Unprecedented Electron‐Poor Octahedral Ta₆ Clusters in a Solid‐State Compound: Synthesis, Characterisations and Theoretical Investigations of Cs₂BaTa₆Br₁₅O₃

Abstract

The crystal structure of Cs2BaTa6Br15O3 has been elucidated by using synchrotron X-ray powder diffraction and absorption experiments. It is built from edge-bridged octahedral [(Ta6Bri9Oi3)Bra6]4− cluster units with a singular poor metallic electron (ME) count equal to thirteen. This leads to a paramagnetic behaviour related to one unpaired electron. The arrangement of the Ta6 clusters is similar to that of Cs2LaTa6Br15O3 exhibiting 14-MEs per [(Ta6Bri9Oi3)Bra6]5− motif. The poorer electron-count cluster presents longer metal–metal distances as foreseen according to the electronic structure of edge-bridged hexanuclear cluster. Density functional theory (DFT) calculations on molecular models were used to rationalise the structural properties of 13- and 14-ME clusters. Periodic DFT calculations demonstrate that the electronic structure of these solid-state compounds is related to those of the discrete octahedral units. Oxygen–barium interactions seem to prevent the geometry of the octahedral cluster to strongly distort, allowing stabilisation of this unprecedented electron-poor Ta6 cluster in the solid state.

Development of a robust tool to extract Mulliken and Löwdin charges from plane waves and its application to solid-state materials

“…2b). [55][56][57][58][59][60][61][62][63][64] The Mulliken charges (given in Table S1 †) evidence that the new method implemented in LOBSTER reproduces the expected ionicity trend of the series, which is even clearer based on the Löwdin charges. The Mulliken charge is around AE0.8e for every alkali halide compound with the exception of CsF (with AE0.87e).…”

Octahedral clusters with mixed inner ligand environment: Self-assembly, modification and isomerism

“…Tantalum oxybromides are quite rare and are limited to two families: A 2 BTa 6 Br 9 O 3 Br 6 (A = Cs; B = Ba, La and Ce) and LnTa 6 Br 9 O 3 Br 4/2 Br 2 (Ln = Sm to Lu except Eu and Yb), respectively [36]. It is worth noting that in Cs 2 LaTa 6 Br 9 O 3 Br 6 and Cs 2 BaTa 6 Br 9 O 3 Br 6 the charges of the [{Ta 6 Br 9 O 3 }Br 6 ] nunits are 4-and 3-, meaning an unusually low VEC value of 13 electrons per cluster [37,38].…”

Order within disorder: The atomic structure of ion-beam sputtered amorphous tantala (a-Ta2O5)

“…Ta-O and Ta-Ta distance distributions of several crystalline tantala models [17][18][19][20][21][22][23][24][25][26][27][28]. The blue dashed lines represent the distances from the EXAFS fits of the amorphous tantala studied in this work.…”