A Lanthanum‐Filled Carbon–Boron Clathrate

Abstract

We report a carbon‐boron clathrate with composition 2 La@B6C6 (LaB3C3). Like recently reported SrB3C3,[1] single‐crystal X‐ray diffraction and computational modelling indicate that the isostructural La member crystallizes in the cubic bipartite sodalite structure (Type‐VII clathrate) with La atoms encapsulated within truncated octahedral cages composed of alternating carbon and boron atoms. The covalent nature of the B−C bonding results in a hard, incompressible framework, and owing to the balanced electron count, La3+[B3C3]3− exhibits markedly improved pressure stability and is a semiconductor with an indirect band gap predicted near 1.3 eV. A variety of different guest atoms may potentially be substituted within Type‐VII clathrate cages, presenting opportunities for a large family of boron‐stabilized, carbon‐based clathrates with ranging physical properties.

Prediction of novel boron–carbon based clathrates

“…21 Besides these bivalent guest atoms, clathrate trapped trivalent La 3+ and Sc 3+ ions are also evaluated as stable compounds. 22,23 La 3+ [B 3 C 3 ] 3− is a semiconductor with an indirect band gap of near 1.3 eV. 22 The distorted Ama2 Sc 3+ [B 3 C 3 ] 3− is ferroelectric showing spontaneous polarization with an above-room-temperature Curie temperature of ∼370 K. 23 Recently, Rb 0.5 Sr 0.5 B 3 C 3 with a predicted T c of 75 K has been reported at ambient pressure, which is obtained via the Rb substitution of guest metal atoms in the SrB 3 C 3 clathrate.…”

Pressure-stabilized graphene-like P layer in superconducting LaP2

“…La atoms have shown an ability to stabilize interesting motifs in compounds, such as LaB 8 with a B 26 cage constructed from 12 twisted rhombuses and 6 twisted hexagons, and possessing the largest atom number in the known B cages, 28 LaB 3 C 3 consisting of a truncated octahedral sp 3 -bonded B-C cage and having a lower synthesis pressure than SrB 3 C 3 , 29 and LaP 5 containing a puckered P layer composed of larger P 12 rings, 30 compared with the P 6 ring in phosphene. 31 Having this in mind and considering that phosphides also exhibit superconductivity related to P configurations (e.g., 2.6 K for Nb 2 P 5 with zigzag P chains, 32 22 K for KP 2 with puckered phosphorus layers, 33 and 10.2 K for MgP 2 with threedimensional P framework 34 ).…”

Clathrate Structure of Fullerite C60

“…An important consequence of having each molecule bonded to its neighbors via the double 5/5 2+3 cycloadditions, is that the resulting fcc polymeric structure has its octahedral interstitial sites enclosed by truncated icosahedron cages (identical to the original C 60 molecular cages) and its tetrahedral interstitial sites enclosed by distorted truncated octahedron cages. These truncated octahedron cages, with 24 atoms arranged in 8 hexagons and 6 rhombi, are a distorted version of the sodalite-type cages displayed by numerous clathrates [9][10][11][12][13]. The original C 60 molecular cages are strongly deformed and their double hexagonal rings, lying perpendicular to the cubic axes, are now perfectly planar.…”

“…Clathrates are open-framework structures with facesharing polyhedral cages that can contain guest species, atoms or molecules [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Hydrates are an important group of clathrate structures, being the focus of intense investigations on the possibility of greenhouse gases storage [1].…”

“…There have been several theoretical studies discussing the stability of different carbon clathrates, such as C 46 , C 34 and C 24 , whose construction is based on polyhedral cages and arrangements exhibited by clathrates of other chemical elements [13][14][15][16]. A significant step towards the synthesis of carbon clathrates has been done recently with the high-pressure synthesis of mixed carbon-boron clathrates, where metal atoms, strontium or lanthanum, are trapped inside ordered sodalite-like cages formed by carbon and boron [9,10].…”