Molecular magnetism incloso-azadodecaborane supericosahedrons

Magnetic Properties of Co(II) Complexes with Polyhedral Carborane Ligands

In this work we present a computational analysis of a new family of magnetic Co(II) single-ion complexes with large magnetic anisotropy based on icosahedral and octahedral carborane ligands. In particular, we extend our previous computational work on mononuclear Co(II) complexes with 1,2-(HS)₂-1,2-C₂B₁₀H₁₀ and 9,12-(HS)₂-1,2-C₂B₁₀H₁₀ icosahedral o-carborane ligands to a larger set of complexes where the Co(II) ion is doubly chelated by those ligands and by other two positional isomers belonging to the 1,2-dicarba- closo-dodecaborane family. We also describe Co(II) complexes with octahedral ligands derived from 1,2-dicarba- closo-hexaborane and study the effects of replacing a thiol group by a hydroxy group in both polyhedral geometries, as well as the influence of the position of the carbon atoms. On analysis of the results for a total of 20 complexes, our results show that carborane-based Co(II) single-ion compounds present a distorted-tetrahedral geometry, high-spin ground states, and high values for the magnetic anisotropy parameters. We point out which of these would be suitable candidates to be synthesized and used as molecular magnets.

Magnetic Properties of Mononuclear Co(II) Complexes with Carborane Ligands

We analyze the magnetic properties of three mononuclear Co(II) coordination complexes using quantum chemical complete active space self-consistent field and N-electron valence perturbation theory approaches. The complexes are characterized by a distorted tetrahedral geometry in which the central ion is doubly chelated by the icosahedral ligands derived from 1,2-(HS)₂-1,2-C₂B₁₀H₁₀ (complex I), from 1,2-(HS)₂-1,2-C₂B₁₀H₁₀ and 9,12-(HS)₂-1,2-C₂B₁₀H₁₀ (complex II), and from 9,12-(HS)₂-1,2-C₂B₁₀H₁₀ (complex III), which are two positional isomers of dithiolated 1,2-dicarba- closo-dodecaborane (complex I). Complex I was realized experimentally recently (Tu, D.; Shao, D.; Yan, H.; Lu, C. Chem. Commun. 2016, 52, 14326) and served to validate the computational protocol employed in this work, while the remaining two proposed complexes can be considered positional isomers of I. Our calculations show that these complexes present different axial and rhombic zero-field splitting anisotropy parameters and different values of the most significant components of the g tensor. The predicted axial anisotropy D = -147.2 cm^-1 for complex II is twice that observed experimentally for complex I, D = -72.8 cm^-1, suggesting that this complex may be of interest for practical applications. We also analyze the temperature dependence of the magnetic susceptibility and molar magnetization for these complexes when subject to an external magnetic field. Overall, our results suggest that o-carborane-incorporated Co(II) complexes are worthwhile candidates for experimental exploration as single-ion molecular magnets.