

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“…Further-more, the normal modes of [BH 4 ] group are very sensitive to the surrounding so that the alterations in a borohydride chemical composition, lattice symmetry, and the bond type can be identiÞed in the spectrum (see reference [12] and references therein).Free [BH 4 ] species belong to T d symmetry point group with four normal modes of vibration:, v2, v3, and v4, out of which the latter two triply degenerate modes are IR-active. The BeH stretching modes (v1 , v3) of [BH4] fall in the 2500e2100 cm region, HeBeH bending vibrations (v2 , v4) can be observed in the 1200e900 cm 1 region.…”

Section: Atr-ir Spectroscopy Of Milled and Hydrogenated Lihemgb 2 Ex mentioning

confidence: 99%

Enhanced hydrogen uptake/release in 2LiH–MgB 2 composite with titanium additives

Saldan

Campesi

Zavorotynska

et al. 2012

International Journal of Hydrogen Energy

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The influence of different titanium additives on hydrogen sorption in LiHeMgB 2 system has been investigated. For all the composites LiHeMgB 2 eX (X ¼ TiF 4 , TiO 2 , TiN, and TiC), prepared by ball-milling in molar ratios 2:1:0.1, Þve hydrogen uptake/release cycles were performed. In-situ synchrotron radiation powder X-ray diffraction (SR-PXD) and attenu-ated total reßection infrared spectroscopy (ATR-IR) have been used to characterize crystal phases developed during the hydrogen absorptionedesorption cycles.All the composites with the titanium additives displayed an improvement of reaction kinetics, especially during hydrogen desorption. The LiHeMgB 2 eTiO 2 system reached a storage of about 7.6 wt % H 2 in w1.8 h for absorption and w2.7 h for desorption. Using in-situ SR-PXD measurements, magnesium was detected as an intermediate phase during hydrogen desorption for all composites. In the composite with TiF 4 addition the formation of new phases (TiB 2 and LiF) were observed. Characteristic diffraction peaks of TiO 2 , TiN and TiC additives were always present during hydrogen absorptionedesorption. For all as-milled composites, ATR-IR spectra did not show any signals for borohydrides, while for all hydrogenated composites BeH stretching (2450e2150 cm 1 ) and BeH bending (1350e1000 cm 1 ) bands were exactly the same as for commercial LiBH 4 . IntroductionHydrogen can be one of the alternative energy carriers, which should replace the traditional fossil fuels in the near future. One of the promising materials for hydrogen mobile applica-tion which has been studied approximately for 10 years is LiBH 4 [1]. Having high gravimetric and volumetric hydrogen density, this material, though, exhibits unfavorable kinetics and thermodynamics for real application in fuel cells. Recently, it was found that LiBH 4 can be destabilized by the addition of MgH 2 , showing better decomposition kinetics with respect to the pure compound [2]. A detailed analysis of the reversible interaction between LiBH 4 and MgH 2 was made in [3] and can be summarized as follow: 2LiBH 4 þ MgH 2 4 2LiBH 4 þ Mg þ H 2 4 2LiH þ MgB 2 þ 4H 2 (1)The direct reactions (1) take place at w400 C. Opposite reactions, with simultaneous formation of LiBH 4 and MgH 2 under 50 bar of H 2 , was conÞrmed at the temperatures 250e300 C [3]. It was observed that suitable additives might decrease reaction temperatures and improve kinetics of Eq. (1). Experimental evidence of kinetic improvement for reversible middle-temperature Na, Li and Al based complex hydrides doped by titanium additives appeared in 1997 [4]. It has also been reported that the kinetic improvement of the reaction (1) was reached by addition of 1 mol% of TiF 3 [5]. The property enhancement arising upon this additive persists well in the subsequent hydrogen uptake/release cycles. Another prom-inent example of the additives effect was the composite LiBH 4 eMgH 2 eTi{OCH(CH 3 ) 2 } 4 mixed in molar ratio 2:1:0.1 [6]. After ball-milling TiO 2 anatase was found and during 1-st hydrogen desorptio...

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Spectroscopy and bonding in ternary metal hydride complexes—Potential hydrogen storage media

Cited by 86 publications

References 153 publications

Bridging-hydride influence on the electronic structure of an [FeFe] hydrogenase active-site model complex revealed by XAES-DFT

Bridging-hydride influence on the electronic structure of an [FeFe] hydrogenase active-site model complex revealed by XAES-DFT

Di-hydrogen contact induced lattice instabilities and structural dynamics in complex hydride perovskites

Enhanced hydrogen uptake/release in 2LiH–MgB 2 composite with titanium additives

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