Methane planar, structure

Varied Methane Cations. The methane molecular ion (methane radical cation, CH4+ ), the parent ion in mass spectrometry, and the methane dication (CH42+) are of great significance and have been studied both experimentally and theoretically.800 802 Recent advanced studies have shown that the methane radical cation, CH4+ has a fivecoordinate planar structure as suggested in early calculations by Olah and Klopman.800... 

A square planar carbon configuration can be achieved only if the HOMO a u is substantially stabilized by good r-acceptor ligands. For example, di- and trilithio-methane are calculated to have a planar structure 9.33a only 2.5 and 3.5 kcal/mol, respectively, higher than the tetrahedral structures 9.33b [18]. As indicated in 9.33c,... 

The characterization and crystal structure of the dimer [Pt2( -dppm)3] (dppm = bis(diphenyl-phosphino)methane), first reported as a deep red complex in 1978, was described by Manojlovic-Muir et al. in 1986.11 The structure, the first of its type, is made up of two parallel and almost eclipsed trigonal-planar platinum moieties bridged by three diphosphine ligands. The Pf Pt separation is 3.0225(3) A, too long to be considered a bond.11 [Pt2(//-dppm)3] catalyzes the hydrogenation/reduction of carbon dioxide with dimethylamine to give dimethylformamide12 (Equation (1)) and the reverse reaction.13... 

We have previously seen examples of the carbon-like formulas of mononuclear and dinuclear osmium compounds, namely the methane-like tetrahydride (4.50c), ethylene-like H20s=CH2 (4.51c) and H2Os = OsH2 (Table 4.15), acetylenelike HOs = CH (4.54c) and HOs = OsH (Table 4.15), allene-like H2C = Os = CH2 (4.55a), and so forth. While the coordination numbers and Lewis-like formulas are formally analogous, the actual structures of Os and C species may be quite similar (e.g., the Td structures of OsfL and CH4) or dissimilar (e.g the strongly bent Cs structure of H20s = CH2 [Fig. 4.13(c)] versus the planar D2h structure of H2C = CH2). 

Most carbon-containing molecules are three-dimensional. In methane, the bonds of C make equal angles of 109.5° with each other, and each of the four H s is at a vertex of a regular tetrahedron whose center is occupied by the C atom. The spatial relationship is indicated as in Fig. l-2(a) (Newman projeetion) or in Fig. l-2(ft) ( wedge projection). Except for ethene, which is planar, and ethyne, which is linear, the structures in Fig. 1-1 are all three-dimensional. 

Figure 1. Idealized structural types for planar metal centers bridged by bis(diphenylphosphino)methane (4) /, side-by-side dimer II, molecular A-frame, III, face-to-face dimer.

The methane dication (CH42+) with a lifetime of only 3 jxs803 has been detected experimentally in the gas phase.804-807 A square-planar D4h symmetrical structure was predicted by early calculations.808,809 However, the planar but not square C2v symmetrical form (443) was shown to be the preferred structure by Wong and Radom.810 The cation contains an, vp2-hybridized carbon, an empty p-orbital perpendicular to the plane of the molecule, and a 2e-3c interaction. It can be visualized as a complex of a hydrogen molecule weakly bounded by a 2e-3c bond to the CH22+ core as shown by ab initio calculations [MP2 and B3LYP levels with 6-311++G(2df,2pd) basis set].811 The pentacoordinate CH52+ radical dication was studied by Stahl... 

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