The crystalline nanocluster phase, in which nanoscale metal oxide clusters are self-assembled in three-dimensional periodic arrays, is described. The crystalline assembly of nanoparticles ...functionalized with technologically relevant ligands offers the opportunity to obtain unambiguous structural information that can be combined with theoretical calculations based on the known geometry and used to interpret spectroscopic and other information. A series of Ti/O clusters up to ∼2.0 nm in diameter have been synthesized and functionalized with the adsorbents catechol and isonicotinic acid. Whereas the isonicotinate is always adsorbed in a bridging monodentate mode, four different adsorption modes of catechol have been identified. The particles show a significantly larger variation of the Ti−O distances than observed in the known TiO2 phases and exhibit both sevenfold overcoordination and five- and fourfold undercoordination of the Ti atoms. Theoretical calculations show only a moderate dependence of the catecholate net charge on the geometry of adsorption. All of the catechol-functionalized clusters have a deep-red color due to penetration of the highest occupied catechol levels into the band gap of the Ti/O particles. Spectroscopic measurements of the band gap of the Ti17 cluster are in good agreement with the theoretical values and show a blue shift of ∼0.22 eV relative to those reported for anatase nanoparticles.
Paramagnetic Fe(II) and Co(II) complexes are utilized as the first transition metal examples of 1H NMR shift agents (paraSHIFT) for thermometry applications using Magnetic Resonance Spectroscopy ...(MRS). The coordinating ligands consist of TACN (1,4,7-triazacyclononane) and CYCLEN (1,4,7,10-tetraazacyclododecane) azamacrocycles appended with 6-methyl-2-picolyl groups, denoted as MPT and TMPC, respectively. 1H NMR spectra of the MPT- and TMPC-based Fe(II) and Co(II) complexes demonstrate narrow and highly shifted resonances that are dispersed as broadly as 440 ppm. The six-coordinate complex cations, M(MPT)2+ and M(TMPC)2+, vary from distorted octahedral to distorted trigonal prismatic geometries, respectively, and also demonstrate that 6-methyl-2-picolyl pendents control the rigidity of these complexes. Analyses of the 1H NMR chemical shifts, integrated intensities, line widths, the distances obtained from X-ray diffraction measurements, and longitudinal relaxation time (T 1) values allow for the partial assignment of proton resonances of the M(MPT)2+ complexes. Nine and six equivalent methyl protons of M(MPT)2+ and M(TMPC)2+, respectively, produce 3-fold higher 1H NMR intensities compared to other paramagnetically shifted proton resonances. Among all four complexes, the methyl proton resonances of Fe(TMPC)2+ and Co(TMPC)2+ at −49.3 ppm and −113.7 ppm (37 °C) demonstrate the greatest temperature dependent coefficients (CT) of 0.23 ppm/°C and 0.52 ppm/°C, respectively. The methyl groups of these two complexes both produce normalized values of |CT|/fwhm = 0.30 °C–1, where fwhm is full width at half-maximum (Hz) of proton resonances. The T 1 values of the highly shifted methyl protons are in the range of 0.37–2.4 ms, allowing rapid acquisition of spectroscopic data. These complexes are kinetically inert over a wide range of pH values (5.6–8.6), as well as in the presence of serum albumin and biologically relevant cations and anions. The combination of large hyperfine shifts, large temperature sensitivity, increased signal-to-noise ratio, and short T 1 values suggests that these complexes, in particular the TMPC-based complexes, show promise as paraSHIFT agents for thermometry.
The use of crystal engineering to convert liquids into crystalline solids remains a powerful method for inhibiting undesired degradation pathways. When nicotine, a liquid sensitive to both light and ...air, is combined with the GRAS-listed compound, gentisic acid, the resulting crystalline solid, exhibits enhanced photo and thermal stability. Despite a modest ΔTm of 42.7 °C, the melting point of 155.9 °C for the nicotinium gentisate salt is the highest reported for nicotine-containing crystalline solids. An analysis of the crystal packing and thermodynamic properties provides context for the observed properties.
Careful control of the temperature and duration of the reaction between titanium tert-butoxide and acetic acid leads to the formation of new polyoxotitanate clusters with 14, 18, and 28 Ti atoms. ...They are considered intermediates in the growth of Ti/O nanoclusters of increasing size. The Ti28 cluster is the largest crystallized to date. UV/vis spectroscopy on this cluster reveals that the optical band gap is blue-shifted with respect to a cluster containing only 17 titanium atoms indicating that the optical properties are more heavily influenced by the internal structure of the particle than its size.
The binding of carboxylate- and acetylacetonate-linked chromophores to homodisperse polyoxotitanate nanoclusters with 17 Ti atoms or more are surveyed and found to be limited to chelate-bidentate and ...the bridging modes, the former being dominant for the acetylacetonate-linked chromophores, the latter for the carboxylate linkers. Chromophores with acetylacetonate linking groups invariably bind in the chelate mode, whereas carboxylic acid terminated chromophores more frequently are observed to have the bridging mode, with the exception of three cases in which a strong electron-donating substituent is present on two different sensitizers. The calculations for isonicotinateand nitrophenylacetylacetonate functionalized Ti17 clusters show the observed binding modes to correspond to the lower energy functionalized clusters, but do not predict the difference between the cinnamic acid and dimethylaminocinnamic acid binding to Ti17, which are bridging and chelate respectively. Both binding modes were never observed to occur for a single chromophore, even when synthetic conditions were varied. Density of state calculations show broadening and splitting of the chromophore LUMO on complexation due to interaction with the cluster’s conduction band, as well as frequent penetration of sensitizer orbitals into the bandgap of the functionalized nanoparticle.
The synthesis and characterization of novel photochromic diarylethene-based linkers for use in metal–organic frameworks is described including crystal structure analysis of nearly all reaction ...intermediates. The bis-carboxylated dithien-3-ylphenanthrenes can be prepared under relatively mild conditions in high yield and were subsequently used to create a photoresponsive metal–organic framework, UBMOF-1. While the photochromism of the ligand TPDC in solution is fully reversible, the cycloreversion reaction is suppressed when this linker is incorporated into the crystalline framework of UBMOF-1.
Nicotine, a widely consumed, yet considered toxic, active pharmaceutical ingredient for recreational use, is known to rapidly deteriorate into unwanted and potentially harmful side products. ...Crystallization with salt formers transforms the unstable oil into solids with tunable properties. However, previously reported salts and co-crystals are not necessarily safe for human consumption, with several containing heavily halogenated coformers. When combined with malic acid, a generally recognized as safe (GRAS) compound, the four resulting crystalline solids exhibited melting points as high as 122 °C and spanned a range of ∼30 °C. The nicotine-based materials also possessed improved degradation properties. A detailed analysis of the crystal packing and thermodynamic properties provides context for the observed properties.
Singlet fission (k SF) and excimer formation (k EXC) rate constants along with other photophysical properties of thin solid layers of 1,3-diphenylisobenzofuran and 11 of its fluorinated derivatives ...have been determined. The molecular properties of these compounds are similar, but their crystal packing varies widely. Most of them undergo singlet fission whereas excitation in others is trapped in excimers. The trend in rate constants k SF agrees qualitatively with results of calculations by a simplified version of the frontier orbital model for a molecular pair. The main shortcoming of the model is discussed.
The quadratic dependence of the rate of photodimerization of α-trans-cinnamic acid induced by 532 nm pulsed laser light confirms a two-photon mechanism in the single crystals. Single crystals in ...well-defined orientations and circularly polarized light were used in the experiments. The reaction rate deviates from first-order kinetics, but fits the JMAK expression with a coefficient indicating a mechanism intermediate between a random distribution of product molecules in the crystal and the existence of growing nuclei. The reaction is accompanied by a large change in the monoclinic β-angle of the unit cell, corresponding to increased π-overlap between adjacent molecules and therefore to an increased reaction rate. The improved penetration of the light in the crystal and more homogeneous product formation are significant advantages in studies of mechanisms of chemical reactions in single crystals.
We report the first instance of observing the phototriggered isomerization of dmso ligands on a bis sulfoxide complex, Ru(bpy)
(dmso)
, in the crystalline solid state. The solid-state UV-vis spectrum ...of the crystal demonstrates an increase in optical density around 550 nm after irradiation, which is consistent with the solution isomerization results. Digital images of the crystal before and after irradiation display a notable color change (pale orange to red) and cleavage occurs along planes, (1̄01) and (100), during irradiation. Single crystal X-ray diffraction data also confirms that isomerization is occurring throughout the lattice and a structure that contains a mix of the
,
and
,
/
,
isomer was attained from a crystal irradiated
.
irradiation XRD studies reveal that the percentage of the O-bonded isomer increases as a function of 405 nm exposure time.
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