title: A new approach to the design of neutral 10-C-5 trigonal-bipyramidal carbon compounds: a "π-electron cap" effect.
abstract: DFT (B3LYP, M06-2X) and MP2 methods are applied to the design of a wide series of the potentially 10-C-5 neutral compounds based on 6-azabicyclotetradecanes: XC(1)(YCH2CH2CH2)3N 1-3, XC(1)(YC6H4CH2)3N 4-6, XC(1)[Y(tBuC6 H3)CH2]3N 7-9 and carbatranophanes C6H3[XC(1)(YC6H3CH2)3N] 10-25 (X = Me, F, Cl; Y = O, NH, CH2, SiH2; Z = O, CH2, (CH2)2, (CH2)3). Carbatranophanes 10-25 are characterized by a sterical compression of their axial 3c-4e XC(1)←N fragment with respect to that in the parent molecules 4-6. A magnitude of the revealed effect depends on a valence surrounding of the central carbon atom C(1), the size and the nature of the side chains (Z) that link the "π-electron cap" with a tetradecane backbone. This circumstance allowed us to obtain 10-C-5 structures with the configuration of the bonds around the C(1) atom, which corresponds to practically an ideal trigonal bipyramid. In these compounds, the values of the covalence ratio χ (C1←N) of approximately 0.6 for the coordination C(1)←N contacts with a covalent contribution (atoms in molecules (AIM) and natural bond orbital (NBO)) are record in magnitude. These values lie close to a low limit of the interval of the χ(Si←D) change (0.6-0.9) being characteristic of the dative and ionic-covalent (by nature) Si←D bond (D = N, O) in the known 10-Si-5 silicon compounds.
authors.affiliation: A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, Favorsky, 1, Irkutsk 664033, Russian Federation. svf@irioch.irk.ru
authors.forename: Valery F
authors.initials: VF
authors.lastname: Sidorkin
authors.forename: Evgeniya P
authors.initials: EP
authors.lastname: Doronina
authors.forename: Elena F
authors.initials: EF
authors.lastname: Belogolova
keywords: ab initio calculations; cage compounds; density functional calculations; hypervalent carbon compounds