Alkaline-earth Clusters Research Articles

The many-body expansion for metals. I. The alkaline earth metals Be, Mg, and Ca

We examine the many-body expansion (MBE) for alkaline earth metal clusters, Ben, Mgn, Can (n = 4, 5, 6), at the Møller–Plesset second order perturbation theory, coupled-cluster singles and doubles with perturbative triples, multi-reference perturbation theory, and multi-reference configuration interaction levels of theory. The magnitude of each term in the MBE is evaluated for several geometrical configurations. We find that the behavior of the MBE for these clusters depends strongly on the geometrical arrangement and, to a lesser extent, on the level of theory used. Another factor that affects the MBE is the in situ (ground or excited) electronic state of the individual atoms in the cluster. For most geometries, the three-body term is the largest, followed by a steady decrease in absolute energy for subsequent terms. Though these systems exhibit non-negligible multi-reference effects, there was little qualitative difference in the MBE when employing single vs multi-reference methods. Useful insights into the connectivity and stability of these clusters have been drawn from the respective potential energy surfaces and quasi-atomic orbitals for the various dimers, trimers, and tetramers. Through these analyses, we investigate the similarities and differences in the binding energies of different-sized clusters for these metals.

A new 2D network polyoxometalate constructed from Strandberg-type phosphomolybdates linked through binuclear Ca(II) clusters

A polyoxometalate cluster based on Strandberg-type phosphomolybdate [K 3 Ca(H 2 O) 4 (HP 2 Mo 5 O 23 )]·6H 2 O ( 1 ) has been synthesized by the conventional solution method and characterized by IR spectrum, UV spectra, electrochemical measurements, thermogravimetric analysis, ICP techniques and X-ray crystallography. X-ray single crystal diffraction analysis shows that 1 contains a novel polyoxoanion [Ca(H 2 O) 4 (HP 2 Mo 5 O 23 )] 3− ( 1a ) based on a Strandberg-type phosphomolybdate [HP 2 Mo 5 O 23 ] 5− . Notably, it represents the first 2D polymolybdate inorganic structure constructed from Strandberg-type phosphomolybdates linked through alkaline earth metal clusters. Interestingly, the phenomenon that 1a and heteropolyoxoanion {[Ca(H 2 O)] 6 [P 4 Mo 6 O 34 ] 2 } 12− can be mutually transformed when the pH of the solution is adjusted to ca. 4.50 in aqueous solution has been observed. A polyoxometalate cluster based on Strandberg-type phosphomolybdate [K 3 Ca(H 2 O) 4 (HP 2 Mo 5 O 23 )]·6H 2 O has been synthesized by the conventional solution method and characterized by IR spectra, UV spectra, electrochemical measurements, TG analyses and X-ray crystallography. The interesting phenomenon that 1a and heteropolyoxoanion {[Ca(H 2 O)] 6 [P 4 Mo 6 O 34 ] 2 } 12− can be mutually transformed when the pH of the solution is adjusted to ca. 4.50 in aqueous solution has been observed. ► A polyoxometalate cluster based on Strandberg-type phosphomolybdate [K 3 Ca(H 2 O) 4 (HP 2 Mo 5 O 23 )]·6H 2 O has been synthesized by the conventional solution method and characterized by IR spectra, UV spectra, electrochemical measurements, TG analyse and X-ray crystallography. ► The polyoxometalate represents the first inorganic 2D layer Strandberg-type phosphomolybdate. ► The polyoxometalate enriches the structural diversity of Strandberg-type polyoxometalates. ► The heteropolyoxoanions [Ca(H 2 O) 4 (HP 2 Mo 5 O 23 )]3– and {[Ca(H 2 O)] 6 [P 4 Mo 6 O 34 ] 2 } 12– can be mutually transformed when the pH of solution is adjusted to ca . 4.50 in aqueous solution.

Erratum: Tuning aromaticity in trigonal alkaline earth metal clusters and their alkali metal salts

Page 2766. After several tests, in our previous manuscript,1 we concluded that “the 1A1′(σ) state is the ground state of cyclo-[M3]2− (M = Be, Mg, and Ca) species.” After the publication of our work, Giri et al.2 reported that the triplet state for these cyclo-[M3]2− species is more stable than the singlet one. In view of this conclusion, we revised our results and we find that the triplet state one reaches depends on the initial molecular orbitals (MOs) guess. Thus when one optimizes the triplet state starting from the (MOs) of the 1A1′(σ) state one reaches a different minimum than when the initial MOs are those of the 1A1′(π) state (see Figure 1). The former guess leads to the triplet states that were found in our previous paper1 and that are higher in energy than the 1A1′(σ) states (see Table1). On the other hand, when the triplet states are optimized starting from the MOs of the 1A1′(π) state, one reaches a more stable triplet state that, in fact, is the ground state for these species at both the B3LYP and CCSD(T) levels of theory (see Table2). Notwithstanding, note that for the cyclo-[Ca3]2− compound the singlet state remains more stable than the triplet state at the CCSD(T) level of theory. In fact, among singlet states, the σ-HOMO singlet configuration is the fundamental electronic state for cyclo-[Ca3]2− at the CCSD(T) level of theory (at variance with the cyclo-[Be3]2− and cyclo-[Mg3]2− where the π-HOMO singlet configuration is more stable). In summary, the ground stateof cyclo-[M3]2− species (M = Be and Mg) species is a triplet state and not a singlet one as we erroneously pointed out in our earlier publication.1 Molecular orbital picture of 1A1′(σ) and 1A1′(π) electronic configurations found in cyclo-[M3]2− clusters (M = Be, Mg, and Ca).

ChemInform Abstract: Formation of Metal Clusters in Alkaline-Earth-Cation-Exchanged X Zeolites.

Alkaline-earth-cation-exchanged X zeolites were reacted with sodium metal vapor and studied by electron spin resonance (ESR), diffuse reflectance (DR), and far-infrared (far-IR) spectroscopies. The ESR results show that alkaline-earth-metal clusters formed inside the zeolites. The temperature dependence of the ESR intensity indicated that the cluster size is constrained by the zeolite so that there is a quantum size effect on the small alkaline-earth metal clusters formed. The DR spectra show colors consistent with discrete energy levels and a quantum size effect. Electron transfer from sodium atoms to exchanged cations in the zeolites is also indicated by far-IR data for Mg-X and Ba-X zeolites. 14 refs., 17 figs., 3 tabs.

Tuning aromaticity in trigonal alkaline earth metal clusters and their alkali metal salts

In this work, we analyze the geometry and electronic structure of the [X(n)M(3)](n-2) species (M = Be, Mg, and Ca; X = Li, Na, and K; n = 0, 1, and 2), with special emphasis on the electron delocalization properties and aromaticity of the cyclo-[M(3)](2-) unit. The cyclo-[M(3)](2-) ring is held together through a three-center two-electron bond of sigma-character. Interestingly, the interaction of these small clusters with alkali metals stabilizes the cyclo-[M(3)](2-) ring and leads to a change from sigma-aromaticity in the bound state of the cyclo-[M(3)](2-) to pi-aromaticity in the XM(3) (-) and X(2)M(3) metallic clusters. Our results also show that the aromaticity of the cyclo-[M(3)](2-) unit in the X(2)M(3) metallic clusters depends on the nature of X and M. Moreover, we explored the possibility for tuning the aromaticity by simply moving X perpendicularly to the center of the M(3) ring. The Na(2)Mg(3), Li(2)Mg(3), and X(2)Ca(3) clusters undergo drastic aromaticity alterations when changing the distance from X to the center of the M(3) ring, whereas X(2)Be(3) and K(2)Mg(3) keep its aromaticity relatively constant along this process.

Accurate ab Initio Binding Energies of Alkaline Earth Metal Clusters

The effects of basis set superposition error (BSSE) and core-correlation on the electronic binding energies of alkaline earth metal clusters Y(n) (Y = Be, Mg, Ca; n = 2-4) at the Moller-Plesset second-order perturbation theory (MP2) and the single and double coupled cluster method with perturbative triples correction (CCSD(T)) levels are examined using the correlation consistent basis sets cc-pVXZ and cc-pCVXZ (X = D, T, Q, 5). It is found that, while BSSE has a negligible effect for valence-electron-only-correlated calculations for most basis sets, its magnitude becomes more pronounced for all-electron-correlated calculations, including core electrons. By utilizing the negligible effect of BSSE on the binding energies for valence-electron-only-correlated calculations, in combination with the negligible core-correlation effect at the CCSD(T) level, accurate binding energies of these clusters up to pentamers (octamers in the case of the Be clusters) are estimated via the basis set extrapolation of ab initio CCSD(T) correlation energies of the monomer and cluster with only the cc-pVDZ and cc-pVTZ sets, using the basis set and correlation-dependent extrapolation formula recently devised. A comparison between the CCSD(T) and density functional theory (DFT) binding energies is made to identify the most appropriate DFT method for the study of these clusters.

Electronic properties of mixed lithium-oxygen clusters

Herein electronic structure as a function of cluster size has been probed through ionization potentials measurements in order to derive general trends in the evolution of the structure and stability of lithium oxide clusters LinOm. The structural evolution was investigated by varying progressively the oxygen rate in order to observe transitions from the metallic Lin to the ionic structure (Li2O)n. We have demonstrated that this structural transition splits into three specific ranges. This result, in contrast with the general behavior observed with other electronegative elements combined with alkaline or alkaline-earth metal clusters, but similar to what is known about BanOm and CsnOm, constitutes a signature of a specific role played by the oxygen atoms when included inside a metallic cluster.

Structures of Alkali and Alkaline Earth Metal Clusters with Oxygen Donor Ligands

AbstractFor Abstract see ChemInform Abstract in Full Text.

Structures of alkali and alkaline earth metal clusters with oxygen donor ligands

This review based on 169 references gives an actual overview on group 1 and 2 clusters with oxygen donor ligands. A first part deals with alkali metal compounds of which synthesis and the most important structurally characterized examples a presented in detail. Homo- and heterometallic aggregates of group 1 metals as well as mixed group 1 and 2 compounds are classified with respect to the ligand type. Finally, alkaline earth metal clusters are treated, starting with Mg-compounds, then pursuing with the heavier homologues. This chapter also contains a brief description of CVD and sol-gel methods.

Recent Advances in the Chemistry of Clusters and Inorganic Polymers of Alkali and Alkaline Earth Metal Compounds

AbstractFor Abstract see ChemInform Abstract in Full Text.

σ-Aromaticity and σ-Antiaromaticity in Alkali Metal and Alkaline Earth Metal Small Clusters

We extended the aromaticity concept to small σ-aromatic alkali metal and alkaline earth metal clusters. We performed ab initio calculations (B3LYP/6-311+G* and CCSD(T)/6-311+G*) on a selected group...

Recent Advances in the Chemistry of Clusters and Inorganic Polymers of Alkali and Alkaline Earth Metal Compounds

This contribution gives an overview on the different subjects treated in our group during the last four years. First, the concept of cutting out structural fragments from a solid-state structure will be explained on behalf of BaI2. Oxygen donor ligands, used as chemical scissors on BaI2, enabled three-, two-, one- and zero-dimensional derived compounds to be obtained depending on their size and concentration. Thus, a structural genealogy tree for BaI2 can be established. A second section deals with the supramolecular approach for the synthesis of different dimensional polymer structures derived from alkaline earth metal iodides, and based on the combination of metal ion coordination with hydrogen bonding between the cationic complexes and their anions. Under certain circumstances, rules can be established for the prediction of the dimensionality of a given compound, thus contributing to the problem of structure prediction in crystal engineering. A third part describes a new synthetic pathway for generating homometallic alkaline earth metal clusters as well as group 1 and 2 mixed metal clusters as potential precursors for oxide materials. Finally, some physical properties of these compounds are described qualitatively in order to show the wide spectrum of possibilities and potential applications for the chemistry in this field.

Nature of binding in the alkaline–earth clusters: Be3, Mg3, and Ca3

The study of the interaction energy and its many-body decomposition in a broad distance interval for the Ben, Mgn, and Can (n=2,3) clusters at the SCF and MP4 levels are performed. A comparative analysis of the obtained results allows one to conclude that the only stabilization factor in the dimers is the dispersion forces. So, the alkaline–earth dimers can be attributed to the van der Waals molecules. The trimers are stabilized by the two-body localized dispersion forces and three-body delocalized exchange forces. The binding in the alkaline–earth trimers has a mixed physical (van der Waals) and chemical (nonadditive exchange) nature. An NBO population analysis reveals a relatively large p-population in all clusters. A surprisingly large p-population at the MP4 level is also obtained for the isolated atoms.

Fission of multiply charged alkaline earth metal clusters

We have studied the fission of multiply photoionized alkaline earth metal clusters having charges up to Z = +5 by means of high-resolution time-of-flight mass spectrometry. The determined appearance sizes can be compared to results of simple model calculations assuming that both fragments can still be treated as metallic liquid droplets. In this case the measured appearance sizes for the alkaline earth metals are found to be smaller than the ones predicted by the calculations. However, if one fixes the small fragment to be an atomic ion, good agreement between measurement and theory is acheived.