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Cooling [Fe(bbtr)3](BF4)2 (bbtr=1,4‐di(1,2,3‐triazol‐1‐yl)butane) triggers very slow spin crossover below 80 K (T1/2↓=76 K). The spin crossover (SCO) is accompanied by a hysteresis loop (T1/2↑=89 K). In contrast to isostructural perchlorate analogue [Fe(bbtr)3](ClO4)2 in which spin crossover during cooling is preceded by phase transition at TPT=126 K in tetrafluoroborate phase transition does not occur to the beginning of spin crossover (80 K). Studies of mixed crystals [Fe(bbtr)3](BF4)2(1‐x)(ClO4)2x (0.5≤x≤0.9) showed that a phase transition precedes spin crossover, however, for x≅0.46 intersection of T1/2(x) and TPT(x) dependencies takes place. The application of pressure of 1 GPa shifts the spin crossover in [Fe(bbtr)3](BF4)2 to a temperature above 270 K. High‐pressure studies of neat tetrafluoroborate and perchlorate, as well as mixed crystals [Fe(bbtr)3](BF4)2(1‐x)(ClO4)2x (0.1≤x≤0.9), revealed that at 295 K P1/2 value changes linearly with x indicating similar mechanism of spin crossover under elevated pressure in all systems under investigation. Variable pressure single crystal X‐ray diffraction studies confirmed that in contrast to thermally induced spin crossover undergoing differently in tetrafluoroborate and perchlorate an application of high pressure removes this differentiation leading to a similar mechanism depending at first on start spin crossover and then P‐3→P‐1 phase transition occurs. In this report we have shown that 2D coordination polymer [Fe(bbtr)3](BF4)2 (bbtr=1,4‐di(1,2,3‐triazol‐1‐yl)butane) treated to date as spin crossover silent shows thermally induced spin crossover phenomenon. Spin crossover in tetrafluoroborate is extremely slow. Determination of the spin crossover curve required carrying measurement in the settle mode‐cooling from 85 to 70 K took about 600 h (average velocity of change of temperature ca. 0.0004 K/min). [ABSTRACT FROM AUTHOR]

The pressure‐induced transformation of plane‐square complex nickel(II) bis(N,N‐diethyldithiocarbamate) between its soft dithiocarbamate (form I) and thioureide (form II) mesomeres is coupled to the interchange of anagostic Ni⋅⋅⋅H−C interactions from methylene to the methyl group, respectively. At 1.23 GPa, the clearly visible giant anomalous compressibility of the crystal reveals a potential‐energy difference of 5.4 kJ mol−1 between the two complex forms. The structural and spectroscopic results, which are supported by quantum‐mechanical calculations, connect this solid‐state phase transition with the mesomeric transition, and this is accompanied by the conformational transformation of anagostic Ni⋅⋅⋅H−C rearrangement and formation of the charge‐assisted S−⋅⋅⋅H−C bond under pressure. [ABSTRACT FROM AUTHOR]

Understanding the factors governing the formation of supramolecular structures and phase transitions between various forms of molecular crystals is pivotal for developing dynamic, stimuli‐responsive materials and polymorph‐controlled syntheses. Here, we investigate the pressure‐induced dynamic of both the intrinsic molecular structure and the supramolecular network of a predesigned polyhedral oxo‐centered zinc cluster incorporating monoanionic N,N'‐diphenylformamidinate and featuring N‐bonded phenyl groups in close proximity to the primary coordination sphere. We demonstrate that the model oxo cluster is prone to undergoing pressure‐induced conformational transformations of the secondary coordination sphere and simultaneous stepwise (initially every second polyhedral molecule undergoes the conformational transformations) and reversible transitions from an ambient phase α to high‐pressure phases β and γ, as single‐crystal‐to‐single‐crystal events. The observed phase transitions illustrate the key role of an interplay between the low‐energy conformation perturbations and cooperative intra‐ and intermolecular noncovalent interactions. [ABSTRACT FROM AUTHOR]

New polymorphs β and γ of bis‐3‐nitrophenyl disulphide, crystallized above 0.3 GPa, are less dense than the ambient‐pressure polymorph α. This counterintuitive density relation results from the high‐entropy nucleation and subsequent kinetic crystallization. The work performed by pressure compensates the high entropy and temperature product, substantiated in varied conformers and increased chemical potential. Pressure‐increased viscosity promotes the kinetic polymorphs, in accordance with empirical Ostwald's rule of stages. It contrasts to mechanochemical techniques, favouring high‐density polymorphs. [ABSTRACT FROM AUTHOR]

The structures and solid‐state dynamics of the supramolecular salts of the general formula [(12‐crown‐4)2⋅DABCOH2](X)2 (where DABCO=1,4‐diazabicyclo[2.2.2]octane, X=BF4, ClO4) have been investigated as a function of temperature (from 100 to 360 K) and pressure (up to 3.4 GPa), through the combination of variable‐temperature and variable‐pressure XRD techniques and variable‐temperature solid‐state NMR spectroscopy. The two salts are isomorphous and crystallize in the enantiomeric space groups P3221 and P3121. All building blocks composing the supramolecular complex display dynamic processes at ambient temperature and pressure. It has been demonstrated that the motion of the crown ethers is maintained on lowering the temperature (down to 100 K) or on increasing the pressure (up to 1.5 GPa) thanks to the correlation between neighboring molecules, which mesh and rotate in a concerted manner similar to spiral gears. Above 1.55 GPa, a collapse‐type transition to a lower‐symmetry ordered structure, not attainable at a temperature of 100 K, takes place, proving, thus, that the pressure acts as the means to couple and decouple the gears. The relationship between temperature and pressure effects on molecular motion in the solid state has also been discussed. [ABSTRACT FROM AUTHOR]

Targeted synthesis of piezoresponsive small molecules and in‐depth understanding of their mechanism is of utmost importance for the development of smart devices. This work reports the synthesis, structure and piezosensitivity of a bola‐amphiphile 1,4‐bis(pentyloxy)‐2,5‐bis(2‐pyridineethynyl)‐benzene (C5‐PPB). Depending on the rate of compression, two different phases in C5‐PPB can be generated. The ambient‐pressure α‐phase is stable up to 0.8 GPa, beyond which it undergoes an isostructural transformation to β‐phase, accompanied by a clearly visible elongation of the crystal. This α‐to‐β phase transition requires the sample to be compressed slowly. When quickly compressed, phase α persists to about 1.5 GPa, beyond which its amorphization starts, accompanied by the appearance of irregular grooves on the largest faces. Mechanical pressure also affects the optical property of C5‐PPB, which shows reversible mechanochromism with a green to cyan transformation in the emission, associated with a 15 nm shift in the maxima. The conductivity of C5‐PPB as a direct outcome of its crystal packing has also been studied. [ABSTRACT FROM AUTHOR]

Abstract: This work describes, for the first time, the application of combined pressure and temperature stimuli in disulfide metathesis reactions. In the system studied, above a pressure of 0.2 GPa, equimolar amounts of symmetric disulfides bis 4‐chlorophenyl disulfide [(4‐ClPhS)2] and bis 2‐nitrophenyl disulfide [(2‐NO2PhS)2] react to give the heterodimeric product 4‐Cl‐PhSSPh‐2‐NO2. In contrast to experiments conducted in solution at atmospheric pressure or in mechanochemical experiments under ball‐mill grinding conditions, there is no necessity to use a base or thiolate anion as a catalyst for the exchange reaction under investigated conditions. Single‐crystal and powder X‐ray diffraction revealed also that, despite the high‐pressure conditions of this reaction, the heterodimeric‐disulfide product unexpectedly crystallizes into the low‐density polymorph A. This counterintuitive result contrasts with the high‐pressure stability of the higher‐density polymorph B, confirmed by its compression up to 2.8 GPa with no signs of a phase transition. [ABSTRACT FROM AUTHOR]

Pressure evolution leads to a gradual relaxation of induced structural strains through stepwise conformational twisting of the phenyl rings with the reorganization of cooperative noncovalent interactions; this propagates the conformational isomerization. Keywords: high-pressure chemistry; molecular crystals; noncovalent interactions; phase transitions; zinc-oxo clusters EN high-pressure chemistry molecular crystals noncovalent interactions phase transitions zinc-oxo clusters 13662 13662 1 10/05/21 20211001 NES 211001 B The understanding of multiple polymorphic phase transitions b in molecular crystals is still in its infancy. High-pressure chemistry, molecular crystals, noncovalent interactions, phase transitions, zinc-oxo clusters. [Extracted from the article]

Crystal growth, high-pressure chemistry, kinetic crystallization, nucleation, polymorphism Front Cover: High-pressure Nucleation of Low-Density Polymorphs (Chem. Eur. J. 24/2021) Keywords: crystal growth; high-pressure chemistry; kinetic crystallization; nucleation; polymorphism EN crystal growth high-pressure chemistry kinetic crystallization nucleation polymorphism 6995 6995 1 04/30/21 20210426 NES 210426 B Low-density polymorphs b obtained in a high-pressure environment are reported in this work. [Extracted from the article]

Cooling [Fe(bbtr)3](BF4)2 (bbtr=1,4‐di(1,2,3‐triazol‐1‐yl)butane) triggers very slow spin crossover below 80 K (T1/2↓=76 K). The spin crossover (SCO) is accompanied by a hysteresis loop (T1/2↑=89 K). In contrast to isostructural perchlorate analogue [Fe(bbtr)3](ClO4)2 in which spin crossover during cooling is preceded by phase transition at TPT=126 K in tetrafluoroborate phase transition does not occur to the beginning of spin crossover (80 K). Studies of mixed crystals [Fe(bbtr)3](BF4)2(1‐x)(ClO4)2x (0.5≤x≤0.9) showed that a phase transition precedes spin crossover, however, for x≅0.46 intersection of T1/2(x) and TPT(x) dependencies takes place. The application of pressure of 1 GPa shifts the spin crossover in [Fe(bbtr)3](BF4)2 to a temperature above 270 K. High‐pressure studies of neat tetrafluoroborate and perchlorate, as well as mixed crystals [Fe(bbtr)3](BF4)2(1‐x)(ClO4)2x (0.1≤x≤0.9), revealed that at 295 K P1/2 value changes linearly with x indicating similar mechanism of spin crossover under elevated pressure in all systems under investigation. Variable pressure single crystal X‐ray diffraction studies confirmed that in contrast to thermally induced spin crossover undergoing differently in tetrafluoroborate and perchlorate an application of high pressure removes this differentiation leading to a similar mechanism depending at first on start spin crossover and then P‐3→P‐1 phase transition occurs. In this report we have shown that 2D coordination polymer [Fe(bbtr)3](BF4)2 (bbtr=1,4‐di(1,2,3‐triazol‐1‐yl)butane) treated to date as spin crossover silent shows thermally induced spin crossover phenomenon. Spin crossover in tetrafluoroborate is extremely slow. Determination of the spin crossover curve required carrying measurement in the settle mode‐cooling from 85 to 70 K took about 600 h (average velocity of change of temperature ca. 0.0004 K/min). [ABSTRACT FROM AUTHOR]