ABSTRACT
The transition-metal centered boron molecular wheels have attracted the attention of chemists. The highest deca-coordination number for central metal atoms was observed in D 10h Ta©B10 - and Nb©B10 - molecular wheels. Here, we report a theoretical study of La©B8C4 q (q = +1, 0, -1) clusters with the dodeca-coordinated La atom. The La©B8C4 q clusters adopt fascinating molecular wheel structures, showing a La atom enclosed by a perfect B8C4 monocyclic ring. The cationic La©B8C4 + cluster has a C 4v symmetry with the distinctly out-of-plane distortion of the La atom (0.70 Å), which is gradually flattened by the sequential reduction reaction. The distortion of the La atom from the plane in the neutral La©B8C4 cluster decreases to 0.46 Å. The La©B8C4 - species turns out to be perfectly planar. Chemical bonding analyses indicate that the neutral La©B8C4 and anionic La©B8C4 - possess 10σ and 9π/10π double aromaticity, respectively, obeying the principle of double aromaticity. However, the cationic La©B8C4 + has 10σ and 8π conflicting aromaticity, representing a counterexample in planar hyper-coordinated molecular wheels. The dodeca-coordination number in La©B8C4 q (q = +1, 0, -1) clusters is unprecedented, which provides a new idea and concept for searching planar hyper-coordinated systems.
ABSTRACT
In the title two-dimensional coordination polymer, [Cd(NCS)(2)(C(6)H(5)N(5))(2)](n), the Cd(II) ion (site symmetry ) is coordinated by two N atoms from two 2-(1H-1,2,3-triazol-1-yl)pyrazine ligands and two N and two S atoms from four thio-cyanate anions. The N-Cd bond lengths range from 2.323â (2) to 2.3655â (19)â Å and the S-Cd bond length is 2.7117â (7)â Å. The associated cisoid angles vary from 84.99â (7) to 95.01â (7)°, indicating that the Cd(II) ion assumes a distorted octa-hedral geometry. In the complex, each thio-cyanate anion functions as a bridging ligand, linking adjacent Cd(II) ions with a separation of 6.4919â (6)â Å, resulting in the formation of a two-dimensional sheet structure in the bc plane.
