Quan-Qin Zhao

A superior fluorescent sensor for Al3+ and UO22+ based on a Co(II) metal–organic framework with exposed pyrimidyl Lewis base sites

A robust 3D pcu Co(II) metal–organic framework (MOF) based on a designed bent pyrimidyl–biimidazole ligand, [Co2(dmimpym)(nda)2]n (1; dmimpym = 4,6-di(2-methyl-imidazol-1-yl)-pyrimidine, H2nda = 1,4-naphthalenedicarboxylic acid), was successfully synthesized under solvothermal conditions and characterized using single-crystal X-ray diffraction. Compound 1 has a 2-fold interpenetrated 6-connected pcu network based on a [Co2(COO)4] paddle-wheel secondary building unit (SBU). It contains exposed pyrimidyl Lewis base sites, has porosity, and exhibits ligand-based blue emission in the solid state, which render it suitable as a fluorescent sensor for the detection of metal ions. Fluorescence titration experiments reveal that 1 is highly selective for Al3+ with exclusively enhanced emission as compared to other metal ions, and the limit of detection (LOD) reaches as low as 0.7 μM. Importantly, 1 can be cycled at least five times without the loss of emission signals. Moreover, 1 is able to detect low concentration of uranyl ions via fluorescence quenching. The present study sheds light on the realization of the practical application of MOFs as luminescent sensors via tailoring of the ligand and extends the way towards low-cost transition metal-based MOF sensors.

Anisotropic Assembly of Ag52 and Ag76 Nanoclusters

Although there has been an upsurge of interest in anisotropic assembly of inorganic nanoparticles, atomically precise self-assembly of anisotropic metal clusters is extremely rare. Herein, we presented two novel silver nanoclusters, Ag52 (SD/Ag23) and Ag76 (SD/Ag24), which are interiorly templated by five MoO42- and a pair of Mo6O228- anions, respectively, and coprotected by bridging RSH and terminal diphosphine ligands exteriorly. Regiospecific distribution diphosphine ligands on the surface and the arrangement of multiple molybdate templates within the nanoclusters synergetically tailor their shapes to anisotropic oblate spheroid and elongated rod, respectively. This work not only open up new avenues for the synthesis of silver nanoclusters with novel metal skeleton shapes and anisotropic surface structures but also give important insights for the anisotropic growth of silver nanoclusters through surface modifications or/and template organizations.

Johnson Solids: Anion-Templated Silver Thiolate Clusters Capped by Sulfonate

Sulfonates were incorporated into six novel high-nuclearity silver(I) thiolate clusters under the guidance of anion templates varied from S2- , SO42- , α-[Mo5 O18 ]6- , β-[Mo5 O18 ]6- , [Mo2 O8 ]4- , to [Mo4 O14 (SO4 )]6- . Single crystal X-ray analysis revealed that SD/Ag1, SD/Ag3, SD/Ag5, and SD/Ag6 are discrete [S@Ag60 ], [α-Mo5 O18 @Ag36 ], [Mo2 O8 @Ag30 ]2 , and [Mo4 O14 (SO4 )@Ag73 ] clusters, respectively, whereas SD/Ag2 and SD/Ag4 are one-dimensional (1D) chains based on the [SO4 @Ag20 ] and [β-Mo5 O18 @Ag36 ] cluster subunits, respectively. Their silver skeletons are protected exteriorly by thiolates and sulfonates and interiorly supported by diverse anions as templates. Structurally, cluster SD/Ag1 is a typical core-shell structure comprised of an inner Ag12 cuboctahedron and an outer Ag48 shell. The sulfate-templated drum-like Ag20 cluster subunits are bridged by PhSO3- to give a 1D chain of SD/Ag2. Complex SD/Ag3 and SD/Ag4 are spindle-like Ag36 clusters with isomeric [Mo5 O18 ]6- inside, and the latter is further extended to a 1D chain through PhSO3- bridges. A pair of [Mo2 O8 ]4- templated gourd-like Ag30 clusters are dimerized in a head-to-head fashion to form SD/Ag5. Complex SD/Ag6 is the largest cluster in this family and doubly templated by unprecedented [Mo4 O14 (SO4 )]6- anions. Geometrically, the silver shells of SD/Ag1-SD/Ag5 show the polyhedral features of Johnson solids, instead of the usual Platonic or Archimedean solids. Solution behaviors and luminescent properties were also investigated in detail.

Elimination‐Fusion Self‐Assembly of a Nanometer‐Scale 72‐Nucleus Silver Cluster Caging a Pair of [EuW10O36]9− Polyoxometalates

The largest known polyoxometalate (POM)-templated silver-alkynyl cluster, [(EuW10 O36 )2 @Ag72 (tBuC≡C)48 Cl2 ⋅4 BF4 ] (SD/Ag20), was isolated under solvothermal conditions and structurally characterized. It was confirmed by single-crystal X-ray diffraction (SCXRD) as a {EuW10 }2 -in-{Ag72 } clusters-in-cluster rod-like compound. The high-resolution electrospray ionization mass spectrometry (HR-ESI-MS) shows that such a double anion-templated cluster is assembled from a crucial single anion-templated Ag42 intermediate in the solution. The crystallization of Ag42 species (SD/Ag21), followed by SCXRD, gave an important clue about the assembly route of SD/Ag20 in solution: the Ag42 cluster eliminates six silver atoms laterally, then fuses together at the vacant face to form the final Ag72 cluster (elimination-fusion mechanism). The characteristic emission of [EuW10 O36 ]9- is well maintained in SD/Ag20. This work not only provides a new method for the synthesis of larger silver clusters as well as the functional integration of the silver cluster and POMs, but also gives deep insights about the high-nuclear silver cluster assembly mechanism.

Anion-Templated Nanosized Silver Alkynyl Clusters: Cluster Engineering and Solution Behavior

Assembly of nanosized polynuclear metal clusters from simple building blocks usually involves complicated self-organization processes and thus is a long-standing challenge. Here, we demonstrate the controllable assembly, single-crystal structures and solution behaviors of four molecular assemblies based on nanosized silver alkynyl clusters, formulated as {[(CrO4 )2 Cl@Ag42 (PhC≡C)34 (CF3 COO)2 ]⋅CF3 COO} (1), {(NH4 )[(CrO4 )2 Cl@Ag42 (PhC≡C)34 (CrO4 )(H2 O)2 ]⋅2BF4 ⋅CH3 OH}n (2), [(CrO4 )@Ag22 (PhC≡C)16 (CF3 SO3 )4 ]n (3), and {[(CrO4 )2 @Ag31 (PhC≡C)22 (CF3 SO3 )4 ]⋅CF3 SO3 ⋅2CH3 OH⋅H2 O}n (4). In the presence of concomitant CrO42- and Cl- templates, we could isolate a discrete cluster 1 and a polymeric chain-like compound 2 by using different silver salts. Both 1 and 2 have a similar 42-metallic cage, which traps two CrO42- and one Cl- as anion templates. Using sole CrO42- template, 3 and 4 were simultaneously isolated in a one-pot reaction. Both of them are 1D chain structures based on single CrO42- templated Ag18 and double CrO42- templated Ag30 clusters, respectively. HR-ESI-MS was used to study the solution behaviors of 1-4. This work has the following purposes: i) it presents the cluster engineering concept used in the assembly of polynuclear silver alkynyl clusters; ii) it exemplifies template effects from hetero and homo anions; and iii) it provides a controllable way to achieve assembly of silver alkynyl clusters.

Benzoate-Induced High-Nuclearity Silver Thiolate Clusters

Compared with the well-known anion-templated effects in shaping silver thiolate clusters, the influence from the organic ligands in the outer shell is still poorly understood. Herein, three new benzoate-functionalized high-nuclearity silver(I) thiolate clusters are isolated and characterized for the first time in the presence of diverse anion templates such as S2- , α-[Mo5 O18 ]6- , and MoO42- . Single-crystal X-ray analysis reveals that the nuclearities of the three silver clusters (SD/Ag28, SD/Ag29, SD/Ag30) vary from 32 to 38 to 78 with co-capped tBuS- and benzoate ligands on the surface. SD/Ag28 is a turtle-like cluster comprising a Ag29 shell caging a Ag3 S3 trigon in the center, whereas SD/Ag29 is a prolate Ag38 sphere templated by the α-[Mo5 O18 ]6- anion. Upon changing from benzoate to methoxyl-substituted benzoate, SD/Ag30 is isolated as a very complicated core-shell spherical cluster composed of a Ag57 shell and a vase-like Ag21 S13 core. Four MoO42- anions are arranged in a supertetrahedron and located in the interstice between the core and shell. Introduction of the bulky benzoate changes elaborately the nuclearity and arrangements of silver polygons on the shell of silver clusters, which is exemplified by comparing SD/Ag28 and a known similar silver thiolate cluster. The three new clusters emit luminescence in the near-infrared (NIR) region and show different thermochromic luminescence properties. This work presents a flexible approach to synthetic studies of high-nuclearity silver clusters decorated by different benzoates, and structural modulations are also achieved.

Three Silver Nests Capped by Thiolate/Phenylphosphonate

Introducing phenylphosphonic acid (H2 PPA) into the Ag/tBuSH assembly system has produced a family of nanoscale-sized, high-atom number, silver thiolate/PPA nests (SD/Ag45 a, SD/Ag66 a, and SD/Ag73 a) with impressive core-shell features. SD/Ag45 a is a 45-atom ellipsoid comprised of an Ag36 shell trapping an Ag9 S2 three-bladed rotor inside. SD/Ag66 a comprises an inner rod-like Ag20 core and an outer Ag44 shell, giving a 64-atom nest. These Ag64 nests are further extended by Ag(CN)2 linkers to form a one-dimensional chain structure. SD/Ag73 a is a three-shell 73-nucleus silver nest with a central silver atom enclosed in a rhombicuboctahedron of 24 silver atoms, which is itself enclosed in the outermost shell of a rectified version of a 48-Ag octahedral Goldberg 2,0 cage. The solution behaviors and optical absorption properties of the three nests are described in detail. Of note, SD/Ag45 a and SD/Ag73 a emit in the near-infrared region and show different luminescent thermochromic behavior. This work demonstrates that the participation of H2 PPA strongly influences the structures of silver thiolate nests, thus providing a new route to fabricate and modify them in a more rational way.