A theoretical study on the magneto-structural correlation in binuclear Cu (Ⅱ) complexes bridged by the imidazolate anion has been performed using the broken-symmetry approach with the framework of density functional theory (DFT). The calculated results show that the variational trends of the magnetic coupling constant J with geometrical parameters are different for two models. The magnetic coupling constant J mainly depends on the Cu-N-C (im) bond angle ф and is insensitive to the variation of the Cu-N (im) distance and the dihedral angle a between the bridged imidazolate ring and copper coordination planes. The dependence of J on the angle ф in the two models shows that the J values are equal when the Cu-N-C(im) angle f 128.

The theoretical study on magneto-structural correlation in axially coordinated copper (Ⅱ)-nitronyl nitroxide complex has been performed using the broken symmetry approach with the framework of density functional theory. The exchange interaction between Cu (Ⅱ) ion and nitronyl nitroxide radical is propagated through a mechanism involving interaction between orthogonal orbitals. The spin density population shows that the electron transfer takes place from the Cu (Ⅱ) ion to nitronyl nitroxide radical. The magnetostructural correlations indicate that both the variations of Cu-O distance and the Cu-O-N angle have significant influence on the magnetic exchange interaction.

The geometrical structures and relative stability of the various possible isomers of silicon-oxygen-sulfur oligomers, (SiOS)n (n=1-6), were studied using quantum chemistry calculations. The linear monomer with Si atom bonding to both O and S atoms is the ground state isomer, and the rhombic chains of four-membered rings are the most stable configurations for n=2-4, while the hybrid structures by the 4MRs and hexagonal six-membered ring become energetically most favorable for n=5 and n=6. Vibrational frequency calculations show that the characteristic IR signatures occur at 1290cm 1 for n=1, at the vicinity of 900cm forn=2-4, and at about 1080cm 1 for n=5-6. These distinctive spectra would provide guide for future experimental detections of these small Si-O-S oligomers.

G-tetrad and other 6-thioguanine (SG) incorporated tetrads have been studied in this Letter. The geometries, energies, charge distributions have been discussed. The effects of different cations (K+ and Na+) on the various tetrads have also been studied. The outcomes show that as the SG number increases the tetrad becomes more and more unstable. The Na+ binds more tightly with the tetrad than that of K+ without hydration correction, while considering hydration effects the stability sequence changes to K+>Na+. Electrostatic potential map of the tetrads have been plotted and the binding sites of cations have been also shown.

In an effort to search for new inorganic fullerene-like structures, we designed a series of novel silicon-carbon cages, (SiC)n (n=6-36), based on the uniformly hybrid Si-C four-and six-membered-rings, and researched their geometrical and electronic structures, as well as their relative stabilities using the density function theory. Among these cages, the structures for n=12, 16, and 36 were found to been energetically more favorable. The calculated disproportionation energy and binding energy per SiC unit show that the (SiC) 12 cage is the most stable one among these designed structures. The present calculations not only indicate that silicon-carbon fullerenes are promised to be synthesized in future, but also provide a new way for stabilizing silicon cages by uniformly doping carbon atoms into silicon structures.