Theoretical investigation of clusters of phosphorus and arsenic: fascination and temptation of high symmetries

We present a theoretical study of the energetic and thermodynamic stability of selected phosphorus and arsenic clusters containing 18 to 168 atoms. For this purpose we employ MP2 as well as DFT functionals BP86 and B3LYP with extended basis sets. All procedures predict the family of one-dimensional polymers X18+12n, each with 2n-1 isomers of virtually identical energy, to be more stable than other structures investigated so far. Furthermore, islands of stability result for ring-shaped clusters X24n with Dnd symmetry for n=4 (only for arsenic), 5, 6, and 7. Phosphorus and arsenic show otherwise a very similar behavior. An investigation of basis set effects shows that a doubly polarized triple zeta valence basis (TZVPP) is both necessary and sufficient. In comparison to the reliable spin component scaled MP2 (SCS-MP2) procedure, DFT methods underestimate and MP2 overestimates the stability of larger clusters; the discrepancy increases with the number of atoms. The addition of a long-range dispersion correction to B3LYP energies does not rectify the shortcomings of DFT in comparison with SCS-MP2.     

Structural and photophysical studies of trans-AB(2)C-substituted porphyrin ligands and their zinc and copper complexes

trans-AB(2)C porphyrins with A = C(6)H(4)-COOR, C = C(6)H(4)-NX(2) and B = C(6)H(5) (R = CH(3), H; X = O, H) have been synthesised by a rational high-yield procedure (1a-1d) and their zinc(ii) and copper(ii) complexes have been prepared (2a-2d, 3a-3d ).1a, 2a .THF and 3a display different distortions of the porphyrin core as shown by single crystal X-ray crystallography and NSD analyses. The Soret and Q bands of free-base and metalated porphyrins with mixed electron donating and withdrawing substituents (NH(2)/COOR) are red-shifted as are the corresponding emission bands of free-base and zinc porphyrins. The electronic asymmetry revealed by spectrocopy is rationalised by DFT calculations.