Face-to-Face Stacks of Trinuclear Gold(I) Trihalides with Benzene, Hexafluorobenzene, and Borazine: Impact of Aromaticity on Stacking Interactions

The interplay of electrostatics, charge transfer, and dispersion forces contributing to the interaction energies in 1:1, 1:2, and 2:1 binary stacks of the c-Au-3(mu(2)-X)(3) (X = F, Cl, Br, I) dusters with benzene, hexafluorobenzene, or borazine were investigated by employing a multitude of electronic structure computational techniques. The molecular and electronic structures, stabilities, bonding features, and magnetotropicity of [c-Au-3(mu(2)-X)(3)](n) (L)(m) (X = halide; L = C6H6, C6F6, B3N3H6; n, m <= 2) columnar binary stacks have been investigated by DFT calculations employing the M05-2X functional. The novel binary stacks could be considered as the building blocks of extended columnar supramolecular assemblies formulated as {[c-Au-3(mu(2)-X)(3)](C6H6)}(infinity), {[c-Au-3(mu(2)-X)(3)](2)(C6F6)}(infinity), and {[c-Au-3(mu(2)-X)(3)](B3N3H6)(2)}(infinity). In all binary stacks, with a few exceptions, the plane of the alternating c-Au-3(mu(2)-X)(3) and L (C6H6, C6F6, B3N3H6) stacking participants adopt an almost parallel face-to-face (pff) orientation. The observed trends in the intermolecular distances R in the [c-Au-3(mu(2)-X)(3)](n)(L)(m) (X = halide; L = C6H6, C6F6, B3N3H6; n, m <= 2) columnar binary stacks are explained by the diverse intermolecular interactions characterizing the stacks, since the three ligands L and the c-Au-3(mu(2)-X)(3) cyclic trinuclear dusters (CTCs) exhibit diverse physical properties being important determinants of the intermolecular interactions (consisting of covalent, electrostatic, and dispersion forces). The properties considered are the zz tensor components of quadrupole moment, Q(zz), polarizability, alpha(zz), nucleus-independent chemical shift, NICSzz(1), along with the molecular electrostatic potential, MEP(0), and surface area (S). Energy decomposition analysis (EDA) at the revPBE-D3/TZ2P level revealed that the dominant term in the stacking interactions arises mainly from dispersion and electrostatic forces, while the contribution of covalent interactions are predicted to be small. On the other hand, charge decomposition analysis (CDA) illustrated very small charge transfer from the L stacking participants toward the c-Au-3(mu(2)-X)(3) dusters. Excellent linear correlations of the interaction energy, Delta E-int, and its components (Delta E-disp, Delta E-elstat, Delta E-orb, and Delta E-Pauli) with calculated physical properties related to dispersion, covalent, and electrostatic forces have been established. The most important finding is the excellent linear relationship between Delta E-int and the NICSzz(1) magnetic criterion of aromaticity, indicating that Delta E-int is also affected by the coupling of the induced magnetic fields of the interacting stacking participants. The magnetotropicity of the binary stacks evaluated by the NICSzz-scan curves indicated an enhancement of the diatropicity in the space between the interacting inorganic and organic rings, probably due to the superposition of the diamagnetic ring currents of the interacting ring systems. The energy splitting in dimer (ESID) model was employed to estimate the charge transport of electrons and holes between the ligands L and the [c-Au-3(mu(2)-X)(3)] clusters in [c-Au-3(mu(2)-X)(3)](L) 1:1 binary stacks.