Density functional study of structural, electronic, and optical properties of small bimetallic ruthenium-copper clusters.

The structural, electronic, bonding, magnetic, and optical properties of bimetallic [Cu(n)Ru(m)](+/0/-) (n + m ≤ 3; n, m = 0-3) clusters were computed in the framework of the density functional theory (DFT) and time-dependent DFT (TD-DFT) using the full-range PBE0 nonlocal hybrid GGA functional combined with the Def2-QZVPP basis sets. Several low-lying states have been investigated and the stability of the ground state spinomers was estimated with respect to all possible fragmentation schemes. Molecular orbital and population analysis schemes along with computed electronic parameters illustrated the details of the bonding mechanisms in the [Cu(n Ru(m)](+/0/-) clusters. The TD-DFT computed UV-visible absorption spectra of the bimetallic clusters have been fully analyzed and assignments of all principal electronic transitions were made and interpreted in terms of contribution from specific molecular orbital excitations.

Diagnosis of magnetoresponsive aromatic and antiaromatic zones in three-membered rings of d- and f-block elements.

Magnetoresponsive three-membered rings of d- and f-block elements have been thoroughly investigated with the help of electronic structure calculation methods. The magnetic response of the clusters was evaluated by the Nucleus Independent Chemical Shifts (NICS)(zz)-scan curves, which in conjunction with symmetry-based selection rules for the most significant translationally and rotationally allowed transitions helped rationalize and predict the orbital-type of aromaticity/antiaromaticity of the clusters. The magnetoresponsive early (Groups 3, 4, and 5) transition metal M(3) rings exhibit successive aromatic and antiaromatic zones separated by a nodal plane. The magnetoresponsive late (Groups 11 and 12) transition metal M(3) rings exhibit long-range aromatic zone with the NICS(zz)(R) values decaying rapidly and monotonically with respect to R. The magnetic response of Group 10 transition metal M(3) rings is similar to that of the early transition metal M(3) rings, but it is long-range antiaromatic only for the [c-Ni(3)] cluster. The NICS(zz)-scan curve of the [(H(t)La)(3)(mu(2)-H)(6)] cluster is indicative of weak pure sigma-aromaticity due to the induced diatropic ring current from the translationally allowed a(1)(') --> e' and e' --> a(1)(') transitions. The aromatic-antiaromatic behavior of the [(H(t)Ce)(3)(mu(2)-H)(6)](+) and [(H(t)Tm)(3)(mu(2)-H)(6)](2-) clusters is similar to that of the early d-block elements. The magnetic response of [(H(t)Yb)(3)(mu(2)-H)(6)](3-) is similar to that of [c-Hg(3)](2-). The [(H(t)Lu)(3)(mu(2)-H)(6)] cluster can be considered as a doubly (sigma + pi) aromatic system, with the sigma-aromatic component being much stronger than the pi-aromatic one. Finally, the [(X(t)Re)(3)(mu(2)-X)(6)] and [(X(t)Ru)(3)(mu(2)-X)(6)](+) (X = Cl, Br, I) clusters exhibit significant aromatic character with the greatest contribution to the induced diatropic ring currents coming from pi-type transitions.