Crystal structure and Hirshfeld surface analysis of 2-bromo-ethyl-ammonium bromide - a possible side product upon synthesis of hybrid perovskites.

This study presents the synthesis, characterization and Hirshfeld surface analysis of a small organic ammonium salt, C2H7BrN+·Br-. Small cations like the one in the title compound are considered promising components of hybrid perovskites, crucial for optoelectronic and photovoltaic applications. While the incorporation of this organic cation into various hybrid perovskite structures has been explored, its halide salt counterpart remains largely uninvestigated. The obtained structural results are valuable for the synthesis and phase analysis of hybrid perovskites. The title compound crystallizes in the solvent-free form in the centrosymmetric monoclinic space group P21/c, featuring one organic cation and one bromide anion in its asymmetric unit, with a torsion angle of -64.8 (2)° between the ammonium group and the bromine substituent, positioned in a gauche conformation. The crystal packing is predominantly governed by Br⋯H inter-actions, which constitute 62.6% of the overall close atom contacts.

Nature of cyanoargentate bridges defining spin crossover in new 2D Hofmann clathrate analogues.

Chemical composition is leading among the numerous factors that determine the spin transition properties of coordination compounds. Classic dicyanometallic bridges {M(CN)2}- are commonly used to build Hofmann-like spin-crossover frameworks, but some extended bridges are also synthetically available. In this paper, we describe a successful synthesis of two very similar spin-crossover frameworks that differ in the cyanometallic bridges involved, namely [Fe(etpz)2{Ag(CN)2}2] (1) and {Fe(etpz)2[Ag2(CN)3][Ag(CN)2]} (2) (where etpz = 2-ethylpyrazine). Magnetic and Mössbauer studies demonstrated the occurrence of abrupt one-step high-spin (HS) ↔ low-spin (LS) transitions for both complexes. The spin transition temperatures are T1/2 ↓ = 233 K and T1/2 ↑ = 243 K for 1 and T1/2 ↓ = 188 K and T1/2 ↑ = 191 K for 2 with thermal hysteresis loops of 10 K for 1 and 3 K for 2. The bridging mononuclear [Ag(CN)2]- units and FeII cations assemble to form infinite 2D layers in the structure of 1. Interestingly, compound 2 forms 2D layers of FeII cations bridged by both binuclear [Ag2(CN)3]- and mononuclear [Ag(CN)2]- units. The structures of 1 and 2 comprise different types of intermolecular interactions including Ag⋯Ag and Ag⋯Netpz, which induce the creation of supramolecular 3D frameworks. The synergy between metallophilic interactions and the spin transition is also confirmed by the variation of Ag⋯Ag distances during spin crossover. The characterization of such analogues allowed us to analyze in detail the effect of the cyanometallic bridge on the structure of new frameworks and on the bistability in Hofmann-like complexes.

Novel NASICON-Type Na-V-Mn-Ni-Containing Cathodes for High-Rate and Long-Life SIBs.

Partial substitution of V by other transition metals in Na3 V2 (PO4 )3 (NVP) can improve the electrochemical performance of NVP as a cathode for sodium-ion batteries (SIBs). Herein, phosphate Na-V-Mn-Ni-containing composites based on NASICON (Natrium Super Ionic Conductor)-type structure have been fabricated by sol-gel method. The synchrotron-based X-ray study, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) studies show that manganese/nickel combinations successfully substitute the vanadium in its site within certain limits. Among the received samples, composite based on Na3.83 V1.17 Mn0.58 Ni0.25 (PO4 )3 (VMN-0.5, 108.1 mAh g-1 at 0.2 C) shows the highest electrochemical ability. The cyclic voltammetry, galvanostatic intermittent titration technique, in situ XRD, ex situ XPS, and bond valence site energy calculations exhibit the kinetic properties and the sodium storage mechanism of VMN-0.5. Moreover, VMN-0.5 electrode also exhibits excellent electrochemical performance in quasi-solid-state sodium metal batteries with PVDF-HFP quasi-solid electrolyte membranes. The presented work analyzes the advantages of VMN-0.5 and the nature of the substituted metal in relation to the electrochemical properties of the NASICON-type structure, which will facilitate further commercialization of SIBs.

Phase Transitions, Dielectric Response, and Nonlinear Optical Properties of Aziridinium Lead Halide Perovskites.

Hybrid organic-inorganic lead halide perovskites are promising candidates for next-generation solar cells, light-emitting diodes, photodetectors, and lasers. The structural, dynamic, and phase-transition properties play a key role in the performance of these materials. In this work, we use a multitechnique experimental (thermal, X-ray diffraction, Raman scattering, dielectric, nonlinear optical) and theoretical (machine-learning force field) approach to map the phase diagrams and obtain information on molecular dynamics and mechanism of the structural phase transitions in novel 3D AZRPbX3 perovskites (AZR = aziridinium; X = Cl, Br, I). Our work reveals that all perovskites undergo order-disorder phase transitions at low temperatures, which significantly affect the structural, dielectric, phonon, and nonlinear optical properties of these compounds. The desirable cubic phases of AZRPbX3 remain stable at lower temperatures (132, 145, and 162 K for I, Br, and Cl) compared to the methylammonium and formamidinium analogues. Similar to other 3D-connected hybrid perovskites, the dielectric response reveals a rather high dielectric permittivity, an important feature for defect tolerance. We further show that AZRPbBr3 and AZRPbI3 exhibit strong nonlinear optical absorption. The high two-photon brightness of AZRPbI3 emission stands out among lead perovskites emitting in the near-infrared region.

Crystal structure and Hirshfeld surface analysis of bis-(3-aminopyrazole-κN1)bis-(3-aminopyrazole-κN2)bis-(nitrato-κO)copper(II).

In the crystal structure of the title compound, [Cu(NO3)2(C3H5N3)4], the CuII atom is situated on an inversion center (Wyckoff position 2c of space group P21/n) and shows an octa-hedral [N4O2] coordination environment. The axial positions are occupied by O atoms of nitrate anions, while the equatorial positions are taken up by the N atoms of four 3-amino-pyrazole ligands. As a result of the tautomerism of the latter, two coordinate with the N1-atom of 3-amino-pyrazole while the other two with the N2-atom. The presence of pyrrole-like N-H groups and amine substituents as donor groups leads to numerous intra- and inter-molecular hydrogen-bonding inter-actions, which were qu-anti-fied by Hirshfeld surface analysis.

Crystal structure of bis-(3-carb-oxy-1-methyl-pyrid-inium) octa-bromide.

The crystal structure of the title salt, bis-(3-carb-oxy-1-methyl-pyridinium) octa-bromide, 2C7H8NO2 +·Br8 2-, consists of 3-carb-oxy-1-methyl-pyridinium (N-methyl-nicotinic acid) cations, which are stacked between relatively rare [Br8]2- anions. The polybromide [Br8]2- anion has point group symmetry and can be described as being composed of two [Br3]- anions connected with a Br2 mol-ecule in a Z-shaped manner. Contacts between neighboring octa-bromide anions ensure the creation of pseudo-polymeric chains propagating along [111]. The organic cations are located between anionic chains and are connected to each other through O-H⋯O hydrogen bonds and to the [Br8]2- anions through π⋯Br inter-actions that induce the creation of a supra-molecular tri-periodic network. In addition, the presence of weak C-H⋯Br contacts leads to the creation of layers, which align parallel to (11).

Structural diversity in proline-based lead bromide chiral perovskites.

Lead halide hybrid perovskites incorporating chiral organic cations attract considerable attention due to their promising application in multifarious optoelectronic devices. However, the examples of chiral hybrid perovskites are still limited, which greatly impedes their further studies in various optoelectronic fields. Herein, we report on new low-dimensional lead-halide hybrid perovskites incorporating the enantiopure chiral α-amino acid L-proline. Two hybrid perovskites (L-proH)PbBr3·H2O (Pro-PbBr3) and (L-proH)4Pb3Br10·4H2O (Pro-Pb3Br10) have been synthesized by employing different ratios of organic and inorganic precursors. According to structural analysis, the inorganic sublattice of compound Pro-PbBr3 is built of one-dimensional (1D) [PbX3]∞n- lead halide chains, whereas the inorganic sublattice of compound Pro-Pb3Br10 is built upon a rare two-dimensional (2D) [Pb3Br10]∞4n- honeycomb-type inorganic framework. Hirshfeld surface analysis revealed an important role of various hydrogen bonding interactions in providing the binding between organic and inorganic parts of these hybrid perovskites. The optical band gap values of new hybrid perovskites as estimated using the Tauc plot approach are 4.19 eV (Pro-PbBr3) and 4.13 eV (Pro-Pb3Br10). Also, new compounds display low-temperature broadband photoluminescence which can be attributed to the self-trapped excitons. These results show the potential of α-proline for constructing novel and highly demanded chiral hybrid perovskites, which will hold great promise for further optoelectronic applications.

Quantum dots assembled from an aziridinium based hybrid perovskite displaying tunable luminescence.

3D hybrid perovskites based upon small organic cations gave start to a new intensively growing class of semiconducting materials. Here we report on the elaboration of quantum dots of a recently emerged new perovskite (AzrH)PbBr3 (AzrH = aziridinium cation). By employing the antisolvent precipitation technique and stabilization with a cationic surfactant we succeeded in obtaining quantum dots that display tunable luminescence. This piece of work shows the perspective of aziridinium-based materials for the elaboration of advanced photonic nanostructures.

Chiral 2D organic-inorganic hybrid perovskites based on L-histidine.

Novel chiral hybrid perovskites are highly demanded for various advanced applications such as spintronics, optoelectronics, photovoltaics etc. However, the scope of these new materials is still limited. Herein, we present new 2D hybrid perovskites based upon chiral α-amino acid L-histidine. The generalized formula of these new compounds can be denoted as (L-HisH)2PbBrxI4-x (where L-His = L-histidine; x = 4, 3, 2, 1, 0.4 and 0). All perovskites are characterized by a very similar structural motif that consists of corner-sharing lead halide octahedra arranged in one-layer thin inorganic slabs interleaved by organic layers established by L-histidinium(1+) cations. L-Histidine provides a breaking of spatial parity of these perovskites that results in their non-centrosymmetric crystal structures. These compounds show a multiband absorption up to 590 nm for iodide perovskite. In addition, new compounds display pronounced single-peak photoluminescence, which finely blue shifts upon the gradual substitution of iodine by bromine. New perovskites exhibit excellent thermal stability up to 490 K and 445 K for bromide and iodide compounds, respectively. These results show the ability of L-histidine to produce novel and highly demanded chiral hybrid perovskites.

Cooperative Spin Crossover above Room Temperature in the Iron(II) Cyanoborohydride-Pyrazine Complex.

Hysteretic spin crossover in coordination complexes of 3d-metal ions represents one of the most spectacular phenomena of molecular bistability. In this paper we describe a self-assembly of pyrazine (pz) and Fe(BH3CN)2 that afforded the new 2D coordination polymer [Fe(pz)2(BH3CN)2]∞. It undergoes an abrupt, hysteretic spin crossover (SCO) with a T1/2 of 338 K (heating) and 326 K (cooling) according to magnetic susceptibility measurements. Mössbauer spectroscopy revealed a complete transition between the low-spin (LS) and the high-spin (HS) states of the iron centers. This LS-to-HS transition induced an increase of the unit cell volume by 10.6%. Meanwhile, a modulation of multiple [C-Hδ+···Hδ--B] dihydrogen bonds stimulates a contraction in direction c (2.2%). The simplicity of the synthesis, mild temperatures of transition, a pronounced thermochromism, stability upon thermal cycling, a striking volume expansion upon SCO, and an easy processability to composite films make this new complex an attractive material for switchable components of diverse applications.

Synthesis and crystal structure of hydrated µ-oxa-lato-bis-{bis-[3-methyl-5-(pyridin-2-yl)-1H-1,2,4-triazole]iron(II)} bis-(toluene-sulfonate) 2.75-hydrate.

In the title compound [Fe2(C2O4)(C8H8N4)4](CH3C6H4SO3)2·2.75H2O, the two FeII ions have a highly distorted octa-hedral FeN4O2 environment formed by two bidentate triazole-based chelating ligands and a bis-bidentate oxalate bridging anion that connects the metal ions. Stabilization within the crystal structure is provided via a system of O-H⋯O and N-H⋯O hydrogen bonding, which determines the formation of a two-dimensional architecture along the a-axis direction.

A Vanadium Dioxide-PMMA Composite For Microwave Radiation Switching.

Reconfigurable radio-frequency components are in high demand for modern communication systems as they can be involved in multiband and multistandard electronic devices. The key part of such components is an active switching element. This work offers a way to obtain an efficient microwave switch using vanadium dioxide-poly (methyl methacrylate) composite. Differential scanning calorimetry, SQUID magnetometery, and impedance spectroscopy measurements were used to characterize the phase transition in the proposed composite. Temperature induced metal-insulator transition occurs at technologically attractive 341 K. The transition leads to a change of microwave transmission trough VO2 -PMMA composite from -4.9 dB for low-temperature monoclinic form to -5.8 dB for high-temperature rutile form. This provides an ability to tune the material's transparency in the microwave range, while the shaping polymer matrix provides the proper mechanical processability of the switching element.

Four-Step Spin Crossover in a New Cyano-Bridged Iron-Silver Coordination Polymer.

Spin-crossover complexes with multistep transitions attract much attention due to their potential applications as multi-switches and for data storage. A four-step spin crossover is observed in the new iron(II)-based cyanometallic guest-free framework compound Fe(2-ethoxypyrazine)2 {Ag(CN)2 }2 during the transition from the low-spin to the high-spin state. A reverse process occurs in three steps. Crystallographic studies reveal an associated stepwise evolution of the crystal structures. Multiple transitions in the reported complex originate from distinct FeII sites which exist due to the packing of the ligand with a bulky substituent.

Crystal growth, layered structure and luminescence properties of K2Eu(PO4)(WO4).

K2Eu(PO4)(WO4) has been prepared via the high-temperature solution growth (HTSG) method using K2WO4-KPO3 molten salts as a self-flux and characterized by single-crystal X-ray diffraction analysis, IR and luminescence spectroscopy. The structure of this new compound features a 2D framework containing [EuPO6]4- layers, which are composed of zigzag chains of [EuO8]n interlinked by slightly distorted PO4 tetrahedra. Isolated WO4 tetrahedra are attached above and below these layers, leaving space for the K+ counter-cations. The photoluminescence (PL) characteristics (spectra, line intensity distribution and decay kinetics) confirm structural data concerning one distinct position for europium ions. The luminescence color coordinates suggest K2Eu(PO4)(WO4) as an efficient red phosphor for lighting applications.

Aziridinium cation templating 3D lead halide hybrid perovskites.

This study describes the synthesis of the first aziridinium-based compounds, namely hybrid perovskites (AzrH)PbHal3 (where AzrH = aziridinium, Hal = Cl, Br or I). This highly reactive species was stabilized in 3D lead halide frameworks and was found to be a small enough organic cation to promote the formation of semiconducting organo-inorganic materials.

Crystal structure of poly[[di-aqua-tetra-µ2-cyanido-platinum(II)iron(II)] methanol 4/3-solvate]: a three-dimensional Hofmann clathrate analogue.

In the title polymeric coordination compound, {[FePt(CN)4(H2O)2]·1.33CH3OH} n , the FeII cation (site symmetry 4/mm.m) is coordinated by the N atoms of four cyanide anions (CN-) and the O atoms of two water mol-ecules, forming a nearly regular [FeN4O2] octa-hedron. According the Fe-N and Fe-O bond lengths, the FeII atom is in the high-spin state. The cyanide anions act in a bridging manner to connect the FeII and PtII atoms. The [Pt(CN)4]2- moieties (Pt with site symmetry 4/mm.m) have a perfect square-planar shape. The latter anion is located perpendicular to the FeN4 plane, thus ensuring the creation of a three-dimensional framework. The crystal structure features methanol solvent mol-ecules of which 4/3 were located per FeII cation. These solvent mol-ecules are located in hexa-gonal pores; they inter-act with coordinating water mol-ecules through weak hydrogen bonds. Other guest mol-ecules could not be modelled in a satisfactory way and their contribution to the scattering was removed by a mask procedure.

1D iron(II)-1,2,4-triazolic chains with spin crossover assembled from discrete trinuclear complexes.

We report on a molecular cationic iron(II) complex with a 4-amino-1,2,4-triazole ligand and a tetraiodomercurate anion exhibiting an incomplete spin crossover (SCO). The complex exhibits an unusual disordered structure with a linear arrangement of ligand and water molecules that can potentially accommodate up to four iron atoms, but both terminal metal positions have half chemical occupancies, while occupancies of all ligands are full. This corresponds to the crystallisation of disordered trinuclear complexes arranged into 1D supramolecular chains. Iron cations have different N6 or N3O3 coordination environments, leading to the thermally induced SCO in two thirds of the metal centres. This SCO behaviour was characterised by magnetic susceptibility measurements and Mössbauer spectroscopy.

Two-Step Spin Crossover in Hofmann-Type Coordination Polymers [Fe(2-phenylpyrazine)2{M(CN)2}2] (M = Ag, Au).

Two 2D Hofmann-type complexes of the composition [Fe(Phpz)2{M(CN)2}2] (where Phpz = 2-phenylpyrazine; M = Ag, Au) have been synthesized, and their spin-crossover (SCO) behavior has been thoroughly characterized. Single-crystal X-ray analysis reveals that these complexes contain a crystallographically unique Fe(II) center surrounded by two axial Phpz ligands and four equatorial cyanide [M(CN)2]- bridges. It is shown that, using of a ligand with two aromatic rings, an advanced system of weak supramolecular interactions (metal-metal, C-H···M, and π···π stacking contacts) is realized. This ensures additional stabilization of the structures and the absence of solvent-accessible voids due to dense packing. Both complexes are characterized by a highly reproducible two-step SCO behavior, as revealed by different techniques (superconducting quantum interference device magnetometry, optical microscopy, etc.). Research shows the exceptional role of the presence of various supramolecular interactions in the structure and the influence of the bulky substituent in the ligand on SCO behavior. Moreover, the perspective of substituted pyrazines for the design of new switchable materials is supported by this work.

Crystal structure of 9-amino-acridinium chloride N,N-di-methyl-formamide monosolvate.

9-Amino-acridinium chloride N,N-di-methyl-formamide monosolvate, C13H11N2 +Cl-·C3H7NO, crystallizes in the monoclinic space group P21/c. The salt was crystallized from N,N-di-methyl-formamide. The asymmetric unit consists of two C13H11N2 +Cl- formula units. The 9-amino-acridinium (9-AA) mol-ecules are protonated with the proton on the N atom of the central ring. This N atom is connected to an N,N-di-methyl-formamide mol-ecule by a hydrogen bond. The H atoms of the amino groups create short contacts with two chloride ions. The 9-AA cations in adjacent layers are oriented in an anti-parallel manner. The mol-ecules are linked via a network of multidirectional π-π inter-actions between the 9-AA rings, and the whole lattice is additionally stabilized by electrostatic inter-actions between ions.

Spin crossover in iron(II) Hofmann clathrates analogues with 1,2,3-triazole.

Hofmann-like cyanometallic complexes represent one of the biggest and well-known classes of FeII spin-crossover compounds. In this paper, we report on the first FeII Hofmann clathrate analogues with unsubstituted 1,2,3-triazole, which exhibit temperature induced spin transition. Two new coordination polymers with the general formula [FeII(1,2,3-triazole)2MII(CN)4] (M = Pt, Pd) undergo abrupt hysteretic spin crossover in the range of 190-225 K as revealed by magnetic susceptibility measurements. Two compounds are isostructural and are built of infinite cyanometallic layers which are supported by 1,2,3-triazole ligands. The thermal hysteresis loop is very stable at different scan rates from 0.5 to 10 K min-1. The compounds display strong thermochromic effect, changing their colour from pink in the low-spin state to white in the high-spin state. Our findings show that 1,2,3-triazole is suitable for elaboration of spin-crossover Hofmann clathrate analogues, and its use instead of more classical azines can advantageously expand this family of complexes.