Fe(II) , Co(II) and Ni(II) complexes of two tetraazamacrocycles (1,4,8,11-tetrakis(carbamoylmethyl)-1,4,8,11-tetraazacyclotetradecane (L1) and ...1,4,7,10-tetrakis(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane (L2) show promise as paraCEST agents for registration of temperature (paraCEST=paramagnetic chemical exchange saturation transfer). The Fe(II) , Co(II) and Ni(II) complexes of L1 show up to four CEST peaks shifted ≤112 ppm, whereas analogous complexes of L2 show only a single CEST peak at ≤69 ppm. Comparison of the temperature coefficients (CT ) of the CEST peaks of Co(L2)(2+) , Fe(L2)(2+) , Ni(L1)(2+) and Co(L1)(2+) showed that a CEST peak of Co(L1)(2+) gave the largest CT (-0.66 ppm (o) C(-1) at 4.7 T). NMR spectral and CEST properties of these complexes correspond to coordination complex symmetry as shown by structural data. The Ni(L1)(2+) and Co(L1)(2+) complexes have a six-coordinate metal ion bound to the 1-, 4-amide oxygen atoms and four nitrogen atoms of the tetraazamacrocycle. The Fe(L2)(2+) complex has an unusual eight-coordinate Fe(II) bound to four amide oxygen atoms and four macrocyclic nitrogen atoms. For Co(L2)(2+) , one structure has seven-coordinate Co(II) with three bound amide pendents and a second structure has a six-coordinate Co(II) with two bound amide pendents.
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Crystallization of nicotine, an oil prone to degradation at room temperature, has been demonstrated to be an effective means of creating nicotine-based materials with tunable thermal properties and ...improved resistance to photo-induced degradation. Herein, we show that both isomers of enantiomerically pure tartaric acid are highly effective salt formers when combined with nicotine. Both salts exhibit enhanced photostability, and with a melting point of 143.1 °C, the salt prepared using d-(−)-tartaric acid possesses one of the highest melting points for a crystalline nicotine solid reported to date.
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Interfacial electron transfer (IET) between a chromophore and a semiconductor nanoparticle is one of the key processes in a dye-sensitized solar cell. Theoretical simulations of the electron transfer ...in polyoxotitanate nanoclusters Ti17O24(OPri)20 (Ti 17 ) functionalized with four p-nitrophenyl acetylacetone (NPA-H) adsorbates, of which the atomic structure has been fully established by X-ray diffraction measurements, are presented. Complementary experimental information showing IET has been obtained by EPR spectroscopy. Evolution of the time-dependent photoexcited electron during the initial 5 fs after instantaneous excitation to the NPA LUMO + 1 has been evaluated. Evidence for delocalization of the excitation over multiple chromophores after excitation to the NPA LUMO + 2 state on a 15 fs time scale is also obtained. While chromophores are generally considered electronically isolated with respect to neighboring sensitizers, our calculations show that this is not necessarily the case. The present work is the most comprehensive study to date of a sensitized semiconductor nanoparticle in which the structure of the surface and the mode of molecular adsorption are precisely defined.
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A phenanthrene-based diarylethene linker with linear pyridyl connectivity, 4,4'-(9,10-bis(2,5-dimethylthiophen-3-yl)phenanthrene-2,7-di yl)dipyridine linker (TPDPy) was prepared and subsequently used ...to synthesize an air-stable metal-organic framework, UBMOF-3 (Zn3(BDC)3(TPDPy)1(DMF)1.5, BDC = 1,4-benzenedicarboxylate, DMF = N,N-dimethylformamide). Upon irradiation with ultraviolet light, this photo-responsive framework, composed of terephthalate, TPDPy, and zinc pinwheels, exhibits strong linear dichroism consistent with the crystal structure. Activation (desolvation) of the crystal leads to a significant change in the crystal structure that improves the ability to crystallographically resolve the photochromic linker.
Organic photochromic molecules including diarylethenes are of particular interest for their numerous potential applications including high-density optical data storage and light-activated switches. ...In this report, we examined the temperature dependence of the light-drive photocyclization reaction in a classic diarylethene. The steady-state populations were monitored spectroscopically and by temperature dependent in situ photocrystallography, the latter being the first reported example of this technique. The observed decrease in the steady-state population with decreasing temperature suggests this classic diarylethene possesses an excited-state potential energy surface topology similar to previously reported “inverted” diarylethenes.
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In this contribution we demonstrate that metal-organic frameworks (MOFs) with suitable underlying topological structure are amenable for the preparation of MOF-based substitutional solid-solutions ...(SSS) that follow Vegard's law. Preparation of multivariate (MTV) libraries of Porous Interpenetrated Zirconia Organic Frameworks (PIZOF) using homeomorphic links of different length (18.6 and 19.3 Å) result in the formation of SSS that exhibit linearity between composition and structure. We prepared seven MTV MOF libraries (40 unique compositions) and observed relations in composition input/output ratio, composition/lattice parameter (Vegard's law), and between composition obtained from NMR and from PXRD. We further show that SSS formation has dependence on linker solubility, stability, and steric hindrance caused by the presence of functional groups. We demonstrate that solid-solution strategies can be utilized as part of the synthetic toolkit for the preperation of reticular crystals with desired composition, structure, and properties.
In this contribution we demonstrate that metal-organic frameworks (MOFs) with suitable underlying topological structure are amenable for the preparation of MOF-based substitutional solid-solutions (SSS) that follow Vegard's law.
The relative stability and accessibility of atropisomers plays a prominent role in the efficacy of diarylethene-based photochromic materials. Herein, DFT methods, using the ωB97XD functional and a ...6-31G(d) basis, are employed to determine the local energetic minima and maxima which describe the rotation of a thiophene group in derivatives of 9,10-bis(2-methyl-5-pheylthiophen-3-yl)phenanthrene-2,7-dicarboxylic acid, a photochromic linker molecule which exhibits atropisomer-formation-related fatigue when incorporated into a metal–organic framework. Results of these potential energy surface mapping calculations as well as their applications to atropisomer separability are discussed.
We report the anisotropic terahertz response of oxalic acid and sucrose crystals in the 0.2–3.0 THz range using terahertz time domain spectroscopy on large, single crystals. We compare the observed ...anisotropic response with the response calculated using solid-state density functional theory and find good agreement in the orientation dependence and relative intensities of the crystal phonons. It was found that oxalic dihydrate can be reversibly converted to anhydrous by controlled relative humidity. In addition, oxalic acid was found to have a large birefringence with Δn = 0.3, suggesting the material may be useful for terahertz polarization manipulation. Sucrose has a smaller birefringence of Δn = 0.05, similar to that of x-cut quartz. The anisotropic measurements provide both mode separation and symmetry determination to more readily achieve mode assignment for the more complex sucrose spectrum.
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In the paper by Kamiński et al. J. Appl. Cryst. (2014), 47, 17651768, Jason B. Benedict is missing from the list of authors. The complete list of authors should be Radosław Kamiński, Jason B. ...Benedict, Gary Nottingham and Philip Coppens.
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2D molecular entities build next-generation electronic devices, where abundant elements of organic molecules are attractive due to the modern synthetic and stimuli control through chemical, ...conformational, and electronic modifications in electronics. Despite its promising potential, the insufficient control over charge states and electronic stabilities must be overcome in molecular electronic devices. Here, we show the reversible switching of modulated charge states in an exfoliatable 2D-layered molecular conductor based on bis(ethylenedithio)tetrathiafulvalene molecular dimers. The multiple stimuli application of cooling rate, current, voltage, and laser irradiation in a concurrent manner facilitates the controllable manipulation of charge crystal, glass, liquid, and metal phases. The four orders of magnitude switching of electric resistance are triggered by stimuli-responsive charge distribution among molecular dimers. The tunable charge transport in 2D molecular conductors reveals the kinetic process of charge configurations under stimuli, promising to add electric functions in molecular circuitry.
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