Two Shared Icosahedral Metallacarboranes through Iron: A Joint Experimental and Theoretical Refinement of Mössbauer Spectrum in [Fe(1,2-C2B9H11)2]Cs

SUBJECTS:Anions,Conformation,Energy,Molecular structure,Quantum mechanicsMössbauer and X-ray photoelectron spectroscopies (XPS) are complemented with high-level quantum-chemical computations in the study of the geometric and electronic structure of the paramagnetic salt of the metallacarborane sandwich complex [Fe(1,2-CBH)]Cs = FeSanCs. Experimental Fe isomer shifts and quadrupole splitting parameters are compared with the theoretical prediction, with good agreement. The appearance of two sets of Cs(3d) doublets in the XPS spectrum, separated by 2 eV, indicates that Cs has two different chemical environments due to ease of the Cs cation moving around the sandwich complex with low-energy barriers, as confirmed by quantum-chemical computations. Several minimum-energy geometries of the FeSanCs structure with the corresponding energies and Mössbauer parameters are discussed, in particular the atomic charges and spin population and the surroundings of the Fe atom in the complex. The Mössbauer spectra were taken at different temperatures showing the presence of a low-spin Fe atom with S = 1/2 and thus confirming a paramagnetic Fe species.We are grateful to Prof. Ibon Alkorta (IQM-CSIC) for providing the MEP of trans-FeSan anion conformer. J.F.M. and J.Z.D.-P. acknowledge financial support from grant RTI2018-095303-B-C51 funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe” and from grant S2018-NMT-4321 funded by the Comunidad de Madrid and by “ERDF A way of making Europe”. M.F., J.E., and J.M.O.-E. are grateful to Ministerio de Ciencia, Innovacióny Universidades, for financial support with grant number PID2021-125207NB-C32. O.B.O. and D.R.A. acknowledge the financial support from the Universidad de Buenos Aires (grant no. 20020190100214BA), the Consejo Nacional de Investigaciones Científicas y Técnicas (grant nos PIP11220200100467CO, PIP 11220130100377CO, and PIP11220130100311CO), and the Agencia Nacional de Promoción Científica y Tecnológica, Argentina (grant no. PICT-201-0381).Peer reviewe

Expanding the structural chemistry of the weakly coordinating <em>closo</em>-carborane CB<sub class="a-plus-plus">11</sub>H₁₂⁻:its monoiodo derivatives with and without C_5v symmetry

Two iodo derivatives of closo-CB11H12 (-), i.e., 12-I-1-CB11H11 (-) (C (5v) symmetry) and 7-I-1-CB11H11 (-) (C (s) symmetry), were prepared (the latter for the first time) and the influence of differently positioned iodine substituents on the geometry of the CB11 icosahedral core was structurally examined both by X-ray diffraction and quantum-chemical computation at the MP2 level. Observed and computed molecular geometries are in overall agreement. Supramolecular architectures of these two anionic substituted monocarboranes are shown. According to DFT computations at the ZORA-SO/BP86 level, the B-11 chemical shifts of the boron atoms to which iodine substituents are bonded are dominated by spin-orbit coupling. Different positions of iodine atoms in these two isomers may result in different acidities of the (C)-H atoms in the icosahedral bodies, as suggested by visually analyzing the corresponding lowest unoccupied molecular orbitals.</p

Expanding the structural chemistry of the weakly coordinating <em>closo</em>-carborane CB<sub class="a-plus-plus">11</sub>H₁₂⁻:its monoiodo derivatives with and without C_5v symmetry

Two iodo derivatives of closo-CB11H12 (-), i.e., 12-I-1-CB11H11 (-) (C (5v) symmetry) and 7-I-1-CB11H11 (-) (C (s) symmetry), were prepared (the latter for the first time) and the influence of differently positioned iodine substituents on the geometry of the CB11 icosahedral core was structurally examined both by X-ray diffraction and quantum-chemical computation at the MP2 level. Observed and computed molecular geometries are in overall agreement. Supramolecular architectures of these two anionic substituted monocarboranes are shown. According to DFT computations at the ZORA-SO/BP86 level, the B-11 chemical shifts of the boron atoms to which iodine substituents are bonded are dominated by spin-orbit coupling. Different positions of iodine atoms in these two isomers may result in different acidities of the (C)-H atoms in the icosahedral bodies, as suggested by visually analyzing the corresponding lowest unoccupied molecular orbitals.</p