Subtle Modification of Imine-linked Helical Receptors to Significantly Alter their Binding Affinities and Selectivities for Chiral Guests

Aromatic helical receptors P- 1 and P- 2 were slightly modified by aerobic oxidation to afford new receptors P- 7 and P- 8 with right-handed helical cavities. This subtle modification induced significant changes in the binding properties for chiral guests. Specifically, P- 1 was reported to bind d -tartaric acid (K_a=35500 M⁻¹), used as a template, much strongly than l -tartaric acid (326 M⁻¹). In contrast, its modified receptor P- 7 exhibited significantly reduced affinities for d -tartaric acid (3600 M⁻¹) and l -tartaric acid (125 M⁻¹). More dramatic changes in the affinities and selectivities were observed for P- 2 and P- 8 upon binding of polyol guests. P- 2 was determined to selectively bind d -sorbitol (52000 M⁻¹) over analogous guests, but P- 8 showed no binding selectivity: d -sorbitol (1890 M⁻¹), l -sorbitol (3330 M⁻¹), d -arabitol (959 M⁻¹), l -arabitol (4970 M⁻¹) and xylitol (4960 M⁻¹) in 5% (v/v) DMSO/CH₂Cl₂ at 25±1 °C. These results clearly demonstrate that even subtle post-modifications of synthetic receptors may significantly alter their binding affinities and selectivities, in particular for guests of long and flexible chains.     

Halide‐Anion Water Clusters in Cucurbit[6]uril Supramolecular Systems

Three types of dihalide water clusters [X₂(H₂O)₈]^2? (X=Cl, Br) and [I₂(H₂O)₁₀]^2? have been observed in cucurbit[6]uril supramolecular systems with same guest. According to the single crystal data and the quantitative theory computation, with the increase of electronegativity of halide ions, dihalide water clusters become more stable. A further comparison of three kinds of guests with different molecule length but the same anions, [p‐phenylenediamine salt, hexamethylenediamine salt and N,N′‐hexamethylenebis(pyrazinylbromide)], gives the result that the dihalide water clusters collapse from 2D to 1D with the increase of the lengths.     

Novel Hydrazone‐Based Tripodal Sensors: Single Selective Colorimetric Chemosensor for Acetate in Aqueous Solution

A series of novel tripodal colorimetric anion sensors based on hydrazone CHN NH groups have been synthesized and their recognition behavior with anionic guests has been studied. In DMSO solutions, sensors 1 and 2 show colorimetric responses for F⁻, H₂PO⁻₄ and AcO⁻, while in DMSO/H₂O (9:1, V/V) solutions, sensor 1 shows single selectivity for AcO⁻. ¹H NMR titration confirms that the tripodal sensors could bind anions through the collaboration of three hydrazone groups and anions residing in the central cavity of the sensors.     

Atmospheric Chemistry of Camphor

Rate constants have been measured at 296 ± 2 K for the gas‐phase reactions of camphor with OH radicals, NO₃ radicals, and O₃. Using relative rate methods, the rate constants for the OH radical and NO₃ radical reactions were (4.6 ± 1.2) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ and <3 × 10⁻¹⁶ cm³ molecule⁻¹ s⁻¹, respectively, where the indicated error in the OH radical reaction rate constant includes the estimated overall uncertainty in the rate constant for the reference compound. An upper limit to the rate constant for the O₃ reaction of <7 × 10⁻²⁰ cm³ molecule⁻¹ s⁻¹ was also determined. The dominant tropospheric loss process for camphor is calculated to be by reaction with the OH radical. Acetone was identified and quantified as a product of the OH radical reaction by gas chromatography, with a formation yield of 0.29 ± 0.04. In situ atmospheric pressure ionization tandem mass spectrometry (API‐MS) analyses indicated the formation of additional products of molecular weight 166 (dicarbonyl), 182 (hydroxydicarbonyl), 186, 187, 213 (carbonyl‐nitrate), 229 (hydroxycarbonyl‐nitrate), and 243. A reaction mechanism leading to the formation of acetone is presented, as are pathways for the formation of several of the additional products observed by API‐MS. © 2000 John Wiley and Sons, Inc. Int J Chem Kinet 33: 56–63, 2001     

A Chiral Emissive Conjugated Corral for High-Affinity and Highly Enantioselective Recognition in Water

Accurately distinguishing between enantiomeric molecules is a fundamental challenge in the field of chemistry. However, there is still significant room for improvement in both the enantiomeric selectivity (K_R(S)/K_S(R)) and binding strength of most reported macrocyclic chiral receptors to meet the demands of practical application scenarios. Herein, we synthesized a water-soluble conjugated tubular host—namely, corral[4]BINOL—using a chiral 1,1′-bi-2-naphthol (BINOL) derivative as the repeating unit. The conjugated chiral backbone endows corral[4]BINOL with good fluorescent emission (QY=34 % ) and circularly polarized luminescence (|g_lum| up to 1.4×10⁻³) in water. Notably, corral[4]BINOL exhibits high recognition affinity up to 8.6×10¹⁰ M⁻¹ towards achiral guests in water, and manifested excellent enantioselectivity up to 18.7 towards chiral substrates, both of which represent the highest values observed among chiral macrocycles in aqueous solution. The ultrastrong binding strength, outstanding enantioselectivity, and facile accessibility, together with the superior fluorescent and chiroptical properties, endow corral[4]BINOL with great potential for a wide range of applications.     

Rate constants for the reactions of Cl atoms with HCOOH and with HOCO radicals

Rate constants have been measured at room temperature for the reactions of Cl atoms with formic acid and with the HOCO radical: Cl + HCOOH → HCl + HOCO (R1) Cl + HOCO → HCl + CO₂ (R2) Cl atoms were generated by flash photolysis of Cl₂ and the progress of reaction was followed by time‐resolved infrared absorption measurements using tunable diode lasers on the CO₂ that was formed either in the pair of reactions ( R1 ) plus ( R2 ), or in reaction ( R1 ) followed by O₂ + HOCO → HO₂ + CO₂ (R3) In a separate series of experiments, conditions were chosen so that the kinetics of CO₂ formation were dominated either by the rate of reaction ( R1 ) or by that of reactions ( R1 ) and ( R2 ) combined. The results of our analysis of these experiments yielded: k₁ = (1.8₃ ± 0.12) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ k₂ = (4.8 ± 1.0) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 85–91, 2000     

Glycoluril‐Derived Molecular Clips are Potent and Selective Receptors for Cationic Dyes in Water

Molecular clip 1 remains monomeric in water and engages in host–guest recognition processes with suitable guests. We report the K_a values for 32 1? guest complexes measured by ¹H NMR, UV/Vis, and fluorescence titrations. The cavity of 1 is shaped by aromatic surfaces of negative electrostatic potential and therefore displays high affinity and selectivity for planar and cationic aromatic guests that distinguishes it from CB[n] receptors that prefer aliphatic over aromatic guests. Electrostatic effects play a dominant role in the recognition process whereby ion–dipole interactions may occur between ammonium ions and the C=O groups of 1 , between the SO₃^? groups of 1 and pendant cationic groups on the guest, and within the cavity of 1 by cation–π interactions. Host 1 displays a high affinity toward dicationic guests with large planar aromatic surfaces (e.g. naphthalene diimide NDI+ and perylene diimide PDI+) and cationic dyes derived from acridine (e.g. methylene blue and azure A). The critical importance of cation–π interactions was ascertained by a comparison of analogous neutral and cationic guests (e.g. methylene violet vs. methylene blue; quinoline vs. N‐methylquinolinium; acridine vs. N‐methylacridinium; neutral red vs. neutral red H⁺) the affinities of which differ by up to 380‐fold. We demonstrate that the high affinity of 1 toward methylene blue (K_a=3.92×10⁷ m ^?1; K_d=25 nm ) allows for the selective sequestration and destaining of U87 cells stained with methylene blue.     

Atmospheric chemistry of di-tert-butyl ether: Rates and products of the reactions with chlorine atoms,hydroxyl radicals,and nitrate radicals

The rate constants for the gas-phase reactions of di-tert-butyl ether (DTBE) with chlorine atoms, hydroxyl radicals, and nitrate radicals have been determined in relative rate experiments using FTIR spectroscopy. Values of k_(DTBE+CI) = (1.4 ± 0.2) × 10⁻¹⁰,k_(DTBE+OH) = (3.7 ± 0.7) × 10⁻¹², and k_(DTBE+N03) = (2.8 ± 0.9) × 10⁻¹⁶ cm³ molecule⁻¹ s⁻¹ were obtained. Tert-butyl acetate was identified as the major product of both Cl atom and OH radical initiated oxidation of DTBE in air in the presence of NO_x. The molar tert-butyl acetate yield was 0.85 ± 0.11 in the Cl atom experiments and 0.84 ± 0.11 in OH radical experiments. As part of this work the rate constant for reaction of Cl atoms with tert-butyl acetate at 295 K was determined to be (1.6 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. The stated errors are two standard deviations (2σ). © 1996 John Wiley & Sons, Inc.     

Kinetics of the gas-phase reactions of NO3 radicals and O3 with 3-methylfuran and the OH radical yield from the O3 reaction

Using relative rate methods, rate constants have been measured for the gas-phase reactions of 3-methylfuran with NO₃ radicals and O₃ at 296 ± 2 K and atmospheric pressure of air. The rate constants determined were (1.31 ± 0.461) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for the NO₃ radical reaction and (2.05 ± 0.52) × 10⁻¹⁷ cm³ molecule⁻¹ s⁻¹ for the O₃ reaction, where the indicated errors include the estimated overall uncertainties in the rate constants for the reference reactions. Based on the cyclohexanone plus cyclohexanol yield in the presence of sufficient cyclohexane to scavenge > 95% of OH radicals formed, it is estimated that the O₃ reaction leads to the formation of OH radicals with a yield of 0.59, uncertain to a factor of ca. 1.5. In the troposphere, 3-methylfuran will react dominantly with the OH radical during daylight hours, and with the NO₃ radical during nighttime hours for nighttime NO₃ radical concentrations > 10⁷ molecule cm ⁻³. © 1996 John Wiley & Sons, Inc.     

Rate constants for the reactions of OH radicals and Cl atoms with Di‐n‐Propyl ether and Di‐n‐Butyl ether and their deuterated analogs

Using relative rate methods, rate constants for the gas‐phase reactions of OH radicals and Cl atoms with di‐n‐propyl ether, di‐n‐propyl ether‐d₁₄, di‐n‐butyl ether and di‐n‐butyl ether‐d₁₈ have been measured at 296 ± 2 K and atmospheric pressure of air. The rate constants obtained (in cm³ molecule⁻¹ s⁻¹ units) were: OH radical reactions, di‐n‐propyl ether, (2.18 ± 0.17) × 10⁻¹¹; di‐n‐propyl ether‐d₁₄, (1.13 ± 0.06) × 10⁻¹¹; di‐n‐butyl ether, (3.30 ± 0.25) × 10⁻¹¹; and di‐n‐butyl ether‐d₁₈, (1.49 ± 0.12) × 10⁻¹¹; Cl atom reactions, di‐n‐propyl ether, (3.83 ± 0.05) × 10⁻¹⁰; di‐n‐propyl ether‐d₁₄, (2.84 ± 0.31) × 10⁻¹⁰; di‐n‐butyl ether, (5.15 ± 0.05) × 10⁻¹⁰; and di‐n‐butyl ether‐d₁₈, (4.03 ± 0.06) × 10⁻¹⁰. The rate constants for the di‐n‐propyl ether and di‐n‐butyl ether reactions are in agreement with literature data, and the deuterium isotope effects are consistent with H‐atom abstraction being the rate‐determining steps for both the OH radical and Cl atom reactions. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 425–431, 1999     

A study of the self reaction of CH2ClO2 and CHCl2O2 radicals at 298 K

A low‐pressure discharge‐flow system equipped with laser‐induced fluorescence (LIF) detection of NO₂ and resonance‐fluorescence detection of OH has been employed to study the self reactions CH₂ClO₂ + CH₂ClO₂ → products (1) and CHCl₂O₂ + CHCl₂O₂ → products (2), at T = 298 K and P = 1–3 Torr. Possible secondary reactions involving alkoxy radicals are identified. We report the phenomenological rate constants (k_obs) k_1obs = (4.1 ± 0.2) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ k_2obs = (8.6 ± 0.2) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ and the rate constants derived from modelling the decay profiles for both peroxy radical systems, which takes into account the proposed secondary chemistry involving alkoxy radicals k₁ = (3.3 ± 0.7) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ k₂ = (7.0 ± 1.8) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ A possible mechanism for these self reactions is proposed and QRRK calculations are performed for reactions (1), (2) and the self‐reaction of CH₃O₂, CH₃O₂ + CH₃O₂ → products (3). These calculations, although only semiquantitative, go some way to explaining why both k₁ and k₂ are a factor of ten larger than k₃ and why, as suggested by the products of reaction (1) and (2), it seems that the favored reaction pathway is different from that followed by reaction (3). The atmospheric fate of the chlorinated peroxy species, and hence the impact of their precursors (CH₃Cl and CH₂Cl₂), in the troposphere are briefly discussed. HC(O)Cl is identified as a potentially important reservoir species produced from the photooxidation of these precursors. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 433–444, 1999     

Kinetic studies of the self‐reaction and reaction with HO2 of a tertiary β‐brominated peroxy radical between 298 and 393 K

The kinetics of reactions of the tertiary β‐brominated peroxy radical BrC(CH₃)₂C(CH₃)₂O₂ (2‐bromo‐1,1,2‐trimethylpropylperoxy) have been studied using the laser flash photolysis technique, photolysing HBr at 248 nm in the presence of O₂ and 2,3‐dimethylbut‐2‐ene. At room temperature, a rate constant of (2.0 ± 0.8) × 10⁻¹⁴ cm³ molecule⁻¹ s⁻¹ was determined for the BrC(CH₃)₂C(CH₃)₂O₂ self‐reaction. The reaction of BrC(CH₃)₂C(CH₃)₂O₂ with HO₂ was investigated in the temperature range 306–393 K, yielding the following Arrhenius expression: k(BrC(CH₃)₂C(CH₃)₂O₂ + HO₂) = (2.04 ± 0.25) × 10⁻¹² exp[(501 ± 36)K/T] cm³ molecule⁻¹ s⁻¹, giving by extrapolation (1.10 ± 0.13) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ at 298 K. These results confirm the enhancement of the peroxy radical self‐reaction reactivity upon β‐substitution, which is similar for Br and OH substituents. In contrast, no significant effect of substituent has been observed on the rate constant for the reactions of peroxy radicals with HO₂. The global uncertainty factors on rate constants are equal to nearly 2 for the self‐reaction and to 1.35 for the reaction with HO₂. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 33: 41–48, 2001     

Kinetics of the gas-phase reactions of the oh radical with selected glycol ethers,glycols, and alcohols

Using a relative rate method, rate constants have been measured for the gas-phase reactions of the OH radical with 1-hexanol, 1-methoxy-2-propanol, 2-butoxyethanol, 1,2-ethanediol, and 1,2-propanediol at 296±2 K, of (in units of 10⁻¹² cm³ molecule⁻¹ s⁻¹): 15.8±3.5; 20.9±3.1; 29.4±4.3; 14.7±2.6; and 21.5±4.0, respectively, where the error limits include the estimated overall uncertainties in the rate constants for the reference compounds. These OH radical reaction rate constants are higher than certain of the literature values, by up to a factor of 2. Rate constants were also measured for the reactions of 1-methoxy-2-propanol and 2-butoxyethanol with NO₃ radicals and O₃, with respective NO₃ radical and O₃ reaction rate constants (in cm³ molecule⁻¹ s⁻¹ units) of: 1-methoxy-2-propanol, (1.7±0.7)×10⁻¹⁵, and <1.1×10⁻¹⁹; and 2-butoxyethanol, (3.0±1.2)×10⁻¹⁵, and <1.1×10⁻¹⁹. The dominant tropospheric loss process for the alcohols, glycols, and glycol ethers studied here is calculated to be by reaction with the OH radical, with lifetimes of 0.4–0.8 day for a 24 h average OH radical concentration of 1.0×10⁶ molecule cm⁻³. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 533–540, 1998     

Temperature-dependent kinetics studies of the reactions of C2H5O2 and n-C3H7O2 radicals with NO

The rate coefficients for the gas-phase reactions of C₂H₅O₂ and n-C₃H₇O₂ radicals with NO have been measured over the temperature range of (201–403) K using chemical ionization mass spectrometric detection of the peroxy radical. The alkyl peroxy radicals were generated by reacting alkyl radicals with O₂, where the alkyl radicals were produced through the pyrolysis of a larger alkyl nitrite. In some cases C₂H₅ radicals were generated through the dissociation of iodoethane in a low-power radio frequency discharge. The discharge source was also tested for the i-C₃H₇O₂ + NO reaction, yielding k_{298 K} = (9.1 ± 1.5) × 10⁻¹² cm³ molecule⁻¹ s⁻¹, in excellent agreement with our previous determination. The temperature dependent rate coefficients were found to be k(T) = (2.6 ± 0.4) × 10⁻¹² exp{(380 ± 70)/T} cm³ molecule⁻¹ s⁻¹ and k(T) = (2.9 ± 0.5) × 10⁻¹² exp{(350 ± 60)/T} cm³ molecule⁻¹ s⁻¹ for the reactions of C₂H₅O₂ and n-C₃H₇O₂ radicals with NO, respectively. The rate coefficients at 298 K derived from these Arrhenius expressions are k = (9.3 ± 1.6) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ for C₂H₅O₂ radicals and k = (9.4 ± 1.6) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ for n-C₃H₇O₂ radicals. © 1996 John Wiley & Sons, Inc.     

Cooperative Binding of Divalent Diamides by N‐Alkyl Ammonium Resorcinarene Chlorides

N‐Alkyl ammonium resorcinarene chlorides, stabilized by an intricate array of hydrogen bonds leading to a cavitand‐like structure, bind amides. The molecular recognition occurs through intermolecular hydrogen bonds between the carbonyl oxygen and the amide hydrogen of the guests and the cation–anion circular hydrogen‐bonded seam of the hosts, as well as through CH ??? π interactions. The N‐alkyl ammonium resorcinarene chlorides cooperatively bind a series of di‐acetamides of varying spacer lengths ranging from three to seven carbons. Titration data fit either a 1:1 or 2:1 binding isotherm depending on the spacer lengths. Considering all the guests possess similar binding motifs, the first binding constants were similar (K₁: 10² M ^?1) for each host. The second binding constant was found to depend on the upper rim substituent of the host and the spacer length of the guests, with the optimum binding observed with the six‐carbon spacer (K₂: 10³ M ^?2). Short spacer lengths increase steric hindrance, whereas longer spacer lengths increase flexibility thus reducing cooperativity. The host with the rigid cyclohexyl upper rim showed stronger binding than the host with flexible benzyl arms. The cooperative binding of these divalent guests was studied in solution through ¹H NMR titration studies and supplemented by diffusion‐ordered spectroscopy (DOSY), X‐ray crystallography, and mass spectrometry.     

A kinetics study on reactions of C6H5O with C6H5O and O3 at 298 k

Kinetics for reactions of phenoxy radical, C₆H₅O, with itself and with O₃ were examined at 298 K and low pressure (1 Torr) using discharge flow coupled with mass spectrometry (DF/MS). The rate constant for the phenoxy radical self‐reaction was determined to be k₁ = (1.49 ± 0.53) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ defined by d[C₆H₅O]/dt=−2 k₁[C₆H₅O]². The rate constant for the C₆H₅O reaction with O₃ was measured to be k₂ = (2.86 ± 0.35) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹, which may be a lower limit value. Because of much higher atmospheric abundance of ozone than that of both NO and phenoxy, the reaction of C₆H₅O with ozone may represent the principal fate of the phenoxy radical in the atmosphere. Products from reaction of C₆H₅O + C₆H₅O, NO, and NO₂ were also investigated, and (C₆H₅O)₂ (m/e = 186), C₆H₅O(NO) (m/e = 123), and C₆H₅O(NO₂) (m/e = 139) adducts were observed as products for the reactions of C₆H₅O with itself, NO, and NO₂, respectively. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 65–72, 1999     

A Tunable Cyclic Container: Guest‐Induced Conformational Switching,Efficient Guest Exchange,and Selective Isolation of C70 from a Fullerene Mixture

An adaptable cyclic porphyrin dimer with highly flexible linkers has been used as an artificial molecular container that can efficiently encapsulate various aromatic guests (TCNQ/C₆₀/C₇₀) through strong π–π interactions by adjusting its cavity size and conformation. The planar aromatic guest (TCNQ) can be easily and selectively exchanged with larger aromatic guests (C₆₀/C₇₀). During the guest‐exchange process, the two porphyrin rings switch their relative orientation according to the size and shape of the guests. This behavior of the cyclic container has been thoroughly investigated by using UV/Vis spectroscopy, NMR spectroscopy, and X‐ray crystal structure determination of the host–guest assemblies. The electrochemical and photophysical studies demonstrated the occurrence of photoinduced electron transfer from bisporphyrin to TCNQ/C₆₀/C₇₀ in the respective host–guest assemblies. The cyclic host can form complexes with C₆₀ and C₇₀ with association constants of (2.8±0.2)×10⁵ and (1.9±0.3)×10⁸ m ⁻¹, respectively; the latter value represents the highest binding affinity for C₇₀ reported so far for zinc(II) bisporphyrinic receptors. This high selectivity for the binding of C₇₀ versus C₆₀ allows the easy extraction and efficient isolation of C₇₀ from a C₆₀/C₇₀ fullerene mixture. Experimental evidence was substantiated by DFT calculations.     

Kinetics and products of propargyl (C3H3) radical self‐reactions and propargyl‐methyl cross‐combination reactions

Propargyl (HCC CH₂) and methyl radicals were produced through the 193‐nm excimer laser photolysis of mixtures of C₃H₃Cl/He and CH₃N₂CH₃/He, respectively. Gas chromatographic and mass spectrometric (GC/MS) product analyses were employed to characterize and quantify the major reaction products. The rate constants for propargyl radical self‐reactions and propargyl‐methyl cross‐combination reactions were determined through kinetic modeling and comparative rate determination methods. The major products of the propargyl radical combination reaction, at room temperature and total pressure of about 6.7 kPa (50 Torr) consisted of three C₆H₆ isomers with 1,5‐hexadiyne(CHC CH₂ CH₂ CCH, about 60%); 1,2‐hexadiene‐5yne (CH₂CC CH₂ CCH, about 25%); and a third isomer of C₆H₆ (∼15%), which has not yet been, with certainty, identified as being the major products. The rate constant determination in the propargyl‐methyl mixed radical system yielded a value of (4.0 ± 0.4) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for propargyl radical combination reactions and a rate constant of (1.5 ± 0.3) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ for propargyl‐methyl cross‐combination reactions. The products of the methyl‐propargyl cross‐combination reactions were two isomers of C₄H₆, 1‐butyne (about 60%) and 1,2‐butadiene (about 40%). © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 118–124, 2000     

Switching Between Giant Positive and Negative Thermal Expansions of a YFe(CN)6-based Prussian Blue Analogue Induced by Guest Species

The control of thermal expansion of solid compounds is intriguing but remains challenging. The effect of guests on the thermal expansion of open-framework structures was investigated. Notably, the presence of guest ions (K⁺) and molecules (H₂O) can substantially switch thermal expansion of YFe(CN)₆ from negative (α_v=−33.67×10⁻⁶ K⁻¹) to positive (α_v=+42.72×10⁻⁶ K⁻¹)—a range that covers the thermal expansion of most inorganic compounds. The mechanism of such substantial thermal expansion switching is revealed by joint studies with synchrotron X-ray diffraction, X-ray absorption fine structure, neutron powder diffraction, and density functional theory calculations. The presence of guest ions or molecules plays a critical damping effect on transverse vibrations, thus inhibiting negative thermal expansion. An effective method is demonstrated to control the thermal expansion in open-framework materials by adjusting the presence of guests.     

Switching Between Giant Positive and Negative Thermal Expansions of a YFe(CN)6‐based Prussian Blue Analogue Induced by Guest Species

The control of thermal expansion of solid compounds is intriguing but remains challenging. The effect of guests on the thermal expansion of open‐framework structures was investigated. Notably, the presence of guest ions (K⁺) and molecules (H₂O) can substantially switch thermal expansion of YFe(CN)₆ from negative (α _v=−33.67×10⁻⁶ K⁻¹) to positive (α _v=+42.72×10⁻⁶ K⁻¹)—a range that covers the thermal expansion of most inorganic compounds. The mechanism of such substantial thermal expansion switching is revealed by joint studies with synchrotron X‐ray diffraction, X‐ray absorption fine structure, neutron powder diffraction, and density functional theory calculations. The presence of guest ions or molecules plays a critical damping effect on transverse vibrations, thus inhibiting negative thermal expansion. An effective method is demonstrated to control the thermal expansion in open‐framework materials by adjusting the presence of guests.