Heteroborospherene clusters Nin ∈ B40 (n = 1–4) and heteroborophene monolayers Ni2 ∈ B14 with planar heptacoordinate transition-metal centers in η7-B7 heptagons

Abstract

With inspirations from recent discoveries of the cage-like borospherene B40 and perfectly planar Co ∈ B18 − and based on extensive global minimum searches and first-principles theory calculations, we present herein the possibility of the novel planar Ni ∈ B18 (1), cage-like heteroborospherenes Nin ∈ B40 (n = 1–4) (2–5), and planar heteroborophenes Ni2 ∈ B14 (6, 7) which all contain planar or quasi-planar heptacoordinate transition-metal (phTM) centers in η7-B7 heptagons. The nearly degenerate Ni2 ∈ B14 (6) and Ni2 ∈ B14 (7) monolayers are predicted to be metallic in nature, with Ni2 ∈ B14 (6) composed of interwoven boron double chains with two phNi centers per unit cell being the precursor of cage-like Nin ∈ B40 (n = 1–4) (2–5). Detailed bonding analyses indicate that Nin ∈ B40 (n = 1–4) (2–5) and Ni2 ∈ B14 (6, 7) possess the universal bonding pattern of σ + π double delocalization on the boron frameworks, with each phNi forming three lone pairs in radial direction (3dz2 2, 3dzx 2, and 3dyz 2) and two effective nearly in-plane 8c-2e σ-coordination bonds between the remaining tangential Ni 3d orbitals (3dx2−y2 and 3dxy) and the η7-B7 heptagon around it. The IR, Raman, and UV-vis absorption spectra of 1–5 are computationally simulated to facilitate their experimental characterizations.

Heptacoordinate transition-metal-decorated metallo-borospherenes and multiple-helix metallo-boronanotubes

“…S1b†), in line with the previously predicted results. 28 C 1 Ni 6 ∈ B 41 + ( 3 , 1 A) with six phNi centers as the GM of the monocation appears to be 0.08 and 0.15 eV more stable than the second lowest-lying isomer C 1 Ni 6 ∈ B 41 + with five phNi and one hexacoordinate Ni at the PBE0 and TPSSh levels, respectively (Fig. S1c†), again supporting the thermodynamic favorability of a phNi center over its hexacoordinate Ni counterpart.…”

“…The elongated axially chiral Ni 6 ∈ B 42 2+ ( 4 ), Ni 6 ∈ B 42 ( 5 ), and Ni 8 ∈ B 56 ( 6 ) can be extended infinitely to form the one-dimensional (1D) phNi-decorated BDC double-helix metallo-boronanotube Ni 4 ∈ B 28 (2, 0) ( 8 ) ( P 4̄ m 2), which can be rolled up from the previously predicted two-dimensional (2D) metallo-borophene Ni 2 B 14 ( P 2 1 / m ) ( 7 ) with a = 9.317 Å and b = 4.729 Å 28 in the a direction, as shown in Fig. 4.…”

“…The two original B 6 hexagons on the top and bottom of the parent borospherene C 2 B 39 − have been enlarged to two equivalent η 7 -B 7 heptagons in C 2 Ni 6 ∈ B 39 − ( 1 ) to host two Ni atoms more comfortably on the cage surface, further demonstrating that phNi centers are better favoured over their hexacoordinate Ni counterparts in thermodynamics due to size effects, which is similar to the situation observed in Ni 6 ∈ B 40 . 28 The second lowest-lying isomer C 1 Ni 6 ∈ B 39 − ( 1b , 1 A) with six phNi centers lies 0.17 eV higher, while its triplet counterpart C 2 Ni 6 ∈ B 39 − ( 1c , 3 A) appears to be 0.24 eV less stable (Fig. S1a†).…”

“…26,27 Based on the structural motif of the first experimentally observed neutral borospherene D 2d B 40 , 8 a series of metallo-borospherenes Ni m ∈ B 40 ( m = 1–6) with 1–4 quasi-planar heptacoordinate Ni (phNi) centers and 1–2 hexacoordinate Ni centers on the cage surface and two nearly degenerate two-dimensional (2D) metallo-borophenes Ni 2 ∈ B 14 ( P 2 1 / m ) and Ni 2 ∈ B 14 ( P 1̄) with two phNi centers in each unit cell have also been predicted. 28 PhNi centers in η 7 -B 7 pentagons on the cage surface of B 40 were found to be better favoured in thermodynamics than their hexacoordinate Ni counterparts in η 6 -B 6 hexagons due to size effects. However, metallo-borospherenes smaller or larger than Ni 6 ∈ B 40 and one-dimensional (1D) metallo-boronanotubes decorated exclusively with the thermodynamically most favoured heptacoordinate transition-metal (phTM) centers have still remained unknown to date in both experiments and theory.…”

Theoretical study on exohedral complexes C6H6TMB40 (TM = Sc-Ni)

“…, Cu, Ag, Au, Sc, Y, La, U, and Ni). 18–23 At the same time, theoretical studies predict that metal-doped B 40 also has strong adsorption to small molecules, 24–27 and the B 40 borospherene can be used as a promising DNA base sensor 28 and effectively employed in determining the sequence of nucleobases in DNA. 29…”