Perfect Spherical Tetrahedral Metallo-Borospherene Ta₄B₁₈ as a Superatom Following the 18-Electron Rule

Abstract

Cage-like metallo-borospherenes exhibit unique structures and bonding. Inspired by the newly reported smallest spherical trihedral metallo-borospherene D 3h Ta 3 B 12 – ( 1 ), which contains two equivalent B 3 triangles interconnected by three B 2 units on the cage surface, we present herein a first-principles theory prediction of the perfect spherical tetrahedral metallo-borospherene T d Ta 4 B 18 ( 2 ), which possesses four equivalent B 3 triangles interconnected by six B atoms, with four equivalent nonacoordinate Ta centers in four η 9 -B 9 rings as integrated parts of the cage surface. As the well-defined global minimum of the neutral, Ta 4 B 18 ( 2 ) possesses four 10c-2e B 9 (π)–Ta(d σ ) and eight 10c-2e B 9 (π)–Ta(d δ ) coordination bonds evenly distributed over four Ta-centered Ta@B 9 nonagons, with the remaining 18 valence electrons in nine 22c-2e totally delocalized bonds following the 18-electron principle (1S 2 1P 6 1D 10 ) of a superatom. Such a bonding pattern renders spherical aromaticity to the tetrahedral complex, which can be used as building blocks to form the face-centered cubic crystal Ta 4 B 15 ( 3 ). The IR, Raman, and UV–vis spectra of Ta 4 B 18 ( 2 ) are theoretically simulated to facilitate its future experimental characterizations.

La@[La5&B30]0/−/2−: endohedral trihedral metallo-borospherenes with spherical aromaticity

“…22 The smallest metallo-borospherene D 3h Ta 3 B 12 − with three equivalent octa-coordinate Ta centers in three η 8 -B 8 rings and spherical aromatic T d Ta 4 B 18 with four equivalent nona-coordinate Ta centers in four η 9 -B 9 rings were late predicted in theory. 23,24 Endohedral metallo-borospherene D 2 Ta@B 22 − was also predicted to be a superatom matching the 18-electron rule. 25 The experimentally observed organometallic complexes T d An@C 28 (An = Th, Pa + , U 2+ , Pu 4+ ) were found to be superatoms following 32-electron principle.…”

Large B7 Triangles in Hollow Spherical Trihedral Metallo-borospherenes and Their Endohedral Complexes of B20TMn (TM = Sc, Y; n = 3, 4): a Theoretical Characterization

“…It is the first report that hollow and endohedral spherical trihedral metallo-borospherenes have been found simultaneously in the same B-skeleton, whereas the ordinary situation is that the addition of an impurity will cause a great structural change. Taking spherical metallo-borospherenes B 18 Ln 3 – and B 18 Ta 4 as examples, , all the atoms are as the integrated parts of the cage surface, where three equivalent deca-coordinate Ln atoms are located at the center of three conjoined η 10 -B 10 rings and an additional Ta atom resulting in four conjoined η 9 -B 9 rings centered with four equivalent nonacoordinate Ta atoms, instead of the fourth Ta atom at the center of the whole B 18 framework. Due to the same effective valance electrons to the Sc atom, these geometric structures of B 20 Sc 3 and B 20 Sc 4 can be further expanded to the elements in the same main group as dopants, viz., B 20 Y 3 and B 20 Y 4 , where the A 1 and B 1 structures are still most stable among the isomers with same compositions.…”

“…Another derivative D 3 h B 15 TM 3 q (TM = Zr, Hf; q = −1, 0, +1), of which the geometric structure can be viewed as one boron atom removed from each linked B 2 unit of B 18 Ln 3 – , was verified as spherical trihedral metallo-borospherenes . Spherical tetrahedral metallo-borospherenes of B 18 Ta 4 with T d symmetry, its cage surface possessed four equivalent B 3 triangles along with six B atoms as the interconnected units, and the four η 9 -B 9 rings centered by four equivalent nonacoordinate Ta atoms . In addition, the incorporation of main group elements, such as alkali metals − or alkaline earth metals, , further flourished the structural diversity of boron-based clusters.…”

Be4B12+: A Covalently Bonded Archimedean Beryllo‐Borospherene

“…[21,22] The same group recently found a perfectly spherical tetrahedral metallo-borospherene in Ta 4 B 18 . [23] The system is intriguing because it shows that boron clusters may adopt a polyhedron form with the proper dopant, a framework that was thought to be exclusive to boranes, carboranes, and some transition-metal substituted boranes. Lanthanides or transition metals have filled f and/ or d electrons to be donated to the vacant p orbitals of boron to form strong interactions, and therefore, such interactions cause to reshape the boron moiety, facilitating the orbital overlap with the dopants.…”