Optical Activity of Metal Nanoclusters Deposited on Regular and Doped Oxide Supports from First-Principles Simulations

We report a computational study and analysis of the optical absorption processes of Ag20 and Au20 clusters deposited on the magnesium oxide (100) facet, both regular and including point defects. Ag20 and Au20 are taken as models of metal nanoparticles and their plasmonic response, MgO as a model of a simple oxide support. We consider oxide defects both on the oxygen anion framework (i.e., a neutral oxygen vacancy) and in the magnesium cation framework (i.e., replacing Mg++ with a transition metal: Cu++ or Co++). We relax the clusters’ geometries via Density-Functional Theory (DFT) and calculate the photo-absorption spectra via Time-Dependent DFT (TDDFT) simulations on the relaxed geometries. We find that the substrate/cluster interaction induces a broadening and a red-shift of the excited states of the clusters, phenomena that are enhanced by the presence of an oxygen vacancy and its localized excitations. The presence of a transition-metal dopant does not qualitatively affect the spectral profile. However, when it lies next to an oxygen vacancy for Ag20, it can strongly enhance the component of the cluster excitations perpendicular to the surface, thus favoring charge injection.

Crystallographic Characterization of the Metal–Organic Framework Fe2(bdp)3 upon Reductive Cation Insertion*

<div><p>Precisely locating extra-framework cations in anionic metal–organic framework compounds remains a long-standing, yet crucial, challenge for elucidating structure-performance relationships in functional materials. Single-crystal X-ray diffraction is one of the most powerful approaches for this task, but single crystals of frameworks often degrade when subjected to post-synthetic metalation or reduction. Here, we demonstrate the growth of sizable single crystals of the robust metal–organic framework Fe₂(bdp)₃ (bdp²⁻ = benzene-1,4-dipyrazolate) and employ single-crystal-to-single-crystal chemical reductions to access the solvated framework materials A₂Fe₂(bdp)₃∙<i>y</i>THF(A = Li⁺, Na⁺, K⁺). X-ray diffraction analysis of the sodium and potassium congeners reveals that the cations are located near the center of the triangular framework channels and are stabilized by weak cation–π interactions with the framework ligands. Freeze-drying with benzene enables isolation of activated single crystals of Na_0.5Fe₂(bdp)₃and Li₂Fe₂(bdp)₃ and the first structural characterization of activated metal–organic frameworks wherein extra-framework alkali metal cations are also structurally located. Comparison of the solvated and activated sodium-containing structures reveals that the cation positions differ in the two materials, likely due to cation migration that occurs upon solvent removal to maximize stabilizing cation­–π interactions. Hydrogen adsorption data indicate that these cation-framework interactions are sufficient to diminish the effective cationic charge, leading to little or no enhancement in gas uptake relative to Fe₂(bdp)₃. In contrast, Mg_0.85Fe₂(bdp)₃ exhibits enhanced H₂ affinity and capacity over the non-reduced parent material. This observation shows that increasing the charge density of the pore-residing cation serves to compensate for charge dampening effects resulting from cation–framework interactions and thereby promotes stronger cation–H₂ interactions.</p></div>

Crystallographic Characterization of the Metal–Organic Framework Fe2(bdp)3 upon Reductive Cation Insertion*

<div><p>Precisely locating extra-framework cations in anionic metal–organic framework compounds remains a long-standing, yet crucial, challenge for elucidating structure-performance relationships in functional materials. Single-crystal X-ray diffraction is one of the most powerful approaches for this task, but single crystals of frameworks often degrade when subjected to post-synthetic metalation or reduction. Here, we demonstrate the growth of sizable single crystals of the robust metal–organic framework Fe₂(bdp)₃ (bdp²⁻ = benzene-1,4-dipyrazolate) and employ single-crystal-to-single-crystal chemical reductions to access the solvated framework materials A₂Fe₂(bdp)₃∙<i>y</i>THF(A = Li⁺, Na⁺, K⁺). X-ray diffraction analysis of the sodium and potassium congeners reveals that the cations are located near the center of the triangular framework channels and are stabilized by weak cation–π interactions with the framework ligands. Freeze-drying with benzene enables isolation of activated single crystals of Na_0.5Fe₂(bdp)₃and Li₂Fe₂(bdp)₃ and the first structural characterization of activated metal–organic frameworks wherein extra-framework alkali metal cations are also structurally located. Comparison of the solvated and activated sodium-containing structures reveals that the cation positions differ in the two materials, likely due to cation migration that occurs upon solvent removal to maximize stabilizing cation­–π interactions. Hydrogen adsorption data indicate that these cation-framework interactions are sufficient to diminish the effective cationic charge, leading to little or no enhancement in gas uptake relative to Fe₂(bdp)₃. In contrast, Mg_0.85Fe₂(bdp)₃ exhibits enhanced H₂ affinity and capacity over the non-reduced parent material. This observation shows that increasing the charge density of the pore-residing cation serves to compensate for charge dampening effects resulting from cation–framework interactions and thereby promotes stronger cation–H₂ interactions.</p></div>

ELECTRICAL INVESTIGATION OF THE WATER ADSORPTION MECHANISM ON NATURAL CLINOPTILOLITE

Zeolites are ionic conductors and the cation electrical mobility in zeolites depends on their hydration state; consequently, the water adsorption/desorption process can be simply investigated by measuring the temporal evolution of current intensity in samples exposed to an environment with constant humidity or dry air, respectively. According to this kinetic analysis, a mechanism has been formulated for the water adsorption process able to justify the Lagergren pseudo-first-order kinetics observed for adsorption and the first-order kinetics observed for desorption. In this mechanism water molecules are first attract by the electric field of the cations and then they move at cation-framework interface to maximize the hydrogen bond interactions.

Tetraphenylphosphonium Salts for Small Molecule Capture

Tetraphenylphosphonium salts are useful tools for capturing (and crystallizing) small molecules. The packing of the cations in such salts leads to channels or cavities suitable for trapping of the small molecule by the anion. For example, we have prepared the complex salts [PPh4][SO2X] (X = Cl, Br, I) through the exposure of solutions of [PPh4]X to an atmosphere of SO2. Churakov et al. have reported the preparation of [PPh4]X·nH2O2 (X = Cl, Br; n = 0.98–1.90) after trapping hydrogen peroxide using the precursor halide salts (1). Envisioning a similar result, a concentrated solution of [PPh4]CN·xH2O was exposed to an atmosphere of CO2. Colourless crystals were isolated and characterised as [PPh4][NCCO2] using crystallographic and spectroscopic techniques. The packing of the ions in the product, in the tetragonal space group I-4, is similar to that observed in many other simple [PPh4]X salts, where X = Br, I, SCN, OCN, N(CN)2, etc. Solution of the crystal structure was complicated by the high symmetry and disorder in the anion, with only three unique atoms being necessary for its characterization. Thus the utility of our chosen cation can also become a hindrance. Crystals can usually be grown and data obtained but structure solution is not a certainty. For example, the structures of [PPh4]CN·xH2O have not been reported, likely because of the rapid spinning of the anions in the cation framework, even though they are hydrogen bonded to the water which is clearly visible. Similarly, we have data collected for the products from a number of related reactions, [PPh4][CN]·xH2O + PhC(O)F, [PPh4]F + SO2, [PPh4]X (X = Cl, Br, I, CN, N3) + CS2, and can clearly identify the cation in the unit cell. However, elucidation of the structures of the anions has not been possible. It is hoped that this presentation will engender discussion of possible solutions to the observed disorder problems.

Pengaruh Kemahiran Generik dalam Kemahiran Pemikiran Kritikal, Penyelesaian Masalah dan Komunikasi Pelajar Universiti Kebangsaan Malaysia (UKM)

Kemahiran generik adalah kemahiran yang diperlukan oleh pelajar selain akademik untuk menjadi lebih berjaya dan cemerlang sebagai pengamal dalam bidang akademik, pekerjaan, dan kehidupan. Kemahiran generik diintegrasikan dalam pengajaran dan pembelajaran dalam konteks subjek pengajian dan merupakan kemahiran boleh pindah atau transferable skills. Penilaian kemahiran generik di Institusi Pengajian Tinggi (IPT) mula diberi fokus apabila Malaysian Qualifi cation Framework (MQF) di laksanakan pada tahun 2006. Tujuan kajian ini adalah untuk mengenal pasti pengaruh atau petunjuk utama kemahiran generik terhadap kemahiran berfi kiran kritikal, penyelesaian masalah dan komunikasi pelajar. Kajian ini menggunakan Instrumen Kemahiran Generik Pengajian Tinggi (GeSIHE) yang dibina oleh sekumpulan penyelidik Universiti Kebangsaan Malaysia (UKM). Instrumen GeSIHE mengandungi 13 konstruk dengan 102 item dan ditadbirkan kepada 1,262 orang pelajar prasiswazah di 12 fakulti UKM yang dipilih secara rawak berkelompok. Kebolehpercayaan GeSIHE adalah tinggi iaitu dari 0.98 hingga 0.99. Analisis multi-regresi stepwise menunjukkan secara signifi kan kemahiran kepimpinan dalam aspek menghasilkan idea dan sering berinteraksi pada masa yang singkat adalah petunjuk utama menyebabkan pelajar UKM mahir dalam berkomunikasi. Manakala kemahiran pembelajaran sepanjang hayat atau keupayaan pembelajaran sepanjang masa merupakan petunjuk utama yang menyebabkan pelajar university mahir dalam kemahiran pemikiran kritikal dan menyelesaikan masalah.