Rb Huang

A theoretical study for the isomers of neutral, cationic and anionic phosphorus clusters P5, P7, P9

Abstract The cations and anions of P 5 , P 7 and P 9 exhibit intensities of significance on the mass spectra of phosphorus clusters produced in direct laser vaporization. We have acquired in the total fifty isomers of P 5 , P 7 , P 9 and their cations and anions by means of the B3LYP, DFT method. According to total energies, the most stable isomers have been predicted. A cationic cluster prefers to adopt structures with an atom(s) which is four-fold coordinated. The planar pentagon structure is a frequent sub-unit in the phosphorus clusters. Both tetrahedral P 4 and cuneane P 8 are common components of the clusters and can be considered as important units for the construction of large clusters.

The prediction of isomers for phosphorus clusters P-8 and P-9(+)

Abstract In the study of cationic phosphorus clusters produced in direct laser vaporization, it has been realized that P 8 and P 9 + are entities to be considered in mass spectrum interpretation. We acquired 20 P 8 and 19 P 9 + isomers with molecular graphics and then carried out optimizations with molecular mechanics, PM3 semi-empirical and ADF density functional calculations. In these isomers, the phosphorus atoms adopt twofold, threefold or fourfold coordination. According to the bonding energies, the cage-shape models are more stable than the planar ones, and the models with a large planar ring are the least stable. The most stable cuneane P 8 structure with 12 single bonds was adopted as the basic unit for polymerization. By adding a phosphorus atom to the bottom right side of cuneane and assuming a positive charge for optimization, we derived P 9 + isomers and identified the one with the lowest bonding energy. We detected that the P 9 + isomers with double bonds are less stable and the distortion of P 9 + isomers with high symmetry would result in lower bonding energies.

Crystal structure of a 3D coordination polymer: Zinc terephthalate hydrate

Figure 1. ORTEP plot of a portion of the ID zigzag chain formed in zinc terephthalate hydrate. The diagram was drawn at the 50% probability level and hydrogen atoms have been omitted for clarity. Selected bond distances and angles: Znl-Ol 1.9446(17), Zn l -03 1.978(3), Zn l -026 2.1829(17) Ä; O l -Zn l -O la 138.68(12), 01 -Zn l -03 110.66(6), 01-Znl -026 88.43(7), 03-Znl -02b 87.14(5), 01-Znl -02c 93.58(7), 02A-Zn 1 -02c 174.28(9)°. Symmetry transformation: a = x, y, z+5/2, b = x, -y+1, z+1/2, c = x, y+1, -z+2.

MASS-DISTRIBUTION OF CLUSTER IONS PRODUCED FROM LASER-ABLATION OF METAL-COMPOSITE-OXIDES Y-M-CU-O (M=BA, SR, CA, MG)

Laser ablation of YMCuO metal-composite-oxides (M=Ba, Sr, Ca, Mg) in high vacuum produced cluster ions with various sizes and compositions. Mass spectra of the cluster ions were recorded by a home-built time-of-flight (TOF) mass spectrometer and the mass distributions were analyzed by a statistical model. For YBa2Cu3O7−x (YBCO) high-Tc superconducting samples, six series of cluster ions were observed. Replacement of barium in the metal-composite-oxide sample with other alkaline earth metal, such as strontium, calcium, or magnesium, not only removed the superconductivity, but also changed the compositions and distributions of the laser generated cluster ions. For instance, copper was only found in the compositions of cluster ions generated from YBCO sample. From comparison of the experimental results, interactions among components of the metal-composite-oxides and the function of alkaline earth metal in superconducting material were discussed.

THE PREDICTION OF ISOMERS FOR THE PHOSPHORUS CLUSTERS P7

In the study of cationic phosphorus cluster produced in direct laser vaporization, it has been observed P7· shows the highest intensity in the mass spectrum. We acquired twenty-four P7· isomers with molecular graphics and then carried out optimizations with molecular mechanics, PM3 semi-empirical and ADF density functional calculations. In these isomers, the phosphorus atoms could be in two-fold, three-fold, four-fold or six-fold coordination. P7 which derived from the most stable Ρβ by adding a phosphorus atom against the double bond has the lowest bonding energy. When there is a six-fold atom in the structure, the d orbital is involved in bonding. According to the bonding energies, the models with a planar ring or a six-fold atom are relatively less stable.