Molecular and Electronic Structure, Magnetotropicity and Absorption Spectra of Benzene-Trinuclear Copper(I) and Silver(I) Trihalide Columnar Binary Stacks

The molecular and electronic structures, stabilities, bonding features, magnetotropicity and absorption spectra of benzene-trinuclear Cu(I) and Ag(I) trihalide columnar binary stacks with the general formula [c-M-3(mu(2)-X)(3)](n)(C6H6)(m) (M = Cu, Ag; X = halide; n, m <= 2) have been investigated by means of electronic structure calculation methods. The interaction of c-M-3(mu(2)-X)(3) clusters with one and two benzene molecules yields 1:1 and 1:2 binary stacks, while benzene sandwiched 2:1 stacks are formed upon interaction of two c-M-3(mu(2)-X)(3) clusters with one benzene molecule. In all binary stacks the plane of the alternating c-M-3(mu(2)-X)(3) and benzene components adopts an almost parallel orientation. The separation distance between the centroids of the benzene and the proximal c-M-3(mu(2)-X)(3) metallic cluster found in the range 2.97-3.33 angstrom at the B97D/Def2-TZVP level is indicative of a pi center dot center dot center dot pi stacking interaction mode, for the centroid separation distance is very close to the sum of the van der Waals radii of Cu center dot center dot center dot C (3.10 angstrom) and Ag center dot center dot center dot C (3.44 angstrom). Energy decomposition analysis (EDA) at the SSB-D/TZP level revealed that the dominant term in the c-M-3(mu(2)-X)(3)center dot center dot center dot C6H6 interaction arises from dispersion and electrostatic forces while the covalent interactions are predicted to be negligible. On the other hand, charge decomposition analysis (CDA) illustrated very small charge transfer from C6H6 toward the c-M-3(mu(2)-X)(3) clusters, thus reflecting weak pi-base/pi-acid interactions which are further corroborated by the respective electrostatic potentials and the fact that the total dipole moment vector points to the center of the metallic ring of the c-M-3(mu(2)-X)(3) cluster. The absorption spectra of all aromatic columnar binary stacks simulated by means of TD-DFT calculations showed strong absorptions in the UV region. The main features of the simulated absorption spectra are thoroughly analyzed, and assignments of the contributing electronic transitions are given. The magnetotropicity of the binary stacks evaluated by the NICSzz-scan curves indicated an enhancement of the diatropicity of the inorganic ring upon interaction with the aromatic benzene molecule. Noteworthy is the slight enhancement of the diatropicity of the benzene ring, particularly in the region between the interacting rings, probably due to the superposition (coupling) of the diamagnetic ring currents of the interacting aromatic ring systems.