Metal Halide Clusters Research Articles

Predesigned synthesis of dinuclear to unusual hexanuclear to 1D coordination polymer of Cu(I)-halides and their and photophysical properties

Six new CuI− complexes, [CuI2(Br)2(L1)(PPh3)2] (1) [CuI2I2(L2)(PPh3)2] (2), [CuI2Cl2(L3)(PPh3)4] (3), [CuI2Br2(L3)(PPh3)4] (4), [(CuI)2{Cu2(μ-I2)}2(L4)3(PPh3)8] (5) and [CuI2(μ-I)2(μ-L5)(PPh3)2]n (6) (where PPh3 is triphenylphosphine and L1–L5 are N-heterocyclic ligands) have been designed, synthesized and characterized by single crystal X-ray diffraction (SC-XRD) study along with IR spectroscopic study. By changing the disposition of binding sites in ligands, metal-salts and reaction conditions we have controlled the structure of the complexes. SC-XRD analysis reveals that complex 1 and 2 have similar dinuclear structure, 3 and 4 have also similar dinuclear structures but different from the previous model, complex 5 is a hexanuclear and complex 6 is a 1D coordination polymer. Among these six crystal structures, only multimeric structures (5 and 6) contain -{CuI2-μ-X2} cores in their architecture. A detailed structural analysis reveals that -{CuI2-μ-X2}-core formation acts as the key step to design multimeric to higher dimensional structures and these core formation takes place at high temperature upon stoichiometric mixing of CuI–iodide, PPh3 with bidentate bridging N-heterocyclic ligands. The supramolecular structures of all the complexes have also been studied. Besides their intriguing structures, these complexes have rich photophysical properties. 1 and 2 have similar luminescence spectra, 3 and 4 have also similar luminescence spectra but different from the previous one. Complex 5 has complicated luminescence spectra having three peaks and complex 6 shows two peaks in the luminescence spectra. Molecular orbital calculation reveals that emissions of the complexes arise due to the charge transfer from metal-halide cluster to N-heterocyclic ligand.

Three silver (I) supramolecular compounds constructed from pyridinium or methylimidazolium polycations: Synthesis, crystal structure and properties

Three metal halide cluster supramolecular polymers, {(TBP)[Ag3Br6]}n (1), {(TBI)[Ag3Br6]}n (2) and {(TBP)[Ag3I6]}n(3) (TBP =1, 3, 5-tris(N-pyridinium methyl)benzene, TBI =1, 3, 5-tris(methylimidazole methyl)benzene), have been synthesized and characterized by thermoanalysis and spectroscopic methods, as well as single-crystal X-ray diffraction. Complexes 1, 2 and 3 all feature a one-dimensional chain structure, which is further extended by electrostatic attraction. The TGA, UV-Vis diffuse reflectance spectra in the solid state and optical band gap properties of the three complexes were also investigated.

Thermodynamics of small alkali metal halide cluster ions: comparison of classical molecular simulations with experiment and quantum chemistry.

We evaluate the ability of selected classical molecular models to describe the thermodynamic and structural aspects of gas-phase hydration of alkali metal halide ions and the formation of small water clusters. To understand the effect of many-body interactions (polarization) and charge penetration effects on the accuracy of a force field, we perform Monte Carlo simulations with three rigid water models using different functional forms to account for these effects: (i) point charge nonpolarizable SPC/E, (ii) Drude point charge polarizable SWM4-DP, and (iii) Drude Gaussian charge polarizable BK3. Model predictions are compared with experimental Gibbs free energies and enthalpies of ion hydration, and with microscopic structural properties obtained from quantum DFT calculations. We find that all three models provide comparable predictions for pure water clusters and cation hydration but differ significantly in their description of anion hydration. None of the investigated classical force fields can consistently and quantitatively reproduce the experimental gas-phase hydration thermodynamics. The outcome of this study highlights the relation between the functional form that describes the effective intermolecular interactions and the accuracy of the resulting ion hydration properties.

ChemInform Abstract: Characterization of Catalytically Active Octahedral Metal Halide Cluster Complexes

AbstractReview: 43 refs.

Characterization of Catalytically Active Octahedral Metal Halide Cluster Complexes

Halide clusters have not been used as catalysts. Hexanuclear molecular halide clusters of niobium, tantalum, molybdenum, and tungsten possessing an octahedral metal framework are chosen as catalyst precursors. The prepared clusters have no metal–metal multiple bonds or coordinatively unsaturated sites and therefore required activation. In a hydrogen or helium stream, the clusters are treated at increasingly higher temperatures. Above 150–250 °C, catalytically active sites develop, and the cluster framework is retained up to 350–450 °C. One of the active sites is a Brønsted acid resulting from a hydroxo ligand that is produced by the elimination of hydrogen halide from the halogen and aqua ligands. The other active site is a coordinatively unsaturated metal, which can be isoelectronic with the platinum group metals by taking two or more electrons from the halogen ligands. In the case of the rhenium chloride cluster Re3Cl9, the cluster framework is stable at least up to 300 °C under inert atmosphere; however, it is reduced to metallic rhenium at 250–300 °C under hydrogen. The activated clusters are characterized by X-ray diffraction analyses, Raman spectrometry, extended X-ray absorption fine structure analysis, thermogravimetry–differential thermal analysis, infrared spectrometry, acid titration with Hammett indicators, and elemental analyses.

Two new halide-containing polyoxometalate-based compounds

Two new compounds, [CuCl(Phen)(H2O)][PW12O40][4,4′-H2bpy]·1.5H2O (1) and [Cd2(Phen)4Cl2][HPMo12O40](4,4′-bpy) (2) (bpy = bipyridine, Phen = phenanthroline), have been hydrothermally prepared and characterized by IR, UV–vis, XPS, XRD, elemental analysis, cyclic voltammetry analysis, and single-crystal X-ray diffraction analysis. Compound 1 exhibits a 1-D chain structure constructed from polyoxometalates (POMs) and transition metal complexes, whereas 2 presents a supramolecular structure constructed from POMs, metal halide clusters, and organic ligands.

Heteroleptic, Dinuclear Copper(I) Complexes for Application in Organic Light-Emitting Diodes

A series of highly luminescent, heteroleptic copper(I) complexes has been synthesized using a modular approach based on easily accessible P^N ligands, triphenylphosphine, and copper(I) halides, allowing for an independent tuning of the emission wavelength with low synthetic efforts. The molecular structure has been investigated via X-ray analysis, confirming a dinuclear copper(I) complex consisting of a butterfly shaped metal-halide cluster and two different sets of ligands. The bidentate P^N ligand bridges the two metal centers and can be used to tune the energy of the frontier orbitals and therefore the photophysical characteristics, as confirmed by emission spectroscopy and theoretical investigations, whereas the two monodentate triphenylphosphine ligands on the periphery of the cluster core mainly influence the solubility of the complex. By using electron-rich or electron-poor heterocycles as part of the bridging ligand, emission colors can be adjusted, respectively, between yellow (581 nm) and deep blue (451 nm). These complexes have been further investigated in particular with regard to their photophysical properties in thin films and polymer matrix as well as in solution. Furthermore, the suitability of this class of materials for being applied in organic light-emitting diodes (OLEDs) has been demonstrated in a solution-processed device with a maximum current efficiency of 9 cd/A and a low turn-on voltage of 4.1 V using a representative complex as an emitting compound.

Two Challenges for Experimenters

In recent years, several theoretical studies have indicated potentially interesting, even perhaps surprising phenomena that could be observed by experiment--but have not yet been studied in the laboratory. Here we give the background and motivation for two of these, with the admitted goal of stimulating those experimental studies. The two topics: (1) the production and study of amorphous alkali metal halide clusters; (2) Penning detachment, the analogue of the well-studied Penning ionization, but in which an electron is detached from a negative ion, rather than from a neutral atom, by energy transfer in collision with an excited atom. The latter phenomenon could be particularly relevant for stellar atmospheres where negative ions are abundant. In each case, we indicate the implications and potential of having substantive experimental information about each, in effect explaining the motivation to carry out the experiments.

Holding onto Electrons in Alkali Metal Halide Clusters: Decreasing Polarizability with Increasing Coordination

The connection between the electronic polarizability and the decrease of the system size from macroscopic solid to nanoscale clusters has been addressed in a combined experimental and model-calculation study. A beam of free neutral potassium chloride clusters has been probed using synchrotron-radiation-based photoelectron spectroscopy. The introduction of "effective" polarizability for chlorine, lower than that in molecules and dimers and decreasing with increasing coordination, has allowed us to significantly improve the agreement between the experimental electron binding energies and the electrostatic model predictions. Using the calculated site-specific binding energies, we have been able to assign the spectral details of the cluster response to the ionizing X-ray radiation, and to explain its change with cluster size. From our assignments we find that the higher-coordination face-atom responses in the K 3p spectra increase significantly with increasing cluster size relative to that of the edge atoms. The reasons behind the decrease of polarizability predicted earlier by ab initio calculations are discussed in terms of the limited mobility of the electron clouds caused by the interaction with the neighboring ions.

First examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands

Two new organic–inorganic compounds based on polyoxometalates, metal halide clusters and organic ligands: [BW12O40]2[Cu2(Phen)4Cl](H24, 4′-bpy)4·H3O·5H2O (1) and [HPW12O40][Cd2(Phen)4Cl2](4, 4′-bpy) (2) (Phen=1, 10-phenanthroline, bpy=bipyridine), have been prepared and characterized by IR, UV–vis, XPS, XRD and single crystal X-ray diffraction analyses. Crystal structure analyses reveal that compound 1 is constructed from [BW12O40]5−, metal halide clusters [Cu2(Phen)4Cl]+and 4, 4′-bpy ligands, while compound 2 is constructed from [PW12O40]3−, metal halide cluster [Cd2(Phen)4Cl2]2+ and 4, 4′-bpy ligands. Compound 1 and compound 2 are not common hybrids based on polyoxometalates and metal halide clusters, they also contain dissociated organic ligands, therefore, compound 1 and 2 are the first examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands.

Structure and Bonding in Coinage Metal Halide Clusters MnXn, M = Cu, Ag, Au; X = Br, I; n = 1–6

Ab initio calculations in the framework of density functional theory (DFT) were performed to study the lowest-energy isomers of noble metal halide clusters M(n)Br(n) and M(n)I(n), for M = Cu, Ag, or Au and n = 1-6. For all species, the most stable structures were found to be cyclic arrangements. Calculated bond lengths and infrared frequencies were compared with the available experimental data. The nature of the ionocovalent bonding was characterized. The stability and fragmentation were also investigated. The present work confirms previous observations on the particular stability of the trimer.

New compounds based on polyoxometalates and metal halide clusters

Seven new compounds based on polyoxometalates and metal halide clusters have been synthesized and characterized by IR, XPS, UV-vis, XRD, elemental analyses and single crystal X-ray diffraction analyses. Compounds 1, 2, 3 and 4 are hybrids based on polyoxometalates and ennea-nuclear metal halide clusters, which are isomorphous to the compounds we reported recently. Compounds 5–7 are new examples of hybrids based on polyoxometalates and metal halide clusters, of which compounds 5 and 6 are the first examples of hybrids based on polyoxometalates and a new kind of hepta-nuclear metal halide cluster and compound 7 is the first example of hybrid based on polyoxometalates and octakaideca-nuclear metal halide clusters. In addition, compounds 2, 3 and 4 are the first examples of hybrids based on polyoxometalates and metal bromide clusters, and compounds 5 and 6 are the second examples of hybrids based on polyoxometalates and metal iodine clusters. Furthermore, compound 7 is the first example of compounds based on POMs and metal halide extended structures.

W3Cl10(Hg2Cl2)2, A Reactive One-Dimensional Polymer of Triangular Tritungsten Clusters with Terminal and Intercluster-Bridging Mercurous Chloride Ligands: Main Group Metal Halide By-Products as Versatile Ligands in Reductive Synthesis of Early Transition Metal Halide Clusters

Solid-state reduction of WCl6 with Hg followed by incomplete sublimation of mercury chlorides generated the tritungsten decachloride—mercury chloride adducts W3Cl10(Hg2Cl2)2−x(HgCl2)x. Thermal equilibration of the solid-state products followed by sublimation of HgCl2 afforded single crystals that include the mercurous chloride adduct W3Cl10(Hg2Cl2)2. Single-crystal diffractometry revealed a one-dimensional polymer of tritungsten decachloride triangular clusters with novel terminal and inter-cluster-bridging ClHgHgCl ligands. The W3 cluster core has similar metrics to that of the benzyltriethylammonium salt of W3(μ3-Cl)(μ-Cl)3Cl9 3−. W3Cl10(Hg2Cl2)2 is the first reported adduct of the binary tungsten chloride W3Cl10. The ClHgHgCl ligands are more labile that the terminal chlorine atoms of W3(μ3-Cl)(μ-Cl)3Cl9 3−. These results demonstrate diverse roles and potential utility of main group element halide by-product ligands in solid-state reductions of transition metal halides.

Coinage Metal Halide Clusters: From Two‐Dimensional Ring to Three‐Dimensional Solid‐State‐Like Structures

Coinage Metal Halide Clusters: From Two‐Dimensional Ring to Three‐Dimensional Solid‐State‐Like Structures

Vapor-phase synthesis of 1,2-dihydro-2,2,4-trimethylquinolines from anilines and acetone over group 5–7 metal halide clusters as catalysts

Reaction of aniline with acetone to form 1,2-dihydro-2,2,4-trimethylquinoline ( 1) was studied in a gas-phase reaction over halide clusters as solid acid catalysts. After activation of a niobium halide cluster, [(Nb 6Cl 12)Cl 2(H 2O) 4]·4H 2O ( 2), which has an octahedral metal framework, at an elevated temperature in a hydrogen stream for 1 h, reaction was initiated by introduction of stoichiometric amounts of aniline and acetone at the activation temperature. The catalysis to yield 1 became evident above 200 °C. Both the catalytic activity of 2 and the selectivity for 1 increased with increasing temperature, having a local maximum at 300 °C. The selectivity for 1 was 76% with 34% conversion at 450 °C. Reactions of o-, m-, and p-toluidines with acetone also produced the corresponding quinolines. The chloride clusters of tantalum with the same metal framework and rhenium with a triangular metal framework also catalyzed the condensation. Thus, a halide cluster can be a substitute for liquid acid, particularly at high temperatures.

Superionicity Study from Electronic State Calculation of Metal Halide Cluster

The electronic states of silver halides and sodium halides are calculated by the DV-Xα cluster method to get more microscopic evidence for the p – d hybridization in noble metal halides. The calculations are carried out for the (A 13 B 14 ) - (A=Ag + and Na + , B = halogen ion) clusters. It is found that both components of anti-bonding and bonding exist in the diagram of overlap population (DOP) for AgX (X=halogen) and these two components are made up of the 4 d band of Ag + and the p band of halogen ion, which form the p – d hybridization. On the other hand, the DOP of alkali halides is occupied by almost only bonding component. It is inferred that the origin of AgI type superionic conductor is in the weakness of p – d hybridization. The hypothetical rock-salt AgI is also discussed to investigate the unstableness of rock-salt AgI.

Beyond the Conventional Number of Electrons in M6X12 Type Metal Halide Clusters: W6Cl18, (Me4N)2[W6Cl18], and Cs2[W6Cl18

AbstractFor Abstract see ChemInform Abstract in Full Text.

Electronic fine tuning of the structures of reduced rare-earth metal halides.

Electronic band-structure calculations on Pr3I3Ru and Y3I3Ru have been performed in order to analyze the large structural differences found in these isoelectronic compounds. These constitute two structural extremes within the family of monoclinic Re3I3Ru phases (RE = rare-earth metal) that exhibit distortions ranging from one-dimensional double chains of trans-edge-sharing octahedra (bioctahedral chains, BOH) to one-dimensional chains of trans-edge-sharing square pyramidal units bonded base to base (bisquare pyramidal chains, BSP). The structure of La3I3Ru was established by single-crystal X-ray diffraction (monoclinic, P2(1)/m, Z = 4, a = 9.343(1) A, b = 4.3469(8) A, c = 12.496(3) A, beta = 93.42(2) degrees) and found to be isomorphous with the BOH Pr3I3Ru. It is determined that the structural variation in this RE3I3Z family of materials depends largely on the differences in orbital energies between the corresponding rare-earth metal and the interstitial. These bonding considerations can be generalized to account for structural variations in a variety of other rare-earth halides as well as several group 4 or 5 reduced metal halide cluster phases.

Structures and Stabilities of CaO and MgO Clusters and Cluster Ions: An Alternative Interpretation of the Experimental Mass Spectra

The structures and relative stabilities of doubly charged nonstoichiometric (CaO)nCa2+ (n = 1−29) cluster ions and of neutral stoichiometric (MgO)n and (CaO)n (n = 3, 6, 9, 12, 15, 18) clusters are studied through ab initio perturbed ion plus polarization calculations. The large coordination-dependent polarizabilities of oxide anions favor the formation of surface sites, making the critical cluster size where anions with bulk coordination first appear larger than that found in the related case of alkali metal halides. Thus, we show that there are substantial structural differences between alkali metal halide and alkaline earth oxide cluster ions, contrary to what is suggested by the similarities in the experimental mass spectra. An alternative interpretation of the magic numbers for the case of oxides is proposed, which involves an explicit consideration of isomer structures different from the ground states. A comparison with the previously studied (MgO)nMg2+ cluster ions shows that the emergence of bulklike structural properties with size is slower for calcium oxide. Nevertheless, the structures of the doubly charged clusters are rather similar for the two materials. By contrast, the study of the neutrals reveals interesting structural differences between MgO and CaO, similar to those found in the case of alkali metal halides.

Binding energies of alkali metal halide cluster ions: calculated by electrostatic models and measured by the kinetic method

Experimental measurement of the binding energy of gaseous alkali halide clusters has been difficult. Recently, Chen and Cooks (J. Mass Spectrom. 1997;32:1258) reported the application of the kinetic method to the measurement of relative bond dissociation energies via competitive fragmentation of mixed ionic clusters [M1XM2]+ generated in a mass spectrometer. In this study the binding energies of various alkali metal halide cluster ions of the form [M1XM2]+ or [X1MX2]− have been calculated using both the rigid-ion model and the polarizable-ion model. The kinetic method was employed to measure the dissociation energies of triatomic cluster ions consisting of different alkali metal ions and halides. Good correlations between the calculated and measured differences in competitive dissociation energies were found for both positively and negatively charged cluster ions. Results further demonstrate the applicability of the kinetic method to measuring the relative bond dissociation energies for ionic compounds. However, it is noted that the kinetic method does not measure the absolute bond dissociation energy between a cation and an anion in the initial state of the tri-atomic cluster ion.