High-nuclearity Metal Clusters Research Articles

Heterometallic Electrocatalysts Derived from High-Nuclearity Metal Clusters for Efficient Overall Water Splitting.

The development of cost-effective electrocatalysts with an optimal surface affinity for intermediates is essential for sustainable hydrogen fuel production, but this remains insufficient. Here we synthesize Ni2P/MoS2-CoMo2S4@C heterometallic electrocatalysts based on the high-nuclearity cluster {Co24(TC4A)6(MoO4)8Cl6}, in which Ni2P nanoparticles were anchored to the surface of the MoS2-CoMo2S4@C nanosheets via strong interfacial interactions. Theoretical calculations revealed that the introduction of Ni2P phases induces significant disturbances in the surface electronic configuration of Ni2P/MoS2-CoMo2S4@C, resulting in more relaxed d-d orbital electron transfers between the metal atoms. Moreover, continuous electron transport was established by the formation of multiple heterojunction interfaces. The optimized Ni2P/MoS2-CoMo2S4@C electrocatalyst exhibited ultralow overpotentials of 198 and 73 mV for oxygen and hydrogen evolution reactions, respectively, in alkaline media, at 10 mA cm-2. The alkali electrolyzer constructed using Ni2P/MoS2-CoMo2S4@C required a cell voltage of only 1.45 V (10 mA cm-2) to drive overall water splitting with excellent long-term stability.

Rationally designed Ni2P/WS2/Co9S8@C multi-interfacial electrocatalyst for efficient overall water splitting

Exploring cost-efficient electrocatalysts for water electrolysis is imperative and urgent. Herein, we have successfully synthesized the novel Ni2P/WS2/Co9S8@C electrocatalyst with the multi-heterojunction interfaces via pyrolysis and in situ phosphorization processes by employing high-nuclearity metal clusters {Co24W8} as preassembly molecular platform. As expected, Ni2P/WS2/Co9S8@C exhibits outstanding oxygen evolution and hydrogen evolution performances with ultralow overpotentials of 204 mV and 67 mV at 10 mA cm−2 in alkaline media, respectively. The alkali-electrolyzer using Ni2P/WS2/Co9S8@C as cathode and anode electrodes delivers a low cell voltage of 1.48 V achieving 10 mA cm−2 with good durability. Density functional theory calculations suggest that the interfacial electrons transfer from Co9S8 and Ni2P to WS2 obviously lower the binding energies of adsorbed species and thus enhance their intrinsic activity. This work demonstrates unique advantages of interfacial structure modulation for the rational design of high-performance bifunctional electrocatalysts.

Cu{SC(O)OiPr}]96: A Giant Self-Assembled Copper(I) Supramolecular Wheel Exhibiting Photoluminescence Tuning and Correlations with Dynamic Solvation and Solventless Synthesis.

The hierarchical self-organization of structurally complex high-nuclearity metal clusters with metallosupramolecular wheel architectures that are obtained from the self-assembly of smaller solvated cluster units is rare and unique. Here, we use the potentially heteroditopic monothiocarbonate ligand and demonstrate for the first time the synthesis and structure of a solvated non-cyclic hexadecanuclear cluster [Cu{SC(O)OiPr}]16·2THF (1) that can simultaneously desolvate and self-assemble in solution and subsequently form a giant metallaring, [Cu{SC(O)OiPr}]96 (2). We also demonstrate a luminescent precursor to cluster (2) can be achieved through a solventless and rapid mechanochemical synthesis. Cluster (2) is the highest nuclearity copper(I) wheel and the largest metal cluster containing a heterodichalcogen (O, S) ligand reported to date. Cluster (2) also exhibits solid-state luminescence with relatively long emission lifetimes at 4.1, 13.9 (μs). The synthetic strategy described here opens new research avenues by replacing solvent molecules in stable {Cu16} clusters with designed building units that can form new hybrid and multifunctional finite supramolecular materials. This finding may lead to the development of novel high-nuclearity materials self-assembled in a facile manner with tunable optical properties.

Single-Molecule Magnets: From Mn12-ac to dysprosium metallocenes, a travel in time

• A brief introduction concerning origin and detection of Single-Molecule Magnets. • A time travel in single-molecule magnetism. • Highly anisotropic systems are prevailing over high nuclearity metal clusters. • Synergistic multifunctionality, a key feature in molecular magnetism. • Hybrid materials based on Single-Molecule Magnets, towards future devices. The discovery of the first Single-Molecule Magnet, Mn12-ac, in 1993 changed the perspective of how information can be stored. The current bit, occupying few hundreds of nanometers in present devices, would be minimized to tens of angstroms at molecular level. However, until a couple of years these materials could only operate at temperatures near to the absolute zero. From 1993 to date, the field of Single-Molecule Magnets (SMMs) has continuously evolved thanks to the close collaboration of chemists and physicists obtaining materials already operating above the liquid nitrogen temperature. This long journey, however, has involved the study of many different routes towards high performance SMMs, being each of them essential in order to deeply understand the quantum dynamics behind these molecules. An era of high spin 3d metal clusters was the beginning of everything, but it went through highly anisotropic low coordinate 3d compounds, lanthanide based magnets, radical bridged compounds and 3d-4f mixed systems, among others, to end up in the current state of the art dysprosium metallocenes. Furthermore, after the magnetic studies in bulk, SMM based hybrid systems are emerging for future application devices, which also involve very interesting multifunctionalities. All in all, this work aims to explain how these materials work and show the trajectory and some of the major advances that have been made during recent years in this field.

Two Nanometer-Sized High-Nuclearity Homometallic Bromide Clusters (M26Br38)12- (M = Cu, Ag): Syntheses, Crystal Structures, and Efficient Adsorption Properties.

The spontaneous formation of discrete spherical nanosized molecules is ubiquitous in nature; however, the actual structural imitation of such high-symmetry polyhedra from the edge sharing of regular polygons has still proved to be elusive. Herein, two high-nuclearity metal clusters, namely (TTB)4·M26Br38 (M = Cu (1), Ag (2), TTB·Br3 = 1, 3, 5-tris(triethylammoniomethyl)benzene tribromide), have been rationally and solvothermally synthesized and structurally characterized. Single-crystal X-ray analysis confirmed that 1 has I4̅3m symmetry with a (Cu25Br34)12- anion shell enwrapping a CuBr4 tetrahedron and 2 has I4̅3m symmetry with a [Ag26Br34]12- anion shell enwrapping a Br4 pyramid. The diffuse-reflectance UV-vis measurements showed that both compounds possess proper semiconductor behaviors with tunable band gaps of 1.87 eV for 1 and 1.90 eV for 2. Interestingly, all the samples feature distinct adsorption speed and compound 1 shows good adsorption activity for methyl orange (MO) under the same reaction conditions. The effects of pH, temperature, and cyclicity on dye adsorption, together with the thermal stabilities and luminescence properties of the compounds, were also studied. From the cyclic adsorption of compound 1 to the anionic dye MO, it was found that the adsorption of MO was good over three cycles, and the third adsorption rate was still 93.90%.

Nickel(II) cluster-based mixed-cation coordination polymer synthesized from 2-mercaptobenzoic acid and its application.

High-nuclearity metal clusters have received considerable attention not only because of their diverse architectures and topologies, but also because of their potential applications as functional materials in many fields. To explore new types of clusters and their potential applications, a new nickel(II) cluster-based mixed-cation coordination polymer, namely poly[hexakis[μ4-(2-carboxylatophenyl)sulfanido]di-μ3-chlorido-tri-μ2-hydroxido-octanickel(II)sodium(I)], [Ni8NaCl2(OH)3(C7H4O2S)6]n, 1, was synthesized using nickel chloride hexahydrate and mercaptobenzoic acid (H2mba) as starting reactants under hydrothermal conditions. The material was characterized by single-crystal X-ray diffraction (SCXRD), Fourier transform IR spectroscopy, thermogravimetric analysis, powder X-ray diffraction and X-ray photoelectron spectroscopy analysis. SCXRD shows that 1 consists of a hexanuclear nickel(II) [Ni6] cluster, dinuclear NiII nodes and a mononuclear NaI node, resulting in the formation of a complex covalent three-dimensional network. In addition, a tightly packed NiO/C&S nanocomposite is fabricated by sintering the coordination precursor at 400 °C. The uniform nanocomposite consists of NiO nanoparticles, incompletely carbonized carbon and incompletely vulcanized sulfur. When used as a supercapacitor electrode, the synthesized composite shows an extra-long cycling stability (>5000 cycles) during the charge/discharge process.

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.

ChemInform Abstract: Role of Anions Associated with the Formation and Properties of Silver Clusters

AbstractReview: 40 refs.

Role of Anions Associated with the Formation and Properties of Silver Clusters.

Metal clusters have been very attractive due to their aesthetic structures and fascinating properties. Different from nanoparticles, each cluster of a macroscopic sample has a well-defined structure with identical composition, size, and shape. As the disadvantages of polydispersity are ruled out, informative structure-property relationships of metal clusters can be established. The formation of a high-nuclearity metal cluster involves the organization of metal ions into a complex entity in an ordered way. To achieve controllable preparation of metal clusters, it is helpful to introduce a directing agent in the formation process of a cluster. To this end, anion templates have been used to direct the formation of high nuclearity clusters. In this Account, the role of anions played in the formation of a variety of silver clusters has been reviewed. Silver ions are positively charged, so anionic species could be utilized to control the formation of silver clusters on the basis of electrostatic interactions, and the size and shape of the resulted clusters can be dictated by the templating anions. In addition, since the anion is an integral component in the silver clusters described, the physical properties of the clusters can be modulated by functional anions. The templating effects of simple inorganic anions and polyoxometales are shown in silver alkynyl clusters and silver thiolate clusters. Intercluster compounds are also described regarding the importance of anions in determining the packing of the ion pairs and making contribution to electron communications between the positive and negative counterparts. The role of the anions is threefold: (a) an anion is advantageous in stabilizing a cluster via balancing local positive charges of the metal cations; (b) an anion template could help control the size and shape of a cluster product; (c) an anion can be a key factor in influencing the function of a cluster through bringing in its intrinsic properties. Properties including electron communication, luminescent thermochromism, single-molecule magnet, and intercluster charge transfer associated with anion-directed silver clusters have been discussed. We intend to attract chemists' attention to the role that anions could play in determining the structures and properties of metal complexes, especially clusters. We hope that this Account will stimulate more efforts in exploiting new role of anions in various metal cluster systems. Anions can do much more than counterions for charge balance, and they should be considered in the design and synthesis of cluster-based functional materials.

Spin-glass behavior of a hierarchically-organized, hybrid microporous material, based on an extended framework of octanuclear iron-oxo units.

Inspired by the stepwise addition of octanuclear iron units into mammalian ferritin, a "stop-and-go" synthesis strategy was used to prepare two microporous (Langmuir surface area, 490 m(2) g(-1); effective pore size, 4-5 Å) hierarchical materials {[Fe8(μ4-O)4(μ-pz)12Cl0.3(μ-O)1.85}n () and {[Fe8(μ4-O)4(μ-4-Me-pz)12Cl0.4(μ-O)1.8}n (), which are new members of the EO2 family of polymeric materials (E = C, Si and Ge). The secondary building units (SBUs) E = [Fe8(μ4-O)4(μ-4-R-pz)12] (Fe8) are nanoscale pseudo-spherical clusters, rather than single atoms, forming μ-oxo Fe-O-Fe linkages between Fe8-SBUs. The characteristic Fe-O-Fe asymmetric stretching mode in the infrared (IR) spectra of these compounds appearing at around 800 cm(-1) suggest the formation of approximately linear μ-oxo Fe-O-Fe linkages between Fe8-SBUs in and . We employ the concept of continuous random network (CRN) to describe for the first time the framework features of a Fe8-based amorphous materials, in which the average connecting numbers of each Fe8-cluster are ∼3.7 and ∼3.6 for and , respectively. (57)Fe-Mössbauer spectroscopic analysis provides insights to the intercluster connectivity of and on one hand and to their magnetic properties on the other, evident by a magnetic split sextet below 30 K. The combination of Mössbauer spectroscopy and magnetism measurements reveals a spin-glass behavior with Tg of ∼30 K. The hierarchical porous materials and straddle the gap between metal oxides and metal-organic frameworks (MOFs). This study may open an alternative way for the development of multifunctional materials based on high nuclearity metal clusters.

Tripodal Tris-tacn and Tris-dpa Platforms for Assembling Phosphate-Templated Trimetallic Centers

Multidentate tripodal ligands, N(CH2-m-C6H4-CH2tacn)3 (L1) and N(CH2-o-C6H4-CH2N(CH2py)2)3 (L2), have been devised for assembling high-nuclearity metal clusters. By using the same tripodal platform with different ligand appendages, either triazacyclononanes or dipicolylamines, and functionalizing either the ortho or the meta positions on the tris(xylyl) linker arms, discrete trimetal phosphate units of relevance to phosphate-metabolizing trimetallic centers in biology were prepared. Four such compounds, [(Cu(II)Cl)3(HPO4)L1](PF6) (1), [(Cu(II)Cl)3(HAsO4)L1](PF6) (2), Na2[Mn(III)6Mn(II)2(H2O)2(HPO4)6(PO4)4(L1)2] (3), and [Co(II)3(H2PO4)Cl2(MeCN)L2](PF6)3 (4), all containing three metal centers bound to a central phosphate or arsenate unit bridging oxygen atoms, have been synthesized and structurally characterized. These results demonstrate the propensity of this novel tripodal ligand platform, in the presence of phosphate or arsenate, to assemble {M3(EO4)} units and thus structurally mimic trimetallic active sites of proteins involved in phosphate metabolism. Reactivity studies reveal that the tricopper complex 1 is more efficient than monocopper analogues in catalyzing the hydrolysis of 4-nitrophenyl phosphate.

Synthesis, structures, adsorption behaviour and magnetic properties of a new family of polynuclear iron clusters

Solvothermal reactions of 1,10-phenanthroline-2,9-dicarbaldehyde dioxime (H(2)phendox) with FeCl(3)·6H(2)O or FeBr(3) under solvothermal conditions yielded two trinuclear iron(III) clusters [Fe(III)(3)(mu(3)-O)(phendox)(3)]X·14H(2)O (X = Cl 1·14H(2)O, Br 2·14H(2)O) and three hexanuclear iron(III) and iron(II) clusters, [Fe(III)(6)(mu(4)-O)(2)(MeO)(6)X(4)(phendox)(2)]·MeOH (X = Cl , Br 4) and (H(3)O)[Fe(II)(6)(mu(6)-Cl)(phenda)(6)]·6H(2)O (5·6H(2)O). The phendox(2-) ligand is very useful in constructing magnetically active and stable high-nuclearity metal clusters in that the phenanthroline rings and the oxime nitrogen atoms grasp the metal ions tightly while the two oxygen atoms on the oximates can link other metal centres in the shortest pairwise magnetic exchange pathway. Adjacent Fe(3)(mu(3)-O)(phendox)(3)(+) motifs in 1 and 2 are packed by off-set pi-pi interactions of the aromatic rings on phendox(2-) to generate a 3D supramolecular architecture in the honeycomb topology and with 1D hexagonal channels in the dimension of 13 x 13 Å along the c-axis. 2 is stable upon the removal of guest molecules and the desolvated compound absorbed considerable amount of N(2), CO(2) and H(2). 3 and 4 are isostructural. Two mu(4)-O(2-) and two phendox(2-) units link four metal atoms into a coplanar butterfly-shaped unit with the mu(4)-O(2-) slightly above and below the plane (+/-0.264 Å). The other two Fe(III) ions are capped on the alternate planes via the three bridging mu(2)-methoxides and accordingly form an unprecedented hexanuclear Fe(III) cluster. Furthermore, the oximes underwent hydrolysis to yield carboxylate groups and the resulted 1,10-phenanthroline-2,9-dicarboxylate link the iron atoms to form a hexanuclear cluster of 5. Magnetic studies show that the antiferromagnetic interactions are present in the Fe(3)O core of 2 and in the (mu(6)-Cl)Fe(6)(mu-O)(12) core of 5.

Highly Porous and Robust 4,8-Connected Metal−Organic Frameworks for Hydrogen Storage

Highly porous and robust metal-organic frameworks (MOFs) were constructed based on aromatics-rich octa-carboxylate ligands and copper paddle-wheel building units. Each octa-carboxylate ligand is linked to eight copper paddle wheels via the bridging carboxylate groups in a rectangular prismatic fashion to lead to very rare (4,8)-connected networks of the scu topology. The high-connectivity MOFs show remarkably high porosity and framework stability, as evidenced by a perfect agreement between experimental and theoretical surface areas and the maintenance of framework powder X-ray diffraction patterns after solvent removal. These aromatics-rich MOFs exhibit an exceptionally high hydrogen uptake of up to 2.5 wt% at 77 K and 1 atm. This work thus demonstrates the ability to construct highly porous and robust functional MOFs using multidentate bridging ligands of high connectivity. Such a rational synthetic strategy is complementary to the common reliance on high-nuclearity metal clusters for building stable and porous MOFs.

Initial employment of α-benzoin oxime as a route to high-nuclearity metal clusters: decanuclear CuII complexes with a wheel topology

The initial employment of alpha-benzoin oxime (bzoxH2) in metal cluster chemistry has provided access to a new family of decanuclear CuII complexes with a loop or single-strand wheel topology; the CuII10 clusters are antiferromagnetically-coupled with an S=0 spin ground state, as expected for even-membered loop arrays of CuII atoms.

Employment of 2,6-Diacetylpyridine Dioxime as a New Route to High Nuclearity Metal Clusters: Mn6 and Mn8 Complexes

The employment of the anion of 2,6-diacetylpyridine dioxime (dapdoH2) as a pentadentate chelate in transition metal cluster chemistry is reported. The syntheses, crystal structures, and magnetochemical characterization are described for [Mn6O2(OMe)2(dapdo)2(dapdoH)4](ClO4)2 (1), [Mn6O2(OMe)2(dapdo)2(dapdoH)4][Ca(NO3)4] (2), and [Mn8O4(OH)4(OMe)2(N3)2(dapdo)2(dapdoH)2(H2O)2] (3). The reaction of [Mn3O(O2CMe)6(py)3](ClO4) with 3 equiv of dapdoH2 (with or without 2 equiv of NEt3) in MeOH gave 1. The same cation, but with a [Ca(NO3)4]2- anion, was found in complex 2, which was obtained from the reaction in MeOH between Mn(NO3)2, Ca(NO3)2, and dapdoH2 in the presence of NEt3. In contrast, addition of NaN3 to several reactions comprising MnCl2, dapdoH2, and NEt3 in MeOH gave the octanuclear complex 3. Complexes 1-3 all possess rare topologies and are mixed-valence: 2MnII, 4MnIII for 1 and 2, and 2MnII, 6MnIII for 3. The core of the cation of 1 and 2 consists of two edge-sharing Mn4 tetrahedra at the center of each of which is a micro4-O2- ion. Peripheral ligation is provided by two micro-OMe-, four micro-dapdoH-, and two micro3-dapdo2- groups. The core of 3 consists of two [MnIIMnIII3(micro3-O)2]7+ "butterfly" units linked together by one of the micro3-O2- ions, which thus becomes micro4. Peripheral ligation is provided by four micro-OMe-, two micro-OH-, two micro-dapdoH-, and two micro4-dapdo2- groups. Variable-temperature, solid-state dc and ac magnetization studies were carried out on complexes 1-3 in the 5.0-300 K range; the data for 1 and 2 are identical. Fitting of the obtained magnetization versus field (H) and temperature (T) data by matrix diagonalization and including only axial anisotropy (zero-field splitting, D) established that 1 possesses an S=5 ground state with D=-0.24 cm(-1). For 3, low-lying excited states precluded obtaining a good fit from the magnetization data, and the ground state was instead determined from the ac data, which indicated an S=1 ground state for 3. The combined work demonstrates the ligating flexibility of pyridyl-dioxime chelates and their usefulness in the synthesis of new polynuclear Mnx clusters without requiring the co-presence of carboxylate ligands.

Self-assembly of high-nuclearity metal clusters: programmed expansion of a metallasiloxane cage to an octacopper(II) cluster.

The novel octanuclear copper(II) cluster [Cu6[(PhSiO2)6]2[NCCu(Me6tren)]2(MeOH)4]2+ (1) has been isolated as a perchlorate salt by reacting the hexacopper(II) metallasiloxane cage [Cu6[(PhSiO2)6]2(nBuOH)x] (x = 4, 6) with [Cu(Me6tren)CN]ClO4 in a methanol/chloroform mixture (Me6tren = tris(2-(dimethylamino)ethyl) amine). Crystal data for 1(ClO4)2 x MeOH: monoclinic, space group P2(1)/n (no. 14), a = 16.8490(3) angstroms, b = 22.2966(4) angstroms, c = 17.2508(3) angstroms, beta = 94.7658(5) degrees, V = 6458.3(2) angstroms3, Z = 2. The structure comprises a highly distorted hexagonal Cu6 array linked to two [Cu(Me6tren)] units via cyanide bridges. Magnetic measurements reveal that the addition of the copper cyanide complexes dramatically affects the magnetism of the Cu6 unit, whose ground spin state changes from S = 3 to S = 0.

Gold nanoparticles a renaissance in gold chemistry

Vapour synthesis techniques have been used to prepare nanoparticulate dispersions of gold and other precious metals in non-aqueous solvents. The dimensions of these solvent-stabilised particles, which can be controlled within the 1–3nm size regime, effectively encompass the areas of molecular chemistry (as typified by high-nuclearity metal clusters) and the smaller colloidal metals. Gold nanoparticles differ from those of the other metals in exhibiting unusual time— and concentration-dependent behaviour. A regime of preparative conditions under which 1–3nm size gold particles, which are stable with respect to aggregation as a function of time, is defined. Some implications for these new developments are indicated.

Preparation, characterisation and properties of groups VIII and IB metal manoparticles

Vapour synthesis techniques have been used to prepare nanoparticulate dispersions of ruthenium, rhodium, palladium, platinum, silver and gold in non-aqueous solvents. The dimensions of these solvent-stabilised particles, which can be controlled within the 1–3 nm size regime, effectively encompass the areas of molecular chemistry (as typified by high-nuclearity metal clusters) and the smaller colloidal metals. The nanostructures have been characterised by high-resolution transmission electron microscopy and evidence for face-centred cubic (f.c.c.) octahedral, f.c.c. cuboctahedral and icosahedral metal particles obtained; quasi-molten states have also been observed in a number of these systems. In addition to discrete particles, larger aggregates of the small primary particles have been observed, some of which appear to be organometallic in nature. Gold nanoparticles differ from those of the Group VIII metals in exhibiting unusual time and concentration-dependent behaviour. A regime of preparative conditions under which 1–3 nm size gold particles, which are stable with respect to aggregation as a function of time, is defined. Some preliminary results of attempts to use laser mass spectrometry as a rapid method for the molecular mass determination of some of these materials are also described.

Paramagnetism of high nuclearity metal cluster compounds as derived from local density functional calculations

The electronic structure of high nuclearity carbonylated Ni clusters [Ni32C6(CO)32]n− and [Ni44(CO)48]n− (n=0–6) has been investigated by means of all-electron calculations within the local density functional approach. The transition from the molecular to the metallic state was studied by determining the magnetic properties of bare and carbonylated clusters. The appearance of the metallic magnetic behavior is connected with the presence of metal atoms with bulklike coordination. The effect of interstitial impurity atoms in quenching the magnetic moment is also discussed.

High nuclearity metal clusters: Miniature bulk of unusual structures and properties?

Recent developments in cluster synthesis have produced many high nuclearity metal clusters of discretesize andshape approaching that of small particles. Some of these clusters have metal arrangements resemblingfragments of metallic lattices and thus may be considered as aminiature bulk. Some are related to the quasicrystalline phase. Yet others have little or no structural features in common with that of the bulk. These metal clusters of definitivesize andshape provide an opportunity for the study of the evolution of band structure fromatomic tomolecular to thebulk. The focus of this review is on the unusual structures and properties of well-defined high nuclearity metal clusters and their possible relations or variant to the bulk state. Specifically, interesting electronic, optical, and magnetic properties of metal clusters in the quantum-size regime are described. Structural systematics of high nuclearity metal clusters, ranging from thecluster-of-clusters to thelayer-by-layer growth sequence, are discussed. It is hoped that further studies of the structures and properties of large metal cluster compounds of discretesize andshape will shed light on how, when, and why metallic or other bulk behavior begins and ends.