Computation Provides Chemical Insight into the Diverse Hydride NMR Chemical Shifts of [Ru(NHC)₄(L)H]^0/+ Species (NHC = N-heterocyclic carbene; L = vacant, H₂, N₂, CO, MeCN, O₂, P₄, SO₂, H^-, F^- and Cl^-) and their [Ru(R₂PCH₂CH₂PR₂)₂(L)H]⁺ Congeners

Relativistic density functional theory calculations, both with and without the effects of spin–orbit coupling, have been employed to model hydride NMR chemical shifts for a series of [Ru(NHC)4(L)H]0/+ species (NHC = N-heterocyclic carbene; L = vacant, H2, N2, CO, MeCN, O2, P4, SO2, H−, F− and Cl−), as well as selected phosphine analogues [Ru(R2PCH2CH2PR2)2(L)H]+ (R = iPr, Cy; L = vacant, O2). Inclusion of spin–orbit coupling provides good agreement with the experimental data. For the NHC systems large variations in hydride chemical shift are shown to arise from the paramagnetic term, with high net shielding (L = vacant, Cl−, F−) being reinforced by the contribution from spin–orbit coupling. Natural chemical shift analysis highlights the major orbital contributions to the paramagnetic term and rationalizes trends via changes in the energies of the occupied Ru dπ orbitals and the unoccupied σ*Ru–H orbital. In [Ru(NHC)4(η2-O2)H]+ a δ-interaction with the O2 ligand results in a low-lying LUMO of dπ character. As a result this orbital can no longer contribute to the paramagnetic shielding, but instead provides additional deshielding via overlap with the remaining (occupied) dπ orbital under the Lz angular momentum operator. These two effects account for the unusual hydride chemical shift of +4.8 ppm observed experimentally for this species. Calculations reproduce hydride chemical shift data observed for [Ru(iPr2PCH2CH2PiPr2)2(η2-O2)H]+ (δ = −6.2 ppm) and [Ru(R2PCH2CH2PR2)2H]+ (ca. −32 ppm, R = iPr, Cy). For the latter, the presence of a weak agostic interaction trans to the hydride ligand is significant, as in its absence (R = Me) calculations predict a chemical shift of −41 ppm, similar to the [Ru(NHC)4H]+ analogues. Depending on the strength of the agostic interaction a variation of up to 18 ppm in hydride chemical shift is possible and this factor (that is not necessarily readily detected experimentally) can aid in the interpretation of hydride chemical shift data for nominally unsaturated hydride-containing species. The synthesis and crystallographic characterization of the BArF4− salts of [Ru(IMe4)4(L)H]+ (IMe4 = 1,3,4,5-tetramethylimidazol-2-ylidene; L = P4, SO2; ArF = 3,5-(CF3)2C6H3) and [Ru(IMe4)4(Cl)H] are also reported

Computation Provides Chemical Insight into the Diverse Hydride NMR Chemical Shifts of [Ru(NHC)₄(L)H]^0/+ Species (NHC = N-heterocyclic carbene; L = vacant, H₂, N₂, CO, MeCN, O₂, P₄, SO₂, H^-, F^- and Cl^-) and their [Ru(R₂PCH₂CH₂PR₂)₂(L)H]⁺ Congeners

International audienceRelativistic density functional theory calculations, both with and without the effects of spin–orbit coupling, have been employed to model hydride NMR chemical shifts for a series of [Ru(NHC)4(L)H]0/+ species (NHC = N-heterocyclic carbene; L = vacant, H2, N2, CO, MeCN, O2, P4, SO2, H−, F− and Cl−), as well as selected phosphine analogues [Ru(R2PCH2CH2PR2)2(L)H]+ (R = iPr, Cy; L = vacant, O2). Inclusion of spin–orbit coupling provides good agreement with the experimental data. For the NHC systems large variations in hydride chemical shift are shown to arise from the paramagnetic term, with high net shielding (L = vacant, Cl−, F−) being reinforced by the contribution from spin–orbit coupling. Natural chemical shift analysis highlights the major orbital contributions to the paramagnetic term and rationalizes trends via changes in the energies of the occupied Ru dπ orbitals and the unoccupied σ*Ru–H orbital. In [Ru(NHC)4(η2-O2)H]+ a δ-interaction with the O2 ligand results in a low-lying LUMO of dπ character. As a result this orbital can no longer contribute to the paramagnetic shielding, but instead provides additional deshielding via overlap with the remaining (occupied) dπ orbital under the Lz angular momentum operator. These two effects account for the unusual hydride chemical shift of +4.8 ppm observed experimentally for this species. Calculations reproduce hydride chemical shift data observed for [Ru(iPr2PCH2CH2PiPr2)2(η2-O2)H]+ (δ = −6.2 ppm) and [Ru(R2PCH2CH2PR2)2H]+ (ca. −32 ppm, R = iPr, Cy). For the latter, the presence of a weak agostic interaction trans to the hydride ligand is significant, as in its absence (R = Me) calculations predict a chemical shift of −41 ppm, similar to the [Ru(NHC)4H]+ analogues. Depending on the strength of the agostic interaction a variation of up to 18 ppm in hydride chemical shift is possible and this factor (that is not necessarily readily detected experimentally) can aid in the interpretation of hydride chemical shift data for nominally unsaturated hydride-containing species. The synthesis and crystallographic characterization of the BArF4− salts of [Ru(IMe4)4(L)H]+ (IMe4 = 1,3,4,5-tetramethylimidazol-2-ylidene; L = P4, SO2; ArF = 3,5-(CF3)2C6H3) and [Ru(IMe4)4(Cl)H] are also reported

Ring-expanded N-heterocyclic carbene complexes of ruthenium

The six-membered N-heterocyclic carbene 1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene (6-Mes) reacts with Ru(PPh3)3(CO)HF to afford Ru(6-Mes)(PPh3)(CO)HF (1), which is converted to the five-coordinate C−H activated carbene complex Ru(6-Mes)′(PPh3)(CO)H (2) upon treatment with Et3SiH. The hydride chloride precursor Ru(PPh3)3(CO)HCl affords a mixture of products with 6-Mes, but reacts cleanly with 1,3-bis(isopropyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene (6-iPr) to give the six-coordinate activated complex Ru(6-iPr)′(PPh3)2(CO)H (3a), in which the hydride is trans to the methylene arm of the activated NHC. This complex isomerizes in solution with ΔH and ΔS values of 98.2 ± 4.6 kJ mol−1 and 15.5 ± 14.5 J mol−1 K−1. The major product from the isomerization, 3b, in which the hydride ligand is trans to carbene, can be made directly by reaction of 6-iPr with Ru(PPh3)3(CO)H2

Comparison of simulation models for Perovskite solar cells

In this work, a comparison of two models for the simulation of the electrical behavior of perovskite solar cells is presented. The two models considered are the well-known one diode model and an analytical model recently presented by Sun et al. These models are detailed in section 3. A perovskite solar cell was fabricated and characterized in order to compare real measurement results with simulation results obtained by using both models. The fabrication and characterization processes are also summarized in the experimental section.Peer ReviewedPostprint (published version

Comparison of simulation models for Perovskite solar cells

In this work, a comparison of two models for the simulation of the electrical behavior of perovskite solar cells is presented. The two models considered are the well-known one diode model and an analytical model recently presented by Sun et al. These models are detailed in section 3. A perovskite solar cell was fabricated and characterized in order to compare real measurement results with simulation results obtained by using both models. The fabrication and characterization processes are also summarized in the experimental section.Peer Reviewe

Simulation study of tandems of perovskite and IBC c-Si solar cells

In this work, the simulation results obtained for a tandem configuration of perovskite, as top cell, and Interdigitated Back-Contacted (IBC) c-Si as bottom cell are presented. Two different models were used for the modelling and simulation of the perovskite and the IBC c-Si solar cells. The fabrication and characterization processes are also summarized in the experimental section. The models were validated by comparison of simulated current-voltage characteristics and real data measured in two fabricated devices. The best efficiency obtained in this study is 25% for a tandem device with the top and bottom solar cells connected in series.Postprint (published version

Substitution Reactions in Dinuclear Ru-Hbpp Complexes: An Evaluation of Through-Space Interactions

The synthesis of new dinuclear complexes of the general formula in,in-{[RuII(trpy)(L)](μ-bpp)[RuII(trpy)(L′)]}3+ [bpp– is the bis(2-pyridyl)-3,5-pyrazolate anionic ligand; trpy is the 2,2′:6′,2″-terpyridine neutral meridional ligand, and L and L′ are monodentate ligands; L = L′ = MeCN, 3a3+; L = L′ = 3,5-lutidine (Me2-py), 3c3+; L = MeCN, L′ = pyridine (py), 43+], have been prepared and thoroughly characterized. Further, the preparation and isolation of dinuclear complexes containing dinitrile bridging ligands of the general formula in,in-{[RuII(trpy)]2(μ-bpp)(μ-L-L)}3+ [μ-L-L = 1,4-dicyanobutane (adiponitrile, adip), 6a3+; 1,3-dicyanopropane (glutaronitrile, glut), 6b3+; 1,2-dicyanoethane (succinonitrile; succ), 6c3+] have also been carried out. In addition, a number of homologous dinuclear complexes previously described, containing the anionic bis(pyridyl)indazolate (bid–) tridentate meridional ligand in lieu of trpy, have also been prepared for comparative purposes. In the solid state, six complexes have been characterized by X-ray crystallography, and in solution, all of them have been spectroscopically characterized by NMR and UV–vis spectroscopy. In addition, their redox properties have also been investigated by means of cyclic voltammetry and differential pulse voltammetry and show the existence of two one-electron waves assigned to the formation of the II,III and III,III species. Dinitrile complexes 6a3+, 6b3+, and 6c3+ display a dynamic behavior involving their enantiomeric interconversion. The energy barrier for this interconversion can be controlled by the number of methylenic units between the dinitrile ligand. On the other hand, pyridyl complexes in,in-{[RuII(T)(py)]2(μ-bpp)}n+ (T = trpy, n = 3, 3b3+; T = bid–, n = 1, 3b′+) and 3c3+ undergo two consecutive substitution reactions of their monodentate ligands by MeCN.The substitution kinetics have been monitored by 1H NMR and UV–vis spectroscopy and follow first-order behavior with regard to the initial ruthenium complex. For the case of 3b3+, the first-order rate constant k1 = (2.9 ± 0.3) × 10–5 s–1, whereas for the second substitution, the k obtained is k2 = (1.7 ± 0.7) × 10–6 s–1, both measured at 313 K. Their energies of activation at 298 K are 114.7 and 144.3 kJ mol–1, respectively. Density functional theory (DFT) calculations have been performed for two consecutive substitution reactions, giving insight into the nature of the intermediates. Furthermore, the energetics obtained by DFT calculations of the two consecutive substitution reactions agree with the experimental values obtained. The kinetic properties of the two consecutive substitution reactions are rationalized in terms of steric crowding and also in terms of through-space interactions. [from publishers website]

Simulation study of tandems of perovskite and IBC c-Si solar cells

In this work, the simulation results obtained for a tandem configuration of perovskite, as top cell, and Interdigitated Back-Contacted (IBC) c-Si as bottom cell are presented. Two different models were used for the modelling and simulation of the perovskite and the IBC c-Si solar cells. The fabrication and characterization processes are also summarized in the experimental section. The models were validated by comparison of simulated current-voltage characteristics and real data measured in two fabricated devices. The best efficiency obtained in this study is 25% for a tandem device with the top and bottom solar cells connected in series

The Influence of N-Heterocyclic Carbenes (NHC) on the Reactivity of [Ru(NHC)(4)H](+) With H-2, N-2, CO and O-2

The five-coordinate ruthenium N-heterocyclic carbene (NHC) hydrido complexes [Ru(IiPr2Me2)4H][BArF 4] (1; IiPr2Me2 = l,3-diisopropyl4,5- dimethylimidazol-2-ylidene ; ArF = 3,5-(CF3) 2C6H3), [Ru(IEt2Me2) 4H]-[BArF4] (2; IEt2Me2 = l,3-diethyl-4,5-dimethylimidazol-2-ylidene) and [Ru(IMe4) 4H][BArF4] (3; IMe4=l,3,4,5- tetramethylimidazol-2-ylidene) have been synthesised following reaction of [Ru(PPh3)3HCl] with 4-8 equivalents of the free carbenes at ambient temperature. Complexes 1-3 have been structurally characterised and show square pyramidal geometries with apical hydride ligands. In both dichloromethane or pyridine solution, 1 and 2 display very low frequency hydride signals at about (3 -41. The tetramethyl carbene complex 3 exhibits a similar chemical shift in toluene, but shows a higher frequency signal in acetonitrile arising from the solvent adduct [Ru(IMe4)4(MeCN)H] [BArF4], 4. The reactivity of 1-3 towards H2 and N2 depends on the size of the N-substituent of the NHC ligand. Thus, 1 is unreactive towards both gases, 2 reacts with both H2 and N2 only at low temperature and incom-pletely, while 3 affords [Ru(IMe4)4(η2H2)H] [BAr F4] (7) and [Ru(IMe4)4(N 2)H][BArF4] (8) in quantitative yield at room temperature. CO shows no selectivity, reacting with 1-3 to give [Ru(NHC) 4(CO)H][BArF4] (911). Addition of O2 to solutions of 2 and 3 leads to rapid oxidation, from which the Ru III species [Ru(NHC)4(OH)2][BAr F4] and the RuIV oxo chlorido complex [Ru(IEt2Me2)4(O)Cl][BArF 4] were isolated. DFT calculations reproduce the greater ability of 3 to bind small molecules and show relative binding strengths that follow the trend CO ≫ O2 &gt; N2 &gt; H2.</p

Influence of the substrate on the bulk properties of hybrid lead halide perovskite films

In addition to the known effect of the substrate on the interfacial properties of perovskite films, here we show that the bulk properties of hybrid lead halide perovskite films depend on the type of substrate used for film growth. Despite the relative large film thickness, ∼600 nm, the roughness and nature of the substrate layer (glass, FTO, TiO and PEDOT:PSS) affect not just the degree of preferential orientation and crystal grain size but also the lattice parameters of CHNHPbI films synthesized from the PbCl precursor. The obtained changes in lattice parameters indicate that the Pb-Pb distance varies by around 0.7%. We suggest that the substrate roughness and chemical nature determine the concentration of defects mainly by varying the chlorine content and probably by the incorporation of oxygen and iodine vacancies during film nucleation and growth. These differences also have consequences in the observed light induced transformations. Upon laser illumination, the formation of additional defects, most probably related to oxygen, is revealed by 110 and 165 cm Raman peaks. With increasing laser power the chemical transformation into PbO is clearly identified by the 140 and 275 cm Raman peaks. The irreversible photoluminescence enhancement observed at low power with illumination time, also dependent on the substrate nature, is proposed to be due to the localization of the electron-hole excitons created in the vicinity of the light generated defects. These results shed light on the performance of the perovskite layer and help to understand how bulk processes, where ion migration is a conspicuous example, are severely affected by interfacial properties such as those imposed by the substrate.Funding by the Spanish Ministerio de Economía y Competitividad (MINECO) under Projects MAT2015-65356-C3-1-R and 2-R, MAT2014-54852-R and MAT2015-70611-ERC and Comunidad de Madrid Excellence Network under Project S2013/MIT-2740 (and Associated Lab LABCADIO belonging to CM net labs ref. 351) is acknowledged. We also acknowledge the MINECO for financial support and provision of synchrotron radiation facilities at ESRF, and thank María Vila for her assistance in using beamline BM25-SpLine. B. C. H. is grateful to the support of the National Council of Technological and Scientific Development (CNPq), Brazil, through the Science without Borders program