Elusive Magnetic Compounds Originated from Planar Tetracoordinate Silicon, a Theoretical Prediction

A family of novel compounds with planar tetracoordinate silicon (ptSi) supported by B-heterocyclic carbenes (BHCs) have been theoretically investigated. The lowest energy molecules (a3, b3, and c3) with single ptSi are a triplet. We further designed 1D and 2D compounds with multi-ptSi atoms by condensation of a3 along latitudinal (m) and longitudinal (n) directions. The lowest energy 1D compounds prefer to be zigzag conformation along the m direction. The lowest energy 2D compounds (m,n) (m ≥ n) are zigzag conformation along both m and n directions. The total spin quantum number (S) of the lowest energy compounds with ptSi is equal to the number of ptSi. Thus, the compounds with ptSi stabilized by BHCs are magnetic. The singly occupied molecular orbitals (SOMOs) of such compounds are mainly the linear combination of the 3p orbitals of ptSi, indicating that the magnetism of the compounds originates from ptSi.

Relevant and unprecedented C-H/σ supramolecular interactions involving σ-aromatic M2X2 cores

A novel type of C-H/σ supramolecular interaction involving σ-aromatic M2X2 (M = Cu, Hg; X = Cl, Br, I, S) cores is reported for the first time. Three new polymeric coordination copper complexes, {[Cu(μ-Cl)(Cl)(μ-L)]2}n (1), {[Cu(μ-I)(μ-L)]2}n (2) and [Cu(Br)2(μ-L)(CH3CN)2]2 (3), have been synthesized with the organic ligand α,ω-bis(benzotriazoloxy)propane system (L) and halides as counterions. A very interesting C-H/σ supramolecular interaction has been observed in the solid state structure of compound 2, similar to a C-Hπ interaction, which has been confirmed by Bader's "atoms-in-molecules" AIM analysis. The Nucleus Independent Chemical Shift (NICs) method was used to evaluate the aromatic character of the different cores in this study. The influence of the nature of the metal ions, bridging atoms, oxidation states, and coordination environments around the metal centers on the strength of the aromaticity of the M2X2 cores was theoretically analyzed and explained. The binding ability of the 1-alkoxy-1,2,3-benzotriazole ring to establish π-π and C-H/π interactions and how its coordination to Cu(I) and Cu(II) ions affects the strength of the aforementioned interactions have been discussed. The electron deficient triazole ring and its π-acidity increases upon coordination of the Cu ion, leading to the formation of a lone pair (lp)-π interaction involving the five-membered ring of the ligand, which has also been analyzed. We have also analyzed the C-H/σ interactions of previously reported X-ray crystal structures of different coordination polymers based on a binuclear copper(I) complex and 2,3-dimethylpyrazine, dithioethers, and benzotriazol-1-yl-based pyridyl units as ligands using I- as a counter-ion. Complex 1 shows antiferromagnetic behavior with a magnetic coupling constant of J = -7.9 cm(-1). Moreover, photoluminescence and TGA studies of the complexes were also carried out.