M6 Clusters Research Articles

Exceptional proton conduction in two robust zirconium(IV)/hafnium(IV)-organic frameworks constructed by tetratopic carboxylate

Exceptional proton conduction in two robust zirconium(IV)/hafnium(IV)-organic frameworks constructed by tetratopic carboxylate

Unveiling the contribution of hexanuclear clusters for highly selective glucose conversion on Metal–Organic frameworks

Unveiling the contribution of hexanuclear clusters for highly selective glucose conversion on Metal–Organic frameworks

Structure, stability, and electronic and optical properties of TMDC-coinage metal composites: vertical atomically thin self-assembly of Au clusters.

Composites of metal clusters supported on transition metal dichalcogenides (TMDCs) often provide promising opportunities for applications in nanoelectronics, catalysis, sensing, etc. In the present investigation, a systematic attempt has been made to unveil the structure and stability of coinage M6 clusters supported on TMDC (MoS2 and WS2) monolayers. The more prominent objective is to explore potential candidates that stabilize the two-dimensional (2D) M6 clusters on their surface. Periodic energy decomposition analysis (pEDA) was carried out to probe the various interaction energy (IE) components that govern the stability of the M6 clusters in the composites. Attention has also been devoted to unravelling the electronic and optical properties of these TMDCs/M6 composites. Moreover, ab initio molecular dynamics (AIMD) simulations were performed to scrutinize the dynamic behaviour of Au cluster on WS2 monolayer. The results reveal that the coinage M6 clusters form energetically more stable composites on MoS2 than WS2 monolayer. It is worth mentioning that WS2 promotes the stability of 2D M6 clusters. Inclusion of dispersion correction marginally altered the geometries of the TMDCs/M6 composites but its impact on the IE values was significant. AIMD simulation explicitly emphasizes that the WS2 surface preferentially facilitates the vertical 2D self-assembling of Au atoms and, interestingly, the planarity is mostly retained during the course of simulations. The adsorption of coinage M6 clusters substantially influences the electronic and optical properties of the TMDCs. HSE06 calculation confirms that the decrease in energy gap is more pronounced in MoS2/M6 composites. The outcomes of this study render fundamental insights into the various TMDCs/M6 composites that would certainly be worthwhile probing for diverse practical applications.

Structure and assembly of a hexanuclear AuNi bimetallic nanocluster.

An Au4Ni2 nanocluster containing a square-planar [-PPh2-Au-S-Au-]2 ring and two nickel-pincer arms is reported here. Abundant intra- and inter-cluster noncovalent interactions promote the assembly of the nanocluster into a porous framework material. The assembly-dependent unique solubility and photoluminescence were also investigated.

Alcoholate and Mixed Alcoholate/Iodide Supported Hexanuclear Niobium Cluster Compounds with a Mixed Face-Bridged/Edge-Bridged Cluster Pair Example

Chemical reactions of ball-mill activated [Nb6I11] with alcohol solutions of Mg alcoholates result in the formation of the three new hexanuclear Nb cluster compounds [Nb6I8(HOCH3)6][Nb6(OCH3)18]·2CH3OH (1), (PPh4)2[Nb6(OC2H5)12I6]·C2H5OH (2) and (PPN)2[Nb6(OC2H5)12I6] (3). They contain cluster anions, which have the edges of the Nb6 octahedra, i.e. the inner coordination sites, μ2-bridged by the O atoms of methanolato or ethanolato ligands. Thereby, they represent further characterized members of the so far very small group of hexanuclear cluster alcoholates. The terminal metal sites are bonded to further methanolato (1) or iodido ligands (2 and 3). Sterically demanding organic cations (PPh4+, PPN+, 2 and 3) or a cationic Nb6 cluster complex with terminal methanol ligands [Nb6I8(HOCH3)6]2+ in 1 compensate the negative charges of the cluster anions. Compound 1 is the first example of a M6 cluster ion pair of both the text-book known edge-bridged [M6X12] and face-bridged [M6X8] cluster units. The structures of the three title compounds were determined by means of single-crystal X-ray structure analysis.Graphical

Unveiling the nature of boric acid adsorption by metal-organic frameworks with hexanuclear clusters

A growing demand of boric acid has been forecasted with the rapid development of industries while the world is suffering the consequence from boron-containing wastewater. Metal–organic frameworks (MOFs) with exceptional stability and remarkable surface area have been preliminarily identified as effective boron adsorbents, adsorption mechanism has yet been elucidated though. Herein Zr6/Hf6-based NU-1008 and NU-903 were studied for boron removal from water for the first time where around 4.82, 6.27, 3.49 and 6.34 boron were captured per Zr6/Hf6 cluster for Zr-NU-1008, Hf-NU-1008, Zr-NU-903 and Hf-NU-903 through a spontaneous endothermic process with fast kinetics by means of chemisorption. Larger capacity of Hf6-based MOFs than Zr6-based MOFs can be explained by the weaker electronegativity of hafnium than zirconium. The increased binding energy of Zr 3d, Hf 4f and O 1s as well as reduced binding energy of B 1s suggested the interaction between electron-deficient boron and the hexanuclear clusters (M6). Owing to the crystalline nature of NU-1008, the boron binding sites were precisely elucidated by single crystal X-ray diffraction where boric acid was attached to the available coordinative sites on the M6 clusters through the M6-O-B(OH)2 connection.

Exploring the Role of Cluster Formation in UiO Family Hf Metal-Organic Frameworks with in Situ X-ray Pair Distribution Function Analysis.

The structures of Zr and Hf metal-organic frameworks (MOFs) are very sensitive to small changes in synthetic conditions. One key difference affecting the structure of UiO MOF phases is the shape and nuclearity of Zr or Hf metal clusters acting as nodes in the framework; although these clusters are crucial, their evolution during MOF synthesis is not fully understood. In this paper, we explore the nature of Hf metal clusters that form in different reaction solutions, including in a mixture of DMF, formic acid, and water. We show that the choice of solvent and reaction temperature in UiO MOF syntheses determines the cluster identity and hence the MOF structure. Using in situ X-ray pair distribution function measurements, we demonstrate that the evolution of different Hf cluster species can be tracked during UiO MOF synthesis, from solution stages to the full crystalline framework, and use our understanding to propose a formation mechanism for the hcp UiO-66(Hf) MOF, in which first the metal clusters aggregate from the M6 cluster (as in fcu UiO-66) to the hcp-characteristic M12 double cluster and, following this, the crystalline hcp framework forms. These insights pave the way toward rationally designing syntheses of as-yet unknown MOF structures, via tuning the synthesis conditions to select different cluster species.

Apical Cyanide Ligand Substitution in Heterometallic Clusters [Re3Mo3Q8(CN)6]n– (Q = S, Se)

A number of transition metal cluster compounds can be obtained only in the melt of inorganic cyanides and, therefore, contain terminal cyanide ligands. Substitution of these ligands, which is often necessary to change the physicochemical properties of the clusters, is an urgent problem because of their low reactivity in substitution reactions. In this work, a synthetic approach has been developed for the substitution of CN‐ligands in the heterometallic cluster anions [Re3Mo3Q8(CN)6]n– (Q = S, n = 6; Q = Se, n = 5) by the 4‐tert‐butylpyridine (TBP) molecules. Two new compounds, namely [Re3Mo3S8(TBP)6] (1) and [Re3Mo3Se8(TBP)6] (2), were obtained with high yields and crystallized under solvothermal conditions. It has been shown that compounds 1 and 2 are based on the paramagnetic cluster cores {Re3Mo3Q8}0 containing 23 cluster valence electrons (CVE). The geometry of the new compounds has been investigated using X‐ray structural analysis. The electronic structure has been analyzed using the DFT calculations showing large distortion of M6 cluster core.

A Hexanuclear Niobium Cluster Compound With Intra-Cluster Chelate Ligands: [Nb6 (OC2 H4 NH2 )12 ]I3.

From the reaction of [Nb6 I11 ] with 2-aminoethanol in pyridine the cluster compound [Nb6 (OC2 H4 NH2 )12 ]I3 has been obtained and the single-crystal X-ray structure determined. It represents the first example of a group VB metal cluster compound with hexanuclear, octahedral metal atom core, which carries intra-cluster chelate ligands. With the formation of this unprecedented cluster cation we report for the first time a transformation of a 6-8 to a 6-12 type cluster unit. The formation of the cluster cation goes along with a one-electron oxidation of the cluster starting material. Furthermore, it adds a second entry to the so far very small group of M6 cluster compounds with organic ligands on the inner cluster sites.

Octahedral metal clusters as building blocks of trimetallic superexpanded Prussian blue analogues.

The self-assembly of octahedral metal clusters (diamagnetic [Nb(6)Cl(12)(CN)(6)](4-) or paramagnetic [Ta(6)Cl(12)(CN)(6)](3-)), [Mn(salen)](+) [salen = N,N'-ethylenebis(salicylidene)iminate] and mononuclear {M'(CN)(x)} polycyanometallates ([Fe(CN)(6)](4-), [Cr(CN)(6)](3-), [Fe(CN)(5)(NO)](2-), or [Ni(CN)(4)](2-)) building blocks results in the formation of a series of six cluster-containing 3D heterotrimetallic frameworks: [H(3)O](2)[Nb(6)Cl(12)(CN)(6)[Mn(salen)](6)Fe(CN)(6)]·3H(2)O (1), [H(3)O][Nb(6)Cl(12)(CN)(6)[Mn(salen)](6)Cr(CN)(6)]·4H(2)O (2), [Nb(6)Cl(12)(CN)(6)[Mn(salen)](6)Fe(CN)(5)(NO)]·5H(2)O (3), [Nb(6)Cl(12)(CN)6[Mn(salen)](6)Ni(CN)4]·7H(2)O (4), [H(3)O][Ta(6)Cl(12)(CN)(6)[Mn(salen)](6)Fe(CN)6]·4H(2)O (5), and [Ta(6)Cl(12)(CN)(6)[Mn(salen)](6)Cr(CN)(6)]·7H(2)O (6). Single-crystal X-ray diffraction analyses show that compounds 1, 2, 5, and 6 have distorted face-centered-cubic frameworks that can be considered as superexpanded Prussian blue analogues built of two different hexacyanometallate nodes and expanded by insertion of the [Mn(salen)](+) complex, while 4 features a quasi-superexpanded Prussian blue framework because the structure is based on the hexacyano metal cluster and disordered tetracyano [Ni(CN)(4)](2-) nodes. The powder X-ray diffraction of 3 indicates that it possesses a quasi-superexpanded Prussian blue framework based on the hexacyano cluster and disordered pentacyano [Fe(CN)(5)(NO)](2-) nodes. Compound 6 is the first compound containing three 3d-3d'-M6 cluster (4d) spin centers. Magnetic measurements reveal that the overall magnetic nature can be systematically controlled by the choice of the octahedral metal cluster and polycyanometallate nodes. H(2)/N(2) adsorption and thermal stability of the compounds were investigated.

ChemInform Abstract: Low‐Dimensional Frameworks in Solid State Chemistry of Mo6 and Re6 Cluster Chalcohalides

AbstractReview: 82 refs.

Low‐Dimensional Frameworks in Solid State Chemistry of Mo6 and Re6 Cluster Chalcohalides

AbstractThe low‐dimensional Mo6 and Re6 cluster chalcohalides synthesised from solid‐state reactions at high temperature are reviewed. Their crystal structures are described in terms of interunit connectivities involving inner and apical ligands shared between adjacent cluster units. It will be shown that such architectures are controlled by the geometry of the M6L14 cluster units, the steric hindrance of the ligands linked to the M6 cluster, the specific location imposed on the halogen or chalcogen ligand and the most favourable electron count on the cluster core, considering halogen and chalcogen stoichiometries.

Elaboration of hybrid nanocluster materials by solution chemistry

The [(M6L12i)L6a]n− and [(M6L8i)L6a] units (a = apical, i = inner) constitute the basic building blocks in the octahedral cluster chemistry. Nano-sized metallic clusters are easily obtained by solid state synthesis with transition elements associated with halogen or chalcogen. The intrinsic properties of M6 cluster units—one or two electron reversible redox process, magnetism and luminescence—depend on the nature of the metal and ligands. The solubilisation of M6 solid state compounds provides [(M6L12i)L6a]n− or [(M6L8i)L6a]n− building blocks with individual properties that can be further used for the design of hybrid organic/inorganic materials. Several examples of solid state precursors are presented as well as substitution reactions of apical ligands in solution. Indeed, hexacyano M6 clusters are obtained by direct reaction of solid state precursors in aqueous KCN solutions. Low dimensional frameworks are subsequently obtained by recrystallisation of hexacyano M6 clusters with transition elements. The functionalisation of cluster proceeds in two steps. The first one consists in the replacement of apical halogens of cluster unit precursors by labile groups as CF3SO3 (triflate) or solvent molecules after solution reaction. The second one consists in the substitution of the labile groups by functionalised phenolate or pyridine ligands.

The octahedral cluster compounds of early transition metals: An original class of dielectric materials

Octahedral clusters of early transition elements appear either in the face-capped M6Li 8La 6 units for M = Mo, W, Re or in the edge-capped M6Li 2La 6 ones for M = Nb, Ta (L = oxygen, halogen, chalcogen). These units constitute the building blocks of a large variety of crystal structures. In most of them, owing to the steric hindrance of the ligands, the M6 clusters cannot interact and such materials are insulators. These units are usually centro-symmetric when all inner or apical positions are occupied by a same ligand. In contrast, in oxyhalides, chalcohalides and chlorofluorides, these positions are occupied by two different ligands either ordered or randomly distributed and thus, an acentric distribution of the anionic charges around the M6 cluster can appear. In this case the units act as permanent dipoles and dielectric relaxations can be observed. In this paper we recall the crystal structures of M6 cluster compounds built from acentric units and some relevant examples of unusual dielectric behaviour.

Thresholds for the Collision-Induced Dissociation of Clusters by Rare Gas Impact

Classical trajectory simulations are used to study collision-induced dissociation (CID) of octahedral Al6 and M6 clusters, by rare gas impact. M represents a first-row transition metal atom with a mass of 60 amu. Both an analytic Al6 potential derived from ab initio calculations [J. Chem. Phys. 1987, 87, 2205] and a model analytic function with adjustable parameters were used for the Al6 and M6 cluster potentials. Ab initio and model intermolecular potentials were also used for interactions between the Ne, Ar, and Xe rare gases and the Al6 and M6 clusters. CID cross sections versus relative translational energy Erel are calculated for collisions between the rare gas atoms and clusters, from which CID thresholds are determined. For all cases is larger than the actual threshold, which results from inefficient transfer of Erel to cluster vibrational modes. The efficiency of energy transfer to the cluster depends on the cluster vibrational frequencies, masses of the rare gas and cluster atoms, repulsiveness o...

Tetrahedral Clusters of GaMo4S8-Type Compounds: A Metal Bonding Analysis

Extended Huckel tight binding calculations have been performed on ligated as well as on ligand-free Mo4 and Mo6 extended frames, in order to analyze the metal-metal bonding within the clusters and particularly the appreciable changes of the metal-metal bond lengths through the M4 tetrahedral units contained in GaM4X8 (M = Mo, Nb, V, Ta; X = S, Se, Te), Mo4S4Y4 (Y = Cl, Br, I). A comparison with the M6 octahedral units of the M Mo6X8 (M = Pb, Ag, La; X = S, Se) series is made. By means of DOS, COOP curves, and overlap populations, results clearly display the strong reorganization of the electronic structure of the bare metal clusters network while the ligand interactions occur, inducing a strong reduction of the strength of the metal-metal bonds. We outline the relationship between the metal-metal bond lengths and various parameters such as the valence electron count (VEC) per cluster and the nature of the ligands. Our results indicate that the two series M4 and M6 differ: M-M bond lengths are unaffected by the VEC in the regular M4 cluster, whereas some M-M bond lengths undergo a significant change when the VEC increases in the distorded M6 clusters. Likewise, it is worthy to note that metal d orbitals have a more significant effect in M4 cluster series. In contrast, the metal-ligand covalency induces similar elongations of metal-metal bonds in the two series.

Splitting of degenerate vibrational modes due to symmetry perturbations in tetrahedral M4 and octahedral M6 clusters

Splitting of degenerate vibrational modes due to symmetry perturbations in tetrahedral M4 and octahedral M6 clusters