Plane and simple: planar tetracoordinate carbon centers in small molecules

Abstract

A class of neutral 18-electron molecules with planar tetracoordinate carbon (ptC) centers is introduced. We show computationally that when n = 3 the neutral singlet molecule C(BeH)(n)(BH(2))(4-n) and other isoelectronic (18-valence electron) molecules of main group elements collapse from locally tetrahedral arrangements at the C-center to (near) planar tetracoordinate structures. For C(BeH)(3)BH(2) and C(CH(3))(BH(2))Li(2), for example, the tetrahedral type conformation is not even a minimum on the potential energy surface at the B3PW91, MP2(full), or CCSD levels of theory. The Mg analogue C(MgH)(3)BH(2) of the Be system also features a completely flat global minimum (with even higher energy planar minima in both cases as well). Other neutral compounds that may prefer planar geometries are apparent, and new openings for experimental investigations and theoretical analyses of planar tetracoordinate main group systems are identified. The planar conformation persists at one center in the C(BeH)(3)BH(2) dimer, and may be identifiable in higher order clusters of ptC molecules as well.

Four Decades of the Chemistry of Planar Hypercoordinate Compounds

“…Thea romaticity in Lis series ( Figure 21) also contributes to the stability of these unusual structures.I n2 012, several (nearly) ptC configurations in small molecules have also been predicted by Crigger and co-workers. [62] Carbon-aluminum binary clusters have attracted attention because of their non-classical structures and exotic chemical bonds.I n2 008, Naumkin [63] explored the flat structural motifs in small alumino-carbon clusters C n Al m (n = 2-3, m = 2-8) using ab initio MP2 calculations.T hey identified some clusters featuring planar tetra-and hypercoordinate carbon motifs.O nt he basis of simple models potentially containing double ptC motifs,W ua nd co-workers [64] predicted that the simplest neutral singlet C 2 E 4 (E = Al, Ga, In, and Tl;Scheme 8) is aglobal minimum with two ptCs.…”

Identifying the Hydrogenated Planar Tetracoordinate Carbon: A Combined Experimental and Theoretical Study of CAl4H and CAl4H–

“…26 Moreover, the simplicity of these penta-atomic species has allowed them to act as building blocks for more complicated complexes. [27][28][29] Clearly, in all the known ptC compounds (except the simplest penta-atomic ptCs), the ptC cores are stabilized by metallic or organometallic ligands. No hydrogenated ptCs have been reported in experiments.…”

Structure and Bonding in CE5− (E=Al–Tl) Clusters: Planar Tetracoordinate Carbon versus Pentacoordinate Carbon

“…Planar tetracoordinate carbon (ptC) atoms are not just af igment of the chemist's imagination;t hey do exist in the gas phase and in the best cases also in bottles. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] One of the most representative systemso ft hese nonclassicalm olecules is CAl 4 2À . [20] It was detected in the gas phase throughp hotoelectron spectroscopy and structural assignment was achieved in combination with computations.…”