A stable superatomic Cu6(SMPP)6 nanocluster with dual emission.

We have synthesized single crystals of a highly stable Cu6 nanocluster protected by six ligands of 2-mercapto-5-n-propylpyrimidine (SMPP). This Cu6(SMPP)6 cluster has a quasi-octahedral superatomic Cu6 core, with the Cu atoms being protected by both -S- and N-bidentate coordination of the SMPP ligands. Interestingly, each Cu atom is linked with an N atom, while the two neighboring Cu atoms on the same triangular facet are linked by the -S- bridge of the ligand. Single-crystal parsing results show that the altered orientation of the SMPP ligands give rise to three packing modes (named as 1, 2, and 3) of the Cu6(SMPP)6 NCs. Apart from the well-organized coordination, this Cu6(SMPP)6 nanocluster exhibits superatomic stability with a metallic core of 4 valence electrons (1S22S2||3S2), enabling to largely balance the interactions between the polynuclear core and delocalized electrons. Interestingly, the Cu6(SMPP)6 NCs display dual emissions in both ultraviolet-visible (UV-Vis) and near-infrared (NIR) regions. First-principles calculations well reproduce the experimental spectrum, shedding light on the nature of excitation states and metal-ligand interactions in the Cu6(SMPP)6 cluster.

A mono-copper doped undeca-gold cluster with up-converted and anti-stokes emissions of fluorescence and phosphorescence.

We have synthesized single crystals of a highly stable Cu-doped undeca-gold cluster protected by both triphenylphosphine (PPh3) and 2-pyridinethiol (-SPy) ligands, formulated as [Au11Cu1(PPh3)7(SPy)3]+. This cluster (Au11Cu1 NCs for short) has a metallic core of C3v Au@Au10 with the Cu atom capped on one of the nine triangular facets and it is triply-coordinated to three N atoms of the SPy ligands of which the sulfur atom simultaneously binds to three adjacent Au atoms via singly-coordinated S-Au bonds, respectively. The other seven gold atoms form a crown structure by a link of three orthogons with common sides and are protected by seven PPh3 ligands. Besides the well-organized coordination, this Au11Cu1 nanocluster is demonstrated to exhibit superatom stability of the metallic core within 8 valence electrons (assuming that the 3 electrophilic-SPy ligands capture 3 electrons from the metal center). More interestingly, this Au11Cu1 nanocluster shows interesting emissions in both ultraviolet visible (UV-Vis) and near infrared (NIR) regions, and the emissions display novel anti-Stokes up-conversion lasing characteristics. TD-DFT calculated UV-vis and emission spectra well reproduce the experimental results, shedding light on the nature of excitation states and underlying mechanism of electronic transitions between diverse energy levels of such a monolayer-protected bimetallic cluster.

Cl@Ag22 Au6 (4-TBBT)28 (PPh4 ): A Chloride-Centered Ag-Au Bimetallic Cluster for Optics.

We report the single-crystal synthesis of a chlorine-centered bimetallic cluster, Cl@Ag22 Au6 (4-TBBT)28 (PPh4 ), which bears a quatrefoil-structured Cl@Ag22 (SR)16 core studded by six Au(SR)2 staples showing a quasi Td symmetry. This cluster bears 28 metal atoms and 28 ligands, with a chlorine atom hosted in the center of the metallic Ag22 Au6 core. Single-crystal analysis shows that this cluster possesses essentially a different bonding nature compared with other monolayer-protected metal clusters (MPCs) or traditional metal-sulfur complexes. We fully dissect the structure evolution in forming such a chlorine-centered cluster. Interestingly, this cluster, Cl@Ag22 Au6 (4-TBBT)28 (PPh4 ), displays a fluorescence emission at 570 nm and supports the solid emission with a minor red shift at 574 nm. On the other hand, we have tested the nonlinear optical property and observed unambiguous nonlinear optical property with a normal valley-shaped transmittance curve corresponding to reverse saturated absorption (RSA) of the cluster.

Ligand accommodation causes the anti-centrosymmetric structure of Au13Cu4 clusters with near-infrared emission.

We synthesized an [Au13Cu4(PPh3)4(SPy)8]+ nanocluster co-capped by phosphine and thiolate ligands. Interestingly, this Au13Cu4 cluster corresponds to an anti-centrosymmetric structure with the four copper atoms coordinated to the mixed ligands on the same side of the Au13 icosahedron, which is in sharp contrast to the [Au13Cu4(PPh2Py)4(SPhtBu)8]+ and [Au13Cu2(PPh3)6(SPy)6]+ clusters which possess highly symmetric structures with well-separated Cu adatoms. Both [Au13Cu4(PPh3)4(SPy)8]+ and [Au13Cu2(PPh3)6(SPy)6]+ clusters correspond to 8 valence electron superatoms with large HOMO-LUMO gaps, respectively. The difference in structure is rooted in the nature of the mixed ligands, with the bidentate SPy binding strongly to Cu on both binding sites (-N-Cu and Au-SR-Cu) leading to the co-linking of adjacent Cu atoms, while the bidentate PPh2Py binds Cu on one site and Au on the other giving rise to a separation of the Cu atoms even in the presence of relatively higher monomer concentration. Both [Au13Cu4(PPh3)4(SPy)8]+ and [Au13Cu2(PPh3)6(SPy)6]+ display emissions in the near-IR regions. TD-DFT calculations reproduce the spectroscopic results with specified excited states, shedding light on the geometric and electronic behaviors of the ligand-protected Au13Mx clusters.

A small bimetallic Ag3Cu2 nanocluster with dual emissions within and against Kasha's rule.

Single crystals of a small bimetallic Ag3Cu2 nanocluster protected by six ligands of 2,4-dimethylbenzene thiol are synthesized by a one-pot procedure of wet chemistry. This Ag3Cu2 nanocluster bears a trigonal bipyramid metallic core with two copper atoms located on both sides of a triangular Ag3. Interestingly, the six Cu-Ag side edges of the trigonal bipyramid are fully protected by the six ligands giving rise to reinforced stability and high chemical purity. More interestingly, this Ag3Cu2 cluster shows strong dual fluorescence emissions in both ultraviolet visible (UV-vis) and near infrared (NIR) regions. Theoretical calculations reproduce the absorption and fluorescence spectra where the NIR emission at 824 nm is assigned to the S1→ S0 transition, while the simultaneous emission in the visible band is due to the radiation of highly excited states and is against Kasha's rule.

Correction: A hexagonal Ni6 cluster protected by 2-phenylethanethiol for catalytic conversion of toluene to benzaldehyde.

Correction for 'A hexagonal Ni6 cluster protected by 2-phenylethanethiol for catalytic conversion of toluene to benzaldehyde' by Anthony M. S. Pembere et al., Phys. Chem. Chem. Phys., 2019, 21, 17933-17938.

Synthesis of new multivalent metal ion functionalized mesoporous silica and studies of their enhanced antimicrobial and cytotoxicity activities.

In the present study, we have reported the synthesis of a transition metal (Me = Ti, V, and Pd) incorporated into MCM-41 mesoporous molecular sieves (Si/Me = 20) synthesized by the sol-gel method. Their physicochemical properties were studied in detail by standard techniques like low angle powder X-ray diffraction (XRD), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDXS), transmission electron microscopy (TEM), N2 adsorption/desorption studies, and thermogravimetric-differential thermal (TG-DTA) analysis and spectral studies like Fourier transform infrared spectroscopic analysis (FT-IR), diffuse reflectance ultraviolet-visible spectroscopic analysis (UV-Visible-DRS), and X-ray photoelectron spectroscopy (XPS). The XRD patterns prove that the material's phase identity is the same irrespective of metal incorporation. SEM displayed the uniform shape and size of the nanoparticles. The presence of elements such as Ti, V, Pd, Si and O in respective materials is revealed using the EDXS analysis. Around 30% weight loss arose upon calcination from room temperature to 800 °C. BET surface area analysis presented that the parent materials have a high surface area (1024 m2 g-1) which was reduced upon metal incorporation. FT-IR analysis exhibited the framework vibrations of the synthesised materials. UV-Visible-DRS analysis indicated the presence of tetrahedrally coordinated transition metal ions. The multivalent-metal-ion-functionalized mesoporous materials showed significant enhancement in potent antimicrobial and anticancer activity. The antimicrobial activity is because of its low lipophilicity, which no longer allows the materials to enter via the lipid membrane. Thus, the new materials neither obstruct the metal-binding sites nor inhibit the growth of microbe enzymes. Further, the results show that the transition metal ion-containing mesoporous materials possessing good anticancer activity arising from their excessive surface area to volume ratio provided appropriate association with a tumour cell due to the direct penetration of mesoporous materials into the cell wall, causing membrane damage and cell death.

A hexagonal Ni6 cluster protected by 2-phenylethanethiol for catalytic conversion of toluene to benzaldehyde.

We have synthesized single crystals of a 2-phenylethanethiol-protected Ni6 nanocluster, namely Ni6(C8H9S)12, which shows a hexagonal metallic core structure and reasonable stability. Interestingly this cluster is found to be an excellent candidate for the catalytic oxidation of toluene to benzaldehyde, with 100% conversion and 91% selectivity, showing application potential as an aromatic aldehyde in industry. Using DFT calculations, we rationalize the catalytic reaction mechanism for the conversion of toluene to benzaldehyde, and demonstrate that the presence of H2O2 initiates the Ni6 cluster via a highly exothermic step to form a Ni6O* intermediate which then results in active sites for the oxidation of toluene. What is interesting is that the likely steric geometry matching of the six-ring Ni6 core, a dozen phenylethanethiol ligands and the aromatic reactant toluene could attain a synergistic effect to facilitate the production of benzaldehyde free of catalyst support.

Charge transfer interactions of pyrazine with Ag12 clusters towards precise SERS chemical mechanism.

We have synthesized Ag12 nanoclusters (NCs) with mercaptosuccinic acid (H2SMA) as the ligand. This cluster is found to be water-soluble and has satisfactory stability with [Ag12(HSMA)6Na6]2+, as determined by high-resolution mass spectrometry. Interestingly, it is noted that both the H2SMA ligand and Ag12 clusters do not display interference Raman signals, suggesting that this material is a good candidate as a substrate for surface-enhanced Raman spectroscopy (SERS). As a result, we observe enhanced Raman activity of pyrazine molecules adsorbed on Ag12 NCs along with a large red-shift up to ∼27 cm-1. To fully demonstrate the charge transfer interactions between pyrazine and Ag12 clusters, by utilizing first-principles calculations, we estimate polarizability tensor and conduct electronic natural population analysis (NPA), natural bond orbital (NBO) analysis, deformation density analysis (DDA) and charge decomposition analysis (CDA). In view of the minimized contribution from local surface plasmon resonance (LSPR), such a comprehensive study of metal NCs, which are free of Raman interference, provides a modelling method towards the long-debated chemical mechanism in SERS theory.