<i>Rhombus</i>-Shaped Tetranuclear [Ln₄] Complexes [Ln = Dy(III) and Ho(III)]: Synthesis, Structure, and SMM Behavior

The reaction of a new hexadentate Schiff base hydrazide ligand (LH₃) with rare earth­(III) chloride salts in the presence of triethylamine as the base afforded two planar tetranuclear neutral complexes: [{(LH)₂Dy₄}­(μ₂-O)₄]­(H₂O)₈·2CH₃OH·8H₂O (<b>1</b>) and [{(LH)₂Ho₄}­(μ₂-O)₄]­(H₂O)₈·6CH₃OH·4H₂O (<b>2</b>). These neutral complexes possess a structure in which all of the lanthanide ions and the donor atoms of the ligand remain in a perfect plane. Each doubly deprotonated ligand holds two Ln­(III) ions in its two distinct chelating coordination pockets to form [LH­(Ln)₂]⁴⁺ units. Two such units are connected by four [μ₂-O]^2– ligands to form a planar tetranuclear assembly with an Ln­(III)₄ core that possesses a rhombus-shaped structure. Detailed static and dynamic magnetic analysis of <b>1</b> and <b>2</b> revealed single-molecule magnet (SMM) behavior for complex <b>1.</b> A peculiar feature of the χ_M″ versus temperature curve is that two peaks that are frequency-dependent are revealed, indicating the occurrence of two relaxation processes that lead to two energy barriers (16.8 and 54.2 K) and time constants (τ₀ = 1.4 × 10^–6 s, τ₀ = 7.2 × 10^–7 s). This was related to the presence of two distinct geometrical sites for Dy­(III) in complex <b>1</b>

<i>Rhombus</i>-Shaped Tetranuclear [Ln₄] Complexes [Ln = Dy(III) and Ho(III)]: Synthesis, Structure, and SMM Behavior

The reaction of a new hexadentate Schiff base hydrazide ligand (LH₃) with rare earth­(III) chloride salts in the presence of triethylamine as the base afforded two planar tetranuclear neutral complexes: [{(LH)₂Dy₄}­(μ₂-O)₄]­(H₂O)₈·2CH₃OH·8H₂O (<b>1</b>) and [{(LH)₂Ho₄}­(μ₂-O)₄]­(H₂O)₈·6CH₃OH·4H₂O (<b>2</b>). These neutral complexes possess a structure in which all of the lanthanide ions and the donor atoms of the ligand remain in a perfect plane. Each doubly deprotonated ligand holds two Ln­(III) ions in its two distinct chelating coordination pockets to form [LH­(Ln)₂]⁴⁺ units. Two such units are connected by four [μ₂-O]^2– ligands to form a planar tetranuclear assembly with an Ln­(III)₄ core that possesses a rhombus-shaped structure. Detailed static and dynamic magnetic analysis of <b>1</b> and <b>2</b> revealed single-molecule magnet (SMM) behavior for complex <b>1.</b> A peculiar feature of the χ_M″ versus temperature curve is that two peaks that are frequency-dependent are revealed, indicating the occurrence of two relaxation processes that lead to two energy barriers (16.8 and 54.2 K) and time constants (τ₀ = 1.4 × 10^–6 s, τ₀ = 7.2 × 10^–7 s). This was related to the presence of two distinct geometrical sites for Dy­(III) in complex <b>1</b>

Multicomponent Assembly of Anionic and Neutral Decanuclear Copper(II) Phosphonate Cages

A multicomponent synthetic strategy involving copper­(II) ions, <i>tert</i>-butylphosphonic acid (<i>t</i>-BuPO₃H₂) and 3-substituted pyrazole ligands has been adopted for the synthesis of soluble molecular copper­(II) phosphonates. The use of six different 3-substituted pyrazoles, 3-R-PzH [R = H, Me, CF₃, Ph, 2-pyridyl (2-Py), and 2-methoxyphenyl (2-MeO-C₆H₄)] as ancillary ligands afforded nine different decanuclear cages, [Cu₅(μ₃-OH)₂(O₃P-<i>t</i>-Bu)₃(3-R-Pz)₂(X)₂]₂·(Y) where R = H, X = <i>t</i>-BuPO₃H, and Y = (Et₃NH⁺)₄(solvent) (<b>1</b>); R = Me, X = 3-MePzH, and Y = solvent (<b>2</b>); R = Me, X = <i>t</i>-BuPO₃H, and Y = (Et₃NH⁺)₄(solvent) (<b>3</b>); R = CF₃, X = <i>t</i>-BuPO₃H, and Y = (Et₃NH⁺)₄(solvent) (<b>4</b>); R = Ph, X = 3-PhPzH, and Y = solvent (<b>5</b>); R = 2-Py, X = 0.5 MeOH, and Y = solvent (<b>6</b>); R = 2-Py, X = none, and Y = solvent (<b>7</b>); R = 2-Py, X = H₂O, and Y = (Et₃NH⁺·PF₆^–)₂(solvent) (<b>8</b>); R = 2-MeO-C₆H₄, X = MeOH or 0.5:0.5 MeOH/H₂O, and Y = solvent (<b>9</b>). Compounds <b>1</b>–<b>6</b>, <b>8</b>, and <b>9</b> were isolated using a direct synthetic method which involves the reaction of copper­(II) salts and the ligands, while <b>7</b> was obtained from an indirect route involving the reaction of preformed copper-pyridylpyrazolate precursor complexes and <i>t</i>-BuPO₃H₂. The decametallic compounds <b>1</b>–<b>9</b> possess a butterfly shaped core. The core of the cages <b>1</b>, <b>3</b>, and <b>4</b> are tetraanionic and contain more phosphonates than pyrazole ligands, while the other cages are neutral and contain more pyrazoles than phosphonate ligands. Compounds <b>1</b>–<b>6</b> have been studied by electrospray ionization-high-resolution mass spectrometry (ESI-HRMS). The decanuclear cage <b>6</b> was shown to be a good plasmid modifier

Multicomponent Assembly of Anionic and Neutral Decanuclear Copper(II) Phosphonate Cages

A multicomponent synthetic strategy involving copper­(II) ions, <i>tert</i>-butylphosphonic acid (<i>t</i>-BuPO₃H₂) and 3-substituted pyrazole ligands has been adopted for the synthesis of soluble molecular copper­(II) phosphonates. The use of six different 3-substituted pyrazoles, 3-R-PzH [R = H, Me, CF₃, Ph, 2-pyridyl (2-Py), and 2-methoxyphenyl (2-MeO-C₆H₄)] as ancillary ligands afforded nine different decanuclear cages, [Cu₅(μ₃-OH)₂(O₃P-<i>t</i>-Bu)₃(3-R-Pz)₂(X)₂]₂·(Y) where R = H, X = <i>t</i>-BuPO₃H, and Y = (Et₃NH⁺)₄(solvent) (<b>1</b>); R = Me, X = 3-MePzH, and Y = solvent (<b>2</b>); R = Me, X = <i>t</i>-BuPO₃H, and Y = (Et₃NH⁺)₄(solvent) (<b>3</b>); R = CF₃, X = <i>t</i>-BuPO₃H, and Y = (Et₃NH⁺)₄(solvent) (<b>4</b>); R = Ph, X = 3-PhPzH, and Y = solvent (<b>5</b>); R = 2-Py, X = 0.5 MeOH, and Y = solvent (<b>6</b>); R = 2-Py, X = none, and Y = solvent (<b>7</b>); R = 2-Py, X = H₂O, and Y = (Et₃NH⁺·PF₆^–)₂(solvent) (<b>8</b>); R = 2-MeO-C₆H₄, X = MeOH or 0.5:0.5 MeOH/H₂O, and Y = solvent (<b>9</b>). Compounds <b>1</b>–<b>6</b>, <b>8</b>, and <b>9</b> were isolated using a direct synthetic method which involves the reaction of copper­(II) salts and the ligands, while <b>7</b> was obtained from an indirect route involving the reaction of preformed copper-pyridylpyrazolate precursor complexes and <i>t</i>-BuPO₃H₂. The decametallic compounds <b>1</b>–<b>9</b> possess a butterfly shaped core. The core of the cages <b>1</b>, <b>3</b>, and <b>4</b> are tetraanionic and contain more phosphonates than pyrazole ligands, while the other cages are neutral and contain more pyrazoles than phosphonate ligands. Compounds <b>1</b>–<b>6</b> have been studied by electrospray ionization-high-resolution mass spectrometry (ESI-HRMS). The decanuclear cage <b>6</b> was shown to be a good plasmid modifier

Molecular Magnets Based on Homometallic Hexanuclear Lanthanide(III) Complexes

The reaction of lanthanide­(III) chloride salts (Gd­(III), Dy­(III), Tb­(III), and Ho­(III)) with the hetero donor chelating ligand <i>N</i>′-(2-hydroxy-3-methoxybenzylidene)-6-(hydroxymethyl)­picolinohydrazide (LH₃) in the presence of triethylamine afforded the hexanuclear Ln­(III) complexes [{Ln₆(L)₂(LH)₂}­(μ₃-OH)₄]­[MeOH]_<i>p</i>[H₂O]_<i>q</i>[Cl]₄·<i>x</i>H₂O·<i>y</i>CH₃OH (<b>1</b>, Ln = Gd­(III), <i>p</i> = 4, <i>q</i> = 4, <i>x</i> = 8, <i>y</i> = 2; <b>2</b>, Ln = Dy­(III), <i>p</i> = 2, <i>q</i> = 6, <i>x</i> = 8, <i>y</i> = 4; <b>3</b>, Ln = Tb­(III), <i>p</i> = 2, <i>q</i> = 6, <i>x</i> = 10, <i>y</i> = 4; <b>4</b>, Ln = Ho­(III), <i>p</i> = 2, <i>q</i> = 6, <i>x</i> = 10, <i>y</i> = 2). X-ray diffraction studies revealed that these compounds possess a hexanuclear [Ln₆(OH)₄]¹⁴⁺ core consisting of four fused [Ln₃(OH)]⁸⁺ subunits. Both static (dc) and dynamic (ac) magnetic properties of <b>1</b>–<b>4</b> have been studied. Single-molecule magnetic behavior has been observed in compound <b>2</b> with an effective energy barrier and relaxation time pre-exponential parameters of Δ/<i>k</i>_B = 46.2 K and τ₀ = 2.85 × 10^–7 s, respectively

Novel Chemosensor for the Visual Detection of Copper(II) in Aqueous Solution at the ppm Level

A new water-soluble, multisite-coordinating ligand LH₇ was prepared by the condensation of tris­(hydroxymethyl)­aminomethane with 2,6-diformyl-<i>p</i>-cresol. LH₇ is a selective chemosensor for Cu²⁺, under physiological conditions, with visual detection limits of 20 ppm (ambient light conditions) and 4 ppm (UV light conditions). LH₇ can also be used in biological cell lines for the detection of Cu²⁺

Ligand Exchange Reactions in Thiolate-Protected Au₂₅ Nanoclusters with Selenolates or Tellurolates: Preferential Exchange Sites and Effects on Electronic Structure

Ligand exchange reactions can introduce new ligands onto clusters to afford new physical/chemical properties and functions. Many studies on the ligand exchange reactions of thiolate-protected gold clusters using other chalcogenates (i.e., selenolates or tellurolates) as exchange ligands have been conducted in recent years. However, there is limited information on the preferential exchange sites and electronic structure of the exchanged products. In this study, we investigated the geometric and electronic structures of the products obtained by reacting [Au₂₅(SC₂H₄Ph)₁₈]⁻ with PhSeH or (PhTe)₂ by single-crystal X-ray structural analysis, differential pulse voltammetry, and optical absorption spectroscopy. The results revealed that these exchange reactions preferentially produce products containing substituted ligands close to the gold core. In addition, we quantitatively determined the changes in the redox potentials and optical transition energies induced by continuous ligand exchange. This systematic investigation revealed that exchange with SePh induces nonlinear changes in the electronic structure of the clusters with the number of exchanged ligands. These findings are expected to lead to the improved design guidelines to produce clusters with new functions by ligand exchange with other chalcogenates

Ligand Exchange Reactions in Thiolate-Protected Au₂₅ Nanoclusters with Selenolates or Tellurolates: Preferential Exchange Sites and Effects on Electronic Structure

Ligand exchange reactions can introduce new ligands onto clusters to afford new physical/chemical properties and functions. Many studies on the ligand exchange reactions of thiolate-protected gold clusters using other chalcogenates (i.e., selenolates or tellurolates) as exchange ligands have been conducted in recent years. However, there is limited information on the preferential exchange sites and electronic structure of the exchanged products. In this study, we investigated the geometric and electronic structures of the products obtained by reacting [Au₂₅(SC₂H₄Ph)₁₈]⁻ with PhSeH or (PhTe)₂ by single-crystal X-ray structural analysis, differential pulse voltammetry, and optical absorption spectroscopy. The results revealed that these exchange reactions preferentially produce products containing substituted ligands close to the gold core. In addition, we quantitatively determined the changes in the redox potentials and optical transition energies induced by continuous ligand exchange. This systematic investigation revealed that exchange with SePh induces nonlinear changes in the electronic structure of the clusters with the number of exchanged ligands. These findings are expected to lead to the improved design guidelines to produce clusters with new functions by ligand exchange with other chalcogenates

[Pt₁₇(CO)₁₂(PPh₃)₈]^<i>n</i>+ (<i>n</i> = 1, 2): Synthesis and Geometric and Electronic Structures

Recently, platinum (Pt) clusters have attracted attention as miniaturized fuel-cell redox catalysts. Although Pt clusters can be synthesized with atomic accuracy using carbon monoxide (CO) and phosphine as ligands, few studies have examined their electronic structure. We obtained experimental information about the electronic structure of these Pt clusters. We precisely synthesized the cationic Pt₁₇ cluster, [Pt₁₇(CO)₁₂(PPh₃)₈]^<i>n</i>+ (<i>n</i> = 1, 2), protected by CO and triphenylphosphine (PPh₃) by a simple method and studied its geometric and electronic structures by single-crystal X-ray structure analysis, X-ray photoelectron spectroscopy, optical absorption spectroscopy, differential pulse voltammetry, and photoluminescence spectroscopy. The results indicated that cationic [Pt₁₇(CO)₁₂(PPh₃)₈]^<i>n</i>+ (<i>n</i> = 1, 2) has a geometric structure similar to that of previously reported neutral Pt₁₇(CO)₁₂(PEt₃)₈. The Pt₁₇ skeleton of Pt₁₇(CO)₁₂(PPh₃)₈ depended on the charge state of the cluster ([Pt₁₇(CO)₁₂(PPh₃)₈]⁺ or [Pt₁₇(CO)₁₂(PPh₃)₈]²⁺). [Pt₁₇(CO)₁₂(PPh₃)₈]^<i>n</i>+ (<i>n</i> = 1, 2) possessed a discretized electronic structure, similar to that of fine gold clusters, and exhibited photoluminescence in the near-infrared region. This research will aid fundamental and applied research on Pt clusters

Au₂₅-Loaded BaLa₄Ti₄O₁₅ Water-Splitting Photocatalyst with Enhanced Activity and Durability Produced Using New Chromium Oxide Shell Formation Method

We report herein remarkable improvement of activity and stability of an Au₂₅-loaded BaLa₄Ti₄O₁₅ water-splitting photocatalyst. We first examined the influence of refining the gold cocatalyst on the individual reactions over the BaLa₄Ti₄O₁₅ photocatalyst in this water-splitting system. The results revealed that refining the gold cocatalyst accelerates not only the hydrogen generation reaction, but also oxygen photoreduction reaction, which suppresses the H₂ generation via photoreduction of protons. This finding suggests that photocatalytic activity will be enhanced if the O₂ photoreduction reaction can be selectively suppressed by covering Au₂₅ with a Cr₂O₃ shell which is impermeable to O₂ but permeable to H⁺. Then, we developed new method for the formation of the Cr₂O₃ shell onto Au₂₅. Our method utilizes the strong metal–support interaction between them. Water-splitting photoactivity of Au₂₅–BaLa₄Ti₄O₁₅ was improved by 19 times under an optimized coverage of the Cr₂O₃ shell. The Cr₂O₃ shell also elongated the lifetime of the photocatalysts by preventing the agglomeration of Au₂₅ cocatalysts