Thermally Triggered Solid‐State Single‐Crystal‐to‐Single‐Crystal Structural Transformation Accompanies Property Changes

The 1D complex [(CuL_0.5H₂O) ? H₂O]_n ( 1 ) (H₄L=2,2′‐bipyridine‐3,3′,6,6′‐tetracarboxylic acid) undergoes an irreversible thermally triggered single‐crystal‐to‐single‐crystal (SCSC) transformation to produce the 3D anhydrous complex [CuL_0.5]_n ( 2 ). This SCSC structural transformation was confirmed by single‐crystal X‐ray diffraction analysis, thermogravimetric (TG) analysis, powder X‐ray diffraction (PXRD) patterns, variable‐temperature powder X‐ray diffraction (VT–PXRD) patterns, and IR spectroscopy. Structural analyses reveal that in complex 2 , though the initial 1D chain is still retained as in complex 1 , accompanied with the Cu‐bound H₂O removed and new O(carboxyl)?Cu bond forming, the coordination geometries around the Cu^II ions vary from a distorted trigonal bipyramid to a distorted square pyramid. With the drastic structural transition, significant property changes are observed. Magnetic analyses show prominent changes from antiferromagnetism to weak ferromagnetism due to the new formed Cu1‐O‐C‐O‐Cu4 bridge. The catalytic results demonstrate that, even though both solid‐state materials present high catalytic activity for the synthesis of 2‐imidazolines derivatives and can be reused, the activation temperature of complex 1 is higher than that of complex 2 . In addition, a possible pathway for the SCSC structural transformations is proposed.     

Flexible Viologen‐Based Porous Framework Showing X‐ray Induced Photochromism with Single‐Crystal‐to‐Single‐Crystal Transformation

A viologen‐based Borromean entangled porous framework was found to be sensitive to both Cu_Kα and Mo_Kα X‐ray sources, showing rapid photochromic response and recovery within one minute. The X‐ray‐induced photochromic process is accompanied by a reversible single‐crystal‐to‐single‐crystal (SC‐SC) structural transformation, an unprecedented phenomenon for X‐ray sensitive materials. The complex can be further processed into portable thin films for detecting the dose of the X‐ray exposure. Moreover, the photochromism can occur over a broad temperature range of 100–333 K, both in the form of single crystals and thin films, making it a potential candidate for practical indoor and outdoor applications.     

An Atomic View of Cation Diffusion Pathways from Single‐Crystal Topochemical Transformations

The diffusion pathways of Li‐ions as they traverse cathode structures in the course of insertion reactions underpin many questions fundamental to the functionality of Li‐ion batteries. Much current knowledge derives from computational models or the imaging of lithiation behavior at larger length scales; however, it remains difficult to experimentally image Li‐ion diffusion at the atomistic level. Here, by using topochemical Li‐ion insertion and extraction to induce single‐crystal‐to‐single‐crystal transformations in a tunnel‐structured V₂O₅ polymorph, coupled with operando powder X‐ray diffraction, we leverage single‐crystal X‐ray diffraction to identify the sequence of lattice interstitial sites preferred by Li‐ions to high depths of discharge, and use electron density maps to create a snapshot of ion diffusion in a metastable phase. Our methods enable the atomistic imaging of Li‐ions in this cathode material in kinetic states and provide an experimentally validated angstrom‐level 3D picture of atomic pathways thus far only conjectured through DFT calculations.     

Thermodynamic Phase Transition Through Crystal‐to‐Crystal Process of Photochromic 1,2‐Bis(5‐phenyl‐2‐propyl‐3‐thienyl)perfluorocyclopentene

A photochromic diarylethene, 1,2‐bis(5‐phenyl‐2‐propyl‐3‐thienyl)perfluorocyclopentene ( 1a ), was found to have two polymorphic crystal forms, α‐ and β‐crystals. From X‐ray crystallographic analysis, the space groups of α‐ and β‐crystals were determined to be P2₁/c and C2/c, respectively. The difference between two crystal forms is ascribed to the orientation of two of four molecules in the unit cell. The thermodynamic phase transition from α‐ to β‐forms occurred via a crystal‐to‐crystal process, as confirmed by differential scanning calorimetry measurements, optical microscopic observations in the reflection mode and under crossed Nicols, and powder X‐ray diffraction measurements. The movement of the molecules in the crystal was evaluated by analyzing the change of face indices before and after the phase transition.     

Visible‐Light‐Induced Photodimerization of a Photoactive Yellow Protein (PYP) Chromophore Model in a Single Crystal

The chromophore of the photoactive yellow protein (PYP), the photoreceptor in the photomotility of the bacterium Halorhodospira halophila, is a deprotonated para‐coumaric thioester linked to the side residue of a cysteine residue. The photophysics of the PYP chromophore is conveniently modeled with para‐hydroxycinnamic thiophenyl esters. Herein, we report the first direct evidence, obtained with X‐ray diffraction, of photodimerization of a para‐hydroxycinnamic thiophenyl ester in single crystalline state. This result represents the first direct observation of [2+2] dimerization of a model PYP chromophore, and demonstrates that even very weak light in the visible region is capable of inducing parallel radical reactions in PYP from the excited state of the chromophore, in addition to the main reaction pathway (trans–cis isomerization). This PYP model system adds an interesting example to the known solid‐state photodimerizations, because unlike the anhydrous crystal (which is not capable of sustaining the stress and disintegrates in the course of photodimerization), a single water molecule “dilutes” the structure to the extent sufficient for single‐crystal‐to‐single‐crystal reaction.     

Dynamic Gas‐Inclusion in a Single Crystal

In solid‐state science, most changing phenomena have been mysterious. Furthermore, the changes in chemical composition should be added to mere physical changes to also cover the chemical changes. Here, the first success in characterizing the nature of gas inclusion in a single crystal is reported. The gas inclusion process has been thoroughly investigated by in situ optical microscopy, single‐crystal X‐ray diffraction analyses, and gas adsorption measurements. The results demonstrated an inclusion action of a first‐order transition behavior induced by a critical concentration on the phase boundary. The transfer of phase boundary and included gas are strongly related. This relationship can generate the dynamic features hidden in the inclusion phenomena, which can lead to the guest capturing and transfer mechanism that can apply to spatiotemporal inclusion applications by using host solids.     

Spontaneous Single‐Crystal‐to‐Single‐Crystal Evolution of Two Cross‐Laminated Polymers

Two cases of spontaneous evolution of monomers to linear polymers having novel cross‐laminated topology are reported. We synthesized two peptide monomers N₃‐Gly‐Gly‐NH‐CH₂‐CCH and N₃‐Gly‐Gly‐Gly‐CH₂‐CCH and solved their crystal structures by single‐crystal X‐ray diffraction. They adopt H‐bonded crisscrossed layered packing in their crystals such that: (a) the monomers are aligned head‐to‐tail in 1D‐chain‐like arrays and parallel arrangement of such arrays forms a layer; (b) the proximally placed azide and alkyne motifs are in an orientation apt for their regiospecific cycloaddition; (c) each monomer having x peptide bonds is H‐bonded with 2x monomers disposed in intersecting arrangement, which pre‐organize 1D‐chain‐like arrays in adjacent layers in perpendicular orientation. These crystals underwent spontaneous single‐crystal‐to‐single‐crystal (SCSC) polymerization via azide–alkyne cycloaddition reaction to form triazolyl‐polyglycines, at room temperature. The crisscrossed arrangement of monomers in adjacent layers ensured the formation of cross‐laminated polymers.     

Crystal structure of a high‐pressure phase of magnesium chloride hexahydrate determined by in‐situ X‐ray and neutron diffraction methods

A high‐pressure phase of magnesium chloride hexahydrate (MgCl₂·6H₂O‐II) and its deuterated counterpart (MgCl₂·6D₂O‐II) have been identified for the first time by in‐situ single‐crystal X‐ray and powder neutron diffraction. The crystal structure was analyzed by the Rietveld method for the neutron diffraction pattern based on the initial structure determined by single‐crystal X‐ray diffraction. This high‐pressure phase has a similar framework to that in the known ambient‐pressure phase, but exhibits some structural changes with symmetry reduction caused by a subtle modification in the hydrogen‐bond network around the Mg(H₂O)₆ octahedra. These structural features reflect the strain in the high‐pressure phases of MgCl₂ hydrates.     

Spin‐State Ordering on One Sub‐lattice of a Mononuclear Iron(III) Spin Crossover Complex Exhibiting LIESST and TIESST

The two‐step spin crossover in mononuclear iron(III) complex [Fe(salpm)₂]ClO₄ ? 0.5 EtOH ( 1 ) is shown to be accompanied by a structural phase transition as concluded from ⁵⁷Fe Mössbauer spectroscopy and single crystal X‐ray diffraction, with spin‐state ordering on just one of two sub‐lattices in the intermediate magnetic and structural phase. The complex also exhibits thermal‐ and light‐induced spin‐state trapping (TIESST and LIESST), and relaxation from the LIESST and TIESST excited states occurs via the broken symmetry intermediate phase. Two relaxation events are evident in both experiments, that is, two T(LIESST) and two T(TIESST) values are recorded. The change in symmetry which accompanies the TIESST effect was followed in real time using single crystal diffraction. After flash freezing at 15 K the crystal was warmed to 40 K at which temperature superstructure reflections were observed to appear and disappear within a 10 000 s time range. In the frame of the international year of crystallography, these results illustrate how X‐ray diffraction makes it possible to understand complex ordering phenomena.     

Anion‐Exchange Properties of Trifluoroacetate and Triflate Salts of N‐Alkylammonium Resorcinarenes

The synthesis of N‐benzyl‐ and N‐cyclohexylammonium resorcinarene trifluoroacetate (TFA) and triflate (OTf) salt receptors was investigated. Solid‐state analysis by single‐crystal X‐ray diffraction revealed that the N‐alkylammonium resorcinarene salts (NARSs) with different upper substituents had different cavity sizes and different affinities for anions. Anion‐exchange experiments by mixing equimolar amounts of N‐benzylammonium resorcinarene trifluoroacetate and N‐cyclohexylammonium resorcinarene triflate, as well as N‐benzylammonium resorcinarene triflate and N‐cyclohexylammonium resorcinarene trifluoroacetate showed that the NARS with flexible benzyl groups preferred the larger OTf anion, whereas the rigid cyclohexyl groups preferred the smaller TFA anions. The anion‐exchange processes were confirmed in the solid state by single‐crystal and powder X‐ray diffraction experiments and in the gas phase by electrospray ionization mass spectrometry.     

Fusing Dicarbollide Ions with N‐Heterocyclic Carbenes

Discovered by Hawthorne in 1965, dicarbollide ions are an intriguing class of nido ‐carboranes that mimic the behavior of the cyclopentadienyl anion. Herein, we show that it is possible to directly link the dicarbollide ion to an N‐heterocyclic carbene (NHC) to form an isolable N‐dicarbollide‐substituted NHC dianion. This molecule can be accessed by the sequential double deprotonation of a mono‐nido ‐carboranyl imidazolium zwitterion. As revealed by a single‐crystal X‐ray diffraction study, the first deprotonation leads to a monoanionic dicarbollide ion that adopts a bis(dicarbollide) structure in the solid state. Subsequent deprotonation of this monoanion leads to the first N‐dicarbollide NHC, which was fully characterized by multinuclear NMR spectroscopy as well as single‐crystal X‐ray diffraction.     

Synthesis,Characterization, and Photoluminescence Properties of a Planar Copper Triazolate Coordination Polymer with Cyanide as Co‐Ligand

A new copper coordination polymer [Cu₃(CN)(dmtz)₂] ( 1 ) (Hdmtz = 3,5‐dimethyl‐1,2,4‐triazole) was solvothermally synthesized and characterized by IR spectroscopy, X‐ray power diffraction, and single‐crystal X‐ray diffraction. The single‐crystal diffraction analysis shows that compound 1 belongs to the orthorhombic space group Pmmn, and exhibits a 2D planar framework constructed by the ligand dmtz and cyanide anions, in which the cyanide anion was generated from in situ decomposition of acetonitrile. The photoluminescent study indicates that 1 emits strong blue‐green luminescence with long emission lifetimes in the solid state at room temperature.     

Unusually Stable Triazine‐based Organic Superstructures

Solid‐state reactions have been rapidly gaining popularity in organic chemistry owing to their simplicity, efficiency, and selectivity compared to liquid‐phase reactions. Herein, we describe the formation of superstructures through the solid‐state reaction of an organic single‐crystal. The superstructure of 5,5′,5′′‐(1,3,5‐triazine‐2,4,6‐triyl)triisophthalonitrile (TIPN) can be formed by cyclotrimerization of 1,3,5‐tricyanobenzene (TCB) single crystals. The TIPN superstructure was confirmed by single crystal X‐ray diffraction and visualized by transmission electron microscopy. The superstructure has hexagonally packed 1‐dimensional (1D) channels along the crystal axis. Furthermore, the superstructure arises from interdigitated nitrile interactions in the crystal lattice, and thus has electron‐beam tolerance and very high thermal stability.     

Crystal‐to‐Crystal Transformation: An HgII Metal–Organic Polymer Constructed with a Triazole Ligand

A new one‐dimensional double‐chain Hg^II coordination polymer containing the ligand 3,5‐bis(4‐pyridyl)‐4‐amino‐1,2,4‐triazole (bpatrz) and thiocyanate anions, namely, {[Hg₂(μ‐bpatrz)(μ‐SCN)₂(SCN)₂] · MeOH}_n ( 1 ), has been synthesized and structurally characterized by single‐crystal X‐ray diffraction. Compound 1 displays bright blue luminescence with emission maxima around 370 and 440 nm in solution and the solid state, respectively. Uptake and release of MeOH by 1 were investigated by powder X‐ray diffraction, thermogravimetric analysis, elemental analysis, and IR and NMR spectroscopy.     

Ba3V2S4O3: A Mott Insulating Frustrated Quasi‐One‐Dimensional S=1 Magnet

Through a solid‐state reaction, a practically phase pure powder of Ba₃V₂S₄O₃ was obtained. The crystal structure was confirmed by X‐ray single‐crystal and synchrotron X‐ray powder diffraction (P6₃, a=10.1620(2), c=5.93212(1) Å). X‐ray absorption spectroscopy, in conjunction with multiplet calculations, clearly describes the vanadium in charge‐disproportionated V^IIIS₆ and V^VSO₃ coordinations. The compound is shown to be a strongly correlated Mott insulator, which contradicts previous predictions. Magnetic and specific heat measurements suggest dominant antiferromagnetic spin interactions concomitant with a weak residual ferromagnetic component, and that intrinsic geometric frustration prevents long‐range order from evolving.     

Disodium[hydroxotetranitronitrosyl]ruthenate(II), a Photochromic Substance with Long‐lived Metastable States: Structure at 110 K,Spectroscopic and Thermal Properties

Disodium[hydroxotetranitronitrosyl]ruthenate(II) is a photochromic compound excitable with blue‐green light which exhibits at least one unusually long‐lived metastable state at low temperature. At 298 K, the compound crystallises in the space group C2/m. A reversible phase transition occurs at 240 K upon cooling, as detected by Differential Scanning Calorimetry and X‐ray powder diffraction which causes a lowering of the crystal symmetry to the space group P2₁/n. Synchrotron X‐ray single crystal diffraction and FT‐IR spectroscopy data obtained on the ground and the excited states of the title compound low temperature phase are presented.     

Structural Aspects of the β‐Polymorph of (E)‐4‐Formylcinnamic Acid: Structure Determination Directly from Powder Diffraction Data and Elucidation of Structural Disorder from Solid‐State NMR

Among the derivatives of (E)‐cinnamic acid for which the solid‐state photochemical properties have been studied, (E)‐4‐formylcinnamic acid ( 1 ) has already received much attention. Given the inability to prepare single crystals of the β‐polymorph of 1 that are of suitable size and quality for structural characterization by single‐crystal X‐ray diffraction, the structure of this material was determined directly from powder X‐ray‐diffraction data by means of the genetic‐algorithm technique for structure solution, followed by Rietveld refinement. High‐resolution solid‐state ¹³CNMR was also applied to elucidate details of structural disorder concerning the orientation of the formyl group, and provided independent support for the disorder model established form the Rietveld refinement. The reported structure establishes that the β‐phase of 1 is not structurally anomalous among photoreactive (E)‐cinnamic acid crystals, and finally resolves a long‐standing controversy concerning the structural properties of this material.     

Luminescence Color‐Tuning through Polymorph Doping: Preparation of a White‐Emitting Solid from a Single Gold(I)–Isocyanide Complex by Simple Precipitation

We report the luminescent color tuning of a new complex, 2‐benzothiophenyl(4‐methoxyphenyl isocyanide)gold(I) ( 1 ), by using a new “polymorph doping” approach. The slow crystallization of the complex 1 afforded three different pure polymorphic crystals with blue, green, and orange emission under UV‐light irradiation. The crystal structures of pure polymorphs of 1 were investigated in detail by means of single‐crystal X‐ray analyses. Theoretical calculations based on the single‐crystal structures provided qualitative explanation of the difference in the excited energy‐levels of the three polymorphs of 1 . In sharp contrast, the rapid precipitation of 1 , with the optimized conditions reproducibly afforded homogeneous powder materials showing solid‐state white‐emission with Commission Internationale de l’Éclairage (CIE) 1931 chromaticity coordinates of (0.33, 0.35), which is similar to pure white. New “polymorphic doping” has been revealed to be critical to this white emission through spectroscopic and X‐ray diffraction analyses. The coexistence of the multiple polymorphs of 1 within the homogeneous powder materials and the ideal mixing of multiple luminescent colors gave its white emission accompanied with energy transfer from the predominant green‐emitting polymorph to the minor orange‐emitting polymorph.     

Perfluoroalcohols: The Preparation and Crystal Structures of Heptafluorocyclobutanol and Hexafluorocyclobutane‐1,1‐diol

The first X‐ray crystal structure of an α‐fluoroalcohol is reported. Heptafluorocyclobutanol was obtained in quantitative yield from hexafluorocyclobutanone by HF addition in anhydrous hydrogen fluoride. The compound was characterized by its X‐ray single crystal structure. Heptafluorocyclobutanol readily undergoes hydrolysis to hexafluorocyclobutane‐1,1‐diol, which was also structurally characterized by X‐ray diffraction.