Bonding Characteristics of the Intermetallic Compound Al_3Ti+Cr

Based on our structural model and a tight-binding Hamiltonian the eIectronic structure has been calculated by use of a recursion method (RM) for two models of the tetragonal DO22 and the cubic Ll2 crystal structures in Al3Ti+Cr for contrast, from which bonding characteristics have been discussed. The results for the interaction energy (IE) show that Cr prefers to replacing Al site. Cr partly replacing Al can change the IE between the atoms and make the constriction of lattice constant c and the elongation of lattice constant a for the DO22 and thereby may induce the change of crystal structure from DO22 to L12. The results for bond order integral (BOI) and IE between the atoms also show that the strong (110) directional Cr-Ti bondings are existed.Thus, Al3Ti-base intermetallic compounds with addition of the Cr atom still remain brittle.

Bonding, Structure and Uses of Metals

This work briefly describes some of the different features of groups of metals.It highlights recent progress in research into metals.It details the structures and defects in solid metals.The common theories of metals including the free electron theory,band theory,the ions in a sea of electrons model and the soft sphere model are discussed and their merits are considered.It describes distinctions between the bonding in metals and inter-metallic compounds.It shows the influence of bonding on the properties of metals and alloys and provides a summary of tradition and newer uses of metals.

AROMATIC BOND INCLUDING METALLIC ATOM IN COORDINATE COMPOUNDS AND SOME OF ITS PROPERTIES

Aromatic bond including metallic atom (Ni) is investigated by EHMO calculation.The NMR spectra and the mechanism for hydrolysis are discussed on the ground of results of computation.

The role of 3d orbitals in the bonding of phosphorus compounds

Ab initio LCAO-MO-SCF calculations for several typical molecules containing phosphorus have been undertaken to study the role of phosphorus 3d orbitals in the bonding.It is emphasized that the discussion about the 3d orbital participation in bonding should be based on a reasonable choice of basis sets and it seems suitable to choose the atomic orbitals in proper molecular environment as the basis set.As an approximation,the optimized minimal STO-NG basis sets have been adopted in the present paper.The results obtained well exhibit the model of 3d orbital participation in bonding. It is shown that under the influence of highly electronegative ligands the phosphorus 3d orbitals con- tract greatly,their energy levels drop considerably,and thus they can effectively participate in bond- ing.The presence of highly electronegative ligands seems necessary.The contribution of 3d orbitals to bonding is achieved mainly through the concertedformation of σ bonds and p-d backbonds,though the contribution to σ bonding is minor.The three-center,four-electron bond modelis only approxi- mately correct.The results of the present paper demonstrate that the model of 3d orbital participation in bonding favoured by experimental chemists is reasonable and possesses sound ground.

The role of the sulfur 3d orbitals in bond formation in sulfur-containing compounds

The role of the sulfur 3d orbitals in bond formation is discussed by taking into account the influence of the environment on the orbitals of the sulfur atom in the molecules. The ca cula- tion results of a series of prototype molecules containing sulfur such as SF_2, SF_4, NSF_3, SF_1, H_2S are reported. It is convincingly shown that in highly electronegative environment the energy levels of the sulfur 3d orbitals are reduced to the vicinity of those of the ligand valence orbitals and their spatial distributions are contracted to the bonding area, and therefore they can participate in bond formation to a certain extent, which is enhanced by the formation of the d-p π back bonds. It seems that the result reported in this paper is helpful for the solution of the long-standing debate about the sulfur 3d orbital participation in bond formation.

Recent Progresses in Experimental and Theoretical Studies of Actinide Clusters

Actinide-containing cluster compounds are highly important in radio-and nuclear chemistry.Until three decades ago,little attention had been paid to these heavy-element clusters because of difficulties in their syntheses and characterization as well as handling of these radioactive and chemotoxic elements.In this overview article we have selectively summarized the recent progresses in experimental and theoretical studies on actinide clusters,including actinide(An=Th,Pa,U,Np and Pu)oxide clusters as well as uranyl(UO22+)peroxide clusters and so on.It shows that An(Ⅳ)(An=Th,U,Np and Pu)is able to form highly symmetric AnⅣ6O8 core clusters and further merge into larger clusters up to An38O56 clusters(An=U,Np and Pu)with the same topology.Meanwhile,An with higher oxidation states such as U(Ⅵ)in uranyl is capable to form fullerene-like peroxide cage clusters of U20,U60 with the same topology as C20 and C60.Relativistic quantum chemistry investigations on the geometric structures,electronic structures and chemical bonding patterns have also been briefly summarized herein to provide an understanding on the structural chemistry of these peculiar clusters.The advances in electronic structure studies of actinide clusters help to develop robust theoretical and computational techniques for the future development of actinide cluster chemistry.Further experimental and computational studies of actinide clusters are needed and helpful to accelerate the development of radio-and nuclear chemistry.

Recent Progresses in the Investigation of Rare-earth Boron Inverse Sandwich Clusters

While rare-earth borides represent a class of important materials in modern industries,there are few fundamental researches on their electronic structures and physicochemical properties.Recently,we have performed combined experimental and theoretical studies on rare-earth boron clusters and their cluster-assembled complexes,revealing a series of rare-earth inverse sandwich clusters with fascinating electronic structures and chemical bonding patterns.In this overview article,we summarize recent progresses in this area and provide a perspective view on the future development of rare-earth boride clusters.Understanding the electronic structures of these clusters helps to design materials of f-element(lanthanide and actinide)borides with critical physiochemical properties.