Meltable Spin Transition Molecular Materials with Tunable Tc and Hysteresis Loop Width

Herein, we report a way to achieve abrupt high‐spin to low‐spin transition with controllable transition temperature and hysteresis width, relying not on solid‐state cooperative interactions, but utilizing coherency between phase and spin transitions in neutral Fe^II meltable complexes.     

Chemistry in Ukraine

In this special issue, we highlight recent advances in chemical research by scientists in Ukraine, as well as by their compatriots and collaborators outside the country. Besides spotlighting their contributions, we see our task in fostering global partnerships and multi-, inter-, and trans-disciplinary collaborations, including much-needed co-funded projects and initiatives. The three decades of the renewed Ukraine independence have seen rather limited integration of Ukrainian (chemical) science into global research communities.^[1] At the same time, the recent surge of collaborative science initiatives between European Union (EU) and Ukraine echoes the unfolding steps towards Ukraine's full research participation to the Horizon Europe Program. This recently implemented step opens enormous possibilities for Ukrainian researchers to apply for diverse EU research grants. Moreover, a number of journal special issues and collections were launched to highlight Ukrainian chemistry (i. e., by Chemistry of Heterocyclic Compounds^[2] and ChemistrySelect^[3]). Other scientific initiatives include ‘European Chemistry School for Ukrainians’^[4] and ‘Kharkiv Chemical Seminar’^[5] as voluntary projects aimed at engaging Ukrainian scientists into European and international chemical research.     

New reaction of 1H-pyrazoles with selenium dioxide: one-pot synthesis of bis(1H-pyrazol-4-yl)selenides

A novel reaction between 3- and 3,5-substituted pyrazoles with selenium dioxide proceeds with formation of bis(3R,5R′-1H-pyrazol-4-yl)selenides in high yield. On this basis, an efficient one-pot synthetic procedure has been developed. In the case of the unsubstituted pyrazole a selenonium compound has been obtained. The identity and structure of the isolated selenium derivatives have been confirmed by spectral methods and their molecular structures investigated by X-ray analysis.     

Synthesis of morpholin-2-ones by chemoselective intramolecular rhodium-catalyzed reductive ring expansion of oxazolidines

The rhodium-catalyzed reductive intramolecular ring expansion of N-(ethoxycarboxymethyl)oxazolidines was carried out under an atmosphere of carbon monoxide and hydrogen to afford N-methylmorpholin-2-ones in good to excellent yields.     

The Rb7Bi3−3xSb3xCl16 Family: A Fully Inorganic Solid Solution with Room-Temperature Luminescent Members

Low-dimensional ns²-metal halide compounds have received immense attention for applications in solid-state lighting, optical thermometry and thermography, and scintillation. However, these are based primarily on the combination of organic cations with toxic Pb²⁺ or unstable Sn²⁺, and a stable inorganic luminescent material has yet to be found. Here, the zero-dimensional Rb₇Sb₃Cl₁₆ phase, comprised of isolated [SbCl₆]³⁻ octahedra and edge-sharing [Sb₂Cl₁₀]⁴⁻ dimers, shows room-temperature photoluminescence (RT PL) centered at 560 nm with a quantum yield of 3.8±0.2 % at 296 K (99.4 % at 77 K). The temperature-dependent PL lifetime rivals that of previous low-dimensional materials with a specific temperature sensitivity above 0.06 K⁻¹ at RT, making it an excellent thermometric material. Utilizing both DFT and chemical substitution with Bi³⁺ in the Rb₇Bi_3−3xSb_3xCl₁₆ (x≤1) family, we present the edge-shared [Sb₂Cl₁₀]⁴⁻ dimer as a design principle for Sb-based luminescent materials.     

Pressure-assisted strategy for the synthesis of vinyl pyrrolidone-based macro-star photoiniferters. A route to star block copolymers

Star-shaped 1-vinyl-2-pyrrolidone (VP)-based polymers having four pendant arms were produced via high-pressure RAFT using the trithiocarbonate-functionalized core. The use of compression (p = 250 MPa) significantly reduced or eliminated star-star/star-chain coupling side reactions and termination process characteristics the for “core-first” R-type approach, still allowing for a “pseudo-living” reaction course up to very high monomer conversion (>98%). Consequently, tailored and highly living star-shaped poly(1-vinyl-2-pyrrolidone)s (PVP) in a wide range of molecular weights M _n = 2.0–175.6 kg/mol (Đ = 1.18–1.80) have been obtained. The chain extension of the produced polymer was carried out with methyl methacrylate (MMA) via photo-induced RAFT (λ = 365 nm) in the presence of tertiary amine catalyst, yielding well-defined amphiphilic star-shaped block copolymers. DSC measurements showed that synthesized star-shaped PVP homopolymers revealed much lower glass transition temperature values compared to their commercially supplied linear analogs.     

Guest induced reversible on–off switching of elastic frustration in a 3D spin crossover coordination polymer with room temperature hysteretic behaviour

A binary reversible switch between low-temperature multi-step spin crossover (SCO), through the evolution of the population γ_HS(T) with high-spin (HS)-low-spin (LS) sequence: HS₁LS₀ (state 1) ↔ HS_2/3LS_1/3 (state 2) ↔ HS_1/2LS_1/2 (state 3) ↔ HS_1/3LS_2/3 (state 4) ↔ HS₀LS₁ (state 5), and complete one step hysteretic spin transition featuring 20 K wide thermal hysteresis centred at 290 K occurs in the three-dimensional (3D) Hofmann-type porous coordination polymer {Fe^II(3,8phen)[Au(CN)₂]₂}·xPhNO₂ (3,8phen = 3,8-phenanthroline, PhNO₂ = nitrobenzene), made up of two identical interpenetrated pcu-type frameworks. The included PhNO₂ guest (x = 1, 1·PhNO₂) acts as a molecular wedge between the interpenetrated 3D frameworks via PhNO₂-3,8phen intermolecular recognition and is the source of the strong elastic frustration responsible for the multi-step regime. Detailed X-ray single crystal analysis reflects competition between spatial periodicities of structurally inequivalent HS and LS SCO centres featuring: (i) symmetry breaking (state 3) with ⋯HS–LS⋯ ordering with γ_HS = 1/2; and (ii) occurrence of spatial modulation of the structure providing evidence for stabilization of local or aperiodic ordered mixed spin states for states 2 and 4 (with γ_HS ≈ 2/3) and 4 (with γ_HS ≈ 1/3), respectively. Below c.a. 20 K, structural and magnetic analyses show the photogeneration of a metastable HS*, state 6. The room-temperature single-step hysteretic regime appears with release of the guest (x = 0, 1) and the elastic frustration, and reversibly switches back to the original four-step behaviour upon guest re-adsorption. Both uncommon relevant SCO events meeting in the same material represent a rare opportunity to compare them in the frame of antiferro- and ferro-elastic transitions.

Reversible switch between a robust bistable two-state room temperature spin crossover (SCO) and its transformation in a four-stepped elastically frustrated SCO due to guest inclusion in a metal–organic Hofmann framework.     

Reversible pH-Controlled Catenation of a Benzobisimidazole-Based Tetranuclear Rectangle

The development of methodologies to control on demand and reversibly supramolecular transformations from self-assembled metalla-structures requires the rational design of architectures able to answer to an applied stimulus. While solvent or concentration changes, light exposure or addition of a chemical have been largely explored to provide these transformations, the case of pH sensitive materials is less described. Herein, we report the first example of a pH-triggered dissociation of a coordination-driven self-assembled interlocked molecular link. It incorporates a pH sensitive benzobisimidazole-based ligand that can be selectively protonated on its bisimidazole moieties. This generates intermolecular electrostatic repulsions that reduces drastically the stability of the interlocked structure, leading to its dissociation without any sign of protonation of the pyridine moieties involved in the coordination bonds. Importantly, the dissociation process is reversible through addition of a base.