The simplest planar tetracoordinate carbon: CLi3H+

Abstract

Although numerous planar hypercoordinate atoms have been reported, we describe the first planar tetracoordinate carbon (ptC) stabilized by a distinct electronic mechanism. In the global minimum C2v structure of CLi3H+, the ptC is bonded to one hydrogen and three lithium atoms. This structure lies over 39 kcal/mol below the next isomer on the potential energy surface. Its stabilization arises solely from direct carbon ligand interactions, without contributions from ligand–ligand bonding. The carbon atom adopts a 2s22pσ12pπ22pπ′1 configuration, forming a strong C–H σ bond, while the C–Li interactions are weak and polar. CLi3H+ is therefore the smallest electron-deficient planar hypercoordinate species known, revealing a new bonding motif in cluster chemistry.