Tandem Protocol for Diversified Deuteration of Secondary Aliphatic Amines under Mild Conditions.

Deuteration of amine compounds has been widely of concern because of its practical role in organic reaction mechanisms and drug research; however, only limited deuteration label methods are accessible with D2O as a deuterium source. Herein, we propose a convenient deuteration protocol, including preparing D2 by the AlGa activation method, using PtRu nanowires as catalysts, and utilizing the elementary step in the couple reaction involving an imine unit, to realize the rapid preparation of a secondary amine with a diversified deuteration label. The self-coupling between nitriles not only provides a symmetric secondary amine with four α-D atoms but also produces high-valued ND3 in an atomic-economic way.

Zwitterionic Thiolate-Protected Ag22(0/I) and Ag20(I) Clusters: Assembly, Structural Characterization, and Antibacterial Activity.

Zwitterionic thiolate ligands have the potential to introduce novel assembly modes and functions for noble metal clusters. However, their utilization in the synthesis of silver clusters remains understudied, particularly for the clusters containing reductive Ag(0) species. In this article, we report the first synthesis of a mixed-valence silver(0/I) cluster protected by zwitterionic Tab as thiolate ligands (Tab = 4-(trimethylammonio)benzenethiolate), denoted as [Ag22(Tab)24](PF6)20·16CH3OH·6Et2O (Ag22·16CH3OH·6Et2O), alongside an Ag(I) cluster [Ag20(Tab)12(PhCOO)10(MeCN)2(H2O)](PF6)10·11MeCN (Ag20·11MeCN). Ag22 has a distinct hierarchical supratetrahedral structure with a central {Ag6} kernel surrounded by four [Ag4(Tab)6]4+ units. High-resolution electrospray ionization mass spectra demonstrate that Ag22 has two free electrons, indicating a superatomic core. Ag20 has a drum-like [Ag12(Tab)6(PhCOO)6(H2O)]6+ inner core capped by two tetrahedral-like [Ag4(Tab)3(PhCOO)2(MeCN)]2+ units. Ag20 can be transformed into Ag22 after its reaction with NaBH4 in solution. Antibacterial measurements reveal that Ag22 has a significantly lower minimum inhibitory concentration than that of the Ag20 cluster. This work not only extends the stabilization of silver(0/I) clusters to neutral thiol ligands but also offers new materials for the development of novel antibacterial materials.

A Cut-to-Link Strategy for Cubane-Based Heterometallic Sulfide Clusters with Giant Third-Order Nonlinear Optical Response.

Although the synthesis of low-dimensional metal sulfides by assembling cluster-based units is expected to promote the development of optical materials and models of enzyme active centers such as dinitrogenase, it is faced with limited assembly methodology. Herein we present a cut-to-link strategy to generate high-nuclearity assemblies, inspired by the formation of a Z-type dimer of the W-S-Cu analogues of PN cluster through in situ release of active linkers. Four new compounds with structures based on the same {Tp*WS3Cu3} incomplete cubane-like units were obtained using varied combinations of mild reagents. Open-aperture Z-scan measurements demonstrated the highest-nuclearity complex has the largest nonlinear optical absorption coefficient among discrete cluster-based materials reported to date. This approach enables building high-nuclearity metal sulfide clusters through cluster-based building blocks and opens a way to the design and exploration of materials based on well-identified building blocks.

From Helices to Crystals: Multiscale Representation of Chirality in Double-Helix Structures.

Single crystals with chiral shapes aroused the interest of chemists due to their fascinating polarization rotation properties. Although the formation of large-scale spiral structures is considered to be a potential factor in chiral crystals, the precise mechanism behind their formation remains elusive. Herein, we present a rare phenomenon involving the multitransfer and expression of chirality at micro-, meso-, and macroscopic levels, starting from chiral carbon atoms and extending to the double-helical secondary structure, ultimately resulting in the chiral geometry of crystals. The assembly of the chiral double helices is facilitated by the dual characteristics of amide groups derived from amino acids, which serve as both hydrogen bond donors and receptors, similar to the assembly pattern observed in DNA. Crystal face analysis and theoretical morphology reveal two critical factors for the mechanism of the chiral crystal: inherent intrinsically symmetrical distribution of crystal faces and their acquired growth. Importantly, the magnetic circular dichroism (MCD) study reveals the strong magneto-optical response of the hypersensitive f-f transition in the UV-vis-NIR region, which is much stronger than previously observed signals. Remarkably, an external magnetic field can reverse the CD signal. This research highlights the potential of lanthanide-based chiral helical structures as promising magneto-optical materials.

Exploration and Insights on Topology Adjustment of Giant Heterometallic Cages Featuring Inorganic Skeletons Assisted by Machine Learning.

Inorganic molecular cages are emerging multifunctional molecular-based platforms with the unique merits of rigid skeletons and inherited properties from constituent metal ions. However, the sensitive coordination bonds and vast synthetic space have limited their systematic exploration. Herein, two giant cage-like clusters featuring the organic ligand-directed inorganic skeletons of Ni4[La74Ni104(IDA)96(OH)184(C2O4)12(H2O)76]·(NO3)38·(H2O)120 (La74Ni104, 5 × 5 × 3 - C2O4) and [La84Ni132(IDA)108(OH)168(C2O4)24(NO3)12(H2O)116]·(NO3)72·(H2O)296 (La84Ni132, 5 × 5 × 5 - C2O4) were discovered by a high-throughput synthetic search. With the assistance of machine learning analysis of the experimental data, phase diagrams of the two clusters in a four-parameter synthetic space were depicted. The effect of alkali, oxalate, and other parameters on the formation of clusters and the mechanism regulating the size of two n × m × l clusters were elucidated. This work uses high-throughput synthesis and machine learning methods to improve the efficiency of 3d-4f cluster discovery and finds the highest-nuclearity 3d-4f cluster to date by regulating the size of the n × m × l inorganic cages through oxalate ions, which pushes the synthetic methodology study on elusive inorganic giant cages in a significantly systematic way.

Self-Assembly of Cluster-Mediated 3D Catenanes with Size-Specific Recognition Behavior.

Although interlocked three-dimensional molecules display unique properties associated with their spatial structures, their synthesis and study of their host-guest properties remain challenging. We report the formation of a novel [2]catenane, [Et4N]@[(Tp*WS3Cu3Cl)2(cis-bpype)3]2(OTf)5 ([Et4N][1](OTf)5), by self-assembly of the cluster node [Tp*WS3Cu3Cl]+ and the organic linker (Z)-1,2-diphenyl-1,2-bis(4-(pyridin-4-yl)phenyl)ethene (cis-bpype). Single-crystal X-ray and NMR analyses established that [1]4+ is formed by the interpenetration of two cluster-organic cages. Unique cation-in-cation host-guest complexes were observed with this catenane. The crystalline, empty catenane was formed by taking advantage of the electrostatic repulsion-induced weak binding of the host. Encapsulation experiments also reveal that the empty catenane can adaptively encapsulate cations such as [Et4N]+ and [Pr4N]+ in the cross cavity but is unable to encapsulate [Bu4N]+ and [Me4N]+, although the size of the latter is compatible with that of the cavity. Theoretical calculations and volume analysis allow to unravel the ingenious role of catenane structures and the interplay between electrostatic repulsion and attractive noncovalent interactions for size-specific recognition behavior in host-guest systems involving species with similar electric charges.

Counterintuitive Lanthanide Hydrolysis-Induced Assembly Mechanism.

The understanding of the hydrolysis mechanism of lanthanide ions is limited by their elusive coordination configuration and undeveloped technology. A potential solution by high-resolution mass spectroscopy studies is hindered by the lack of a stable model under electrospray ionization (ESI) conditions and the complexity of the spectra. Herein, it is demonstrated that diketonate ligands can efficiently stabilize the hydrolyzed intermediate cluster of Ln3+ under ESI conditions, and an effective mass difference fingerprint of isomorphism (MDFI) method is proposed, which can allow the determination of the nuclearity-number of the species without depth resolution. Thus, the hydrolysis of Ln3+ into an atomically precise hydroxide cluster is observed at the level of precise formulae. The species evolution upon hydrolysis is along the dominant path of {Eu3}-{Eu4}-{Eu9}-{Eu10}-{Eu11}-{Eu15}-{Eu16} and a nondominant path of {Eu3}-{Eu4}-{Eu8-1}-{Eu8-2} under the investigated conditions. The crystal of the {Eu16} species was obtained via low-temperature crystallization, and single-crystal X-ray diffraction studies show that its structure contains three octahedral {o-Ln6} units. The contradiction between multiple {o-Ln6} units in the structure and the absence in the formation process indicates that the repetitive subunit observed in the structure does not necessarily correspond to the construction units of high-nuclearity clusters. Photophysical measurements indicate that Eu16 cluster has a high total emission quantum efficacy of 12.8% in the solid state. This study provides fundamental insights into the formation, evolution, and assembly of small lanthanide hydroxide units upon hydrolysis, which is vital for the goal of directional synthesis of lanthanide hydroxide clusters.

Photoluminescence of Lanthanide-Titanium-Oxo Clusters Eu9Ti2 and Tb9Ti2 Based on a ß-Diketone Ligand.

A series of acetylacetone-protected lanthanide-titanium-oxo clusters (LTOCs), formulated as [La6Ti(µ3-OH)8(acac)12(CH3O)2(CH3OH)6] (La6Ti; Hacac = acetylacetone) and [Ln9Ti2(µ4-O)(µ3-OH)14(acac)17(CH3O)2(CH3OH)3] [Ln = Eu (Eu9Ti2) and Tb (Tb9Ti2)], were synthesized through the reactions of LnCl3·6H2O (Ln = La, Eu, and Tb), Hacac, Ti(OiPr)4, and triethylamine in methanol. Crystal structural analysis shows that La6Ti exhibits an hourglass-like structure consisting of two La3Ti cubane subunits by sharing one Ti4+ ion, while Eu9Ti2 can be viewed as a combination of four Eu3Ti cubane subunits by sharing three corners and one side. The photoluminescence (PL) measurements show that Tb9Ti2 exhibits excellent PL properties with a high quantum yield (QY) of 34.8%, while Eu9Ti2 only has a QY of 1.4% because of the different photosensitizations of ligands to Eu3+ and Tb3+ ions in the photophysical process.

Modification of Multi-Component Building Blocks for Assembling Giant Chiral Lanthanide-Titanium Molecular Rings.

Building blocks with multiple components are promising for the synthesis of complex molecular assemblies, but are rarely available. Herein, we report a modification procedure for a multi-component building block [Ln3 Ti(HSA)6 (SA)4 (H2 O)]- ({Ln3 Ti-SA}, H2 SA=salicylic acid, Ln=Eu/Gd) to form new building blocks {Ln3 Tix -MSA} (H2 MSA=5-methoxysalicylic acid, x=1, 2, 3) by constructing [Ti(MSA)3 ]2- units. The obtained {Ln3 Tix -MSA} can further assemble into a chiral Ln22 Ti14 ring with the formulae [Eu22 Ti14 (MSA)48 (HMSA)22 (CH3 COO)4 (H2 O)10 (iPrOH)] and [Gd22 Ti14 (MSA)46 (HMSA)26 (CH3 COO)4 (H2 O)8 ]. Parallel experiments without Ti4+ result in linear Ln chains. Detailed analysis shows that the [Ti(MSA)4 ]4- unit makes the originally variable Ln chains become available building blocks and the modified [Ti(MSA)3 ]2- further triggers interesting chiral-sorting behavior. Finally, the electronic adsorption and magneto-optic responses of these molecular rings are investigated.

Hierarchical Assembly of Coordination Macromolecules with Atypical Geometries: Gd44 Co28 Crown and Gd95 Co60 Cage.

The discovered giant clusters are always highly symmetric owing to the spontaneous assembly of one or two basic units. Herein we report the Gd44 Co28 crown and Gd95 Co60 cage, formulated as [Gd44 Co28 (IDA)20 (OH)72 (CO3 )12 (OAc)28 (H2 O)64 ]⋅(ClO4 )24 and [Na4 Gd95 Co60 (IDA)40 (OH)150 (CO3 )40 (OAc)58 (H2 O)164 ] ⋅ (ClO4 )41 (H2 IDA=iminodiacetic acid), respectively, by providing a library containing multiple low-nuclearity units. The heart-like units and crown-like tetramer found in both compounds indicate unprecedented assembly levels, leading to an atypical geometry characteristic compared to the giant clusters directly assembled by regular units. These two clusters not only significantly increase the size of Ln-Co clusters but also exhibit the enhanced magnetic entropy change at ultra-low temperatures. This work provided an effective way to fabricate cluster compounds with giant size and geometry complexity simultaneously.

Cocrystallization of Chiral 3d-4f Clusters {Mn10Ln6} and {Mn6Ln2}.

Cocrystallization of different metal nanoclusters facilitates the preparation of cluster-based nanomaterials with enhanced properties. Herein, two pairs of enantiomeric 3d-4f cocrystallization structures of clusters R/S-[Mn10Ln6] and R/S-[Mn6Ln2] (Ln = Dy for 1R and 1S, Y for 2R and 2S) have been reported. Compounds R/S-[Mn10Ln6][Mn6Ln2] exhibit a large optical activity and magneto-optic effect as verified by natural circular dichroism (NCD) and magnetic circular dichroism (MCD). In addition, alternating current (ac) magnetic measurements show that the chiral R/S-[Mn10Dy6][Mn6Dy2] cocrystallization structure displays slow magnetic relaxation with Ueff = 25.1 K.

Capturing Lacunary Iron-Oxo Keggin Clusters and Insight Into the Keggin-Fe13 Cluster Rotational Isomerization.

The formation mechanism of ferrihydrite is the key to understand its treatment of pollutants in waste water and purification of surface water and groundwater. Although emerging evidence suggests that formation of the ferrihydrite occurs through the aggregation of prenucleation clusters, rather than classical atom-by-atom growth, its formation mechanism remains unclear. Herein, an iron-oxo anionic cluster of [Fe22 (µ4 -O)8 (µ3 -OH)20 (µ2 -OH)18 (CH3 COO)16 (H2 O)2 ]4- viewed as a dimer of bivacant ß-Keggin-Fe13 clusters was for the first time obtained by using lanthanide ions as stabilizers. Upon dissolution in a mixed solution of isopropanol and water, the lacunary ß-Keggin-Fe13 cluster can transform into an α-Keggin-Fe13 cluster, distinctly demonstrating that the Keggin-Fe13 cluster rotational isomerization can be realized through the vacant Keggin-Fe13 cluster.

Atomically Precise Lanthanide-Iron-Oxo Clusters Featuring the ϵ-Keggin Ion.

Atomically precise molecular metal-oxo clusters provide ideal models to understand metal oxide surfaces, self-assembly, and form-function relationships. Devising strategies for synthesis and isolation of these molecular forms remains a challenge. Here, the synthesis of four Ln-Fe oxo clusters that feature the ϵ-{Fe13 } Keggin cluster in their core is reported. The {Fe13 } metal-oxo cluster motif is the building block of two important iron oxyhydroxyide phases in nature and technology, ferrihydrite (as the δ-isomer) and magnetite (the ϵ-isomer). The reported ϵ-{Fe13 } Keggin isomer as an isolated molecule provides the opportunity to study the formation of ferrihydrite and magnetite from this building unit. The four currently reported isostructural lanthanide-iron-oxo clusters are fully formulated [Y12 Fe33 (TEOA)12 (Hyp)6 (µ3 -OH)20 (µ4 -O)28 (H2 O)12 ](ClO4 )23 ⋅50 H2 O (1, Y12 Fe33 ), [Gd12 Fe33 (TEOA)12 (Hyp)6 (µ3 -OH)20 (µ4 -O)32 (H2 O)12 ](ClO4 )15 ⋅50 H2 O (2, Gd12 Fe33 ) and [Ln16 Fe29 (TEOA)12 (Hyp)6 (µ3 -OH)24 (µ4 -O)28 (H2 O)16 ](ClO4 )16 (NO3 )3 ⋅n H2 O (Ln=Y for 3, Y16 Fe29 , n=37 and Ln=Gd for 4, Gd16 Fe29 n=25; Hyp=trans-4-Hydroxyl-l-proline and TEOA=triethanolamine). The next metal layer surrounding the ϵ-{Fe13 } core within these clusters exhibits a similar arrangement as the magnetite lattice, and Fe and Ln can occupy the same positions. This provides the opportunity to construct a family of compounds and optimize magnetic exchange in these molecules through composition tuning. Small-angle X-ray scattering (SAXS) and high-resolution electrospray ionization mass spectrometry (HRESI-MS) show that these clusters are stable upon dissolution in both water and organic solvents, as a first step to performing further chemistry towards building magnetic arrays or investigating ferrihydrite and magnetite assembly from pre-nucleation clusters.

Double-Propeller-like Heterometallic 3d-4f Clusters Ln18Co7.

Two high-nuclearity lanthanide-transition metal clusters with the general formula [Ln18CoIICoIII6(OH)14(CO3)9(CH3CH2COO)6(dea)12(H2O)30]·(NO3)8·Cl4·(CH3CH2OH)6·(H2O)12 (Ln18Co7, Ln = Gd (1) and Dy (2)) have been obtained by reacting CoCl2·6H2O, Ln(NO3)3·6H2O, and a mixture of ligands consisting of propionate and diethanolamine (H2dea). Crystal structural analysis exhibits two three-blade propellers composed of the CoIII3Ln9 units connected by one CoII ion and three CO32- ions, which assemble into a double-propeller-like structure (Ln18CoIICoIII6). Magnetocaloric effect (MCE) studies indicate that Gd18Co7 exhibits a large entropy change (-ΔSm) of 36.9 J kg-1 K-1.

Assembly of a Wheel-Like Eu24 Ti8 Cluster under the Guidance of High-Resolution Electrospray Ionization Mass Spectrometry.

A building blocks strategy is an effective approach for constructing the large molecular systems. Herein, we demonstrate that high-resolution electro-spray ionization mass spectrometry (HRESI-MS) provides an effective chance to insight the assemble process of the building blocks and guides the construction of high-nuclearity metal clusters on the basis of the reaction of Ti(Oi Pr)4 , Eu(acac)3 , and salicylic acid. The time-dependent HRESI-MS indicates that not only a Eu3 Ti building block can be formed, but that it can further assemble into a Eu24 Ti8 compound. Temperature-dependent HRESI-MS reveals that increase of the reaction temperature favors the formation and crystallization of the stable Eu24 Ti8 structure. Single-crystal structural analysis demonstrates that the Eu24 Ti8 has a wheel-like structure with diameter of ca. 4.1 nm and is the highest nuclearity lanthanide-titanium oxo cluster reported to date.

Insights into Magnetic Interactions in a Monodisperse Gd12 Fe14 Metal Cluster.

The largest Ln-Fe metal cluster [Gd12 Fe14 (µ3 -OH)12 (µ4 -OH)6 (µ4 -O)12 (TEOA)6 (CH3 COO)16 (H2 O)8 ]⋅(CH3 COO)2 (CH3 CN)2 ⋅(H2 O)20 (1) and the core-shell monodisperse metal cluster of 1 a@SiO2 (1 a=[Gd12 Fe14 (µ3 -OH)12 (µ4 -OH)6 (µ4 -O)12 (TEOA)6 (CH3 COO)16 (H2 O)8 ]2+ ) were prepared. Experimental and theoretical studies on the magnetic properties of 1 and 1 a@SiO2 reveal that encapsulation of one cluster into one silica nanosphere not only effectively decreases intermolecular magnetic interactions but also significantly increases the zero-field splitting effect of the outer layer Fe3+ ions.

Polyhedral {Ag12} and {Ag16} Clusters: Synthesis, Structural Characterization and Third-Order Nonlinear Optical Properties.

Two polyhedral silver-thiolate clusters, [S@Ag16(Tab)10(MeCN)8](PF6)14 (Ag16) and [Ag12(Tab)6(DMF)12](PF6)12 (Ag12), were synthesized by using electroneutral Tab species as protective ligands (Tab=4-(trimethylammonio)benzenethiolate, DMF=N,N-dimethylformamide, MeCN=acetonitrile). Ag16 has a decahedral shape composed of eight pentagon {Ag5} units and two square {Ag4} units. The structure of Ag12 is a cuboctahedron, a classical Archimedean structure composed of six triangular faces and eight square faces. The former configuration is discovered in silver-thiolate cluster for the first time, possibly benefited from the more flexible coordination between the Tab ligand and Ag+ facilitated by the electropositive -N(CH3)3 + substituent group. Third-order nonlinear optical studies show that both clusters in DMF exhibit reverse saturate absorption response under the irradiation of 532 nm laser.

Bottom-up construction of chiral metal-peptide assemblies from metal cluster motifs.

The exploration of artificial metal-peptide assemblies (MPAs) is one of the most exciting fields because of their great potential for simulating the dynamics and functionality of natural proteins. However, unfavorable enthalpy changes make forming discrete complexes with large and adaptable cavities from flexible peptide ligands challenging. Here, we present a strategy integrating metal-cluster building blocks and peptides to create chiral metal-peptide assemblies and get a family of enantiopure [R-/S-Ni3L2]n (n = 2, 3, 6) MPAs, including the R-/S-Ni6L4 capsule, the S-Ni9L6 trigonal prism, and the R-/S-Ni18L12 octahedron cage. X-ray crystallography shows MPA formation reactions are highly solvent-condition-dependent, resulting in significant changes in ligand conformation and discrete cavity sizes. Moreover, we demonstrate that a structure transformation from Ni18L12 to Ni9L6 in the presence of benzopyrone molecules depends on the peptide conformational selection in crystallization. This work reveals that a metal-cluster building block approach enables facile bottom-up construction of artificial metal-peptide assemblies.

Circularly polarized luminescence and performance modulation of chiral europium-titanium (Eu2Ti4)-oxo clusters.

The designed synthesis of chiral luminescent molecules with excellent circularly polarized luminescence (CPL) performance and high quantum yield (QY) levels has attracted great interest but remains very challenging. Herein, we report three pairs of chiral europium-titanium-oxo clusters featuring both modest CPL characteristics and high QY levels (up to 79%), which can be regulated by switching between different ligand substituents.

Interplay between anisotropy and magnetic exchange to modulate the magnetic relaxation behaviours of phenoxo bridged Dy2 dimers with axial ß-diketonate co-ligands.

A series of Schiff base LH ((E)-2-((pyridin-2-ylmethylene)amino)phenol) supported phenoxo bridged symmetric [Dy2(L)2(hfac)4] (1), [Dy2(L)2(tfac)4] (2) and asymmetric [Dy2(L)2(thd)3(NO3)]·1.5H2O (3) binuclear complexes were isolated using differently substituted ß-diketonate co-ligands (Hhfac = hexafluoroacetylacetonate, Htfac = trifluoroacetylacetonate, and Hthd = 2,2,6,6-tetramethyl-3,5-heptanedione). In all the three complexes 1-3, the two LH ligands provide phenoxo bridging and N-donor atoms. The {Dy2(µ2-O)2} magnetic core structures with LH ligands are found to be the same in 1-3 while the dissimilar functionalities of the axially coordinated different ß-diketonate co-ligands play a crucial role in modulating the magnetic anisotropy of individual DyIII sites and magnetic exchange between them. The experimental static magnetic behaviour suggests the presence of intramolecular antiferromagnetic interactions in all the three complexes 1-3. The strength of the magnetic exchange coupling decreases with increasing magnetic anisotropy of individual DyIII ions from complex 1 to complex 3 and simultaneously their zero-field slow magnetic relaxation behaviors were found to increase with effective energy barriers (ΔE/kB) of 9.04 K, 24.06 K and 25.65 K, respectively. Furthermore, the DFT and ab initio theoretical calculations performed on the X-ray structures of complexes 1-3 support our experimental findings.