Plane and simple: planar tetracoordinate carbon centers in small moleculesElectronic supplementary information (ESI) available: The complete Gaussian 03 citation, Geometrical data and coordinates for system considered in this work. See DOI: 10.1039/c2cp41986f

• Main Authors: Crigger, Chad, Wittmaack, Bernard K, Tawfik, Marina, Merino, Gabriel, Donald, Kelling J
• Format: Journal Article
• Language: English
• Published: 17.10.2012
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c2cp41986f

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. We identify a broad class of neutral 18 e singlet molecules that are expected to be locally tetrahedral at the C center but which strongly prefer the planar tetracoordinate geometry over the three-dimensional alternative.