Nanoscale Visualization of Photodegradation Dynamics of MAPbI3 Perovskite Films.

Herein, we report the nanoscale visualization of the photochemical degradation dynamics of MAPbI3 (MA = CH3NH3+) using infrared scattering scanning near-field microscopy (IR s-SNOM) combined with a series of complementary analytical techniques such as UV-vis and FTIR-spectroscopy, XRD, and XPS. Light exposure of the MAPbI3 films resulted in a gradual loss of MA+ cations starting from the grain boundaries at the film surface and slowly progressing toward the center of the grains and deeper into the bulk perovskite phase. The binary lead iodide PbI2 was found to be the major perovskite photochemical degradation product under the experimental conditions used. Interestingly, the formation of the PbI2 skin over the perovskite grains resulted in a largely enhanced photoluminescence, which resembles the effects observed for core-shell quantum dots. The obtained results demonstrate that IR s-SNOM represents a powerful technique for studying the spatially resolved degradation dynamics of perovskite absorbers and revealing the associated material aging pathways.

Abrupt Spin-State Switching in Mn(III) Complexes with BPh4 Anion: Effect of Halide Substituents on Crystal Structure and Magnetic Properties.

Three tetraphenylborates of mononuclear Mn(III) cation complexes with hexadentate ligands, the products of the reaction between a N,N'-bis(3-aminopropyl)ethylenediamine and salicylaldehydes with the different haloid substitutions at the 5 or 3,5 positions, have been synthesized: [Mn(5-F-sal-N-1,5,8,12)]BPh4 (1), [Mn(3,5-diCl-sal-N-1,5,8,12)]BPh4 (2) and [Mn(3,5-Br,Cl-sal-N-1,5,8,12)]BPh4 (3). Their crystal structure, dielectric constant (ϵ) and magnetic properties have been studied. Ligand substituents have a dramatic effect on the structure and magnetic properties of the complexes. With decreasing temperature, the complex (1) shows a gradual spin crossover from the high-spin state (HS) to the HS:LS intermediate phase, followed by an abrupt transition to the low-spin state (LS) without changing the crystal symmetry. The complexes 2 and 3 are isostructural, but have fundamentally different properties. Complex 2 demonstrates two structural phase transitions related to sharp spin crossovers from the HS to the HS:LS intermediate phase at 137 K and from the intermediate phase to the LS at 87 K, while complex 3 exhibits only one spin transition from the HS to the HS:LS intermediate phase at 83 K.

Temperature Dynamics of MAPbI3 and PbI2 Photolysis: Revealing the Interplay between Light and Heat, Two Enemies of Perovskite Photovoltaics.

Regardless of the impressive photovoltaic performances demonstrated for lead halide perovskite solar cells, their practical implementation is severely impeded by the low device stability. Complex lead halides are sensitive to both light and heat, which are unavoidable under realistic solar cell operational conditions. Suppressing these intrinsic degradation pathways requires a thorough understanding of their mechanistic aspects. Herein, we explored the temperature effects in the light-induced decomposition of MAPbI3 and PbI2 thin films under anoxic conditions. The analysis of the aging kinetics revealed that MAPbI3 photolysis and PbI2 photolysis have quite high effective activation energies of ∼85 and ∼106 kJ mol-1, respectively, so decreasing the temperature from 55 to 30 °C can extend the perovskite lifetime by factors of >10-100. These findings suggest that controlling the temperature of the perovskite solar panels might allow the long operational lifetimes (>20 years) required for the practical implementation of this promising technology.

Biomimetic Water Oxidation Catalyzed by a Binuclear Ruthenium (IV) Nitrido-Chloride Complex with Lithium Counter-Cations.

The lithium salt of the binuclear nitrido complex of ruthenium (IV) Li3(Ru2NCl8·2H2O) was synthesized. Using UV spectroscopy and voltammetry, we studied complex behavior in aqueous solutions. It was found that in dilute solutions of this compound, Cl- ions are replaced by H2O molecules, and the intra-sphere redox reaction between Ru (IV) and H2O, as well as the oxidation of water with the formation of oxygen and the acidic dissociation of coordinated water molecules also have been taking place. It was established by IR spectroscopy and ESI mass spectrometric analysis that not only the binuclear structure of the complex is preserved in acidic solutions, but also its dimerization product into the tetra-ruthenium dinitrido cluster Ru4N2O5+, which is a catalyst for the water oxidation reaction. The activity of the catalyst was TOF = 0.33 s-1, TON = 304.

Synthesis and study of C-substituted methylthio derivatives of cobalt bis(dicarbollide).

The C-methylthio derivatives of cobalt bis(dicarbollide) were synthesized by reaction of anhydrous CoCl2 with nido-carborane [7-MeS-7,8-C2B9H11]- and isolated as a mixture of rac-[1,1'-(MeS)2-3,3'-Co(1,2-C2B9H10)2]- and meso-[1,2'-(MeS)2-3,3'-Co(1,2-C2B9H10)2]- isomers. The structures of both isomers were studied using DFT quantum chemical calculations. The most preferable geometry of rotamers and the stabilization energy of C-methylthio derivatives of cobalt bis(dicarbolide) were calculated. The (BEDT-TTF)[1,1'-(MeS)2-3,3'-Co(1,2-C2B9H10)2] salt was prepared and its structure was determined by single crystal X-ray diffraction. The cisoid conformation of the rac-[1,1'-(MeS)2-3,3'-Co(1,2-C2B9H10)2]- anion is stabilized by short intramolecular CH⋯S hydrogen and BH⋯S chalcogen bonds between the dicarbollide ligands, that is in good agreement with the data of quantum chemical calculations.

The First Conducting Spin-Crossover Compound Combining a MnIII Cation Complex with Electroactive TCNQ Demonstrating an Abrupt Spin Transition with a Hysteresis of 50†K.

We present herein the synthesis, crystal structure, and electric and magnetic properties of the spin-crossover salt [Mn(5-Cl-sal-N-1,5,8,12)]TCNQ1.5 ⋅2 CH3 CN (I), where 5-Cl-sal-N-1,5,8,12=N,N'-bis(3-(2-oxy-5-chlorobenzylideneamino)propyl)-ethylenediamine, containing distinct conductive and magnetic blocks along with acetonitrile solvent molecules. The MnIII complex with a Schiff-base ligand, [Mn(5-Cl-sal-N-1,5,8,12)]+ , acts as the magnetic unit, and the π-electron acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ- ) is the conducting unit. The title compound (I) exhibits semiconducting behavior with room temperature conductivity σRT ≈1×10-4  ohm-1 cm-1 and activation energy Δ ≈0.20 eV. In the temperature range 73-123 K, it experiences a hysteretic phase transition accompanied by a crossover between the low-spin S=1 and high-spin S=2 states of MnIII and changes in bond lengths within the MnN4 O2 octahedra. The pronounced shrinkage of the basal Mn-N bonds in I at the spin crossover suggests that the d x 2 - y 2 orbital is occupied/deoccupied in this transition. Interestingly, the bromo isomorphic counterpart [Mn(5-Br-sal-N-1,5,8,12)]TCNQ1.5 ⋅2 CH3 CN (II) of the title compound evidences no spin-crossover phenomena and remains in the high-spin state in the temperature range 2-300 K. Comparison of the chloro and bromo compounds allows the thermal and spin-crossover contributions to the overall variation in bond lengths to be distinguished. The difference in magnetic behavior of these two salts has been ascribed to intermolecular supramolecular effects on the spin transition. Discrete hydrogen bonding exists between cations and cations and anions in both compounds. However, the hydrogen bonding in the crystals of II is much stronger than in I. The relatively close packing arrangement of the [Mn(5-Br-sal-N-1,5,8,12)]+ cations probably precludes their spin transformation.

Evidence of field induced slow magnetic relaxation in cis-[Co(hfac)2(H2O)2] exhibiting tri-axial anisotropy with a negative axial component.

We report a combined experimental characterization and theoretical modeling of the hexa-coordinated high-spin Co(ii) complex cis-[Co(hfac)2(H2O)2] (I). The magnetic static field (DC) data and EPR spectra (measurements were carried out on the powder samples of diluted samples cis-[Co0.02Zn0.98 (hfac)2(H2O)2]) were analyzed with the aid of the parametric Griffith Hamiltonian for the high-spin Co(ii) supported by the ab initio calculations of the crystal field (CF) parameters, g-factors and superexchange parameters between H-bonded Co(ii) ions in the neighboring molecules in a 1D network. This analysis suggests the presence of the easy axis of magnetic anisotropy and also shows the existence of a significant rhombic component. The detected frequency dependent (AC) susceptibility signal shows that complex I exhibits slow paramagnetic relaxation in the applied DC field belonging thus to the class of non-uniaxial field induced single ion magnets with a negative axial component of anisotropy. It is demonstrated that the main contributions to the relaxation come from the direct one-phonon process dominating at low temperatures, while the contribution of the two-phonon Raman process becomes important with increasing temperature.

Single-Ion Magnet Et4N[CoII(hfac)3] with Nonuniaxial Anisotropy: Synthesis, Experimental Characterization, and Theoretical Modeling.

In this article we report the synthesis and structure of the new Co(II) complex Et4N[CoII(hfac)3] (I) (hfac = hexafluoroacetylacetonate) exhibiting single-ion magnet (SIM) behavior. The performed analysis of the magnetic characteristics based on the complementary experimental techniques such as static and dynamic magnetic measurements, electron paramagnetic resonance spectroscopy in conjunction with the theoretical modeling (parametric Hamiltonian and ab initio calculations) demonstrates that the SIM properties of I arise from the nonuniaxial magnetic anisotropy with strong positive axial and significant rhombic contributions.

Singularity of proton transport in salts of orthoperiodic and orthotellurium acids: theoretical modeling using density functional calculations.

Density functional B3LYP calculations have been performed to investigate proton transport in orthoperiodic and orthotellurium acids, their salts MIO(6)H(4)(M = Li, Rb, Cs) and CsH(5)TeO(6), dimers of the salt*acid type MIO(6)H(4)*H(5)IO(6)(M = Rb, Cs), CsIO(6)H(4)*H(6)TeO(6), CsHSO(4)*H(6)TeO(6), Cs(2)SO(4)*H(6)TeO(6), and also in double-substituted and binary salts Rb(2)H(3)IO(6) and Rb(4)H(2)I(2)O(10). It has been shown that the energy of salt dimerization is 33-35 kcal mol(-1) and the activation barrier for proton migration between the neighboring octahedrons of the salt*acid --> acid*salt type is calculated to be 3-13 kcal mol(-1). The activation energy of the proton migration along the octahedron, 20-30 kcal mol(-1), is comparable with the barrier for water molecule separation. Quantum-chemical calculations correlate with the results of X-ray and electrochemical studies.