Two‐Orbital Three‐Electron Stabilizing Interaction for Direct Co²⁺As³⁺ Bonds involving Square‐Planar CoO₄ in BaCoAs₂O₅

Abstract

The quest for new oxides with cations containing active lone-pair electrons (E) covers a broad field of targeted specificities owing to asymmetric electronic distribution and their particular band structure. Herein, we show that the novel compound BaCoAs2 O5, with lone-pair As(3+) ions, is built from rare square-planar Co(2+) O4 involved in direct bonding between As(3+) E and Co(2+) dz2 orbitals (Co-As=2.51 Å). By means of DFT and Hückel calculations, we show that this σ-type overlapping is stabilized by a two-orbital three-electron interaction allowed by the high-spin character of the Co(2+) ions. The negligible experimental spin-orbit coupling is expected from the resulting molecular orbital scheme in O3 AsE-CoO4 clusters.

Synthesis and Magnetism of Extended Solids Containing Transition-Metal Cations in Square-Planar, MO4 Coordination Sites

“…A further mechanism to stabilize approximately square-planar Co II O 4 units is observed for the oxypnictide phase BaCoAsO 5 in which the interaction between what would be a doubly filled Co d z 2 orbital in an isolated CoO 4 unit and a doubly filled E orbital (stereoactive lone pair) of an isolated AsO 3 unit leads to a net bonding interaction via two-orbital, three-electron stabilization. While the resulting system still retains a high degree of orbital degeneracy in the Co d states, the observed paramagnetic moment of the system ( T > 50 K) is close to the expected spin-only value for Co 2+ , indicating that, in contrast to the other oxychalcogenides and oxyhalides, strong spin–orbital coupling is not in operation in BaCoAsO 5 .…”

Bonding Scheme, Hydride Character, and Magnetic Paths of (HPO3)2– Versus (SeO3)2– Building Units in Solids

“…Since the recent reports of unexpected P···HO hydrogen bonds in gas phases and direct As 3+ ···Co 2+ bond in oxide, the bonding possibilities of lone pair cation P 3+ , As 3+ , and Se 4+ have generated renewed interest. The phosphite anion (HPO 3 ) 2– is commonly encountered as a tridentate tetrahedral ligand in solids, and can be regarded as resulting from phosphonic acid HPO­(OH) 2 upon deprotonation.…”

CNRS Silver and Bronze Medals / Elected to the European Academy of Sciences and Arts: M. Scheer / Honorary Doctorate: L. Oro

“…Kabbour’s research involves a combined theoretical and experimental approach to predict, synthesize, and modulate inorganic compounds with a broad range of properties, including magnetism. She is co‐author of recent reports in Angewandte Chemie on the structure and properties of BaCoAs 2 O 5 ,6a and on reversible iron exsolution 6b …”