Unprecedented Phthalocyanines Bearing Eight Di-butylamino Peripheral Substituents: Synthesis, Spectroscopy, and Structure

Unprecedented 2,3,9,10,16,17,23,24-octakis­(di-butylamino)­phthalocyanine compounds M­{Pc­[N­(C₄H₉)₂]₈} (M = 2H, Mg, Cu, Zn) (<b>1</b>–<b>4</b>) were prepared and structurally characterized on the basis of single-crystal X-ray diffraction analysis, representing the first structurally characterized alkylamino-substituted phthalocyanine examples. These novel phthalocyanine derivatives have also been characterized by a wide range of spectroscopic methods including MALDI-TOF mass spectra, NMR, electronic absorption, and IR spectroscopy in addition to elemental analysis. Their electrochemistry was also studied by cyclic voltammetry

Unprecedented Phthalocyanines Bearing Eight Di-butylamino Peripheral Substituents: Synthesis, Spectroscopy, and Structure

Unprecedented 2,3,9,10,16,17,23,24-octakis­(di-butylamino)­phthalocyanine compounds M­{Pc­[N­(C₄H₉)₂]₈} (M = 2H, Mg, Cu, Zn) (<b>1</b>–<b>4</b>) were prepared and structurally characterized on the basis of single-crystal X-ray diffraction analysis, representing the first structurally characterized alkylamino-substituted phthalocyanine examples. These novel phthalocyanine derivatives have also been characterized by a wide range of spectroscopic methods including MALDI-TOF mass spectra, NMR, electronic absorption, and IR spectroscopy in addition to elemental analysis. Their electrochemistry was also studied by cyclic voltammetry

Unprecedented Phthalocyanines Bearing Eight Di-butylamino Peripheral Substituents: Synthesis, Spectroscopy, and Structure

Unprecedented 2,3,9,10,16,17,23,24-octakis­(di-butylamino)­phthalocyanine compounds M­{Pc­[N­(C₄H₉)₂]₈} (M = 2H, Mg, Cu, Zn) (<b>1</b>–<b>4</b>) were prepared and structurally characterized on the basis of single-crystal X-ray diffraction analysis, representing the first structurally characterized alkylamino-substituted phthalocyanine examples. These novel phthalocyanine derivatives have also been characterized by a wide range of spectroscopic methods including MALDI-TOF mass spectra, NMR, electronic absorption, and IR spectroscopy in addition to elemental analysis. Their electrochemistry was also studied by cyclic voltammetry

Magic Size Au₆₄(S‑<i>c</i>‑C₆H₁₁)₃₂ Nanocluster Protected by Cyclohexanethiolate

We report a new magic-sized gold nanocluster of atomic precision formulated as Au₆₄(S-<i>c</i>-C₆H₁₁)₃₂. The Au₆₄ nanocluster was obtained in relatively high yield (∼15%, Au atom basis) by a two-step size-focusing methodology. Obtaining this new magic size through the previously established “size focusing” method relies on the introduction of a new synthetic “parameter”the type of protecting thiolate ligand. It was found that Au₆₄(S-<i>c</i>-C₆H₁₁)₃₂ was the most thermodynamically stable specie of the cyclohexanethiolate-protected gold nanoclusters in the size range from ~5k to 20k (where, k = 1000 dalton); hence, it can be selectively synthesized through a careful control of the size-focusing kinetics. The Au₆₄ nanocluster is the first gold nanocluster achieved through direct synthesis (i.e., without postsynthetic size separation) in the medium size range (i.e., ∼40 to ∼100 gold atoms). This medium-sized Au₆₄(S-<i>c</i>-C₆H₁₁)₃₂ exhibits a highly structured optical absorption spectrum, reflecting its discrete electronic states. The discovery of this new Au₆₄(S-<i>c</i>-C₆H₁₁)₃₂ nanocluster bridges the gap of the gold nanoclusters in the medium size range and will facilitate the understanding of the structure and property evolution of magic-size gold nanoclusters

Tuning the Magic Size of Atomically Precise Gold Nanoclusters via Isomeric Methylbenzenethiols

Toward controlling the magic sizes of atomically precise gold nanoclusters, herein we have devised a new strategy by exploring the para<i>-</i>, meta<i>-</i>, ortho-methylbenzenethiol (MBT) for successful preparation of pure Au₁₃₀(<i>p</i>-MBT)₅₀, Au₁₀₄(<i>m</i>-MBT)₄₁ and Au₄₀(<i>o</i>-MBT)₂₄ nanoclusters. The decreasing size sequence is in line with the increasing hindrance of the methyl group to the interfacial Au–S bond. That the subtle change of ligand structure can result in drastically different magic sizes under otherwise similar reaction conditions is indeed for the first time observed in the synthesis of thiolate-protected gold nanoclusters. These nanoclusters are highly stable as they are synthesized under harsh size-focusing conditions at 80–90 °C in the presence of excess thiol and air (i.e., without exclusion of oxygen)

Gold–Thiolate Ring as a Protecting Motif in the Au₂₀(SR)₁₆ Nanocluster and Implications

Understanding how gold nanoclusters nucleate from Au^ISR complexes necessitates the structural elucidation of nanoclusters with decreasing size. Toward this effort, we herein report the crystal structure of an ultrasmall nanocluster formulated as Au₂₀(TBBT)₁₆ (TBBT = SPh-<i>t</i>-Bu). The structure features a vertex-sharing bitetrahedral Au₇ kernel and an unprecedented “ring” motifAu₈(SR)₈. This large ring protects the Au₇ kernel through strong Au_ring–Au_kernel bonding but does not involve S–Au_kernel bonding, in contrast to the common “staple” motifs in which the S–Au_kernel bonding is dominant but the Au_staple–Au_kernel interaction is weak (i.e., aurophilic). As the smallest member in the TBBT “magic series”, Au₂₀(TBBT)₁₆, together with Au₂₈(TBBT)₂₀, Au₃₆(TBBT)₂₄, and Au₄₄(TBBT)₂₈, reveals remarkable size-growth patterns in both geometric structure and electronic nature. Moreover, Au₂₀(TBBT)₁₆, together with the Au₂₄(SR)₂₀ and Au₁₈(SR)₁₄ nanoclusters, forms a “4e” nanocluster family, which illustrates a trend of shrinkage of bitetrahedral kernels from Au₈⁴⁺ to Au₇³⁺ and possibly to Au₆²⁺ with decreasing size

Size Dependence of Atomically Precise Gold Nanoclusters in Chemoselective Hydrogenation and Active Site Structure

We investigate the catalytic properties of water-soluble Au_<i>n</i>(SG)_<i>m</i> nanocluster catalysts (H-SG = glutathione) of different sizes, including Au₁₅(SG)₁₃, Au₁₈(SG)₁₄, Au₂₅(SG)₁₈, Au₃₈(SG)₂₄, and captopril-capped Au₂₅(Capt)₁₈ nanoclusters. These Au_<i>n</i>(SR)_<i>m</i> nanoclusters (SR represents thiolate generally) are used as homogeneous catalysts (i.e., without supports) in the chemoselective hydrogenation of 4-nitrobenzaldehyde (4-NO₂PhCHO) to 4-nitrobenzyl alcohol (4-NO₂PhCH₂OH) with ∼100% selectivity in water using H₂ gas (20 bar) as the hydrogen source. These nanocluster catalysts, except Au₁₈(SG)₁₄, remain intact after the catalytic reaction, evidenced by UV–vis spectra, which are characteristic of nanoclusters of each size and thus serve as spectroscopic “fingerprints”. We observe a drastic size dependence and steric effect of protecting ligands on the gold nanocluster catalysts in the hydrogenation reaction. Density functional theory (DFT) modeling of the 4-nitrobenzaldehyde adsorption shows that both the -CHO and -NO₂ groups closely interact with the S-Au-S staples on the gold nanocluster surface. The adsorptions of the 4-nitrobenzaldehyde molecule on the four different sized Au_<i>n</i>(SR)_<i>m</i> nanoclusters are moderately strong and similar in strength. The DFT results suggest that the catalytic activity of the Au_<i>n</i>(SR)_<i>m</i> nanoclusters is primarily determined by the surface area of the Au nanocluster, consistent with the observed trend of the conversion of 4-nitrobenzaldehyde versus the cluster size. Overall, this work offers molecular insight into the hydrogenation of 4-nitrobenzaldehyde and the catalytically active site structure on gold nanocluster catalysts

Nonperipheral Tetrakis(dibutylamino)phthalocyanines. New Types of 1,8,15,22-Tetrakis(substituted)phthalocyanine Isomers

Cyclic tetramerization of 3-(dibutylamino)­phthalonitrile in refluxing <i>n</i>-pentanol in the presence of magnesium pentanoate afforded the four regioisomer-containing nonperipheral 1,8-/11,15-/18,22-/25-tetrakis­(dibutylamino)­phthalocyaninato magnesium complexes with the 1,8,15,22-tetrakis­(dibutylamino)­phthalocyanine isomer Mg­{Pc­[α-N­(C₄H₉)₂]₄-<i>C</i>₄} (<b>2</b>). This, in combination with its much superior crystallinity over the remaining three isomers, renders the easy isolation of <b>2</b> only through two simple recrystallizations from THF and methanol. Treatment of <b>2</b> with trifluoroacetic acid induced the isolation of metal-free 1,8,15,22-tetrakis­(dibutylamino)­phthalocyanine, H₂{Pc­[α-N­(C₄H₉)₂]₄-<i>C</i>₄} (<b>1</b>), which further reacted with M­(OAc)₂·<i>n</i>H₂O (M = Ni, Zn) in refluxing <i>n</i>-pentanol, giving the 1,8,15,22-tetrakis­(dibutylamino)­phthalocyaninato metal complexes M­{Pc­[α-N­(C₄H₉)₂]₄-<i>C</i>₄} (M = Ni (<b>3</b>), Zn (<b>4</b>)). The full series of four 1,8,15,22-tetrakis­(dibutylamino)­phthalocyanine isomeric compounds have been characterized by a series of spectroscopic methods and single-crystal X-ray diffraction analyses. Obviously, the present result provides a simple and effective pathway for the synthesis and isolation of novel 1,8,15,22-tetrakis­(dibutylamino)­phthalocyanine isomeric derivatives, providing one step forward toward completing bis­(alkyl)­amino-incorporated phthalocyanine species

Electronic Transitions in Highly Symmetric Au₁₃₀ Nanoclusters by Spectroelectrochemistry and Ultrafast Spectroscopy

Rich and discrete energy states in gold nanoclusters enable different combinations of electronic transitions and correspondingly electrochemical and optical properties for a variety of applications. The impacts on those electronic transitions by the emergence and magnitude/alignment of a band gap and by the contributions from different atomic/molecular orbitals require further study. Au nanoclusters with 130 core Au atoms are of interest in this report because they are at the transition size regime where a small yet well-defined band gap can be resolved along with continuous quantized frontier core orbitals. Here, electrochemical analysis is combined with UV–vis–near infrared optical measurements to unveil previously unresolved electronic transitions. Finite changes in the steady-state optical absorption spectrum are captured by spectroelectrochemistry when the Au nanoclusters are charged to different states via electrolysis. Multiple previously unresolved peaks and valleys as well as isosbestic “points/regions” are observed in the differential spectrum. The detailed spectral features are explained by the respective electronic transitions to those affected energy states. Key features are also well correlated with ultrafast absorption analysis which provides additional insights, such as the lifetime of the corresponding transitions. The experimentally measured energy states and transitions could serve as references for future theoretical study to learn the respective contributions from different atomic orbitals and, importantly, to explore routes to enhance or suppress certain transition so as to modulate the corresponding electrochemical and optical properties for better applications

Experimental and Mechanistic Understanding of Aldehyde Hydrogenation Using Au₂₅ Nanoclusters with Lewis Acids: Unique Sites for Catalytic Reactions

The catalytic activity of Au₂₅(SR)₁₈ nanoclusters (R = C₂H₄Ph) for the aldehyde hydrogenation reaction in the presence of a base, e.g., ammonia or pyridine, and transition-metal ions M^z+, such as Cu⁺, Cu²⁺, Ni²⁺ and Co²⁺, as a Lewis acid is studied. The addition of a Lewis acid is found to significantly promote the catalytic activity of Au₂₅(SR)₁₈/CeO₂ in the hydrogenation of benzaldehyde and a number of its derivatives. Matrix-assisted laser desorption ionization (MALDI) and electrospray ionization (ESI) mass spectrometry in conjunction with UV–vis spectroscopy confirm the generation of new species, Au_{25‑<i>n</i>}(SR)_{18‑<i>n</i>} (<i>n</i> = 1–4), in the presence of a Lewis acid. The pathways for the speciation of Au₂₄(SR)₁₇ from its parent Au₂₅(SR)₁₈ nanocluster as well as its structure are investigated via the density functional theory (DFT) method. The adsorption of M^<i>z</i>+ onto a thiolate ligand “SR” of Au₂₅(SR)₁₈, followed by a stepwise detachment of “SR” and a gold atom bonded to “SR” (thus an “Au-SR” unit) is found to be the most likely mechanism for the Au₂₄(SR)₁₇ generation. This in turn exposes the Au₁₃-core of Au₂₄(SR)₁₇ to reactants, providing an active site for the catalytic hydrogenation. DFT calculations indicate that M^z+ is also capable of adsorbing onto the Au₁₃-core surface, producing a possible active metal site of a different kind to catalyze the aldehyde hydrogenation reaction. This study suggests, for the first time, that species with an open metal site like adducts [nanoparticle-M]^{(<i>z</i>‑1)+} or fragments Au_{25‑<i>n</i>}(SR)_{18‑<i>n</i>} function as the catalysts rather than the intact Au₂₅(SR)₁₈