A two-dimensional TiB₄monolayer exhibits planar octacoordinate Ti

Abstract

At present, the concept of planar hypercoordination in chemistry meets the fast development of two-dimensional (2D) nanomaterials, leading to considerable interest in searching for 2D materials with planar hypercoordinate atoms. In this work, by means of the swarm-intelligence structure search method and first-principles calculations, we predict a hitherto unknown 2D TiB monolayer with a planar octacoordinate Ti moiety, in which each Ti atom binds to eight B atoms with equal distances in a perfect plane, and has the highest coordination of Ti known for 2D materials thus far. Systematic ab initio calculations demonstrate the superior thermodynamic and dynamic stabilities of the predicted TiB monolayer, indicating the high feasibility for experimental synthesis. The stabilization of this perfect planar structure originates from the geometric fit between the atomic radius of Ti and the size of the 8-membered B ring, as well as the electron transfer from Ti to B atoms which compensates the electron deficiency of the full sp hybridized B network. Motivated by the unforeseen geometry of the TiB monolayer, a series of other 2D transition metal borides (TMB, TM = V, Cr, Mo, W and Os) with quasi-planar octacoordinate TM atoms are further designed and discussed. The present work provides a useful roadmap for the discovery of 2D hypercoordinate materials.

Unveiling the Electric-Current-Limiting and Photodetection Effect in Two-Dimensional Hydrogenated Borophene

“…The borophene MLs such as the out-of-plane buckling sheets [1] and β12 and χ3 boron sheets [2] are often fabricated on metal (Ag) substrates, as a truly free-standing two-dimensional (2D) borophene is unstable according to theoretical studies [14,15]. Many fabrication strategies have been proposed to produce free-standing 2D borophene, such as using transition metal adatoms [16][17][18] and hydrogenation to saturate the dangling bonds [3,14,15,19].…”

Half-Auxeticity and Anisotropic Transport in Pd Decorated Two-Dimensional Boron Sheets

“…To achieve free-standing boron sheets, embedding metal atoms that can donate electrons to the boron frameworks has been considered as an effective strategy. Consequently, some metal-boron monolayers including MgB2, 8 BeB2, 9 FeB2, 10 FeB6,, 11 MnB, 12 TiB2 13 and TiB4 14 have been designed and found to possess novel features including planar hypercoordination, Dirac cones and high Curie temperature. 10,12,14 With many intriguing chemical and physical properties, new 2D metal-boron compounds are expected to have important application potential for nanomechanics and nanoelectronics.…”

Half-Auxeticity and Anisotropic Transport in Pd Decorated Two-Dimensional Boron Sheets

“…Such peculiar hypercoordinated structures with B have been attracting great interest for a long time, originally found in molecules/clusters [33][34][35][36] and most recently extended to periodic 2D systems. 11,14 The PdB4 phase crystallizes in the C2/M space group with in-plane anisotropy. More importantly, the structure is not completely planar, but is corrugated with a thickness (d1) of 1.61 Å.…”