Searching for Systems with Planar Hexacoordinate Carbons

Abstract

Here, we present evidence that the D2h M2C50/2+ (M = Li-K, Be-Ca, Al-In, and Zn) species comprises planar hexacoordinate carbon (phC) structures that exhibit four covalent and two electrostatic interactions. These findings have been made possible using evolutionary methods for exploring the potential energy surface (AUTOMATON program) and the Interacting Quantum Atoms (IQA) methodology, which support the observed bonding interactions. It is worth noting, however, that these structures are not the global minimum. Nonetheless, incorporating two cyclopentadienyl anion ligands (Cp) into the CaC52+ system has enhanced the relative stability of the phC isomer. Moreover, cycloparaphenylene ([8]CPP) provides system protection and kinetic stability. These results indicate that using appropriate ligands presents a promising approach for expanding the chemistry of phC species.

Global minimum and a heap of low-lying isomers with planar tetracoordinate carbon in the CAl3MgH2− system

“…5 Since then, ptC has progressed enormously both theoretically [6][7][8][9][10][11][12][13] and experimentally [14][15][16][17][18][19][20] and has also been extended to planar hypercoordination in the main group and s-block elements. [21][22][23][24][25][26][27] The magic number for planar species, known as the ''18-valence electron rule'', 28 has been designed in the past and shown to be effective for various systems 6,7,29,30 to understand the bonding and stability of these species.…”

Five Bonds to Carbon through Tri-Coordination in Al3C3−/0

“…The iron-molybdenum nitrogenase cofactor existing in diazotrophs is a clear example of hexa-coordinate carbon in biological systems [14]. From the well-known concept of molecules with a planar tetra-coordinate carbon (ptC) atom [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30], the idea was extended to planar penta-coordinate carbon (ppC) [31][32][33][34][35][36][37][38][39][40] and planar hexacoordinate carbon (phC) [41][42][43][44]. Hill and coworkers experimentally reported the existence of a penta-coordinate carbon atom in 1981 [45].…”